Effects of Ag addition on FePt L1{sub 0} ordering transition: A direct observation of ordering transition and Ag segregation in FePtAg alloy films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Lei; Yu, Youxing, E-mail: yuyouxing@buaa.edu.cn; Gao, Tenghua

FePt and (FePt){sub 91.2}Ag{sub 8.8} alloy films were deposited by magnetron sputtering. The average coercivity of (FePt){sub 91.2}Ag{sub 8.8} films reaches 8.51 × 10{sup 5} A/m, which is 0.63 × 10{sup 5} A/m higher than that of the corresponding FePt films. Ag addition effectively promotes the FePt L1{sub 0} ordering transition at a relatively low annealing temperature of 400 °C. The promotion mechanism was investigated by using in situ high-resolution transmission electron microscopy (HRTEM) and ex situ X-ray absorption fine structure (XAFS). The concurrence of ordering transition and Ag segregation in FePtAg alloy films was first observed by using in situ heating HRTEM. The time-resolved evolution revealsmore » more details on the role of Ag addition in FePt low-temperature ordering. Ex situ XAFS results further confirm that Ag replaces Fe sites in the as-deposited films and segregates from FePt-Ag solid solution phase through annealing at elevated temperatures. The segregation of Ag atoms leaves vacancies in the grain. The vacancy formation is believed to accelerate the diffusion of Fe and Pt atoms, which is critical for the L1{sub 0} ordering transition.« less

Fabrication and characterization of L10-ordered FeNi thin films

NASA Astrophysics Data System (ADS)

Takanashi, Koki; Mizuguchi, Masaki; Kojima, Takayuki; Tashiro, Takayuki

2017-12-01

L10-ordered FeNi, showing high uniaxial magnetic anisotropy (K u), is promising as a ‘rare metal-free’ high K u material. We have worked on L10-ordered FeNi thin films prepared by two methods: one is molecular beam epitaxy (MBE) with alternate deposition of Fe and Ni monatomic layers, and the other is sputtering with co-deposition or multilayer-deposition of Fe and Ni followed by rapid thermal annealing (RTA). For the MBE films prepared by alternate monatomic layer deposition (leading to the stoichiometric composition: Fe 50 at.%- Ni 50 at.%), a clear relationship between K u and the long-range order parameter S estimated by synchrotron x-ray diffraction (XRD) was found with maximum values of S  =  0.48 and K u  =  7.0  ×  106 erg cm-3. The composition dependence of K u was also investigated by deviating the thickness from monatomic layer, showing a maximum of 9.3  ×  106 erg cm-3 around 60 at.%Fe. In addition, the effect of Co addition to L10-ordered FeNi was investigated, suggesting that a small amount (<10 at.%) of Co substitution for Ni would enhance K u if S keeps the same. The experiments were in qualitatively good agreement with the first-principles calculations. The magnetic damping constant α was also measured to be approximately 0.01 irrespective of S, suggesting that L10-FeNi is a candidate material with high K u and low α. For the sputtered films with RTA, no major difference between co-deposition and multilayer-deposition was found: in both cases the formation of L10-ordered phase after RTA was definitely confirmed by XRD. Transmission electron microscopy observations indicated that nanometer-sized L10-ordered clusters were dispersed in a disordered phase, in contrast to that of MBE films showing the homogeneous formation of L10-ordered phase. The enhancement of coercivity (H c) and residual magnetization (M r/M s) was observed associated with the appearance of L10-ordered phase. The maxima of H c and M r/M s were obtained to be 1.35 kOe and 0.22, respectively.

Appearance of superconductivity at the vacancy order-disorder boundary in KxFe2 -ySe2

NASA Astrophysics Data System (ADS)

Duan, Chunruo; Yang, Junjie; Ren, Yang; Thomas, Sean M.; Louca, Despina

2018-05-01

The role of phase separation and the effect of Fe-vacancy ordering in the emergence of superconductivity in alkali metal doped iron selenides AxFe2 -ySe2 (A = K, Rb, Cs) is explored. High energy x-ray diffraction and Monte Carlo simulation were used to investigate the crystal structure of quenched superconducting (SC) and as-grown nonsuperconducting (NSC) KxFe2 -ySe2 single crystals. The coexistence of superlattice structures with the in-plane √{2 }×√{2 } K-vacancy ordering and the √{5 }×√{5 } Fe-vacancy ordering were observed in both the SC and NSC crystals alongside the I4/mmm Fe-vacancy-free phase. Moreover, in the SC crystals, an Fe-vacancy-disordered phase is additionally proposed to be present. Monte Carlo simulations suggest that it appears at the boundary between the I4/mmm vacancy-free phase and the I4/m vacancy-ordered phases (√{5 }×√{5 } ). The vacancy-disordered phase is nonmagnetic and is most likely the host of superconductivity.

Crystallization induced ordering of hard magnetic L1{sub 0} phase in melt-spun FeNi-based ribbons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sato, Kazuhisa, E-mail: sato@uhvem.osaka-u.ac.jp; Sharma, Parmanand; Zhang, Yan

2016-05-15

The microstructure of newly developed hard magnetic Fe{sub 42}Ni{sub 41.3}Si{sub x}B{sub 12-x}P{sub 4}Cu{sub 0.7} (x = 2 to 8 at%) nanocrystalline alloy ribbons has been studied by transmission electron microscopy (TEM) and electron diffraction. A high-density polycrystalline grains, ∼30 nm in size, were formed in a ribbon after annealing at 673 K for 288 hours. Elemental mapping of the annealed specimen revealed the coexistence of three regions, Fe-rich, Ni-rich, and nearly equiatomic Fe-Ni, with areal fractions of 37%, 40%, and 23 %, respectively. The equiatomic L1{sub 0}-type ordered phase of FeNi was detected in between the Fe and Ni-rich phases.more » The presence of superlattice reflections in nanobeam electron diffraction patterns confirmed the formation of the hard magnetic L1{sub 0} phase beyond any doubt. The L1{sub 0} phase of FeNi was detected in alloys annealed in the temperature range of 673 to 813 K. The present results suggest that the order-disorder transition temperature of L1{sub 0} FeNi is higher than the previously reported value (593 K). The high diffusion rates of the constituent elements induced by the crystallization of an amorphous phase at relatively low temperature (∼673 K) are responsible for the development of atomic ordering in FeNi.« less

Ordered mesoporous porphyrinic carbons with very high electrocatalytic activity for the oxygen reduction reaction

PubMed Central

Cheon, Jae Yeong; Kim, Taeyoung; Choi, YongMan; Jeong, Hu Young; Kim, Min Gyu; Sa, Young Jin; Kim, Jaesik; Lee, Zonghoon; Yang, Tae-Hyun; Kwon, Kyungjung; Terasaki, Osamu; Park, Gu-Gon; Adzic, Radoslav R.; Joo, Sang Hoon

2013-01-01

The high cost of the platinum-based cathode catalysts for the oxygen reduction reaction (ORR) has impeded the widespread application of polymer electrolyte fuel cells. We report on a new family of non-precious metal catalysts based on ordered mesoporous porphyrinic carbons (M-OMPC; M = Fe, Co, or FeCo) with high surface areas and tunable pore structures, which were prepared by nanocasting mesoporous silica templates with metalloporphyrin precursors. The FeCo-OMPC catalyst exhibited an excellent ORR activity in an acidic medium, higher than other non-precious metal catalysts. It showed higher kinetic current at 0.9 V than Pt/C catalysts, as well as superior long-term durability and MeOH-tolerance. Density functional theory calculations in combination with extended X-ray absorption fine structure analysis revealed a weakening of the interaction between oxygen atom and FeCo-OMPC compared to Pt/C. This effect and high surface area of FeCo-OMPC appear responsible for its significantly high ORR activity. PMID:24056308

Tailoring of magnetoimpedance effect and magnetic softness of Fe-rich glass-coated microwires by stress- annealing.

PubMed

Zhukova, V; Blanco, J M; Ipatov, M; Churyukanova, M; Taskaev, S; Zhukov, A

2018-02-16

There is a pressing need for improving of the high-frequency magneto-impedance effect of cost-effective soft magnetic materials for use in high-performance sensing devices. The impact of the stress-annealing on magnetic properties and high frequency impedance of Fe-rich glass-coated microwires was studied. Hysteresis loops of Fe-rich microwires have been considerably affected by stress- annealing. In stress-annealed Fe- rich microwire we obtained drastic decreasing of coercivity and change of character of hysteresis loop from rectangular to linear. By controlling stress-annealing conditions (temperature and time) we achieved drastic increasing (by order of magnitude) of giant magnetoimpedance ratio. Coercivity, remanent magnetization, diagonal and of-diagonal magnetoimpedance effect of Fe-rich microwires can be tuned by stress-annealing conditions: annealing temperature and time. Observed experimental results are discussed considering relaxation of internal stresses, compressive "back-stresses" arising after stress annealing and topological short range ordering.

Phase diagram of URu 2-xFe xSi 2 in high magnetic fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ran, S.; Jeon, I.; Kanchanavatee, N.

2017-03-01

The search for the order parameter of the hidden order (HO) phase in URu 2Si 2 has attracted an enormous amount of attention for the past three decades. Measurements in high magnetic fields H up to 45~T reveal that URu 2Si 2 displays behavior that is consistent with quantum criticality at a field near 35~T, where a cascade of novel quantum phases was found at and around the quantum critical point, suggesting the existence of competing order parameters. Experiments at high pressure P reveal that a first order transition from the HO phase to a large moment antiferromagnetic (LMAFM) phasemore » occurs under pressure at a critical pressure Pc. We have recently demonstrated that tuning URu 2Si 2 by substitution of Fe for Ru offers an opportunity to study the HO and LMAFM phases at atmospheric pressure. In this study, we conducted electrical resistance measurements on URu 2-xFe xSi 2 for H < 65 T using the pulsed field facility at the NHMFL in Los Alamos, in order to establish the temperature T vs. H phase diagram of URu 2-xFe xSi 2 under magnetic fields.« less

A study of cytocompatibility and degradation of iron-based biodegradable materials.

PubMed

Oriňaková, Renáta; Oriňak, Andrej; Giretová, Mária; Medvecký, L'ubomír; Kupková, Miriam; Hrubovčáková, Monika; Maskal'ová, Iveta; Macko, Ján; Kal'avský, František

2016-02-01

Biodegradable metallic implants are of significant importance in the replacement of bones or the repair of bone defects. Iron-phosphate-coated carbonyl iron powder (Fe/P) was prepared by the phosphating method. Moreover, Fe/P-Mn alloy was produced by sintering the Fe/P powder mixed with manganese powder. Bare carbonyl iron samples and the Fe/P and Fe/P-Mn sintered samples were evaluated for their microstructure, cytotoxicity, and hemocompatibility. The microstructure of the sintered samples was examined using an optical microscope and scanning electron microscopic analysis. Corrosion behavior was evaluated by potentiodynamic polarization in Hank's solution. The in vitro biocompatibilities were investigated by cytotoxicity and hemolysis tests. The results obtained demonstrate that the addition of Mn resulted in higher surface inhomogeneity, porosity and roughness as well as in increased cytotoxicity. The phosphate coating has a moderately negative effect on the cytotoxicity. The corrosion rates determined from Tafel diagrams were ordered in the following sequence: Fe/P-Mn, Fe, Fe/P from high to low. The hemocompatibility of experimental samples was ordered in the following sequence: Fe/P, Fe/P-Mn, Fe from high to low. All samples were found to be hemocompatible. © The Author(s) 2015.

Synthesis and characterization of magnetically hard Fe-Pt alloy nanoparticles and nano-islands

NASA Astrophysics Data System (ADS)

Hu, Xiaocao

In this dissertation, we explored the fabrication of FePt nanoparticles and nano-islands with the face-centered tetragonal (fct, L10) phase prepared by both chemical synthesis routes and physical vapor deposition. Microstructure and magnetic properties characterizations were used to gain a fundamental understanding of the nano-structure formation and atomic ordering behavior and determine the possible applications in the next generation ultra-high density magnetic storage media. FePt nanoparticles prepared by thermal decomposition of iron pentacarbonyl [Fe(CO)5] have been widely investigated and by tuning the processing procedure monodispersed FePt nanoparticles with good assembly can be obtained. The as-made FePt nanoparticles are usually in the magnetically soft face-centered cubic (fcc) phase. To transformation to the fct phase, post-annealing at above 600°C is needed which, however, introduces undesirable agglomeration and sintering. To address this problem, we used three different fabrication processes which are discussed below. In the first fabrication experiment, the FePt nanoparticles were fabricated by a novel environmental friendly method involving crystalline saline complex hexaaquairon (II) hexachloroplatinate ([Fe(H2O)6]PtCl 6) with a special layered structure. Then the precursor was ball milled with NaCl and annealed at temperatures above 400°C under a reducing atmosphere of forming gas (95% Ar and 5% H2) FePt nanoparticles were obtained after washing away NaCl with deionized water. This method avoids the use of the very poisonous Fe(CO)5 and other organic solvents such as oleylamine and oleic acid. Instead, environmentally friendly NaCl and water were used. The size of FePt nanoparticles was controlled by varying the proportion of precursor and NaCl (from 10mg/20g to 50mg/20g). Particles with size in the range of 6.2--13.2 nm were obtained. All the nanoparticles annealed above 400°C are in the highly ordered fct phase with a coercivity range of 4.7 kOe to 10.7 kOe. Compared with reported high annealing temperatures above 600°C, this fabrication process led to a significantly decreased temperature to achieve the L10 phase FePt by 200°C. A qualitative model was set up to explain the surprising low L10 phase achievement temperature and the influence of annealing temperature on the microstructure and magnetic properties was investigated. Although FePt nanoparticles with high coercivity and small size were successfully obtained by the first fabrication method, agglomeration happened during the washing procedure due to the large inter-particle magnetostatic force caused by their high magnetization. To avoid this agglomeration, exfoliated graphene was introduced in the second preparation method to keep the nanoparticles separated. Different from the traditional solvent-phase reaction to disperse FePt nanoparticles onto the exfoliated graphene, a novel solid-phase reaction was used in this dissertation involving the layered precursor [Fe(H2 O)6]PtCl6 molecule. The [Fe(H2O) 6]PtCl6 water solution was mixed with exfoliated graphene oxide (GO) and then the top solution was removed. Fe2+ and Pt2+ ions were absorbed onto the surface of GO. The remaining product was annealed under a reducing atmosphere of forming gas at different temperatures (500°C to 950°C). During the reduction process, GO was reduced to "graphene" and FePt nanoparticles were formed on the surface of exfoliated graphene. The separation effect by the exfoliated graphene increased the phase transformation temperature to 600°C compared to the first method. However, even at an annealing temperature as high as 750°C, we could still obtained separated, small size FePt nanoparticles with coercivity of 8.3 kOe. The third preparation method used in this dissertation is the traditional magnetron sputtering with very short deposition time (10 s to 25 s) on heated MgO (001) substrate to form separate nano-islands instead of continuous thin films. The ordering of FePt nano-islands were studied by high resolution transmission electron microscopy. Because of the low degree of atomic ordering of the as-prepared nano-islands, post annealing at 700°C under an atmosphere of forming gas was introduced. Ordering of nano-islands of as small as 3 nm was revealed. We discovered that in the ordered FePt nano-islands, there are defects present. Particularly, we observed an onion like structure in a FePt nano-island composed of c-domains perpendicular to each other. These defects explained the low coercivity of the L10 ordered FePt nano-islands, which was envisioned theoretically. In summary, in this dissertation, novel solid-phase, environmentally friendly synthesis methods to fabricate FePt nanoparticles and FePt nanoparticles on "graphene" with high coercivity are first reported. Also, a special onion-like structure was first discovered by high-resolution microscopy and theoretical simulation was done with good agreement with the experimental results.

Magnetic ordered mesoporous Fe3O4/CeO2 composites with synergy of adsorption and Fenton catalysis

NASA Astrophysics Data System (ADS)

Li, Keyan; Zhao, Yongqin; Song, Chunshan; Guo, Xinwen

2017-12-01

Magnetic Fe3O4/CeO2 composites with highly ordered mesoporous structure and large surface area were synthesized by impregnation-calcination method, and the mesoporous CeO2 as support was synthesized via the hard template approach. The composition, morphology and physicochemical properties of the materials were characterized by XRD, SEM, TEM, XPS, Raman spectra and N2 adsorption/desorption analysis. The mesoporous Fe3O4/CeO2 composite played a dual-function role as both adsorbent and Fenton-like catalyst for removal of organic dye. The methylene blue (MB) removal efficiency of mesoporous Fe3O4/CeO2 was much higher than that of irregular porous Fe3O4/CeO2. The superior adsorption ability of mesoporous materials was attributed to the abundant oxygen vacancies on the surface of CeO2, high surface area and ordered mesoporous channels. The good oxidative degradation resulted from high Ce3+ content and the synergistic effect between Fe and Ce. The mesoporous Fe3O4/CeO2 composite presented low metal leaching (iron 0.22 mg L-1 and cerium 0.63 mg L-1), which could be ascribed to the strong metal-support interactions for dispersion and stabilization of Fe species. In addition, the composite can be easily separated from reaction solution with an external magnetic field due to its magnetic property, which is important to its practical applications.

Interfacial superconductivity in a bi-collinear antiferromagnetically ordered FeTe monolayer on a topological insulator

NASA Astrophysics Data System (ADS)

Manna, S.; Kamlapure, A.; Cornils, L.; Hänke, T.; Hedegaard, E. M. J.; Bremholm, M.; Iversen, B. B.; Hofmann, Ph.; Wiebe, J.; Wiesendanger, R.

2017-01-01

The discovery of high-temperature superconductivity in Fe-based compounds triggered numerous investigations on the interplay between superconductivity and magnetism, and on the enhancement of transition temperatures through interface effects. It is widely believed that the emergence of optimal superconductivity is intimately linked to the suppression of long-range antiferromagnetic (AFM) order, although the exact microscopic picture remains elusive because of the lack of atomically resolved data. Here we present spin-polarized scanning tunnelling spectroscopy of ultrathin FeTe1-xSex (x=0, 0.5) films on bulk topological insulators. Surprisingly, we find an energy gap at the Fermi level, indicating superconducting correlations up to Tc~6 K for one unit cell FeTe grown on Bi2Te3, in contrast to the non-superconducting bulk FeTe. The gap spatially coexists with bi-collinear AFM order. This finding opens perspectives for theoretical studies of competing orders in Fe-based superconductors and for experimental investigations of exotic phases in superconducting layers on topological insulators.

Magnetic phase separation and strong enhancement of the Néel temperature at high pressures in a new multiferroic Ba3TaFe3Si2O14

NASA Astrophysics Data System (ADS)

Lyubutin, I. S.; Starchikov, S. S.; Gavriliuk, A. G.; Troyan, I. A.; Nikiforova, Yu. A.; Ivanova, A. G.; Chumakov, A. I.; Rüffer, R.

2017-01-01

The high-pressure properties of a new multiferroic of the langasite family Ba3TaFe3Si2O14 were investigated in diamond-anvil cells (DAC) in the temperature range of 4.2-295 K by a new method of synchrotron Mössbauer spectroscopy. Strong enhancement of the Néel temperature T N was observed at pressures above 20 GPa associated with the structural transformation. The highest value of T N is about 130 K which is almost five times larger than the value at ambient pressure (about 27 K). It was suggested that the high value of T N appears due to redistribution of Fe ions over 3 f and 2 d tetrahedral sites of the langasite structure. In this case, the short Fe-O distances and favorable Fe-O-Fe bond angles create conditions for strong superexchange interactions between iron ions, and effective two-dimensional (2D) magnetic ordering appears in the ( ab) plane. The separation of the sample into two magnetic phases with different T N values of about 50 and 130 K was revealed, which can be explained by the strong 2D magnetic ordering in the ab plane and 3D ordering involving inter-plane interaction.

Phase relations in KxFe2-ySe2 and the structure of superconducting KxFe2Se2 via high-resolution synchrotron diffraction

NASA Astrophysics Data System (ADS)

Shoemaker, Daniel P.; Chung, Duck Young; Claus, Helmut; Francisco, Melanie C.; Avci, Sevda; Llobet, Anna; Kanatzidis, Mercouri G.

2012-11-01

Superconductivity in iron selenides has experienced a rapid growth, but not without major inconsistencies in the reported properties. For alkali-intercalated iron selenides, even the structure of the superconducting phase is a subject of debate, in part because the onset of superconductivity is affected much more delicately by stoichiometry and preparation than in cuprate or pnictide superconductors. If high-quality, pure, superconducting intercalated iron selenides are ever to be made, the intertwined physics and chemistry must be explained by systematic studies of how these materials form and by and identifying the many coexisting phases. To that end, we prepared pure K2Fe4Se5 powder and superconductors in the KxFe2-ySe2 system, and examined differences in their structures by high-resolution synchrotron and single-crystal x-ray diffraction. We found four distinct phases: semiconducting K2Fe4Se5, a metallic superconducting phase KxFe2Se2 with x ranging from 0.38 to 0.58, the phase KFe1.6Se2 with full K occupancy and no Fe vacancy ordering, and a oxidized phase K0.51(5)Fe0.70(2)Se that forms the PbClF structure upon exposure to moisture. We find that the vacancy-ordered phase K2Fe4Se5 does not become superconducting by doping, but the distinct iron-rich minority phase KxFe2Se2 precipitates from single crystals upon cooling from above the vacancy ordering temperature. This coexistence of separate metallic and semiconducting phases explains a broad maximum in resistivity around 100 K. Further studies to understand the solubility of excess Fe in the KxFe2-ySe2 structure will shed light on the maximum fraction of superconducting KxFe2Se2 that can be obtained by solid state synthesis.

Developing precipitation hardenable high entropy alloys

NASA Astrophysics Data System (ADS)

Gwalani, Bharat

High entropy alloys (HEAs) is a concept wherein alloys are constructed with five or more elements mixed in equal proportions; these are also known as multi-principle elements (MPEs) or complex concentrated alloys (CCAs). This PhD thesis dissertation presents research conducted to develop precipitation-hardenable high entropy alloys using a much-studied fcc-based equi-atomic quaternary alloy (CoCrFeNi). Minor additions of aluminium make the alloy amenable for precipitating ordered intermetallic phases in an fcc matrix. Aluminum also affects grain growth kinetics and Hall-Petch hardenability. The use of a combinatorial approach for assessing composition-microstructure-property relationships in high entropy alloys, or more broadly in complex concentrated alloys; using laser deposited compositionally graded AlxCrCuFeNi 2 (0 < x < 1.5) complex concentrated alloys as a candidate system. The composition gradient has been achieved from CrCuFeNi2 to Al 1.5CrCuFeNi2 over a length of ˜25 mm, deposited using the laser engineered net shaping process from a blend of elemental powders. With increasing Al content, there was a gradual change from an fcc-based microstructure (including the ordered L12 phase) to a bcc-based microstructure (including the ordered B2 phase), accompanied with a progressive increase in microhardness. Based on this combinatorial assessment, two promising fcc-based precipitation strengthened systems have been identified; Al0.3CuCrFeNi2 and Al0.3CoCrFeNi, and both compositions were subsequently thermo-mechanically processed via conventional techniques. The phase stability and mechanical properties of these alloys have been investigated and will be presented. Additionally, the activation energy for grain growth as a function of Al content in these complex alloys has also been investigated. Change in fcc grain growth kinetic was studied as a function of aluminum; the apparent activation energy for grain growth increases by about three times going from Al0.1CoCrFeNi (3% Al (at%)) to Al0.3CoCrFeNi. (7% Al (at%)). Furthermore, Al addition leads to the precipitation of highly refined ordered L12 (gamma') and B2 precipitates in Al0.3CoCrFeNi. A detailed investigation of precipitation of the ordered phases in Al0.3CoCrFeNi and their thermal stability is done using atom probe tomography (APT), transmission electron microscopy (TEM) and Synchrotron X-ray in situ and ex situ analyses. The alloy strengthened via grain boundary strengthening following the Hall-Petch relationship offers a large increment of strength with small variation in grain size. Tensile strength of the Al0.3CoFeNi is increased by 50% on precipitation fine-scale gamma' precipitates. Furthermore, precipitation of bcc based ordered phase B2 in Al0.3CoCrFeNi can further strengthen the alloy. Fine-tuning the microstructure by thermo-mechanical treatments achieved a wide range of mechanical properties in the same alloy. The Al0.3CoCrFeNi HEA exhibited ultimate tensile strength (UTS) of ˜250 MPa and ductility of ˜65%; a UTS of ˜1100 MPa and ductility of ˜30%; and a UTS of 1850 MPa and a ductility of 5% after various thermo-mechanical treatments. Grain sizes, precipitates type and size scales manipulated in the alloy result in different strength ductility combinations. Henceforth, the alloy presents a fertile ground for development by grain boundary strengthening and precipitation strengthening, and offers very high activation energy of grain growth aptly suitable for high-temperature applications.

Predicting the Crystal Structure and Phase Transitions in High-Entropy Alloys

NASA Astrophysics Data System (ADS)

King, D. M.; Middleburgh, S. C.; Edwards, L.; Lumpkin, G. R.; Cortie, M.

2015-06-01

High-entropy alloys (HEAs) have advantageous properties compared with other systems as a result of their chemistry and crystal structure. The transition between a face-centered cubic (FCC) and body-centered cubic (BCC) structure in the Al x CoCrFeNi high-entropy alloy system has been investigated on the atomic scale in this work. The Al x CoCrFeNi system, as well as being a useful system itself, can also be considered a model HEA material. Ordering in the FCC structure was investigated, and an order-disorder transition was predicted at ~600 K. It was found that, at low temperatures, an ordered lattice is favored over a truly random lattice. The fully disordered BCC structure was found to be unstable. When partial ordering was imposed (lowering the symmetry), with Al and Ni limited specific sites of the BCC system, the BCC packing was stabilized. Decomposition of the ordered BCC single phase into a dual phase (Al-Ni rich and Fe-Cr rich) is also considered.

Interrogating the superconductor Ca- 10(Pt 4As 8)(Fe 2-xPt xAs 2) 5 Layer-by-layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Jisun; Zhu, Yimei; Nam, Hyoungdo

2016-10-14

Ever since the discovery of high-Tc superconductivity in layered cuprates, the roles that individual layers play have been debated, due to difficulty in layer-by-layer characterization. While there is similar challenge in many Fe-based layered superconductors, the newly-discovered Ca 10(Pt 4As 8)(Fe 2As 2) 5 provides opportunities to explore superconductivity layer by layer, because it contains both superconducting building blocks (Fe 2As 2 layers) and intermediate Pt 4As 8 layers. Cleaving a single crystal under ultra-high vacuum results in multiple terminations: an ordered Pt 4As 8 layer, two reconstructed Ca layers on the top of a Pt 4As 8 layer, andmore » disordered Ca layer on the top of Fe 2As 2 layer. The electronic properties of individual layers are studied using scanning tunneling microscopy/spectroscopy (STM/S), which reveals different spectra for each surface. Remarkably superconducting coherence peaks are seen only on the ordered Ca/Pt 4As 8 layer. Our results indicate that an ordered structure with proper charge balance is required in order to preserve superconductivity.« less

Interrogating the superconductor Ca10(Pt4As8)(Fe2-xPtxAs2)5 Layer-by-layer.

PubMed

Kim, Jisun; Nam, Hyoungdo; Li, Guorong; Karki, A B; Wang, Zhen; Zhu, Yimei; Shih, Chih-Kang; Zhang, Jiandi; Jin, Rongying; Plummer, E W

2016-10-14

Ever since the discovery of high-T c superconductivity in layered cuprates, the roles that individual layers play have been debated, due to difficulty in layer-by-layer characterization. While there is similar challenge in many Fe-based layered superconductors, the newly-discovered Ca 10 (Pt 4 As 8 )(Fe 2 As 2 ) 5 provides opportunities to explore superconductivity layer by layer, because it contains both superconducting building blocks (Fe 2 As 2 layers) and intermediate Pt 4 As 8 layers. Cleaving a single crystal under ultra-high vacuum results in multiple terminations: an ordered Pt 4 As 8 layer, two reconstructed Ca layers on the top of a Pt 4 As 8 layer, and disordered Ca layer on the top of Fe 2 As 2 layer. The electronic properties of individual layers are studied using scanning tunneling microscopy/spectroscopy (STM/S), which reveals different spectra for each surface. Remarkably superconducting coherence peaks are seen only on the ordered Ca/Pt 4 As 8 layer. Our results indicate that an ordered structure with proper charge balance is required in order to preserve superconductivity.

Antisite-disorder, magnetic and thermoelectric properties of Mo-rich Sr2Fe1-yMo1+yO6 (0 ≤y≤ 0.2) double perovskites.

PubMed

Popuri, Srinivasa R; Redpath, Debbie; Chan, Gavin; Smith, Ronald I; Cespedes, Oscar; Bos, Jan-Willem G

2015-06-21

Structure analysis using X-ray and neutron powder diffraction and elemental mapping has been used to demonstrate that nominal A-site deficient Sr(2-x)FeMoO(6-δ) (0 ≤x≤ 0.5) compositions form as Mo-rich Sr(2)Fe(1-y)Mo(1+y)O(6) (0 ≤y≤ 0.2) perovskites at high temperatures and under reducing atmospheres. These materials show a gradual transition from the Fe and Mo rock salt ordered double perovskite structure to a B-site disordered arrangement. Analysis of the fractions of B-O-B' linkages revealed a gradual increase in the number of Mo-O-Mo linkages at the expense of the ferrimagnetic (FIM) Fe-O-Mo linkages that dominate the y = 0 material. All samples contain about 10-15% antiferromagnetic (AF) Fe-O-Fe linkages, independent of the degree of B-site ordering. The magnetic susceptibility of the y = 0.2 sample is characteristic of a small domain ferrimagnet (T(c)∼ 250 K), while room temperature neutron powder diffraction demonstrated the presence of G-type AF ordering linked to the Fe-O-Fe linkages (m(Fe) = 1.25(7)μ(B)). The high temperature thermoelectric properties are characteristic of a metal with a linear temperature dependence of the Seebeck coefficient, S (for all y) and electrical resistivity ρ (y≥ 0.1). The largest thermoelectric power factor S(2)/ρ = 0.12 mW m(-1) K(-1) is observed for Sr(2)FeMoO(6) at 1000 K.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sturza, Mihai; Allred, Jared M.; Malliakas, Christos D.

Effecting and controlling ferromagnetic-like properties hi senticonductors has proven to be a complex problem, especially when approaching room temperature. Here, we demonstrate the important role of defects in the magnetic properties of semiconductors by reporting the structures and properties of the iron chalcogenides (BaF)(2)Fe2-x Q(3) (Q= S, Se), which exhibit anomalous Magnetic properties that are correlated' with detects in the Fe-sublattice, The compounds form in both long-range ordered and disordered polytypes of a new structure typified by the alternate stacking of fluorite (BaF)(2)(2+) and (Fe(2-x)Q(3))(2-) layers. The latter layers exhibit an ordered array of strong Pe-Pe dimers in edge-Sharing tetrahedra.more » Given the strong Fe-Fe interaction, it is expected that the Fe-Fe dimer is,antiferromagnetically coupled, yet crystals exhibit a Weak ferromagnetic moment that orders at relatively-high temperature: below 280-315 K and 240275 K for the sulfide and selenide analogues, respectively. This transition temperature positively correlates with the concentration of defect in the Fe-sublattice, as determined by single-crystal X-ray diffraction. Our results indicate that internal defects in Fe(2-x)Q(3) layers play an important role in dictating the magnetic properties of newly discovered (BaF)2Fe(2),Q-3, (Q= 5-, Se), which can yield switchable ferromagnetically ordered mother-its at or above room temperature.« less

Atomistic clustering-ordering and high-strain deformation of an Al0.1CrCoFeNi high-entropy alloy

PubMed Central

Sharma, Aayush; Singh, Prashant; Johnson, Duane D.; Liaw, Peter K.; Balasubramanian, Ganesh

2016-01-01

Computational investigations of structural, chemical, and deformation behavior in high-entropy alloys (HEAs), which possess notable mechanical strength, have been limited due to the absence of applicable force fields. To extend investigations, we propose a set of intermolecular potential parameters for a quinary Al-Cr-Co-Fe-Ni alloy, using the available ternary Embedded Atom Method and Lennard-Jones potential in classical molecular-dynamics simulations. The simulation results are validated by a comparison to first-principles Korringa-Kohn-Rostoker (KKR) - Coherent Potential Approximation (CPA) [KKR-CPA] calculations for the HEA structural properties (lattice constants and bulk moduli), relative stability, pair probabilities, and high-temperature short-range ordering. The simulation (MD)-derived properties are in quantitative agreement with KKR-CPA calculations (first-principles) and experiments. We study AlxCrCoFeNi for Al ranging from 0 ≤ x ≤2 mole fractions, and find that the HEA shows large chemical clustering over a wide temperature range for x < 0.5. At various temperatures high-strain compression promotes atomistic rearrangements in Al0.1CrCoFeNi, resulting in a clustering-to-ordering transition that is absent for tensile loading. Large fluctuations under stress, and at higher temperatures, are attributed to the thermo-plastic instability in Al0.1CrCoFeNi. PMID:27498807

Atomistic clustering-ordering and high-strain deformation of an Al 0.1CrCoFeNi high-entropy alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sharma, Aayush; Singh, Prashant; Johnson, Duane D.

2016-08-08

Here, computational investigations of structural, chemical, and deformation behavior in high-entropy alloys (HEAs), which possess notable mechanical strength, have been limited due to the absence of applicable force fields. To extend investigations, we propose a set of intermolecular potential parameters for a quinary Al-Cr-Co-Fe-Ni alloy, using the available ternary Embedded Atom Method and Lennard-Jones potential in classical molecular-dynamics simulations. The simulation results are validated by a comparison to first-principles Korringa-Kohn-Rostoker (KKR) - Coherent Potential Approximation (CPA) [KKR-CPA] calculations for the HEA structural properties (lattice constants and bulk moduli), relative stability, pair probabilities, and high-temperature short-range ordering. The simulation (MD)-derived propertiesmore » are in quantitative agreement with KKR-CPA calculations (first-principles) and experiments. We study Al xCrCoFeNi for Al ranging from 0 ≤ x ≤2 mole fractions, and find that the HEA shows large chemical clustering over a wide temperature range for x < 0.5. At various temperatures high-strain compression promotes atomistic rearrangements in Al 0.1CrCoFeNi, resulting in a clustering-to-ordering transition that is absent for tensile loading. Large fluctuations under stress, and at higher temperatures, are attributed to the thermo-plastic instability in Al 0.1CrCoFeNi.« less

Ordered mesoporous MFe(2)O(4) (M = Co, Cu, Mg, Ni, Zn) thin films with nanocrystalline walls, uniform 16 nm diameter pores and high thermal stability: template-directed synthesis and characterization of redox active trevorite.

PubMed

Haetge, Jan; Suchomski, Christian; Brezesinski, Torsten

2010-12-20

In this paper, we report on ordered mesoporous NiFe(2)O(4) thin films synthesized via co-assembly of hydrated ferric nitrate and nickel chloride with an amphiphilic diblock copolymer, referred to as KLE. We establish that the NiFe(2)O(4) samples are highly crystalline after calcination at 600 °C, and that the conversion of the amorphous inorganic framework comes at little cost to the ordering of the high quality cubic network of pores averaging 16 nm in diameter. We further show that the synthesis method employed in this work can be readily extended to other ferrites, such as CoFe(2)O(4), CuFe(2)O(4), MgFe(2)O(4), and ZnFe(2)O(4), which could pave the way for innovative device design. While this article focuses on the self-assembly and characterization of these materials using various state-of-the-art techniques, including electron microscopy, grazing incidence small-angle X-ray scattering (GISAXS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), X-ray photoelectron spectroscopy (XPS), as well as UV-vis and Raman spectroscopy, we also examine the electrochemical properties and show the benefits of combining a continuous mesoporosity with nanocrystalline films. KLE-templated NiFe(2)O(4) electrodes exhibit reasonable levels of lithium ion storage at short charging times which stem from facile pseudocapacitance.

Long-range ordering in the Bi 1-xAe xFeO 3-x/2 perovskites: Bi 1/3Sr 2/3FeO 2.67 and Bi 1/2Ca 1/2FeO 2.75

NASA Astrophysics Data System (ADS)

Lepoittevin, C.; Malo, S.; Barrier, N.; Nguyen, N.; Van Tendeloo, G.; Hervieu, M.

2008-10-01

Two-ordered perovskites, Bi 1/3Sr 2/3FeO 2.67 and Bi 1/2Ca 1/2FeO 2.75, have been stabilized and characterized by transmission electron microscopy, Mössbauer spectroscopy and X-ray powder diffraction techniques. They both exhibit orthorhombic superstructures, one with a≈ b≈2 ap and c≈3 ap (S.G.: Pb2 n or Pbmn) for the Sr-based compound and one with a≈ b≈2 ap and c≈8 ap (S.G.: B222, Bmm2, B2 mm or Bmmm) for the Ca-based one. The high-resolution transmission electron microscopy (HRTEM) images evidence the existence of one deficient [FeO x] ∞ layer, suggesting that Bi 1/3Sr 2/3FeO 2.67 and Bi 1/2Ca 1/2FeO 2.75 behave differently compared to their Ln-based homolog. The HAADF-STEM images allow to propose a model of cation ordering on the A sites of the perovskite. The Mössbauer analyses confirm the trivalent state of iron and its complex environment with three types of coordination. Both compounds exhibit a high value of resistivity and the inverse molar susceptibility versus temperature curves evidence a magnetic transition at about 730 K for the Bi 1/3Sr 2/3FeO 2.67 and a smooth reversible transition between 590 and 650 K for Bi 1/2Ca 1/2FeO 2.75.

Microstructural Evolution during the Dynamic Deformation of High Strength Navy Steels

DTIC Science & Technology

2008-05-19

phase particles (Figures 23d,e). These include carbides as well as copper precipitates that are of the order of 10 nm or less in size. These particles ...Microstructure and kinetics of martensite transformations in splat-quenched Fe and Fe-Ni alloys - I pure Fe: Acta Metallurgica 30(1982)323. 22. Y. Inokuti...and B. Cantor, Microstructure and kinetics of martensite transformations in splat-quenched Fe and Fe-Ni alloys - II Fe-Ni alloys : Acta

High-T c superconductivity in undoped ThFeAsN.

PubMed

Shiroka, T; Shang, T; Wang, C; Cao, G-H; Eremin, I; Ott, H-R; Mesot, J

2017-07-31

Unlike the widely studied ReFeAsO series, the newly discovered iron-based superconductor ThFeAsN exhibits a remarkably high critical temperature of 30 K, without chemical doping or external pressure. Here we investigate in detail its magnetic and superconducting properties via muon-spin rotation/relaxation and nuclear magnetic resonance techniques and show that ThFeAsN exhibits strong magnetic fluctuations, suppressed below ~35 K, but no magnetic order. This contrasts strongly with the ReFeAsO series, where stoichiometric parent materials order antiferromagnetically and superconductivity appears only upon doping. The ThFeAsN case indicates that Fermi-surface modifications due to structural distortions and correlation effects are as important as doping in inducing superconductivity. The direct competition between antiferromagnetism and superconductivity, which in ThFeAsN (as in LiFeAs) occurs at already zero doping, may indicate a significant deviation of the s-wave superconducting gap in this compound from the standard s ± scenario.Exploring the interplay between the superconducting gap and the antiferromagnetic phase in Fe-based superconductors remains an open issue. Here, the authors show that Fermi-surface modifications by means of structural distortions and correlation effects are as important as doping in inducing superconductivity in undoped ThFeAsN.

Oxygen-Vacancy-Induced Polar Behavior in (LaFeO 3) 2/(SrFeO 3) Superlattices

DOE PAGES

Mishra, Rohan; Kim, Young-Min; Salafranca, Juan; ...

2014-04-15

Complex oxides displaying ferroelectric and/or multiferroic behavior are of high fundamental and applied interest. In this work, for the first time, we show that it is possible to achieve polar order in a superlattice made up of two nonpolar oxides by means of oxygen vacancy ordering. Using scanning transmission electron microscopy imaging, we show the polar displacement of magnetic Fe ions in a superlattice of (LaFeO 3) 2/(SrFeO 3) grown on a SrTiO 3 substrate. Using density functional theory calculations, we systematically study the effect of epitaxial strain, octahedral rotations, and surface terminations in the superlattice and find them tomore » have a negligible effect on the antipolar displacements of the Fe ions lying in between SrO and LaO layers of the superlattice (i.e., within La 0.5Sr 0.5FeO 3 unit cells). The introduction of oxygen vacancies, on the other hand, triggers a polar displacement of the Fe ions. We confirm this important result using electron energy loss spectroscopy, which shows partial oxygen vacancy ordering in the region where polar displacements are observed and an absence of vacancy ordering outside of that area.« less

The Iron Project & Opacity Project: Photoionization, radiative transitions of iron ions for Opacities and Astrophysical Applications

NASA Astrophysics Data System (ADS)

Zhao, Lianshui; Nahar, Sultana; Pradhan, Anil; Eissner, Werner

2017-04-01

We have carried out converged close coupling R-Matrix (CCC-RM) calculations for photoionization of Ne-like Fe XVII and demonstrate orders-of-magnitude enhancements in cross section due to successive core excitations. Convergence criteria are: (i) inclusion of sufficient number of residual ion Fe XVIII core states, (ii) high-resolution of myriad autoionizing resonances, and (iii) high-energy cross sections. We discuss verification of the conventional oscillator strength sum-rule in limited energy regions for bound-free plasma opacity. High energy cross sections are also under investigation. In order to obtain solar iron opacity at the boundary of the radiative and convection zones, we have studied the residual ion states that should provide convergence of resonances of other L-shell iron ions, Fe XIV - Fe XX, in the plasma region. Preliminary results from R-matrix calculations of photoionization cross sections will be reported. NSF, DOE, OSC.

Orbital ordering in FeV2O4: Spinel with two orbitally active sites

NASA Astrophysics Data System (ADS)

Sarkar, Soumyajit; Saha-Dasgupta, T.

2011-12-01

By employing first-principles electronic structure calculations, we investigate orbital ordering in FeV2O4, a spinel with orbital degrees of freedom both at Fe and V sites that exhibits two tetragonal phases, one compressed at high temperature and another elongated at low temperature. Our first-principles study shows the ferro-orbital ordering of dx2-y2 and d3z2-r2 types at Fe sites at the high- and low-temperature phases, respectively. The orbital ordering at V sites is found to consist of orbital chains running along different directions with orbitals rotated alternatively within each chain, similar to that found for MnV2O4 [S. Sarkar , Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.102.216405 102, 216405 (2009)]. Further, we find that the single-ion anisotropy effect with hard and easy c axis favors the compressed and elongated tetrahedral shapes. This gives rise to magnetocrystalline anisotropy-dependent shapes, similar to that reported in the context of rare-earth-based magnetic shape memory alloys.

Formation of ferric oxides from aqueous solutions: A polyhedral approach by X-ray absorption spectroscopy. I. Hydrolysis and formation of ferric gels

DOE Office of Scientific and Technical Information (OSTI.GOV)

Combes, J.M.; Manceau, A.; Calas, G.

1989-03-01

X-ray absorption spectroscopy (XAS) was used to follow the evolution of local structural environments around ferric ions during the formation of ferric hydrous oxide gels from 1 M chloride and 0.1 M nitrate solutions. Fe K-XANES and EXAFS confirm that ferric ions remain 6-fold coordinated during this evolution. With increasing OH availability in the solution, Cl{sup {minus}} anions tend gradually to be exchanged for (O, OH, OH{sub 2}) ligands. Below OH/Fe = 1, no structural order is detected beyond the first coordination sphere. Above this ratio, two Fe-Fe distances at 3.05 {angstrom} and 3.44 {angstrom} are observed and correspond tomore » the presence of edge- and vertex-sharing Fe-octahedra. XAS results show that ferric gels and highly polymerized aqueous species are short-range ordered. The main contribution to disorder in the gels arises from the small size of coherently scattering domains also responsible for their X-ray amorphous character. From the initial to the final stage of hydrolysis, particles possess a nearly spherical shape with a minimum average diameter ranging from 10-30 {angstrom} for polymers formed from chloride and nitrate solutions. As polymerization proceeds, the local order extends to several tens of angstroms and the particle structures becomes progressively closer to that of akaganeite ({beta}-FeOOH) or goethite ({alpha}-FeOOH). This local structure is distinct from that of the lepidocrocite ({gamma}-FeOOH)-like structure of ferric gels precipitated after oxidation of divalent Fe solutions. The growth of the crystalline Fe-oxyhydroxides from gels takes place by the progressive long-range ordering in the ferric polymers without modifying the short-range order around Fe.« less

Modification of local order in FePd films by low energy He{sup +} irradiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Merkel, D. G.; Tancziko, F.; Sajti, Sz.

2008-07-01

Owing to their strong perpendicular magnetic anisotropy, FePd, CoPd, and their Co(Fe)Pt counterparts are candidate materials for ultrahigh density magnetic recording. The stability and magnetic properties of such films are largely dependent on the orientation and local distribution of the L1{sub 0} FePd phase fraction. Therefore, the formation and transformation of the L1{sub 0} phase in such thin films have been the subject of continued interest. Highly ordered epitaxial FePd(001) thin films (with an L1{sub 0} phase fraction of 0.81) were prepared by molecular-beam epitaxy on a MgO(001) substrate. The effect of postgrown room temperature, 130 keV He{sup +} irradiationmore » was investigated at fluences up to 14.9x10{sup 15} ions/cm{sup 2}. X-ray diffraction and conversion electron Moessbauer spectroscopy revealed that with increasing fluence, the L1{sub 0} FePd phase decomposes into the face centered cubic phase with random Fe and Pd occupation of the sites. A partially ordered local environment exhibiting a large hyperfine magnetic field also develops. Upon He{sup +} irradiation, the lattice parameter c of the FePd L1{sub 0} structure increases and the long range order parameter S steeply decreases. The Fe-Fe nearest-neighbor coordination in the Fe-containing environments increases on average from Fe{sub 47}Pd{sub 53} to Fe{sub 54}Pd{sub 46}, indicating a tendency of formation iron-rich clusters. The equilibrium parameters corresponding to the equiatomic L1{sub 0} phase were found at different fluences by conversion electron Moessbauer spectroscopy and by x-ray diffraction a difference, from which a plane-perpendicular compressive stress and a corresponding in-plane tensile stress are conjectured. The steep increase in the interface roughness above 7.4x10{sup 15} ions/cm{sup 2} is interpreted as a percolation-type behavior related to the high diffusion anisotropy in the L1{sub 0} phase.« less

Rate-induced solubility and suppression of the first-order phase transition in olivine LiFePO4.

PubMed

Zhang, Xiaoyu; van Hulzen, Martijn; Singh, Deepak P; Brownrigg, Alex; Wright, Jonathan P; van Dijk, Niels H; Wagemaker, Marnix

2014-05-14

The impact of ultrahigh (dis)charge rates on the phase transition mechanism in LiFePO4 Li-ion electrodes is revealed by in situ synchrotron diffraction. At high rates the solubility limits in both phases increase dramatically, causing a fraction of the electrode to bypass the first-order phase transition. The small transforming fraction demonstrates that nucleation rates are consequently not limiting the transformation rate. In combination with the small fraction of the electrode that transforms at high rates, this indicates that higher performances may be achieved by further optimizing the ionic/electronic transport in LiFePO4 electrodes.

Influence of nonmagnetic Al ions on magnetoresistance of double-perovskite Sr2Fe1-xAlxMoO6 (0<=x<=0.30)

NASA Astrophysics Data System (ADS)

Sui, Yu; Wang, Xianjie; Cheng, Jinguang; Liu, Zhiguo; Miao, Jipeng; Huang, Xiqiang; Lu, Zhe; Qian, Zhengnan; Su, Wenhui; Tang, Jinke; Ong, C. K.

2005-09-01

The structural, magnetic, and magnetoresistance properties of the double-perovskite series Sr2Fe1-xAlxMoO6 (0<=x<=0.30) were systematically investigated in order to clarify the influence of nonmagnetic Al ions on the magnetoresistance. The structural refinements of these samples show that the degree of cationic order increases gradually from 88.5% for x=0 to 92% for x=0.30 without any change in the crystal structure. The magnetization measurements reveal that the substitution of nonmagnetic Al ion for Fe ion enhances the magnetic moment per Fe ion significantly. In addition, the magnetic-field dependence of magnetization and magnetoresistance of these Sr2Fe1-xAlxMoO6 samples were all fitted excellently by taking into account the contributions from ferromagnetic-coupled Fe-O-Mo region and nonferromagnetic-coupled regions. The fitting results indicate that the low-field magnetoresistance can be greatly enhanced due to the separation of the cationic-ordered Fe-O-Mo regions by the paramagnetic Mo-O-Al-O-Mo chains introduced through Al doping. Furthermore, doping nonmagnetic Al ions also suppress the formation of antiferromagnetic Fe-O-Fe antiphase boundaries, and then lead to the improvement of cation ordering and the reduction of magnetoresistance under high field.

Alloying effects of Ni, Si, and S on the phase diagram and sound velocities of Fe under high pressures and high temperatures

NASA Astrophysics Data System (ADS)

Lin, J.; Fei, Y.; Sturhahn, W.; Zhao, J.; Mao, H.; Hemley, R.

2004-05-01

Iron-nickel is the most abundant constituent of the Earth's core. The amount of Ni in the core is about 5.5 wt%. Geophysical and cosmochemical studies suggest that the Earth's outer core also contains approximately 10% of light element(s) and a certain amount of light element(s) may be present in the inner core. Si and S are believed to be alloying light elements in the iron-rich planetary cores such as the Earth and Mars. Therefore, understanding the alloying effects of Ni, Si, and S on the phase diagram and physical properties of Fe under core conditions is crucial for geophysical and geochemical models of planetary interiors. The addition of Ni and Si does not appreciably change the compressibility of hcp-Fe under high pressures. Studies of the phase relations of Fe and Fe-Ni alloys indicate that Fe with up to 10 wt% Ni is likely to be in the hcp structure under inner core conditions. On the other hand, adding Si into Fe strongly stabilizes the bcc structure to much higher pressures and temperatures (Lin et al., 2002). We have also studied the sound velocities and magnetic properties of Fe0.92Ni0.08, Fe0.85Si0.15, and Fe3S alloys with nuclear resonant inelastic x-ray scattering and nuclear forward scattering up to 106 GPa, 70 GPa, and 57 GPa, respectively. The sound velocities of the alloys are obtained from the measured partial phonon density of states for 57Fe incorporated in the alloys. Addition of Ni slightly decreases the VP and VS of Fe under high pressures (Lin et al., 2003). Si or S alloyed with Fe increases the VP and VS under high pressures, which provides a better match to seismological data of the Earth's core. We note that the increase in the VP and VS of Fe0.85Si0.15 and Fe3S is mainly contributed from the density decrease of adding Si and S in iron. Time spectra of the nuclear forward scattering reveal that the most iron rich sulfide, Fe3S, undergoes a magnetic to non-magnetic transition at approximately 18 GPa from a low-pressure magnetically ordered state to a high-pressure non-magnetic ordered state. The magnetic transition significantly affects the elastic, thermodynamic, and vibrational properties of Fe3S. It is conceivable that the magnetic collapse of Fe3S may also affect the binary phase diagram of the iron-sulfur system, changing the solubility of sulfur in iron under higher pressures. Study of the non-magnetic phase is more relevant to understand the properties of the Fe3S under planetary core conditions where high pressures and high temperature ensure the non-magnetic ordering state, affecting the interpretation of the amount and properties of sulfur being in the planetary cores. If the Martian core is in the solid state containing 14.2 wt% sulfur, it is likely that the non-magnetic Fe3S phase is a dominant component and that our measured sound velocities of Fe3S can be used to understand the velocity profile in the Martian core.

Phase stability and magnetic behavior of FeCrCoNiGe high-entropy alloy

NASA Astrophysics Data System (ADS)

Huang, Shuo; Vida, Ádám; Molnár, Dávid; Kádas, Krisztina; Varga, Lajos Károly; Holmström, Erik; Vitos, Levente

2015-12-01

We report an alternative FeCrCoNiGe magnetic material based on FeCrCoNi high-entropy alloy with Curie point far below the room temperature. Investigations are done using first-principles calculations and key experimental measurements. Results show that the equimolar FeCrCoNiGe system is decomposed into a mixture of face-centered cubic and body-centered cubic solid solution phases. The increased stability of the ferromagnetic order in the as-cast FeCrCoNiGe composite, with measured Curie temperature of 640 K, is explained using the exchange interactions.

Three-dimensionally ordered macroporous Li2FeSiO4/C composite as a high performance cathode for advanced lithium ion batteries

NASA Astrophysics Data System (ADS)

Ding, Zhengping; Liu, Jiatu; Ji, Ran; Zeng, Xiaohui; Yang, Shuanglei; Pan, Anqiang; Ivey, Douglas G.; Wei, Weifeng

2016-10-01

Li2MSiO4 (M = Mn, Fe, Co, Ni, et al.) has received great attention because of the theoretical possibility to reversibly deintercalate two Li+ ions from the structure. However, the silicates still suffer from low electronic conductivity, sluggish lithium ion diffusion and structural instability upon deep cycling. In order to solve these problems, a "hard-soft" templating method has been developed to synthesize three-dimensionally ordered macroporous (3DOM) Li2FeSiO4/C composites. The 3DOM Li2FeSiO4/C composites show a high reversible capacity (239 mAh g-1) with ∼1.50 lithium ion insertion/extraction, a capacity retention of nearly 100% after 420 cycles and excellent rate capability. The enhanced electrochemical performance is ascribed to the interconnected carbon framework that improves the electronic conductivity and the 3DOM structure that offers short Li ion diffusion pathways and restrains volumetric changes.

High Temperature Oxidation of Hot-Dip Aluminized T92 Steels

NASA Astrophysics Data System (ADS)

Abro, Muhammad Ali; Hahn, Junhee; Lee, Dong Bok

2018-03-01

The T92 steel plate was hot-dip aluminized, and oxidized in order to characterize the high-temperature oxidation behavior of hot-dip aluminized T92 steel. The coating consisted of Al-rich topcoat with scattered Al3Fe grains, Al3Fe-rich upper alloy layer with scattered (Al, Al5Fe2, AlFe)-grains, and Al5Fe2-rich lower alloy layer with scattered (Al5Fe2, AlFe)-grains. Oxidation at 800 °C for 20 h formed (α-Al2O3 scale)/(AlFe layer)/(AlFe3 layer)/(α-Fe(Al) layer), while oxidation at 900 °C for 20 h formed (α-Al2O3 scale plus some Fe2O3)/(AlFe layer)/(AlFe3 layer)/(α-Fe(Al) layer) from the surface. During oxidation, outward migration of all substrate elements, inward diffusion of oxygen, and back and forth diffusion of Al occurred according to concentration gradients. Also, diffusion transformed and broadened AlFe and AlFe3 layers dissolved with some oxygen and substrate alloying elements. Hot-dip aluminizing improved the high-temperature oxidation resistance of T92 steel through preferential oxidation of Al at the surface.

High Temperature Oxidation of Hot-Dip Aluminized T92 Steels

NASA Astrophysics Data System (ADS)

Abro, Muhammad Ali; Hahn, Junhee; Lee, Dong Bok

2018-05-01

The T92 steel plate was hot-dip aluminized, and oxidized in order to characterize the high-temperature oxidation behavior of hot-dip aluminized T92 steel. The coating consisted of Al-rich topcoat with scattered Al3Fe grains, Al3Fe-rich upper alloy layer with scattered (Al, Al5Fe2, AlFe)-grains, and Al5Fe2-rich lower alloy layer with scattered (Al5Fe2, AlFe)-grains. Oxidation at 800 °C for 20 h formed (α-Al2O3 scale)/(AlFe layer)/(AlFe3 layer)/(α-Fe(Al) layer), while oxidation at 900 °C for 20 h formed (α-Al2O3 scale plus some Fe2O3)/(AlFe layer)/(AlFe3 layer)/(α-Fe(Al) layer) from the surface. During oxidation, outward migration of all substrate elements, inward diffusion of oxygen, and back and forth diffusion of Al occurred according to concentration gradients. Also, diffusion transformed and broadened AlFe and AlFe3 layers dissolved with some oxygen and substrate alloying elements. Hot-dip aluminizing improved the high-temperature oxidation resistance of T92 steel through preferential oxidation of Al at the surface.

Growth of L1{sub 0}-ordered crystal in FePt and FePd thin films on MgO(001) substrate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Futamoto, Masaaki, E-mail: futamoto@elect.chuo-u.ac.jp; Nakamura, Masahiro; Ohtake, Mitsuru

2016-08-15

Formation of L1{sub 0}-oredered structure from disordered A1 phase has been investigated for FePt and FePd films on MgO(001) substrates employing a two-step method consisting of low temperature deposition at 200 °C followed by high-temperature annealing at 600 °C. L1{sub 0}-(001) variant crystal with the c-axis perpendicular to the substrate grows preferentially in FePd films whereas L1{sub 0}-(100), (010) variants tend to be mixed with the L1{sub 0}-(001) variant in FePt films. The structure analysis by X-ray diffraction indicates that a difference in A1 lattice strain is the influential factor that determines the resulting L1{sub 0}-variant structure in ordered thinmore » films. Misfit dislocations and anti-phase boundaries are observed in high-resolution transmission electron micrographs of 10 nm-thick Fe(Pt, Pd) film consisting of L1{sub 0}-(001) variants which are formed through atomic diffusion at 600 °C in a laterally strained FePt/PeFd epitaxial thin film. Based on the experimental results, a nucleation and growth model for explaining L1{sub 0}-variant formation is proposed, which suggests a possibility in tailoring the L1{sub 0} variant structure in ordered magnetic thin films by controlling the alloy composition, the layer structure, and the substrate material.« less

Orbital frustration induced unusual ordering in semiconductor alloys

NASA Astrophysics Data System (ADS)

Liu, Kai; Yin, Wanjian; Chen, Shiyou; Gong, Xingao; Wei, Suhuai; Xiang, Hongjun

It is well known that ternary zinc-blende semiconductors are always more stable in the chalcopyrite (CH) structure than the Cu-Au (CA) structure because CH structure has large Coulomb interaction and reduced strain energy. Surprisingly, an experimental study showed that ZnFeSe2 alloy takes the CA order as the ground state structure, which is consistent with our density function theory (DFT) calculations showing that the CA order has lower energy than the CH order for ZnFeSe2. We reveal that the orbital degree of freedom of high-spin Fe2+ ion (d6) in the tetrahedral crystal field plays a key role in stabilizing the CA order. First, the spin-minority d electron of the Fe2+ ion tends to occupy the dx2-y 2 -like orbital instead of the d3z2 -r2 -like orbital because of its large negative Coulomb energy. Second, for a nearest-neighboring Fe2+ pair, two spin-minority d electrons with occupied dx2-y 2 -like orbitals in the plane containing the Fe-Fe bond has lower electronic kinetic energy. Both conditions can be satisfied in the CA ordered ZnFeSe2 alloy, while there is an orbital frustration in the CH structure. Our results suggest that orbital degree of freedom provides a new way to manipulate the structure and properties of alloys. Work at Fudan was supported by NSFC (11374056), the Special Funds for Major State Basic Research (2012CB921400, 2015CB921700), Program for Professor of Special Appointment (Eastern Scholar), and Fok Ying Tung Education Foundation.

Large-moment antiferromagnetic order in overdoped high-Tc superconductor 154SmFeAsO1-x D x .

PubMed

Iimura, Soshi; Okanishi, Hiroshi; Matsuishi, Satoru; Hiraka, Haruhiro; Honda, Takashi; Ikeda, Kazutaka; Hansen, Thomas C; Otomo, Toshiya; Hosono, Hideo

2017-05-30

In iron-based superconductors, high critical temperature ( T c ) superconductivity over 50 K has only been accomplished in electron-doped hRE FeAsO ( hRE is heavy rare earth ( RE ) element). Although hRE FeAsO has the highest bulk T c (58 K), progress in understanding its physical properties has been relatively slow due to difficulties in achieving high-concentration electron doping and carrying out neutron experiments. Here, we present a systematic neutron powder diffraction study of 154 SmFeAsO 1- x D x , and the discovery of a long-range antiferromagnetic ordering with x ≥ 0.56 (AFM2) accompanying a structural transition from tetragonal to orthorhombic. Surprisingly, the Fe magnetic moment in AFM2 reaches a magnitude of 2.73 μ B /Fe, which is the largest in all nondoped iron pnictides and chalcogenides. Theoretical calculations suggest that the AFM2 phase originates in kinetic frustration of the Fe-3 d xy orbital, in which the nearest-neighbor hopping parameter becomes zero. The unique phase diagram, i.e., highest- T c superconducting phase adjacent to the strongly correlated phase in electron-overdoped regime, yields important clues to the unconventional origins of superconductivity.

Well-isolated FePt grains with high coercivity on TiN underlayers for heat-assisted magnetic recording media

NASA Astrophysics Data System (ADS)

Santos, Tiffany; Jain, Shikha; Hirotsune, Akemi; Hellwig, Olav

2015-03-01

MgO is the underlayer material of choice for granular FePt thin film media for heat assisted magnetic recording, because MgO (001) seeds L10-ordered FePt with c-axis perpendicular to the film plane and high perpendicular magnetic anisotropy. MgO is also an effective diffusion barrier between the FePt grains and the metallic underlayers beneath the MgO. However, there are possible concerns associated with using MgO in the media structure. MgO is highly sensitive to moisture, and hydration of MgO could potentially degrade film properties. In addition, many particulates are incorporated into the film during the RF-sputter process, which can be sources of delamination, pinholes and damage to the low-flying recording heads. TiN is an attractive alternative to MgO because it is chemically and mechanically robust, and TiN can be DC-sputtered, which produces fewer particles and has a faster deposition rate. Even though TiN has the same rocksalt crystal structure and lattice constant as MgO, the higher surface energy of TiN causes more wetting of the FePt grains on the TiN surface. As a result, deposition of granular FePt on TiN most often produces inter-connected, worm-like grains with low coercivity. We will show that by optimizing the deposition of FePt and segregant material on the TiN underlayer, we are able to fabricate FePt media with well-isolated grains and high coercivity reaching nearly 4 Tesla. In addition, the FePt has excellent structural properties with a high degree of L10 atomic ordering and minimal c-axis in-plane oriented grains.

Crystal structures of (Mg1-x,Fe(x))SiO3 postperovskite at high pressures.

PubMed

Yamanaka, Takamitsu; Hirose, Kei; Mao, Wendy L; Meng, Yue; Ganesh, P; Shulenburger, Luke; Shen, Guoyin; Hemley, Russell J

2012-01-24

X-ray diffraction experiments on postperovskite (ppv) with compositions (Mg(0.9)Fe(0.1))SiO(3) and (Mg(0.6)Fe(0.4))SiO(3) at Earth core-mantle boundary pressures reveal different crystal structures. The former adopts the CaIrO(3)-type structure with space group Cmcm, whereas the latter crystallizes in a structure with the Pmcm (Pmma) space group. The latter has a significantly higher density (ρ = 6.119(1) g/cm(3)) than the former (ρ = 5.694(8) g/cm(3)) due to both the larger amount of iron and the smaller ionic radius of Fe(2+) as a result of an electronic spin transition observed by X-ray emission spectroscopy (XES). The smaller ionic radius for low-spin compared to high-spin Fe(2+) also leads to an ordered cation distribution in the M1 and M2 crystallographic sites of the higher density ppv structure. Rietveld structure refinement indicates that approximately 70% of the total Fe(2+) in that phase occupies the M2 site. XES results indicate a loss of 70% of the unpaired electronic spins consistent with a low spin M2 site and high spin M1 site. First-principles calculations of the magnetic ordering confirm that Pmcm with a two-site model is energetically more favorable at high pressure, and predict that the ordered structure is anisotropic in its electrical and elastic properties. These results suggest that interpretations of seismic structure in the deep mantle need to treat a broader range of mineral structures than previously considered.

Kinetic hindrance of Fe(II) oxidation at alkaline pH and in the presence of nitrate and oxygen in a facultative wastewater stabilization pond.

PubMed

Rockne, Karl J

2007-02-15

To better understand the dynamics of Fe2 + oxidation in facultative wastewater stabilization ponds, water samples from a three-pond system were taken throughout the period of transition from anoxic conditions with high aqueous Fe2 + levels in the early spring to fully aerobic conditions in late spring. Fe2 + levels showed a highly significant correlation with pH but were not correlated with dissolved oxygen (DO). Water column Fe2 + levels were modeled using the kinetic rate law for Fe2 + oxidation of Sung and Morgan.[5] The fitted kinetic coefficients were 5 +/- 3 x 10(6) M(- 2) atm(-1) min(-1); more than six orders of magnitude lower than typically reported. Comparison of four potential Fe redox couples demonstrated that the rhoepsilon was at least 3-4 orders of magnitude higher than would be expected based on internal equilibrium. Surprisingly, measured nitrate and DO (when present) were typically consistent with both nitrate (from denitrification) and DO levels (from aerobic respiration) predicted from equilibrium. Although the hydrous Fe oxide/FeCO3 couple was closest to equilibrium and most consistent with the observed pH dependence (in contrast to predicted lepidocrocite), Fe2 + oxidation is kinetically hindered, resulting in up to 10(7)-fold higher levels than expected based on both kinetic and equilibrium analyses.

High-precision QEC values of superallowed 0+ → 0+β-emitters 46Cr, 50Fe and 54Ni

NASA Astrophysics Data System (ADS)

Zhang, P.; Xu, X.; Shuai, P.; Chen, R. J.; Yan, X. L.; Zhang, Y. H.; Wang, M.; Litvinov, Yu. A.; Blaum, K.; Xu, H. S.; Bao, T.; Chen, X. C.; Chen, H.; Fu, C. Y.; He, J. J.; Kubono, S.; Lam, Y. H.; Liu, D. W.; Mao, R. S.; Ma, X. W.; Sun, M. Z.; Tu, X. L.; Xing, Y. M.; Yang, J. C.; Yuan, Y. J.; Zeng, Q.; Zhou, X.; Zhou, X. H.; Zhan, W. L.; Litvinov, S.; Audi, G.; Uesaka, T.; Yamaguchi, Y.; Yamaguchi, T.; Ozawa, A.; Sun, B. H.; Sun, Y.; Xu, F. R.

2017-04-01

Short-lived 46Cr, 50Fe and 54Ni were studied by isochronous mass spectrometry at the HIRFL-CSR facility in Lanzhou. The measured precision mass excesses (ME) of 46Cr, 50Fe and 54Ni are - 29471 (11) keV, - 34477 (6) keV and - 39278 (4) keV, respectively. The superallowed 0+ →0+β-decay Q values were derived to be QEC (46Cr) = 7604 (11) keV, QEC (50Fe) = 8150 (6) keV and QEC (54Ni) = 8731 (4) keV. The values for 50Fe and 54Ni are by one order of magnitude more precise than the adopted literature values. By combining the existing half-lives and branching ratios, we obtained the corrected Ft values to be Ft (50Fe) = 3103 (70) s and Ft (54Ni) = 3076 (50) s. The main contribution to the Ft uncertainties is now due to β-decay branching ratios, still, more high-precision measurements of the half-lives, the masses, and especially the branching ratios are needed in order to satisfy the requirements for a stringent CVC test.

Orbital occupancy evolution across spin- and charge-ordering transitions in YBaFe2O5

NASA Astrophysics Data System (ADS)

Lindén, J.; Lindroos, F.; Karen, P.

2017-08-01

Thermal evolution of the Fe2+-Fe3+ valence mixing in YBaFe2O5 is investigated using Mössbauer spectroscopy. In this high-spin double-cell perovskite, the d6 and d5 Fe states differ by the single minority-spin electron which then controls all the spin- and charge-ordering transitions. Orbital occupancies can be extracted from the spectra in terms of the dxz , dz2 and either dx2-y2 (Main Article) or dxy (Supplement) populations of this electron upon conserving its angular momentum. At low temperatures, the minority-spin electrons fill up the ordered dxz orbitals of Fe2+, in agreement with the considerable orthorhombic distortion of the structure. Heating through the Verwey transition supplies 93% of the mixing entropy, at which point the predominantly mixing electron occupies mainly the dx2-y2 /dxy orbitals weakly bonding the two Fe atoms that face each other across the bases of their coordination pyramids. This might stabilize a weak coulombic checkerboard order suggested by McQueeney et alii in Phys. Rev. B 87(2013)045127. When the remaining 7% of entropy is supplied at a subsequent transition, the mixing electron couples the two Fe atoms predominantly via their dz2 orbitals. The valence mixing concerns more than 95% of the Fe atoms present in the crystalline solid; the rest is semi-quantitatively interpreted as domain walls and antiphase boundaries formed upon cooling through the Néel and Verwey-transition temperatures, respectively.

High pressure-temperature electrical conductivity of magnesiowustite as a function of iron oxide concentration

NASA Technical Reports Server (NTRS)

Li, Xiaoyuan; Jeanloz, Raymond

1990-01-01

The electrical conductivity of (Mg, Fe)O magnesiowustite containing 9 and 27.5 mol pct FeO has been measured at simultaneously high pressures (30-32 GPa) and temperatures using a diamond anvil cell heated with a continuous wave Nd:YAG laser and an external resistance heater. The conductivity depends strongly on the FeO concentration at both ambient and high pressures. At the pressures and temperatures of about 30 GPa and 2000 K, conditions expected in the lower mantle, the magnesiowustite containing 27.5 percent FeO is 3 orders of magnitude more conductive than that containing 9 percent FeO. The activation energy of magnesiowustite decreases with increasing iron concentration from 0.38 (+ or - 0.09) eV at 9 percent FeO to 0.29 (+ or - 0.05) eV at 27.5 percent FeO.

Nb-Based Nb-Al-Fe Alloys: Solidification Behavior and High-Temperature Phase Equilibria

NASA Astrophysics Data System (ADS)

Stein, Frank; Philips, Noah

2018-03-01

High-melting Nb-based alloys hold significant promise for the development of novel high-temperature materials for structural applications. In order to understand the effect of alloying elements Al and Fe, the Nb-rich part of the ternary Nb-Al-Fe system was investigated. A series of Nb-rich ternary alloys were synthesized from high-purity Nb, Al, and Fe metals by arc melting. Solidification paths were identified and the liquidus surface of the Nb corner of the ternary system was established by analysis of the as-melted microstructures and thermal analysis. Complementary analysis of heat-treated samples yielded isothermal sections at 1723 K and 1873 K (1450 °C and 1600 °C).

Synthesis of magnetic CoFe2O4/ordered mesoporous carbon nanocomposites and application in Fenton-like oxidation of rhodamine B.

PubMed

Deng, Jing; Chen, Yi-Jing; Lu, Yu-An; Ma, Xiao-Yan; Feng, Shan-Fang; Gao, Naiyun; Li, Jun

2017-06-01

CoFe 2 O 4 /ordered mesoporous carbon (OMC) nanocomposites were synthesized and tested as heterogeneous peroxymonosulfate (PMS) activator for the removal of rhodamine B. Characterization confirmed that CoFe 2 O 4 nanoparticles were tightly bonded to OMC, and the hybrid catalyst possessed high surface area, pore volume, and superparamagnetism. Oxidation experiments demonstrated that CoFe 2 O 4 /OMC nanocomposites displayed favorable catalytic activity in PMS solution and rhodamine B degradation could be well described by pseudo-first-order kinetic model. Sulfate radicals (SO 4 - ·) were verified as the primary reactive species which was responsible for the decomposition of rhodamine B. The optimum loading ratio of CoFe 2 O 4 and OMC was determined to be 5:1. Under optimum operational condition (catalyst dosage 0.05 g/L, PMS concentration 1.5 mM, pH 7.0, and 25 °C), CoFe 2 O 4 /OMC-activated peroxymonosulfate system could achieve almost complete decolorization of 100 mg/L rhodamine B within 60 min. The enhanced catalytic activity of CoFe 2 O 4 /OMC nanocomposites compared to that of CoFe 2 O 4 nanoparticles could be attributable to the increased adsorption capacity and accelerated redox cycles between Co(III)/Co(II) and Fe(III)/Fe(II).

Electronic origin of structural transition in 122 Fe based superconductors

NASA Astrophysics Data System (ADS)

Ghosh, Haranath; Sen, Smritijit; Ghosh, Abyay

2017-03-01

Direct quantitative correlations between the orbital order and orthorhombicity is achieved in a number of Fe-based superconductors of 122 family. The former (orbital order) is calculated from first principles simulations using experimentally determined doping and temperature dependent structural parameters while the latter (the orthorhombicity) is taken from already established experimental studies; when normalized, both the above quantities quantitatively corresponds to each other in terms of their doping as well as temperature variations. This proves that the structural transition in Fe-based materials is electronic in nature due to orbital ordering. An universal correlations among various structural parameters and electronic structure are also obtained. Most remarkable among them is the mapping of two Fe-Fe distances in the low temperature orthorhombic phase, with the band energies Edxz, Edyz of Fe at the high symmetry points of the Brillouin zone. The fractional co-ordinate zAs of As which essentially determines anion height is inversely (directly) proportional to Fe-As bond distances (with exceptions of K doped BaFe2As2) for hole (electron) doped materials as a function of doping. On the other hand, Fe-As bond-distance is found to be inversely (directly) proportional to the density of states at the Fermi level for hole (electron) doped systems. Implications of these results to current issues of Fe based superconductivity are discussed.

Heat capacity and magnetic properties of fluoride CsFe{sup 2+}Fe{sup 3+}F{sub 6} with defect pyrochlore structure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gorev, M.V., E-mail: gorev@iph.krasn.ru; Institute of Engineering Physics and Radio Electronics, Siberian State University, 660074 Krasnoyarsk; Flerov, I.N.

2016-05-15

Heat capacity, Mössbauer and Raman spectra as well as magnetic properties of fluoride CsFe{sub 2}F{sub 6} with defect pyrochlore structure were studied. In addition to recently found above room temperature three successive structural transformations Pnma-Imma-I4{sub 1}amd-Fd-3m, phase transition of antiferromagnetic nature with the 13.7 K Neel temperature and a broad heat capacity anomaly with a maximum at about 30 K were observed. The room temperature symmetry Pnma is unchanged at least down to 7 K. Simple model of indirect bond used to estimate the exchange interactions and to propose a magnetic structure model. - Graphical abstract: The ordered arrangement ofmore » Fe{sup 2+} and Fe{sup 3+} ions in high-spin states as well as antiferromagnetic phase transition followed by significant magnetic frustrations were found in pyrocholore-related CsFe{sup 2+}Fe{sup 3+}F{sub 6}. A magnetic structure was proposed using a simple model of indirect bonds. - Highlights: • The Pnma structure in pyrocholore CsFe{sub 2}F{sub 6} is stable down to helium temperature. • Mössbauer spectra confirmed the ordering of Fe{sup 2+} and Fe{sup 3+} ions. • Antiferromagnetic transformation and significant magnetic frustrations are found. • Experimental magnetic entropy agrees with entropy for Fe ions in high-spin state. • Superexchange interactions were calculated and a magnetic structure was proposed.« less

The effect of Fe-coverage on the structure, morphology and magnetic properties of α-FeSi2 nanoislands.

PubMed

Tripathi, J K; Garbrecht, M; Kaplan, W D; Markovich, G; Goldfarb, I

2012-12-14

Self-assembled α-FeSi(2) nanoislands were formed using solid-phase epitaxy of low (~1.2 ML) and high (~21 ML) Fe coverages onto vicinal Si(111) surfaces followed by thermal annealing. At a resulting low Fe-covered Si(111) surface, we observed in situ, by real-time scanning tunneling microscopy and surface electron diffraction, the entire sequence of Fe-silicide formation and transformation from the initially two-dimensional (2 × 2)-reconstructed layer at 300 °C into (2 × 2)-reconstructed nanoislands decorating the vicinal step-bunch edges in a self-ordered fashion at higher temperatures. In contrast, the silicide nanoislands at a high Fe-covered surface were noticeably larger, more three-dimensional, and randomly distributed all over the surface. Ex situ x-ray photoelectron spectroscopy and high-resolution transmission electron microscopy indicated the formation of an α-FeSi(2) island phase, in an α-FeSi(2){112} // Si{111} orientation. Superconducting quantum interference device magnetometry showed considerable superparamagnetism, with ~1.9 μ(B)/Fe atom at 4 K for the low Fe-coverage, indicating stronger ferromagnetic coupling of individual magnetic moments, as compared to high Fe-coverage, where the calculated moments were only ~0.8 μ(B)/Fe atom. Such anomalous magnetic behavior, particularly for the low Fe-coverage case, is radically different from the non-magnetic bulk α-FeSi(2) phase, and may open new pathways to high-density magnetic memory storage devices.

Dependence of the structure and electronic state of SrFeO/sub x/ (2. 5 less than or equal to x less than or equal to 3) on composition and temperature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Takano, N.; Okita, T.; Nakayama, N.

1988-03-01

The system SrFeO/sub x/, 2.5 less than or equal to x less than or equal to 3, forms a continuous solid solution at temperatures T greater than or equal to T/sub t/(x), but a series of discrete ordered-vacancy phases SrFeO/sub 3-(1/n)/ (n = infinity, 8, 4, 2) below temperatures T/sub t/(n =8) = 523 K, T/sub t/(n = 4) = 598 K, and T/sub t/(n = 2) = 1103 K. The most probable vacancy-ordering schemes for Sr/sub 8/Fe/sub 8/O/sub 23/ (n = 8) and Sr/sub 4/Fe/sub 4/O/sub 11/ (n = 4) are proposed. Formation of fivefold-coordinated iron sites on eithermore » side of an oxygen vacancy is characteristic of both phases, which contrasts with Sr/sub 2/Fe/sub 2/O/sub 5/ (n = 2) where four-coordinated sites coexist with six-coordinated sites. The high-spin Fe/sup 4 +/(t/sub 2//sup 3/sigma*/sup 1/) configuration of SrFeO/sub 3/ (n = infinity) evolves as follows: (a) for x approx. 3, random vacancies trap Fe/sup 3 +/ ions at five-coordinated sites; (b) for n = 8, Fe/sup 4 +/ ions remain high spin, a localized-electron /sup 5/E/sub g/ configuration giving rise to a cooperative Jahn-Teller distortion with c/a less than or equal to 1 and a (220)/sub n8/ unique axis imposed by structural symmetry; fast Fe/sup 3 +/ + Fe/sup 4 +/ = Fe/sup 4 +/ + Fe/sup 3 +/ electron transfer occurs parallel to this axis at room temperature, but Fe/sup 3 +/ ions are ordered at five-coordinated sites at 4 K; (c) for n = 4, the octahedral-site Fe/sup 4 +/ ions have a low-spin t/sub 2//sup 4/ configuration with four near-neighbor Fe/sup 3 +/ ions in five-coordinated sites not making an Fe/sup 3 +/-O-Fe/sup 4 +/-O-Fe/sup 3 +/ linear chain as in n = 8. Oxygen-vacancy hopping times tau/sub h/ greater than or equal to 10/sup -8/ sec persist for 200 K above T/sub t/ in n = 2, and short-range ordering in this temperature interval is inferred. For n = 8 and n = 4, motional narrowing to single Moessbauer peak occurs within tens of degrees above T/sub t/, and this narrowing is assumed to reflect rapid electron hopping in a mixed-valence state.« less

Effects of Au content on the structure and magnetic properties of L1{sub 0}-FePt nanoparticles synthesized by the sol–gel method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Yang; Institute of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013; Jiang, Yuhong

2014-07-01

(FePt){sub 100−x}Au{sub x} (x=0, 5, 10, and 20) nanoparticles were synthesized by the sol–gel method, and effects of Au content on the structural and magnetic properties of samples were investigated. Au doping reduced the phase transition temperature from face-centered cubic (FCC) to face-centered tetragonal (FCT) structure. In addition, additive Au promotes the chemical ordering of L1{sub 0} FePt NPs and increases the grain size of L1{sub 0} FePt NPs. When Au content increased from 0 to 10 at%, the coercivity (H{sub c}) increased due to the increase in degree of ordering S and grain size of L1{sub 0} FePt NPs.more » By increasing the Au content to 20 at%, H{sub c} decreased. - Graphical abstract: (FePt){sub 100}Au{sub 0} NPs are the coexistence of FCT and FCC phases. However, no hints of FCC phase were found for the (FePt){sub 100−x}Au{sub x} NPs (x=5, 10 and 20), which indicates that addition of gold greatly promotes the FCC to FCT phase transition. - Highlights: • (FePt){sub 100−x}Au{sub x} (x=0, 5, 10 and 20) nanoparticles (NPs) were synthesized. • Au addition promotes the chemical ordering of L1{sub 0} FePt NPs. • Au addition reduces ordering temperature of L1{sub 0} FePt NPs from FCC to FCT phase. • (FePt){sub 90}Au{sub 10} NPs show a high coercivity of 9585 Oe at room temperature.« less

Highly Loaded Fe-MCM-41 Materials: Synthesis and Reducibility Studies

PubMed Central

Mokhonoana, Malose P.; Coville, Neil J.

2009-01-01

Fe-MCM-41 materials were prepared by different methods. The Fe was both incorporated into the structure and formed crystallites attached to the silica. High Fe content MCM-41 (~16 wt%) with retention of mesoporosity and long-range order was achieved by a range of new synthetic methodologies: (i) by delaying the addition of Fe3+(aq) to the stirred synthesis gel by 2 h, (ii) by addition of Fe3+ precursor as a freshly-precipitated aqueous slurry, (iii) by exploiting a secondary synthesis with Si-MCM-41 as SiO2 source. For comparative purposes the MCM-41 was also prepared by incipient wetness impregnation (IWI). Although all these synthesis methods preserved mesoporosity and long-range order of the SiO2 matrix, the hydrothermally-fabricated Fe materials prepared via the secondary synthesis route has the most useful properties for exploitation as a catalyst, in terms of hydrothermal stability of the resulting support. Temperature-programmed reduction (TPR) studies revealed a three-peak reduction pattern for this material instead of the commonly observed two-peak reduction pattern. The three peaks showed variable intensity that related to the presence of two components: crystalline Fe2O3 and Fe embedded in the SiO2 matrix (on the basis of ESR studies). The role of secondary synthesis of Si-MCM-41 on the iron reducibility was also demonstrated in IWI of sec-Si-MCM-41.

Effect of soil parameters on the kinetics of the displacement of Fe from FeEDDHA chelates by Cu.

PubMed

Schenkeveld, Walter D C; Reichwein, Arjen M; Temminghoff, Erwin J M; van Riemsdijk, Willem H

2012-06-28

In soil application, o,o-FeEDDHA (iron (3+) ethylene diamine-N,N'-bis(2-hydroxy phenyl acetic acid) complex) is the active ingredient of FeEDDHA chelate-based Fe fertilizers. The effectiveness of o,o-FeEDDHA is potentially compromised by the displacement of Fe from FeEDDHA by Cu. The actual impact of Cu competition is codetermined by the kinetics of the displacement reaction. In this study, the influence of soil parameters on the displacement kinetics has been examined in goethite suspensions. The displacement reaction predominantly takes place on the reactive surface rather than in solution. The rate at which the o,o-FeEDDHA concentration declined depended on the available reactive surface area, the Cu loading, and the FeEDDHA loading. Soil factors reducing FeEDDHA adsorption (high ionic strength, humic acid adsorption onto the goethite surface, and monovalent instead of divalent cations in the electrolyte) decreased the displacement rate. For meso o,o-FeEDDHA, the displacement rate equation was derived, which is first order in FeEDDHA loading and half order in Cu loading. For soil conditions, the equation can be simplified to an exponential decay function in meso o,o-FeEDDHA solution concentration.

Octahedral cation partitioning in Mg,Fe2+-olivine. Mössbauer spectroscopic study of synthetic (Mg0.5 Fe2+ 0.5)2SiO4 (Fa50)

NASA Astrophysics Data System (ADS)

Morozov, Mikhail; Brinkmann, Christian; Grodzicki, Michael; Lottermoser, Werner; Tippelt, Gerold; Amthauer, Georg; Kroll, Herbert

2005-11-01

The high-temperature partitioning of Fe2+ and Mg between the two non-equivalent octahedral M1 and M2 sites in synthetic olivine (Fa50) was studied by Mössbauer spectroscopy. Powder samples have been equilibrated in annealing experiments performed under reducing oxygen fugacity at temperatures between 500 and 800°C followed by rapid quenching in order to prevent redistribution of cations. M-site ordering with Fe2+ preferring M1, Mg preferring M2 sites increases continuously with rising equilibrium temperature. K D values increase from 1.21 at 500°C to 1.48 at 750°C. The results are consistent with both room temperature as well as in situ high temperature single crystal X-ray diffraction experiments of Heinemann et al. [8, 9].

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cagnoli, M.V.; Marchetti, S.G.; Gallegos, N.G.

In order to study the influence of the support on high dispersion catalysts used for the CO hydrogenation reaction, two catalysts, Fe/SiO{sub 2} and Fe/Al{sub 2}O{sub 3}, were prepared by the dry impregnation method. Selective chemisorption of CO, volumetric oxidation, and Moessbauer spectroscopy were used to determine the Fe species present as well as the metallic crystal size, the degree of dispersion, and the reduction percentage. The presence of small Fe{sup 0} crystallites with high dispersion was determined in both catalysts. Reaction rates were measured in a differential reactor and significant differences, about one order of magnitude less for themore » Al{sub 2}O{sub 3} than for the SiO{sub 2} supported catalysts, were found in the methane turnover frequencies. They are attributed to the interaction between the metal and the supports. The selectivity differences is also discussed in connection with distinct surface properties.« less

Hf 3 Fe 4 Sn 4 and Hf 9 Fe 4-x Sn 10+x : Two stannide intermetallics with low-dimensional iron sublattices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Calta, Nicholas P.; Kanatzidis, Mercouri G.

2016-04-01

This article reports two new Hf-rich intermetallics synthesized using Sn flux: Hf 3Fe 4Sn 4 and Hf 9Fe 4-xSn 10+x. Hf 3Fe 4Sn 4 adopts an ordered variant the Hf 3Cu 8 structure type in orthorhombic space group Pnma with unit cell edges of a=8.1143(5) Å, b=8.8466(5) Å, and c=10.6069(6) Å. Hf 9Fe 4-xSn 10+x, on the other hand, adopts a new structure type in Cmc21 with unit cell edges of a=5.6458(3) Å, b=35.796(2) Å, and c=8.88725(9) Å for x=0. It exhibits a small amount of phase width in which Sn substitutes on one of the Fe sites. Both structuresmore » are fully three-dimensional and are characterized by pseudo one- and two-dimensional networks of Fe–Fe homoatomic bonding. Hf 9Fe 4-xSn 10+x exhibits antiferromagnetic order at TN=46(2) K and its electrical transport behavior indicates that it is a normal metal with phonon-dictated resistivity. Hf 3Fe 4Sn 4 is also an antiferromagnet with a rather high ordering temperature of TN=373(5) K. Single crystal resistivity measurements indicate that Hf 3Fe 4Sn 4 behaves as a Fermi liquid at low temperatures, indicating strong electron correlation.« less

Enhanced output-performance of piezoelectric poly(vinylidene fluoride trifluoroethylene) fibers-based nanogenerator with interdigital electrodes and well-ordered cylindrical cavities

NASA Astrophysics Data System (ADS)

Gui, Jinzheng; Zhu, Yezi; Zhang, Lingling; Shu, Xi; Liu, Wei; Guo, Shishang; Zhao, Xingzhong

2018-02-01

A piezoelectric nanogenerator based on poly(vinylidene fluoride trifluoroethylene) [P(VDF-TrFE)] nanofibers with an Au interdigital electrode (IDT)/P(VDF-TrFE) nanofiber film/well-ordered cylindrical cavity structure was prepared by combining Au IDTs with a rotary collector to obtain highly aligned P(VDF-TrFE) nanofiber arrays. The Au IDTs work not only as parallel electrodes to collect P(VDF-TrFE) nanofibers during electrospinning but also as charge-collecting electrodes in the nanogenerator. The well-ordered cylindrical cavities improve output performance by enhancing the deformation of P(VDF-TrFE) nanofiber films when subjected to external force. The nanogenerator performs well; as an example of application, we demonstrate energy harvesting from human walking, with a peak output voltage of 5 V and a peak short-circuit current of 1.2 μA. Such a device could have practical applications in wearable, self-powered devices.

Magnetic ground state of FeSe

PubMed Central

Wang, Qisi; Shen, Yao; Pan, Bingying; Zhang, Xiaowen; Ikeuchi, K.; Iida, K.; Christianson, A. D.; Walker, H. C.; Adroja, D. T.; Abdel-Hafiez, M.; Chen, Xiaojia; Chareev, D. A.; Vasiliev, A. N.; Zhao, Jun

2016-01-01

Elucidating the nature of the magnetism of a high-temperature superconductor is crucial for establishing its pairing mechanism. The parent compounds of the cuprate and iron-pnictide superconductors exhibit Néel and stripe magnetic order, respectively. However, FeSe, the structurally simplest iron-based superconductor, shows nematic order (Ts=90 K), but not magnetic order in the parent phase, and its magnetic ground state is intensely debated. Here we report inelastic neutron-scattering experiments that reveal both stripe and Néel spin fluctuations over a wide energy range at 110 K. On entering the nematic phase, a substantial amount of spectral weight is transferred from the Néel to the stripe spin fluctuations. Moreover, the total fluctuating magnetic moment of FeSe is ∼60% larger than that in the iron pnictide BaFe2As2. Our results suggest that FeSe is a novel S=1 nematic quantum-disordered paramagnet interpolating between the Néel and stripe magnetic instabilities. PMID:27431986

Magnetic ground state of FeSe.

PubMed

Wang, Qisi; Shen, Yao; Pan, Bingying; Zhang, Xiaowen; Ikeuchi, K; Iida, K; Christianson, A D; Walker, H C; Adroja, D T; Abdel-Hafiez, M; Chen, Xiaojia; Chareev, D A; Vasiliev, A N; Zhao, Jun

2016-07-19

Elucidating the nature of the magnetism of a high-temperature superconductor is crucial for establishing its pairing mechanism. The parent compounds of the cuprate and iron-pnictide superconductors exhibit Néel and stripe magnetic order, respectively. However, FeSe, the structurally simplest iron-based superconductor, shows nematic order (Ts=90 K), but not magnetic order in the parent phase, and its magnetic ground state is intensely debated. Here we report inelastic neutron-scattering experiments that reveal both stripe and Néel spin fluctuations over a wide energy range at 110 K. On entering the nematic phase, a substantial amount of spectral weight is transferred from the Néel to the stripe spin fluctuations. Moreover, the total fluctuating magnetic moment of FeSe is ∼60% larger than that in the iron pnictide BaFe2As2. Our results suggest that FeSe is a novel S=1 nematic quantum-disordered paramagnet interpolating between the Néel and stripe magnetic instabilities.

Nano-sized Superlattice Clusters Created by Oxygen Ordering in Mechanically Alloyed Fe Alloys

NASA Astrophysics Data System (ADS)

Hu, Yong-Jie; Li, Jing; Darling, Kristopher A.; Wang, William Y.; Vanleeuwen, Brian K.; Liu, Xuan L.; Kecskes, Laszlo J.; Dickey, Elizabeth C.; Liu, Zi-Kui

2015-07-01

Creating and maintaining precipitates coherent with the host matrix, under service conditions is one of the most effective approaches for successful development of alloys for high temperature applications; prominent examples include Ni- and Co-based superalloys and Al alloys. While ferritic alloys are among the most important structural engineering alloys in our society, no reliable coherent precipitates stable at high temperatures have been found for these alloys. Here we report discovery of a new, nano-sized superlattice (NSS) phase in ball-milled Fe alloys, which maintains coherency with the BCC matrix up to at least 913 °C. Different from other precipitates in ferritic alloys, this NSS phase is created by oxygen-ordering in the BCC Fe matrix. It is proposed that this phase has a chemistry of Fe3O and a D03 crystal structure and becomes more stable with the addition of Zr. These nano-sized coherent precipitates effectively double the strength of the BCC matrix above that provided by grain size reduction alone. This discovery provides a new opportunity for developing high-strength ferritic alloys for high temperature applications.

Phase diagram and neutron spin resonance of superconducting NaFe 1 - x Cu x As

DOE PAGES

Tan, Guotai; Song, Yu; Zhang, Rui; ...

2017-02-03

In this paper, we use transport and neutron scattering to study the electronic phase diagram and spin excitations of NaFe 1-xCu xAs single crystals. Similar to Co- and Ni-doped NaFeAs, a bulk superconducting phase appears near x≈2% with the suppression of stripe-type magnetic order in NaFeAs. Upon further increasing Cu concentration the system becomes insulating, culminating in an antiferromagnetically ordered insulating phase near x≈50%. Using transport measurements, we demonstrate that the resistivity in NaFe 1-xCu xAs exhibits non-Fermi-liquid behavior near x≈1.8%. Our inelastic neutron scattering experiments reveal a single neutron spin resonance mode exhibiting weak dispersion along c axis inmore » NaFe 0.98Cu 0.02As. The resonance is high in energy relative to the superconducting transition temperature T c but weak in intensity, likely resulting from impurity effects. These results are similar to other iron pnictides superconductors despite that the superconducting phase in NaFe 1-xCu xAs is continuously connected to an antiferromagnetically ordered insulating phase near x≈50% with significant electronic correlations. Finally, therefore, electron correlations is an important ingredient of superconductivity in NaFe 1-xCu xAs and other iron pnictides.« less

A combined experimental and finite element analysis method for the estimation of eddy-current loss in NdFeB magnets.

PubMed

Fratila, Radu; Benabou, Abdelkader; Tounzi, Abdelmounaïm; Mipo, Jean-Claude

2014-05-14

NdFeB permanent magnets (PMs) are widely used in high performance electrical machines, but their relatively high conductivity subjects them to eddy current losses that can lead to magnetization loss. The Finite Element (FE) method is generally used to quantify the eddy current loss of PMs, but it remains quite difficult to validate the accuracy of the results with complex devices. In this paper, an experimental test device is used in order to extract the eddy current losses that are then compared with those of a 3D FE model.

Suppression of magnetic order in CaCo 1.86 As 2 with Fe substitution: Magnetization, neutron diffraction, and x-ray diffraction studies of Ca ( Co 1 – x Fe x ) y As 2

DOE PAGES

Jayasekara, W. T.; Pandey, Abhishek; Kreyssig, A.; ...

2017-02-23

Magnetization, neutron diffraction, and high-energy x-ray diffraction results for Sn-flux grown single-crystal samples of Ca(Co 1–xFe x) yAs 2, 0 ≤ x ≤ 1, 1.86 ≤ y ≤ 2, are presented and reveal that A-type antiferromagnetic order, with ordered moments lying along the c axis, persists for x ≲ 0.12(1). The antiferromagnetic order is smoothly suppressed with increasing x, with both the ordered moment and Néel temperature linearly decreasing. Stripe-type antiferromagnetic order does not occur for x ≤ 0.25, nor does ferromagnetic order for x up to at least x = 0.104, and a smooth crossover from the collapsed-tetragonal (cT)more » phase of CaCo 1.86As 2 to the tetragonal (T) phase of CaFe 2As 2 occurs. Furthermore, these results suggest that hole doping CaCo 1.86As 2 has a less dramatic effect on the magnetism and structure than steric effects due to substituting Sr for Ca.« less

Suppression of magnetic order in CaCo 1.86 As 2 with Fe substitution: Magnetization, neutron diffraction, and x-ray diffraction studies of Ca ( Co 1 – x Fe x ) y As 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jayasekara, W. T.; Pandey, Abhishek; Kreyssig, A.

Magnetization, neutron diffraction, and high-energy x-ray diffraction results for Sn-flux grown single-crystal samples of Ca(Co 1–xFe x) yAs 2, 0 ≤ x ≤ 1, 1.86 ≤ y ≤ 2, are presented and reveal that A-type antiferromagnetic order, with ordered moments lying along the c axis, persists for x ≲ 0.12(1). The antiferromagnetic order is smoothly suppressed with increasing x, with both the ordered moment and Néel temperature linearly decreasing. Stripe-type antiferromagnetic order does not occur for x ≤ 0.25, nor does ferromagnetic order for x up to at least x = 0.104, and a smooth crossover from the collapsed-tetragonal (cT)more » phase of CaCo 1.86As 2 to the tetragonal (T) phase of CaFe 2As 2 occurs. Furthermore, these results suggest that hole doping CaCo 1.86As 2 has a less dramatic effect on the magnetism and structure than steric effects due to substituting Sr for Ca.« less

Ascorbic acid/Fe@Fe2O3: A highly efficient combined Fenton reagent to remove organic contaminants.

PubMed

Hou, Xiaojing; Huang, Xiaopeng; Ai, Zhihui; Zhao, Jincai; Zhang, Lizhi

2016-06-05

In this study, we demonstrate that the combination of ascorbic acid and Fe@Fe2O3 core-shell nanowires (AA/Fe@Fe2O3) offers a highly efficient Fenton reagent. This combined Fenton reagent exhibited extremely high activity on the decomposition of H2O2 to produce OH for the degradation of various organic contaminants, including rhodamine B, methylene blue, alachlor, atrazine, siduron, lincomycin, and chloroamphenicol. The contaminant degradation constants in the AA/Fe@Fe2O3/H2O2 Fenton systems were 38-53 times higher than those in the conventional homogeneous Fenton system (Fe(II)/H2O2) at pH 3.8. Moreover, the OH generation rate constant in the AA/Fe@Fe2O3/H2O2 Fenton system was 1-3 orders of magnitudes greater than those of heterogeneous Fenton systems developed with other iron-containing materials (α-FeOOH, α-Fe2O3, FeOCl, and so on). The high activity of AA/Fe@Fe2O3 was attributed to the effective Fe(III)/Fe(II) cycle and the iron-ascorbate complex formation to stabilize ferrous ions with desirable and steady concentrations. During the AA/Fe@Fe2O3/H2O2 Fenton process, ascorbic acid served as a reducing and complexing reagent, enabling the reuse of Fe@Fe2O3 nanowires. We systematically investigated the alachlor and ascorbic acid degradation and found that they could be effectively degraded in the AA/Fe@Fe2O3/H2O2 system, accompanying with 100% of dechlorination and 92% of denitrification. This study sheds light on the importance of Fe(III)/Fe(II) cycle for the design of high efficient Fenton system and provides an alternative pathway for the organic contaminants removal. Copyright © 2016 Elsevier B.V. All rights reserved.

Large-moment antiferromagnetic order in overdoped high-Tc superconductor 154SmFeAsO1-xDx

NASA Astrophysics Data System (ADS)

Iimura, Soshi; Okanishi, Hiroshi; Matsuishi, Satoru; Hiraka, Haruhiro; Honda, Takashi; Ikeda, Kazutaka; Hansen, Thomas C.; Otomo, Toshiya; Hosono, Hideo

2017-05-01

In iron-based superconductors, high critical temperature (Tc) superconductivity over 50 K has only been accomplished in electron-doped hREFeAsO (hRE is heavy rare earth (RE) element). Although hREFeAsO has the highest bulk Tc (58 K), progress in understanding its physical properties has been relatively slow due to difficulties in achieving high-concentration electron doping and carrying out neutron experiments. Here, we present a systematic neutron powder diffraction study of 154SmFeAsO1-xDx, and the discovery of a long-range antiferromagnetic ordering with x ≥ 0.56 (AFM2) accompanying a structural transition from tetragonal to orthorhombic. Surprisingly, the Fe magnetic moment in AFM2 reaches a magnitude of 2.73 μB/Fe, which is the largest in all nondoped iron pnictides and chalcogenides. Theoretical calculations suggest that the AFM2 phase originates in kinetic frustration of the Fe-3dxy orbital, in which the nearest-neighbor hopping parameter becomes zero. The unique phase diagram, i.e., highest-Tc superconducting phase adjacent to the strongly correlated phase in electron-overdoped regime, yields important clues to the unconventional origins of superconductivity.

Three-Dimensional Ordered Macroporous FePO4 as High-Efficiency Catalyst for Rechargeable Li-O2 Batteries.

PubMed

Li, Chao; Guo, Ziyang; Pang, Ying; Sun, Yunhe; Su, Xiuli; Wang, Yonggang; Xia, Yongyao

2016-11-23

The Li-O 2 battery is receiving much recent attention because of its superhigh theoretical energy density. However, its performance is limited by the irreversible formation/decomposition of Li 2 O 2 on the cathode and the undesired electrolyte decomposition. In this work, low-cost three-dimensional ordered macroporous (3DOM) FePO 4 is synthesized by using polystyrene (PS) spheres template in a facile experimental condition and applied as a high-efficiency catalyst for rechargeable Li-O 2 batteries, including good rate performance, high specific capacity, and perfect cycling stability. The superior performances can be attributed to the unique structure of 3DOM FePO 4 cathodes, which can provide an efficient buffer space for O 2 /Li 2 O 2 conversion. In addition, it is demonstrated that the Li + intercalation/deintercalation behavior of 3DOM FePO 4 in ether-based electrolyte can contribute to capacity for Li-O 2 batteries over cycling. As a result, when there is no O 2 in the environment, the Li-O 2 cell can also be operated as a rechargeable Li-FePO 4 cell with a perfect cycle capability.

Crystal structure and magnetic properties of high-oxygen pressure annealed Sr{sub 1-x}La{sub x}Co{sub 0.5}Fe{sub 0.5}O{sub 3-{delta}} (0{<=}x{<=}0.5)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Swierczek, Konrad; Materials Science Division, Argonne National Laboratory, Argonne, IL 60439; Dabrowski, Bogdan

2009-02-15

Structural and magnetic studies are presented for the perovskite type Sr{sub 1-x}La{sub x}Co{sub 0.5}Fe{sub 0.5}O{sub 3-{delta}} (0{<=}x{<=}0.5) materials annealed under moderately high-oxygen pressures of {approx}200 atm. A detailed analysis of the room temperature neutron time-of-flight diffraction data reveals that the crystal structure of the sample SrCo{sub 0.5}Fe{sub 0.5}O{sub 2.89(1)}, previously described as vacancy-disordered cubic, is similar to the formerly reported, oxygen-vacancy ordered Sr{sub 8}Fe{sub 8}O{sub 23} compound, i.e. Sr{sub 8}Co{sub 4}Fe{sub 4}O{sub 23} is tetragonal with the I4/mmm symmetry. With an increase of the La content the studied materials become nearly oxygen stoichiometric and a lowering of the crystal symmetrymore » is observed from cubic Pm3-barm (x=0.1 and 0.2) to tetragonal I4/mcm (x=0.3 and 0.4), and finally to monoclinic I12/c1 (x=0.5). Low-temperature structural and magnetic measurements show a ferromagnetic ordering with the maximum Curie temperature near 290 K at x=0.2. - Graphical Abstract: Room temperature Rietveld refinement profile using I4/mmm space group for the oxygen vacancy ordered SrCo{sub 0.5}Fe{sub 0.5}O{sub 2.89} (Sr{sub 8}Co{sub 4}Fe{sub 4}O{sub 23}). Top tick-marks denote allowed reflections in I4/mmm, bottom one emphasize the possibility of inexact indexing using Pm3-barm symmetry. Previous reports indicate that similar ordering is common for SrCo{sub 1-x}Fe{sub x}O{sub 3-{delta}} compounds possibly hindering their applications.« less

Phonon spectrum of single-crystalline FeSe probed by high-resolution electron energy-loss spectroscopy

NASA Astrophysics Data System (ADS)

Zakeri, Khalil; Engelhardt, Tobias; Le Tacon, Matthieu; Wolf, Thomas

2018-06-01

Utilizing high-resolution electron energy-loss spectroscopy (HREELS) we measure the phonon frequencies of β-FeSe(001), cleaved under ultra-high vacuum conditions. At the zone center (Γ bar-point) three prominent loss features are observed at loss energies of about ≃ 20.5 and 25.6 and 40 meV. Based on the scattering selection rules we assign the observed loss features to the A1g, B1g, and A2u phonon modes of β-FeSe(001). The experimentally measured phonon frequencies do not agree with the results of density functional based calculations in which a nonmagnetic, a checkerboard or a strip antiferromagnetic order is assumed for β-FeSe(001). Our measurements suggest that, similar to the other Fe-based materials, magnetism has a profound impact on the lattice dynamics of β-FeSe(001).

Structure and property correlations in FeS

NASA Astrophysics Data System (ADS)

Kuhn, S. J.; Kidder, M. K.; Parker, D. S.; dela Cruz, C.; McGuire, M. A.; Chance, W. M.; Li, Li; Debeer-Schmitt, L.; Ermentrout, J.; Littrell, K. C.; Eskildsen, M. R.; Sefat, A. S.

2017-03-01

For iron-sulfide (FeS), we investigate the correlation between the structural details, including its dimensionality and composition, with its magnetic and superconducting properties. We compare, theoretically and experimentally, the two-dimensional (2D) layered tetragonal (;t-FeS;) phase with the 3D hexagonal ("h-FeS") phase. X-ray diffraction reveals iron-deficient chemical compositions of t-Fe0.93(1)S and h-Fe0.84(1)S that show no low-temperature structural transitions. First-principles calculations reveal a high sensitivity of the 2D structure to the electronic and magnetic properties, predicting marginal antiferromagnetic instability for our compound (sulfur height of zS = 0.252) with an ordering energy of about 11 meV/Fe, while the 3D phase is magnetically stable. Experimentally, h-Fe0.84S orders magnetically well above room temperature, while t-Fe0.93S shows coexistence of antiferromagnetism at TN = 116 and filamentary superconductivity below Tc = 4 K. Low temperature neutron diffraction data reveals antiferromagnetic commensurate ordering with wave vector km = (0.25,0.25,0) and 0.46(2) μB/Fe. Additionally, neutron scattering measurements were used to find the particle size and iron vacancy arrangement of t-FeS and h-FeS. The structure of iron sulfide has a delicate relationship with the superconducting transition; while our sample with a = 3.6772(7) Å is a filamentary superconductor coexisting with an antiferromagnetic phase, previously reported samples with a > 3.68 Å are bulk superconductors with no magnetism, and those with a ≈ 3.674 Å show magnetic properties.

Electric double-layer transistor using layered iron selenide Mott insulator TlFe1.6Se2

PubMed Central

Katase, Takayoshi; Hiramatsu, Hidenori; Kamiya, Toshio; Hosono, Hideo

2014-01-01

A1–xFe2–ySe2 (A = K, Cs, Rb, Tl) are recently discovered iron-based superconductors with critical temperatures (Tc) ranging up to 32 K. Their parent phases have unique properties compared with other iron-based superconductors; e.g., their crystal structures include ordered Fe vacancies, their normal states are antiferromagnetic (AFM) insulating phases, and they have extremely high Néel transition temperatures. However, control of carrier doping into the parent AFM insulators has been difficult due to their intrinsic phase separation. Here, we fabricated an Fe-vacancy-ordered TlFe1.6Se2 insulating epitaxial film with an atomically flat surface and examined its electrostatic carrier doping using an electric double-layer transistor (EDLT) structure with an ionic liquid gate. The positive gate voltage gave a conductance modulation of three orders of magnitude at 25 K, and further induced and manipulated a phase transition; i.e., delocalized carrier generation by electrostatic doping is the origin of the phase transition. This is the first demonstration, to the authors' knowledge, of an EDLT using a Mott insulator iron selenide channel and opens a way to explore high Tc superconductivity in iron-based layered materials, where carrier doping by conventional chemical means is difficult. PMID:24591598

Multimetallic nanoparticle catalysts with enhanced electrooxidation

DOEpatents

Sun, Shouheng; Zhang, Sen; Zhu, Huiyuan; Guo, Shaojun

2015-07-28

A new structure-control strategy to optimize nanoparticle catalysis is provided. The presence of Au in FePtAu facilitates FePt structure transformation from chemically disordered face centered cubic (fcc) structure to chemically ordered face centered tetragonal (fct) structure, and further promotes formic acid oxidation reaction (FAOR). The fct-FePtAu nanoparticles show high CO poisoning resistance, achieve mass activity as high as about 2810 mA/mg Pt, and retain greater than 90% activity after a 13 hour stability test.

Hf{sub 3}Fe{sub 4}Sn{sub 4} and Hf{sub 9}Fe{sub 4−x}Sn{sub 10+x}: Two stannide intermetallics with low-dimensional iron sublattices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Calta, Nicholas P.; Kanatzidis, Mercouri G., E-mail: m-kanatzidis@northwestern.edu; Materials Science Division, Argonne National Laboratory

This article reports two new Hf-rich intermetallics synthesized using Sn flux: Hf{sub 3}Fe{sub 4}Sn{sub 4} and Hf{sub 9}Fe{sub 4−x}Sn{sub 10+x}. Hf{sub 3}Fe{sub 4}Sn{sub 4} adopts an ordered variant the Hf{sub 3}Cu{sub 8} structure type in orthorhombic space group Pnma with unit cell edges of a=8.1143(5) Å, b=8.8466(5) Å, and c=10.6069(6) Å. Hf{sub 9}Fe{sub 4−x}Sn{sub 10+x}, on the other hand, adopts a new structure type in Cmc2{sub 1} with unit cell edges of a=5.6458(3) Å, b=35.796(2) Å, and c=8.88725(9) Å for x=0. It exhibits a small amount of phase width in which Sn substitutes on one of the Fe sites. Bothmore » structures are fully three-dimensional and are characterized by pseudo one- and two-dimensional networks of Fe–Fe homoatomic bonding. Hf{sub 9}Fe{sub 4−x}Sn{sub 10+x} exhibits antiferromagnetic order at T{sub N}=46(2) K and its electrical transport behavior indicates that it is a normal metal with phonon-dictated resistivity. Hf{sub 3}Fe{sub 4}Sn{sub 4} is also an antiferromagnet with a rather high ordering temperature of T{sub N}=373(5) K. Single crystal resistivity measurements indicate that Hf{sub 3}Fe{sub 4}Sn{sub 4} behaves as a Fermi liquid at low temperatures, indicating strong electron correlation. - Graphical abstract: Slightly different growth conditions in Sn flux produce two new intermetallic compounds: Hf{sub 3}Fe{sub 4}Sn{sub 4} and Hf{sub 9}Fe{sub 4−x}Sn{sub 10+x}. - Highlights: • Single crystals of both Hf{sub 3}Fe{sub 4}Sn{sub 4} and Hf{sub 9}Fe{sub 4−x}Sn{sub 10+x} were grown using Sn flux. • The crystal structures were determined using single crystal X-ray diffraction. • The Fe moments in Hf{sub 3}Fe{sub 4}Sn{sub 4} display AFM order below T{sub N}=373 K. • The Fe moments in Hf{sub 9}Fe{sub 4−x}Sn{sub 10+x} display AFM order below T{sub N}=46 K.« less

Structure of short-range-ordered iron(III)-precipitates formed by iron(II) oxidation in water containing phosphate, silicate, and calcium

NASA Astrophysics Data System (ADS)

Voegelin, A.; Frommer, J.; Vantelon, D.; Kaegi, R.; Hug, S. J.

2009-04-01

The oxidation of Fe(II) in water leads to the formation of Fe(III)-precipitates that strongly affect the fate of nutrients and contaminants in natural and engineered systems. Examples include the cycling of As in rice fields irrigated with As-rich groundwater or the treatment of drinking water for As removal. Knowledge of the types of Fe(III)-precipitates forming in such systems is essential for the quantitative modeling of nutrient and contaminant dynamics and for the optimization of water purification techniques on the basis of a mechanistic understanding of the relevant biogeochemical processes. In this study, we investigated the local coordination of Fe, P, and Ca in Fe(III)-precipitates formed by aeration of synthetic Fe(II)-containing groundwater with variable composition (pH 7, 2-30 mg/L Fe(II), 2-20 mg/L phosphate-P, 2-20 mg/L silicate-Si, 8 mM Na-bicarbonate or 2.5 mM Ca-&1.5 mM Mg-bicarbonate). After 4 hours of oxidation, Fe(III)-precipitates were collected on 0.2 µm nylon filters and dried. The precipitates were analyzed by Fe K-edge EXAFS (XAS beamline, ANKA, Germany) and by P and Ca K-edge XANES spectroscopy (LUCIA beamline, SLS, Switzerland). The Fe K-edge EXAFS spectra indicated that local Fe coordination in the precipitates systematically shifted with water composition. As long as water contained P, mainly short-range-ordered Fe(III)-phosphate formed (with molar P/Fe ~0.5). In the absence of P, Fe(III) precipitated as hydrous ferric oxide at high Si/Fe>0.5, as ferrihydrite at intermediate Si/Fe, and mainly as lepidocrocite at Si/Fe<0.2. Analysis of the EXAFS by shell-fitting indicated that Fe(III)-phosphates mainly contained mono- or oligomeric (edge- or corner-sharing) Fe and that the linkage between neighboring Fe(III)-octahedra changed from predominantly edge-sharing in Si-rich hydrous ferric oxide to edge- and corner-sharing in ferrihydrite. Electron microscopic data showed that changes in local precipitate structure were systematically reflected in particle morphology and SAED patterns. The P K-edge XANES spectra revealed that phosphate was bound to both Fe as well as Ca (if present). The Ca K-edge XANES spectra showed that the mode of Ca uptake by the Fe(III)-precipitates shifted from mainly adsorption at high Fe/P to coprecipitation at low Fe/P ratio. Despite oversaturation, neither calcite nor hydroxyapatite formed to a significant extent. The results from this study indicated that, depending on water composition, Fe(II) oxidation in natural waters leads to different types of short-range-ordered Fe(III)-phases. Since these phases are expected to differ in their effect on contaminant and nutrient dynamics, their specific physical and chemical properties warrant further research. Methodologically, this work demonstrated the usefulness of investigating the local structure of short-range-ordered precipitates along compositional gradients and by combining the element-selective information from different X-ray absorption edges.

High-precision Q EC values of superallowed 0 + → 0 + β-emitters 46Cr, 50Fe and 54Ni

DOE PAGES

Zhang, P.; Xu, X.; Shuai, P.; ...

2017-01-23

Short-lived 46Cr, 50Fe and 54Ni were studied by isochronous mass spectrometry at the HIRFL-CSR facility in Lanzhou. The measured precision mass excesses (ME) of 46Cr, 50Fe and 54Ni are -29471(11) keV, -34477(6) keV and -39278(4) keV, respectively. The superallowed 0 +→0+β-decay Q values were derived to be Q EC( 46Cr) =7604(11) keV, Q EC( 50Fe) =8150(6) keV and Q EC( 54Ni) =8731(4) keV. The values for 50Fe and 54Ni are by one order of magnitude more precise than the adopted literature values. By combining the existing half-lives and branching ratios, we obtained the corrected ℱt values to be ℱt(more » 50Fe) =3103(70) s and ℱt( 54Ni) =3076(50) s. The main contribution to the ℱt uncertainties is now due to β-decay branching ratios, still, more high-precision measurements of the half-lives, the masses, and especially the branching ratios are needed in order to satisfy the requirements for a stringent CVC test.« less

High-precision Q EC values of superallowed 0 + → 0 + β-emitters 46Cr, 50Fe and 54Ni

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, P.; Xu, X.; Shuai, P.

Short-lived 46Cr, 50Fe and 54Ni were studied by isochronous mass spectrometry at the HIRFL-CSR facility in Lanzhou. The measured precision mass excesses (ME) of 46Cr, 50Fe and 54Ni are -29471(11) keV, -34477(6) keV and -39278(4) keV, respectively. The superallowed 0 +→0+β-decay Q values were derived to be Q EC( 46Cr) =7604(11) keV, Q EC( 50Fe) =8150(6) keV and Q EC( 54Ni) =8731(4) keV. The values for 50Fe and 54Ni are by one order of magnitude more precise than the adopted literature values. By combining the existing half-lives and branching ratios, we obtained the corrected ℱt values to be ℱt(more » 50Fe) =3103(70) s and ℱt( 54Ni) =3076(50) s. The main contribution to the ℱt uncertainties is now due to β-decay branching ratios, still, more high-precision measurements of the half-lives, the masses, and especially the branching ratios are needed in order to satisfy the requirements for a stringent CVC test.« less

Tailoring magnetic behavior of CoFeMnNiX (X = Al, Cr, Ga, and Sn) high entropy alloys by metal doping

DOE PAGES

Zuo, Tingting; Gao, Michael C.; Ouyang, Lizhi; ...

2017-03-07

Magnetic materials with excellent performances are desired for functional applications. Based on the high-entropy effect, a system of CoFeMnNiX (X = Al, Cr, Ga, and Sn) magnetic alloys are designed and investigated. The dramatic change in phase structures from face-centered-cubic (FCC) to ordered body-centered-cubic (BCC) phases, caused by adding Al, Ga, and Sn in CoFeMnNiX alloys, originates from the potent short-range chemical order in the liquid state predicted by ab initio molecular dynamics (AIMD) simulations. This phase transition leads to the significant enhancement of the saturation magnetization (M s), e.g., the CoFeMnNiAl alloy has M s of 147.86 Am 2/kg.more » In conclusion, first-principles density functional theory (DFT) calculations on the electronic and magnetic structures reveal that the anti-ferromagnetism of Mn atoms in CoFeMnNi is suppressed especially in the CoFeMnNiAl HEA because Al changes the Fermi level and itinerant electron-spin coupling that lead to ferromagnetism.« less

Ligand-hole localization in oxides with unusual valence Fe

PubMed Central

Chen, Wei-Tin; Saito, Takashi; Hayashi, Naoaki; Takano, Mikio; Shimakawa, Yuichi

2012-01-01

Unusual high-valence states of iron are stabilized in a few oxides. A-site-ordered perovskite-structure oxides contain such iron cations and exhibit distinct electronic behaviors at low temperatures, e.g. charge disproportionation (4Fe4+ → 2Fe3+ + 2Fe5+) in CaCu3Fe4O12 and intersite charge transfer (3Cu2+ + 4Fe3.75+ → 3Cu3+ + 4Fe3+) in LaCu3Fe4O12. Here we report the synthesis of solid solutions of CaCu3Fe4O12 and LaCu3Fe4O12 and explain how the instabilities of their unusual valence states of iron are relieved. Although these behaviors look completely different from each other in simple ionic models, they can both be explained by the localization of ligand holes, which are produced by the strong hybridization of iron d and oxygen p orbitals in oxides. The localization behavior in the charge disproportionation of CaCu3Fe4O12 is regarded as charge ordering of the ligand holes, and that in the intersite charge transfer of LaCu3Fe4O12 is regarded as a Mott transition of the ligand holes. PMID:22690318

Spatially and size selective synthesis of Fe-based nanoparticles on ordered mesoporous supports as highly active and stable catalysts for ammonia decomposition.

PubMed

Lu, An-Hui; Nitz, Joerg-Joachim; Comotti, Massimiliano; Weidenthaler, Claudia; Schlichte, Klaus; Lehmann, Christian W; Terasaki, Osamu; Schüth, Ferdi

2010-10-13

Uniform and highly dispersed γ-Fe(2)O(3) nanoparticles with a diameter of ∼6 nm supported on CMK-5 carbons and C/SBA-15 composites were prepared via simple impregnation and thermal treatment. The nanostructures of these materials were characterized by XRD, Mössbauer spectroscopy, XPS, SEM, TEM, and nitrogen sorption. Due to the confinement effect of the mesoporous ordered matrices, γ-Fe(2)O(3) nanoparticles were fully immobilized within the channels of the supports. Even at high Fe-loadings (up to about 12 wt %) on CMK-5 carbon no iron species were detected on the external surface of the carbon support by XPS analysis and electron microscopy. Fe(2)O(3)/CMK-5 showed the highest ammonia decomposition activity of all previously described Fe-based catalysts in this reaction. Complete ammonia decomposition was achieved at 700 °C and space velocities as high as 60,000 cm(3) g(cat)(-1) h(-1). At a space velocity of 7500 cm(3) g(cat)(-1) h(-1), complete ammonia conversion was maintained at 600 °C for 20 h. After the reaction, the immobilized γ-Fe(2)O(3) nanoparticles were found to be converted to much smaller nanoparticles (γ-Fe(2)O(3) and a small fraction of nitride), which were still embedded within the carbon matrix. The Fe(2)O(3)/CMK-5 catalyst is much more active than the benchmark NiO/Al(2)O(3) catalyst at high space velocity, due to its highly developed mesoporosity. γ-Fe(2)O(3) nanoparticles supported on carbon-silica composites are structurally much more stable over extended periods of time but less active than those supported on carbon. TEM observation reveals that iron-based nanoparticles penetrate through the carbon layer and then are anchored on the silica walls, thus preventing them from moving and sintering. In this way, the stability of the carbon-silica catalyst is improved. Comparison with the silica supported iron oxide catalyst reveals that the presence of a thin layer of carbon is essential for increased catalytic activity.

Cube-like α-Fe2O3 supported on ordered multimodal porous carbon as high performance electrode material for supercapacitors.

PubMed

Chaudhari, Nitin K; Chaudhari, Sudeshna; Yu, Jong-Sung

2014-11-01

Well-dispersed cube-like iron oxide (α-Fe2O3) nanoparticles (NPs) supported on ordered multimodal porous carbon (OMPC) are synthesized for the first time by a facile and efficient glycine-assisted hydrothermal route. The effect of OPMC support on growth and formation mechanism of the Fe2O3 NPs is discussed. OMPC as a supporting material plays a pivotal role of controlling the shape, size, and dispersion of the Fe2O3 NPs. As-synthesized α-Fe2O3/OMPC composites reveal significant improvement in the performance as electrode material for supercapacitors. Compared to the bare Fe2O3 and OMPC, the composite exhibits excellent cycling stability, rate capability, and enhanced specific capacitances of 294 F g(-1) at 1.5 A g(-1), which is twice that of OMPC (145 F g(-1)) and about four times higher than that of bare Fe2O3 (85 F g(-1)). The improved electrochemical performance of the composite can be attributed to the well-defined structure, high conductivity, and hierarchical porosity of OMPC as well as the unique α-Fe2O3 NPs with cube-like morphology well-anchored on the OMPC support, which makes the composite a promising candidate for supercapacitors. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Assessment of kinetic models on Fe adsorption in groundwater using high-quality limestone

NASA Astrophysics Data System (ADS)

Akbar, N. A.; Kamil, N. A. F. Mohd; Zin, N. S. Md; Adlan, M. N.; Aziz, H. A.

2018-04-01

During the groundwater pumping process, dissolved Fe2+ is oxidized into Fe3+ and produce rust-coloured iron mineral. Adsorption kinetic models are used to evaluate the performance of limestone adsorbent and describe the mechanism of adsorption and the diffusion processes of Fe adsorption in groundwater. This work presents the best kinetic model of Fe adsorption, which was chosen based on a higher value of coefficient correlation, R2. A batch adsorption experiment was conducted for various contact times ranging from 0 to 135 minutes. From the results of the batch study, three kinetic models were analyzed for Fe removal onto limestone sorbent, including the pseudo-first order (PFO), pseudo-second order (PSO) and intra-particle diffusion (IPD) models. Results show that the adsorption kinetic models follow the sequence: PSO > PFO > IPD, where the values of R2 are 0.997 > 0.919 > 0.918. A high value of R2 (0.997) reveals better fitted experimental data. Furthermore, the value of qe cal in the PSO kinetic model is very near to qe exp rather than that in other models. This finding therefore suggests that the PSO kinetic model has the good fitted with the experimental data which involved chemisorption process of divalent Fe removal in groundwater solution. Thus, limestone adsorbent media found to be an alternative and effective treatment of Fe removal from groundwater.

Highly ordered Fe3+/TiO2 nanotube arrays for efficient photocataltyic degradation of nitrobenzene

NASA Astrophysics Data System (ADS)

Zhang, Yiyang; Gu, Di; Zhu, Lingyue; Wang, Baohui

2017-10-01

Highly ordered TiO2 nanotube arrays (TiO2 NTs) were prepared through a facile two-step electrochemical anodization, subsequently, active iron ions were introduced into the TiO2 NTs via a direct impregnation method. The XPS results showed that the iron elements existed in TiO2 NTs in the form of Fe3+ ions. Compared with the undoped TiO2 NTs, the absorption edge of Fe3+/TiO2 NTs showed an overt red shift and the photocurrent improved obviously, which indicated that Fe3+/TiO2 had a much higher photocatalytic activity. The optimal doping content was tested to be 0.1 mol/L which could make the photocatalytic activity of TiO2 NTs obviously improves under both visible and ultraviolent light. The prepared samples were adopted as photocatalyst to degrade nitrobenzene (NB). The reaction rate constants ks under UV light were in the order kone-stepTiO2NTs = 0.00338

Magnetic cluster expansion model for random and ordered magnetic face-centered cubic Fe-Ni-Cr alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lavrentiev, M. Yu., E-mail: Mikhail.Lavrentiev@ukaea.uk; Nguyen-Manh, D.; Dudarev, S. L.

A Magnetic Cluster Expansion model for ternary face-centered cubic Fe-Ni-Cr alloys has been developed, using DFT data spanning binary and ternary alloy configurations. Using this Magnetic Cluster Expansion model Hamiltonian, we perform Monte Carlo simulations and explore magnetic structures of alloys over the entire range of compositions, considering both random and ordered alloy structures. In random alloys, the removal of magnetic collinearity constraint reduces the total magnetic moment but does not affect the predicted range of compositions where the alloys adopt low-temperature ferromagnetic configurations. During alloying of ordered fcc Fe-Ni compounds with Cr, chromium atoms tend to replace nickel rathermore » than iron atoms. Replacement of Ni by Cr in ordered alloys with high iron content increases the Curie temperature of the alloys. This can be explained by strong antiferromagnetic Fe-Cr coupling, similar to that found in bcc Fe-Cr solutions, where the Curie temperature increase, predicted by simulations as a function of Cr concentration, is confirmed by experimental observations. In random alloys, both magnetization and the Curie temperature decrease abruptly with increasing chromium content, in agreement with experiment.« less

Insights into ionic transport and structural changes in magnetite during multiple-electron transfer reactions

DOE PAGES

Zhang, Wei; Bock, David C.; Pelliccione, Christopher J.; ...

2016-03-08

Metal oxides, such as Fe 3O 4, hold promise for future battery applications due to their abundance, low cost, and opportunity for high lithium storage capacity. In order to better understand the mechanisms of multiple-electron transfer reactions leading to high capacity in Fe 3O 4, a comprehensive investigation on local ionic transport and ordering is made by probing site occupancies of anions (O 2–) and cations (Li +, Fe 3+/Fe 2+) using multiple synchrotron X-ray and electron-beam techniques, in combination with ab-initio calculations. Results from this study provide the first experimental evidence that the cubic-close-packed (ccp) O-anion array in Femore » 3O 4 is sustained throughout the lithiation and delithiation processes, thereby enabling multiple lithium intercalation and conversion reactions. Cation displacement/reordering occurs within the ccp O-anion framework, which leads to a series of phase transformations, starting from the inverse spinel phase and turning into intermediate rock-salt-like phases (Li xFe 3O 4; 0 < x < 2), then into a cation-segregated phase (Li 2O•FeO), and finally converting into metallic Fe and Li 2O. Subsequent delithiation and lithiation processes involve interconversion between metallic Fe and FeO-like phases. Lastly, these results may offer new insights into the structure-determined ionic transport and electrochemical reactions in metal oxides, and those of other compounds sharing a ccp anion framework, reminiscent of magnetite.« less

Strong cooperative coupling of pressure-induced magnetic order and nematicity in FeSe

NASA Astrophysics Data System (ADS)

Kreyssig, Andreas

In iron-based superconductors, the lattice, magnetism and electronic system show a fascinating interplay. Nematic order breaks the tetragonal symmetry and yields an orthorhombic lattice distortion. The same symmetry is broken by the stripe-like antiferromagnetic order suggesting a symmetry-related coupling between both phenomena. The phase transitions in to both ordered states can be simultaneous and of first-order character like in CaFe2As2, or separated in temperature like in Co-doped BaFe2As2 with second or first-order character depending on the doping level. Stripe-type magnetic fluctuations are discussed as correlation-driven electronic mechanism of the nematicity and important for the superconducting electron pairing establishing a coupling mechanism. However, a universal picture has been confounded by measurements of FeSe where the nematic and magnetic transitions appear to be decoupled by the observation of the lattice distortion without antiferromagnetic order at ambient pressure. In this talk I will present our recent study on the relation between the nematic and magnetic order in FeSe single crystals investigated by synchrotron-based high-energy x-ray diffraction and time-domain Moessbauer spectroscopy as function of temperature and pressure. Distinct nematic and magnetic transitions are observed for low pressures and merge into a single first-order transition for higher pressures reminiscent of what has been found for the evolution of these transitions in Co-doped BaFe2As2. Our results are consistent with a spin-driven mechanism for nematic order in FeSe and provide an important step towards a universal description of the interplay between the different ordering phenomena in the iron-based superconductors. This work was performed in collaboration with K. Kothapalli, A. E. Böhmer, W. T. Jayasekara, B. G. Ueland, P. Das, A. Sapkota, V. Taufour, Y. Xiao, E. Alp, S. L. Bud'ko, P.C. Canfield, and A.I. Goldman; and supported by the Department of Energy, Basic Energy Sciences, Division of Materials Sciences and Engineering, under Contract No. DE-AC02-07CH11358.

L10-Ordered Thin Films with High Perpendicular Magnetic Anisotropy for STT-MRAM Applications

NASA Astrophysics Data System (ADS)

Huang, Efrem Yuan-Fu

The objective of the research conducted herein was to develop L10-ordered materials and thin film stack structures with high perpendicular magnetic anisotropy (PMA) for spin-transfertorque magnetoresistive random access memory (STT-MRAM) applications. A systematic approach was taken in this dissertation, culminating in exchange coupled L1 0-FePt and L10- MnAl heterogeneous structures showing great promise for developing perpendicular magnetic tunnel junctions (pMTJs) with both high thermal stability and low critical switching current. First, using MgO underlayers on Si substrates, sputtered MnAl films were systematically optimized, ultimately producing a Si substrate/MgO (20 nm)/MnAl (30)/Ta (5) film stack with a high degree of ordering and large PMA. Next, noting the incompatibility of insulating MgO underlayers with industrial-scale CMOS processes, attention was turned to using conductive underlayers. TiN was found to excel at promoting growth of L10-MnAl, with optimized films showing improved magnetic properties over those fabricated on MgO underlayers. The use of different post-annealing processes was then studied as an alternative to in situ annealing. Rapid thermal annealing (RTA) was found to produce PMA in films at lower annealing temperatures than tube furnace annealing, but tube furnace annealing produced films with higher maximum PMA than RTA. While annealed samples had lower surface roughness than those ordered by high in situ deposition temperatures, relying solely on annealing to achieve L10-ordering resulted drastically reduced PMA. Finally, heterogeneous L10-ordered FePt/MgO/MnAl film stacks were explored for pMTJs. Film stacks with MgO barrier layers thinner than 2 nm showed significant interdiffusion between the FePt and MnAl, while film stacks with thicker MgO barrier layers exhibited good ordering and high PMA in both the FePt and MnAl films. It is believed that this limitation is caused by the roughness of the underlying FePt, which was thicker than 2 nm. Unfortunately, MgO barrier layers thinner than 2 nm are needed to make good MTJs. With further study, thin, continuous barriers may be achievable for high-PMA, L10- ordered materials with more materials exploration, deposition optimization, and more advanced thin film processing techniques and fabrication equipment. Use of appropriate underlayers, capping layers, dopant elements, and improved fabrication techniques may help reduce surface roughness while preserving PMA. If smooth electrodes can be developed, the heterogeneous structures discussed have great potential in taking advantage of exchange coupling for developing pMTJs with both high thermal stability and low critical switching current. (Abstract shortened by ProQuest.).

Long range ordered alloys modified by group IV-B metals

DOEpatents

Liu, Chain T.; Inouye, Henry; Schaffhauser, Anthony C.

1983-01-01

Ductile long range ordered alloys having high critical ordering temperatures exist in the (V,M)(Fe,Ni,Co).sub.3 system having the composition comprising by weight 20.6%-22.6% V, 14-50% Fe, 0-64% Co, and 0-40% Ni, and 0.4-1.4% M, where M is a metal selected from the group consisting of Ti, Zr, Hf, and their mixtures. These modified alloys have an electron density no greater than 8.00 and exhibit marked increases at elevated temperature in ductility and other mechanical properties over previously known ordered alloys.

Beneficial Role of Copper in the Enhancement of Durability of Ordered Intermetallic PtFeCu Catalyst for Electrocatalytic Oxygen Reduction.

PubMed

Arumugam, Balamurugan; Tamaki, Takanori; Yamaguchi, Takeo

2015-08-05

Design of Pt alloy catalysts with enhanced activity and durability is a key challenge for polymer electrolyte membrane fuel cells. In the present work, we compare the durability of the ordered intermetallic face-centered tetragonal (fct) PtFeCu catalyst for the oxygen reduction reaction (ORR) relative to its counterpart bimetallic catalysts, i.e., the ordered intermetallic fct-PtFe catalyst and the commercial catalyst from Tanaka Kikinzoku Kogyo, TKK-PtC. Although both fct catalysts initially exhibited an ordered structure and mass activity approximately 2.5 times higher than that of TKK-Pt/C, the presence of Cu at the ordered intermetallic fct-PtFeCu catalyst led to a significant enhancement in durability compared to that of the ordered intermetallic fct-PtFe catalyst. The ordered intermetallic fct-PtFeCu catalyst retained more than 70% of its mass activity and electrochemically active surface area (ECSA) over 10 000 durability cycles carried out at 60 °C. In contrast, the ordered intermetallic fct-PtFe catalyst maintained only about 40% of its activity. The temperature of the durability experiment is also shown to be important: the catalyst was more severely degraded at 60 °C than at room temperature. To obtain insight into the observed enhancement in durability of fct-PtFeCu catalyst, a postmortem analysis of the ordered intermetallic fct-PtFeCu catalyst was carried out using scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDX) line scan. The STEM-EDX line scans of the ordered intermetallic fct-PtFeCu catalyst over 10 000 durability cycles showed a smaller degree of Fe and Cu dissolution from the catalyst. Conversely, large dissolution of Fe was identified in the ordered intermetallic fct-PtFe catalyst, indicating a lesser retention of Fe that causes the destruction of ordered structure and gives rise to poor durability. The enhancement in the durability of the ordered intermetallic fct-PtFeCu catalyst is ascribed to the synergistic effects of Cu presence and the ordered structure of catalyst.

Comparative study on the reactivity of Fe/Cu bimetallic particles and zero valent iron (ZVI) under different conditions of N2, air or without aeration.

PubMed

Xiong, Zhaokun; Lai, Bo; Yang, Ping; Zhou, Yuexi; Wang, Juling; Fang, Shuping

2015-10-30

In order to further compare the degradation capacity of Fe(0) and Fe/Cu bimetallic system under different aeration conditions, the mineralization of PNP under different aeration conditions has been investigated thoroughly. The results show that the removal of PNP by Fe(0) or Fe/Cu system followed the pseudo-first-order reaction kinetics. Under the optimal conditions, the COD removal efficiencies obtained through Fe(0) or Fe/Cu system under different aeration conditions followed the trend that Fe/Cu (air)>Fe/Cu (N2: 0-30 min, air: 30-120 min)>control-Fe (air)>Fe/Cu (without aeration)>Fe/Cu (N2)>control-Fe (N2). It revealed that dissolved oxygen (DO) could improve the mineralization of PNP, and Cu could enhance the reactivity of Fe(0). In addition, the degradation of PNP was further analyzed by using UV-vis, FTIR and GC/MS, and the results suggest that Fe/Cu bimetallic system with air aeration could completely break the benzene ring and NO2 structure of PNP and could generate the nontoxic and biodegradable intermediate products. Meanwhile, most of these intermediate products were further mineralized into CO2 and H2O, which brought about a high COD removal efficiency (83.8%). Therefore, Fe/Cu bimetallic system with air aeration would be a promising process for toxic refractory industry wastewater. Copyright © 2015 Elsevier B.V. All rights reserved.

The role of order-disorder transitions in the quest for molecular multiferroics: structural and magnetic neutron studies of a mixed valence iron(II)-iron(III) formate framework.

PubMed

Cañadillas-Delgado, Laura; Fabelo, Oscar; Rodríguez-Velamazán, J Alberto; Lemée-Cailleau, Marie-Hélène; Mason, Sax A; Pardo, Emilio; Lloret, Francesc; Zhao, Jiong-Peng; Bu, Xian-He; Simonet, Virginie; Colin, Claire V; Rodríguez-Carvajal, Juan

2012-12-05

Neutron diffraction studies have been carried out to shed light on the unprecedented order-disorder phase transition (ca. 155 K) observed in the mixed-valence iron(II)-iron(III) formate framework compound [NH(2)(CH(3))(2)](n)[Fe(III)Fe(II)(HCOO)(6)](n). The crystal structure at 220 K was first determined from Laue diffraction data, then a second refinement at 175 K and the crystal structure determination in the low temperature phase at 45 K were done with data from the monochromatic high resolution single crystal diffractometer D19. The 45 K nuclear structure reveals that the phase transition is associated with the order-disorder of the dimethylammonium counterion that is weakly anchored in the cavities of the [Fe(III)Fe(II)(HCOO)(6)](n) framework. In the low-temperature phase, a change in space group from P31c to R3c occurs, involving a tripling of the c-axis due to the ordering of the dimethylammonium counterion. The occurrence of this nuclear phase transition is associated with an electric transition, from paraelectric to antiferroelectric. A combination of powder and single crystal neutron diffraction measurements below the magnetic order transition (ca. 37 K) has been used to determine unequivocally the magnetic structure of this Néel N-Type ferrimagnet, proving that the ferrimagnetic behavior is due to a noncompensation of the different Fe(II) and Fe(III) magnetic moments.

Probing magnetic order in CuFeO2 through nuclear forward scattering in high magnetic fields

NASA Astrophysics Data System (ADS)

Strohm, C.; Lummen, T. T. A.; Handayani, I. P.; Roth, T.; Detlefs, C.; van der Linden, P. J. E. M.; van Loosdrecht, P. H. M.

2013-08-01

Determining the magnetic order of solids in high magnetic fields is technologically challenging. Here we probe the cascade of magnetic phase transitions in frustrated multiferroic CuFeO2 using nuclear forward scattering (NFS) in pulsed magnetic fields up to 30 T. Our results are in excellent agreement with detailed neutron diffraction experiments, currently limited to 15 T, while providing experimental confirmation of the proposed higher field phases for both H∥c and H⊥c. We thus establish NFS as a valuable tool for spin structure studies in very high fields, both complementing and expanding on the applicability of existing techniques.

Effects of carbonate species on the kinetics of dechlorination of 1,1,1-trichloroethane by zero-valent iron.

PubMed

Agrawal, Abinash; Ferguson, William J; Gardner, Bruce O; Christ, John A; Bandstra, Joel Z; Tratnyek, Paul G

2002-10-15

The effect of precipitates on the reactivity of iron metal (Fe0) with 1,1,1-trichloroethane (TCA) was studied in batch systems designed to model groundwaters that contain dissolved carbonate species (i.e., C(IV)). At representative concentrations for high-C(IV) groundwaters (approximately 10(-2) M), the pH in batch reactors containing Fe0 was effectively buffered until most of the aqueous C(IV) precipitated. The precipitate was mainly FeCO3 (siderite) but may also have included some carbonate green rust. Exposure of the Fe0 to dissolved C(IV) accelerated reduction of TCA, and the products formed under these conditions consisted mainly of ethane and ethene, with minor amounts of several butenes. The kinetics of TCA reduction were first-order when C(IV)-enhanced corrosion predominated but showed mixed-order kinetics (zero- and first-order) in experiments performed with passivated Fe0 (i.e., before the onset of pitting corrosion and after repassivation by precipitation of FeCO3). All these data were described by fitting a Michaelis-Menten-type kinetic model and approximating the first-order rate constant as the ratio of the maximum reaction rate (Vm) and the concentration of TCA at half of the maximum rate (K(1/2)). The decrease in Vm/K(1/2) with increasing C(IV) exposure time was fit to a heuristic model assuming proportionality between changes in TCA reduction rate and changes in surface coverage with FeCO3.

Unveiling the high-activity origin of single-atom iron catalysts for oxygen reduction reaction.

PubMed

Yang, Liu; Cheng, Daojian; Xu, Haoxiang; Zeng, Xiaofei; Wan, Xin; Shui, Jianglan; Xiang, Zhonghua; Cao, Dapeng

2018-06-26

It is still a grand challenge to develop a highly efficient nonprecious-metal electrocatalyst to replace the Pt-based catalysts for oxygen reduction reaction (ORR). Here, we propose a surfactant-assisted method to synthesize single-atom iron catalysts (SA-Fe/NG). The half-wave potential of SA-Fe/NG is only 30 mV less than 20% Pt/C in acidic medium, while it is 30 mV superior to 20% Pt/C in alkaline medium. Moreover, SA-Fe/NG shows extremely high stability with only 12 mV and 15 mV negative shifts after 5,000 cycles in acidic and alkaline media, respectively. Impressively, the SA-Fe/NG-based acidic proton exchange membrane fuel cell (PEMFC) exhibits a high power density of 823 mW cm -2 Combining experimental results and density-functional theory (DFT) calculations, we further reveal that the origin of high-ORR activity of SA-Fe/NG is from the Fe-pyrrolic-N species, because such molecular incorporation is the key, leading to the active site increase in an order of magnitude which successfully clarifies the bottleneck puzzle of why a small amount of iron in the SA-Fe catalysts can exhibit extremely superior ORR activity.

Synthesis, crystal structure, and magnetic properties of quaternary iron selenides: Ba{sub 2}FePnSe{sub 5} (Pn=Sb, Bi)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Jian; Greenfield, Joshua T.; Kovnir, Kirill

Two new barium iron pnictide–selenides, Ba{sub 2}FeSbSe{sub 5} and Ba{sub 2}FeBiSe{sub 5}, were synthesized by a high-temperature solid-state route and their crystal structures were determined using single crystal X-ray diffraction. Both compounds are isomorphic to the high pressure phase Ba{sub 3}FeS{sub 5} and crystallize in the orthorhombic space group Pnma (No. 62) with cell parameters of a=12.603(2)/12.619(2) Å, b=9.106(1)/9.183(1) Å, c=9.145(1)/9.123(1) Å and Z=4 for Ba{sub 2}FeSbSe{sub 5} and Ba{sub 2}FeBiSe{sub 5}, respectively. According to differential scanning calorimetry, Ba{sub 2}FePnSe{sub 5} compounds exhibit high thermal stability and melt congruently at 1055(5) K (Pn=Sb) and 1105(5) K (Pn=Bi). Magnetic characterizations revealmore » strong antiferromagnetic nearest-neighbor interactions in both compounds resulting in an antiferromagnetic ordering at 58(1) K for Ba{sub 2}FeSbSe{sub 5} and 79(2) K for Ba{sub 2}FeBiSe{sub 5}. The magnetic interactions between Fe{sup 3+} centers, which are at least 6 Å apart from each other, are mediated by superexchange interactions. - Graphical abstract: In Ba{sub 2}FeSbSe{sub 5} and Ba{sub 2}FeBiSe{sub 5} the magnetic interactions between Fe{sup 3+} centers, which are at least 6 Å apart from each other, are mediated by superexchange interactions. - Highlights: • New compounds Ba{sub 2}FeSbSe{sub 5} and Ba{sub 2}FeBiSe{sub 5} have been synthesized. • The crystal structure was determined by single crystal X-ray diffraction. • Both compounds melt congruently at temperatures above 1000 K. • Ba{sub 2}FeSbSe{sub 5} and Ba{sub 2}FeBiSe{sub 5} exhibit AFM ordering at 58 K (Sb) and 70 K (Bi). • Magnetic exchange between Fe{sup 3+} is mediated by either Se–Sb(Bi)–Se or Se–Ba–Se bridges.« less

Molecular dynamics simulations of proton-ordered water confined in low-diameter carbon nanotubes.

PubMed

Li, Shujuan; Schmidt, Burkhard

2015-03-21

The present work deals with molecular dynamics simulations of water confined in single-walled carbon nanotubes (CNTs), with emphasis on the proton-ordering of water and its polarization. First, the water occupancy of open-ended armchair and zigzag CNTs immersed in water under ambient NPT conditions is calculated for various water models, and for varying Lennard-Jones parameters of the water-carbon interaction. As a function of the CNT diameter, the water density displays several oscillations before converging to the bulk value. Based on these results, the water structures encapsulated in 10 nm long armchair CNTs (n,n) with 5 ≤ n ≤ 10, are investigated under NVT conditions. Inside the smallest nanotubes (n = 5, 6) highly ferroelectric (FE), quasi-one-dimensional water chains are found while inside the other CNTs water molecules assemble into single-walled ice nanotubes (INTs). There are several, near-degenerate minimum energy INT structures: single helical structures were found for 7 ≤ n ≤ 10, in all cases in FE arrangement. In addition, a double helical INT structure was found for n = 8 with an even higher polarization. Prism-like structures were found only for 8 ≤ n ≤ 10 with various FE, ferrielectric (FI), and antiferroelectric (AF, n = 9, 10) proton ordering. The coexistence of the nearly iso-energetic FE, FI, and AF INT structures separated by high barriers renders the molecular dynamics highly metastable, typically with nanosecond timescales at room temperature. Hence, the replica exchange simulation method is used to obtain populations of different INT states at finite temperatures. Many of the FE INT structures confined in low-diameter CNTs are still prevalent at room temperature. Both helix-helix and helix-prism structural transitions are detected which can be either continuous (around 470 K for n = 8) or discontinuous (at 218 K for n = 9). Also melting-like transitions are found in which the INT structures are disrupted leading to a loss of FE or FI ordering of the water orientations. Also these transitions can be either smooth (for n = 7, 8) or abrupt, first-order transitions, at T = 362 K for n = 9 and at T = 285 K for n = 10.

Hedgehog spin-vortex crystal stabilized in a hole-doped iron-based superconductor

DOE PAGES

Meier, William R.; Ding, Qing-Ping; Kreyssig, Andreas; ...

2018-02-09

Magnetism is widely considered to be a key ingredient of unconventional superconductivity. In contrast to cuprate high-temperature superconductors, antiferromagnetism in most Fe-based superconductors (FeSCs) is characterized by a pair of magnetic propagation vectors, (π,0) and (0,π). Consequently, three different types of magnetic order are possible. Of these, only stripe-type spin-density wave (SSDW) and spin-charge-density wave (SCDW) orders have been observed. A realization of the proposed spin-vortex crystal (SVC) order is noticeably absent. We report a magnetic phase consistent with the hedgehog variation of SVC order in Ni-doped and Co-doped CaKFe 4As 4 based on thermodynamic, transport, structural and local magneticmore » probes combined with symmetry analysis. The exotic SVC phase is stabilized by the reduced symmetry of the CaKFe 4As 4 structure. Thus, our results suggest that the possible magnetic ground states in FeSCs have very similar energies, providing an enlarged configuration space for magnetic fluctuations to promote high-temperature superconductivity.« less

Hedgehog spin-vortex crystal stabilized in a hole-doped iron-based superconductor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meier, William R.; Ding, Qing-Ping; Kreyssig, Andreas

Magnetism is widely considered to be a key ingredient of unconventional superconductivity. In contrast to cuprate high-temperature superconductors, antiferromagnetism in most Fe-based superconductors (FeSCs) is characterized by a pair of magnetic propagation vectors, (π,0) and (0,π). Consequently, three different types of magnetic order are possible. Of these, only stripe-type spin-density wave (SSDW) and spin-charge-density wave (SCDW) orders have been observed. A realization of the proposed spin-vortex crystal (SVC) order is noticeably absent. We report a magnetic phase consistent with the hedgehog variation of SVC order in Ni-doped and Co-doped CaKFe 4As 4 based on thermodynamic, transport, structural and local magneticmore » probes combined with symmetry analysis. The exotic SVC phase is stabilized by the reduced symmetry of the CaKFe 4As 4 structure. Thus, our results suggest that the possible magnetic ground states in FeSCs have very similar energies, providing an enlarged configuration space for magnetic fluctuations to promote high-temperature superconductivity.« less

Strong cooperative coupling of pressure-induced magnetic order and nematicity in FeSe

DOE PAGES

Kothapalli, K.; Bohmer, A. E.; Jayasekara, W. T.; ...

2016-09-01

A hallmark of the iron-based superconductors is the strong coupling between magnetic, structural and electronic degrees of freedom. However, a universal picture of the normal state properties of these compounds has been confounded by recent investigations of FeSe where the nematic (structural) and magnetic transitions appear to be decoupled. Here, using synchrotron-based high-energy x-ray diffraction and time-domain Mossbauer spectroscopy, we show that nematicity and magnetism in FeSe under applied pressure are indeed strongly coupled. Distinct structural and magnetic transitions are observed for pressures between 1.0 and 1.7 GPa and merge into a single first-order transition for pressures ≳1.7 GPa, reminiscentmore » of what has been found for the evolution of these transitions in the prototypical system Ba(Fe 1–xCo x) 2As 2. Lastly, our results are consistent with a spin-driven mechanism for nematic order in FeSe and provide an important step towards a universal description of the normal state properties of the iron-based superconductors.« less

Evidence of Nematicity in K 0.8Fe 1.7Se 2

DOE PAGES

Duan, Chunruo; Yang, Junjie; Ye, Feng; ...

2015-12-11

We proposed that the superconducting state of K 0.8Fe 1.7Se 2 is phase separated from a non-superconducting magnetic state. These results from a recent neutron diffraction study on a single crystal of K 0.8Fe 1.7Se 2 provide evidence for a continuous transition between the I 4/m m m high temperature phase in which the Fe vacancies are randomly distributed and the I4/m vacancy ordered phase in the temperature range between T (C) and T (S). Upon cooling, the I 4/m phase becomes more populated, increasing the √5 X√5 X 1 superlattice structure, resulting in an enhancement of the (101) superlatticemore » peak. Moreover, the same temperature dependence is observed for the magnetic peak as well. Moreover, due to the Fe site splitting with the transition, its z-coordinate fluctuates, and so must the d xz and d y z orbitals. Finally, the orbital fluctuations couple to the magnetic ordering as seen here and may lead to a realization of nematic order in this system.« less

Muon spin relaxation study of the layered magnetoelectric FeTe2O5Br with spin amplitude modulated magnetic structure

NASA Astrophysics Data System (ADS)

Zorko, A.; Pregelj, M.; Berger, H.; Arčon, D.

2010-05-01

Local-probe weak-transverse-field and zero-field μSR measurements have been employed to investigate magnetic ordering in the new magnetoelectric compound FeTe2O5Br. Below the Néel transition temperature TN=10.6 K a static local magnetic field starts to develop at the μ+ sites. Fast μ+ polarization decay below TN speaks in favor of a broad distribution of internal magnetic fields, in agreement with the incommensurate magnetic structure suggested by neutron diffraction experiments. Above TN the presence of short-range order is detected as high as at 2TN, which suggests only weak interlayer magnetic coupling. On the other hand, strong Fe3+ spin fluctuations likely reflect geometrically frustrated structure of [Fe4O16]20- spin clusters, which are the main building blocks of the layered FeTe2O5Br structure.

Matrix-mediated synthesis of nanocrystalline gamma-Fe2O3 - A new optically transparent magnetic material

NASA Astrophysics Data System (ADS)

Ziolo, Ronald F.; Giannelis, Emmanuel P.; Weinstein, Bernard A.; O'Horo, Michael P.; Ganguly, Bishwanath N.; Mehrotra, Vivek; Russell, Michael W.; Huffman, Donald R.

1992-07-01

A magnetic material with appreciable optical transmission in the visible region at room temperature is isolated as a gamma-Fe2O3/polymer nanocomposite. The synthesis is carried out in an ion-exchange resin at 60 C. Magnetization and susceptibility data demonstrate loading-dependent saturation moments as high as 46 electromagnetic units per gram and superparamagnetism for lower loadings where particle sizes are less than 100 angstroms. Optical absorption studies show that the small-particle form of gamma-Fe2O3 is considerably more transparent to visible light than the single-crystal form. The difference in absorption ranges from nearly an order of magnitude in the 'red' spectral region to a factor of 3 at 5400 angstroms. The magnetization of the nanocomposite is greater by more than an order of magnitude than those of the strongest room-temperature transparent magnets, FeBO3 and FeF3.

In situ Investigation of Magnetism in Metastable Phases of Levitated Fe83 B17 During Solidification

NASA Astrophysics Data System (ADS)

Quirinale, D. G.; Messina, D.; Rustan, G. E.; Kreyssig, A.; Prozorov, R.; Goldman, A. I.

2017-11-01

In situ measurements of structure, density, and magnetization on samples of Fe83 B17 using an electrostatic levitation furnace allow us to identify and correlate the magnetic and structural transitions in this system during its complex solidification process. In particular, we identify magnetic ordering in the metastable Fe23 B6 /fcc Fe coherently grown structures and primitive tetragonal Fe3 B metastable phase in addition to characterizing the equilibrium Fe2 B phase. Our measurements demonstrate that the incorporation of a tunnel-diode oscillator circuit within an electrostatic levitation furnace enables investigations of the physical properties of high-temperature metastable structures.

Characterization of stoichiometric nanocrystalline spinel ferrites dispersed on porous silica aerogel.

PubMed

Casula, M F; Concas, G; Congiu, F; Corrias, A; Loche, D; Marras, C; Spano, G

2011-11-01

Stoichiometric magnetic nanosized ferrites MFe2O4 (M = Mn, Co, Ni) were prepared in form of nearly spherical nanocrystals supported on a highly porous silica aerogel matrix, by a sol-gel procedure. X-ray diffraction and transmission electron microscopy indicate that these materials are made out of non-agglomerated ferrite nanocrystals having size in the 5-10 nm range. Investigation by Mössbauer Spectroscopy was used to gain insights on the superparamagnetic relaxation and on the inversion degree. Magnetic ordering at room temperature varies from superparamagnetic in the NiFe2O4 sample, highly blocked (approximately 70%) in the MnFe2O4 sample and nearly fully blocked in the CoFe2O4 sample. A fitting procedure of the Mössbauer data has been used in order to resolve the spectrum into the tetrahedral and octahedral components; in this way, an inversion degree of 0.68 (very close to bulk values) was obtained for 6 nm silica-supported CoFe2O4 nanocrystals.

Fe hydroxyphosphate precipitation and Fe(II) oxidation kinetics upon aeration of Fe(II) and phosphate-containing synthetic and natural solutions

NASA Astrophysics Data System (ADS)

van der Grift, B.; Behrends, T.; Osté, L. A.; Schot, P. P.; Wassen, M. J.; Griffioen, J.

2016-08-01

Exfiltration of anoxic Fe-rich groundwater into surface water and the concomitant oxidative precipitation of Fe are important processes controlling the transport of phosphate (PO4) from agricultural areas to aquatic systems. Here, we explored the relationship between solution composition, reaction kinetics, and the characteristics of the produced Fe hydroxyphosphate precipitates in a series of aeration experiments with anoxic synthetic water and natural groundwater. A pH stat device was used to maintain constant pH and to record the H+ production during Fe(II) oxidation in the aeration experiments in which the initial aqueous P/Fe ratios ((P/Fe)ini), oxygen concentration and pH were varied. In general, Fe(II) oxidation proceeded slower in the presence of PO4 but the decrease of the PO4 concentration during Fe(II) oxidation due to the formation of Fe hydroxyphosphates caused additional deceleration of the reaction rate. The progress of the reaction could be described using a pseudo-second-order rate law with first-order dependencies on PO4 and Fe(II) concentrations. After PO4 depletion, the Fe(II) oxidation rates increased again and the kinetics followed a pseudo-first-order rate law. The first-order rate constants after PO4 depletion, however, were lower compared to the Fe(II) oxidation in a PO4-free solution. Hence, the initially formed Fe hydroxyphosphates also affect the kinetics of continuing Fe(II) oxidation after PO4 depletion. Presence of aqueous PO4 during oxidation of Fe(II) led to the formation of Fe hydroxyphosphates. The P/Fe ratios of the precipitates ((P/Fe)ppt) and the recorded ratio of H+ production over decrease in dissolved Fe(II) did not change detectably throughout the reaction despite a changing P/Fe ratio in the solution. When (P/Fe)ini was 0.9, precipitates with a (P/Fe)ppt ratio of about 0.6 were formed. In experiments with (P/Fe)ini ratios below 0.6, the (P/Fe)ppt decreased with decreasing (P/Fe)ini and pH value. Aeration experiments with natural groundwater showed no principal differences in Fe(II) oxidation kinetics and in PO4 immobilisation dynamics compared with synthetic solutions with corresponding P/Fe ratio, pH and oxygen pressure. However, aeration of groundwater with relative high DOC concentrations and a low salinity lead to P-rich Fe colloids that were colloidally stable. The formation of a Fe hydroxyphosphate phase with a molar P/Fe ratio of 0.6 can be used for predictive modelling of PO4 immobilisation upon aeration of pH-neutral natural groundwater with an (P/Fe)ini ratio up to 1.5. These findings provide a solid basis for further studies on transport and bioavailability of phosphorus in streams, ditches and channels that receive anoxic Fe-rich groundwater.

Structure evolution upon chemical and physical pressure in (Sr{sub 1−x}Ba{sub x}){sub 2}FeSbO{sub 6}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tiittanen, T.; Karppinen, M., E-mail: maarit.karppinen@aalto.fi

Here we demonstrate the gradual structural transformation from the monoclinic I2/m to tetragonal I4/m, cubic Fm-3m and hexagonal P6{sub 3}/mmc structure upon the isovalent larger-for-smaller A-site cation substitution in the B-site ordered double-perovskite system (Sr{sub 1−x}Ba{sub x}){sub 2}FeSbO{sub 6}. This is the same transformation sequence previously observed up to Fm-3m upon heating the parent Sr{sub 2}FeSbO{sub 6} phase to high temperatures. High-pressure treatment, on the other hand, transforms the hexagonal P6{sub 3}/mmc structure of the other end member Ba{sub 2}FeSbO{sub 6} back to the cubic Fm-3m structure. Hence we may conclude that chemical pressure, physical pressure and decreasing temperature allmore » work towards the same direction in the (Sr{sub 1−x}Ba{sub x}){sub 2}FeSbO{sub 6} system. Also shown is that with increasing Ba-for-Sr substitution level, i.e. with decreasing chemical pressure effect, the degree-of-order among the B-site cations, Fe and Sb, decreases. - Graphical abstract: In the (Sr{sub 1−x}Ba{sub x}){sub 2}FeSbO{sub 6} double-perovskite system the gradual structural transformation from the monoclinic I2/m to tetragonal I4/m, cubic Fm-3m and hexagonal P6{sub 3}/mmc structure is seen upon the isovalent larger-for-smaller A-site cation substitution. High-pressure treatment under 4 GPa extends stability of the cubic Fm-3m structure within a wider substitution range of x. - Highlights: • Gradual structural transitions upon A-cation substitution in (Sr{sub 1−x}Ba{sub x}){sub 2}FeSbO{sub 6.} • With increasing x structure changes from I2/m to I4/m, Fm-3m and P6{sub 3}/mmc. • Degree of B-site order decreases with increasing x and A-site cation radius. • High-pressure treatment extends cubic Fm-3m phase stability for wider x range. • High-pressure treatment affects bond lengths mostly around the A-cation.« less

Pressure-driven phase transition from antiferromagnetic semiconductor to nonmagnetic metal in the two-leg ladders A Fe 2 X 3 ( A = Ba , K ; X = S , Se )

DOE PAGES

Zhang, Yang; Lin, Lingfang; Zhang, Jun -Jie; ...

2017-03-15

The recent discovery of superconductivity in BaFe 2S 3 has stimulated considerable interest in 123-type iron chalcogenides. This material is the first reported iron-based two-leg ladder superconductor, as opposed to the prevailing two-dimensional layered structures of the iron superconductor family. Once the hydrostatic pressure exceeds 11 GPa, BaFe 2S 3 changes from a semiconductor to a superconductor below 24 K. Although previous calculations correctly explained its ground-state magnetic state and electronic structure, the pressure-induced phase transition was not successfully reproduced. In this work, our first-principles calculations show that with increasing pressure the lattice constants as well as local magnetic momentsmore » are gradually suppressed, followed by a first-order magnetic transition at a critical pressure, with local magnetic moments dropping to zero suddenly. Our calculations suggest that the self-doping caused by electrons transferred from S to Fe may play a key role in this transition. The development of a nonmagnetic metallic phase at high pressure may pave the way to superconductivity. As extensions of this effort, two other 123-type iron chalcogenides, KFe 2S 3 and KFe 2Se 3, have also been investigated. KFe 2S 3 also displays a first-order transition with increasing pressure, but KFe 2Se 3 shows instead a second-order or weakly first-order transition. Here, the required pressures for KFe 2S 3 and KFe 2Se 3 to quench the magnetism are higher than for BaFe 2S 3. Further experiments could confirm the predicted first-order nature of the transition in BaFe 2S 3 and KFe 2S 3, as well as the possible metallic/superconductivity state in other 123-type iron chalcogenides under high pressure.« less

Spin correlated dielectric memory and rejuvenation in multiferroic CuCrS{sub 2}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Karmakar, A.; Dey, K.; Majumdar, S.

We report a rare consequence of memory effect in dielectric response (ϵ) and magnetic field induced rejuvenation in a relaxor-type multiferroic chalcogenide, CuCrS{sub 2}. Despite reasonably high conductivity, we are able to detect significant spontaneous polarization using an improvised technique verifying ferroelectric (FE) order. Concomitant appearance of both FE and antiferromagnetic orders authenticates multiferroicity. A smeared out FE transition and strong frequency dependence of the broadened peak in ϵ obeying Dynamical scaling law signify relaxor properties. We discuss the role of geometrical frustration in the antiferromagnetically coupled layered triangular lattice and metal ligand hybridization for these unusual properties.

Fluid Fe(1 - x)Hx under extreme conditions

NASA Astrophysics Data System (ADS)

Seclaman, Alexandra; Wilson, Hugh F.; Cohen, Ronald E.

We study the fluid Fe-H binary system using first principles molecular dynamics (FPMD) and a new FPMD-based method, CATS, in order to compute efficiently and accurately the equation of state of Fe-H fluids up to 5 TPa and 30,000K. We constructed GRBV-type LDA pseudopotentials for Fe and H with small rcuts in order to avoid pseudo-core overlap. In the liquid Fe regime we find good agreement with previous works, up to the pressures where data is available. In the high density regime of pure H we also find good agreement with previous results. Previous work has been focused on low Fe concentrations in metallic liquid H. We extend previous studies by investigating several intermediate Fe(1 - x)Hx liquid compositions, as well as metallic liquid H and Fe. Preliminary results indicate extreme compositional pressure effects under isothermic and isochoric conditions, 3.9 TPa difference between Fe and H at 20,000K. Thermal pressure effects are comparatively small, 0.12-0.15 TPa per 10,000K for H and Fe, respectively. Equations of state will be presented and fluid immiscibility will be discussed. This work has been supported by the ERC Advanced Grant ToMCaT and NSF and the Carnegie Institution.

Tuning the Curie temperature of L1{sub 0} ordered FePt thin films through site-specific substitution of Rh

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Dongbin, E-mail: dongbin.xu@seagate.com; Department of Materials Science and Engineering, National University of Singapore, Singapore 117576; Sun, Cheng-Jun, E-mail: cjsun@aps.anl.gov, E-mail: msecgm@nus.edu.sg

2014-10-14

In structurally ordered magnetic thin films, the Curie temperature (T{sub C}) of ferromagnetic films depends on the exchange integral of the short range ordered neighboring atoms. The exchange integral may be adjusted by controlling the elemental substitutional concentration at the lattice site of interest. We show how to control the T{sub C} in high anisotropy L1{sub 0} Fe{sub 50}Pt{sub 50} magnetic thin films by substituting Rh into the Pt site. Rh substitution in L1{sub 0} FePt modified the local atomic environment and the corresponding electronic properties, while retaining the ordered L1{sub 0} phase. The analysis of extended x-ray Absorption Finemore » Structure spectra shows that Rh uniformly substitutes for Pt in L1{sub 0} FePt. A model of antiferromagnetic defects caused by controlled Rh substitution of the Pt site, reducing the T{sub C,} is proposed to interpret this phenomenon and its validity is further examined by ab initio density functional calculations.« less

Effect of Mn and Fe on the Formation of Fe- and Mn-Rich Intermetallics in Al-5Mg-Mn Alloys Solidified Under Near-Rapid Cooling.

PubMed

Liu, Yulin; Huang, Gaoren; Sun, Yimeng; Zhang, Li; Huang, Zhenwei; Wang, Jijie; Liu, Chunzhong

2016-01-29

Mn was an important alloying element used in Al-Mg-Mn alloys. However, it had to be limited to a low level (<1.0 wt %) to avoid the formation of coarse intermetallics. In order to take full advantage of the benefits of Mn, research was carried out to investigate the possibility of increasing the content of Mn by studying the effect of cooling rate on the formation of Fe- and Mn-rich intermetallics at different content levels of Mn and Fe. The results indicated that in Al-5Mg-Mn alloy with low Fe content (<0.1 wt %), intermetallic Al₆(Fe,Mn) was small in size and amount. With increasing Mn content, intermetallic Al₆(Fe,Mn) increased, but in limited amount. In high-Fe-containing Al-5Mg-Mn alloys (0.5 wt % Fe), intermetallic Al₆(Fe,Mn) became the dominant phase, even in the alloy with low Mn content (0.39 wt %). Cooling rate played a critical role in the refinement of the intermetallics. Under near-rapid cooling, intermetallic Al₆(Fe,Mn) was extremely refined. Even in the high Mn and/or high-Fe-containing alloys, it still demonstrated fine Chinese script structures. However, once the alloy composition passed beyond the eutectic point, the primary intermetallic Al₆(Fe,Mn) phase displayed extremely coarse platelet-like morphology. Increasing the content of Fe caused intermetallic Al₆(Fe,Mn) to become the primary phase at a lower Mn content.

Sorption, desorption, and speciation of Cd, Ni, and Fe by four calcareous soils as affected by pH.

PubMed

Tahervand, Samaneh; Jalali, Mohsen

2016-06-01

The sorption, desorption, and speciation of cadmium (Cd), nickel (Ni), and iron (Fe) in four calcareous soils were investigated at the pH range of 2-9. The results indicated that sorption of Fe by four soils was higher than 80 % at pH 2, while in the case of Cd and Ni was less than 30 %. The most common sequence of metal sorption at pH 2-9 for four soils was in the order of Fe ≫ Ni > Cd. Cadmium and Ni sorption as a function of pH showed the predictable trend of increasing metal sorption with increase in equilibrium pH, while the Fe sorption trend was different and characterized by three phases. With regard to the order of Cd, Ni, and Fe sorption on soils, Cd and Ni showed high affinity for organic matter (OM), whereas Fe had high tendency for calcium carbonate (CaCO3). Results of metal desorption using 0.01 M NaCl demonstrated that metal sorption on soils containing high amounts of CaCO3 was less reversible in comparison to soils containing high OM. In general, Cd and Ni desorption curves were characterized by three phases; (1) the greatest desorption at pH 2, (2) the low desorption at pH 3-7, and (3) the least desorption at pH > 7. The MINTEQ speciation solubility program showed that the percentage of free metals declined markedly with increase of pH, while the percentage of carbonate and hydroxyl species increased. Furthermore, MINTEQ predicted that saturation index (SI) of metals increased with increasing pH.

A Polar Corundum Oxide Displaying Weak Ferromagnetism at Room Temperature

PubMed Central

2012-01-01

Combining long-range magnetic order with polarity in the same structure is a prerequisite for the design of (magnetoelectric) multiferroic materials. There are now several demonstrated strategies to achieve this goal, but retaining magnetic order above room temperature remains a difficult target. Iron oxides in the +3 oxidation state have high magnetic ordering temperatures due to the size of the coupled moments. Here we prepare and characterize ScFeO3 (SFO), which under pressure and in strain-stabilized thin films adopts a polar variant of the corundum structure, one of the archetypal binary oxide structures. Polar corundum ScFeO3 has a weak ferromagnetic ground state below 356 K—this is in contrast to the purely antiferromagnetic ground state adopted by the well-studied ferroelectric BiFeO3. PMID:22280499

Room Temperature Ferromagnetic, Anisotropic, Germanium Rich FeGe(001) Alloys.

PubMed

Lungu, George A; Apostol, Nicoleta G; Stoflea, Laura E; Costescu, Ruxandra M; Popescu, Dana G; Teodorescu, Cristian M

2013-02-21

Ferromagnetic Fe x Ge 1- x with x = 2%-9% are obtained by Fe deposition onto Ge(001) at high temperatures (500 °C). Low energy electron diffraction (LEED) investigation evidenced the preservation of the (1 × 1) surface structure of Ge(001) with Fe deposition. X-ray photoelectron spectroscopy (XPS) at Ge 3d and Fe 2p core levels evidenced strong Fe diffusion into the Ge substrate and formation of Ge-rich compounds, from FeGe₃ to approximately FeGe₂, depending on the amount of Fe deposited. Room temperature magneto-optical Kerr effect (MOKE) evidenced ferromagnetic ordering at room temperature, with about 0.1 Bohr magnetons per Fe atom, and also a clear uniaxial magnetic anisotropy with the in-plane easy magnetization axis. This compound is a good candidate for promising applications in the field of semiconductor spintronics.

Crystal structures of (Mg1-x,Fex)SiO3postperovskite at high pressures

PubMed Central

Yamanaka, Takamitsu; Hirose, Kei; Mao, Wendy L.; Meng, Yue; Ganesh, P.; Shulenburger, Luke; Shen, Guoyin; Hemley, Russell J.

2012-01-01

X-ray diffraction experiments on postperovskite (ppv) with compositions (Mg0.9Fe0.1)SiO3 and (Mg0.6Fe0.4)SiO3 at Earth core-mantle boundary pressures reveal different crystal structures. The former adopts the CaIrO3-type structure with space group Cmcm, whereas the latter crystallizes in a structure with the Pmcm (Pmma) space group. The latter has a significantly higher density (ρ = 6.119(1) g/cm3) than the former (ρ = 5.694(8) g/cm3) due to both the larger amount of iron and the smaller ionic radius of Fe2+ as a result of an electronic spin transition observed by X-ray emission spectroscopy (XES). The smaller ionic radius for low-spin compared to high-spin Fe2+ also leads to an ordered cation distribution in the M1 and M2 crystallographic sites of the higher density ppv structure. Rietveld structure refinement indicates that approximately 70% of the total Fe2+ in that phase occupies the M2 site. XES results indicate a loss of 70% of the unpaired electronic spins consistent with a low spin M2 site and high spin M1 site. First-principles calculations of the magnetic ordering confirm that Pmcm with a two-site model is energetically more favorable at high pressure, and predict that the ordered structure is anisotropic in its electrical and elastic properties. These results suggest that interpretations of seismic structure in the deep mantle need to treat a broader range of mineral structures than previously considered. PMID:22223656

Formation mechanism of superconducting phase and its three-dimensional architecture in pseudo-single-crystal K xFe 2-ySe 2

DOE PAGES

Liu, Yong; Xing, Qingfeng; Straszheim, Warren E.; ...

2016-02-11

Here, we report how the superconducting phase forms in pseudo-single-crystal K xFe 2-ySe 2. In situ scanning electron microscopy (SEM) observation reveals that, as an order-disorder transition occurs, on cooling, most of the high-temperature iron-vacancy-disordered phase gradually changes into the iron-vacancy-ordered phase whereas a small quantity of the high-temperature phase retains its structure and aggregates to the stripes with more iron concentration but less potassium concentration compared to the iron-vacancy-ordered phase. The stripes that are generally recognized as the superconducting phase are actually formed as a remnant of the high-temperature phase with a compositional change after an “imperfect” order-disorder transition.more » It should be emphasized that the phase separation in pseudo-single-crystal K xFe 2-ySe 2 is caused by the iron-vacancy order-disorder transition. The shrinkage of the high-temperature phase and the expansion of the newly created iron-vacancy-ordered phase during the phase separation rule out the mechanism of spinodal decomposition proposed in an early report [Wang et al, Phys. Rev. B 91, 064513 (2015)]. Since the formation of the superconducting phase relies on the occurrence of the iron-vacancy order-disorder transition, it is impossible to synthesize a pure superconducting phase by a conventional solid state reaction or melt growth. By focused ion beam-scanning electron microscopy, we further demonstrate that the superconducting phase forms a contiguous three-dimensional architecture composed of parallelepipeds that have a coherent orientation relationship with the iron-vacancy-ordered phase.« less

The role of water in generating Fe-depletion and the calc-alkaline trend

NASA Astrophysics Data System (ADS)

Zimmer, M. M.; Plank, T.

2006-12-01

Describing a magmatic suite as calc-alkaline (CA) or tholeiitic (TH) is a first order characterization, but existing classification schemes (AFM ternary plots and FeO*/MgO vs. SiO2) may convolute magmatic processes and can result in contradictory classification. The salient feature of TH vs. CA evolution is the extent of Fe enrichment or depletion in the magma. A plot of FeO* vs. MgO provides the most straightforward way to quantify Fe enrichment and to develop models for its origin. We present a new quantitative classification utilizing the FeO*-MgO plot, the tholeiitic index (THI) = Fe3-5/Fe8 (Fe3-5=average FeO* at 3-5 wt% MgO; Fe8=FeO* at 8 wt% MgO). THI of 1.2 indicates 20% FeO* enrichment from a magma's starting composition at Fe8, while THI of 0.8 indicates 20% depletion in FeO*. A magmatic suite is CA if THI is <1, and TH if THI is >1. Arcs range from 0.6 to 1.1, back arc basins from 1.1-1.3, and MORBs are \\ge1.6. This classification allows comparison of magmatic evolution on a global basis, regardless of starting composition, and is useful for quantitative comparison to liquid line of descent models. Hypotheses for generating CA magmas include high water contents, high pressure of crystallization, high oxygen fugacity, and high Mg# andesitic starting compositions. In order to test the control of H2O, we compare the THI to average magmatic water contents from undegassed melt inclusions and glasses (S>1000 ppm or CO2>50 ppm) from twenty-eight arc volcanoes and back arc basins, including new water contents from seven Aleutian volcanoes. The resulting negative correlation (R2=0.8) between water concentration and THI (with end-members at 0.8 wt% H2O, THI =1.3 and 6.1 wt% H2O, THI = 0.6) suggests water plays a fundamental role in generating the CA fractionation trend. MORB data plot off the trend at a higher THI, possibly related to lower oxygen fugacity during melting and/or crystallization. Models using the pMelts program are consistent with experimentally- and observationally-demonstrated effects of water on suppression of plagioclase and early formation of oxides relative to silicates during magma fractionation, and the resulting FeO* depletion with respect to decreasing MgO.

Role of the orbital degree of freedom in iron-based superconductors

NASA Astrophysics Data System (ADS)

Yi, Ming; Zhang, Yan; Shen, Zhi-Xun; Lu, Donghui

2017-10-01

Almost a decade has passed since the serendipitous discovery of the iron-based high temperature superconductors (FeSCs) in 2008. The fact that, as in the copper oxide high temperature superconductors, long-range antiferromagnetism in the FeSCs arises in proximity to superconductivity immediately raised the question of the degree of similarity between the two. Despite the great resemblance in their phase diagrams, there exist important differences between the FeSCs and the cuprates that need to be considered in order to paint a full picture of these two families of high temperature superconductors. One of the key differences is the multi-orbital multi-band nature of the FeSCs, which contrasts with the effective single-band nature of the cuprates. Systematic studies of orbital related phenomena in FeSCs have been largely lacking. In this review, we summarize angle-resolved photoemission spectroscopy (ARPES) measurements across various FeSC families that have been reported in literature, focusing on the systematic trends of orbital dependent electron correlations and the role of different Fe 3d orbitals in driving the nematic transition, the spin-density-wave transition, and superconductivity.

Oxypnictide SmFeAs(O,F) superconductor: a candidate for high-field magnet applications

NASA Astrophysics Data System (ADS)

Iida, Kazumasa; Hänisch, Jens; Tarantini, Chiara; Kurth, Fritz; Jaroszynski, Jan; Ueda, Shinya; Naito, Michio; Ichinose, Ataru; Tsukada, Ichiro; Reich, Elke; Grinenko, Vadim; Schultz, Ludwig; Holzapfel, Bernhard

2013-07-01

The recently discovered oxypnictide superconductor SmFeAs(O,F) is the most attractive material among the Fe-based superconductors due to its highest transition temperature of 56 K and potential for high-field performance. In order to exploit this new material for superconducting applications, the knowledge and understanding of its electro-magnetic properties are needed. Recent success in fabricating epitaxial SmFeAs(O,F) thin films opens a great opportunity to explore their transport properties. Here we report on a high critical current density of over 105 A/cm2 at 45 T and 4.2 K for both main field orientations, feature favourable for high-field magnet applications. Additionally, by investigating the pinning properties, we observed a dimensional crossover between the superconducting coherence length and the FeAs interlayer distance at 30-40 K, indicative of a possible intrinsic Josephson junction in SmFeAs(O,F) at low temperatures that can be employed in electronics applications such as a terahertz radiation source and a superconducting Qubit.

Effect of wheel speed on magnetic and mechanical properties of melt spun Fe-6.5 wt.% Si high silicon steel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ouyang, Gaoyuan; Jensen, Brandt; Tang, Wei

Here, Fe-Si electric steel is the most widely used soft magnetic material in electric machines and transformers. Increasing the silicon content from 3.2 wt.% to 6.5 wt.% brings about large improvement in the magnetic and electrical properties. However, 6.5 wt.% silicon steel is inherited with brittleness owing to the formation of B2 and D0 3 ordered phase. To obtain ductility in Fe-6.5wt.% silicon steel, the ordered phase has to be bypassed with methods like rapid cooling. In present paper, the effect of cooling rate on magnetic and mechanical properties of Fe-6.5wt.% silicon steel is studied by tuning the wheel speedmore » during melt spinning process. The cooling rate significantly alters the ordering and microstructure, and thus the mechanical and magnetic properties. X-ray diffraction data shows that D0 3 ordering was fully suppressed at high wheel speeds but starts to nucleate at 10m/s and below, which correlates with the increase of Young’s modulus towards low wheel speeds as tested by nanoindentation. The grain sizes of the ribbons on the wheel side decrease with increasing wheel speeds, ranging from ~100 μm at 1m/s to ~8 μm at 30m/s, which lead to changes in coercivity.« less

Effect of wheel speed on magnetic and mechanical properties of melt spun Fe-6.5 wt.% Si high silicon steel

DOE PAGES

Ouyang, Gaoyuan; Jensen, Brandt; Tang, Wei; ...

2017-12-19

Here, Fe-Si electric steel is the most widely used soft magnetic material in electric machines and transformers. Increasing the silicon content from 3.2 wt.% to 6.5 wt.% brings about large improvement in the magnetic and electrical properties. However, 6.5 wt.% silicon steel is inherited with brittleness owing to the formation of B2 and D0 3 ordered phase. To obtain ductility in Fe-6.5wt.% silicon steel, the ordered phase has to be bypassed with methods like rapid cooling. In present paper, the effect of cooling rate on magnetic and mechanical properties of Fe-6.5wt.% silicon steel is studied by tuning the wheel speedmore » during melt spinning process. The cooling rate significantly alters the ordering and microstructure, and thus the mechanical and magnetic properties. X-ray diffraction data shows that D0 3 ordering was fully suppressed at high wheel speeds but starts to nucleate at 10m/s and below, which correlates with the increase of Young’s modulus towards low wheel speeds as tested by nanoindentation. The grain sizes of the ribbons on the wheel side decrease with increasing wheel speeds, ranging from ~100 μm at 1m/s to ~8 μm at 30m/s, which lead to changes in coercivity.« less

Ordered arrays of multiferroic epitaxial nanostructures.

PubMed

Vrejoiu, Ionela; Morelli, Alessio; Biggemann, Daniel; Pippel, Eckhard

2011-01-01

Epitaxial heterostructures combining ferroelectric (FE) and ferromagnetic (FiM) oxides are a possible route to explore coupling mechanisms between the two independent order parameters, polarization and magnetization of the component phases. We report on the fabrication and properties of arrays of hybrid epitaxial nanostructures of FiM NiFe(2)O(4) (NFO) and FE PbZr(0.52)Ti(0.48)O(3) or PbZr(0.2)Ti(0.8)O(3), with large range order and lateral dimensions from 200 nm to 1 micron. The structures were fabricated by pulsed-laser deposition. High resolution transmission electron microscopy and high angle annular dark-field scanning transmission electron microscopy were employed to investigate the microstructure and the epitaxial growth of the structures. Room temperature ferroelectric and ferrimagnetic domains of the heterostructures were imaged by piezoresponse force microscopy (PFM) and magnetic force microscopy (MFM), respectively. PFM and MFM investigations proved that the hybrid epitaxial nanostructures show ferroelectric and magnetic order at room temperature. Dielectric effects occurring after repeated switching of the polarization in large planar capacitors, comprising ferrimagnetic NiFe2O4 dots embedded in ferroelectric PbZr0.52Ti0.48O3 matrix, were studied. These hybrid multiferroic structures with clean and well defined epitaxial interfaces hold promise for reliable investigations of magnetoelectric coupling between the ferrimagnetic / magnetostrictive and ferroelectric / piezoelectric phases.

Effect of wheel speed on magnetic and mechanical properties of melt spun Fe-6.5 wt.% Si high silicon steel

NASA Astrophysics Data System (ADS)

Ouyang, Gaoyuan; Jensen, Brandt; Tang, Wei; Dennis, Kevin; Macziewski, Chad; Thimmaiah, Srinivasa; Liang, Yongfeng; Cui, Jun

2018-05-01

Fe-Si electric steel is the most widely used soft magnetic material in electric machines and transformers. Increasing the silicon content from 3.2 wt.% to 6.5 wt.% brings about large improvement in the magnetic and electrical properties. However, 6.5 wt.% silicon steel is inherited with brittleness owing to the formation of B2 and D03 ordered phase. To obtain ductility in Fe-6.5wt.% silicon steel, the ordered phase has to be bypassed with methods like rapid cooling. In present paper, the effect of cooling rate on magnetic and mechanical properties of Fe-6.5wt.% silicon steel is studied by tuning the wheel speed during melt spinning process. The cooling rate significantly alters the ordering and microstructure, and thus the mechanical and magnetic properties. X-ray diffraction data shows that D03 ordering was fully suppressed at high wheel speeds but starts to nucleate at 10m/s and below, which correlates with the increase of Young's modulus towards low wheel speeds as tested by nanoindentation. The grain sizes of the ribbons on the wheel side decrease with increasing wheel speeds, ranging from ˜100 μm at 1m/s to ˜8 μm at 30m/s, which lead to changes in coercivity.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Song, Yu; Yamani, Zahra; Cao, Chongde

Iron-based superconductivity develops near an antiferromagnetic order and out of a bad-metal normal state, which has been interpreted as originating from a proximate Mott transition. Whether an actual Mott insulator can be realized in the phase diagram of the iron pnictides remains an open question. Here we use transport, transmission electron microscopy, X-ray absorption spectroscopy, resonant inelastic X-ray scattering and neutron scattering to demonstrate that NaFe 1-xCu xAs near x≈0.5 exhibits real space Fe and Cu ordering, and are antiferromagnetic insulators with the insulating behaviour persisting above the Néel temperature, indicative of a Mott insulator. On decreasing x from 0.5,more » the antiferromagnetic-ordered moment continuously decreases, yielding to superconductivity ~x=0.05. Our discovery of a Mott-insulating state in NaFe 1-xCu xAs thus makes it the only known Fe-based material, in which superconductivity can be smoothly connected to the Mott-insulating state, highlighting the important role of electron correlations in the high-T c superconductivity.« less

Exchange Interactions on the Highest-Spin Reported Molecule: the Mixed-Valence Fe42 Complex

NASA Astrophysics Data System (ADS)

Aravena, Daniel; Venegas-Yazigi, Diego; Ruiz, Eliseo

2016-04-01

The finding of high-spin molecules that could behave as conventional magnets has been one of the main challenges in Molecular Magnetism. Here, the exchange interactions, present in the highest-spin molecule published in the literature, Fe42, have been analysed using theoretical methods based on Density Functional Theory. The system with a total spin value S = 45 is formed by 42 iron centres containing 18 high-spin FeIII ferromagnetically coupled and 24 diamagnetic low-spin FeII ions. The bridging ligands between the two paramagnetic centres are two cyanide ligands coordinated to the diamagnetic FeII cations. Calculations were performed using either small Fe4 or Fe3 models or the whole Fe42 complex, showing the presence of two different ferromagnetic couplings between the paramagnetic FeIII centres. Finally, Quantum Monte Carlo simulations for the whole system were carried out in order to compare the experimental and simulated magnetic susceptibility curves from the calculated exchange coupling constants with the experimental one. This comparison allows for the evaluation of the accuracy of different exchange-correlation functionals to reproduce such magnetic properties.

High temperature extended x-ray absorption fine structure study of multiferroic BiFeO3

NASA Astrophysics Data System (ADS)

Raghavendra Reddy, V.; Meneghini, Carlo; Kothari, Deepti; Gupta, Ajay; Aquilanti, Giuliana

2012-08-01

Local atomic structure modifications around Fe atoms in polycrystalline multiferroic BiFeO3 are studied by Fe K edge x-ray absorption spectroscopy as a function of temperature across the Néel temperature (TN = 643 K) in order to reveal local structure modifications related to the magnetic transition. This work demonstrates that on crossing TN the local structure around Fe shows peculiar changes: the Fe-O bond lengths get shorter, the ligand symmetry increases and the Fe-O bond length disorder (σ2) deviates from Debye behaviour. These results suggest that the structural transition at the ferroelectric Curie temperature (TC = 1103 K) is anticipated by early local rearrangement of the structure starting already at TN.

Kambersky Damping in L10 Magnetic Materials of Ordered and Disordered States with Substitutional Defects

NASA Astrophysics Data System (ADS)

Qu, Tao; Victora, Randall

2015-03-01

L10 phase alloys with high magnetic anisotropy play a key role in spintronic devices. The damping constant α represents the elimination of the magnetic energy and affects the efficiency of devices. However, the intrinsic Kambersky damping reported experimentally differs among investigators and the effect of defects on α is never investigated. Here, we apply Kambersky's torque correlation technique, within the tight-binding method, to L10 ordered and disordered alloys FePt, FePd,CoPt and CoPd. In the ordered phase, CoPt has the largest damping of 0.067 while FePd has the minimum value of 0.009 at room temperature. The calculated damping value of FePt and FePd agrees well with experiment. Artificially shifting Ef, as might be accomplished by doping with impurity atoms, shows that α follows the density of states (DOS) at Ef in these four L10 alloys. We introduce lattice defects through exchanging the positions of 3d and non-3d transition elements in 36 atom supercells. The damping increases with reduced degree of chemical order, owing to the enhanced spin-flip channel allowed by the broken symmetry. This prediction is confirmed by measurements in FePt. It is demonstrated that this corresponds to an enhanced DOS at the Fermi level, owing to the rounding of the DOS with loss of long-range order. This work was supported primarily by C-SPIN (one of the six SRC STAR-net Centers) and partly by the MRSEC Program under Contract No. DMR-0819885.

Crystal structure refinement and Mössbauer spectroscopy of an ordered, triclinic clinochlore

USGS Publications Warehouse

Smyth, Joseph R.; Dyar, M. Darby; May, Howard M.; Bricker, Owen P.; Acker, James G.

1997-01-01

The crystal structure of a natural, ordered IIb-4 triclinic clinochlore has been refined in space group C1¯ from 4282 unique X-ray intensity measurements of which 3833 are greater than 3 times the statistical counting error (3σ). Unit cell parameters are a = 5.3262(6) Å; b = 9.226(1) Å; c = 14.334(3) Å; α = 90.56(2)°; β = 97.47(2)°; and γ = 89.979(9)°, which represents the greatest deviation from monoclinic symmetry yet recorded for a triclinic chlorite. The final weighted R is 0.059 for reflections with I > 3σ and 0.064 for all reflections. The chemical formula is (Mg0.966Fe0.034)M1(Mg0.962Fe0.038)M22(Si2.96Al1.04)O10 (OH)2(Mg0.996Fe0.004)M32(Al0.841FeIII0.102Cr0.004Ti0.004)M4(OH)6, which is consistent with electron microprobe (EMP), wet chemical analyses, Mössbauer spectroscopy and X-ray structure refinement. The high degree of ordering of the divalent versus trivalent octahedral cations in the interlayer is noteworthy, with FeIII and Al in M4 and virtually no Fe in M3. In the 2:1 layer, M1 and M2 each contain similar amounts of Fe. The 2 tetrahedral sites have nearly identical mean oxygen distances and volumes, and thus show no evidence of long-range cation ordering.

Influence of the chemically synthesis conditions on the microstructure and magnetic properties of the Co-Fe-B nanoparticles

NASA Astrophysics Data System (ADS)

Ababei, G.; Gaburici, M.; Budeanu, L.-C.; Grigoras, M.; Porcescu, M.; Lupu, N.; Chiriac, H.

2018-04-01

Co-Fe-B particles present a high potential for applications in microwave domain (electromagnetic shielding, toroidal transformer, etc.) due to their special soft magnetic properties like high saturation magnetization, low coercivity, large anisotropy and high magnetic permeability. However, their microwave applications are limited to about few gigahertzes due to the eddy current losses if the size of the particles is larger than few hundred of nanometers. Chemical synthesis method gives the possibility to obtain nanoparticles with diameters from few nanometers to tens of nanometers by varying the parameters of the chemical synthesis. One way to avoids the agglomeration of the particles in the utilization of the polyvinyl-pyrrolidone (PVP) which is acting as dispersant and dimensions controlling agent for nanoparticles. The aim of this paper is to study the influence of the synthesis conditions on the magnetic properties and microstructure of Co-Fe-B nanoparticles prepared by chemical reduction method in order to obtains nanoparticles with magnetic properties suitable for high frequency applications in the 0.1 ÷ 12 GHz frequency range. Co-Fe-B nanoparticles were prepared by chemical reduction of CoCl2·6H2O and FeSO4·7H2O salts in aqueous solution of sodium borohydride (NaBH4) in presence of the polyvinyl-pirrolydone (PVP). The experimental results indicate that the amount of PVP, Fe/Co ratio and the temperature of the chemical synthesis are important parameters which have to be controlled in order to obtain nanoparticles with desired dimensions, nanostructure and soft magnetic properties with suitable properties for high frequency applications.

In situ Investigation of Magnetism in Metastable Phases of Levitated Fe 83 B 17 During Solidification

DOE Office of Scientific and Technical Information (OSTI.GOV)

Quirinale, D. G.; Messina, D.; Rustan, G. E.

In situ measurements of structure, density, and magnetization on samples of Fe 83 B 17 using an electrostatic levitation furnace allow us to identify and correlate the magnetic and structural transitions in this system during its complex solidification process. In particular, we identify magnetic ordering in the metastable Fe 23 B 6 / fcc Fe coherently grown structures and primitive tetragonal Fe 3 B metastable phase in addition to characterizing the equilibrium Fe 2 B phase. Our measurements demonstrate that the incorporation of a tunnel-diode oscillator circuit within an electrostatic levitation furnace enables investigations of the physical properties of high-temperaturemore » metastable structures.« less

Fluorescence Properties of Fe2+- and Co2+-doped Hosts of CdMnTe Compositions as Potential Mid-Infrared Laser Materials

DTIC Science & Technology

2011-09-01

composition also affects the Co2+ and Fe2+ dopant lifetimes and temperature dependencies. Crystal growth effort is underway in order to improve the...single-crystalline samples of Fe2+ or divalent cobalt ion (Co2+)-doped CMT crystals were produced by Brimrose Corporation using a modified vertical...Bridgman technique (18). The starting high purity ingredients Cd, Mn, and Te along with the dopants (Fe and Co) are placed in a pre-cleaned and baked

Pressure-induced magnetic order in FeSe: A muon spin rotation study

NASA Astrophysics Data System (ADS)

Khasanov, Rustem; Guguchia, Zurab; Amato, Alex; Morenzoni, Elvezio; Dong, Xiaoli; Zhou, Fang; Zhao, Zhongxian

2017-05-01

The magnetic order induced by the pressure was studied in FeSe by means of muon spin rotation (μ SR ) technique. By following the evolution of the oscillatory part of the μ SR signal as a function of angle between the initial muon spin polarization and 101 axis of the studied FeSe sample, it was found that the pressure-induced magnetic order in FeSe corresponds either to the collinear (single-stripe) antiferromagnetic order as observed in parent compounds of various FeAs-based superconductors or to the bi-collinear order as obtained in the FeTe system, but with the Fe spins turned by 45o within the a b plane. The value of the magnetic moment per Fe atom was estimated to be ≃0.13 -0.14 μB at p ≃1.9 GPa.

Iron Redox Dynamics in Humid Tropical Forest Soils: Carbon Stabilization vs. Degradation?

NASA Astrophysics Data System (ADS)

Hall, S. J.; Silver, W. L.; Hammel, K.

2015-12-01

Most terrestrial soils exhibit a patchwork of oxygen (O2) availability that varies over spatial scales of microsites to catenas to landscapes, and over temporal scales of minutes to seasons. Oxygen fluctuations often drive microbial iron (Fe) reduction and abiotic/biotic Fe oxidation at the microsite scale, contributing to anaerobic carbon (C) mineralization and changes in soil physical and chemical characteristics, especially the dissolution and precipitation of short-range ordered Fe phases thought to stabilize C. Thus, O2 fluctuations and Fe redox cycling may have multiple nuanced and opposing impacts on different soil C pools, illustrated by recent findings from Fe-rich Oxisols and Ultisols in the Luquillo Experimental Forest, Puerto Rico. Spatial patterns in surface soil C stocks at the landscape scale correlated strongly (R2 = 0.98) with concentrations of reduced Fe (Fe(II)), reflecting constitutive differences in reducing conditions within and among sites that promote C accumulation in mineral soil horizons. Similarly, turnover times of a decadal-cycling pool of mineral-associated organic matter increased with Fe(II) across a catena, possibly reflecting the role of anaerobic microsites in long-term C stabilization. However, two different indices of short-range order Fe showed highly significant opposing relationships (positive and negative) with spatial variation in soil C concentrations, possibly reflecting a dual role of Fe in driving C stabilization via co-precipitation, and C solubilization and loss following dissimilatory Fe reduction. Consistent with the field data, laboratory incubations demonstrated that redox fluctuations can increase the contribution of biochemically recalcitrant C (lignin) to soil respiration, whereas addition of short-range order Fe dramatically suppressed lignin mineralization but had no impact on bulk soil respiration. Thus, understanding spatial and temporal patterns of Fe redox cycling may provide insight into explaining the relatively rapid turnover of biochemically recalcitrant and mineral-associated C in soils.

Double perovskite Sr2FeMoO6-xNx (x=0.3, 1.0) oxynitrides with anionic ordering

NASA Astrophysics Data System (ADS)

Retuerto, M.; de la Calle, C.; Martínez-Lope, M. J.; Porcher, F.; Krezhov, K.; Menéndez, N.; Alonso, J. A.

2012-01-01

Two new oxynitride double perovskites of composition Sr2FeMoO6-xNx (x=0.3, 1.0) have been synthesized by annealing precursor powders obtained by citrate techniques in flowing ammonia at 750 °C and 650 °C, respectively. The polycrystalline samples have been characterized by chemical analysis, x-ray and neutron diffraction (NPD), Mössbauer spectroscopy and magnetic measurements. They exhibit a tetragonal structure with a=5.5959(1) Å, c=7.9024(2) Å, V=247.46(2) Å3 for Sr2FeMoO5.7N0.3; and a=5.6202(2) Å, c=7.9102(4) Å, V=249.85(2) Å3 for Sr2FeMoO5N; space group I4/m, Z=2. The nitridation process seems to extraordinarily improve the long-range Fe/Mo ordering, achieving 95% at moderate temperatures of 750 °C. The analysis of high resolution NPD data, based on the contrast existing between the scattering lengths of O and N, shows that both atoms are located at (O,N)2 anion substructure corresponding to the basal ab plane of the perovskite structure, whereas the O1 site is fully occupied by oxygen atoms. The evolution of the and distances suggests a shift towards a configuration close to Fe4+(3d4, S=2):Mo5+(4d1, S=1/2). The magnetic susceptibility shows a ferrimagnetic transition with a reduced saturation magnetization compared to Sr2FeMoO6, due to the different nature of the magnetic double exchange interactions through Fe-N-Mo-N-Fe paths in contrast to the stronger Fe-O-Mo-O-Fe interactions. Also, the effect observed by low-temperature NPD seems to reduce the ordered Fe moments and enhance the Mo moments, in agreement with the evolution of the oxidation states, thus decreasing the saturation magnetization.

Effects of ordered mesoporous structure and La-doping on the microwave absorbing properties of CoFe2O4

NASA Astrophysics Data System (ADS)

Shang, Tao; Lu, Qingshan; Chao, Luomeng; Qin, Yanli; Yun, Yuehou; Yun, Guohong

2018-03-01

Low-density ordered mesoporous CoFe2O4 (Osbnd CFO) and CoLa0.12Fe1.88O4 (Osbnd CLFO) are prepared by nanocasting method using mesoporous silica SBA-15 as a hard-template. The crystal structure, surface chemical state, magnetic properties and electromagnetic parameters are characterized by X-ray diffraction, transmission electron microscopy, N2 adsorption-desorption measurement, X-ray photoelectron spectroscopy, physical property measurement system and vector network analyzer. The results show that all the samples formed a single phase with cubic spinel structure. Meanwhile Osbnd CFO and Osbnd CLFO possess a highly ordered mesostructure. Comparing with particle CoFe2O4 (P-CFO), Osbnd CFO with high specific surface area exhibits lower magnetic saturation (Ms), higher imaginary part of complex permittivity (ε‧‧) and imaginary part of the complex permeability (μ‧‧). The minimum reflection loss (RL) of Osbnd CFO reaches -27.36 dB with a matching thickness of 3.0 mm. The enhancement of the microwave absorbing performances of Osbnd CFO can be mainly attributed to the good impedance matching, high electromagnetic wave attenuation and multiple reflections of electromagnetic wave originated from the ordered mesoporous structure. The Ms of Osbnd CLFO decreases after La3+ doping, while the specific surface area, coercivity value, ε‧‧ and μ‧‧ of Osbnd CLFO increase. The minimum RL of Osbnd CLFO reaches -46.47 dB with a thickness of 3.0 mm, and the effective absorption frequency bandwidth reaches 4.9 GHz.

High-pressure phase transitions of Fe 3-xTi xO 4 solid solution up to 60 GPa correlated with electronic spin transition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yamanaka, Takamitsu; Kyono, Atsushi; Nakamoto, Yuki

2013-06-12

The structural phase transition of the titanomagnetite (Fe 3–xTi xO 4) solid solution under pressures up to 60 GPa has been clarified by single-crystal and powder diffraction studies using synchrotron radiation and a diamond-anvil cell. Present Rietveld structure refinements of the solid solution prove that the prefered cation distribution is based on the crystal field preference rather than the magnetic spin ordering in the solid solution. The Ti-rich phases in 0.734 ≤ x ≤1.0 undergo a phase transformation from the cubic spinel of Fd3m to the tetragonal spinel structure of I4 1/amd with c/a < 1.0. The transition is drivenmore » by a Jahn-Teller effect of IVFe 2+ (3d 6) on the tetrahedral site. The c/a < 1 ratio is induced by lifting of the degeneracy of the e orbitals by raising the d x2-y2 orbital below the energy of the d z2 orbital. The distortion characterized by c/a < 1 is more pronounced with increasing Ti content in the Fe 3–xTi xO 4 solid solutions and with increasing pressure. An X-ray emission experiment of Fe 2TiO 4 at high pressures confirms the spin transition of FeKβ from high spin to intermediate spin (IS) state. The high spin (HS)-to-low spin (LS) transition starts at 14 GPa and the IS state gradually increases with compression. The VIFe 2+ in the octahedral site is more prone for the HS-to-LS transition, compared with Fe 2+ in the fourfold- or eightfold-coordinated site. The transition to the orthorhombic post-spinel structure with space group Cmcm has been confirmed in the whole compositional range of Fe 3–xTi xO 4. The transition pressure decreases from 25 GPa (x = 0.0) to 15 GPa (x = 1.0) with increasing Ti content. There are two cation sites in the orthorhombic phase: M1 and M2 sites of eightfold and sixfold coordination, respectively. Fe 2+ and Ti 4+ are disordered on the M2 site. This structural change is accelerated at higher pressures due to the spin transition of Fe 2+ in the octahedral site. This is because the ionic radius of VIFe 2+ becomes 20% shortened by the spin transition. At 53 GPa, the structure transforms to another high-pressure polymorph with Pmma symmetry with the ordered structure of Ti and Fe atoms in the octahedral site. This structure change results from the order-disorder transition.« less

Galvanostatically deposited Fe: MnO2 electrodes for supercapacitor application

NASA Astrophysics Data System (ADS)

Dubal, D. P.; Kim, W. B.; Lokhande, C. D.

2012-01-01

The present investigation describes the addition of iron (Fe) in order to improve the supercapacitive properties of MnO2 electrodes using galvanostatic mode. These amorphous worm like Fe: MnO2 electrodes are characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDAX), Fourier transform infrared spectroscopy (FTIR) and wettability test. The supercapacitive properties of MnO2 and Fe: MnO2 electrodes are investigated using cyclic voltammetry, chronopotentiometry and impedance techniques. It is seen that the supercapacitance increases with increase in Fe doping concentration and achieved a maximum of 173 F g-1 at 2 at% Fe doping. The maximum supercapacitance obtained is 218 F g-1 for 2 at% Fe: MnO2 electrode. This hydrous binary oxide exhibited ideal capacitive behavior with high reversibility and high pulse charge-discharge property between -0.1 and +0.9 V/SCE in 1 M Na2SO4 electrolyte indicating a promising electrode material for electrochemical supercapacitors.

Adsorption properties of kaolinite-based nanocomposites for Fe and Mn pollutants from aqueous solutions and raw ground water: kinetics and equilibrium studies.

PubMed

Shaban, Mohamed; Hassouna, Mohamed E M; Nasief, Fadya M; AbuKhadra, Mostafa R

2017-10-01

Raw kaolinite was used in the synthesis of metakaolinite/carbon nanotubes (K/CNTs) and kaolinite/starch (K/starch) nanocomposites. Raw kaolinite and the synthetic composites were characterized using XRD, SEM, and TEM techniques. The synthetic composites were used as adsorbents for Fe and Mn ions from aqueous solutions and natural underground water. The adsorption by the both composites is highly pH dependent and achieves high efficiency within the neutral pH range. The experimental adsorption data for the uptake of Fe and Mn ions by K/CNTs were found to be well represented by the pseudo-second-order kinetic model rather than the intra-particle diffusion model or Elovich model. For the adsorption using K/starch, the uptake results of Fe ions was well fitted by the second-order model, whereas the uptake of Mn ions fitted well to the Elovich model rather than pseudo-second-order and intra-particle diffusion models The equilibrium studies revealed the excellent fitting of the removal of Fe and Mn ions by K/CNTs and Fe using K/starch with the Langmuir isotherm model rather than with Freundlich and Temkin models. But the adsorption of Mn ions by K/starch is well fitted with Freundlich rather than Temkin and Langmuir isotherm models. The thermodynamic studies reflected the endothermic nature and the exothermic nature for the adsorption by K/CNTs and K/starch nanocomposites, respectively. Natural ground water contaminated by 0.4 mg/L Fe and 0.5 mg/L Mn was treated at the optimum conditions of pH 6 and 120 min contact time. Under these conditions, 92.5 and 72.5% Fe removal efficiencies were achieved using 20 mg of K/CNTs and K/starch nanocomposites, respectively. Also, K/CNTs nanocomposite shows higher efficiency in the removal of Mn ions as compared to K/starch nanocomposite.

78 FR 53737 - ConocoPhillips Company; Application for Blanket Authorization To Export Previously Imported...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-08-30

... application, FE applies the principles described in DOE Delegation Order No. 0204-111 which states that... LNG Development, L.P., DOE/FE Order No. 3317 (July 19, 2013); ENI USA Gas Marketing LLC, DOE/FE Order No. 3247 (March 5, 2013); Sempra LNG Marketing, LLC, DOE/FE Order No. 3231 (February 13, 2013...

From mean-field localized magnetism to itinerant spin fluctuations in the "nonmetallic metal" FeCrAs

NASA Astrophysics Data System (ADS)

Plumb, K. W.; Stock, C.; Rodriguez-Rivera, J. A.; Castellan, J.-P.; Taylor, J. W.; Lau, B.; Wu, W.; Julian, S. R.; Kim, Young-June

2018-05-01

FeCrAs displays an unusual electrical response that is neither metallic in character nor divergent at low temperatures, as expected for an insulating response, and therefore it has been termed a "nonmetal metal." The anomalous resistivity occurs for temperatures below ˜900 K. We have carried out neutron scattering experiments on powder and single crystal samples to study the magnetic dynamics and critical fluctuations in FeCrAs. Magnetic neutron diffraction measurements find Cr3 + magnetic order setting in at TN=115 K ˜10 meV with a mean-field critical exponent. Using neutron spectroscopy we observe gapless, high velocity, magnetic fluctuations emanating from magnetic positions with propagation wave vector q⃗0=(1/3 ,1/3 ) , which persists up to at least 80 meV ˜927 K, an energy scale much larger than TN. Despite the mean-field magnetic order at low temperatures, the magnetism in FeCrAs therefore displays a response which resembles that of itinerant magnets at high energy transfers. We suggest that the presence of stiff high-energy spin fluctuations extending up to a temperature scale of ˜900 K is the origin of the unusual temperature dependence of the resistivity.

Effect of Mn and Fe on the Formation of Fe- and Mn-Rich Intermetallics in Al–5Mg–Mn Alloys Solidified Under Near-Rapid Cooling

PubMed Central

Liu, Yulin; Huang, Gaoren; Sun, Yimeng; Zhang, Li; Huang, Zhenwei; Wang, Jijie; Liu, Chunzhong

2016-01-01

Mn was an important alloying element used in Al–Mg–Mn alloys. However, it had to be limited to a low level (<1.0 wt %) to avoid the formation of coarse intermetallics. In order to take full advantage of the benefits of Mn, research was carried out to investigate the possibility of increasing the content of Mn by studying the effect of cooling rate on the formation of Fe- and Mn-rich intermetallics at different content levels of Mn and Fe. The results indicated that in Al–5Mg–Mn alloy with low Fe content (<0.1 wt %), intermetallic Al6(Fe,Mn) was small in size and amount. With increasing Mn content, intermetallic Al6(Fe,Mn) increased, but in limited amount. In high-Fe-containing Al–5Mg–Mn alloys (0.5 wt % Fe), intermetallic Al6(Fe,Mn) became the dominant phase, even in the alloy with low Mn content (0.39 wt %). Cooling rate played a critical role in the refinement of the intermetallics. Under near-rapid cooling, intermetallic Al6(Fe,Mn) was extremely refined. Even in the high Mn and/or high-Fe-containing alloys, it still demonstrated fine Chinese script structures. However, once the alloy composition passed beyond the eutectic point, the primary intermetallic Al6(Fe,Mn) phase displayed extremely coarse platelet-like morphology. Increasing the content of Fe caused intermetallic Al6(Fe,Mn) to become the primary phase at a lower Mn content. PMID:28787888

Upward magnetic relaxation in self organizing Fe nanoparticle system

NASA Astrophysics Data System (ADS)

Pal, Satyendra Prakash; Sharma, Gyaneshwar; Sen, P.

2018-04-01

Study of the thermoremanent magnetic relaxation behavior of Fe nanoparticles and its nanocomposite with activated carbon has been systematically performed. Magnetic relaxation data shows the spontaneous collective periodic oscillations of the spins superimposed on the magnetic decay curves. At sufficiently high temperature, due to thermal noise induced ordering of the magnetic moment an inflexion with an increase in the absolute value of the magnetization takes place. Due to insufficient interaction on account of dilution in the case of nanocomposite, the spin - spin interaction which was responsible for magnetic ordering in the case of bare Fe nanoparticles, collective oscillations of the system do not sustain upto longer times in the case of carbon diluted system.

Highly efficient and porous TiO2-coated Ag@Fe3O4@C-Au microspheres for degradation of organic pollutants

NASA Astrophysics Data System (ADS)

Shen, Mao; Chen, Suqing; Jia, Wenping; Fan, Guodong; Jin, Yanxian; Liang, Huading

2016-12-01

In this paper, we reported a novel hierarchical porous Ag@Fe3O4@C-Au@TiO2 core@shell microspheres with a highly photocatalytic activity and magnetically separable properties. The synthesis method is included of a Fe3O4 magnetic embedded Ag core (Ag@Fe3O4), an interlayer of carbon modified by PEI to form sufficient amounts of amine functional groups (Ag@Fe3O4@C-PEI), the grafting of Au nanoparticles on the surface of Ag@Fe3O4@C-PEI (Ag@Fe3O4@C-Au), and an ordered porous TiO2 structured shell. As an example of the applications, the photocatalytic activities of the samples were investigated by the reduction of Rhodamine B (RhB) under visible-light irradiation. The results show that the porous Ag@Fe3O4@C-Au@TiO2 core@shell microspheres display higher adsorption and photocatalytic activities compared to the pure porous TiO2 and Ag@Fe3O4@C@TiO2 microspheres, which are attributed to the local surface plasmon resonance (LSPR) by the Ag and Au nanoparticles and the high specific surface area.

Phase stability, ordering tendencies, and magnetism in single-phase fcc Au-Fe nanoalloys

DOE PAGES

Zhuravlev, I. A.; Barabash, S. V.; An, J. M.; ...

2017-10-01

Bulk Au-Fe alloys separate into Au-based fcc and Fe-based bcc phases, but L1 0 and L1 2 orderings were reported in single-phase Au-Fe nanoparticles. Motivated by these observations, we study the structural and ordering energetics in this alloy by combining density functional theory (DFT) calculations with effective Hamiltonian techniques: a cluster expansion with structural filters, and the configuration-dependent lattice deformation model. The phase separation tendency in Au-Fe persists even if the fcc-bcc decomposition is suppressed. The relative stability of disordered bcc and fcc phases observed in nanoparticles is reproduced, but the fully ordered L1 0 AuFe, L1 2 Au 3Fe,more » and L1 2 AuFe 3 structures are unstable in DFT. But, a tendency to form concentration waves at the corresponding [001] ordering vector is revealed in nearly-random alloys in a certain range of concentrations. Furthermore, this incipient ordering requires enrichment by Fe relative to the equiatomic composition, which may occur in the core of a nanoparticle due to the segregation of Au to the surface. Effects of magnetism on the chemical ordering are also discussed.« less

Phase stability, ordering tendencies, and magnetism in single-phase fcc Au-Fe nanoalloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhuravlev, I. A.; Barabash, S. V.; An, J. M.

Bulk Au-Fe alloys separate into Au-based fcc and Fe-based bcc phases, but L1 0 and L1 2 orderings were reported in single-phase Au-Fe nanoparticles. Motivated by these observations, we study the structural and ordering energetics in this alloy by combining density functional theory (DFT) calculations with effective Hamiltonian techniques: a cluster expansion with structural filters, and the configuration-dependent lattice deformation model. The phase separation tendency in Au-Fe persists even if the fcc-bcc decomposition is suppressed. The relative stability of disordered bcc and fcc phases observed in nanoparticles is reproduced, but the fully ordered L1 0 AuFe, L1 2 Au 3Fe,more » and L1 2 AuFe 3 structures are unstable in DFT. But, a tendency to form concentration waves at the corresponding [001] ordering vector is revealed in nearly-random alloys in a certain range of concentrations. Furthermore, this incipient ordering requires enrichment by Fe relative to the equiatomic composition, which may occur in the core of a nanoparticle due to the segregation of Au to the surface. Effects of magnetism on the chemical ordering are also discussed.« less

Large magnetoelectric coupling in magnetically short-range ordered Bi₅Ti₃FeO₁₅ film.

PubMed

Zhao, Hongyang; Kimura, Hideo; Cheng, Zhenxiang; Osada, Minoru; Wang, Jianli; Wang, Xiaolin; Dou, Shixue; Liu, Yan; Yu, Jianding; Matsumoto, Takao; Tohei, Tetsuya; Shibata, Naoya; Ikuhara, Yuichi

2014-06-11

Multiferroic materials, which offer the possibility of manipulating the magnetic state by an electric field or vice versa, are of great current interest. However, single-phase materials with such cross-coupling properties at room temperature exist rarely in nature; new design of nano-engineered thin films with a strong magneto-electric coupling is a fundamental challenge. Here we demonstrate a robust room-temperature magneto-electric coupling in a bismuth-layer-structured ferroelectric Bi₅Ti₃FeO₁₅ with high ferroelectric Curie temperature of ~1000 K. Bi₅Ti₃FeO₁₅ thin films grown by pulsed laser deposition are single-phase layered perovskit with nearly (00l)-orientation. Room-temperature multiferroic behavior is demonstrated by a large modulation in magneto-polarization and magneto-dielectric responses. Local structural characterizations by transmission electron microscopy and Mössbauer spectroscopy reveal the existence of Fe-rich nanodomains, which cause a short-range magnetic ordering at ~620 K. In Bi₅Ti₃FeO₁₅ with a stable ferroelectric order, the spin canting of magnetic-ion-based nanodomains via the Dzyaloshinskii-Moriya interaction might yield a robust magneto-electric coupling of ~400 mV/Oe·cm even at room temperature.

High-Frequency Spin-Based Devices for Nanoscale Signal Processing

DTIC Science & Technology

2009-01-20

feedback on the devices in order to improve their spectral properties . Deliverable: Microwave signals without an Applied Field. We have successfully...additionally have the advantage of higher operating frequencies than the more conventional devices based on NiFe alloys. By combining several of...Output from a Co/Ni based STNO. Corresponds to approximately 20 nW, about 10 times larger than typical NiFe .device. 6 High-Frequency Spin-Based

High resolution positron annihilation induced Auger electron spectroscopy of the CuM 2,3VV-transition and of Cu sub-monolayers on Pd and Fe

NASA Astrophysics Data System (ADS)

Mayer, J.; Hugenschmidt, C.; Schreckenbach, K.

2010-09-01

We present a high resolution positron annihilation induced Auger Electron Spectroscopy (PAES) of the CuM 2,3VV-transition with the unprecedented energy resolution of Δ/EE <1%. This energy resolution and the highly intense positron source NEPOMUC enabled us to resolve the double peak structure with PAES for the first time within a measurement time of only 5.5 h. In addition, sub-monolayers of Cu were deposited on Fe- and Pd-samples in order to investigate the surface selectivity of PAES in comparison with EAES. The extremely high surface selectivity of PAES due to the different positron affinity of Cu and Fe lead to the result that with only 0.96 monolayer of Cu on Fe more than 55% of the emitted Auger electrons stem from Cu, whereas with EAES the Cu Auger fraction amounted to less than 6%.

A Synthetic Single-Site Fe Nitrogenase: High Turnover, Freeze-Quench (57)Fe Mössbauer Data, and a Hydride Resting State.

PubMed

Del Castillo, Trevor J; Thompson, Niklas B; Peters, Jonas C

2016-04-27

The mechanisms of the few known molecular nitrogen-fixing systems, including nitrogenase enzymes, are of much interest but are not fully understood. We recently reported that Fe-N2 complexes of tetradentate P3(E) ligands (E = B, C) generate catalytic yields of NH3 under an atmosphere of N2 with acid and reductant at low temperatures. Here we show that these Fe catalysts are unexpectedly robust and retain activity after multiple reloadings. Nearly an order of magnitude improvement in yield of NH3 for each Fe catalyst has been realized (up to 64 equiv of NH3 produced per Fe for P3(B) and up to 47 equiv for P3(C)) by increasing acid/reductant loading with highly purified acid. Cyclic voltammetry shows the apparent onset of catalysis at the P3(B)Fe-N2/P3(B)Fe-N2(-) couple and controlled-potential electrolysis of P3(B)Fe(+) at -45 °C demonstrates that electrolytic N2 reduction to NH3 is feasible. Kinetic studies reveal first-order rate dependence on Fe catalyst concentration (P3(B)), consistent with a single-site catalyst model. An isostructural system (P3(Si)) is shown to be appreciably more selective for hydrogen evolution. In situ freeze-quench Mössbauer spectroscopy during turnover reveals an iron-borohydrido-hydride complex as a likely resting state of the P3(B)Fe catalyst system. We postulate that hydrogen-evolving reaction activity may prevent iron hydride formation from poisoning the P3(B)Fe system. This idea may be important to consider in the design of synthetic nitrogenases and may also have broader significance given that intermediate metal hydrides and hydrogen evolution may play a key role in biological nitrogen fixation.

Fe/Si(001) Ferromagnetic Layers: Reactivity, Local Atomic Structure and Magnetism

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lungu, G. A.; Costescu, R. M.; Husanu, M. A.

2011-10-03

Ultrathin ferromagnetic Fe layers on Si(001) have recently been synthesized using the molecular beam epitaxy (MBE) technique, and their structural and magnetic properties, as well as their interface reactivity have been investigated. The study was undertaken as function of the amount of Fe deposited and of substrate temperature. The interface reactivity was characterized by Auger electron spectroscopy (AES). The surface structure was characterized by low-energy electron diffraction (LEED). The magnetism was investigated by magneto-optical Kerr effect (MOKE). A higher deposition temperature stabilizes a better surface ordering, but it also enhances Fe and Si interdiffusion and it therefore decreases the magnetism.more » Despite the rapid disappearance of the long range order with Fe deposition at room temperature, the material exhibits a significant uniaxial in-plane magnetic anisotropy. For the Fe deposition performed at high temperature (500 deg. C), a weak ferromagnetism is still observed, with saturation magnetization of about 10% of the value obtained previously. MOKE studies allowed inferring the main properties of the distinct formed layers.« less

Determination of Magneto-crystalline Anisotropy Energy (MAE) Of ordered L10 CoPt and FePt nanoparticles

NASA Astrophysics Data System (ADS)

Alsaad, A.; Ahmad, A. A.; Shukri, A. A.; Bani-Younes, O. A.

2018-02-01

The structural and magnetic properties of both L10 ordered FePt and CoPt nanoparticles make them potential candidates for optical-electronic and magneto-optical devices. First, we carried out an ab initio total energy minimization study to find the geometrical optimization of both L10 phases of FePt and CoPt nanoparticles. Then, we investigated the magnetocrystalline anisotropy energy (MAE) of both systems along special line joining the points of high symmetry (A,B and C points) using super-cell slap approach with alternating layers Fe/Co and Pt along the (001) direction. We found that the point (A) has the highest MAE value for both systems, where the value of MAE in FePt is 8.89 × 107 erg/cm3 and in CoPt is 6.40 × 107 erg/cm3. Our spin density based calculations indicate that large spin-orbit interaction and the hybridization between Pt 5d states and Fe/Co 3d states are the dominant factors in determining the MAE in both systems.

Superconductivity pairing mechanism from cobalt impurity doping in FeSe: Spin (s±) or orbital (s++) fluctuation

NASA Astrophysics Data System (ADS)

Urata, T.; Tanabe, Y.; Huynh, K. K.; Yamakawa, Y.; Kontani, H.; Tanigaki, K.

2016-01-01

In high-superconducting transition temperature (Tc) iron-based superconductors, interband sign reversal (s±) and sign preserving (s++) s -wave superconducting states have been primarily discussed as the plausible superconducting mechanism. We study Co impurity scattering effects on the superconductivity in order to achieve an important clue on the pairing mechanism using single-crystal Fe1 -xCoxSe and depict a phase diagram of a FeSe system. Both superconductivity and structural transition/orbital order are suppressed by the Co replacement on the Fe sites and disappear above x = 0.036. These correlated suppressions represent a common background physics behind these physical phenomena in the multiband Fermi surfaces of FeSe. By comparing experimental data and theories so far proposed, the suppression of Tc against the residual resistivity is shown to be much weaker than that predicted in the case of general sign reversal and full gap s± models. The origin of the superconducting paring in FeSe is discussed in terms of its multiband electronic structure.

EFFECT OF PRE-ALLOYING CONDITION ON THE BULK AMORPHOUS ALLOY ND(60)FE(30)AL(10).

DOE Office of Scientific and Technical Information (OSTI.GOV)

OCONNOR,A.S.; LEWIS,L.H.; MCCALLUM,R.W.

Bulk metallic glasses are materials that require only modest cooling rates to obtain amorphous solids directly from the melt. Nd{sub 60}Fe{sub 30}Al{sub 10} has been reported to be a ferromagnetic bulk metallic glass that exhibits high coercivity, a combination unlike conventional Nd-based amorphous magnetic alloys. To clarify the relationship between short-range order and high coercivity in glassy Nd{sub 60}Fe{sub 30}Al{sub 10}, experiments were performed to verify the existence of a homogeneous liquid state prior to rapid solidification. Alloys were prepared by various pre-alloying routes and then melt-spun. Arc-melted alloys were prepared for melt spinning using three different protocols involving: (1)more » alloying all three elements at once, (2) forming a Nd-Fe alloy which was subsequently alloyed with Al, and (3) forming a Fe-Al alloy for subsequent alloying with Nd. XRD, DTA, and magnetic measurement data from the resultant ribbons indicate significant differences in both the glassy fraction and the crystalline phase present in the as-spun material. These observed differences are attributed to the presence of highly stable nanoscopic aluminide-and/or silicide-phases, or motes, present in the melt prior to solidification. These motes would affect the short-range order and coercivity of the resultant glassy state and are anticipated to provide heterogeneous nucleation sites for crystallization.« less

Intralayer doping effects on the high-energy magnetic correlations in NaFeAs

DOE PAGES

Pelliciari, Jonathan; Huang, Yaobo; Das, Tanmoy; ...

2016-04-26

We used resonant inelastic x-ray scattering (RIXS) and dynamical susceptibility calculations to study the magnetic excitations in NaFe 1$-$xCo xAs ( x=0 , 0.03, and 0.08). Despite a relatively low ordered magnetic moment, collective magnetic modes are observed in parent compounds (x=0) and persist in optimally (x= 0.03) and overdoped (x = 0.08) samples. Their magnetic bandwidths are unaffected by doping within the range investigated. High-energy magnetic excitations in iron pnictides are robust against doping and present irrespectively of the ordered magnetic moment. Nonetheless, Co doping slightly reduces the overall magnetic spectral weight, differently from previous studies on hole-doped BaFemore » 2As 2 , where it was observed constant. Finally, we demonstrate that the doping evolution of magnetic modes is different for the dopants being inside or outside the Fe-As layer.« less

What makes the T c of monolayer FeSe on SrTiO 3 so high: a sign-problem-free quantum Monte Carlo study

DOE PAGES

Li, Zi-Xiang; Wang, Fa; Yao, Hong; ...

2016-04-30

Monolayer FeSe films grown on SrTiO 3 (STO) substrate show superconducting gap-opening temperatures (T c) which are almost an order of magnitude higher than those of the bulk FeSe and are highest among all known Fe-based superconductors. Angle-resolved photoemission spectroscopy observed “replica bands” suggesting the importance of the interaction between FeSe electrons and STO phonons. These facts rejuvenated the quest for T c enhancement mechanisms in iron-based, especially iron-chalcogenide, superconductors. Here, we perform the first numerically-exact sign-problem-free quantum Monte Carlo simulations to iron-based superconductors. We (1) study the electronic pairing mechanism intrinsic to heavily electron doped FeSe films, and (2)more » examine the effects of electron–phonon interaction between FeSe and STO as well as nematic fluctuations on T c. Armed with these results, we return to the question “what makes the T c of monolayer FeSe on SrTiO 3 so high?” in the conclusion and discussions.« less

High-Tc superconductivity near the anion height instability in Fe-based superconductors: analysis of LaFeAsO(1-x)H(x).

PubMed

Onari, Seiichiro; Yamakawa, Youichi; Kontani, Hiroshi

2014-05-09

The isostructural transition in the tetragonal phase with a sizable change in the anion height, is realized in heavily H-doped LaFeAsO and (La,P) codoped CaFe2As2. In these compounds, the superconductivity with higher Tc (40-50 K) is realized near the isostructural transition. To find the origin of the anion-height instability and the role in realizing the higher-Tc state, we develop the orbital-spin fluctuation theory by including the vertex correction. We analyze LaFeAsO(1-x)H(x) and find that the non-nematic orbital fluctuations, which induce the anion-height instability, are automatically obtained at x∼0.5, in addition to the conventional nematic orbital fluctuations at x∼0. The non-nematic orbital order triggers the isostructural transition, and its fluctuation would be a key ingredient to realize higher-Tc superconductivity of order 50 K.

Complex magnetic structure of clusters and chains of Ni and Fe on Pt(111)

PubMed Central

Bezerra-Neto, Manoel M.; Ribeiro, Marcelo S.; Sanyal, Biplab; Bergman, Anders; Muniz, Roberto B.; Eriksson, Olle; Klautau, Angela B.

2013-01-01

We present an approach to control the magnetic structure of adatoms adsorbed on a substrate having a high magnetic susceptibility. Using finite Ni-Pt and Fe-Pt nanowires and nanostructures on Pt(111) surfaces, our ab initio results show that it is possible to tune the exchange interaction and magnetic configuration of magnetic adatoms (Fe or Ni) by introducing different numbers of Pt atoms to link them, or by including edge effects. The exchange interaction between Ni (or Fe) adatoms on Pt(111) can be considerably increased by introducing Pt chains to link them. The magnetic ordering can be regulated allowing for ferromagnetic or antiferromagnetic configurations. Noncollinear magnetic alignments can also be stabilized by changing the number of Pt-mediated atoms. An Fe-Pt triangularly-shaped nanostructure adsorbed on Pt(111) shows the most complex magnetic structure of the systems considered here: a spin-spiral type of magnetic order that changes its propagation direction at the triangle vertices. PMID:24165828

Iron-platinum multilayer thin film reactions to form L1(0) iron-platinum and exchange spring magnets

NASA Astrophysics Data System (ADS)

Yao, Bo

FePt films with the L10 phase have potential applications for magnetic recording and permanent magnets due to its high magnetocrystalline anisotropy energy density. Heat treatment of [Fe/Pt] n multilayer films is one approach to form the L10 FePt phase through a solid state reaction. This thesis has studied the diffusion and reaction of [Fe/Pt]n multilayer films to form the L10 FePt phase and has used this understanding to construct exchange spring magnets. The process-structure-property relations of [Fe/Pt] n multilayer films were systematically examined. The transmission electron microscopy (TEM) study of the annealed multilayers indicates that the Pt layer grows at the expense of Fe during annealing, forming a disordered fcc FePt phase by the interdiffusion of Fe into Pt. This thickening of the fcc Pt layer can be attributed to the higher solubilities of Fe into fcc Pt, as compared to the converse. For the range of film thickness studied, a continuous L10 FePt product layer that then thickens with further annealing is not found. Instead, the initial L10 FePt grains are distributed mainly on the grain boundaries within the fcc FePt layer and at the Fe/Pt interfaces and further transformation of the sample to the ordered L10 FePt phase proceeds coupled with the growth of the initial L10 FePt grains. A comprehensive study of annealed [Fe/Pt]n films is provided concerning the phase fraction, grain size, nucleation/grain density, interdiffusivity, long-range order parameter, and texture, as well as magnetic properties. A method based on hollow cone dark field TEM is introduced to measure the volume fraction, grain size, and density of ordered L10 FePt phase grains in the annealed films, and low-angle X-ray diffraction is used to measure the effective Fe-Pt interdiffusivity. The process-structure-properties relations of two groups of samples with varying substrate temperature and periodicity are reported. The results demonstrate that the processing parameters (substrate temperature, periodicity) have a strong influence on the structure (effective interdiffusivity, L1 0 phase volume fraction, grain size, and density) and magnetic properties. The correlation of these parameters suggests that the annealed [Fe/Pt]n multilayer films have limited nuclei, and the subsequent growth of L10 phase is very important to the extent of ordered phase formed. A correlation between the grain size of fcc FePt phase, grain size of the L10 FePt phase, the L10 FePt phase fraction, and magnetic properties strongly suggests that the phase transformation of fcc →L10 is highly dependent on the grain size of the parent fcc FePt phase. A selective phase growth model is proposed to explain the phenomena observed. An investigation of the influence of total film thickness on the phase formation of the L10 FePt phase in [Fe/Pt] n multilayer films and a comparison of this to that of FePt co-deposited alloy films is also conducted. A general trend of greater L1 0 phase formation in thicker films was observed in both types of films. It was further found that the thickness dependence of the structure and of the magnetic properties in [Fe/Pt]n multilayer films is much stronger than that in FePt alloy films. This is related to the greater chemical energy contained in [Fe/Pt]n films than FePt alloy films, which is helpful for the L10 FePt phase growth. However, the initial nucleation temperature of [Fe/Pt]n multilayers and co-deposited alloy films was found to be similar. An investigation of L10 FePt-based exchange spring magnets is presented based on our understanding of the L10 formation in [Fe/Pt] n multilayer films. It is known that exchange coupling is an interfacial magnetic interaction and it was experimentally shown that this interaction is limited to within several nanometers of the interface. A higher degree of order of the hard phase is shown to increase the length scale slightly. Two approaches can be used to construct the magnets. For samples with composition close to stoichiometric L10 FePt, the achievement of higher energy product is limited by the average saturation magnetization, and therefore, a lower annealing temperature is beneficial to increase the energy product, allowing a larger fraction of disordered phase. For samples with higher Fe concentration, the (BH)max is limited by the low coercivity of annealed sample, and a higher annealing temperature is beneficial to increase the energy product.

Block copolymer directed one-pot simple synthesis of L10-phase FePt nanoparticles inside ordered mesoporous aluminosilicate/carbon composites.

PubMed

Kang, Eunae; Jung, Hyunok; Park, Je-Geun; Kwon, Seungchul; Shim, Jongmin; Sai, Hiroaki; Wiesner, Ulich; Kim, Jin Kon; Lee, Jinwoo

2011-02-22

A "one-pot" synthetic method was developed to produce L1(0)-phase FePt nanoparticles in ordered mesostructured aluminosilicate/carbon composites using polyisoprene-block-poly(ethylene oxide) (PI-b-PEO) as a structure-directing agent. PI-b-PEO block copolymers with aluminosilicate sols are self-assembled with a hydrophobic iron precursor (dimethylaminomethyl-ferrocene) and a hydrophobic platinum precursor (dimethyl(1,5-cyclooctadiene)platinum(II)) to obtain mesostructured composites. The as-synthesized material was heat-treated to 800 °C under an Ar/H(2) mixture (5% v/v), resulting in the formation of fct FePt nanocrystals encapsulated in ordered mesopores. By changing the quantities of the Fe and Pt precursors in the composite materials, the average particle size of the resulting fct FePt, estimated using the Debye-Scherer equation with X-ray diffraction patterns, can be easily controlled to be 2.6-10.4 nm. Using this simple synthetic method, we can extend the size of directly synthesized fct FePt up to ∼10 nm, which cannot be achieved directly in the colloidal synthetic method. All fct FePt nanoparticles show hysteresis behavior at room temperature, which indicates that ferromagnetic particles are obtained inside mesostructued channels. Well-isolated, ∼10 nm fct FePt have a coercivity of 1100 Oe at 300 K. This coercivity value is higher than values of fct FePt nanoparticles synthesized through the tedious hard template method by employing SBA-15 as a host material. The coercivity value for FePt-1 (2.6 nm) at 5 K is as high as 11 900 Oe, which is one of the largest values reported for FePt nanoparticles, or any other magnetic nanoparticles. The fct FePt nanoparticles also showed exchange-bias behavior.

An enhanced sensing platform for ultrasensitive impedimetric detection of target genes based on ordered FePt nanoparticles decorated carbon nanotubes.

PubMed

Zhang, Wei; Zong, Peisong; Zheng, Xiuwen; Wang, Libin

2013-04-15

We demonstrate a novel high-performance DNA hybridization biosensor with a carbon nanotubes (CNTs)-based nanocomposite membrane as the enhanced sensing platform. The platform was constructed by homogenously distributing ordered FePt nanoparticles (NPs) onto the CNTs matrix. The surface structure and electrochemical performance of the FePt/CNTs nanocomposite membrane were systematically investigated. Such a nanostructured composite membrane platform could combine with the advantages of FePt NPs and CNTs, greatly facilitate the electron-transfer process and the sensing behavior for DNA detection, leading to excellent sensitivity and selectivity. The complementary target genes from acute promyelocytic leukemia could be quantified in a wide range of 1.0×10⁻¹² mol/L to 1.0×10⁻⁶ mol/L using electrochemical impedance spectroscopy, and the detection limit was 2.1×10⁻¹³ mol/L under the optimal conditions. In addition, the DNA electrochemical biosensor was highly selective to discriminate single-base or double-base mismatched sequences. Copyright © 2012 Elsevier B.V. All rights reserved.

Room Temperature Ferromagnetic, Anisotropic, Germanium Rich FeGe(001) Alloys

PubMed Central

Lungu, George A.; Apostol, Nicoleta G.; Stoflea, Laura E.; Costescu, Ruxandra M.; Popescu, Dana G.; Teodorescu, Cristian M.

2013-01-01

Ferromagnetic FexGe1−x with x = 2%–9% are obtained by Fe deposition onto Ge(001) at high temperatures (500 °C). Low energy electron diffraction (LEED) investigation evidenced the preservation of the (1 × 1) surface structure of Ge(001) with Fe deposition. X-ray photoelectron spectroscopy (XPS) at Ge 3d and Fe 2p core levels evidenced strong Fe diffusion into the Ge substrate and formation of Ge-rich compounds, from FeGe3 to approximately FeGe2, depending on the amount of Fe deposited. Room temperature magneto-optical Kerr effect (MOKE) evidenced ferromagnetic ordering at room temperature, with about 0.1 Bohr magnetons per Fe atom, and also a clear uniaxial magnetic anisotropy with the in-plane [110] easy magnetization axis. This compound is a good candidate for promising applications in the field of semiconductor spintronics. PMID:28809330

Charge ordering in stoichiometric FeTe: Scanning tunneling microscopy and spectroscopy

DOE PAGES

Li, Wei; Yin, Wei -Guo; Wang, Lili; ...

2016-01-04

In this study, we use scanning tunneling microscopy and spectroscopy to reveal a unique stripy charge order in a parent phase of iron-based superconductors in stoichiometric FeTe epitaxy films. The charge order has unusually the same—usually half—period as the spin order. We also found highly anisotropic electron band dispersions being large and little along the ferromagnetic (crystallographic b) and antiferromagnetic (a) directions, respectively. Our data suggest that the microscopic mechanism is likely of the Stoner type driven by interatomic Coulomb repulsion V ij, and that V ij and charge fluctuations, so far much neglected, are important to the understanding ofmore » iron-based superconductors.« less

High-coercivity FePt nanoparticle assemblies embedded in silica thin films.

PubMed

Yan, Q; Purkayastha, A; Singh, A P; Li, H; Li, A; Ramanujan, R V; Ramanath, G

2009-01-14

The ability to process assemblies using thin film techniques in a scalable fashion would be a key to transmuting the assemblies into manufacturable devices. Here, we embed FePt nanoparticle assemblies into a silica thin film by sol-gel processing. Annealing the thin film composite at 650 degrees C transforms the chemically disordered fcc FePt phase into the fct phase, yielding magnetic coercivity values H(c)>630 mT. The positional order of the particles is retained due to the protection offered by the silica host. Such films with assemblies of high-coercivity magnetic particles are attractive for realizing new types of ultra-high-density data storage devices and magneto-composites.

Iron dissolution kinetics of mineral dust at low pH during simulated atmospheric processing

NASA Astrophysics Data System (ADS)

Shi, Z.; Bonneville, S.; Krom, M. D.; Carslaw, K. S.; Jickells, T. D.; Baker, A. R.; Benning, L. G.

2010-11-01

We investigated the iron (Fe) dissolution kinetics of African (Tibesti) and Asian (Beijing) dust samples at acidic pH with the aim of reproducing the low pH conditions in atmospheric aerosols. The Beijing dust and three size fractions of the Tibesti dust (<20 μm: PM20; <10 μm: PM10; and <2.5 μm: PM2.5) were dissolved at pH 1, 2 and/or 3 for up to 1000 h. In the first 10 min, all dust samples underwent an extremely fast Fe solubilisation. Subsequently, the Fe dissolution proceeded at a much slower rate before reaching a stable dissolution plateau. The time-dependant Fe dissolution datasets were best described by a model comprising three acid-extractable Fe pools each dissolving according to first-order kinetics. The dissolution rate constant k of each pool was independent of the source (Saharan or Asian) and the size (PM20, PM10 or PM2.5) of the dust but highly dependent on pH. The "fast" Fe pool had a k (25 h-1 at pH=1) of a similar magnitude to "dry" ferrihydrite nanoparticles and/or poorly crystalline Fe(III) oxyhydroxide, while the "intermediate" and "slow" Fe pools had k values respectively 50-60 times and 3000-4000 times smaller than the "fast" pool. The "slow" Fe pool was likely to consist of both crystalline Fe oxide phases (i.e., goethite and/or hematite) and Fe contained in the clay minerals. The initial mass of the "fast", "intermediate" and "slow" Fe pools represented respectively about 0.5-2%, 1-3% and 15-40% of the total Fe in the dust samples. Furthermore, we showed that in systems with low dust/liquid ratios, Fe can be dissolved from all three phases, whereas at high dust/liquid ratios (e.g., in aerosols), sufficient Fe is solubilised from the "fast" phase to dominate the Fe dissolved and to suppress the dissolution of Fe from the other Fe pools. These data demonstrated that dust/liquid ratio and pH are fundamental parameters controlling Fe dissolution kinetics in the dust. In order to reduce errors in atmospheric and climate models, these fundamental controlling factors need to be included.

Iron dissolution kinetics of mineral dust at low pH during simulated atmospheric processing

NASA Astrophysics Data System (ADS)

Shi, Z.; Bonneville, S.; Krom, M. D.; Carslaw, K. S.; Jickells, T. D.; Baker, A. R.; Benning, L. G.

2011-02-01

We investigated the iron (Fe) dissolution kinetics of African (Tibesti) and Asian (Beijing) dust samples at acidic pH with the aim of reproducing the low pH conditions in atmospheric aerosols. The Beijing dust and three size fractions of the Tibesti dust (<20 μm: PM20; <10 μm: PM10; and <2.5 μm: PM2.5) were dissolved at pH 1, 2 and/or 3 for up to 1000 h. In the first 10 min, all dust samples underwent an extremely fast Fe solubilisation. Subsequently, the Fe dissolution proceeded at a much slower rate before reaching a stable dissolution plateau. The time-dependant Fe dissolution datasets were best described by a model comprising three acid-extractable Fe pools each dissolving according to first-order kinetics. The dissolution rate constant k (h-1) of each pool was independent of the source (Saharan or Asian) and the size (PM20, PM10 or PM2.5) of the dust but highly dependent on pH. The "fast" Fe pool had a k (25 h-1 at pH = 1) of a similar magnitude to "dry" ferrihydrite nanoparticles and/or poorly crystalline Fe(III) oxyhydroxide, while the "intermediate" and "slow" Fe pools had k values respectively 50-60 times and 3000-4000 times smaller than the "fast" pool. The "slow" Fe pool was likely to consist of both crystalline Fe oxide phases (i.e., goethite and/or hematite) and Fe contained in the clay minerals. The initial mass of the "fast", "intermediate" and "slow" Fe pools represented respectively about 0.5-2%, 1-3% and 15-40% of the total Fe in the dust samples. Furthermore, we showed that in systems with low dust/liquid ratios, Fe can be dissolved from all three pools, whereas at high dust/liquid ratios (e.g., in aerosols), sufficient Fe may be solubilised from the "fast" phase to dominate the Fe dissolved and to suppress the dissolution of Fe from the other Fe pools. These data demonstrated that dust/liquid ratio and pH are fundamental parameters controlling Fe dissolution kinetics in the dust. In order to reduce errors in atmospheric and climate models, these fundamental controlling factors need to be included.

Oxypnictide SmFeAs(O,F) superconductor: a candidate for high–field magnet applications

PubMed Central

Iida, Kazumasa; Hänisch, Jens; Tarantini, Chiara; Kurth, Fritz; Jaroszynski, Jan; Ueda, Shinya; Naito, Michio; Ichinose, Ataru; Tsukada, Ichiro; Reich, Elke; Grinenko, Vadim; Schultz, Ludwig; Holzapfel, Bernhard

2013-01-01

The recently discovered oxypnictide superconductor SmFeAs(O,F) is the most attractive material among the Fe-based superconductors due to its highest transition temperature of 56 K and potential for high-field performance. In order to exploit this new material for superconducting applications, the knowledge and understanding of its electro-magnetic properties are needed. Recent success in fabricating epitaxial SmFeAs(O,F) thin films opens a great opportunity to explore their transport properties. Here we report on a high critical current density of over 105 A/cm2 at 45 T and 4.2 K for both main field orientations, feature favourable for high-field magnet applications. Additionally, by investigating the pinning properties, we observed a dimensional crossover between the superconducting coherence length and the FeAs interlayer distance at 30–40 K, indicative of a possible intrinsic Josephson junction in SmFeAs(O,F) at low temperatures that can be employed in electronics applications such as a terahertz radiation source and a superconducting Qubit. PMID:23823976

Effects of cation ordering on the elastic and electronic properties of Mg-Fe silicate phases at high pressures

NASA Astrophysics Data System (ADS)

Das, Pratik Kr.; Mandal, Nibir; Arya, A.

2017-12-01

Olivine [(Mg, Fe)2SiO4] and pyroxene [(Mg, Fe)Si2O6] are naturally occurring silicate phases. Both the phases crystallize with orthorhombic symmetry, displaying ordering of Mg2+ and Fe2+ in their non-equivalent octahedral lattice sites (M1, M2). We address two major issues: (1) how far an inversion of the cation ordering: type I (Mg2+ in M1; Fe2+ in M2) to type II (Mg2+ in M2; Fe2+in M1) can modify their elastic properties and (2) what are the effects of this inversion on their electronic properties? Using density functional theory, we calculate the elastic constant tensors (Cij) as a function of hydrostatic pressure for types I and II ordering. Our calculations suggest that the inversion (types I to II) in olivine significantly reduces the shear elastic constant C55 (˜25%). This has little effect on the Cij of pyroxene in ambient condition, but the effects become strong at elevated pressures (100 GPa), resulting in large variations (>40%) of all the shear elastic constants: C44, C55, and C66. We predict contrasting variations in compressional (VP) and shear (VS) wave velocities by 1% and 9% and by 2% and 11% for olivine and pyroxene, respectively, on types I to II switchover. Our Debye temperature (θD) calculations show that θD of olivine is less sensitive to ordering inversion, whereas that of pyroxene varies substantially (˜22%) under ambient condition. We evaluate the electronic DOS of pyroxene, and obtain a large difference in the magnetic moment between types I and II.

Cation non-stoichiometry in pulsed laser deposited Sr{sub 2+y}Fe{sub 1+x}Mo{sub 1-x}O₆ epitaxial films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meyer, T. L.; Woodward, P. M., E-mail: woodward.55@osu.edu; Dixit, M.

2014-07-07

Sr₂FeMoO₆ (SFMO) films were grown on SrTiO₃ (100)- and (111)-oriented substrates via pulsed laser deposition (PLD). In order to study the fundamental characteristics of deposition, films were grown in two different PLD chambers. In chamber I, the best films were grown with a relatively long substrate-to-target distance (89 mm), high substrate temperature (850 °C), and low pressure (50 mTorr) in a 95% Ar/5% H₂ atmosphere. Although X-ray diffraction (XRD) measurements indicate these films are single phase, Rutherford Backscattering (RBS) measurements reveal considerable non-stoichiometry, corresponding to a Sr₂Fe{sub 1–x}Mo{sub 1+x}O₆ composition with x≅0.2–0.3. This level of non-stoichiometry results in inferior magneticmore » properties. In chamber II, the best films were grown with a much shorter substrate-to-target distance (38 mm), lower temperature (680 °C), and higher pressure (225 mTorr). XRD measurements show that the films are single phase, and RBS measurements indicate that they are nearly stoichiometric. The degree of ordering between Fe and Mo was dependent on both the temperature and pressure used during deposition, reaching a maximum order parameter of 85%. The saturation magnetization increases as the Fe/Mo ordering increases, reaching a maximum of 2.4 μ B/f.u. Based on prior studies of bulk samples, one would expect a higher saturation magnetization for this degree of Fe/Mo order. The presence of extra strontium oxide layers in the form of Ruddlesden-Popper intergrowths appears to be responsible for the lower than expected saturation magnetization of these films.« less

Record high magnetic ordering temperature in a lanthanide at extreme pressure

DOE PAGES

Lim, J.; Fabbris, G.; Haskel, D.; ...

2017-11-07

Today's best permanent magnet materials, SmCo 5 and Nd 2Fe 14B, could likely be made signi fi cantly more powerful were it not necessary to dilute the strong magnetism of the rare earth ions (Sm, Nd) with the 3 d transition elements (Fe, Co). Since the rare-earth metals order magnetically at relatively low temperatures T o <= 292 K, transition elements must be added to bring T o to temperatures well above ambient. Under pressure T o (P) for the neighboring lanthanides Gd, Tb, and Dy follows a notably nonmonotonic, but nearly identical, dependence to similar to 60 GPa. Atmore » higher pressures, however, Tb and Dy exhibit highly anomalous behavior, T o for Dy soaring to temperatures well above ambient. In conclusion, we suggest that this anomalously high magnetic ordering temperature is an heretofore unrecognized feature of the Kondo lattice state.« less

Templated synthesis of highly ordered mesoporous cobalt ferrite and its microwave absorption properties

NASA Astrophysics Data System (ADS)

Li, Guo-Min; Wang, Lian-Cheng; Xu, Yao

2014-08-01

Based on the nanocasting strategy, highly ordered mesoporous CoFe2O4 is synthesized via the ‘two-solvent’ impregnation method using a mesoporous SBA-15 template. An ordered two-dimensional (P6mm) structure is preserved for the CoFe2O4/SBA-15 composite after the nanocasting. After the SBA-15 template is dissolved by NaOH solution, a mesoporous structure composed of aligned nanoparticles can be obtained, and the P6mm structure of the parent SBA-15 is preserved. With a high specific surface area (above 90 m2/g) and ferromagnetic behavior, the obtained material shows potential in light weight microwave absorption application. The minimum reflection loss (RL) can reach -18 dB at about 16 GHz with a thickness of 2 mm and the corresponding absorption bandwidth is 4.5 GHz.

Record high magnetic ordering temperature in a lanthanide at extreme pressure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lim, J.; Fabbris, G.; Haskel, D.

Today's best permanent magnet materials, SmCo 5 and Nd 2Fe 14B, could likely be made signi fi cantly more powerful were it not necessary to dilute the strong magnetism of the rare earth ions (Sm, Nd) with the 3 d transition elements (Fe, Co). Since the rare-earth metals order magnetically at relatively low temperatures T o <= 292 K, transition elements must be added to bring T o to temperatures well above ambient. Under pressure T o (P) for the neighboring lanthanides Gd, Tb, and Dy follows a notably nonmonotonic, but nearly identical, dependence to similar to 60 GPa. Atmore » higher pressures, however, Tb and Dy exhibit highly anomalous behavior, T o for Dy soaring to temperatures well above ambient. In conclusion, we suggest that this anomalously high magnetic ordering temperature is an heretofore unrecognized feature of the Kondo lattice state.« less

The Effect of deposition rate on FePt/MgO crystal orientation

NASA Astrophysics Data System (ADS)

Sheikhi, M.; Sebt, S. A.; Khajehnezhad, A.

2018-06-01

FePt granular layers which are made in suitable conditions can have three types of ordering that are crystalline, compositional orders and directional configuration of nanoparticles. Formation of fct structure with L10 compositional ordering requires high temperature. At this temperature, a problem is the size control of the nanoparticles and another problem is control of their crystal orientation. Fabrication method and the use of suitable substrates can help solving these problems. In direct synthesis by sputtering method on the warm substrate the size of FePt nanoparticles in L10 compositional ordered phase can be controlled. We show that crystal orientation of L10-FePt nanoparticles on a thin layer of MgO depends on the rate of deposition. This becomes clear from the results of the XRD analyses of samples. Based on these results in synthesis at room temperature with deposition rate of upper than 1.5 Å/s after annealing, (001) peak is dominated and at rate of lower than 1.0 Å/s just (111) peak is appeared. In direct synthesis with intermediate rate (111) and (110) peaks can be seen. Moreover, the difference of the shape of hysteresis loops of samples in parallel and vertical directions are the witnesses for orientation of samples in presence of MgO layer and the effect of FePt deposition rate on it.

Temperature-dependence of current-perpendicular-to-the-plane giant magnetoresistance spin-valves using Co{sub 2}(Mn{sub 1−x}Fe{sub x})Ge Heusler alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Page, M. R.; Nakatani, T. M., E-mail: nakatani.tomoya@nims.go.jp; Stewart, D. A.

2016-04-21

The properties of Co{sub 2}(Mn{sub 1−x}Fe{sub x})Ge (CMFG) (x = 0–0.4) Heusler alloy magnetic layers within polycrystalline current-perpendicular-to-the plane giant magnetoresistance (CPP-GMR) spin-valves are investigated. CMFG films annealed at 220–320 °C exhibit partly ordered B2 structure with an order parameter S{sub B2} = 0.3–0.4, and a lower S{sub B2} was found for a higher Fe content. Nevertheless, CPP-GMR spin-valve devices exhibit a relatively high magnetoresistance ratio of ∼13% and a magnetoresistance-area product (ΔRA) of ∼6 mΩ μm{sup 2} at room temperature, which is almost independent of the Fe content in the CMFG films. By contrast, at low temperatures, ΔRA clearly increases with higher Fe content,more » despite the lower B2 ordering for increasing the Fe content. Indeed, first-principles calculations reveal that the CMFG alloy with a partially disordered B2 structure has a greater density of d-state at the Fermi level in the minority band compared to the Fe-free (Co{sub 2}MnGe) alloy. This could explain the larger ΔRA measured on CMFG at low temperatures by assuming that s-d scattering mainly determines the spin asymmetry of resistivity as described in Mott's theory.« less

Elliptical vortex and oblique vortex lattice in the FeSe superconductor based on the nematicity and mixed superconducting orders

NASA Astrophysics Data System (ADS)

Lu, Da-Chuan; Lv, Yang-Yang; Li, Jun; Zhu, Bei-Yi; Wang, Qiang-Hua; Wang, Hua-Bing; Wu, Pei-Heng

2018-03-01

The electronic nematic phase is characterized as an ordered state of matter with rotational symmetry breaking, and has been well studied in the quantum Hall system and the high-Tc superconductors, regardless of cuprate or pnictide family. The nematic state in high-Tc systems often relates to the structural transition or electronic instability in the normal phase. Nevertheless, the electronic states below the superconducting transition temperature is still an open question. With high-resolution scanning tunneling microscope measurements, direct observation of vortex core in FeSe thin films revealed the nematic superconducting state by Song et al. Here, motivated by the experiment, we construct the extended Ginzburg-Landau free energy to describe the elliptical vortex, where a mixed s-wave and d-wave superconducting order is coupled to the nematic order. The nematic order induces the mixture of two superconducting orders and enhances the anisotropic interaction between the two superconducting orders, resulting in a symmetry breaking from C4 to C2. Consequently, the vortex cores are stretched into an elliptical shape. In the equilibrium state, the elliptical vortices assemble a lozenge-like vortex lattice, being well consistent with experimental results.

The effect of fluence on the magnetic properties of superparamagnetic iron-nickel nanoparticles in SiO2 made by dual Ni and Fe low energy ion implantation

NASA Astrophysics Data System (ADS)

Williams, G. V. M.; Prakash, T.; Kennedy, J.

2017-10-01

Superparamagnetic Ni1-yFey nanoparticles were made in a SiO2 film by 10 keV ion beam implantation of Ni followed by Fe with a Ni fluence of 4 × 1016 at.cm-2 and a Fe fluence fraction of 0.47. Nearly all of the moments magnetically ordered, which was not reported for an implanted film made with a Fe fluence fraction of 0.56 and half the Ni fluence. The temperature dependence of the saturation moment is remarkably similar for low and high Ni fluences where there is also the presence of very thin spin-disordered shells. The higher Ni fluence leads to a significant enhancement of the susceptibility by a factor of 9 when compared with the lower fluence sample. This enhancement is likely to be due to a larger magnetically ordered volume fraction.

Exchange Interactions on the Highest-Spin Reported Molecule: the Mixed-Valence Fe42 Complex

PubMed Central

Aravena, Daniel; Venegas-Yazigi, Diego; Ruiz, Eliseo

2016-01-01

The finding of high-spin molecules that could behave as conventional magnets has been one of the main challenges in Molecular Magnetism. Here, the exchange interactions, present in the highest-spin molecule published in the literature, Fe42, have been analysed using theoretical methods based on Density Functional Theory. The system with a total spin value S = 45 is formed by 42 iron centres containing 18 high-spin FeIII ferromagnetically coupled and 24 diamagnetic low-spin FeII ions. The bridging ligands between the two paramagnetic centres are two cyanide ligands coordinated to the diamagnetic FeII cations. Calculations were performed using either small Fe4 or Fe3 models or the whole Fe42 complex, showing the presence of two different ferromagnetic couplings between the paramagnetic FeIII centres. Finally, Quantum Monte Carlo simulations for the whole system were carried out in order to compare the experimental and simulated magnetic susceptibility curves from the calculated exchange coupling constants with the experimental one. This comparison allows for the evaluation of the accuracy of different exchange-correlation functionals to reproduce such magnetic properties. PMID:27033418

MnFe2O4-graphene oxide magnetic nanoparticles as a high-performance adsorbent for rare earth elements: Synthesis, isotherms, kinetics, thermodynamics and desorption.

PubMed

Ghobadi, Misagh; Gharabaghi, Mahdi; Abdollahi, Hadi; Boroumand, Zohreh; Moradian, Marzieh

2018-06-05

In recent decades, considerable amounts of rare earth elements have been used and then released into industrial wastewater, which caused serious environmental problems. In this work, in order to recycle rare earth cations (La 3+ and Ce 3+ ) from aqueous solutions, MnFe 2 O 4 -Graphene oxide magnetic nanoparticles were synthesized and after characterization studies, their adsorption isotherms, kinetics, thermodynamics and desorption were comprehensively investigated. Characterized was performed using XRD, FE-SEM, FT-IR, Raman spectroscopy, VSM, BET and DLS. REE adsorption on MnFe 2 O 4 -GO was studied for the first time in the present work and the maximum adsorption capacity at the optimum condition (room temperature and pH = 7) for La 3+ and Ce 3+ were 1001 and 982 mg/g respectively, and the reactions were completed within 20 min. In addition, the adsorption data were well matched with the Langmuir model and the adsorption kinetics were fitted with the pseudo-second order model. The thermodynamic parameters were calculated and the reactions were found to be endothermic and spontaneous. Moreover, the Dubinin-Radushkevich model predicted chemical ion-exchange adsorption. Desorption studies also demonstrated that MnFe 2 O 4 -GO can be regenerated for multiple reuses. Overall, high adsorption capacity, chemical stability, reusability, fast kinetics, easy magnetic separation, and simple synthesis method indicated that MnFe 2 O 4 -GO is a high-performance adsorbent for REE. Copyright © 2018. Published by Elsevier B.V.

Shape induced magnetic vortex state in hexagonal ordered cofe nanodot arrays using ultrathin alumina shadow mask

NASA Astrophysics Data System (ADS)

Sellarajan, B.; Saravanan, P.; Ghosh, S. K.; Nagaraja, H. S.; Barshilia, Harish C.; Chowdhury, P.

2018-04-01

The magnetization reversal process of hexagonal ordered CoFe nanodot arrays was investigated as a function of nanodot thickness (td) varying from 10 to 30 nm with fixed diameter. For this purpose, ordered CoFe nanodots with a diameter of 80 ± 4 nm were grown by sputtering using ultra-thin alumina mask. The vortex annihilation and the dynamic spin configuration in the ordered CoFe nanodots were analyzed by means of magnetic hysteresis loops in complement with the micromagnetic simulation studies. A highly pinched hysteresis loop observed at 20 nm thickness suggests the occurrence of vortex state in these nanodots. With increase in dot thickness from 10 to 30 nm, the estimated coercivity values tend to increase from 80 to 175 Oe, indicating irreversible change in the nucleation/annihilation field of vortex state. The measured magnetic properties were then corroborated with the change in the shape of the nanodots from disk to hemisphere through micromagnetic simulation.

Phase relations in the Fe-FeSi system at high pressures and temperatures

NASA Astrophysics Data System (ADS)

Fischer, Rebecca A.; Campbell, Andrew J.; Reaman, Daniel M.; Miller, Noah A.; Heinz, Dion L.; Dera, Przymyslaw; Prakapenka, Vitali B.

2013-07-01

The Earth's core is comprised mostly of iron and nickel, but it also contains several weight percent of one or more unknown light elements, which may include silicon. Therefore it is important to understand the high pressure, high temperature properties and behavior of alloys in the Fe-FeSi system, such as their phase diagrams. We determined melting temperatures and subsolidus phase relations of Fe-9 wt% Si and stoichiometric FeSi using synchrotron X-ray diffraction at high pressures and temperatures, up to ~200 GPa and ~145 GPa, respectively. Combining this data with that of previous studies, we generated phase diagrams in pressure-temperature, temperature-composition, and pressure-composition space. We find the B2 crystal structure in Fe-9Si where previous studies reported the less ordered bcc structure, and a shallower slope for the hcp+B2 to fcc+B2 boundary than previously reported. In stoichiometric FeSi, we report a wide B2+B20 two-phase field, with complete conversion to the B2 structure at ~42 GPa. The minimum temperature of an Fe-Si outer core is 4380 K, based on the eutectic melting point of Fe-9Si, and silicon is shown to be less efficient at depressing the melting point of iron at core conditions than oxygen or sulfur. At the highest pressures reached, only the hcp and B2 structures are seen in the Fe-FeSi system. We predict that alloys containing more than ~4-8 wt% silicon will convert to an hcp+B2 mixture and later to the hcp structure with increasing pressure, and that an iron-silicon alloy in the Earth's inner core would most likely be a mixture of hcp and B2 phases.

Fe3O4@Polypyrrole Microspheres with High Magnetization and Superparamagnetism for Efficient and Fast Removal of Pb(II) Ions

NASA Astrophysics Data System (ADS)

Zhang, Wei; Zhu, Wanyan; Xu, Wutong; Wang, Yan; Li, Ning; Zhang, Tingting; Wang, Hui

2017-12-01

Core-shell structured Fe3O4@PPy microspheres are synthesized successfully through a facile polyol reduction method in combination with a modified Stöber method. We show that the as-prepared Fe3O4@PPy microspheres with high saturation magnetization, superparamagnetism, and good dispersibility have a high efficient adsorption capacity for high efficient removal of Pb(II) ions of up to 391.71 mg g-1 and a fast adsorption equilibrium time of 20 min. Furthermore, the lead-adsorbed Fe3O4@PPy microspheres can be rapidly separated from solution because of the excellent superparamagnetic properties. The composite Fe3O4@PPy microspheres are characterized using X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and vibrating sample magnetometer (VSM). The adsorption data from our experiments show that the adsorption process fits well with the pseudosecond- order kinetic model and the adsorption isotherm follows the Langmuir isotherm model. The thermodynamic studies show that the adsorption of Pb(II) on Fe3O4@PPy microspheres is an endothermic and spontaneous process. Comprehensive comparison among adsorbents for the removal of Pb(II) ions that literature reported, reusability, high adsorption efficiency, fast adsorption equilibrium, and rapid magnetic separation make these Fe3O4@PPy microspheres very promising application for removal of Pb(II) ions from contaminated water.

Scale structure of aluminised Manet steel after HIP treatment

NASA Astrophysics Data System (ADS)

Glasbrenner, H.; Stein-Fechner, K.; Konys, J.

2000-12-01

Coatings on low activation steels are required in fusion technology in order to reduce the tritium permeation rate through the steel into the cooling water system by a factor of at least 100. Alumina seems to be a promising coating material. However, an appropriate coating system must also have the potential for self-healing since the ceramic alumina scale tends to fail if mechanical stress is applied. A technology is introduced here to form a ductile Al enriched surface scale on Manet II steel (Fe-10.3%Cr) with an alumina overlayer. This technology consists of two main process steps. Hot dip aluminising has been performed at 700°C for 30 s in order to introduce Al to the near surface zone. The very hard intermetallic scale Fe 2Al 5 which forms during the immersion process gets completely transformed into FeAl 2, FeAl and α-Fe(Al) phases during a subsequent hot isostatic press (HIP) process step at high pressure at 1040°C for 30 min. The pressures chosen for the HIPing were 1000 and 2000 bar. Without HIPing pores form due to the Kirkendall effect. The influence of the high pressure on the heat treatment (1040°C, 30 min) will be discussed in this paper.

A Comparison of Density Functional Theory with Ab initio Approaches for Systems Involving First Transition Row Metals

NASA Technical Reports Server (NTRS)

Ricca, Alessandra; Bauschlicher, Charles W.; Langhoff, Stephen R. (Technical Monitor)

1994-01-01

Density functional theory (DFT) is found to give a better description of the geometries and vibrational frequencies of FeL and FeL(sup +) systems than second order Moller Plesset perturbation theory (MP2). Namely, the DFT correctly predicts the shift in the CO vibrational frequency between free CO and the Sigma(sup -) state of FeCO and yields a good result for the Fe-C distance in the quartet states of FeCH4(+) 4 These are properties where the MP2 results are unsatisfactory. Thus DFT appears to be an excellent approach for optimizing the geometries and computing the zero-point energies of systems containing first transition row atoms. Because the DFT approach is biased in favor of the 3d(exp 7) occupation, whereas the more traditional approaches are biased in favor of the 3d(exp 6) occupation, differences are found in the relative ordering of states. It is shown that if the dissociation is computed to the most appropriate atomic asymptote and corrected to the ground state asymptote using the experimental separations, the DFT results are in good agreement with high levels of theory. The energetics at the DFT level are much superior to the MP2 and in most cases in good agreement with high levels of theory.

Fe-vacancy ordering in superconducting K 1–xFe 2–ySe 2: First-principles calculations and Monte Carlo simulations

DOE PAGES

Fang, Yong; Tai, Yuan -Yen; Deng, Junkai; ...

2015-07-20

Fe vacancies in the 33 K superconductor K 1–xFe 2–ySe 2 show ordering schemes that may be correlated with its superconducting properties. First-principles calculations and kinetic Monte Carlo simulations lead to a very simple model for vacancy ordering. Repulsive dipolar interactions between Fe vacancies show three ground states: amore » $$\\sqrt{8}\\times \\sqrt{10}$$ rhombus-ordered structure for 12.5% vacancies, a $$\\sqrt{5}\\times \\sqrt{5}$$ squared lattice for 20% vacancies, and a $$\\sqrt{5}\\times \\sqrt{5}$$ rhombus-ordered structure for 25% vacancies. Other structural states are derived from these three ground states and may contain additional disordered spatial regions. As a result, the repulsive interaction between Fe vacancies arises from enhanced Fe–Se covalent bonds, which differs from the well-known attractive interaction of Fe vacancies in body-centered cubic Fe.« less

Degradation of high energetic and insensitive munitions compounds by Fe/Cu bimetal reduction.

PubMed

Koutsospyros, Agamemnon; Pavlov, Julius; Fawcett, Jacqueline; Strickland, David; Smolinski, Benjamin; Braida, Washington

2012-06-15

A reductive technology based on a completely mixed two-phase reactor (bimetallic particles and aqueous stream) was developed for the treatment of aqueous effluents contaminated with nitramines and nitro-substituted energetic materials. Experimental degradation studies were performed using solutions of three high energetics (RDX, HMX, TNT) and three insensitive-munitions components (NTO, NQ, DNAN). The study shows that, on laboratory scale, these energetic compounds are easily degraded in solution by suspensions of bimetallic particles (Fe/Ni and Fe/Cu) prepared by electro-less deposition. The type of bimetal pair (Fe/Cu or Fe/Ni) does not appear to affect the degradation kinetics of RDX, HMX, and TNT. The degradation of all components followed apparent first-order kinetics. The half-lives of all compounds except NTO were under 10 min. Additional parameters affecting the degradation processes were solids loading and initial pH. Copyright © 2012 Elsevier B.V. All rights reserved.

A Mott insulator continuously connected to iron pnictide superconductors

DOE PAGES

Song, Yu; Yamani, Zahra; Cao, Chongde; ...

2016-12-19

Iron-based superconductivity develops near an antiferromagnetic order and out of a bad-metal normal state, which has been interpreted as originating from a proximate Mott transition. Whether an actual Mott insulator can be realized in the phase diagram of the iron pnictides remains an open question. Here we use transport, transmission electron microscopy, X-ray absorption spectroscopy, resonant inelastic X-ray scattering and neutron scattering to demonstrate that NaFe 1-xCu xAs near x≈0.5 exhibits real space Fe and Cu ordering, and are antiferromagnetic insulators with the insulating behaviour persisting above the Néel temperature, indicative of a Mott insulator. On decreasing x from 0.5,more » the antiferromagnetic-ordered moment continuously decreases, yielding to superconductivity ~x=0.05. Our discovery of a Mott-insulating state in NaFe 1-xCu xAs thus makes it the only known Fe-based material, in which superconductivity can be smoothly connected to the Mott-insulating state, highlighting the important role of electron correlations in the high-T c superconductivity.« less

A Mott insulator continuously connected to iron pnictide superconductors

PubMed Central

Song, Yu; Yamani, Zahra; Cao, Chongde; Li, Yu; Zhang, Chenglin; Chen, Justin S.; Huang, Qingzhen; Wu, Hui; Tao, Jing; Zhu, Yimei; Tian, Wei; Chi, Songxue; Cao, Huibo; Huang, Yao-Bo; Dantz, Marcus; Schmitt, Thorsten; Yu, Rong; Nevidomskyy, Andriy H.; Morosan, Emilia; Si, Qimiao; Dai, Pengcheng

2016-01-01

Iron-based superconductivity develops near an antiferromagnetic order and out of a bad-metal normal state, which has been interpreted as originating from a proximate Mott transition. Whether an actual Mott insulator can be realized in the phase diagram of the iron pnictides remains an open question. Here we use transport, transmission electron microscopy, X-ray absorption spectroscopy, resonant inelastic X-ray scattering and neutron scattering to demonstrate that NaFe1−xCuxAs near x≈0.5 exhibits real space Fe and Cu ordering, and are antiferromagnetic insulators with the insulating behaviour persisting above the Néel temperature, indicative of a Mott insulator. On decreasing x from 0.5, the antiferromagnetic-ordered moment continuously decreases, yielding to superconductivity ∼x=0.05. Our discovery of a Mott-insulating state in NaFe1−xCuxAs thus makes it the only known Fe-based material, in which superconductivity can be smoothly connected to the Mott-insulating state, highlighting the important role of electron correlations in the high-Tc superconductivity. PMID:27991514

Ab-initio study of pressure evolution of structural, mechanical and magnetic properties of cementite (Fe3C) phase

NASA Astrophysics Data System (ADS)

Gorai, S.; Ghosh, P. S.; Bhattacharya, C.; Arya, A.

2018-04-01

The pressure evolution of phase stability, structural and mechanical properties of Fe3C in ferro-magnetic (FM) and high pressure non magnetic (NM) phase is investigated from first principle calculations. The 2nd order FM to NM phase transition of Fe3C is identified around 60 GPa. Pressure (or density) variation of sound velocities from our ab-initio calculated single crystal elastic constants are determined to predict these parameters at Earth's outer core pressure.

Nematic quantum critical point without magnetism in FeSe1-xSx superconductors.

PubMed

Hosoi, Suguru; Matsuura, Kohei; Ishida, Kousuke; Wang, Hao; Mizukami, Yuta; Watashige, Tatsuya; Kasahara, Shigeru; Matsuda, Yuji; Shibauchi, Takasada

2016-07-19

In most unconventional superconductors, the importance of antiferromagnetic fluctuations is widely acknowledged. In addition, cuprate and iron-pnictide high-temperature superconductors often exhibit unidirectional (nematic) electronic correlations, including stripe and orbital orders, whose fluctuations may also play a key role for electron pairing. In these materials, however, such nematic correlations are intertwined with antiferromagnetic or charge orders, preventing the identification of the essential role of nematic fluctuations. This calls for new materials having only nematicity without competing or coexisting orders. Here we report systematic elastoresistance measurements in FeSe1-xSx superconductors, which, unlike other iron-based families, exhibit an electronic nematic order without accompanying antiferromagnetic order. We find that the nematic transition temperature decreases with sulfur content x; whereas, the nematic fluctuations are strongly enhanced. Near [Formula: see text], the nematic susceptibility diverges toward absolute zero, revealing a nematic quantum critical point. The obtained phase diagram for the nematic and superconducting states highlights FeSe1-xSx as a unique nonmagnetic system suitable for studying the impact of nematicity on superconductivity.

Prevention of nanoparticle coalescence under high-temperature annealing.

PubMed

Mizuno, Mikihisa; Sasaki, Yuichi; Yu, Andrew C C; Inoue, Makoto

2004-12-21

An effective method of employing 3-aminopropyldimethylethoxysilane linker molecules to stabilize 4.4 nm FePt nanoparticle monolayer films on a SiO2 substrate as well as to prevent coalescence of the particles under 800 degrees C annealing is reported. As-deposited FePt nanoparticle films in chemically disordered face-centered-cubic phase transform to mostly chemically ordered L1 0 structure after annealing, while the nanoparticles are free from serious coalescence. The method may fulfill the pressing need to prevent nanoparticle coalescence under high-temperature annealing for the development of FePt nanoparticle based products, such as ultrahigh-density magnetic recording media and novel memory devices.

Spin and lattice structures of single-crystalline SrFe2As2

NASA Astrophysics Data System (ADS)

Zhao, Jun; Ratcliff, W., II; Lynn, J. W.; Chen, G. F.; Luo, J. L.; Wang, N. L.; Hu, Jiangping; Dai, Pengcheng

2008-10-01

We use neutron scattering to study the spin and lattice structure of single-crystal SrFe2As2 , the parent compound of the FeAs-based superconductor (Sr,K)Fe2As2 . We find that SrFe2As2 exhibits an abrupt structural phase transition at 220 K, where the structure changes from tetragonal with lattice parameters c>a=b to orthorhombic with c>a>b . At almost the same temperature, Fe spins develop a collinear antiferromagnetic structure along the orthorhombic a axis with spin direction parallel to this a axis. These results are consistent with earlier work on the RFeAsO ( R=rare earth) families of materials and on BaFe2As2 , and therefore suggest that static antiferromagnetic order is ubiquitous for the parent compounds of these FeAs-based high-transition temperature superconductors.

The effect of bonding environment on iron isotope fractionation between minerals at high temperature

NASA Astrophysics Data System (ADS)

Sossi, Paolo A.; O'Neill, Hugh St. C.

2017-01-01

Central to understanding the processes that drive stable isotope fractionation in nature is their quantification under controlled experimental conditions. The polyvalent element iron, given its abundance in terrestrial rocks, exerts controls on the structural and chemical properties of minerals and melts. The iron isotope compositions of typical high temperature minerals are, however, poorly constrained and their dependence on intensive (e.g. fO2) and extensive (e.g. compositional) variables is unknown. In this work, experiments involving a reference phase, 2 M FeCl2·4H2O(l), together with an oxide mix corresponding to the bulk composition of the chosen mineral were performed in a piston cylinder in Ag capsules. The oxide mix crystallised in situ at 1073 K and 1 GPa, in equilibrium with the iron chloride, and was held for 72 h. In order to characterise the effect of co-ordination and oxidation state on the isotope composition independently, exclusively Fe2+ minerals were substituted in: VIII-fold almandine, VI-fold ilmenite, fayalite and IV-fold chromite and hercynite. Δ57FeMin-FeCl2 increases in the order VIII < VI < IV, consistent with a decrease in the mean Fe-O bond length. Magnetite, which has mixed VI- and IV-fold co-ordination, has the heaviest Δ57Fe by virtue of 2/3 of its iron being the smaller, ferric ion. The composition of the VIFe2+-bearing minerals is similar to that of the aqueous FeCl2 fluid. To the degree that this represents the speciation of iron in fluids exsolving from magmas, the fractionation between them should be small, unless the iron is hosted in magnetite. By contrast, predominantly Fe2+-bearing mantle garnets should preserve a much lighter δ57Fe than their lower pressure spinel counterparts, a signature that may be reflected in partial melts from these lithologies. As the Fe-O bond lengths in fayalite and ilmenite are comparable, their isotope compositions overlap, suggesting that high Ti mare basalts acquired their heavy isotopic signature from ilmenite that crystallised late during lunar magma ocean solidification.

The influence of structural fluorine on biotite oxidation in copper-bearing, aqueous solutions at low temperatures and pressures

NASA Astrophysics Data System (ADS)

Earley, Drummond, III; Darby Dyar, M.; Ilton, Eugene S.; Granthem, Allen A.

1995-06-01

High-F (5.4 wt%) and low-F (0.8 wt%) biotites were reacted with aqueous (Cu, Na 2)Cl 2 solutions at ambient conditions to investigate biotite oxidation mechanisms at low temperatures and pressures and at atmospheric pO 2. The exchange of Cu +2 for interlayer cations increases the rate of biotite oxidation under these conditions. Solid reactants and products were characterized by Mössbauer spectroscopy, X-ray diffraction, and comprehensive bulk chemical analyses. Even though both biotites were pretreated with a sodium tetraphenylboron (NaTPB) solution, which rapidly exchanges Na for K, only about 50% of the interlayer K was exchanged during most of these experiments. As a result, the exchange reactions produced variably expanded phases with d(001) ranging from approximately 10 to 14 Å. Octahedral Fe +2 in samples of high- and low-F biotite was oxidized rapidly during Cu exchange. The degree of Fe +2 oxidation amounted to about 50% of the total Fe in most experiments and was nearly independent of the total mass of Cu introduced into the interlayer which ranged from 2.0 to 9.2 wt% CuO. The Mössbauer spectra also show that the Fe +2 in M(1) octahedra of the high-F biotite was oxidized more slowly than Fe +2 in M(2) sites, whereas in the low-F biotite experiments M(1) Fe +2 was oxidized at a slightly faster rate than the Fe +2 in M(2) sites. Our study suggests that the total amount of Fe oxidized was limited by the amount of K exchanged, and that preferred oxidation of Fe +2 at M(2) sites relative to M(1) sites was a function of the F content of these biotites. Charge transfer from octahedral Fe +2 to the interlayer may be facilitated by deprotonation. In exchange experiments conducted on the F-rich biotite, Fe +2 oxidation at M(1) sites was limited indicating that preferential substitution of F for OH might occur at the M(1) site. We used the Fe-F avoidance law to develop an F-OH ordering model that preferentially distributes F on selected trans positions of Fe-filled M(1) octahedra in Fe- and F-rich biotites. If charge transfer is facilitated by the presence of OH then the proposed F-OH ordering model could account for the selective deactivation of the Fe +2 oxidation mechanism at the M(1) site.

High magnetic coercivity of FePt-Ag/MgO granular nanolayers

NASA Astrophysics Data System (ADS)

Roghani, R.; Sebt, S. A.; Khajehnezhad, A.

2018-06-01

L10-FePt ferromagnetic nanoparticles have a hight coercivity of Tesla order. Thus, these nanoparticles, with size of 10 to 15 nm and uniform surface distribution, are suitable in magnetic data storage technology with density of more than 1GB. In order to improve structural and magnetic properties of FePt nanoparticles, some elements and combinations have been added to compound. In this research, we show that due to the presence of the Ag, the phase transition temperature of FePt from fcc to L10-fct phase decreases. The presence of Ag as an additive in FePt-Ag nanocomposite, increases the magnetic coercivity. This nanocomposite, with 10% Ag, was deposited by magnetron sputtering on the MgO heat layer. VSM results of 10 nm nanoparticles show that coercivity has increased up to 1.4 T. XRD and FESEM results confirm that the size of the L10-FePt nanoparticles are 10 nm and their surface distribution are uniform. Ag gradually form nano scale clusters with separate lattice and FePt-Ag nanocomposite appears. The result of this process is emptiness of Ag position in FePt-fcc lattice. So, the mobility of Fe and Pt atoms in this lattice increases and it can be possible for them to move in lower temperature. This mechanism explain the effect of Ag on decreasing the transition temperature to fct-L10 phase, and hight coercivity of FePt nanoparticles.

Electron density determination and bonding in tetragonal binary intermetallics by convergent beam electron diffraction

NASA Astrophysics Data System (ADS)

Sang, Xiahan

Intermetallics offer unique property combinations often superior to those of more conventional solid solution alloys of identical composition. Understanding of bonding in intermetallics would greatly accelerate development of intermetallics for advanced and high performance engineering applications. Tetragonal intermetallics L10 ordered TiAl, FePd and FePt are used as model systems to experimentally measure their electron densities using quantitative convergent beam electron diffraction (QCBED) method and then compare details of the 3d-4d (FePd) and 3d-5d (FePt) electron interactions to elucidate their role on properties of the respective ferromagnetic L10-ordered intermetallics FePd and FePt. A new multi-beam off-zone axis condition QCBED method has been developed to increase sensitivity of CBED patterns to change of structure factors and the anisotropic Debye-Waller (DW) factors. Unprecedented accuracy and precision in structure and DW factor measurements has been achieved by acquiring CBED patterns using beam-sample geometry that ensures strong dynamical interaction between the fast electrons and the periodic potential in the crystalline samples. This experimental method has been successfully applied to diamond cubic Si, and chemically ordered B2 cubic NiAl, tetragonal L10 ordered TiAl and FePd. The accurate and precise experimental DW and structure factors for L10 TiAl and FePd allow direct evaluation of computer calculations using the current state of the art density functional theory (DFT) based electron structure modeling. The experimental electron density difference map of L1 0 TiAl shows that the DFT calculations describe bonding to a sufficient accuracy for s- and p- electrons interaction, e. g., the Al-layer. However, it indicate significant quantitative differences to the experimental measurements for the 3d-3d interactions of the Ti atoms, e.g. in the Ti layers. The DFT calculations for L10 FePd also show that the current DFT approximations insufficiently describe the interaction between Fe-Fe (3d-3d), Fe-Pd (3d-4d) and Pd-Pd (4d-4d) electrons, which indicates the necessity to evaluate applicability of different DFT approximations, and also provides experimental data for the development of new DFT approximation that better describes transition metal based intermetallic systems.

Determination of COD based on Photoelectrocatalysis of FeTiO3.TiO2/Ti Electrode

NASA Astrophysics Data System (ADS)

Wibowo, D.; Ruslan; Maulidiyah; Nurdin, M.

2017-11-01

Iron infrastructure technology of (Fe)-doped TiO2 nanotubes arrays (NTAs) was prepared for COD photoelectrocatalysis sensor. Fe-TiO2 NTAs was prepared using sol-gel method and coated with TiO2/Ti electrode by immersion technique. The optimization of COD photoelectrocatalytic sensor against Rhodamine B, Methyl Orange, and Methylene Blue organic dyes using photoelectrochemical system in a batch reactor. The high ordered FeTiO3.TiO2/Ti NTAs to determine COD value showed the high photocurrent response linearity and sensitivity to MO organic dye from the concentration of 5 ppm to 75 ppm with an average RSD value of 3.35. The development in this research is to utilize ilmenite mineral as model applied to COD sensor.

Beyond Yolk–Shell Nanoparticles: Fe 3 O 4 @Fe 3 C Core@Shell Nanoparticles as Yolks and Carbon Nanospindles as Shells for Efficient Lithium Ion Storage

DOE PAGES

Zhang, Jianan; Wang, Kaixi; Xu, Qun; ...

2015-02-25

In order to well address the problems of large volume change and dissolution of Fe 3O 4 nanomaterials during Li + intercalation/extraction, herein we demonstrate a one-step in situ nanospace-confined pyrolysis strategy for robust yolk–shell nanospindles with very sufficient internal void space (VSIVS) for high-rate and long-term lithium ion batteries (LIBs), in which an Fe 3O 4@Fe 3C core@shell nanoparticle is well confined in the compartment of a hollow carbon nanospindle. This structure can not only introduce VSIVS to accommodate volume change of Fe 3O 4 but also afford a dual shell of Fe 3C and carbon to restrict Femore » 3O 4 dissolution, thus providing dual roles for greatly improving the capacity retention. Consequently, Fe 3O 4@Fe 3C–C yolk–shell nanospindles deliver a high reversible capacity of 1128.3 mAh g –1 at even 500 mA g –1, excellent high rate capacity (604.8 mAh g –1 at 2000 mA g –1), and prolonged cycling life (maintaining 1120.2 mAh g –1 at 500 mA g –1 for 100 cycles) for LIBs, which are much better than those of Fe 3O 4@C core@shell nanospindles and Fe 3O 4 nanoparticles. The present Fe 3O 4@Fe 3C–C yolk–shell nanospindles are the most efficient Fe 3O 4-based anode materials ever reported for LIBs.« less

High Ms Fe16N2 thin film with Ag under layer on GaAs substrate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Allard Jr, Lawrence Frederick

2016-01-01

(001) textured Fe16N2 thin film with Ag under layer is successfully grown on GaAs substrate using a facing target sputtering (FTS) system. After post annealing, chemically ordered Fe16N2 phase is formed and detected by X-ray diffraction (XRD). High saturation magnetization (Ms) is measured by a vibrating sample magnetometer (VSM). In comparison with Fe16N2 with Ag under layer on MgO substrate and Fe16N2 with Fe under layer on GaAs substrate, the current layer structure shows a higher Ms value, with a magnetically softer feature in contrast to the above cases. In addition, X-ray photoelectron spectroscopy (XPS) is performed to characterize themore » binding energy of N atoms. To verify the role of strain that the FeN layer experiences in the above three structures, Grazing Incidence X-ray Diffraction (GIXRD) is conducted to reveal a large in-plane lattice constant due to the in-plane biaxial tensile strain. INTRODUCTION« less

Temperature dependent magnon-phonon coupling in bcc Fe from theory and experiment.

PubMed

Körmann, F; Grabowski, B; Dutta, B; Hickel, T; Mauger, L; Fultz, B; Neugebauer, J

2014-10-17

An ab initio based framework for quantitatively assessing the phonon contribution due to magnon-phonon interactions and lattice expansion is developed. The theoretical results for bcc Fe are in very good agreement with high-quality phonon frequency measurements. For some phonon branches, the magnon-phonon interaction is an order of magnitude larger than the phonon shift due to lattice expansion, demonstrating the strong impact of magnetic short-range order even significantly above the Curie temperature. The framework closes the previous simulation gap between the ferro- and paramagnetic limits.

Mechanisms for chelator stimulation of microbial Fe(III) -oxide reduction

USGS Publications Warehouse

Lovley, D.R.; Woodward, J.C.

1996-01-01

The mechanisms by which nitrilotriacetic acid (NTA) stimulated Fe(III) reduction in sediments from a petroleum-contaminated aquifer were investigated in order to gain insight into how added Fe(III) chelators stimulate the activity of hydrocarbon-degrading, Fe(III)-reducing microorganisms in these sediments, and how naturally occurring Fe(III) chelators might promote Fe(III) reduction in aquatic sediments. NTA solubilized Fe(III) from the aquifer sediments. NTA stimulation of microbial Fe(III) reduction did not appear to be the result of making calcium, magnesium, potassium, or trace metals more available to the microorganisms. Stimulation of Fe(III) reduction could not be attributed to NTA serving as a source of carbon or fixed nitrogen for Fe(III)-reducing bacteria as NTA was not degraded in the sediments. Studies with the Fe(III)-reducing microorganism, Geobacter metallireducens, and pure Fe(III)-oxide forms, demonstrated that NTA stimulated the reduction of a variety of Fe(III) forms, including highly crystalline Fe(III)-oxides such as goethite and hematite. The results suggest that NTA solubilization of insoluble Fe(III)-oxide is an important mechanism for the stimulation of Fe(III) reduction by NTA in aquifer sediments.

Impacts of Co-doping on the superconductivity and the orbital ordering state in Fe1-xCoxSe single crystal studied by the electrical transport.

NASA Astrophysics Data System (ADS)

Urata, Takahiro; Tanabe, Yoichi; Heguri, Satoshi; Tanigaki, Katsumi

2015-03-01

In the FeSe with the simplest crystal structure in the Fe-based superconductor families, although both the superconductivity and the orbital ordering states are investigated, the relation between them is still unclear. Here, we report Co doping effects on the superconductivity and the orbital ordering state in Fe1-xCoxSe single crystals. The electrical transport measurements demonstrated that the superconductivity vanishes at 4 % Co doping while the orbital ordering state may be robust against Co doping. Present results suggest that the orbital ordering state is not related to the emergence of the superconductivity in FeSe.

Electric transport of a single-crystal iron chalcogenide FeSe superconductor: Evidence of symmetry-breakdown nematicity and additional ultrafast Dirac cone-like carriers

NASA Astrophysics Data System (ADS)

Huynh, K. K.; Tanabe, Y.; Urata, T.; Oguro, H.; Heguri, S.; Watanabe, K.; Tanigaki, K.

2014-10-01

An SDW antiferromagnetic (SDW-AF) low-temperature phase transition is generally observed and the AF spin fluctuations are considered to play an important role for the superconductivity pairing mechanism in FeAs superconductors. However, a similar magnetic phase transition is not observed in FeSe superconductors, which has caused considerable discussion. We report on the intrinsic electronic states of FeSe as elucidated by electric transport measurements under magnetic fields using a high quality single crystal. A mobility spectrum analysis, an ab initio method that does not make assumptions on the transport parameters in a multicarrier system, provides very important and clear evidence that another hidden order, most likely the symmetry broken from the tetragonal C4 symmetry to the C2 symmetry nematicity associated with the selective d -orbital splitting, exists in the case of superconducting FeSe other than the AF magnetic order spin fluctuations. The intrinsic low-temperature phase in FeSe is in the almost compensated semimetallic states but is additionally accompanied by Dirac cone-like ultrafast electrons ˜104cm2(VS) -1 as minority carriers.

Observation of super high energy big family with large scale Fe emulsion chambers

NASA Technical Reports Server (NTRS)

1985-01-01

In order to get higher efficiencies for detecting hadrons and to make technical improvements in the chamber structure, the Mt. Kambala Emulsion Chamber Collaboration constructed 57 sq. m. of Fe chamber, with thickness 29 c.u.(1c.u.=17.6 mm Fe), using 300 tons of Fe plates and made the first exposure from Sept., 1982 to May, 1984. The photosensitive layers consist of X-ray films of Sakura N type, Fuji No. 100 type and Tianjin III type, some of them contain also emulsion plates of Fuji ET7B type. They are inserted between the Fe plates at 2 c.u., beginning at 5 c.u. from the chamber top. In a number of blocks, 3 mm spacings are provided at every 2 c.u. of Fe plates to facilitate the replacement of photosensitive layers, without disassembling the chamber. On the bottom of the chamber Fe plates of thickness 9 mm are placed in order to shield the chamber from the radioactivities of the ground. An event, numbered K2 58 of visible energy sigma E sub gamma = 7345 TeV was found in this exposure. No obvious halo is seen in the event and all the showers are clearly separated and easy to measure. A brief report of the preliminary results is presented.

Ba3Fe1.56Ir1.44O9: A Polar Semiconducting Triple Perovskite with Near Room Temperature Magnetic Ordering.

PubMed

Ferreira, Timothy; Carone, Darren; Huon, Amanda; Herklotz, Andreas; Stoian, Sebastian A; Heald, Steve M; Morrison, Gregory; Smith, Mark D; Loye, Hans-Conrad Zur

2018-05-29

The crystal chemistry and magnetic properties for two triple perovskites, Ba 3 Fe 1.56 Ir 1.44 O 9 and Ba 3 NiIr 2 O 9 , grown as large, highly faceted single crystals from a molten strontium carbonate flux, are reported. Unlike the idealized A 3 MM 2 'O 9 hexagonal symmetry characteristic of most triple perovskites, including Ba 3 NiIr 2 O 9, Ba 3 Fe 1.56 Ir 1.44 O 9 possesses significant site-disorder, resulting in a noncentrosymmetric polar structure with trigonal symmetry. The valence of iron and iridium in the heavily distorted Fe/Ir sites was determined to be Fe(III) and Ir(V) by X-ray absorption near edge spectroscopy (XANES). Density functional theory calculations were conducted to understand the effect of the trigonal distortion on the local Fe(III)O 6 electronic structure, and the spin state of iron was determined to be S = 5/2 by Mössbauer spectroscopy. Conductivity measurements indicate thermally activated semiconducting behavior in the trigonal perovskite. Magnetic properties were measured and near room temperature magnetic ordering (T N = 270 K) was observed for Ba 3 Fe 1.56 Ir 1.44 O 9 .

Exchange bias effect in L10-ordered FePt and FeCo-based bilayer structure: effect of increasing applied field

NASA Astrophysics Data System (ADS)

Singh, Sadhana; Kumar, Dileep; Bhagat, Babli; Choudhary, R. J.; Reddy, V. R.; Gupta, Ajay

2018-02-01

The applied magnetic field (H APP) dependence of the exchange bias (EB) is studied in an exchange-coupled thin-film bilayer composed of a hard ferromagnetic FePt layer in the proximity of a soft ferromagnetic FeCo layer. FePt/FeCo structure is deposited in an ultra-high vacuum chamber, where the FePt layer was first annealed at 823 K for 30 min and subsequently cooled to room temperature in the presence of an in-plane magnetic field, H MAX ~ 1.5 kOe to promote L10-ordered hard magnetic phase with magnetic moments aligned in one of the in-plane directions in the FePt layer. In-situ magneto-optical Kerr effect measurements during different stages of bilayer growth and detailed ex-situ superconducting quantum interference device-vibrating sample magnetometer measurements jointly revealed that due to the interplay between exchange coupling at the interface and dipolar energies of the saturated hard FePt layer, a hysteresis loop of FeCo layer shifts along the magnetic field axis. A clear dependence of EB field (H EB) on increasing maximum value of the H APP during the hysteresis loop measurement is understood in terms of the magnetic state of soft and hard magnetic layers, where EB increases with increasing H APP until the hard layer moment remains undisturbed in its remanence state. As soon as the field was sufficient to rotate the spins of the FePt layer, the loop became symmetric with respect to the field axis.

Low temperature texture development in Nd2Fe14B/α-Fe nanocomposite magnets via equal channel angular pressing

NASA Astrophysics Data System (ADS)

Besley, L.; Garitaonandia, J. S.; Molotnikov, A.; Kishimoto, H.; Kato, A.; Davies, C.; Suzuki, K.

2018-05-01

While suitable texture has been developed in Nd2Fe14B/α-Fe nanocomposites via thermomechanical processing methods such as die upsetting by incorporating low melting point eutectic Nd-Cu additives, significant grain coarsening occurs during this process due to the high temperature and long timescales involved, resulting in a loss of exchange coupling. Equal channel angular pressing (ECAP) is a severe plastic deformation technique which has been successfully used to produce a suitable texture in single-phase Nd2Fe14B at temperatures on the order of 500°C while preserving grain sizes on the order of 20-30nm. We investigate the development of texture in a commercial Nd2Fe14B/α-Fe nanocomposite alloy with added Nd90Cu10 produced via ECAP and then characterise it using texture x-ray diffraction and magnetic measurements. It is found that initial texture can be developed in this nanocomposite system at T = 520°C via ECAP. The average grain size of Nd2Fe14B as measured via X-ray diffraction after ECAP remains below 50nm with a developed texture. The effect of varying the amount of Nd90Cu10 additive is also investigated. It is found that with decreasing Nd90Cu10, the degree of texture is reduced while the volume fraction of α-Fe increases. This work demonstrates the development of texture in nanocomposite Nd2Fe14B/α-Fe with Nd-Cu additives whilst maintaining a grain size of approximately 50nm.

Electronic and magnetic structures of Fe3O4 ferrimagnetic investigated by first principle, mean field and series expansions calculations

NASA Astrophysics Data System (ADS)

Masrour, R.; Hlil, E. K.; Hamedoun, M.; Benyoussef, A.; Mounkachi, O.; El Moussaoui, H.

2015-03-01

Self-consistent ab initio calculations, based on density functional theory (DFT) approach and using a full potential linear augmented plane wave (FLAPW) method, are performed to investigate both electronic and magnetic properties of the Fe3O4. Polarized spin and spin-orbit coupling are included in calculations within the framework of the antiferromagnetic state between two adjacent Fe plans. Magnetic moment considered to lie along (010) axes are computed. Obtained data from ab initio calculations are used as input for the high temperature series expansions (HTSEs) calculations to compute other magnetic parameters. The exchange interactions between the magnetic atoms Fe-Fe in Fe3O4 are given using the mean field theory. The high temperature series expansions (HTSEs) of the magnetic susceptibility of with the magnetic moments, mFe in Fe3O4 is given up to seventh order series in (1/kBT). The Néel temperature TN is obtained by HTSEs of the magnetic susceptibility series combined with the Padé approximant method. The critical exponent γ associated with the magnetic susceptibility is deduced as well.

The Correlation of Adsorption Behavior between Ciprofloxacin Hydrochloride and the Active Sites of Fe-doped MCM-41.

PubMed

Wu, Ying; Tang, Yiming; Li, Laisheng; Liu, Peihong; Li, Xukai; Chen, Weirui; Xue, Ying

2018-01-01

HIGHLIGHTS Fe incorporation significantly accelerated the adsorption of CPX on MCM-41.Fe leaching can be ignored when pH was higher than 4.0.pH played an important role in CPX adsorption on Fe-MCM-41.Co-effect of CPX and metal cations on Fe-MCM-41 was investigated. Fe-MCM-41s with various molar ratios of silicon to iron (20, 40, 80, and 160) were prepared to investigate adsorption properties of ciprofloxacin hydrochloride (CPX) in aqueous solutions. Fe-MCM-41s were characterized by transmission electron microscope (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption/desorption isotherms, and infrared spectroscopy (FT-IR). Effects of silicon-iron ratio, adsorbent dosage, pH, and temperature were conducted to explore the adsorption mechanism of CPX on Fe-MCM-41. The results showed that the introduction of iron facilitated the absorption quantity for CPX from 20.04 to 83.33 mg g -1 at 120 min of reaction time, which was mainly attributed to surface complexation. The promotion of hydrophobic effect, electrostatic interactions, and π-π electron donor-acceptor interaction also played coordinate roles in the adsorption process. The experimental kinetic data followed both the pseudo-second-order and intra-particle diffusion models, while the adsorption isotherm data fit well to Freundlich model at high temperature. Thermodynamic study showed that the adsorption was spontaneous. Under the effect of electrostatic interaction, pH of the solution strongly affected CPX adsorption. Five representative metal cations (Ca, Cu, Ni, Pb, and Cd) were chosen to study the effects on CPX adsorption and their complexation. The inhibiting effect of metal cations on CPX adsorption was sequenced in the order of Cu > Ni > Pb > Cd > Ca, which followed the same order as the complexation stability constants between CPX and cations. The Fe-MCM-41 adsorbent possessed excellent reusability for 4 cycles use, suggesting a potential applicability of Fe-MCM-41 to remove CPX in water.

The Correlation of Adsorption Behavior between Ciprofloxacin Hydrochloride and the Active Sites of Fe-doped MCM-41

PubMed Central

Wu, Ying; Tang, Yiming; Li, Laisheng; Liu, Peihong; Li, Xukai; Chen, Weirui; Xue, Ying

2018-01-01

HIGHLIGHTS Fe incorporation significantly accelerated the adsorption of CPX on MCM-41.Fe leaching can be ignored when pH was higher than 4.0.pH played an important role in CPX adsorption on Fe-MCM-41.Co-effect of CPX and metal cations on Fe-MCM-41 was investigated. Fe-MCM-41s with various molar ratios of silicon to iron (20, 40, 80, and 160) were prepared to investigate adsorption properties of ciprofloxacin hydrochloride (CPX) in aqueous solutions. Fe-MCM-41s were characterized by transmission electron microscope (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption/desorption isotherms, and infrared spectroscopy (FT-IR). Effects of silicon-iron ratio, adsorbent dosage, pH, and temperature were conducted to explore the adsorption mechanism of CPX on Fe-MCM-41. The results showed that the introduction of iron facilitated the absorption quantity for CPX from 20.04 to 83.33 mg g−1 at 120 min of reaction time, which was mainly attributed to surface complexation. The promotion of hydrophobic effect, electrostatic interactions, and π-π electron donor-acceptor interaction also played coordinate roles in the adsorption process. The experimental kinetic data followed both the pseudo-second-order and intra-particle diffusion models, while the adsorption isotherm data fit well to Freundlich model at high temperature. Thermodynamic study showed that the adsorption was spontaneous. Under the effect of electrostatic interaction, pH of the solution strongly affected CPX adsorption. Five representative metal cations (Ca, Cu, Ni, Pb, and Cd) were chosen to study the effects on CPX adsorption and their complexation. The inhibiting effect of metal cations on CPX adsorption was sequenced in the order of Cu > Ni > Pb > Cd > Ca, which followed the same order as the complexation stability constants between CPX and cations. The Fe-MCM-41 adsorbent possessed excellent reusability for 4 cycles use, suggesting a potential applicability of Fe-MCM-41 to remove CPX in water. PMID:29468153

Phase diagram of (Li(1-x)Fe(x))OHFeSe: a bridge between iron selenide and arsenide superconductors.

PubMed

Dong, Xiaoli; Zhou, Huaxue; Yang, Huaixin; Yuan, Jie; Jin, Kui; Zhou, Fang; Yuan, Dongna; Wei, Linlin; Li, Jianqi; Wang, Xinqiang; Zhang, Guangming; Zhao, Zhongxian

2015-01-14

Previous experimental results have shown important differences between iron selenide and arsenide superconductors which seem to suggest that the high-temperature superconductivity in these two subgroups of iron-based families may arise from different electronic ground states. Here we report the complete phase diagram of a newly synthesized superconducting (SC) system, (Li1-xFex)OHFeSe, with a structure similar to that of FeAs-based superconductors. In the non-SC samples, an antiferromagnetic (AFM) spin-density-wave (SDW) transition occurs at ∼127 K. This is the first example to demonstrate such an SDW phase in an FeSe-based superconductor system. Transmission electron microscopy shows that a well-known √5×√5 iron vacancy ordered state, resulting in an AFM order at ∼500 K in AyFe2-xSe2 (A = metal ions) superconductor systems, is absent in both non-SC and SC samples, but a unique superstructure with a modulation wave vector q = (1)/2(1,1,0), identical to that seen in the SC phase of KyFe2-xSe2, is dominant in the optimal SC sample (with an SC transition temperature Tc = 40 K). Hence, we conclude that the high-Tc superconductivity in (Li1-xFex)OHFeSe stems from the similarly weak AFM fluctuations as FeAs-based superconductors, suggesting a universal physical picture for both iron selenide and arsenide superconductors.

Antiferromagnetic Order in Epitaxial FeSe Films on SrTiO3

NASA Astrophysics Data System (ADS)

Zhou, Y.; Miao, L.; Wang, P.; Zhu, F. F.; Jiang, W. X.; Jiang, S. W.; Zhang, Y.; Lei, B.; Chen, X. H.; Ding, H. F.; Zheng, Hao; Zhang, W. T.; Jia, Jin-feng; Qian, Dong; Wu, D.

2018-03-01

Single monolayer FeSe film grown on a Nb-doped SrTiO3 (001 ) substrate shows the highest superconducting transition temperature (TC˜100 K ) among the iron-based superconductors (iron pnictides), while the TC value of bulk FeSe is only ˜8 K . Although bulk FeSe does not show antiferromagnetic order, calculations suggest that the parent FeSe /SrTi O3 films are antiferromagnetic. Experimentally, because of a lack of a direct probe, the magnetic state of FeSe /SrTi O3 films remains mysterious. Here, we report direct evidence of antiferromagnetic order in the parent FeSe /SrTi O3 films by the magnetic exchange bias effect measurements. The magnetic blocking temperature is ˜140 K for a single monolayer film. The antiferromagnetic order disappears after electron doping.

Electrical resistivity of liquid iron with high concentration of light element impurities

NASA Astrophysics Data System (ADS)

Wagle, F.; Steinle-Neumann, G.

2017-12-01

The Earth's outer core mainly consists of liquid iron, enriched with several weight percent of lighter elements, such as silicon, oxygen, sulfur or carbon. Electrical resistivities of alloys of this type determine the stability of the geodynamo. Both computational and experimental results show that resistivites of Fe-based alloys deviate significantly from values of pure Fe. Using optical conductivity values computed with the Kubo-Greenwood formalism for DFT-based molecular dynamics results, we analyze the high-P and T behavior of resitivities for Fe-alloys containing various concentrations of sulfur, oxygen and silicon. As the electron mean free path length in amorphous and liquid material becomes comparable to interatomic distances at high P and T, electron scattering is expected to be dominated by the short-range order, rather than T-dependent vibrational contributions, and we describe such correlations in our results. In analogy to macroscopic porous media, we further show that resistivity of a liquid metal-nonmetal alloy is determined to first order by the resistivity of the metallic matrix and the volume fraction of non-metallic impurities.

Search for the elusive magnetic state of hexagonal iron: The antiferromagnetic Fe71Ru29 hcp alloy

NASA Astrophysics Data System (ADS)

Petrillo, C.; Postorino, P.; Orecchini, A.; Sacchetti, F.

2018-03-01

The magnetic states of iron and their dependence on crystal structure represent an important case study for the physics of magnetism and its role in fundamental and applied science, including geophysical sciences. hcp iron is the most elusive structure as it exists only at high pressure but, at the same time, it is expected to be stable up to very high temperature. Exploring the magnetic state of pure Fe at high pressure is difficult and no conclusive results have been obtained. Simple binary alloys where the hexagonal phase of Fe is stabilized, offer a more controllable alternative to investigate iron magnetism. We carried out a neutron diffraction experiment on hcp Fe71Ru29 disordered alloy as a function of temperature. Fe in the hexagonal lattice of this specific alloy results to be antiferromagnetically aligned with a rather complex structure and a small magnetic moment. The temperature dependence suggests a Néel temperature TN = 124 ± 10 K, a value consistent with the low magnetic moment of 1.04 ± 0.10 μB obtained from the diffraction data that also suggest a non-commensurate magnetic structure with magnetic moments probably aligned along the c axis. The present data provide evidence for magnetic ordering in hcp Fe and support the theoretical description of magnetism of pure Fe at high pressure.

Tuning Ni-catalyzed CO 2 hydrogenation selectivity via Ni-ceria support interactions and Ni-Fe bimetallic formation

DOE PAGES

Winter, Lea R.; Gomez, Elaine; Yan, Binhang; ...

2017-10-16

CO 2 hydrogenation over Fe-modified Ni/CeO 2 catalysts was investigated in a batch reactor using time-resolved in situ FTIR spectroscopy. Low loading of Ni/CeO 2 was associated with high selectivity to CO over CH 4, while higher Ni loading improved CO 2 hydrogenation activity with a reduced CO selectivity. X-ray absorption near-edge structure (XANES) analysis revealed Ni to be metallic for all catalysts including the CO-selective low loading 0.5% Ni catalyst, suggesting that the selectivity trend is due to structural rather than oxidation state effects. The loading amount of 1.5% Ni was selected for co-impregnation with Fe, based on themore » significant shift in product selectivity towards CH 4 for that loading amount, in order to shift the selectivity towards CO while maintaining high activity. Temperature programmed reduction (TPR) results indicated bimetallic interactions between Ni and Fe, and XANES analysis showed that about 70% of Fe in the bimetallic catalysts was oxidized. The Ni-Fe catalysts demonstrated improved selectivity towards CO without significantly compromising activity, coupling the high activity of Ni catalysts and the high CO selectivity of Fe. The general trends in Ni loading and bimetallic modification should guide efforts to develop non-precious metal catalysts for the selective production of CO by CO 2 hydrogenation.« less

Performance Enhancement and Side Reactions in Rechargeable Nickel-Iron Batteries with Nanostructured Electrodes.

PubMed

Lei, Danni; Lee, Dong-Chan; Magasinski, Alexandre; Zhao, Enbo; Steingart, Daniel; Yushin, Gleb

2016-01-27

We report for the first time a solution-based synthesis of strongly coupled nanoFe/multiwalled carbon nanotube (MWCNT) and nanoNiO/MWCNT nanocomposite materials for use as anodes and cathodes in rechargeable alkaline Ni-Fe batteries. The produced aqueous batteries demonstrate very high discharge capacities (800 mAh gFe(-1) at 200 mA g(-1) current density), which exceed that of commercial Ni-Fe cells by nearly 1 order of magnitude at comparable current densities. These cells also showed the lack of any "activation", typical in commercial batteries, where low initial capacity slowly increases during the initial 20-50 cycles. The use of a highly conductive MWCNT network allows for high-capacity utilization because of rapid and efficient electron transport to active metal nanoparticles in oxidized [such as Fe(OH)2 or Fe3O4] states. The flexible nature of MWCNTs accommodates significant volume changes taking place during phase transformation accompanying reduction-oxidation reactions in metal electrodes. At the same time, we report and discuss that high surface areas of active nanoparticles lead to multiple side reactions. Dissolution of Fe anodes leads to reprecipitation of significantly larger anode particles. Dissolution of Ni cathodes leads to precipitation of Ni metal on the anode, thus blocking transport of OH(-) anions. The electrolyte molarity and composition have a significant impact on the capacity utilization and cycling stability.

Facile synthesis of pyrite (FeS2/C) nanoparticles as an electrode material for non-aqueous hybrid electrochemical capacitors.

PubMed

Pham, Duong Tung; Baboo, Joseph Paul; Song, Jinju; Kim, Sungjin; Jo, Jeonggeun; Mathew, Vinod; Alfaruqi, Muhammad Hilmy; Sambandam, Balaji; Kim, Jaekook

2018-03-29

Pyrite (FeS2) is a promising electrode material for lithium ion batteries (LIBs) because of its high natural availability, low toxicity, cost-effectiveness, high theoretical capacity (894 mA h g-1) and high theoretical specific energy density (1270 W h kg-1, 4e-/FeS2). Nevertheless, the use of FeS2 in electrochemical capacitors was restricted due to fast capacity fading as a result of polysulfide (S/Sn2-) formation during the initial electrochemical cycling. In order to avoid the formation of polysulfides, we employed the strategy of utilizing an ether based electrolyte (1.0 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)/diglyme (DGM)). Herein, we introduce FeS2/C as the Faradaic electrode for a non-aqueous hybrid electrochemical capacitor (NHEC) in combination with activated carbon (AC) as a non-Faradaic electrode, and 1.0 M LiTFSI/DGM as a non-aqueous electrolyte. Specifically, FeS2/C nanoparticles have been prepared via the sulfidation of a room temperature synthesized Fe-based MOF (metal organic framework) precursor. The fabricated FeS2/C∥AC NHEC, operating within the chosen voltage window of 0-3.2 V, delivered energy densities in the range of 63-9 W h kg-1 at power densities of 152-3240 W kg-1. Remarkable cycling stability with stable energy density retention for 2500 cycles at high power densities (729, 1186 and 3240 W kg-1) was observed.

Spin dynamics near a putative antiferromagnetic quantum critical point in Cu-substituted BaFe 2 As 2 and its relation to high-temperature superconductivity

DOE PAGES

Kim, M. G.; Wang, M.; Tucker, G. S.; ...

2015-12-02

We present the results of elastic and inelastic neutron scattering measurements on nonsuperconducting Ba(Fe 0.957Cu 0.043) 2As 2, a composition close to a quantum critical point between antiferromagnetic (AFM) ordered and paramagnetic phases. By comparing these results with the spin fluctuations in the low-Cu composition as well as the parent compound BaFe 2As 2 and superconducting Ba(Fe 1–xNi x) 2As 2 compounds, we demonstrate that paramagnon-like spin fluctuations are evident in the antiferromagnetically ordered state of Ba(Fe 0.957Cu 0.043) 2As 2, which is distinct from the AFM-like spin fluctuations in the superconducting compounds. Our observations suggest that Cu substitution decouplesmore » the interaction between quasiparticles and the spin fluctuations. In addition, we show that the spin-spin correlation length ξ(T) increases rapidly as the temperature is lowered and find ω/T scaling behavior, the hallmark of quantum criticality, at an antiferromagnetic quantum critical point.« less

Structure and magnetism of Fe-doped BaSnO 3 thin films

DOE PAGES

Alaan, Urusa S.; N’Diaye, Alpha T.; Shafer, Padraic; ...

2017-02-28

BaSnO 3 is an excellent candidate system for developing a new class of perovskite-based dilute magnetic semiconductors. Here in this study, we show that BaSn 0.95Fe 0.05O 3 can be grown from a background pressure of ~2×10-3 mTorr to oxygen pressures of 300 mTorr with high crystallinity and excellent structural quality. When grown in vacuum, the films may be weakly ferromagnetic with a nonzero x-ray magnetic circular dichroism signal on the Fe L 3 edge. Growth with oxygen flow appears to suppress magnetic ordering. Even for very thick films grown in 100 mTorr O 2, the films are paramagnetic. Finally,more » the existence of ferromagnetism in vacuum-grown BaSnO 3 may be attributed to the F-center exchange mechanism, which relies on the presence of oxygen vacancies to facilitate the ferromagnetism. However, other possible extrinsic contributions to the magnetic ordering, such as clusters of Fe 3O 4 and FeO or contamination can also explain the observed behavior.« less

Tuning the Curie temperature of L 1 0 ordered FePt thin films through site-specific substitution of Rh

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Dongbin; Sun, Cheng-Jun; Chen, Jing-Sheng

2014-10-14

In structurally ordered magnetic thin films, the Curie temperature (TC) of ferromagnetic films depends on the exchange integral of the short range ordered neighboring atoms. The exchange integral may be adjusted by controlling elemental substitutional concentration at the lattice site of interest. We show how to control the TC in high anisotropy L10 Fe50Pt50 magnetic thin films by substituting Rh into the Pt site. Rh substitution in L10 FePt modified the local atomic environment and corresponding electronic properties while retaining the ordered L10 phase. The analysis of extended x-ray Absorption Fine Structure (EXAFS) spectra shows that Rh uniformly substitutes formore » Pt in L10 FePt. With 15 at. % of Rh substitution, temperature-dependent magnetic measurements show that the saturation magnetization (Ms) decreases from 1152 emu/cc to 670 emu/cc, the magnetocrystalline anisotropy (Ku) drops from 5×107 erg/cc to 2×107 erg/cc, and TC decreased from 750 to 500 K. A model of antiferromagnetic (AFM) defects caused by controlled Rh substitution of the Pt site, reducing the TC, is proposed to interpret this phenomenon and the validity is further examined by ab initio density functional calculations.« less

Spin-isotropic continuum of spin excitations in antiferromagnetically ordered Fe1.07Te

NASA Astrophysics Data System (ADS)

Song, Yu; Lu, Xingye; Regnault, L.-P.; Su, Yixi; Lai, Hsin-Hua; Hu, Wen-Jun; Si, Qimiao; Dai, Pengcheng

2018-02-01

Unconventional superconductivity typically emerges in the presence of quasidegenerate ground states, and the associated intense fluctuations are likely responsible for generating the superconducting state. Here we use polarized neutron scattering to study the spin space anisotropy of spin excitations in Fe1.07Te exhibiting bicollinear antiferromagnetic (AF) order, the parent compound of FeTe1 -xSex superconductors. We confirm that the low-energy spin excitations are transverse spin waves, consistent with a local-moment origin of the bicollinear AF order. While the ordered moments lie in the a b plane in Fe1.07Te , it takes less energy for them to fluctuate out of plane, similar to BaFe2As2 and NaFeAs. At energies above E ≳20 meV, we find magnetic scattering to be dominated by an isotropic continuum that persists up to at least 50 meV. Although the isotropic spin excitations cannot be ascribed to spin waves from a long-range-ordered local-moment antiferromagnet, the continuum can result from the bicollinear magnetic order ground state of Fe1.07Te being quasidegenerate with plaquette magnetic order.

Moessbauer spectroscopy of Mg(0.9)Fe(0.1)SiO3 perovskite

NASA Technical Reports Server (NTRS)

Jeanloz, Raymond; O'Neill, Bridget; Pasternak, Moshe P.; Taylor, R. D.; Bohlen, Steven R.

1992-01-01

Ambient pressure Moessbauer spectra of Mg(0.9)Fe-57(0.1)SiO3 perovskite synthesized at pressure-temperature conditions of about 50 GPa and 1700 K show that the iron is entirely high-spin Fe(2+) and appears to be primarily located in the octahedral site within the crystal structure. We observe broad Moessbauer lines, suggesting a distribution of electric-field gradients caused by disorder associated with the Fe ions. Also, the perovskite exhibits magnetic ordering at temperatures lower than 5 K, implying that there is a magnetic contribution to the absolute ('third-law') entropy of this phase.

Spatial Associations and Chemical Composition of Organic Carbon Sequestered in Fe, Ca, and Organic Carbon Ternary Systems.

PubMed

Sowers, Tyler D; Adhikari, Dinesh; Wang, Jian; Yang, Yu; Sparks, Donald L

2018-05-25

Organo-mineral associations of organic carbon (OC) with iron (Fe) oxides play a major role in environmental OC sequestration, a process crucial to mitigating climate change. Calcium has been found to have high coassociation with OC in soils containing high Fe content, increase OC sorption extent to poorly crystalline Fe oxides, and has long been suspected to form bridging complexes with Fe and OC. Due to the growing realization that Ca may be an important component of C cycling, we launched a scanning transmission X-ray microscopy (STXM) investigation, paired with near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, in order to spatially resolve Fe, Ca, and OC relationships and probe the effect of Ca on sorbed OC speciation. We performed STXM-NEXAFS analysis on 2-line ferrihydrite reacted with leaf litter-extractable dissolved OC and citric acid in the absence and presence of Ca. Organic carbon was found to highly associate with Ca ( R 2 = 0.91). Carboxylic acid moieties were dominantly sequestered; however, Ca facilitated the additional sequestration of aromatic and phenolic moieties. Also, C NEXAFS revealed polyvalent metal ion complexation. Our results provide evidence for the presence of Fe-Ca-OC ternary complexation, which has the potential to significantly impact how organo-mineral associations are modeled.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morozkin, A.V., E-mail: morozkin@general.chem.msu.r; Mozharivskyj, Yu.; SvitlyK, V.

The magnetic ordering of the Fe{sub 2}P-type Tb{sub 6}FeTe{sub 2}, Tb{sub 6}CoTe{sub 2} Tb{sub 6}NiTe{sub 2} and Er{sub 6}FeTe{sub 2} phases (space group P6-bar 2m) has been investigated through magnetization measurement and neutron powder diffraction. Tb{sub 6}FeTe{sub 2}, Tb{sub 6}CoTe{sub 2} and Tb{sub 6}NiTe{sub 2} demonstrate high-temperature ferromagnetic and low-temperature spin reorientation transitions, whereas Er{sub 6}FeTe{sub 2} shows antiferromagnetic transition, only. The Tb{sub 6}FeTe{sub 2} and Tb{sub 6}NiTe{sub 2} phases show same high-temperature collinear ferromagnetic structure, whereas Tb{sub 6}FeTe{sub 2} is the commensurate non-collinear ferromagnet and Tb{sub 6}NiTe{sub 2} is the canted ferromagnetic cone with K{sub 1}=[0, 0, {+-}3/10] andmore » K{sub 2}=[{+-}2/9, {+-}2/9, 0] wave vectors at 2 K. The magnetic structure of Er{sub 6}FeTe{sub 2} is a flat spiral with K{sub 1}=[0, 0, {+-}1/10] at 2 K. The magnetic entropy change for Tb{sub 6}NiTe{sub 2} is {Delta}S{sub m}=-4.86 J/kg K at 229 K for the field change {Delta}{mu}{sub 0}H=0-5 T. In addition, novel Fe{sub 2}P-type Gd{sub 6}FeTe{sub 2}, Zr{sub 6}FeTe{sub 2}, Hf{sub 6}FeTe{sub 2}, Dy{sub 6}NiTe{sub 2}, Zr{sub 6}NiTe{sub 2} and Hf{sub 6}NiTe{sub 2} phases have been obtained. -- Graphical abstract: The novel Fe{sub 2}P-type Tb{sub 6{l_brace}}Fe, Co, Te{r_brace}Te{sub 2} and Er{sub 6}FeTe{sub 2} phases (space group P6-bar 2m) show the complex magnetic ordering below 18-228 K. The magnetocaloric effect for Tb{sub 6}NiTe{sub 2} in terms of the isothermal entropy change, -{Delta}S{sub m}, has the maximum value of 4.86 J/kg K at 229 K for the 0-5 T field change.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Winter, Lea R.; Gomez, Elaine; Yan, Binhang

CO 2 hydrogenation over Fe-modified Ni/CeO 2 catalysts was investigated in a batch reactor using time-resolved in situ FTIR spectroscopy. Low loading of Ni/CeO 2 was associated with high selectivity to CO over CH 4, while higher Ni loading improved CO 2 hydrogenation activity with a reduced CO selectivity. X-ray absorption near-edge structure (XANES) analysis revealed Ni to be metallic for all catalysts including the CO-selective low loading 0.5% Ni catalyst, suggesting that the selectivity trend is due to structural rather than oxidation state effects. The loading amount of 1.5% Ni was selected for co-impregnation with Fe, based on themore » significant shift in product selectivity towards CH 4 for that loading amount, in order to shift the selectivity towards CO while maintaining high activity. Temperature programmed reduction (TPR) results indicated bimetallic interactions between Ni and Fe, and XANES analysis showed that about 70% of Fe in the bimetallic catalysts was oxidized. The Ni-Fe catalysts demonstrated improved selectivity towards CO without significantly compromising activity, coupling the high activity of Ni catalysts and the high CO selectivity of Fe. The general trends in Ni loading and bimetallic modification should guide efforts to develop non-precious metal catalysts for the selective production of CO by CO 2 hydrogenation.« less

Mössbauer spectroscopy study of magnetic fluctuations in superconducting RbGd2Fe4As4O2

NASA Astrophysics Data System (ADS)

Li, Y.; Wang, Z. C.; Cao, G. H.; Zhang, J. M.; Zhang, B.; Wang, T.; Pang, H.; Li, F. S.; Li, Z. W.

2018-05-01

57Fe Mössbauer spectra were measured at different temperatures between 5.9 K and 300 K on the recently discovered self-doped superconducting RbGd2Fe4As4O2 with Tc as high as 35 K. Singlet pattern was observed down to the lowest temperature measured in this work, indicating the absence of static magnetic order on the Fe site. The intermediate isomer shift in comparison with that of the samples RbFe2As2 and GdFeAsO confirms the self doping induced local electronic structure change. Surprisingly, we observe two magnetic fluctuation induced spectral broadenings below ∼ 15 K and ∼ 100 K which are believed to be originated from the transferred magnetic fluctuations of the Gd3+ moments and that of the magnetic fluctuations of the Fe atoms, respectively.

Campbell penetration depth in Fe-based superconductors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Prommapan, Plegchart

A 'true' critical current density, j c, as opposite to commonly measured relaxed persistent (Bean) current, j B, was extracted from the Campbell penetration depth, Λ c(T,H) measured in single crystals of LiFeAs, and optimally electron-doped Ba(Fe 0.954Ni 0.046) 2As 2 (FeNi122). In LiFeAs, the effective pinning potential is nonparabolic, which follows from the magnetic field - dependent Labusch parameter α. At the equilibrium (upon field - cooling), α(H) is non-monotonic, but it is monotonic at a finite gradient of the vortex density. This behavior leads to a faster magnetic relaxation at the lower fields and provides a natural dynamicmore » explanation for the fishtail (second peak) effect. We also find the evidence for strong pinning at the lower fields.The inferred field dependence of the pinning potential is consistent with the evolution from strong pinning, through collective pinning, and eventually to a disordered vortex lattice. The value of jc(2 K) ≅ 1.22 x 10 6 A/cm 2 provide an upper estimate of the current carrying capability of LiFeAs. Overall, vortex behavior of almost isotropic, fully-gapped LiFeAs is very similar to highly anisotropic d-wave cuprate superconductors, the similarity that requires further studies in order to understand unconventional superconductivity in cuprates and pnictides. In addition to LiFeAs, we also report the magnetic penetration depth in BaFe 2As 2 based superconductors including irradiation of FeNi122. In unirradiated FeNi122, the maximum critical current value is, j c(2K) ≅ 3.3 x 10 6 A/cm 2. The magnetic-dependent feature was observed near the transition temperature in FeTe 0.53Se 0.47 and irradiated FeNi122. Because of this feature, further studies are required in order to properly calibrate the Campbell penetration depth. Finally, we detected the crossing between the magnetic penetration depth and London penetration depth in optimally hold-doped Ba 0.6K 0.4Fe 2As 2 (BaK122) and isovalent doped BaFe 2(As 0.7P 0.3) 2 (BaP122). These phenomena probably coincide with anomalous Meissner effect reported in pnicitde superconductors [Prozorov et al. (2010b)] however more studies are needed in order to clarify this.« less

Effect of temperature on magnetic and impedance properties of Fe3BO6 of nanotubular structure with a bonded B2O3 surface layer

NASA Astrophysics Data System (ADS)

Kumari, Kalpana; Ram, S.; Kotnala, R. K.

2018-03-01

In this investigation, we explore a facile synthesis of Fe3BO6 in the form of small crystallites in the specific shape of nanotubes crystallized from a supercooled liquid Fe2O3-B2O3 precursor. This study includes high resolution transmission electron microscopy (HRTEM) images, magnetic, optical, and impedance properties of the sample. HRTEM images reveal small tubes of Fe3BO6 of 20 nm diameter. A well resolved hysteresis loop appears at 5 K in which the magnetization does not saturate even up to as high field as 50 kOe. It means that the Fe3BO6 nanotubes behave as highly antiferromagnetic in nature in which the surface spins do not align along the field so easily. The temperature dependent impedance describes an ionic Fe3BO6 conductor with a reasonably small activation energy Ea ˜ 0.33 eV. Impedance formalism in terms of a Cole-Cole plot shows a deviation from an ideal Debye-like behavior. We have also reported that electronic absorption spectra are over a spectral range 200-800 nm of wavelengths in order to find out how a bonded surface layer present on the Fe3BO6 crystallites tunes the 3d → 3d electronic transitions in Fe3+ ions.

Mössbauer Study and Modeling of Iron Import and Trafficking in Human Jurkat Cells

PubMed Central

Jhurry, Nema D.; Chakrabarti, Mrinmoy; McCormick, Sean P.; Gohil, Vishal M.; Lindahl, Paul A.

2014-01-01

The Fe content of Jurkat cells grown on transferrin-bound iron (TBI) and FeIII citrate (FC) was characterized using Mössbauer, EPR, and UV-vis spectroscopies, electron microscopy, and ICP-MS. Isolated mitochondria were similarly characterized. Fe-limited cells contained ∼ 100 μM of essential Fe, mainly as mitochondrial Fe and non-mitochondrial nonheme high-spin (NHHS) FeII. Fe-replete cells also contained ferritin-bound Fe and FeIII oxyhydroxide nanoparticles. Only 400 ± 100 Fe ions were loaded per ferritin complex, regardless of the growth medium Fe concentration. Ferritin regulation thus appears more complex than is commonly assumed. The magnetic/structural properties of Jurkat nanoparticles differed from those in yeast mitochondria. They were smaller and may be located in the cytosol. The extent of nanoparticle formation scaled nonlinearly with the concentration of Fe in the medium. Nanoparticle formation was not strongly correlated with ROS damage. Cells could utilize nanoparticle Fe, converting such aggregates into essential Fe forms. Cells grown on galactose rather than glucose respired faster, grew slower, exhibited more ROS damage and generally contained more nanoparticles. Cells grown with TBI rather than FC contained lower Fe concentrations, more ferritin and fewer nanoparticles. Cells in which transferrin receptor expression was increased contained more ferritin Fe. Frataxin-deficient cells contained more nanoparticles than comparable WT cells. Data were analyzed by a chemically-based mathematical model. Although simple, it captured essential features of Fe import, trafficking and regulation. TBI import was highly regulated but FC import was not. Nanoparticle formation was not regulated but the rate was third-order in cytosolic Fe. PMID:24180611

Ferroelectric ferrimagnetic LiFe2F6 : Charge-ordering-mediated magnetoelectricity

NASA Astrophysics Data System (ADS)

Lin, Ling-Fang; Xu, Qiao-Ru; Zhang, Yang; Zhang, Jun-Jie; Liang, Yan-Ping; Dong, Shuai

2017-12-01

Trirutile-type LiFe2F6 is a charge-ordered material with an Fe2 +/Fe3 + configuration. Here, its physical properties, including magnetism, electronic structure, phase transition, and charge ordering, are studied theoretically. On one hand, the charge ordering leads to improper ferroelectricity with a large polarization. On the other hand, its magnetic ground state can be tuned from the antiferromagnetic to ferrimagnetic by moderate compressive strain. Thus, LiFe2F6 can be a rare multiferroic with both large magnetization and polarization. Most importantly, since the charge ordering is the common ingredient for both ferroelectricity and magnetization, the net magnetization may be fully switched by flipping the polarization, rendering intrinsically strong magnetoelectric effects and desirable functions.

Stabilization of the high coercivity {epsilon}-Fe{sub 2}O{sub 3} phase in the CeO{sub 2}-Fe{sub 2}O{sub 3}/SiO{sub 2} nanocomposites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mantlikova, A., E-mail: mantlikova@fzu.cz; Poltierova Vejpravova, J.; Bittova, B.

2012-07-15

We have investigated the processes leading to the formation of the Fe{sub 2}O{sub 3} and CeO{sub 2} nanoparticles in the SiO{sub 2} matrix in order to stabilize the {epsilon}-Fe{sub 2}O{sub 3} as the major phase. The samples with two different concentrations of the Fe were prepared by sol-gel method, subsequently annealed at different temperatures up to 1100 Degree-Sign C, and characterized by the Moessbauer spectroscopy, Transmission Electron Microscopy (TEM), Powder X-ray Diffraction (PXRD), Energy Dispersive X-ray analysis (EDX) and magnetic measurements. The evolution of the different Fe{sub 2}O{sub 3} phases under various conditions of preparation was investigated, starting with themore » preferential appearance of the {gamma}-Fe{sub 2}O{sub 3} phase for the sample with low Fe concentration and low annealing temperature and stabilization of the major {epsilon}-Fe{sub 2}O{sub 3} phase for high Fe concentration and high annealing temperature, coexisting with the most stable {alpha}-Fe{sub 2}O{sub 3} phase. A continuous increase of the particle size of the CeO{sub 2} nanocrystals with increasing annealing temperature was also observed. - Graphical abstract: The graphical abstract displays the most important results of our work. The significant change of the phase composition due to the variation of preparation conditions is demonstrated. As a result, significant change of the magnetic properties from superparamagnetic {gamma}-Fe{sub 2}O{sub 3} phase with negligible coercivity to the high coercivity {epsilon}-Fe{sub 2}O{sub 3} phase has been observed. Highlights: Black-Right-Pointing-Pointer Research of the stabilization of the high coercivity {epsilon}-Fe{sub 2}O{sub 3} in CeO{sub 2}-Fe{sub 2}O{sub 3}/SiO{sub 2}. Black-Right-Pointing-Pointer Samples with two different concentrations of Fe and three annealing temperatures. Black-Right-Pointing-Pointer Phase transition {gamma}{yields}{epsilon}{yields}({beta}){yields}{alpha} with increasing annealing temperature and particle size. Black-Right-Pointing-Pointer Elimination of the superparamagnetic phases in samples with higher content of Fe. Black-Right-Pointing-Pointer Best conditions for high coercivity {epsilon}-Fe{sub 2}O{sub 3}-higher Fe content and T{sub A}=1100 Degree-Sign C.« less

Insulating and metallic spin glass in Ni-doped K x Fe 2 - y Se 2 single crystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ryu, Hyejin; Abeykoon, Milinda; Wang, Kefeng

2015-05-01

Here in this paper, we report electron doping effects by Ni in K xFe 2- δ-y Ni ySe 2 (0.06 ≤ y ≤ 1.44) single-crystal alloys. A rich ground-state phase diagram is observed. A small amount of Ni (~4 %) suppressed superconductivity below 1.8 K, inducing insulating spin-glass magnetic ground state for higher Ni content. With further Ni substitution, metallic resistivity is restored. For high Ni concentration in the lattice the unit cell symmetry is high symmetry I4/mmm with no phase separation whereas both I4 / m + I4/mmm space groups were detected in the phase separated crystals when concentrationmore » of Ni< Fe. The absence of superconductivity coincides with the absence of crystalline Fe vacancy order.« less

Facile fabrication of highly ordered poly(vinylidene fluoride-trifluoroethylene) nanodot arrays for organic ferroelectric memory

NASA Astrophysics Data System (ADS)

Fang, Huajing; Yan, Qingfeng; Geng, Chong; Chan, Ngai Yui; Au, Kit; Yao, Jianjun; Ng, Sheung Mei; Leung, Chi Wah; Li, Qiang; Guo, Dong; Wa Chan, Helen Lai; Dai, Jiyan

2016-01-01

Nano-patterned ferroelectric materials have attracted significant attention as the presence of two or more thermodynamically equivalent switchable polarization states can be employed in many applications such as non-volatile memory. In this work, a simple and effective approach for fabrication of highly ordered poly(vinylidene fluoride-trifluoroethylene) P(VDF-TrFE) nanodot arrays is demonstrated. By using a soft polydimethylsiloxane mold, we successfully transferred the 2D array pattern from the initial monolayer of colloidal polystyrene nanospheres to the imprinted P(VDF-TrFE) films via nanoimprinting. The existence of a preferred orientation of the copolymer chain after nanoimprinting was confirmed by Fourier transform infrared spectra. Local polarization switching behavior was measured by piezoresponse force microscopy, and each nanodot showed well-formed hysteresis curve and butterfly loop with a coercive field of ˜62.5 MV/m. To illustrate the potential application of these ordered P(VDF-TrFE) nanodot arrays, the writing and reading process as non-volatile memory was demonstrated at a relatively low voltage. As such, our results offer a facile and promising route to produce arrays of ferroelectric polymer nanodots with improved piezoelectric functionality.

Exploring the mechanism and kinetics of Fe-Cu-Ag trimetallic particles for p-nitrophenol reduction.

PubMed

Yuan, Yue; Yuan, Donghai; Zhang, Yunhong; Lai, Bo

2017-11-01

Preparation conditions of Fe-Cu-Ag trimetallic particles were optimized by single-factor and response surface methodology (RSM) batch experiments to obtain high-reactive Fe 0 -based materials for p-nitrophenol (PNP) removal. Under the optimal conditions (i.e., Fe 0 dosage of 34.86 g L -1 , theoretical Cu mass loading of 81.87 mg Cu/g Fe, theoretical Ag mass loading of 1.15 mg Ag/g Fe, and preparation temperature of 52.1 °C), the actual rate constant (k obs ) of PNP reduction in 5 min was 1.64 min -1 , which shows a good agreement between the model prediction (1.85 min -1 ) of RSM and the experimental data. Furthermore, the high reactivity of Fe 0 -based trimetals was mainly attributed to the plating order of transition metals (i.e., Ag and Cu). Furthermore, we propose a new theory that the pyramid trimetallic structure of Fe-Cu-Ag could improve the electron transport and create active sites with high electron density at the surface (Ag layer) that could enhance the generation of surface-bonded atomic hydrogen ([H] abs ) or the direct reduction of pollutant. Moreover, Fe-Cu-Ag trimetallic particles were characterized by SEM, EDS, and XPS, which also could confirm the proposed theory. In addition, the leached Cu 2+ (<10 μg L -1 ) and Ag + (below detection limits) in Fe-Cu-Ag system could be neglected completely, which suggests that Fe-Cu-Ag is reliable, safe, and environment friendly. Therefore, Fe-Cu-Ag trimetallic system would be promising for the removal of pollutants from industrial wastewater. Copyright © 2017 Elsevier Ltd. All rights reserved.

Structural and optical characterization of p-type highly Fe-doped SnO2 thin films and tunneling transport on SnO2:Fe/p-Si heterojunction

NASA Astrophysics Data System (ADS)

Ben Haj Othmen, Walid; Ben Hamed, Zied; Sieber, Brigitte; Addad, Ahmed; Elhouichet, Habib; Boukherroub, Rabah

2018-03-01

Nanocrystalline highly Fe-doped SnO2 thin films were prepared using a new simple sol-gel method with iron amounts of 5, 10, 15 and 20%. The obtained gel offers a long durability and high quality allowing to reach a sub-5 nm nanocrystalline size with a good crystallinity. The films were structurally characterized through X-ray diffraction (XRD) that confirms the formation of rutile SnO2. High Resolution Transmission Electron Microscopy (HRTEM) images reveals the good crystallinity of the nanoparticles. Raman spectroscopy shows that the SnO2 rutile structure is maintained even for high iron concentration. The variation of the PL intensity with Fe concentration reveals that iron influences the distribution of oxygen vacancies in tin oxide. The optical transmittance results indicate a redshift of the SnO2 band gap when iron concentration increases. The above optical results lead us to assume the presence of a compensation phenomenon between oxygen vacancies and introduced holes following Fe doping. From current-voltage measurements, an inversion of the conduction type from n to p is strongly predicted to follow the iron addition. Electrical characterizations of SnO2:Fe/p-Si and SnO2:Fe/n-Si heterojunctions seem to be in accordance with this deduction. The quantum tunneling mechanism is expected to be important at high Fe doping level, which was confirmed by current-voltage measurements at different temperatures. Both optical and electrical properties of the elaborated films present a particularity for the same iron concentration and adopt similar tendencies with Fe amount, which strongly correlate the experimental observations. In order to evaluate the applicability of the elaborated films, we proceed to the fabrication of the SnO2:Fe/SnO2 homojunction for which we note a good rectifying behavior.

Ordering, nanostructure and high-field magnetization of quenched and annealed metastable ilmenite-hematite solid solutions

NASA Astrophysics Data System (ADS)

Fabian, Karl; Thomas, Christopher I.; McEnroe, Suzanne A.; Robinson, Peter; Mukai, Hiroki

2013-04-01

The ilmenite-hematite solid solution series xFeTiO3-(1 - x)Fe2O3 can generate extremely unusual magnetic properties in natural rocks and has been investigated for more than fifty years. Both, ilmenite (FeTiO3) and hematite (Fe2O3) are antiferromagnetic, but intermediate compositions are either antiferromagnetic or ferrimagnetic, depending on their chemical order. Within a single sample, nano-scale variations in local composition x and ordering state Q depend on minute details of the cooling and annealing history, and have large effects on the magnetic properties, which include self-reversal of thermoremanent magnetization and large exchange bias. We present a systematic study of magnetic properties of samples in the composition range of 0.6 ˜ x ˜ 0.7 with differing nanostructure and consequently differing magnetic properties. Using high-field measurements up to 7 T, together with TEM images and theoretical models we classify nanostructure formation in terms of x, Q, and characteristic size d. These characteristics are then linked to the magnetic properties. The sample characterization relies on average mean-field models of Ms(T). To implement the varying Fe and Ti densities, and the distribution of Fe ions in the variably ordered solid solutions, the models either use statistical interactions between sites, whereby they effectively average over all possible configurations, or they describe specific random configurations. Statistical mean field models are successful in predicting the Curie temperatures TC and Ms(T) curves of the Ilmx solid solutions. The results depend on the interaction coefficients, which either had been determined by neutron diffraction measurements (Samuelson and Shirane, 1979), by Monte-Carlo model fits (Harrison, 2006), or by density-functional theoretic calculations (Nabi et al. 2010). Hysteresis branches have been measured for a wide variety of samples at different temperatures 40 K, 100 K and 300 K. None of them saturate at 7 T, the strongest field available to us so far. Some of the samples show the beginnings of a pseudo-metamagnetic transition at the upper limits of the measurements. In previous models this is explained by anti-phase boundaries and exchange coupling between ordered and disordered regions with differing sizes and hence differing responses to an external field. These effects will be studied further up to 60 T using a European high-field laboratory within the EuroMagNET II/EMFL scheme.

Preparation of metastable CoFeNi alloys with ultra-high magnetic saturation (Bs = 2.4-2.59 T) by reverse pulse electrodeposition

NASA Astrophysics Data System (ADS)

Tabakovic, Ibro; Venkatasamy, Venkatram

2018-04-01

The results of reverse pulse electrodeposition of CoFeNi films with ultra-high magnetic saturation, i.e. Bs values between 2.4 and 2.59 T, are presented in this work. Based on valence-bond theory (Hund's rule) it was assumed that the electronic configuration of MOH obtained by one electron reduction of electroactive intermediate (MOH+ads + e → MOHads) or oxidation of metal (M - e + HOH → MOH + H+) would result with larger number of spins per atom for each of transition metals in MOH-precipitated in CoFeNi deposit- with one more spin than their respective neutral metal in the order: Fe > Co > Ni. The experimental results showed that the increase of Bs value above Slater-Pauling curve was not observed for CoFe alloys, thus FeOH and CoOH compounds were not present in deposit. However, the increase of the Bs values above the Slater-Pauling curve (Bs = 2.4-2.59 T) was observed, for CoFeNi films obtained by reverse pulse electrodeposition. Therefore, NiOH as a stable compound is probably formed in a one-electron oxidation step during anodic pulse oxidation reaction precipitated presumably at the grain boundaries, giving rise to the ultra-high magnetic saturation of CoFeNi films. The effects of experimental conditions on elemental composition, magnetic properties, crystal structure, and thermal stability of CoFeNi films were studied.

Processes and time scales of magmatic evolution as revealed by Fe-Mg chemical and isotopic zoning in natural olivines

NASA Astrophysics Data System (ADS)

Oeser, Martin; Dohmen, Ralf; Horn, Ingo; Schuth, Stephan; Weyer, Stefan

2015-04-01

In this study, we applied high-precision in situ Fe and Mg isotope analyses by femtosecond laser ablation (fs-LA) MC-ICP-MS on chemically zoned olivine xeno- and phenocrysts from intra-plate volcanic regions in order to investigate the magnitude of Fe and Mg isotope fractionation and its suitability to gain information on magma evolution. Our results show that chemical zoning (i.e., Mg#) in magmatic olivines is commonly associated with significant zoning in δ56Fe and δ26Mg (up to 1.7‰ and 0.7‰, respectively). We explored different cases of kinetic fractionation of Fe and Mg isotopes by modeling diffusion in the melt or olivine and simultaneous growth or dissolution. Combining the information of chemical and isotopic zoning in olivine allows to distinguish between various processes that may occur during magma evolution, namely diffusive Fe-Mg exchange between olivine and melt, rapid crystal growth, and Fe-Mg inter-diffusion simultaneous to crystal dissolution or growth. Chemical diffusion in olivine appears to be the dominant process that drives isotope fractionation in magmatic olivine. Simplified modeling of Fe and Mg diffusion is suitable to reproduce both the chemical and the isotopic zoning in most of the investigated olivines and, additionally, provides time information about magmatic processes. For the Massif Central (France), modeling of diffusive re-equilibration of mantle olivines in basanites revealed a short time span (<2 years) between the entrainment of a mantle xenolith in an intra-plate basaltic magma and the eruption of the magma. Furthermore, we determined high cooling rates (on the order of a few tens to hundreds of °C per year) for basanite samples from a single large outcrop in the Massif Central, which probably reflects the cooling of a massive lava flow after eruption. Results from the modeling of Fe and Mg isotope fractionation in olivine point to a systematic difference between βFe and βMg (i.e., βFe/βMg ≈ 2), implying that the diffusivity ratio of 54Fe and 56Fe (i.e., D54Fe/D56Fe) is very similar to that of 24Mg and 26Mg, despite the smaller relative mass difference for the 54Fe-56Fe pair. This study demonstrates that a combined investigation of Fe-Mg chemical and isotopic zoning in olivine provides additional and more reliable information on magma evolution than chemical zoning alone.

Weak ferromagnetism along the third-order axis of the FeBO3 crystals caused by Fe2+ impurity ions

NASA Astrophysics Data System (ADS)

Ovchinnikov, S. G.; Rudenko, V. V.; Vorotynov, A. M.

2018-05-01

Using the single-ion approximation, the weak ferromagnetic moment σZ(Fe2+) along the third-order axis of FeBO3 crystals, which is caused by the contribution of Fe2+ ions, has been investigated in the framework of the model Fe2+ impurity ion -BO3 vacancy. The extreme low-temperature behavior of the total magnetic moment due to the strong dependence of the Fe2+ion contribution is predicted.

Structural stability, enhanced magnetic, piezoelectric, and transport properties in (1-x)BiFeO3-(x)Ba0.70Sr0.30TiO3 nanoparticles

NASA Astrophysics Data System (ADS)

Sharma, Subhash; Singh, Vikash; Anshul, Avneesh; Siqueiros, J. M.; Dwivedi, R. K.

2018-05-01

Multiferroic samples with composition (1-x)BiFeO3-(x)(Ba0.70Sr0.30)TiO3 (BFO-BST) were synthesized using a sol-gel route to study the effect of BST doping on structural, transport, and magnetic properties in BiFeO3 (BFO). X-ray diffraction studies with Rietveld analysis revealed that a phase transition occurred from rhombohedral (R3c) (0.0 ≤ × ≤ 0.15) to tetragonal (P4 mm) for x = 0.20 and nanocrystalline nature confirmed by transmission electron microscopy measurements. Piezoelectric properties improved as x increased from x = 0.0 (58 pC/N) to x = 0.20 (112 pC/N) increasing distortion in the crystal structure as evinced by Williamson-Hall analysis. Ferromagnetism was observed in doped BFO, different from the antiferromagnetic ordering in bulk BFO, indicating the noteworthy size effects and Fe-O-Fe bond angle variations in the magnetic ordering of BFO. An improvement in ferroelectric properties is observed with doping of BST compared to pristine BFO. Thermally activated conduction behavior occurred at low and high temperature regions as revealed by temperature dependent dc resistivity measurement. Effective improvements in dielectric response, meaning high dielectric constant with a low dielectric loss, were found in the doped samples.

Structure-dependent magnetoresistance and spin-transfer torque in antiferromagnetic Fe |MgO |FeMn |Cu tunnel junctions

NASA Astrophysics Data System (ADS)

Jia, Xingtao; Tang, Huimin; Wang, Shizhuo; Qin, Minghui

2017-02-01

We predict large magnetoresistance (MR) and spin transfer torque (STT) in antiferromagnetic Fe |MgO |FeMn |Cu tunnel junctions based on first-principles scattering theory. MR as large as ˜100 % is found in one junction. Magnetic dynamic simulations show that STT acting on the antiferromagnetic order parameter dominates the spin dynamics, and an electronic bias of order 10-1mV and current density of order 105Acm-2 can switches a junction of three-layer MgO, they are about one order smaller than that in Fe |MgO |Fe junction with the same barrier thickness, respectively. The multiple scattering in the antiferromagnetic region is considered to be responsible for the enhanced spin torque and smaller switching current density.

Sequential structural and antiferromagnetic transitions in BaFe2Se3 under pressure

NASA Astrophysics Data System (ADS)

Zhang, Yang; Lin, Ling-Fang; Zhang, Jun-Jie; Dagotto, Elbio; Dong, Shuai

2018-01-01

The discovery of superconductivity in the two-leg ladder compound BaFe2S3 has established the 123-type iron chalcogenides as a novel and interesting subgroup of the iron-based superconductor family. However, in this 123 series, BaFe2Se3 is an exceptional member, with a magnetic order and crystalline structure different from all others. Recently, an exciting experiment reported the emergence of superconductivity in BaFe2Se3 at high pressure [J. Ying et al., Phys. Rev. B 95, 241109(R) (2017), 10.1103/PhysRevB.95.241109]. In this paper, we report a first-principles study of BaFe2Se3 . Our analysis unveils a variety of qualitative differences between BaFe2S3 and BaFe2Se3 , including in the latter an unexpected chain of transitions with increasing pressure. First, by gradually reducing the tilting angle of iron ladders, the crystalline structure smoothly transforms from P n m a to C m c m at ˜6 GPa. Second, the system becomes metallic at 10.4 GPa. Third, its unique ambient-pressure Block antiferromagnetic ground state is replaced by the more common stripe (so-called CX-type) antiferromagnetic order at ˜12 GPa, the same magnetic state as the 123-S ladder. This transition is found at a pressure very similar to the experimental superconducting transition. Finally, all magnetic moments vanish at 30 GPa. This reported theoretical diagram of the complete phase evolution is important because of the technical challenges to capture many physical properties in high-pressure experiments. The information obtained in our calculations suggests different characteristics for superconductivity in BaFe2Se3 and BaFe2S3 : in 123-S pairing occurs when magnetic moments vanish, while in 123-Se the transition region from Block- to CX-type magnetism appears to catalyze superconductivity. Finally, an additional superconducting dome above ˜30 GPa is expected to occur.

Structural characterization of a new vacancy ordered perovskite modification found for Ba{sub 3}Fe{sub 3}O{sub 7}F (BaFeO{sub 2.333}F{sub 0.333}): Towards understanding of vacancy ordering for different perovskite-type ferrites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Clemens, Oliver, E-mail: oliver.clemens@kit.edu; Karlsruher Institut für Technologie, Institut für Nanotechnologie, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen

2015-05-15

The new vacancy ordered perovskite-type compound Ba{sub 3}Fe{sub 3}O{sub 7}F (BaFeO{sub 2.33}F{sub 0.33}) was prepared by topochemical low-temperature fluorination of Ba{sub 2}Fe{sub 2}O{sub 5} (BaFeO{sub 2.5}) using stoichiometric amounts of polyvinylidene difluoride (PVDF). The vacancy order was found to be unique so far for perovskite compounds, and the connectivity pattern can be explained by the formula Ba{sub 3}(FeX{sub 6/2}) (FeX{sub 5/2}) (FeX{sub 3/2}X{sub 1/1}), with X=O/F. Mössbauer measurements were used to confirm the structural analysis and agree with the presence of Fe{sup 3+} in the above mentioned coordination environments. Group–subgroup relationships were used to build a starting model for themore » structure solution and to understand the relationship to the cubic perovskite structure. Furthermore, a comparison of a variety of vacancy-ordered iron-containing perovskite-type structures is given, highlighting the factors which favour one structure type over the other depending on the composition. - Graphical abstract: The crystal structure of Ba{sub 3}Fe{sub 3}O{sub 7}F in comparison to other perovskite type ferrites. - Highlights: • The crystal structure of Ba{sub 3}Fe{sub 3}O{sub 7}F in comparison to other perovskite type ferrites. • Ba{sub 3}Fe{sub 3}O{sub 7}F was synthesized by low temperature fluorination of Ba{sub 2}Fe{sub 2}O{sub 5}. • Ba{sub 3}Fe{sub 3}O{sub 7}F shows a unique vacancy order not found for other perovskite type compounds. • The structure of Ba{sub 3}Fe{sub 3}O{sub 7}F was solved using group–subgroup relationships. • A systematic comparison to other ferrite type compounds reveals structural similarities and differences. • The A-site coordination of the cation is shown to play an important role for the type of vacancy order found.« less

Soft-template construction of three-dimensionally ordered inverse opal structure from Li2FeSiO4/C composite nanofibers for high-rate lithium-ion batteries

NASA Astrophysics Data System (ADS)

Li, Donglin; Zhang, Wei; Sun, Ru; Yong, Hong-Tuan-Hua; Chen, Guangqi; Fan, Xiaoyong; Gou, Lei; Mao, Yiyang; Zhao, Kun; Tian, Miao

2016-06-01

Exploring a new method to fabricate small-sized nanofibers is essential to achieve superior performances for energy conversion and storage devices. Here, a novel soft-template strategy is developed to synthesize a three-dimensionally ordered macroporous (3DOM) architecture constructed from small-sized nanofibers. The effectiveness of a nanofiber-assembled three-dimensional inverse opal material as an electrode for high-rate lithium-ion batteries is demonstrated. The small-sized Li2FeSiO4/C composite nanofibers with a diameter of 20-30 nm are grown by employing a tri-block copolymer P123 as a structure directing agent. Accordingly, the macro-mesoporous hierarchical 3DOM architecture constructed from Li2FeSiO4/C nanofibers is further templated from P123 for the nanofibers and a polystyrene colloidal crystal array for the 3DOM architecture. We find that the thermal stability of the nanofiber morphology depends on the self-limited growth of Li2FeSiO4 nanocrystals in a crystalline-amorphous hybrid. As a cathode for a lithium-ion battery, the 3D hierarchical macro-mesoporous cathodes exhibit outstanding high-rate and ultralong-life performances with a capacity retention of 84% after 1500 cycles at 5 C in the voltage window of 1.5-4.5 V, which is greatly improved compared with a simple 3DOM Li2FeSiO4/C nanocomposite.Exploring a new method to fabricate small-sized nanofibers is essential to achieve superior performances for energy conversion and storage devices. Here, a novel soft-template strategy is developed to synthesize a three-dimensionally ordered macroporous (3DOM) architecture constructed from small-sized nanofibers. The effectiveness of a nanofiber-assembled three-dimensional inverse opal material as an electrode for high-rate lithium-ion batteries is demonstrated. The small-sized Li2FeSiO4/C composite nanofibers with a diameter of 20-30 nm are grown by employing a tri-block copolymer P123 as a structure directing agent. Accordingly, the macro-mesoporous hierarchical 3DOM architecture constructed from Li2FeSiO4/C nanofibers is further templated from P123 for the nanofibers and a polystyrene colloidal crystal array for the 3DOM architecture. We find that the thermal stability of the nanofiber morphology depends on the self-limited growth of Li2FeSiO4 nanocrystals in a crystalline-amorphous hybrid. As a cathode for a lithium-ion battery, the 3D hierarchical macro-mesoporous cathodes exhibit outstanding high-rate and ultralong-life performances with a capacity retention of 84% after 1500 cycles at 5 C in the voltage window of 1.5-4.5 V, which is greatly improved compared with a simple 3DOM Li2FeSiO4/C nanocomposite. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr07783d

High spin polarization and the origin of unique ferromagnetic ground state in CuFeSb

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sirohi, Anshu; Saha, Preetha; Gayen, Sirshendu

CuFeSb is isostructural to the ferro-pnictide and chalcogenide superconductors and it is one of the few materials in the family that are known to stabilize in a ferromagnetic ground state. Majority of the members of this family are either superconductors or antiferromagnets. Therefore, CuFeSb may be used as an ideal source of spin polarized current in spin-transport devices involving pnictide and the chalcogenide superconductors. However, for that the Fermi surface of CuFeSb needs to be sufficiently spin polarized. In this paper we report direct measurement of transport spin polarization in CuFeSb by spin-resolved Andreev reflection spectroscopy. From a number ofmore » measurements using multiple superconducting tips we found that the intrinsic transport spin polarization in CuFeSb is high (∼47%). In order to understand the unique ground state of CuFeSb and the origin of large spin polarization at the Fermi level, we have evaluated the spin-polarized band structure of CuFeSb through first principles calculations. Apart from supporting the observed 47% transport spin polarization, such calculations also indicate that the Sb-Fe-Sb angles and the height of Sb from the Fe plane are strikingly different for CuFeSb than the equivalent parameters in other members of the same family thereby explaining the origin of the unique ground state of CuFeSb.« less

Green synthesis of iron nanoparticles by various tea extracts: comparative study of the reactivity.

PubMed

Huang, Lanlan; Weng, Xiulan; Chen, Zuliang; Megharaj, Mallavarapu; Naidu, Ravendra

2014-09-15

Iron nanoparticles (Fe NPs) are often synthesized using sodium borohydride with aggregation, which is a high cost process and environmentally toxic. To address these issues, Fe NPs were synthesized using green methods based on tea extracts, including green, oolong and black teas. The best method for degrading malachite green (MG) was Fe NPs synthesized by green tea extracts because it contains a high concentration of caffeine/polyphenols which act as both reducing and capping agents in the synthesis of Fe NPs. These characteristics were confirmed by a scanning electron microscope (SEM), UV-visible (UV-vis) and specific surface area (BET). To understand the formation of Fe NPs using various tea extracts, the synthesized Fe NPs were characterized by SEM, X-ray energy-dispersive spectrometer (EDS), and X-ray diffraction (XRD). What emerged were different sizes and concentrations of Fe NPs being synthesized by tea extracts, leading to various degradations of MG. Furthermore, kinetics for the degradation of MG using these Fe NPs fitted well to the pseudo first-order reaction kinetics model with more than 20 kJ/mol activation energy, suggesting a chemically diffusion-controlled reaction. The degradation mechanism using these Fe NPs included adsorption of MG to Fe NPs, oxidation of iron, and cleaving the bond that was connected to the benzene ring. Copyright © 2014 Elsevier B.V. All rights reserved.

Synthesis and characterization of Fe-based metal and oxide based nanoparticles: discoveries and research highlights of potential applications in biology and medicine.

PubMed

Long, Nguyen Viet; Thi, Cao Minh; Yong, Yang; Cao, Yanqin; Wu, Haibo; Nogami, Masayuki

2014-01-01

In this review, we have presented the controlled synthesis of Fe-based metal and oxide nanoparticles with large size by chemical methods. The issues of the size, shape and morphology of Fe nanoparticles are discussed in the certain ranges of practical applications in biology and medicine. The homogeneous nanosystems of Fe-based metal and oxide nanoparticles with various sizes and shapes from the nano-to-micro ranges can be used in order to meet the demands of the treatments of dangerous tumors and cancers through magnetic hyperthermia and magnetic resonance imaging (MRI). In this context, the polyhedral Fe-based metal and oxide nanoparticles having large size in the ranges from 1000 nm to 5000 nm can be potentially used in magnetic hyperthermia and MRI in the innovative drug delivery, diagnosis, treatment, and therapy of tumor and cancer diseases because of their very high bio-adaptability. We have suggested that high stability and durability of Fe-based metal and oxide nanoparticles are very crucial to recent magnetic hyperthermia and MRI technology. The roles of various Fe-based nanostructures are focused in biomedical applications of tumors and cancers diagnostics, targeted drug delivery, and magnetic hyperthermia. Finally, Fe-based, α-, β- and γ-Fe2O3, and Fe3O4-based nanoparticles are shortly discussed in various potential applications in catalysis, biology, and medicine.

Accuracy and Transferability of Ab Initio Electronic Band Structure Calculations for Doped BiFeO3

NASA Astrophysics Data System (ADS)

Gebhardt, Julian; Rappe, Andrew M.

2017-11-01

BiFeO3 is a multiferroic material and, therefore, highly interesting with respect to future oxide electronics. In order to realize such devices, pn junctions need to be fabricated, which are currently impeded by the lack of successful p-type doping in this material. In order to guide the numerous research efforts in this field, we recently finished a comprehensive computational study, investigating the influence of many dopants onto the electronic structure of BiFeO3. In order to allow for this large scale ab initio study, the computational setup had to be accurate and efficient. Here we discuss the details of this assessment, showing that standard density-functional theory (DFT) yields good structural properties. The obtained electronic structure, however, suffers from well-known shortcomings. By comparing the conventional DFT results for alkali and alkaline-earth metal doping with more accurate hybrid-DFT calculations, we show that, in this case, the problems of standard DFT go beyond a simple systematic error. Conventional DFT shows bad transferability and the more reliable hybrid-DFT has to be chosen for a qualitatively correct prediction of doping induced changes in the electronic structure of BiFeO3.

Campbell penetration depth in iron-based superconductors

NASA Astrophysics Data System (ADS)

Prommapan, Plengchart

2011-12-01

A "true" critical current density, jc, as opposite to commonly measured relaxed persistent (Bean) current, jB, was extracted from the Campbell penetration depth, lambda C(T, H) measured in single crystals of LiFeAs, and optimally electron-doped Ba (Fe0.954Ni 0.046)2As2 (FeNi122). In LiFeAs, the effective pinning potential is non-parabolic, which follows from the magnetic field - dependent Labusch parameter alpha. At the equilibrium (upon field - cooling), alpha( H) is non-monotonic, but it is monotonic at a finite gradient of the vortex density. This behavior leads to a faster magnetic relaxation at the lower fields and provides a natural dynamic explanation for the fishtail (second peak) effect. We also find the evidence for strong pinning at the lower fields.The inferred field dependence of the pinning potential is consistent with the evolution from strong pinning, through collective pinning, and eventually to a disordered vortex lattice. The value of j c (2 K) ≃ 1:22 x106 A/cm² provide an upper estimate of the current carrying capability of LiFeAs. Overall, vortex behavior of almost isotropic, fully-gapped LiFeAs is very similar to highly anisotropic d-wave cuprate superconductors, the similarity that requires further studies in order to understand unconventional superconductivity in cuprates and pnictides. In addition to LiFeAs, we also report the magnetic penetration depth in BaFe2As2 based superconductors including irradiation of FeNi122. In unirradiated FeNi122, the maximum critical current value is, jc(2 K) ≃ 3.3 x 106 A/cm². The magnetic-dependent feature was observed near the transition temperature in FeTe0.53Se0.47 and irradiated FeNi122. Because of this feature, further studies are required in order to properly calibrate the Campbell penetration depth. Finally, we detected the crossing between the magnetic penetration depth and London penetration depth in optimally hold-doped Ba0.6K 0.4Fe2As2 (BaK122) and isovalent doped BaFe2(As0.7P0.3)2 (BaP122). These phenomena probably coincide with anomalous Meissner effect reported in pnictide superconductors [Prozorov et al. (2010b)] however more studies are needed in order to clarify this.

Synthesis of 3D porous ferromagnetic NiFe2O4 and using as novel adsorbent to treat wastewater.

PubMed

Hou, Xiangyu; Feng, Jing; Liu, Xiaohan; Ren, Yueming; Fan, Zhuangjun; Wei, Tong; Meng, Jian; Zhang, Milin

2011-10-15

Three dimensions (3D) porous NiFe(2)O(4) is synthesized by a sol-gel method using egg white. The obtained NiFe(2)O(4) shows both good ferromagnetic properties and high adsorption capacity. The porous NiFe(2)O(4) shows good adsorption properties for organic dyes (Methylene Blue (138.50 mg/g), Fuchsine Red (14.61 mg/g), Methyl Violet (19.06 mg/g)) and heavy metal ions (Cu (II) (55.83 mg/g), Cr (VI) (36.95 mg/g) and Ni (II) (37.02 mg/g)) due to its 3D interconnected porous structure. The maximum adsorption of Methylene Blue (MB) fit the pseudo-second-order model and Langmuir isotherm equation well. More interestingly, the ferromagnetic NiFe(2)O(4) can be separated under a magnetic field conveniently and keeps high removal efficiency (>97%) during seven reusable cycles. These results suggest that the porous NiFe(2)O(4) is a promising favorable and reusable adsorbent. Copyright © 2011 Elsevier Inc. All rights reserved.

Microstructural, Magnetic Anisotropy, and Magnetic Domain Structure Correlations in Epitaxial FePd Thin Films with Perpendicular Magnetic Anisotropy

NASA Technical Reports Server (NTRS)

Skuza, J. R.; Clavero, C.; Yang, K.; Wincheski, B.; Lukaszew, R. A.

2009-01-01

L1(sub 0)-ordered FePd epitaxial thin films were prepared using dc magnetron sputter deposition on MgO (001) substrates. The films were grown with varying thickness and degree of chemical order to investigate the interplay between the microstructure, magnetic anisotropy, and magnetic domain structure. The experimentally measured domain size/period and magnetic anisotropy in this high perpendicular anisotropy system were found to be correlated following the analytical energy model proposed by Kooy and Enz that considers a delicate balance between the domain wall energy and the demagnetizing stray field energy.

Aluminium substitution in iron(II-III)-layered double hydroxides: Formation and cationic order

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ruby, Christian; Abdelmoula, Mustapha; Aissa, Rabha

The formation and the modifications of the structural properties of an aluminium-substituted iron(II-III)-layered double hydroxide (LDH) of formula Fe{sub 4}{sup II}Fe{sub (2-6y)}{sup III}Al{sub 6y}{sup III} (OH){sub 12} SO{sub 4}, 8H{sub 2}O are followed by pH titration curves, Moessbauer spectroscopy and high-resolution X-ray powder diffraction using synchrotron radiation. Rietveld refinements allow to build a structural model for hydroxysulphate green rust, GR(SO{sub 4}{sup 2-}), i.e. y=0, in which a bilayer of sulphate anions points to the Fe{sup 3+} species. A cationic order is proposed to occur in both GR(SO{sub 4}{sup 2-}) and aluminium-substituted hydroxysulphate green rust when y<0.08. Variation of the cellmore » parameters and a sharp decrease in average crystal size and anisotropy are detected for an aluminium content as low as y=0.01. The formation of Al-GR(SO{sub 4}{sup 2-}) is preceded by the successive precipitation of Fe{sup III} and Al{sup III} (oxy)hydroxides. Adsorption of more soluble Al{sup III} species onto the initially formed ferric oxyhydroxide may be responsible for this slowdown of crystal growth. Therefore, the insertion of low aluminium amount (y{approx}0.01) could be an interesting way for increasing the surface reactivity of iron(II-III) LDH that maintains constant the quantity of the reactive Fe{sup II} species of the material. - Graphical abstract: (a) Crystallographical structure of sulphated green rust: SO{sub 4}{sup 2-} point to the Fe{sup 3+} cations (red) that form an ordered array with the Fe{sup 2+} cations (green). (b) Width and asymmetry of the synchrotron XRD peaks increase rapidly when some Al{sup 3+} species substitute the Fe{sup 3+} cations; z is molar ratio Al{sup 3+}/Fe{sup 3+}.« less

Simultaneous occurrence of multiferroism and short-range magnetic order in DyFeO 3

DOE PAGES

Wang, Jinchen; Liu, Juanjuan; Sheng, Jieming; ...

2016-04-06

In this paper, we present a combined neutron scattering and magnetization study on the multiferroic DyFeO 3, which shows a very strong magnetoelectric effect. Applying magnetic field along the c axis, the weak ferromagnetic order of the Fe ions is quickly recovered from a spin reorientation transition, and the long-range antiferromagnetic order of Dy becomes a short-range one. We found that the short-range order concurs with the multiferroic phase and is responsible for its sizable hysteresis. In conclusion, our H-T phase diagram suggests that the strong magnetoelectric effect in DyFeO 3 has to be understood with not only the weakmore » ferromagnetism of Fe but also the short-range antiferromagnetic order of Dy.« less

Mixed nickel-gallium tellurides Ni{sub 3−x}GaTe{sub 2} as a matrix for incorporating magnetic cations: A Ni{sub 3−x}Fe{sub x}GaTe{sub 2} series

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kuznetsov, Alexey N., E-mail: alexei@inorg.chem.msu.ru; N.S. Kurnakov Institute of General and Inorganic Chemistry, RAS, Leninsky pr. 31, GSP-1, 119991 Moscow; Stroganova, Ekaterina A.

Using a high-temperature ampoule technique, a series of mixed nickel-iron-gallium metal-rich tellurides with layered structures, Ni{sub 3-x}Fe{sub x}GaTe{sub 2}, were prepared and characterized based on X-ray powder diffraction, energy-dispersive spectroscopy, and {sup 57}Fe Mössbauer spectroscopy data. These compounds may be regarded as a result of partial substitution of nickel by iron in the recently reported ternary Ni{sub 3-x}GaTe{sub 2} series, which are based on NiAs/Ni{sub 2}In type of structure. The compositional boundary for the substitution was found to be at x~1. According to the Mössbauer spectroscopy data, the substitution is not statistical, and iron atoms with the increase in xmore » tend to preferentially occupy those nickel positions that are partially vacant in the initial ternary compound. Magnetic measurements data for the Ni{sub 3-x}Fe{sub x}GaTe{sub 2} series show dramatic change in behavior from temperature-independent paramagnetic properties of the initial matrix to a low-temperature (~75 K) ferromagnetic ordering in the Ni{sub 2}FeGaTe{sub 2}. - Graphical abstract: Ordered substitution of nickel by iron in the Ni{sub 3−x}GaTe{sub 2} series leading to ferromagnetic ordering. - Highlights: • A series of Ni{sub 3−x}Fe{sub x}GaTe{sub 2} compounds were synthesized. • They adopt the NiAs/Ni{sub 2}In type of structure with ordered iron distribution. • The distribution of iron was studied using {sup 57}Fe Mössbauer spectroscopy. • An increase in iron content leads to the strong ferromagnetic coupling.« less

Thermally induced cation redistribution in Fe-bearing oxy-dravite and potential geothermometric implications

NASA Astrophysics Data System (ADS)

Bosi, Ferdinando; Skogby, Henrik; Hålenius, Ulf

2016-05-01

Iron-bearing oxy-dravite was thermally treated in air and hydrogen atmosphere at 800 °C to study potential changes in Fe, Mg and Al ordering over the octahedrally coordinated Y and Z sites and to explore possible applications to intersite geothermometry based on tourmaline. Overall, the experimental data (structural refinement, Mössbauer, infrared and optical absorption spectroscopy) show that heating Fe-bearing tourmalines results in disordering of Fe over Y and Z balanced by ordering of Mg at Y, whereas Al does not change appreciably. The Fe disorder depends on temperature, but less on redox conditions. The degree of Fe3+-Fe2+ reduction is limited despite strongly reducing conditions, indicating that the f O2 conditions do not exclusively control the Fe oxidation state at the present experimental conditions. Untreated and treated samples have similar short- and long-range crystal structures, which are explained by stable Al-extended clusters around the O1 and O3 sites. In contrast to the stable Al clusters that preclude any temperature-dependent Mg-Al order-disorder, there occurs Mg diffusion linked to temperature-dependent exchange with Fe. Ferric iron mainly resides around O2- at O1 rather than (OH)-, but its intersite disorder induced by thermal treatment indicates that Fe redistribution is the driving force for Mg-Fe exchange and that its diffusion rates are significant at these temperatures. With increasing temperature, Fe progressively disorders over Y and Z, whereas Mg orders at Y according to the order-disorder reaction: YFe + ZMg → ZFe + YMg. The presented findings are important for interpretation of the post-crystallization history of both tourmaline and tourmaline host rocks and imply that successful tourmaline geothermometers may be developed by thermal calibration of the Mg-Fe order-disorder reaction, whereas any thermometers based on Mg-Al disorder will be insensitive and involve large uncertainties.

Ferrocene functionalized nanoscale mixed-oxides as a potent phosphate adsorbent from the synthetic and real (Persian Gulf) waters.

PubMed

Arshadi, M; Zandi, H; Akbari, J; Shameli, A

2015-07-15

The application of covalently attached ferrocene groups to the aluminum-silicate nanoparticles (ASNPs) for phosphate (P) removal from the synthetic and real waters has been studied and the prepared nanomaterials were analyzed by XPS, EDS, BET, TEM, chemical analysis (CHN), FTIR, and ICP-AES. The immobilization of the ferrocene on the surface of the inorganic support (mixed oxides) can lead to reduce the drawback of the pristine ferrocene molecules which may have strong tendency to agglomerate into larger particles, resulting in the negative effect on both available active sites and catalyst performance. XPS of Fe ions evidenced that most of the active sites of the nano-adsorbent is in the form of Fe(III) ions at the surface. The heterogeneous Fe(III) ions were effective toward removal of phosphate. The contact time to obtain equilibrium for maximum adsorption of phosphate (100%) was found to be 120 min. The adsorption kinetics of P has been evaluated in terms of pseudo-first- and -second-order kinetics, and the Freundlich and Langmuir isotherm models have also been tested to the equilibrium adsorption results. The adsorption process was spontaneous and endothermic in nature and followed pseudo-second-order kinetic model. FTIR, EDS and XPS results confirmed the formation of Fe-O-P bond on the Si/Al@Fe surface after adsorption of P from aqueous media. The Si/Al@Fe displayed high reusability due to its high removal capacity after 10th adsorption-desorption runs. The proposed adsorbent could also be utilized to adsorb the P ions from the real sample (Persian Gulf water). The high removal capacity of P ions from the real water and the high levels of reusability confirmed the versatility of the heterogenized ferrocene groups on the ASNPs. Copyright © 2015 Elsevier Inc. All rights reserved.

Fabrication of ordered Fe–Ni nitride film with equiatomic Fe/Ni ratio

NASA Astrophysics Data System (ADS)

Takata, Fumiya; Ito, Keita; Suemasu, Takashi

2018-05-01

We successfully grew a single-phase tetragonal FeNiN film with an equiatomic ratio of Fe, Ni, and N on a MgO(001) substrate by molecular beam epitaxy. We then demonstrated the formation of Fe2Ni2N films by extracting N atoms from the FeNiN film. These results suggested that Fe and Ni atoms in the Fe2Ni2N film were L10-ordered along the film plane direction because of the a-axis orientation growth of the FeNiN film on the MgO(001) substrate.

Heat capacities of synthetic hedenbergite, ferrobustamite and CaFeSi2O6 glass

USGS Publications Warehouse

Haselton, H.T.; Robie, R.A.; Hemingway, B.S.

1987-01-01

Heat capacities have been measured for synthetic hedenbergite (9-647 K), ferrobustamite (5-746 K) and CaFeSi2O6 glass (6-380 K) by low-temperature adiabatic and differential scanning calorimetry. The heat capacity of each of these structural forms of CaFeSiO6 exhibits anomalous behavior at low temperatures. The X-peak in the hedenbergite heat-capacity curve at 34.5 K is due to antiferromagnetic ordering of the Fe2+ ions. Ferrobustamite has a bump in its heat-capacity curve at temperatures less than 20 K, which could be due to weak cooperative magnetic ordering or to a Schottky anomaly. Surprisingly, a broad peak with a maximum at 68 K is present in the heat-capacity curve of the glass. If this maximum, which occurs at a higher temperature than in hedenbergite is caused by magnetic ordering, it could indicate that the range of distortions of the iron sites in the glass is quite small and that coupling between iron atoms is stronger in the glass than in the edge-shared octahedral chains of hedenbergite. The standard entropy change, So298.15 - So0, is 174.2 ?? 0.3, 180.5 ?? 0.3 and 185.7 ?? 0.4 J/mol??K for hedenbergite, ferrobustamite and CaFeSi2O6 glass, respectively. Ferrobustamite is partially disordered in Ca-Fe distribution at high temperatures, but the dependence of the configuratonal entropy on temperature cannot be evaluated due to a lack of information. At high temperatures (298-1600 K), the heat capacity of hedenbergite may be represented by the equation Cop(J/mol??K) = 3l0.46 + 0.01257T-2039.93T -1 2 - 1.84604?? l06T-2 and the heat capacity of ferrobustamite may be represented by Cop(J/mol??K) = 403.83-0.04444T+ 1.597?? 10-5T2-3757.3T -1 2. ?? 1987.

Magnetic order and spin dynamics in La2O2Fe2OSe2 probed by 57Fe Mössbauer, 139La NMR, and muon-spin relaxation spectroscopy

NASA Astrophysics Data System (ADS)

Günther, M.; Kamusella, S.; Sarkar, R.; Goltz, T.; Luetkens, H.; Pascua, G.; Do, S.-H.; Choi, K.-Y.; Zhou, H. D.; Blum, C. G. F.; Wurmehl, S.; Büchner, B.; Klauss, H.-H.

2014-11-01

We present a detailed local probe study of the magnetic order in the oxychalcogenide La2O2Fe2OSe2 utilizing 57Fe Mössbauer, 139La NMR, and muon-spin relaxation spectroscopy. This system can be regarded as an insulating reference system of the Fe arsenide and chalcogenide superconductors. From the combination of the local probe techniques we identify a noncollinear magnetic structure similar to Sr2F2Fe2OS2 . The analysis of the magnetic order parameter yields an ordering temperature TN=90.1 K and a critical exponent of β =0.133 , which is close to the two-dimensional Ising universality class as reported in the related oxychalcogenide family.

Characterization of Cu buffer layers for growth of L10-FeNi thin films

NASA Astrophysics Data System (ADS)

Mizuguchi, M.; Sekiya, S.; Takanashi, K.

2010-05-01

A Cu(001) layer was fabricated on a Au(001) layer to investigate the use of Cu as a buffer layer for growing L10-FeNi thin films. The epitaxial growth of a Cu buffer layer was observed using reflection high-energy electron diffraction. The flatness of the layer improved drastically with an increase in the substrate temperature although the layer was an alloy (AuCu3). An FeNi thin film was epitaxially grown on the AuCu3 buffer layer by alternate monatomic layer deposition and the formation of an L10-FeNi ordered alloy was expected. The AuCu3 buffer layer is thus a promising candidate material for the growth of L10-FeNi thin films.

Crossover from Commensurate to Incommensurate Antiferromagnetism in Stoichiometric NaFeAs Revealed by Single-Crystal 23Na,75As-NMR Experiments

NASA Astrophysics Data System (ADS)

Kitagawa, Kentaro; Mezaki, Yuji; Matsubayashi, Kazuyuki; Uwatoko, Yoshiya; Takigawa, Masashi

2011-03-01

We report the results of 23Na and 75As nuclear magnetic resonance (NMR) experiments on a self-flux grown high-quality single crystal of stoichiometric NaFeAs. The NMR spectra reveal a tetragonal to twinned-orthorhombic structural phase transition at TO = 57 K and an antiferromagnetic (AF) transition at TAF = 45 K. The divergent behavior of nuclear relaxation rate near TAF shows significant anisotropy, indicating that the critical slowing down of stripe-type AF fluctuations are strongly anisotropic in spin space. The NMR spectra at sufficiently low temperatures consist of sharp peaks showing a commensurate stripe AF order with a small moment of ˜0.3 μB. However, the spectra just below TAF exhibit a highly asymmetric broadening pointing to an incommensurate modulation. The commensurate-incommensurate crossover in NaFeAs shows a certain similarity to the behavior of SrFe2As2 under high pressure.

An efficient solid-state synthesis of fluorescent surface carboxylated carbon dots derived from C60 as a label-free probe for iron ions in living cells.

PubMed

Lan, Jing; Liu, Chunfang; Gao, Mingxuan; Huang, Chengzhi

2015-11-01

In order to achieve the simple, easily repeated, and large scale preparation of fluorescent CDs, a new solid-state synthesis (SSS) approach was developed by calcining the mixture of fullerenes (C60) and solid sodium hydroxide. The cage of fullerenes could be opened and the hydroxyl and carboxyl were successfully introduced in the presence of sodium hydroxide under high temperature. The as-prepared surface carboxylated CDs possess many good properties, such as high water solubility, good photostability, salt tolerance, and nontoxicity. Especially, the fluorescence of CDs could be highly quenched by Fe(3+) because of the strong interaction of hydroxyl or carboxyl on the as-obtained CDs with Fe(3+), which realized a sensitive detection of Fe(3+) in the linear range of 0.02-0.6 μmol/L. What is more, we further applied the obtained CDs into the intracellular imaging of Fe(3+). Copyright © 2015 Elsevier B.V. All rights reserved.

Frustration relieved ferrimagnetism in novel A- and B-site-ordered quadruple perovskite.

PubMed

Chen, Wei-tin; Mizumaki, Masaichiro; Saito, Takashi; Shimakawa, Yuichi

2013-07-28

A novel A- and B-site-ordered quadruple perovskite CaCu3Fe2Sb2O12 was obtained and it shows ferrimagnetism below about 170 K. The B-site Fe spin sublattice adapts a tetrahedral framework in a cubic structure and the Fe(3+)-Fe(3+) antiferromagnetic interaction can result in a geometrical spin frustration as seen in a simple perovskite Ca2FeSbO6. With the introduction of Cu(2+) into the A' site, the antiferromagnetic spin frustration is relieved by the strong Cu(2+)-Fe(3+) interaction, and a ferrimagnetic ordering appears at a much higher temperature than the spin-glass transition temperature.

Structural and Magnetic Phase Coexistence in Oxygen Deficient Perovskites (Sr,Ca)FeO 2 . 5 + δ

NASA Astrophysics Data System (ADS)

Carlo, J. P.; Evans, M. E.; Anczarski, J. A.; Ock, J.; Boyd, K.; Pollichemi, J. R.; Leahy, I. A.; Vogel, W.; Viescas, A. J.; Papaefthymiou, G. C.

A variety of compounds crystallize into perovskite and similar structures, making them versatile laboratories for many phenomena and applications, including multiferroicity, superconductivity, and photovoltaics. Oxygen-deficient perovskites ABOx have attracted interest for use in fuel cells and related applications due to high oxygen mobility and the possibility of charge disproportionation. Vast chemical flexibility is obtained through reductions in lattice symmetry and rotation/distortion of the BO6 octahedra, as well as ordering of oxygen vacancies. We have synthesized and studied the structural and magnetic properties of oxygen-deficient perovskites (Sr,Ca)FeO2 . 5 + δ using x-ray diffraction and Mossbauer spectroscopy. While the ideal perovskite has δ = 0.5, this requires Fe4+, and hence strongly oxidizing environments. When grown in air, Fe3+ is favored, yielding δ ~ 0. SrFeO2 . 5 + δ exhibits cubic symmetry and paramagnetism at 300K, but CaFeO2 . 5 + δ crystallizes into the orthorhombic brownmillerite structure, and is magnetically ordered at 300K. In the doped intermediaries we find coexistence of cubic/paramagnetic and orthorhombic/magnetic phases over a wide range of Ca content. Financial support from the Villanova Undergraduate Research Fellowship program and the Research Corporation for Science Advancement.

Oxidation of iopamidol with ferrate (Fe(VI)): Kinetics and formation of toxic iodinated disinfection by-products.

PubMed

Dong, Huiyu; Qiang, Zhimin; Liu, Shaogang; Li, Jin; Yu, Jianwei; Qu, Jiuhui

2018-03-01

Presence of iodinated X-ray contrast media (ICMs) in source water is of high concern, because of their potential to form highly toxic iodinated disinfection by-products (I-DBPs). This study investigated kinetics, mechanisms and products for oxidation of one ICMs, iopamidol (IPM) by ferrate (Fe(VI)). The obtained apparent second-order rate constants for oxidation of IPM by Fe(VI) ranged from 0.7 M -1  s -1 to 74.6 M -1  s -1  at pH 6.0-10.0, which were highly dependent on pH. It was found that the oxidation of IPM by Fe(VI) led to the formation of highly toxic I-DBPs. Iodoform (IF), iodoacetic acid and triiodoacetic acid formations were observed during the oxidation and IF dominated the formed I-DBPs. The formation of I-DBPs was also governed by pH and the maximum formation of I-DBPs occurred at pH 9.0. Transformation pathways of IPM by Fe(VI) oxidation were speculated to proceed through deiodination, amide hydrolysis and oxidation of amine reactions. The deiodination reaction during the oxidation of IPM by Fe(VI) contributed to the formation of I-DBPs. The formation of I-DBPs during the oxidation of IPM by Fe(VI) was significantly higher than those of iohexol, diatrizoate and iopromide, which was consistent with the lowest molecular orbital energy gap of IPM. Although Fe(VI) is considered as a green oxidant, the formation of highly toxic I-DBPs during the oxidation of IPM should receive great attention. Copyright © 2017 Elsevier Ltd. All rights reserved.

A simple way to prepare Pd/Fe₃O₄/polypyrrole hollow capsules and their applications in catalysis.

PubMed

Yao, Tongjie; Zuo, Quan; Wang, Hao; Wu, Jie; Xin, Baifu; Cui, Fang; Cui, Tieyu

2015-07-15

Preparation of catalysts with good catalytic activity and high stability, together with magnetic separation property, in a simple way is highly desirable. In this paper, we reported a novel strategy to construct magnetic recyclable hollow capsules with Pd and Fe3O4 nanoparticles embedded in polypyrrole (PPy) shell via only two steps: first, synthesization of Pd nanoparticles, preparation of Fe3O4 nanoparticles, and formation of PPy shell were finished in one-step on the surface of polystyrene (PS) nanospheres; then, the PS core was selectively removed by tetrahydrofuran. The Pd/Fe3O4/PPy hollow capsules exhibited good catalytic property in reduction of 4-nitrophenol with NaBH4 as reducing agent, and the reaction rate constants were calculated through pseudo-first-order reaction equation. Due to incorporation of Fe3O4 nanoparticles, the catalysts could be quickly separated from the reaction solution by magnet and reused without obvious catalytic loss. Besides catalytic property and reusability, their stability was also examined by HNO3 etching experiment. Compared with bare Pd and Fe3O4 nanoparticles, the stability of both Pd and Fe3O4 nanoparticles in hollow capsules was largely improved owing to the protection of PPy shell. The good catalytic performance, ease of separation, high stability and especially a simple preparation procedure, made Pd/Fe3O4/PPy hollow capsules highly promising candidates for diverse applications. Copyright © 2015 Elsevier Inc. All rights reserved.

Enhanced charge ordering transition in doped CaFeO3 through steric templating

NASA Astrophysics Data System (ADS)

Jiang, Lai; Saldana-Greco, Diomedes; Schick, Joseph T.; Rappe, Andrew M.

2014-06-01

We report a density functional theory investigation of B-site doped CaFeO3, a prototypical charge ordered perovskite. At 290 K, CaFeO3 undergoes a metal-insulator transition and a charge disproportionation reaction 2Fe4+→Fe5++Fe3+. We observe that when Zr dopants occupy a (001) layer, the band gap of the resulting solid solution increases to 0.93 eV due to a two-dimensional Jahn-Teller-type distortion, where FeO6 cages on the xy plane elongate along x and y alternatively between neighboring Fe sites. Furthermore, we show that the rock-salt ordering of the Fe5+ and Fe3+ cations can be enhanced when the B-site dopants are arranged in a (111) plane due to a collective steric effect that facilitates the size discrepancy between the Fe5+O6 and Fe3+O6 octahedra and therefore gives rise to a larger band gap. The enhanced charge disproportionation in these solid solutions is verified by rigorously calculating the oxidation states of the Fe cations with different octahedral cage sizes. We therefore predict that the corresponding transition temperature will increase due to the enhanced charge ordering and larger band gap. The compositional, structural, and electrical relationships exploited in this paper can be extended to a variety of perovskites and nonperovskite oxides, providing guidance in the structural manipulation of electrical properties of functional materials.

Quantitative transmission electron microscopy analysis of multi-variant grains in present L1{sub 0}-FePt based heat assisted magnetic recording media

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ho, Hoan, E-mail: hoan.ho@wdc.com; Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213; Zhu, Jingxi, E-mail: jingxiz@andrew.cmu.edu

2014-11-21

We present a study on atomic ordering within individual grains in granular L1{sub 0}-FePt thin films using transmission electron microscopy techniques. The film, used as a medium for heat assisted magnetic recording, consists of a single layer of FePt grains separated by non-magnetic grain boundaries and is grown on an MgO underlayer. Using convergent-beam techniques, diffraction patterns of individual grains are obtained for a large number of crystallites. The study found that although the majority of grains are ordered in the perpendicular direction, more than 15% of them are multi-variant, or of in-plane c-axis orientation, or disordered fcc. It wasmore » also found that these multi-variant and in-plane grains have always grown across MgO grain boundaries separating two or more MgO grains of the underlayer. The in-plane ordered portion within a multi-variant L1{sub 0}-FePt grain always lacks atomic coherence with the MgO directly underneath it, whereas, the perpendicularly ordered portion is always coherent with the underlying MgO grain. Since the existence of multi-variant and in-plane ordered grains are severely detrimental to high density data storage capability, the understanding of their formation mechanism obtained here should make a significant impact on the future development of hard disk drive technology.« less

Leachable particulate iron in the Columbia River, estuary, and near-field plume

NASA Astrophysics Data System (ADS)

Lippiatt, Sherry M.; Brown, Matthew T.; Lohan, Maeve C.; Berger, Carolyn J. M.; Bruland, Kenneth W.

2010-03-01

This study examines the distribution of leachable particulate iron (Fe) in the Columbia River, estuary, and near-field plume. Surface samples were collected during late spring and summer of 2004-2006 as part of four River Influence on Shelf Ecosystems (RISE) cruises. Tidal amplitude and river flow are the primary factors influencing the estuary leachable particulate Fe concentrations, with greater values during high flow and/or spring tides. Near the mouth of the estuary, leachable particulate Fe [defined as the particulate Fe solubilized with a 25% acetic acid (pH 2) leach containing a weak reducing agent to reduce Fe oxyhydroxides and a short heating step to access intracellular Fe] averaged 770 nM during either spring tide or high flow, compared to 320 nM during neap tide, low flow conditions. In the near-field Columbia River plume, elevated leachable particulate Fe concentrations occur during spring tides and/or higher river flow, with resuspended shelf sediment as an additional source to the plume during periods of coastal upwelling and spring tides. Near-field plume concentrations of leachable particulate Fe (at a salinity of 20) averaged 660 nM during either spring tide or high flow, compared to 300 nM during neap tide, low flow conditions. Regardless of tidal amplitude and river flow, leachable particulate Fe concentrations in both the river/estuary and near-field plume are consistently one to two orders of magnitude greater than dissolved Fe concentrations. The Columbia River is an important source of reactive Fe to the productive coastal waters off Oregon and Washington, and leachable particulate Fe is available for solubilization following biological drawdown of the dissolved phase. Elevated leachable Fe concentrations allow coastal waters influenced by the Columbia River plume to remain Fe-replete and support phytoplankton production during the spring and summer seasons.

Phosphorus losses from agricultural land to natural waters are reduced by immobilization in iron-rich sediments of drainage ditches.

PubMed

Baken, Stijn; Verbeeck, Mieke; Verheyen, Dries; Diels, Jan; Smolders, Erik

2015-03-15

Redox reactions involving iron (Fe) strongly affect the mobility of phosphorus (P) and its migration from agricultural land to freshwater. We studied the transfer of P from groundwater to open drainage ditches in an area where, due to Fe(II) rich groundwater, the sediments of these ditches contain accumulated Fe oxyhydroxides. The average P concentrations in the groundwater feeding two out of three studied drainage ditches exceeded environmental limits for freshwaters by factors 11 and 16, but after passing through the Fe-rich sediments, the P concentrations in the ditch water were below these limits. In order to identify the processes which govern Fe and P mobility in these systems, we used diffusive equilibration in thin films (DET) to measure the vertical concentration profiles of P and Fe in the sediment pore water and in the ditchwater. The Fe concentrations in the sediment pore water ranged between 10 and 200 mg L(-1) and exceeded those in the inflowing groundwater by approximately one order of magnitude, due to reductive dissolution of Fe oxyhydroxides in the sediment. The dissolved P concentrations only marginally increased between groundwater and sediment pore water. In the poorly mixed ditchwater, the dissolved Fe concentrations decreased towards the water surface due to oxidative precipitation of fresh Fe oxyhydroxides, and the P concentrations decreased more sharply than those of Fe. These observations support the view that the dynamics of Fe and P are governed by reduction reactions in the sediment and by oxidation reactions in the ditchwater. In the sediment, reductive dissolution of P-containing Fe oxyhydroxides causes more efficient solubilization of Fe than of P, likely because P is buffered by adsorption on residual Fe oxyhydroxides. Conversely, in the ditchwater, oxidative precipitation causes more efficient immobilization of P than of Fe, due to ferric phosphate formation. The combination of these processes yields a natural and highly efficient sink for P. It is concluded that, in Fe-rich systems, the fate of P at the sediment-water interface is determined by reduction and oxidation of Fe. Copyright © 2015 Elsevier Ltd. All rights reserved.

X-Ray Absorption Spectroscopy of Fe-Substituted Allophane and Imogolite

NASA Astrophysics Data System (ADS)

Baker, L. L.; Strawn, D. G.; Nickerson, R. D.; McDaniel, P.

2011-12-01

Martian rocks and sediments contain weathering products including clay minerals formed as a result of interaction between rocks and water, and these materials can act as important indicators of past surface conditions on Mars. Weathering of terrestrial volcanic rocks similar to those on Mars produces nano-sized, variably hydrated aluminosilicate and iron oxide minerals, including allophane, imogolite, halloysite, hisingerite, and ferrihydrite. The nanoaluminosilicates can contain isomorphically substituted Fe, which may affect their spectral and physical properties as well as their eventual recrystallization products. Detection and quantification of such minerals in natural environments on Earth is difficult due to their variable chemical composition and lack of long-range crystalline order. Their accurate detection and quantification on Mars requires a better understanding of how composition affects their spectral properties and evolution to more crystalline phases. Aluminosilicate nanoparticles of varying composition were synthesized with isomorphically substituted Fe at Fe:Al ratios of 1:100. Allophanes were synthesized with Al:Si ratios of 2:1, 1:1, and 1:3. The substituted Fe was probed using Fe K-edge X-ray absorption fine structure spectroscopy (XAFS). The XAFS spectrum contains information about the molecular environment surrounding the target atom, and is an ideal technique for studying poorly crystalline materials that are difficult to characterize using bulk methods such as XRD. The near-edge (XANES) and extended (EXAFS) portions of the XAFS spectrum were examined, and allophane backscattering paths were fit using coordinates for a modified nanoball model (1). XANES spectra rule out ferrihydrite in the synthetic samples, suggesting all Fe was incorporated into the aluminosilicate structure. The XAFS results suggest that Fe substituted into the allophane structure is present as Fe(III) in octahedral coordination in a well-ordered sheet. Some Fe substitution in tetrahedral sites occurs in allophane with Al:Si = 2:1, but not in higher-Si compositions. These results support the nanoball model for allophane (1) based on a rolled octahedral sheet and indicate that sheet is well ordered. They do not support proposed models of an incomplete octahedral sheet in high-Si allophanes. Analysis of Fe distribution suggests considerable Fe clustering in the octahedral sheet which increases with sample aging. This clustering could lead to eventual nucleation of a separate Fe (oxyhydr)oxide phase. (1) Creton et al. (2008) J Phys Chem C 112, 358.

Removal of thallium from aqueous solutions using Fe-Mn binary oxides.

PubMed

Li, Huosheng; Chen, Yongheng; Long, Jianyou; Li, Xiuwan; Jiang, Daqian; Zhang, Ping; Qi, Jianying; Huang, Xuexia; Liu, Juan; Xu, Ruibing; Gong, Jian

2017-09-15

In this study, Fe-Mn binary oxides, which harbor the strong oxidative power of manganese dioxide and the high adsorption capacity of iron oxides, were synthesized for Tl(I) removal using a concurrent chemical oxidation and precipitation method. The adsorption of Tl onto the Fe-Mn adsorbent was fast, effective, and selective, with equilibrium sorption reaching over 95% under a broad operating pH (3-12), and high ionic strength (0.1-0.5mol/L). The adsorption can be well fitted with both Langmuir and Freundlich isotherms, and the kinetics can be well described by the pseudo-second-order model. Fourier transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS) spectra suggest that surface complexation, oxidation and precipitation were the main mechanisms for the removal of Tl. This study shows that the Fe-Mn binary oxides could be a promising adsorbent for Tl removal. Copyright © 2017 Elsevier B.V. All rights reserved.

Insulating and metallic spin glass in K xFe 2-δ-yNi ySe 2 (0.06 ≤ y ≤ 1.44 ) single crystals

DOE PAGES

Ryu, Hyejin; Abeykoon, Milinda; Wang, Kefeng; ...

2015-05-04

We report electron doping effects by Ni in K xFe 2-δ-yNi ySe₂ (0.06 ≤ y ≤ 1.44) single crystal alloys. A rich ground state phase diagram is observed. Thus, a small amount of Ni (~ 4%) suppressed superconductivity below 1.8 K, inducing insulating spin glass magnetic ground state for higher Ni content. With further Ni substitution, metallic resistivity is restored. For high Ni concentration in the lattice the unit cell symmetry is high symmetry I4/ mmm with no phase separation whereas both I4/ m + I4/ mmm space groups were detected in the phase separated crystals when concentration of Nimore » < Fe. The absence of superconductivity coincides with the absence of crystalline Fe vacancy order.« less

Coexistence of short- and long-range ferromagnetic order in nanocrystalline Fe2Mn1-xCuxAl (x=0.0, 0.1 and 0.3) synthesized by high-energy ball milling

NASA Astrophysics Data System (ADS)

Thanh, Tran Dang; Nanto, Dwi; Tuyen, Ngo Thi Uyen; Nan, Wen-Zhe; Yu, YiKyung; Tartakovsky, Daniel M.; Yu, S. C.

2015-11-01

In this work, we prepared nanocrystalline Fe2Mn1-xCuxAl (x=0.0, 0.1 and 0.3) powders by the high energy ball milling technique, and then studied their critical properties. Our analysis reveals that the increase of Cu-doping concentration (up to x=0.3) in these powders leads to a gradual increase of the ferromagnetic-paramagnetic transition temperature from 406 to 452 K. The Banerjee criterion suggests that all the samples considered undergo a second-order phase transition. A modified Arrott plot and scaling analysis indicate that the critical exponents (β=0.419 and 0.442, γ=1.082 and 1.116 for x=0.0 and 0.1, respectively) are located in between those expected for the 3D-Heisenberg and the mean-field models; the values of β=0.495 and γ=1.046 for x=0.3 sample are very close to those of the mean-field model. These features reveal the coexistence of the short- and long-range ferromagnetic order in the nanocrystalline Fe2Mn1-xCuxAl powders. Particularly, as the concentration of Cu increases, values of the critical exponent shift towards those of the mean-field model. Such results prove the Cu doping favors establishing a long-range ferromagnetic order.

Ab initio Studies of Magnetism in the Iron Chalcogenides FeTe and FeSe

NASA Astrophysics Data System (ADS)

Hirayama, Motoaki; Misawa, Takahiro; Miyake, Takashi; Imada, Masatoshi

2015-09-01

The iron chalcogenides FeTe and FeSe belong to the family of iron-based superconductors. We study the magnetism in these compounds in the normal state using the ab initio downfolding scheme developed for strongly correlated electron systems. In deriving ab initio low-energy effective models, we employ the constrained GW method to eliminate the double counting of electron correlations originating from the exchange correlations already taken into account in the density functional theory. By solving the derived ab initio effective models, we reveal that the elimination of the double counting is important in reproducing the bicollinear antiferromagnetic order in FeTe, as is observed in experiments. We also show that the elimination of the double counting induces a unique degeneracy of several magnetic orders in FeSe, which may explain the absence of the magnetic ordering. We discuss the relationship between the degeneracy and the recently found puzzling phenomena in FeSe as well as the magnetic ordering found under pressure.

Ferrimagnetism in EuFe4Sb12 due to the interplay of f-electron moments and a nearly ferromagnetic host

DOE Office of Scientific and Technical Information (OSTI.GOV)

Krishnamurthy, Vemuru; Lang, J. C.; Haskel, D.

2007-03-01

We combine x-ray magnetic circular dichroism spectroscopy at Fe L-2,L-3 edges, at Eu M-4,M-5 edges, x-ray absorption spectroscopy (XAS) investigation of Eu valence, and local spin density calculations, to show that the filled skutterudite Eu0.95Fe4Sb12 is a ferrimagnet in which the Fe 3d moment and the Eu2+ 4f moment are magnetically ordered with dominant antiferromagnetic coupling. From Eu L-3 edge XAS, we find that about 13% of the Eu have a formal valence of 3+. We ascribe the origin of ferrimagnetism at a relatively high transition temperature T-C of 85 K in Eu0.95Fe4Sb12 to f-electron interaction with the nearly ferromagneticmore » [Fe4Sb12](2.2-) host lattice.« less

Room temperature ferromagnetism in Fe-doped semiconductor ZrS2 single crystals

NASA Astrophysics Data System (ADS)

Muhammad, Zahir; Lv, Haifeng; Wu, Chuanqiang; Habib, Muhammad; Rehman, Zia ur; Khan, Rashid; Chen, Shuangming; Wu, Xiaojun; Song, Li

2018-04-01

Two dimensional (2D) layered magnetic materials have obtained much attention due to their intriguing properties with a potential application in the field of spintronics. Herein, room-temperature ferromagnetism with 0.2 emu g‑1 magnetic moment is realized in Fe-doped ZrS2 single crystals of millimeter size, in comparison with diamagnetic behaviour in ZrS2. The electron paramagnetic resonance spectroscopy reveals that 5.2wt% Fe-doping ZrS2 crystal exhibit high spin value of g-factor about 3.57 at room temperature also confirmed this evidence, due to the unpaired electrons created by doped Fe atoms. First principle static electronic and magnetic calculations further confirm the increased stability of long range ferromagnetic ordering and enhanced magnetic moment in Fe-doped ZrS2, originating from the Fe spin polarized electron near the Fermi level.

Uniform 2 nm gold nanoparticles supported on iron oxides as active catalysts for CO oxidation reaction: structure-activity relationship

NASA Astrophysics Data System (ADS)

Guo, Yu; Gu, Dong; Jin, Zhao; Du, Pei-Pei; Si, Rui; Tao, Jing; Xu, Wen-Qian; Huang, Yu-Ying; Senanayake, Sanjaya; Song, Qi-Sheng; Jia, Chun-Jiang; Schüth, Ferdi

2015-03-01

Uniform Au nanoparticles (~2 nm) with narrow size-distribution (standard deviation: 0.5-0.6 nm) supported on both hydroxylated (Fe_OH) and dehydrated iron oxide (Fe_O) have been prepared by either deposition-precipitation (DP) or colloidal-deposition (CD) methods. Different structural and textural characterizations were applied to the dried, calcined and used gold-iron oxide samples. Transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) showed high homogeneity in the supported Au nanoparticles. The ex situ and in situ X-ray absorption fine structure (XAFS) characterization monitored the electronic and short-range local structure of active gold species. The synchrotron-based in situ X-ray diffraction (XRD), together with the corresponding temperature-programmed reduction by hydrogen (H2-TPR), indicated a structural evolution of the iron-oxide supports, correlating to their reducibility. An inverse order of catalytic activity between DP (Au/Fe_OH < Au/Fe_O) and CD (Au/Fe_OH > Au/Fe_O) was observed. Effective gold-support interaction results in a high activity for gold nanoparticles, locally generated by the sintering of dispersed Au atoms on the oxide support in the DP synthesis, while a hydroxylated surface favors the reactivity of externally introduced Au nanoparticles on Fe_OH support for the CD approach. This work reveals why differences in the synthetic protocol translate to differences in the catalytic performance of Au/FeOx catalysts with very similar structural characteristics in CO oxidation.

Uniform 2 nm gold nanoparticles supported on iron oxides as active catalysts for CO oxidation reaction: Structure-activity relationship

DOE PAGES

Guo, Yu; Senanayake, Sanjaya; Gu, Dong; ...

2015-01-12

Uniform Au nanoparticles (~2 nm) with narrow size-distribution (standard deviation: 0.5–0.6 nm) supported on both hydroxylated (Fe_OH) and dehydrated iron oxide (Fe_O) have been prepared by either deposition-precipitation (DP) or colloidal-deposition (CD) methods. Different structural and textural characterizations were applied to the dried, calcined and used gold-iron oxide samples. The transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) described the high homogeneity in the supported Au nanoparticles. The ex-situ and in-situ X-ray absorption fine structure (XAFS) characterization monitored the electronic and short-range local structure of active gold species. The synchrotron-based in-situ X-ray diffraction (XRD), together with the corresponding temperature-programmed reductionmore » by hydrogen (H₂-TPR), indicated a structural evolution of the iron-oxide supports, correlating to their reducibility. An inverse order of catalytic activity between DP (Au/Fe_OH < Au/Fe_O) and CD (Au/Fe_OH > Au/Fe_O) was observed. Effective gold-support interaction results in a high activity for gold nanoparticles, locally generated by the sintering of dispersed Au atoms on the oxide support in the DP synthesis, while a hydroxylated surface favors the reactivity of externally introduced Au nanoparticles on Fe_OH support for the CD approach. This work reveals why differences in the synthetic protocol translate to differences in the catalytic performance of Au/FeO x catalysts with very similar structural characteristics in CO oxidation.« less

Tunable (δπ, δπ)-Type Antiferromagnetic Order in α-Fe(Te,Se) Superconductors

NASA Astrophysics Data System (ADS)

Bao, Wei; Qiu, Y.; Huang, Q.; Green, M. A.; Zajdel, P.; Fitzsimmons, M. R.; Zhernenkov, M.; Chang, S.; Fang, Minghu; Qian, B.; Vehstedt, E. K.; Yang, Jinhu; Pham, H. M.; Spinu, L.; Mao, Z. Q.

2009-06-01

The new α-Fe(Te,Se) superconductors share the common iron building block and ferminology with the LaFeAsO and BaFe2As2 families of superconductors. In contrast with the predicted commensurate spin-density-wave order at the nesting wave vector (π, 0), a completely different magnetic order with a composition tunable propagation vector (δπ, δπ) was determined for the parent compound Fe1+yTe in this powder and single-crystal neutron diffraction study. The new antiferromagnetic order survives as a short-range one even in the highest TC sample. An alternative to the prevailing nesting Fermi surface mechanism is required to understand the latest family of ferrous superconductors.

Local configurations and atomic intermixing in as-quenched and annealed Fe1-xCrx and Fe1-xMox ribbons

NASA Astrophysics Data System (ADS)

Stanciu, A. E.; Greculeasa, S. G.; Bartha, C.; Schinteie, G.; Palade, P.; Kuncser, A.; Leca, A.; Filoti, G.; Birsan, A.; Crisan, O.; Kuncser, V.

2018-04-01

Local atomic configuration, phase composition and atomic intermixing in Fe-rich Fe1-xCrx and Fe1-xMox ribbons (x = 0.05, 0.10, 0.15), of potential interest for high-temperature applications and nuclear devices, are investigated in this study in relation to specific processing and annealing routes. The Fe-based thin ribbons have been prepared by induction melting, followed by melt spinning and further annealed in He at temperatures up to 1250 °C. The complex structural, compositional and atomic configuration characterisation has been performed by means of X-ray diffraction (XRD), transmission Mössbauer spectroscopy and differential scanning calorimetry (TG-DSC). The XRD analysis indicates the formation of the desired solid solutions with body-centred cubic (bcc) structure in the as-quenched state. The Mössbauer spectroscopy results have been analysed in terms of the two-shell model. The distribution of Cr/Mo atoms in the first two coordination spheres is not homogeneous, especially after annealing, as supported by the short-range order parameters. In addition, high-temperature annealing treatments give rise to oxidation of Fe (to haematite, maghemite and magnetite) at the surface of the ribbons. Fe1-xCrx alloys are structurally more stable than the Mo counterpart under annealing at 700 °C. Annealing at 1250 °C in He enhances drastically the Cr clustering around Fe nuclei.

Calculation of Oxygen Fugacity in High Pressure Metal-Silicate Experiments and Comparison to Standard Approaches

NASA Technical Reports Server (NTRS)

Righter, K.; Ghiorso, M.

2009-01-01

Calculation of oxygen fugacity in high pressure and temperature experiments in metal-silicate systems is usually approximated by the ratio of Fe in the metal and FeO in the silicate melt: (Delta)IW=2*log(X(sub Fe)/X(sub FeO)), where IW is the iron-wustite reference oxygen buffer. Although this is a quick and easy calculation to make, it has been applied to a huge variety of metallic (Fe- Ni-S-C-O-Si systems) and silicate liquids (SiO2, Al2O3, TiO2, FeO, MgO, CaO, Na2O, K2O systems). This approach has surely led to values that have little meaning, yet are applied with great confidence, for example, to a terrestrial mantle at "IW-2". Although fO2 can be circumvented in some cases by consideration of Fe-M distribution coefficient, these do not eliminate the effects of alloy or silicate liquid compositional variation, or the specific chemical effects of S in the silicate liquid, for example. In order to address the issue of what the actual value of fO2 is in any given experiment, we have calculated fO2 from the equilibria 2Fe (metal) + SiO2 (liq) + O2 = Fe2SiO4 (liq).

Polyphenolic compounds appear to limit the nutritional benefit of biofortified higher iron black bean (Phaseolus vulgaris L.)

PubMed Central

2014-01-01

Background Our objective was to determine if a biofortified variety of black bean can provide more bioavailable-iron (Fe) than a standard variety. Two lines of black beans (Phaseolus-vulgaris L.), a standard (DOR500; 59μg Fe/g) and biofortified (MIB465; 88μg Fe/g) were used. The DOR500 is a common commercial variety, and the MIB465 is a line developed for higher-Fe content. Given the high prevalence of Fe-deficiency anemia worldwide, it is important to determine if Fe-biofortified black beans can provide more absorbable-Fe. Methods Black bean based diets were formulated to meet the nutrient requirements for the broiler (Gallus-gallus) except for Fe (dietary Fe-concentrations were 39.4±0.2 and 52.9±0.9 mg/kg diet, standard vs. biofortified, respectively). Birds (n=14) were fed the diets for 6-weeks. Hemoglobin-(Hb), liver-ferritin and Fe-related transporter/enzyme gene-expression were measured. Hemoglobin-maintenance-efficiency and total-body-Hb-Fe values were used to estimate Fe-bioavailability. Results Hemoglobin-maintenance-efficiency values were higher (P<0.05) in the group consuming the standard-Fe beans on days 14, 21 and 28; indicating a compensatory response to lower dietary-Fe. Final total-Hb-Fe body content was higher in the biofortified vs. the standard group (26.6±0.9 and 24.4±0.8 mg, respectively; P<0.05). There were no differences in liver-ferritin or in expression of DMT-1, Dcyt-B, and ferroportin. In-vitro Fe-bioavailability assessment indicated very low Fe-bioavailability from both diets and between the two bean varieties (P>0.05). Such extremely-low in-vitro Fe-bioavailability measurement is indicative of the presence of high levels of polyphenolic-compounds that may inhibit Fe-absorption. High levels of these compounds would be expected in the black bean seed-coats. Conclusions The parameters of Fe-status measured in this study indicate that only a minor increase in absorbable-Fe was achieved with the higher-Fe beans. The results also raise the possibility that breeding for increased Fe-concentration elevated the levels of polyphenolic-compounds that can reduce bean Fe-bioavailability, although the higher levels of polyphenolics in the higher-Fe beans may simply be coincidental or an environmental effect. Regardless, Fe-biofortified beans remain a promising vehicle for increasing intakes of bioavailable-Fe in human populations that consume high levels of these beans as a dietary staple, and the bean polyphenol profile must be further evaluated and modified if possible in order to improve the nutritional quality of higher-Fe beans. PMID:24669764

Characterization of Fe-leonardite complexes as novel natural iron fertilizers.

PubMed

Kovács, Krisztina; Czech, Viktória; Fodor, Ferenc; Solti, Adam; Lucena, Juan J; Santos-Rosell, Sheila; Hernández-Apaolaza, Lourdes

2013-12-18

Water-soluble humic substances (denoted by LN) extracted at alkaline pH from leonardite are proposed to be used as complexing agents to overcome micronutrient deficiencies in plants such as iron chlorosis. LN presents oxidized functional groups that can bind Fe(2+) and Fe(3+). The knowledge of the environment of Fe in the Fe-LN complexes is a key point in the studies on their efficacy as Fe fertilizers. The aim of this work was to study the Fe(2+)/Fe(3+) species formed in Fe-LN complexes with (57)Fe Mössbauer spectroscopy under different experimental conditions in relation to the Fe-complexing capacities, chemical characteristics, and efficiency to provide iron in hydroponics. A high oxidation rate of Fe(2+) to Fe(3+) was found when samples were prepared with Fe(2+), although no well-crystalline magnetically ordered ferric oxide formation could be observed in slightly acidic or neutral media. It seems to be the case that the formation of Fe(3+)-LN compounds is favored over Fe(2+)-LN compounds, although at acidic pH no complex formation between Fe(3+) and LN occurred. The Fe(2+)/Fe(3+) speciation provided by the Mössbauer data showed that Fe(2+)-LN could be efficient in hydroponics while Fe(3+)-LN is suggested to be used more effectively under calcareous soil conditions. However, according to the biological assay, Fe(3+)-LN proved to be effective as a chlorosis corrector applied to iron-deficient cucumber in nutrient solution.

Enhancement of magnetic ordering temperature in iron substituted ytterbium manganate (YbMn{sub 1-x}Fe{sub x}O{sub 3})

DOE Office of Scientific and Technical Information (OSTI.GOV)

Samal, S.L.; Magdaleno, T.; Ramanujachary, K.V.

Oxides of the type YbMn{sub 1-x}Fe{sub x}O{sub 3}; x<=0.3 showing multiferroic behavior have been synthesized by the solid state route. These oxides crystallize in the hexagonal structure known for the parent YbMnO{sub 3} with the c/a ratio increasing with Fe substitution. The distortion of the MnO{sub 5} polyhedra (tbp) decreases and the Mn-O-Mn bonds in the a-b plane become shorter with Fe-substitution. Magnetic ordering is observed from the low temperature neutron diffraction study. The compounds were found to be antiferromagnetic and the ordering temperature T{sub N} increased from 82 K for pure YbMnO{sub 3} to 95 K for YbMn{sub 0.7}Fe{submore » 0.3}O{sub 3}. Variable temperature dielectric measurements (15-110 K) show an anomaly in the dielectric constant at temperatures close to the antiferromagnetic ordering temperature for all the compositions, showing a unique correlation between the magnetic and electric field. The increase in the ordering temperature in YbMn{sub 1-x}Fe{sub x}O{sub 3} is explained on the basis of increase in covalence of Mn/Fe-O-Mn/Fe bonds (shorter) with iron substitution. - Graphical abstract: Hexagonal manganites of the type YbMn{sub 1-x}Fe{sub x}O{sub 3}; x<=0.3 have been synthesized by the solid state route. The distortion of the MnO{sub 5} polyhedra (tbp) decreases and the Mn-O-Mn bonds in the a-b plane become shorter with Fe-substitution. The compounds were found to be antiferromagnetic and the ordering temperature T{sub N} increased from 82 K for pure YbMnO{sub 3} to 95 K for YbMn{sub 0.7}Fe{sub 0.3}O{sub 3}. The increase in the ordering temperature in YbMn{sub 1-x}Fe{sub x}O{sub 3} is explained on the basis of increase in covalence of Mn/Fe-O-Mn/Fe bonds with iron substitution. Low temperature dielectric measurements show a unique correlation between the magnetic and electric fields for all compositions.« less

Enhanced Azo-Dyes Degradation Performance of Fe-Si-B-P Nanoporous Architecture

PubMed Central

Weng, Nan; Wang, Feng; Qin, Fengxiang; Tang, Wanying; Dan, Zhenhua

2017-01-01

Nanoporous structures were fabricated from Fe76Si9B10P5 amorphous alloy annealed at 773 K by dealloying in 0.05 M H2SO4 solution, as a result of preferential dissolution of α-Fe grains in form of the micro-coupling cells between α-Fe and cathodic residual phases. Nanoporous Fe-Si-B-P powders exhibit much better degradation performance to methyl orange and direct blue azo dyes compared with gas-atomized Fe76Si9B10P5 amorphous powders and commercial Fe powders. The degradation reaction rate constants of nanoporous powders are almost one order higher than those of the amorphous counterpart powders and Fe powders, accompanying with lower activation energies of 19.5 and 26.8 kJ mol−1 for the degradation reactions of methyl orange and direct blue azo dyes, respectively. The large surface area of the nanoporous structure, and the existence of metalloids as well as residual amorphous phase with high catalytic activity are responsible for the enhanced azo-dyes degradation performance of the nanoporous Fe-Si-B-P powders. PMID:28846622

Growth, structure, and magnetic properties of γ-Fe2O3 epitaxial films on MgO

NASA Astrophysics Data System (ADS)

Gao, Y.; Kim, Y. J.; Thevuthasan, S.; Chambers, S. A.; Lubitz, P.

1997-04-01

Single-crystal epitaxial thin films of γ-Fe2O3(001) have been grown on MgO(001) using oxygen-plasma-assisted molecular beam epitaxy. The structure and magnetic properties of these films have been characterized by a variety of techniques, including reflection high-energy electron diffraction (RHEED), low-energy electron diffraction (LEED), x-ray photoelectron spectroscopy and x-ray photoelectron/Auger electron diffraction (XPD/AED), vibrating sample magnetometry, and ferromagnetic resonance. Real-time RHEED reveals that the film growth occurs in a layer-by-layer fashion. The γ-Fe2O3(001) film surface exhibits a (1×1) LEED pattern. The growth of γ-Fe2Ooverflow="scroll">3 films at 450 °C is accompanied by significant Mg outdiffusion. AED of Mg KLL Auger emission reveals that Mg substitutionally incorporates in the γ-Fe2O3 lattice, occupying the octahedral sites. Magnetic moments are ˜2300 G and ˜4500 G for γ-Fe2O3 films grown at 250 °C and 450 °C, respectively. The high magnetic moment for the films grown at 450 °C could be attributed to the high degree of structural order of the films and Mg substitution at octahedral sites.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Norris, John E.; Yong, David; Dotter, Aaron

We investigate the color–magnitude diagram (CMD) of the Carina dwarf spheroidal galaxy using data of Stetson et al. and synthetic CMDs based on isochrones of Dotter et al., in terms of the parameters [Fe/H], age, and [ α /Fe], for the cases when (i) [ α /Fe] is held constant and (ii) [ α /Fe] is varied. The data are well described by four basic epochs of star formation, having [Fe/H] = −1.85, −1.5, −1.2, and ∼−1.15 and ages ∼13, 7, ∼3.5, and ∼1.5 Gyr, respectively (for [ α /Fe] = 0.1, constant [ α /Fe], and [ α /Fe]more » = 0.2, 0.1, −0.2, −0.2, variable [ α /Fe]), with small spreads in [Fe/H] and age of order 0.1 dex and 1–3 Gyr. Within an elliptical radius 13.′1, the mass fractions of the populations, at their times of formation, were (in decreasing age order) 0.34, 0.39, 0.23, and 0.04. This formalism reproduces five observed CMD features (two distinct subgiant branches of old and intermediate-age populations, two younger, main-sequence components, and the small color dispersion on the red giant branch (RGB). The parameters of the youngest population are less certain than those of the others, and given it is less centrally concentrated, it may not be directly related to them. High-resolution spectroscopically analyzed RGB samples appear statistically incomplete compared with those selected using radial velocity, which contain bluer stars comprising ∼5%–10% of the samples. We conjecture these objects may, at least in part, be members of the youngest population. We use the CMD simulations to obtain insight into the population structure of Carina's upper RGB.« less

The Populations of Carina. I. Decoding the Color-Magnitude Diagram

NASA Astrophysics Data System (ADS)

Norris, John E.; Yong, David; Venn, Kim A.; Dotter, Aaron; Casagrande, Luca; Gilmore, Gerard

2017-06-01

We investigate the color-magnitude diagram (CMD) of the Carina dwarf spheroidal galaxy using data of Stetson et al. and synthetic CMDs based on isochrones of Dotter et al., in terms of the parameters [Fe/H], age, and [α/Fe], for the cases when (I) [α/Fe] is held constant and (II) [α/Fe] is varied. The data are well described by four basic epochs of star formation, having [Fe/H] = -1.85, -1.5, -1.2, and ˜-1.15 and ages ˜13, 7, ˜3.5, and ˜1.5 Gyr, respectively (for [α/Fe] = 0.1, constant [α/Fe], and [α/Fe] = 0.2, 0.1, -0.2, -0.2, variable [α/Fe]), with small spreads in [Fe/H] and age of order 0.1 dex and 1-3 Gyr. Within an elliptical radius 13.‧1, the mass fractions of the populations, at their times of formation, were (in decreasing age order) 0.34, 0.39, 0.23, and 0.04. This formalism reproduces five observed CMD features (two distinct subgiant branches of old and intermediate-age populations, two younger, main-sequence components, and the small color dispersion on the red giant branch (RGB). The parameters of the youngest population are less certain than those of the others, and given it is less centrally concentrated, it may not be directly related to them. High-resolution spectroscopically analyzed RGB samples appear statistically incomplete compared with those selected using radial velocity, which contain bluer stars comprising ˜5%-10% of the samples. We conjecture these objects may, at least in part, be members of the youngest population. We use the CMD simulations to obtain insight into the population structure of Carina's upper RGB.

Magnetic interaction reversal in watermelon nanostructured Cr-doped Fe nanoclusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kaur, Maninder; Dai, Qilin; Bowden, Mark

2013-01-01

Cr-doped core-shell Fe/Fe-oxide nanoclusters (NCs) were synthesized at varied atomic percentages of Cr from 0 at. % to 8 at. %. The low concentrations of Cr (<10 at. %) were selected in order to inhibit the complete conversion of the Fe-oxide shell to Cr2O3 and the Fe core to FeCr alloy. The magnetic interaction in Fe/Fe-oxide NCs (rv25 nm) can be controlled by antiferromagnetic Cr-dopant. We report the origin of r-FeCr phase at very low Cr concentration (2 at. %) unlike in previous studies, and the interaction reversal from dipolar to exchange interaction in watermelon-like Cr-doped core-shell NCs. The giantmore » magnetoresistance (GMR) effect,1,2 where an antiferromagnetic (AFM) exchange coupling exists between two ferromagnetic (FM) layers separated by a certain type of magnetic or non-magnetic spacer,3 has significant potential for application in the magnetic recording industry. Soon after the discovery of the GMR, the magnetic properties of multilayer systems (FeCr) became a subject of intensive study. The application of bulk iron-chromium (Fe-Cr) alloys has been of great interest, as these alloys exhibit favorable prop- erties including corrosion resistance, high strength, hardness, low oxidation rate, and strength retention at elevated temper- ature. However, the structural and magnetic properties of Cr-doped Fe nanoclusters (NCs) have not been investigated in-depth. Of all NCs, Fe-based clusters have unique magnetic properties as well as favorable catalytic characteristics in reactivity, selectivity, and durability.4 The incorporation of dopant of varied type and concentration in Fe can modify its chemical ordering, thereby optimizing its electrical, optical, and magnetic properties and opening up many new applications. The substitution of an Fe atom (1.24 A°) by a Cr atom (1.25 A° ) can easily modify the magnetic properties, since (i) the curie temperature (Tc ) of Fe is 1043 K, while Cr is an itinerant AFM with a bulk Neel temperature TN =311 K, and (ii) Fe and Cr share the same crystal structure (bcc) with only 0.5% difference between their lattice constants.« less

Spin order in FeV2O4 determined by single crystal Mössbauer spectroscopy in applied magnetic field

NASA Astrophysics Data System (ADS)

Nakamura, Shin; Kobayashi, Yasuhiro; Kitao, Shinji; Seto, Makoto

2018-05-01

In order to clarify the spin order of FeV2O4, 57Fe Mössbauer spectroscopy has been conducted by using a single crystal specimen. A measurement in applied magnetic field has been also conducted. By applying a slight compression in the sample plane, almost single domain state was achieved in the low temperature phases. The spectra consist of Fe2+ spectra ( 85%) and Fe2.5+ spectra ( 15%), corresponding to the A- and B-site Fe ions, respectively. The B-site spectrum well represents the local structure and the magnetic structure of V3+ ion on the B-site. Notable changes in the Mössbauer parameters are recognized at 140, 110, and 65 K, where the successive phase transitions take place. The feature well represents the orbital and spin order. In the orthorhombic phase below 110 K, Fe2+ and V3+ spins form a collinear ferrimagnetic order along the a-axis. Below 65 K in the low temperature tetragonal phase, however, both spins incline from the c-axis to form a canted ferrimagnetic structure. The canting angles are about 17° and 52° at 4.2 K for Fe2+ and V3+ spins, respectively.

Experimental cation redistribution in the tourmaline lucchesiite, CaFe2 + 3Al6(Si6O18)(BO3)3(OH)3O

NASA Astrophysics Data System (ADS)

Bosi, Ferdinando; Skogby, Henrik; Hålenius, Ulf; Ciriotti, Marco E.

2018-02-01

Natural Mg-rich lucchesiite was thermally treated in air and hydrogen atmosphere up to 800 °C to study potential changes in Fe-, Mg- and Al ordering over the octahedrally coordinated Y- and Z-sites, and to explore possible applications to intracrystalline geothermometry based on tourmaline. Overall, the experimental data (structural refinement, Mössbauer, infrared and optical absorption spectroscopy) show that thermal treatment of lucchesiite results in an increase of Fetot contents at Z balanced by an increase of Mg and Al at Y. This process is accompanied by a significant deprotonation of the O3 anion site. The Fe order-disorder reaction depends more on temperature, than on redox conditions. During heat treatment in H2, reduction of Fe3+ to Fe2+ was not observed despite strongly reducing conditions, indicating that the f O2 conditions do not exclusively control the Fe oxidation state at the present experimental conditions. On the basis of this and previous studies, the intersite order-disorder process induced by thermal treatment indicates that Fe redistribution is an important factor for Fe-Mg-Al-exchange and is significant at temperatures around 800 °C. As a result, Fe-Mg-Al intersite order-disorder is sensitive to temperature variations, whereas geothermometers based solely on Mg-Al order-disorder appear insensitive and involve large uncertainties. The presented findings are important for interpretation of the post-crystallization history of both tourmaline and tourmaline host rocks, and indicate that successful tourmaline geothermometers may be developed by thermal calibration of the Fe-Mg-Al order-disorder reaction.

Induced anisotropy in FeCo-based nanocomposites: Early transition metal content dependence

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shen, S; DeGeorge, V; Ohodnicki, PR

2014-05-07

Soft magnetic nanocomposites variants of FeCo-based (HTX002) alloys (Fe65Co35)(81+x)B12Nb4-xSi2Cu1, exhibiting high inductions (up to 1.9 T), low losses, and high temperature stability are studied for high frequency inductors and current sensors. For alloys with x 0, 1, 1.5, 2, and 3, we report field induced anisotropy, K-U, after annealing at temperatures of 340-450 degrees C for 1 h in a 2 T transverse magnetic field. The anisotropy field, H-K, measured by AC permeametry on toroidal cores, and by first order reversal curves on square sections of ribbon, decreases with annealing temperature and saturates at high annealing temperatures suggesting a nanostructuremore » related anisotropy mechanism in which the amorphous phase exhibits a higher H-K than the crystalline phase. A high saturation induction nanocrystalline phase and high H-K amorphous phase were achieved by low temperature annealing resulting in a value of K-U exceeding 14 X 10(3) erg/cm(3), more than twice that reported previously for Fe-rich amorphous and nanocomposite alloys. (C) 2014 AIP Publishing LLC.« less

Optical Properties and Electrochemical Performance of LiFePO4 Thin Films Deposited on Transparent Current Collectors.

PubMed

Lee, HyunSeok; Yim, Haena; Kim, Kwang-Bum; Choi, Ji-Won

2015-11-01

LiFePO4 thin film cathodes are deposited on various transparent conducting oxide thin films on glass, which are used as cathode current collectors. The XRD patterns show that the thin films have the phase of LiFePO4 with an ordered olivine structure indexed to the orthorhombic Pmna space group. LiFePO4 thin film deposited on various TCO glass substrates exhibits transmittance of about 53%. The initial specific discharge capacities of LiFePO4 thin films are 25.0 μAh/cm2 x μm on FTO, 33.0 μAh/cm2 x μm on ITO, and 13.0 μAh/cm2 x μm on AZO coated glass substrates. Interestingly, the retention capacities of LiFePO4 thin films are 76.0% on FTO, 31.2% on ITO, and 37.7% on AZO coated glass substrates at 20th cycle. The initial specific discharge capacity of the LiFePO4/FTO electrode is slightly lower, but the discharge capacities of the LiFePO4/FTO electrode relatively decrease less than those of the others such as LiFePO4/ITO and LiFePO4/AZO with cycling. The results reported here provide the high transparency of LiFePO4 thin films cathode materials and the good candidate as FTO current collector of the LiFePO4 thin film cathode of transparent thin film rechargeable batteries due to its high transparency and cyclic retention.

Removal of Cs+ from water and soil by ammonium-pillared montmorillonite/Fe3O4 composite.

PubMed

Zheng, Xianming; Dou, Junfeng; Yuan, Jing; Qin, Wei; Hong, Xiaoxi; Ding, Aizhong

2017-06-01

To remove cesium ions from water and soil, a novel adsorbent was synthesized by following a one-step co-precipitation method and using non-toxic raw materials. By combining ammonium-pillared montmorillonite (MMT) and magnetic nanoparticles (Fe 3 O 4 ), an MMT/Fe 3 O 4 composite was prepared and characterized. The adsorbent exhibited high selectivity of Cs + and could be rapidly separated from the mixed solution under an external magnetic field. Above all, the adsorbent had high removal efficiency in cesium-contaminated samples (water and soil) and also showed good recycling performance, indicating that the MMT/Fe 3 O 4 composite could be widely applied to the remediation of cesium-contaminated environments. It was observed that the pH, solid/liquid ratio and initial concentration affected adsorption capacity. In the presence of coexisting ions, the adsorption capacity decreased in the order of Ca 2+ >Mg 2+ >K + >Na + , which is consistent with our theoretical prediction. The adsorption behavior of this new adsorbent could be expressed by the pseudo-second-order model and Freundlich isotherm. In addition, the adsorption mechanism of Cs + was NH 4 + ion exchange and surface hydroxyl group coordination, with the former being more predominant. Copyright © 2016. Published by Elsevier B.V.

Local order study of YFe 2D x (0⩽ x⩽3.5) compounds by X-ray absorption and Mössbauer spectroscopy

NASA Astrophysics Data System (ADS)

Paul-Boncour, V.; Wiesinger, G.; Reichl, Ch.; Latroche, M.; Percheron-Guégan, A.; Cortes, R.

2001-12-01

The local order in YFe 2D x deuterides has been characterized by EXAFS and 57Fe Mössbauer spectroscopy. For all the deuterides several Fe sites and a large distribution of Fe-Fe distances are observed. The Y-Fe and Y-Y distances are close to those calculated for a cubic C15 type structure, but with significant static disorder. These large distance distributions are related to the influence of hydrogen atoms which induce local distortions of the interstitial sites with a displacement of Y and Fe atoms. However, the bulk and mean local magnetic properties remain sensitive to the long range order structure of the deuterides.

Anomalous double-stripe charge ordering in β -NaFe2O3 with double triangular layers consisting of almost perfect regular Fe4 tetrahedra

NASA Astrophysics Data System (ADS)

Kobayashi, Shintaro; Ueda, Hiroaki; Michioka, Chishiro; Yoshimura, Kazuyoshi; Nakamura, Shin; Katsufuji, Takuro; Sawa, Hiroshi

2018-05-01

The physical properties of the mixed-valent iron oxide β -NaFe2O3 were investigated by means of synchrotron radiation x-ray diffraction, magnetization, electrical resistivity, differential scanning calorimetry, 23Na NMR, and 57FeM o ̈ssbauer measurements. This compound has double triangular layers consisting of almost perfect regular Fe4 tetrahedra, which suggests geometrical frustration. We found that this compound exhibits an electrostatically unstable double-stripe-type charge ordering, which is stabilized by the cooperative compression of Fe3 +O6 octahedra, owing to a valence change and Fe2 +O6 octahedra due to Jahn-Teller distortion. Our results indicate the importance of electron-phonon coupling for charge ordering in the region of strong charge frustration.

Structure Stabilization by Mixed Anions in Oxyfluoride Cathodes for High-Energy Lithium Batteries

DOE PAGES

Kim, Sung-Wook; Pereira, Nathalie; Chernova, Natasha A.; ...

2015-08-24

Mixed-anion oxyfluorides (i.e., FeO xF 2-x) are an appealing alternative to pure fluorides as high-capacity cathodes in lithium batteries, with enhanced cyclability via oxygen substitution. Yet, it is still unclear how the mixed anions impact the local phase transformation and structural stability of oxyfluorides during cycling due to the complexity of electrochemical reactions, involving both lithium intercalation and conversion. Herein, we investigated the local chemical and structural ordering in FeO 0.7F 1.3 at length scales spanning from single particles to the bulk electrode, via a combination of electron spectrum-imaging, magnetization, electrochemistry, and synchrotron X-ray measurements. The FeO 0.7F 1.3more » nanoparticles retain a FeF 2-like rutile structure but chemically heterogeneous, with an F-rich core covered by thin O-rich shell. Upon lithiation the O-rich rutile phase is transformed into Li—Fe—O(—F) rocksalt that has high lattice coherency with converted metallic Fe, a feature that may facilitate the local electron and ion transport. The O-rich rocksalt is highly stable over lithiation/delithiation and thus advantageous to maintain the integrity of the particle, and due to its predominant distribution on the surface, it is expected to prevent the catalytic interaction of Fe with electrolyte. Our findings of the structural origin of cycling stability in oxyfluorides may provide insights into developing viable high-energy electrodes for lithium batteries.« less

Electrochemical performance of potassium-doped wüstite nanoparticles supported on graphene as an anode material for lithium ion batteries

NASA Astrophysics Data System (ADS)

Jung, Dong-Won; Jeong, Jae-Hoon; Han, Sang-Wook; Oh, Eun-Suok

2016-05-01

A graphene composite with potassium-doped FeO nanoparticles (K-FeO/graphene) is synthesized by the thermal diffusion of potassium into Fe2O3/graphene using polyol reduction. This is applied as anode material in lithium ion batteries in order to enhance the electrochemical performance of conventional iron oxides (hematite or magnetite). Rhombohedral Fe2O3 crystals are transformed into face-centered cubic FeO crystals, which show a broad d-spacing (5.2 Å) between their (111) crystal planes, by the calcination of potassium-added Fe2O3/graphene. Because of its structural characteristics, the K-FeO/graphene composite demonstrates an excellent discharge capacity of 1776 mA h g-1 at the 50th cycle at a current of 100 mA h g-1 with stable capacity retention. Even with the very high current density of 18.56 A g-1, its capacity remains at 851 mA h g-1 after 800 cycles.

Effects of magnetic dopants in (Li0.8M0.2OH )FeSe (M =Fe , Mn, Co): Density functional theory study using a band unfolding technique

NASA Astrophysics Data System (ADS)

Chen, M. X.; Chen, Wei; Zhang, Zhenyu; Weinert, M.

2017-12-01

The effects of Fe dopants on the electronic bands structure of (Li0.8Fe0.2OH )FeSe are investigated by a band unfolding (k -projection) technique and first-principles supercell calculations. Doping 20% Fe into the LiOH layers causes electron donation to the FeSe layers, significantly changing the profile of bands around the Fermi level. Because of the weak bonding between the LiOH and FeSe layers the magnetic configuration of the dopants has only minor effects on the band structure. The electronic bands for the surface FeSe layer of (Li0.8Fe0.2OH )FeSe show noticeable differences compared to those of the inner layers, both in the location of the Fermi level and in details of the bands near the high symmetry points, resulting from different effective doping levels and the broken symmetry at the surface. The band structure for the surface FeSe layer with checkerboard antiferromagnetic order is reasonably consistent with angle-resolved photoemission results. The 3 d transition metals Mn and Co have similar doping effects on the band structure of (LiOH)FeSe.

High δ56Fe values in Samoan basalts

NASA Astrophysics Data System (ADS)

Konter, J. G.; Pietruszka, A. J.; Hanan, B. B.; Finlayson, V.

2014-12-01

Fe isotope fractionation spans ~0-0.4 permil in igneous systems, which cannot all be attributed to variable source compositions since peridotites barely overlap these compositions. Other processes may fractionate Fe isotopes such as variations in the degree of partial melting, magmatic differentiation, fluid addition related to the final stages of melt evolution, and kinetic fractionation related to diffusion. An important observation in igneous systems is the trend of increasing Fe isotope values against an index of magmatic fractionation (e.g. SiO2; [1]). The data strongly curve from δ56Fe >0.3 permil for SiO2 >70 wt% down to values around 0.09 permil from ~65 wt% down to 40 wt% SiO2 of basalts. However, ocean island basalts (OIBs) have a slightly larger δ56Fe variability than mid ocean ridge basalts (MORBs; [e.g. 2]). We present Fe isotope data on samples from the Samoan Islands (OIB) that have unusually high δ56Fe values for their SiO2 content. We rule out alteration by using fresh samples, and further test for the effects of magmatic processes on the δ56Fe values. In order to model the largest possible fractionation, unusually small degrees of melting with extreme fractionation factors are modeled with fractional crystallization of olivine alone, but such processing fails to fractionate the Fe isotopes to the observed values. Moreover, Samoan lavas likely also fractionated clinopyroxene, and its lower fractionation factor would limit the final δ56Fe value of the melt. We therefore suggest the mantle source of Samoan lavas must have had unusually high δ56Fe. However, there is no clear correlation with the highly radiogenic isotope signatures that reflect the unique source compositions of Samoa. Instead, increasing melt extraction correlates with lower δ56Fe values in peridotites assumed to be driven by the preference for the melt phase by heavy Fe3+, while high values may be related to metasomatism [3]. The latter would be in line with metasomatized xenoliths from Samoa [4]. [1] Heimann et al., 2008, doi:10.1016/j.gca.2008.06.009 [2] Teng et al., 2013, doi:10.1016/j.gca.2012.12.027 [3] Williams et al., 2004, doi: 10.1126/science.1095679 [4] Hauri et al., 1993, doi: 10.1038/365221a0

Charge ordering and multiferroicity in Fe{sub 3}BO{sub 5} and Fe{sub 2}MnBO{sub 5} oxyborates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maignan, A., E-mail: antoine.maignan@ensicaen.fr; Lainé, F.; Guesdon, A.

2017-02-15

The comparison of Fe{sub 3}BO{sub 5} and Fe{sub 2}MnBO{sub 5} reveals that the 2Fe{sup 2+}: Fe{sup 3+} charge ordering of the former is suppressed in the latter. Spin dynamics probed by ac susceptibility are strongly affected by the substitution, inducing superparamagnetism at low temperature in Fe{sub 2}MnBO{sub 5}. Interestingly, for both oxyborates, glassiness is observed in the dielectric properties at low temperature, but only Fe{sub 3}BO{sub 5} shows a magnetodielectric effect close to its lower magnetic transition. A change in the electrical polarization, measured by pyroelectric current integration, is observed in Fe{sub 3}BO{sub 5} and is even more pronounced inmore » Fe{sub 2}MnBO{sub 5}. Such results suggest that these oxyborates behave like antiferromagnetic relaxor ferroelectrics. These features are proposed to be related to the distribution of the species (Fe{sup 3+}, Fe{sup 2+} and Mn{sup 2+}) over the four transition metal sites forming the ludwigite structure. - Graphical abstract: 90 K [010] electron diffraction patterns of Fe{sub 3}BO{sub 5}. The yellow arrows in the pattern indicate the extra-spots corresponding to the superstructure induced by the charge ordering. - Highlights: • The TEM (ED) study of the Fe{sub 3}BO{sub 5} oxyborate at 90 K reveals a superstructure related to a Fe{sup 2+}/Fe{sup 3+} ordering. • The Fe{sub 2}MnBO{sub 5}, Mn-substituted counterpart, does not show such ordering. • Our magnetic and electric measurements demonstrate that these magnetic ferrites exhibit glassiness in their charges (relaxor-type) with additional superparamagnetism at low T for Fe{sub 2}MnBO{sub 5} and magnetodielectric coupling near T{sub N2}=72 K in Fe{sub 3}BO{sub 5}. • The pyroelectric measurements confirm the existence of a ferroelectric behavior in these antiferromagnets. Accordingly, our results open the route to the study of other large class of the M{sub 2}{sup 2+}M’{sup 3+}BO{sub 5} ludwigites and to their complex magnetism and its relationship to relaxor ferroelectricity.« less

Efficient removal of dyes from aqueous solutions using a novel hemoglobin/iron oxide composite.

PubMed

Essandoh, Matthew; Garcia, Rafael A

2018-05-10

Magnetic particles entrapped in different matrices that display high thermal stability, low toxicity, interactive functions at the surface, and high saturation magnetization are of great interest. The objective of this work was to synthesize a novel hemoglobin/iron oxide composite (Hb/Fe 3 O 4 ) for the removal of different dyes (indigo carmine, naphthol blue black, tartrazine, erythrosine, eriochrome black T and bromophenol blue) from aqueous solutions. The Hb/Fe 3 O 4 composite was characterized using scanning electron microscopy (SEM), laser diffraction particle size analysis, FT-IR spectroscopy, isoelectric point determination and thermogravimetric analysis (TGA). The Hb/Fe 3 O 4 composite showed high removal efficiency toward all the different classes of dyes studied and the mechanism of adsorption was dominated by electrostatic interaction. Adsorption was found to follow pseudo-second order kinetic model and Langmuir isotherm. The Langmuir monolayer adsorption capacities for all the dyes range from 80 to 178 mg/g. The Hb/Fe 3 O 4 composite possesses extra advantage of being easily isolated from aqueous suspension using an external magnet. The stability of the prepared Hb/Fe 3 O 4 composite was also demonstrated. Copyright © 2018 Elsevier Ltd. All rights reserved.

Pseudogap and proximity effect in the Bi2Te3/Fe1+yTe interfacial superconductor.

PubMed

He, M Q; Shen, J Y; Petrović, A P; He, Q L; Liu, H C; Zheng, Y; Wong, C H; Chen, Q H; Wang, J N; Law, K T; Sou, I K; Lortz, R

2016-09-02

In the interfacial superconductor Bi2Te3/Fe1+yTe, two dimensional superconductivity occurs in direct vicinity to the surface state of a topological insulator. If this state were to become involved in superconductivity, under certain conditions a topological superconducting state could be formed, which is of high interest due to the possibility of creating Majorana fermionic states. We report directional point-contact spectroscopy data on the novel Bi2Te3/Fe1+yTe interfacial superconductor for a Bi2Te3 thickness of 9 quintuple layers, bonded by van der Waals epitaxy to a Fe1+yTe film at an atomically sharp interface. Our data show highly unconventional superconductivity, which appears as complex as in the cuprate high temperature superconductors. A very large superconducting twin-gap structure is replaced by a pseudogap above ~12 K which persists up to 40 K. While the larger gap shows unconventional order parameter symmetry and is attributed to a thin FeTe layer in proximity to the interface, the smaller gap is associated with superconductivity induced via the proximity effect in the topological insulator Bi2Te3.

Magnetic switching in granular FePt layers promoted by near-field laser enhancement

DOE PAGES

Granitzka, Patrick W.; Jal, Emmanuelle; Le Guyader, Loic; ...

2017-03-08

Light-matter interaction at the nanoscale in magnetic materials is a topic of intense research in view of potential applications in next-generation high-density magnetic recording. Laser-assisted switching provides a pathway for overcoming the material constraints of high-anisotropy and high-packing density media, though much about the dynamics of the switching process remains unexplored. We use ultrafast small-angle X-ray scattering at an X-ray free-electron laser to probe the magnetic switching dynamics of FePt nanoparticles embedded in a carbon matrix following excitation by an optical femtosecond laser pulse. We observe that the combination of laser excitation and applied static magnetic field, 1 order ofmore » magnitude smaller than the coercive field, can overcome the magnetic anisotropy barrier between “up” and “down” magnetization, enabling magnetization switching. This magnetic switching is found to be inhomogeneous throughout the material with some individual FePt nanoparticles neither switching nor demagnetizing. The origin of this behavior is identified as the near-field modification of the incident laser radiation around FePt nanoparticles. Furthermore, the fraction of not-switching nanoparticles is influenced by the heat flow between FePt and a heat-sink layer.« less

Pseudogap and proximity effect in the Bi2Te3/Fe1+yTe interfacial superconductor

PubMed Central

He, M. Q.; Shen, J. Y.; Petrović, A. P.; He, Q. L.; Liu, H. C.; Zheng, Y.; Wong, C. H.; Chen, Q. H.; Wang, J. N.; Law, K. T.; Sou, I. K.; Lortz, R.

2016-01-01

In the interfacial superconductor Bi2Te3/Fe1+yTe, two dimensional superconductivity occurs in direct vicinity to the surface state of a topological insulator. If this state were to become involved in superconductivity, under certain conditions a topological superconducting state could be formed, which is of high interest due to the possibility of creating Majorana fermionic states. We report directional point-contact spectroscopy data on the novel Bi2Te3/Fe1+yTe interfacial superconductor for a Bi2Te3 thickness of 9 quintuple layers, bonded by van der Waals epitaxy to a Fe1+yTe film at an atomically sharp interface. Our data show highly unconventional superconductivity, which appears as complex as in the cuprate high temperature superconductors. A very large superconducting twin-gap structure is replaced by a pseudogap above ~12 K which persists up to 40 K. While the larger gap shows unconventional order parameter symmetry and is attributed to a thin FeTe layer in proximity to the interface, the smaller gap is associated with superconductivity induced via the proximity effect in the topological insulator Bi2Te3. PMID:27587000

Fe-based magnetic nanomaterials: Wet chemical synthesis, magnetic properties and exploration on applications

NASA Astrophysics Data System (ADS)

Xiaoliang, Hong

Even though the start of research based on Fe-based magnetic nanomaterials could be dated back to hundreds years ago, the considerably large amount of emerging fields for their applications, including spintronic structures in information storage, biomedical and environmental applications, magnetic sensors, magnetic energy harvesters, has spurred renewed interest on the application-related properties of Fe-based nanomaterial in both the nanoparticle and film forms. Besides, an exploration of a simple, wide, effective technique that can be used for growth of high-quality Fe-based magnetic nanoparticles and films is of great importance for better materialization of these potential Fe-based devices. This thesis mainly focuses on fabricating different magnetic Fe-based materials (ferrites and ferrous alloys, nanoparticle and film) with wet chemical method, investigating their growth mechanism and magnetic and electrical properties. In addition, the possible applications of as-fabricated Fe-based nanoparticles and films are studied. The contribution of the work is summarized as below: (1) Investigation indicated that the external magnetic field plays an important role in determining the microstructure, magnetic properties of the Fe3O4 nanoparticles. The magnetic field can promote the change of Fe3O4 nanocuboctahedrons to nanocubes. Compared the hyperthermia property of as-fabricated nanocuboctahedrons and nanocubes Fe3O4, the intrinsic loss power (ILP) of the Fe3O4 nanocubes was much higher than that of nanocuboctahedrons due to the surface magnetic effect. (2) A general and facile method for broadly deposition of thick Fe 3O4 film and other ferrites has been demonstrated. It had been found that the epitaxial high-quality Fe3O4 film could be deposited either on MgO substrates directly or Si substrates with Fe3O4 seed layer deposited by PLD. As-deposited Fe 3O4 film could be easily patterned and shows potential applications for microwave and MEMS supercapacitor. Besides Fe3O4, different ferrite compounds have been successfully fabricated, including Co-ferrite with high coercivity and perpendicular anisotropy, and Ni-ferrite with high resistivity and enhanced magnetization. (3) A typical Fe-3d alloy, FeCo, was studied in our work. Monodispersed FeCo nanoparticles were synthesized by a safe and ecofriendly facile chemical process. The FeCo nanoparticles have saturation magnetization up to 187 emu/g and shows excellent chemical stability. In addition, the control Fe/Co ratio could be achieved by change of precursor ratio and tuning of particle size could be realized through change of surfactant amount used. The cytotoxicity of as-synthesized nanoparticles was investigated after transferring the nanoparticle to water phase by the emulsion process and the results demonstrated high biocompatibility. The results showed that this method could also fabricate spherical Fe 3O4 particles and self-assembly Co nanoneedles. With the similar method that was applied to deposit Fe3O4, bcc-FeCo film could be fabricated through thermal decomposition with the saturation magnetization around 1300 emu/cc. (4) Fe-5d alloy, FePt, was investigated in both nanoparticle and film form. fcc-Fe76Pt24 nanoparticles were synthesized by thermal decomposition. TEM image showed the particle size was around 15 nm. From in-plane hysteresis loop, the coercivity of samples was about 150 Oe. The presence of nonzero value for the coercivity suggests that some amount of ordering should be present in fcc- Fe76Pt24 nanoparticles. In addition, fcc and L10-FePt films had been deposited on Pt substrate via a combination of chemical deposition and post-annealing process. Pt-doped Fe films were deposited on Pt substrate using thermal deposition and the as-deposited films were subsequently annealed from 300°C to 800°C, FePt films were achieved through diffusion and rearrangement of Fe and Pt atoms in post-annealing process. The transformation from disordering fcc to ordering L10 phase had been observed from X-ray diffraction results. The L10-FePt film possessed an out-of-plane anisotropy and a coercivity of 9 kOe after annealing at 600°C. A further increase in annealing temperature led to lower value of coercivity, probably due to grain growth. In addition, the thickness of Pt-doped Fe films was tunable by adjusting amount of surfactant used. Our SQUID analysis showed that Pt dopant could significantly improve the chemical stability of Fe films in air.

Structural short-range order of the β-Ti phase in bulk Ti-Fe-(Sn) nanoeutectic composites

NASA Astrophysics Data System (ADS)

Das, J.; Eckert, J.; Theissmann, R.

2006-12-01

The authors report lattice distortion and "ω-like" structural short-range order (SRO) of the β-Ti phase in a Ti-Fe-(Sn) bulk nanoeutectic composite prepared by slow cooling from the melt. The nanoeuetctic phases are chemically homogeneous, but the addition of Sn releases the local lattice strain, modifies the structural SRO, and prevents the formation of stacking faults in the body centered cubic (bcc) β-Ti phase resulting in improved plastic deformability. The elastic properties and the structural SRO of the β-Ti phase are proposed to be important parameters for developing advanced high strength, ductile Ti-base nanocomposite alloys.

Ferromagnetic Coupling of Mononuclear Fe Centers in a Self-Assembled Metal-Organic Network on Au(111)

NASA Astrophysics Data System (ADS)

Umbach, T. R.; Bernien, M.; Hermanns, C. F.; Krüger, A.; Sessi, V.; Fernandez-Torrente, I.; Stoll, P.; Pascual, J. I.; Franke, K. J.; Kuch, W.

2012-12-01

The magnetic state and magnetic coupling of individual atoms in nanoscale structures relies on a delicate balance between different interactions with the atomic-scale surroundings. Using scanning tunneling microscopy, we resolve the self-assembled formation of highly ordered bilayer structures of Fe atoms and organic linker molecules (T4PT) when deposited on a Au(111) surface. The Fe atoms are encaged in a three-dimensional coordination motif by three T4PT molecules in the surface plane and an additional T4PT unit on top. Within this crystal field, the Fe atoms retain a magnetic ground state with easy-axis anisotropy, as evidenced by x-ray absorption spectroscopy and x-ray magnetic circular dichroism. The magnetization curves reveal the existence of ferromagnetic coupling between the Fe centers.

Electronic structure and magnetic anisotropy of L1{sub 0}-FePt thin film studied by hard x-ray photoemission spectroscopy and first-principles calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ueda, S.; Synchrotron X-ray Station at SPring-8, National Institute for Materials Science, Sayo, Hyogo 679-5148; Mizuguchi, M.

2016-07-25

We have studied the electronic structure of the L1{sub 0} ordered FePt thin film by hard x-ray photoemission spectroscopy (HAXPES), cluster model, and first-principles calculations to investigate the relationship between the electronic structure and perpendicular magneto-crystalline anisotropy (MCA). The Fe 2p core-level HAXPES spectrum of the ordered film revealed the strong electron correlation in the Fe 3d states and the hybridization between the Fe 3d and Pt 5d states. By comparing the experimental valence band structure with the theoretical density of states, the strong electron correlation in the Fe 3d states modifies the valence band electronic structure of the L1{submore » 0} ordered FePt thin film through the Fe 3d-Pt 5d hybridization. These results strongly suggest that the strong electron correlation effect in the Fe 3d states and the Fe 3d-Pt 5d hybridization as well as the spin-orbit interaction in the Pt 5d states play important roles in the perpendicular MCA for L1{sub 0}-FePt.« less

Heterogeneous Fenton-like discoloration of methyl orange using Fe3O4/MWCNTs as catalyst: combination mechanism and affecting parameters

NASA Astrophysics Data System (ADS)

Xu, Huan-Yan; Wang, Yuan; Shi, Tian-Nuo; Zhao, Hang; Tan, Qu; Zhao, Bo-Chao; He, Xiu-Lan; Qi, Shu-Yan

2018-03-01

Multi-walled carbon nanotubes (MWCNTs) can act not only as a support for Fe3O4 nanoparticles (NPs) but also as a coworker with synergistic effect, accordingly improving the heterogeneous Fenton-like efficiency of Fe3O4 NPs. In this study, Fe3O4 NPs were in situ anchored onto MWCNTs by a moderate co-precipitation method and the as-prepared Fe3O4/MWCNTs nanocomposites were employed as the highly efficient Fenton-like catalysts. The analyses of XRD, FTIR, Raman, FESEM, TEM and HRTEM results indicated the formation of Fe3O4 crystals in Fe3O4/MWCNTs nanocomposites prepared at different conditions and the interaction between Fe3O4 NPs and MWCNTs. Over a wide pH range, the surface of modified MWCNTs possessed negative charges. Based on these results, the possible combination mechanism between Fe3O4 NPs and MWCNTs was discussed and proposed. Moreover, the effects of preparation and catalytic conditions on the Fenton-like catalytic efficiency were investigated in order to gain further insight into the heterogeneous Fenton-like reaction catalyzed by Fe3O4/MWCNTs nanocomposites.

Origin of the magnetic transition at 100 K in ɛ-Fe2O3 nanoparticles studied by x-ray absorption fine structure spectroscopy

NASA Astrophysics Data System (ADS)

López-Sánchez, J.; Muñoz-Noval, A.; Castellano, C.; Serrano, A.; del Campo, A.; Cabero, M.; Varela, M.; Abuín, M.; de la Figuera, J.; Marco, J. F.; Castro, G. R.; Rodríguez de la Fuente, O.; Carmona, N.

2017-12-01

The current study unveils the structural origin of the magnetic transition of the ɛ-Fe2O3 polymorph from an incommensurate magnetic order to a collinear ferrimagnetic state at low temperature. The high crystallinity of the samples and the absence of other iron oxide polymorphs have allowed us to carry out temperature-dependent x-ray absorption fine structure spectroscopy experiments out. The deformation of the structure is followed by the Debye-Waller factor for each selected Fe-O and Fe-Fe sub-shell. For nanoparticle sizes between 7 and 15 nm, the structural distortions between the Fete and Fe-D1oc sites are localized in a temperature range before the magnetic transition starts. On the contrary, the inherent interaction between the other sub-shells (named Fe-O1,2 and Fe-Fe1) provokes cooperative magneto-structural changes in the same temperature range. This means that the Fete with Fe-D1oc polyhedron interaction seems to be uncoupled with temperature dealing with these nanoparticle sizes wherein the structural distortions are likely moderate due to surface effects.

77 FR 12274 - Orders Granting Authority To Import and Export Natural Gas and Liquefied Natural Gas During...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-02-29

... Fossil Energy, Department of Energy (DOE). ACTION: Notice of orders. FE Docket Nos. DOMINION COVE POINT... Fossil Energy (FE) of the Department of Energy gives notice that during January 2012, it issued Orders... in the attached appendix and may be found on the FE Web site at http://www.fossil.energy.gov/programs...

Sodium citrate functionalized reusable Fe3O4@TiO2 photocatalyst for water purification

NASA Astrophysics Data System (ADS)

Li, Wenyu; Wu, Haoyi

2017-10-01

Easy-recycle photocatalysts are new materials for water treatment technologies. In order to improve the recyclable ability, we employed Fe3O4 particles, which were functionalized by sodium citrate, to serve as a substrate core to attract the deposition of a shell of TiO2 particles. When compared to the calcining process for preparing the composite, the TiO2 distributed homogeneously on the sodium citrate treated Fe3O4, forming a mesoporous shell layer. Due to the mesoporous structure, this Fe3O4@TiO2 exhibited high photocatalytic degradation activity to Rhodamine B, and it was easily recycled using a magnetic field to recover the catalyst from solution.

Element-resolved thermodynamics of magnetocaloric LaFe 13 – x Si x

DOE PAGES

Gruner, Markus E.; Keune, Werner; Cuenya, B. Roldan; ...

2015-02-04

By combination of two independent approaches, nuclear resonant inelastic x-ray scattering and first-principles calculations in the framework of density functional theory, we demonstrate significant changes in the element-resolved vibrational density of states across the first-order transition from the ferromagnetic low temperature to the paramagnetic high temperature phase of LaFe 13-xSi x. These changes originate from the itinerant electron metamagnetism associated with Fe and lead to a pronounced magneto-elastic softening despite the large volume decrease at the transition. As a result, the increase in lattice entropy associated with the Fe subsystem is significant and contributes cooperatively with the magnetic and electronicmore » entropy changes to the excellent magneto- and barocaloric properties.« less

Effect of annealing on microstructure evolution in CoFeB/MgO/CoFeB heterostructures by positron annihilation

NASA Astrophysics Data System (ADS)

Zhao, Chong-Jun; Lu, Xiang-An; Zhao, Zhi-Duo; Li, Ming-Hua; Zhang, Peng; Wang, Bao-Yi; Cao, Xing-Zhong; Zhang, Jing-Yan; Yu, Guang-Hua

2013-09-01

As one of the most powerful tools for investigation of defects of materials, positron annihilation spectroscopy was employed to explore the thermal effects on the film microstructure evolution in CoFeB/MgO/CoFeB heterostructures. It is found that high annealing temperature can drive vacancy defects agglomeration and ordering acceleration in the MgO barrier. Meanwhile, another important type of defects, vacancy clusters, which are formed via the agglomeration of vacancy defects in the MgO barrier after annealing, still exists inside the MgO barrier. All these behaviors in the MgO barrier could potentially impact the overall performance in MgO based magnetic tunnel junctions.

CaFe2O4 as a self-sufficient solar energy converter

NASA Astrophysics Data System (ADS)

Tablero, C.

2017-10-01

An ideal solar energy to electricity or fuel converter should work without the use of any external bias potential. An analysis of self-sufficiency when CaFe2O4 is used to absorb the sunlight is carried out based on the CaFe2O4 absorption coefficient. We started to obtain this coefficient theoretically within the experimental bandgap range in order to fix the interval of possible values of photocurrents, maximum absorption efficiencies, and photovoltages and thus that of self-sufficiency considering only the radiative processes. Also for single-gap CaFe2O4, we evaluate an alternative for increasing the photocurrent and maximum absorption efficiency based on inserting an intermediate band using high doping or alloying.

Size effect on L10 ordering and magnetic properties of chemically synthesized FePt and FePtAu nanoparticles

NASA Astrophysics Data System (ADS)

Jia, Zhiyong; Kang, Shishou; Shi, Shifan; Nikles, David E.; Harrell, J. W.

2005-05-01

There is growing evidence that FePt nanoparticles become increasingly difficult to chemically order as the size approaches a few nanometers. We have studied the chemical ordering of FePt and FePtAu nanoparticle arrays as a function of particle size. Monodisperse Fe49Pt51 and Fe48Pt44Au8 nanoparticles with a size about 6nm were synthesized by the simultaneous decomposition of iron pentacarbonyl and reduction of platinum acetylacetonate and gold (III) acetate in a mixture of phenyl ether and hexadecylamine (HDA), with 1-adamantanecarboxylic acid and HDA as stabilizers. The nanoparticles were dispersed in toluene, films of the particles were cast onto silicon wafers from the dispersion, and the films were annealed in a tube furnace with flowing Ar +5%H2. The magnetic anisotropy and switching volumes were determined from time- and temperature-dependent coercivity measurements. By comparing with 3-nm FePt and FePtAu nanoparticles of comparable composition, the phase transformation is easier for the larger particles. Under the same annealing conditions, the larger particles have higher anisotropy and order parameter. Additive Au is very effective in enhancing the chemical ordering in both small and large particles, with x-ray diffraction superlattice peaks appearing after annealing at 350°C. Dynamic remnant coercivity measurements and magnetic switching volumes suggest particle aggregation at the higher annealing temperatures in both small and large particles.

Iron catalyst chemistry in modeling a high-pressure carbon monoxide nanotube reactor

NASA Technical Reports Server (NTRS)

Scott, Carl D.; Povitsky, Alexander; Dateo, Christopher; Gokcen, Tahir; Willis, Peter A.; Smalley, Richard E.

2003-01-01

The high-pressure carbon monoxide (HiPco) technique for producing single-wall carbon nanotubes (SWNTs) is analyzed with the use of a chemical reaction model coupled with flow properties calculated along streamlines, calculated by the FLUENT code for pure carbon monoxide. Cold iron pentacarbonyl, diluted in CO at about 30 atmospheres, is injected into a conical mixing zone, where hot CO is also introduced via three jets at 30 degrees with respect to the axis. Hot CO decomposes the Fe(CO)5 to release atomic Fe. Then iron nucleates and forms clusters that catalyze the formation of SWNTs by a disproportionation reaction (Boudouard) of CO on Fe-containing clusters. Alternative nucleation rates are estimated from the theory of hard sphere collision dynamics with an activation energy barrier. The rate coefficient for carbon nanotube growth is estimated from activation energies in the literature. The calculated growth was found be about an order of magnitude greater than measured, regardless of the nucleation rate. A study of cluster formation in an incubation zone prior to injection into the reactor shows that direct dimer formation from Fe atoms is not as important as formation via an exchange reaction of Fe with CO in FeCO.

Iron catalyst chemistry in modeling a high-pressure carbon monoxide nanotube reactor.

PubMed

Scott, Carl D; Povitsky, Alexander; Dateo, Christopher; Gökçen, Tahir; Willis, Peter A; Smalley, Richard E

2003-01-01

The high-pressure carbon monoxide (HiPco) technique for producing single-wall carbon nanotubes (SWNTs) is analyzed with the use of a chemical reaction model coupled with flow properties calculated along streamlines, calculated by the FLUENT code for pure carbon monoxide. Cold iron pentacarbonyl, diluted in CO at about 30 atmospheres, is injected into a conical mixing zone, where hot CO is also introduced via three jets at 30 degrees with respect to the axis. Hot CO decomposes the Fe(CO)5 to release atomic Fe. Then iron nucleates and forms clusters that catalyze the formation of SWNTs by a disproportionation reaction (Boudouard) of CO on Fe-containing clusters. Alternative nucleation rates are estimated from the theory of hard sphere collision dynamics with an activation energy barrier. The rate coefficient for carbon nanotube growth is estimated from activation energies in the literature. The calculated growth was found be about an order of magnitude greater than measured, regardless of the nucleation rate. A study of cluster formation in an incubation zone prior to injection into the reactor shows that direct dimer formation from Fe atoms is not as important as formation via an exchange reaction of Fe with CO in FeCO.

Electrical conductivity and magnetic susceptibility of rutile type CrVNbO/sub 6/, FeVNbO/sub 6/ and NiV/sub 2/Nb/sub 2/O/sub 10/

DOE Office of Scientific and Technical Information (OSTI.GOV)

Greenblatt, M.; McCarroll, W.H.; Nair, K.R.

1984-06-01

Electric conductivity (77-300K) and magnetic susceptibility (4.2-300K) of rutile type polycrystalline samples of CrVNbO/sub 6/, FeVNbO/sub 6/ and NiV/sub 2/Nb/sub 2/O/sub 10/ are reported. All three compounds are n-type semiconductors with room-temperature resistivities of the order of 10/sup 2/-10/sup 3/ ohm-cm. CrVNbO/sub 6/ shows ferromagnetic coupling in the high-temperature region and orders antiferromagnetically below 10K. FeVNbO/sub 6/ transforms to a spin glass state below 20K. NiV/sub 2/Nb/sub 2/O/sub 10/ shows evidence of weak antiferromagnetic interactions. The transport properties of the compounds are discussed in terms of structural properties and unpaired d electrons present on the respective transition metal ions.

Simultaneous magnetic investigations of Cu precipitation and recovery in thermally aged Fe-Cu alloy by first-order-reversal-curves

NASA Astrophysics Data System (ADS)

Kobayashi, Satoru; Kawagoe, Riko; Murakami, Hiroaki

2018-05-01

We have measured first-order reversal curves (FORCs) for Fe-1wt%Cu alloy thermally aged at 753 K up to 20000 min. While hardness exhibits a maximum at around 1000 min, reflecting the formation and growth of Cu precipitates, major-loop coercivity monotonically decreases and becomes almost constant above 100 min.; an increase of coercivity associated with Cu precipitation is masked by a large decrease due to recovery. On the other hand, FORC diagrams exhibit two distribution peaks at low and high switching fields after aging. While the former shifts towards a lower switching field after aging, reflecting recovery, the latter shows up after aging up to ˜1000 min, possibly due to the formation of Cu precipitates. These observations demonstrate that FORCs are useful to separately evaluate competing microstructural changes in thermally aged Fe-Cu alloy where recovery and Cu precipitation take place simultaneously.

Ordered structure of FeGe2 formed during solid-phase epitaxy

NASA Astrophysics Data System (ADS)

Jenichen, B.; Hanke, M.; Gaucher, S.; Trampert, A.; Herfort, J.; Kirmse, H.; Haas, B.; Willinger, E.; Huang, X.; Erwin, S. C.

2018-05-01

Fe3Si /Ge (Fe ,Si ) /Fe3Si thin-film stacks were grown by a combination of molecular beam epitaxy and solid-phase epitaxy (Ge on Fe3Si ). The stacks were analyzed using electron microscopy, electron diffraction, and synchrotron x-ray diffraction. The Ge(Fe,Si) films crystallize in the well-oriented, layered tetragonal structure FeGe2 with space group P 4 m m . This kind of structure does not exist as a bulk material and is stabilized by the solid-phase epitaxy of Ge on Fe3Si . We interpret this as an ordering phenomenon induced by minimization of the elastic energy of the epitaxial film.

Porewater inputs drive Fe redox cycling in the water column of a temperate mangrove wetland

NASA Astrophysics Data System (ADS)

Holloway, Ceylena J.; Santos, Isaac R.; Rose, Andrew L.

2018-07-01

Iron is a vital micronutrient within coastal marine ecosystems, playing an integral role in the scale and dynamics of primary production and carbon cycling in the world's oceans. We investigated the relative importance of in situ Fe(II) production from photochemical, microbial and thermal Fe reduction in the surface water column as well as advective porewater inputs in a temperate saline wetland in Australia containing mangrove and saltmarsh vegetation. The diel average concentration of Fe(II) (0.63 ± 0.21 μM, accounting for >70% of the total dissolved Fe present in surface water) was much higher than commonly reported in oxygenated marine waters despite high dissolved oxygen concentrations (81-112% saturation), pH (7.7-7.8) and salinity (33-36) that favor Fe oxidation. In situ production of Fe(II) in the surface water column was primarily driven by microbial processes rather than photochemical and thermal reduction, with a maximum production rate of 4.9 × 10-3 nM s-1. Advective porewater Fe(II) inputs to the wetland averaged over a diel cycle (3.0 × 10-1 nM s-1) were an order of magnitude greater than the combined Fe(II) production rate from autochthonous water column processes (1.0 × 10-2 nM s-1). A bottom up model based on the estimated individual fluxes was used to explain the high Fe(II) concentrations measured during a 24 h time series experiment. Combined, different lines of evidence suggest that advective porewater exchange provides significant quantities of Fe(II) to the estuarine wetland.

Coupled ferroelectric polarization and magnetization in spinel FeCr2S4

PubMed Central

Lin, L.; Zhu, H. X.; Jiang, X. M.; Wang, K. F.; Dong, S.; Yan, Z. B.; Yang, Z. R.; Wan, J. G.; Liu, J.-M.

2014-01-01

One of the core issues for multiferroicity is the strongly coupled ferroelectric polarization and magnetization, while so far most multiferroics have antiferromagnetic order with nearly zero magnetization. Magnetic spinel compounds with ferrimagnetic order may be alternative candidates offering large magnetization when ferroelectricity can be activated simultaneously. In this work, we investigate the ferroelectricity and magnetism of spinel FeCr2S4 in which the Fe2+ sublattice and Cr3+ sublattice are coupled in antiparallel alignment. Well defined ferroelectric transitions below the Fe2+ orbital ordering termperature Too = 8.5 K are demonstrated. The ferroelectric polarization has two components. One component arises mainly from the noncollinear conical spin order associated with the spin-orbit coupling, which is thus magnetic field sensitive. The other is probably attributed to the Jahn-Teller distortion induced lattice symmetry breaking, occuring below the orbital ordering of Fe2+. Furthermore, the coupled ferroelectric polarization and magnetization in response to magnetic field are observed. The present work suggests that spinel FeCr2S4 is a multiferroic offering both ferroelectricity and ferrimagnetism with large net magnetization. PMID:25284432

Redox Heterogenity in MORB

NASA Astrophysics Data System (ADS)

Cottrell, E.; Kelley, K. A.

2012-12-01

Mantle oxygen fugacity (fO2) has a first-order effect on the petrogenesis of mantle-derived melts and the speciation of mantle fluids. Current debate centers on the spatial uniformity of upper mantle fO2 and its constancy through geologic time. We use iron K-edge X-ray absorption near-edge structure (μXANES) spectroscopy to provide Fe3+ /ΣFe ratios of submarine mantle-derived basalts from mid-ocean ridges (MORB) as a proxy for fO2. A global survey of primitive (>8.75 wt% MgO) MORB glasses at spreading centers, unaffected by plumes, reveals a decrease in Fe3+ /ΣFe ratio of 12% relative with indices of mantle enrichment such as 87/86Sr, 208/204Pb, Ba/La, and Rb/Sr ratios. The strong negative correlation between upper mantle fO2 and enrichment recorded by MORB glasses contrasts with the positive relationship hinted at by abyssal peridotite oxybarometry (e.g. Ballhaus, CMP, 1993) and the general prediction of a positive correlation born of the expectation that Fe3+ can be treated as more incompatible than Fe2+ during mantle melting. These data unequivocally link upper mantle oxidation state to mantle source enrichment. EMORB generation is commonly attributed to subduction-related processes. That EMORB is more reduced than NMORB implies that deeply subducted and recycled lithologies, such as anoxic sediment, may be more reduced than ambient mantle. Negative correlations between traditional tracers of recycled sediment (e.g. +Nb anomaly, high 87/86Sr, high LILE/LREE) and redox support this hypothesis. Preservation of redox signatures on plate-recycling timescales of hundreds of millions to billions of years would require the mantle to be very poorly buffered. Alternatively, MORB Fe3+ /ΣFe ratios may be generated in situ beneath ridges as a function of variable carbon content. The shallow MORB source is too oxidized to stabilize graphite (Cottrell and Kelley, EPSL, 2011) and carbon exists as oxides. Decreasing fO2 with increasing depth eventually stabilizes reduced carbon species (diamond, carbides, alloys), however, and aCO2 may buffer mantle assemblages. Upon ascent, reduced carbon in upwelling mantle must oxidize, reducing Fe in the process such that more carbon-rich mantle would arrive at the surface with a lower Fe3+ /ΣFe ratio. We cannot directly correlate Fe3+ /ΣFe ratios with CO2 concentrations because submarine basalts have variably degassed CO2; however, the unequivocally carbon-rich sample 2πD43 (popping rock) does record a low Fe3+ /ΣFe ratio. CO2 variations on the order of 80 ppm in the mantle source would explain the range of MORB/EMORB Fe3+ /ΣFe ratios we observe, indicating a possible range of carbon concentrations in subduction-related lithologies. The relationships between MORB Fe3+ /ΣFe ratios, trace elements, and isotopes are consistent with modeled mixtures of depleted melts and low-degree carbonatitic melts of ancient subducted igneous crust plus 5-15% sediment (Stracke et al., G3, 2001) using the near-solidus carbonatitic partition coefficients of Dasgupta et al., Chem Geol, (2009). It may be that low degree carbonatitic melts even act through geologic time to scavenge and fractionate trace elements, creating enriched high-carbon reservoirs. Low Fe3+ /ΣFe ratios, and even EMORB itself, may therefore herald greater carbon concentrations, and the influence of low-degree carbonatitic melts, in Earth's mantle.

Increased magnetic moment induced by lattice expansion from α-Fe to α′-Fe{sub 8}N

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dirba, Imants, E-mail: dirba@fm.tu-darmstadt.de; Komissinskiy, Philipp; Alff, Lambert, E-mail: alff@oxide.tu-darmstadt.de

2015-05-07

Buffer-free and epitaxial α-Fe and α′-Fe{sub 8}N{sub x} thin films have been grown by RF magnetron sputtering onto MgO (100) substrates. The film thicknesses were determined with high accuracy by evaluating the Kiessig fringes of X-ray reflectometry measurements allowing a precise volume estimation. A gradual increase of the nitrogen content in the plasma led to an expansion of the iron bcc unit cell along the [001] direction resulting finally in a tetragonal distortion of about 10% corresponding to the formation of α′-Fe{sub 8}N. The α-Fe lattice expansion was accompanied by an increase in magnetic moment to 2.61 ± 0.06μ{sub B} per Femore » atom and a considerable increase in anisotropy. These experiments show that—without requiring any additional ordering of the nitrogen atoms—the lattice expansion of α-Fe itself is the origin of the increased magnetic moment in α′-Fe{sub 8}N.« less

Complex magnetic properties of TbMn{sub 1-x}Fe{sub x}O{sub 3} (x = 0.1 and 0.2) nanoparticles prepared by the sol-gel method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Das, A.; Chatterjee, S.; Das, D., E-mail: ddas@alpha.iuc.res.in

2016-05-23

TbMn{sub 1-x}Fe{sub x}O{sub 3} nanoparticles (NPs) with x = 0, 0.1 and 0.2 have been prepared by adopting the chemical sol-gel method. Phase identification and particle size estimation are done by XRD analysis. M-H measurements at 5 K indicate a complete ferromagnetic behaviour in the Fe-doped samples with large coercivity whereas the pristine sample shows presence of both ferromagnetic and antiferromagnetic orders. ZFC and FC magnetization curves of all samples show signature of antiferromagnetic ordering of both terbium and manganese magnetic moments along with a systematic shift of ordering temperatures with Fe substitution. {sup 57}Fe Mössbauer spectroscopic measurements of the Fe-dopedmore » samples at room temperature confirm the paramagnetic behaviour and reduction of electric field gradient around Fe probe atoms with increase of Fe concentration.« less

Evidence for short-range magnetic order in the nematic phase of FeSe from anisotropic in-plane magnetostriction and susceptibility measurements

NASA Astrophysics Data System (ADS)

He, Mingquan; Wang, Liran; Hardy, Frédéric; Xu, Liping; Wolf, Thomas; Adelmann, Peter; Meingast, Christoph

2018-03-01

The nature of the nematic state in FeSe remains one of the major unsolved mysteries in Fe-based superconductors. Both spin and orbital physics have been invoked to explain the origin of this phase. Here we present experimental evidence for frustrated, short-range magnetic order, as suggested by several recent theoretical works, in the nematic state of FeSe. We use a combination of magnetostriction, susceptibility, and resistivity measurements to probe the in-plane anisotropies of the nematic state and its associated fluctuations. Despite the absence of long-range magnetic order in FeSe, we observe a sizable in-plane magnetic susceptibility anisotropy, which is responsible for the field-induced in-plane distortion inferred from magnetostriction measurements. Further we demonstrate that all three anisotropies in FeSe are very similar to those of BaFe2As2 , which strongly suggests that the nematic phase in FeSe is also of magnetic origin.

Structural, electronic and magnetic properties of the series of double perovskites (Ca , Sr) 2 - xLaxFeIrO6

NASA Astrophysics Data System (ADS)

Bufaiçal, L.; Adriano, C.; Lora-Serrano, R.; Duque, J. G. S.; Mendonça-Ferreira, L.; Rojas-Ayala, C.; Baggio-Saitovitch, E.; Bittar, E. M.; Pagliuso, P. G.

2014-04-01

Polycrystalline samples of the series of double perovskites Sr2-xLaxFeIrO6 were synthesized. Their structural, electronic and magnetic properties were investigated by X-ray powder diffraction, Mössbauer spectroscopy, magnetic susceptibility, heat capacity and electrical resistivity experiments. The compounds crystallize in a monoclinic structure and were fitted in space group P21 / n, with a significant degree of Fe/Ir cationic disorder. As in Ca2-xLaxFeIrO6 the Sr-based system seems to evolve from an antiferromagnetic ground state for the end members (x=0.0 and x=2.0) to a ferrimagnetic order in the intermediate regions (x ~ 1). Since Mössbauer spectra indicate that Fe valence remains 3+ with doping, this tendency of change in the nature of the microscopic interaction could be attributed to Ir valence changes, induced by La3+ electrical doping. Upon comparing both Ca and Sr series, Sr2-xLaxFeIrO6 is more structurally homogenous and presents higher magnetization and transition temperatures. Magnetic susceptibility measurements at high temperatures on Sr1.2La0.8FeIrO6 indicate a very high ferrimagnetic Curie temperature TC ~ 700 K. For the Sr2FeIrO6 compound, electrical resistivity experiments under applied pressure suggest that this material might be a Mott insulator.

Plastic deformation of FeSi at high pressures: implications for planetary cores

NASA Astrophysics Data System (ADS)

Kupenko, Ilya; Merkel, Sébastien; Achorner, Melissa; Plückthun, Christian; Liermann, Hanns-Peter; Sanchez-Valle, Carmen

2017-04-01

The cores of terrestrial planets is mostly comprised of a Fe-Ni alloy, but it should additionally contain some light element(s) in order to explain the observed core density. Silicon has long been considered as a likely candidate because of geochemical and cosmochemical arguments: the Mg/Si and Fe/Si ratios of the Earth does not match those of the chondrites. Since silicon preferentially partition into iron-nickel metal, having 'missing' silicon in the core would solve this problem. Moreover, the evidence of present (e.g. Mercury) or ancient (e.g. Mars) magnetic fields on the terrestrial planets is a good indicator of (at least partially) liquid cores. The estimated temperature profiles of these planets, however, lay below iron melting curve. The addition of light elements in their metal cores could allow reducing their core-alloy melting temperature and, hence, the generation of a magnetic field. Although the effect of light elements on the stability and elasticity of Fe-Ni alloys has been widely investigated, their effect on the plasticity of core materials remains largely unknown. Yet, this information is crucial for understanding how planetary cores deform. Here we investigate the plastic deformation of ɛ-FeSi up to 50 GPa at room temperature employing a technique of radial x-ray diffraction in diamond anvil cells. Stoichiometric FeSi endmember is a good first-order approximation of the Fe-FeSi system and a good starting material to develop new experimental perspectives. In this work, we focused on the low-pressure polymorph of FeSi that would be the stable phase in the cores of small terrestrial planets. We will present the analysis of measured data and discuss their potential application to constrain plastic deformation in planetary cores.

Antiferromagnetic structure and electronic properties of BaCr2As2 and BaCrFeAs2

NASA Astrophysics Data System (ADS)

Filsinger, Kai A.; Schnelle, Walter; Adler, Peter; Fecher, Gerhard H.; Reehuis, Manfred; Hoser, Andreas; Hoffmann, Jens-Uwe; Werner, Peter; Greenblatt, Martha; Felser, Claudia

2017-05-01

Recent theoretical studies suggest that superconductivity may be found in doped chromium pnictides with crystal structures similar to their iron counterparts. Here, we report a comprehensive study on the magnetic arsenides BaCr2As2 and BaCrFeAs2 (space group I 4 /m m m ), which are possible mother compounds with d4 and d5 electron configurations, respectively. DFT-based calculations of the electronic structure evidence metallic antiferromagnetic ground states for both compounds. By powder neutron diffraction, we confirm for BaCr2As2 a robust ordering in the antiferromagnetic G -type structure at TN=580 K with μCr=1.9 μB . Anomalies in the lattice parameters point to magnetostructural coupling effects. In BaCrFeAs2, the Cr and Fe atoms randomly occupy the transition-metal site and G -type order is found below 265 K with μCr /Fe=1.1 μB . 57Fe Mössbauer spectroscopy demonstrates that only a small ordered moment is associated with the Fe atoms, in agreement with electronic structure calculations leading to μFe˜0 . The temperature dependence of the hyperfine field does not follow that of the total moments. Both compounds are metallic but show large enhancements of the linear specific heat. Electrical transport in BaCrFeAs2 is dominated by the atomic disorder and the partial magnetic disorder of Fe. Our results indicate that Néel-type order is unfavorable for Fe moments and thus it is destabilized with increasing Fe content.

Structural chemistry and magnetic properties of the perovskite Sr{sub 3}Fe{sub 2}TeO{sub 9}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tang, Yawei; Hunter, Emily C.; Battle, Peter D., E-mail: peter.battle@chem.ox.ac.uk

2016-10-15

A polycrystalline sample of perovskite-like Sr{sub 3}Fe{sub 2}TeO{sub 9} has been prepared in a solid-state reaction and studied by a combination of electron microscopy, Mössbauer spectroscopy, magnetometry, X-ray diffraction and neutron diffraction. The majority of the reaction product is shown to be a trigonal phase with a 2:1 ordered arrangement of Fe{sup 3+} and Te{sup 6+} cations. However, the sample is prone to nano-twinning and tetragonal domains with a different pattern of cation ordering exist within many crystallites. Antiferromagnetic ordering exists in the trigonal phase at 300 K and Sr{sub 3}Fe{sub 2}TeO{sub 9} is thus the first example of amore » perovskite with 2:1 trigonal cation ordering to show long-range magnetic order. At 300 K the antiferromagnetic phase coexists with two paramagnetic phases which show spin-glass behaviour below ~80 K. - Graphical abstract: Sr{sub 3}Fe{sub 2}TeO{sub 9} has a 2:1 ordered arrangement of Fe{sup 3+} and Te{sup 6+} cations over the octahedral sites of a perovskite structure and is antiferromagnetic at room temperature. - Highlights: • 2:1 Cation ordering in a trigonal perovskite. • Magnetically ordered trigonal perovskite. • Intergrowth of nanodomains in perovskite microstructure.« less

Controlled Phase and Tunable Magnetism in Ordered Iron Oxide Nanotube Arrays Prepared by Atomic Layer Deposition

NASA Astrophysics Data System (ADS)

Zhang, Yijun; Liu, Ming; Peng, Bin; Zhou, Ziyao; Chen, Xing; Yang, Shu-Ming; Jiang, Zhuang-De; Zhang, Jie; Ren, Wei; Ye, Zuo-Guang

2016-01-01

Highly-ordered and conformal iron oxide nanotube arrays on an atomic scale are successfully prepared by atomic layer deposition (ALD) with controlled oxidization states and tunable magnetic properties between superparamagnetism and ferrimagnetism. Non-magnetic α-Fe2O3 and superparamagnetic Fe3O4 with a blocking temperature of 120 K are in-situ obtained by finely controlling the oxidation reaction. Both of them exhibit a very small grain size of only several nanometers due to the nature of atom-by-atom growth of the ALD technique. Post-annealing α-Fe2O3 in a reducing atmosphere leads to the formation of the spinel Fe3O4 phase which displays a distinct ferrimagnetic anisotropy and the Verwey metal-insulator transition that usually takes place only in single crystal magnetite or thick epitaxial films at low temperatures. The ALD deposition of iron oxide with well-controlled phase and tunable magnetism demonstrated in this work provides a promising opportunity for the fabrication of 3D nano-devices to be used in catalysis, spintronics, microelectronics, data storages and bio-applications.

Structural and magnetic phase transitions near optimal superconductivity in BaFe 2(As 1-xP x) 2

DOE PAGES

Hu, Ding; Lu, Xingye; Zhang, Wenliang; ...

2015-04-17

In this study, we use nuclear magnetic resonance (NMR), high-resolution x-ray and neutron scattering to study structural and magnetic phase transitions in phosphorus-doped BaFe 2(As 1-xP x) 2. Thus, previous transport, NMR, specific heat, and magnetic penetration depth measurements have provided compelling evidence for the presence of a quantum critical point (QCP) near optimal superconductivity at x = 0.3. However, we show that the tetragonal-to-orthorhombic structural (T s) and paramagnetic to antiferromagnetic (AF, T N) transitions in BaFe 2(As 1-xP x) 2 are always coupled and approach to T N ≈ T s ≥ T c (≈ 29 K) formore » x = 0.29 before vanishing abruptly for x ≥ 0.3. These results suggest that AF order in BaFe 2(As 1-xP x) 2 disappears in a weakly first order fashion near optimal superconductivity, much like the electron-doped iron pnictides with an avoided QCP.« less

Itinerant Antiferromagnetism in FeMnP 0.8Si 0.2

DOE PAGES

Sales, Brian C.; Susner, Michael A.; Conner, Benjamin S.; ...

2015-09-25

Compounds based on the Fe 2P structure have continued to attract interest because of the interplay between itinerant and localized magnetism in a noncentrosymmetric crystal structure, and because of the recent developments of these materials for magnetocaloric applications. We report the growth and characterization of millimeter-sized single crystals of FeMnP 0.8Si 0.2 with the Fe 2P structure. Single-crystal x-ray diffraction, magnetization, resistivity, and Hall and heat capacity data are reported. The crystals exhibit itinerant antiferromagnetic order below 158 K with no hint of ferromagnetic behavior in the magnetization curves and with the spins ordered primarily in the ab plane. Themore » room-temperature resistivity is close to the Ioffe-Regel limit for a metal. Single-crystal x-ray diffraction indicates a strong preference for Mn to occupy the larger pyramidal 3g site. The cation site preference in the as-grown crystals and the antiferromagnetism were not changed after high-temperature anneals and a rapid quench to room temperature« less

Effects of pressure on the magnetic properties of FeO: A diffusion Monte Carlo study

NASA Astrophysics Data System (ADS)

Townsend, Joshua; Shulenburger, Luke; Mattsson, Thomas; Esler, Ken; Cohen, Ronald

While simple in terms of structure and composition, both experimental and computational investigations have demonstrated that FeO has a rich phase diagram of structural phase transformations, electronic spin transitions, insulator-metal transitions, and magnetic ordering transitions, due to the open-shell occupation of the Fe 3d electrons. We investigated the magnetic and electronic structures of FeO under ambient and high pressure conditions using diffusion Quantum Monte Carlo (QMC) within the fixed-node approximation. QMC techniques are especially well suited to the study of strongly correlated systems because they explicitly include correlation into the ground-state wave function. Here we report on the effects of the choice of trial wave function on the ambient pressure lattice distortion due to AFM ordering, as well as the equation of state, spin collapse, and metal-insulator transitions. Sandia National Laboratories is a multi-mission laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE.

Electric Field Controlled Magnetism in BiFeO3/Ferromagnet Films

NASA Astrophysics Data System (ADS)

Barry, M.; Lee, K.; Chu, Y. H.; Yang, P. L.; Martin, L. W.; Jenkins, C. A.; Ramesh, R.; Scholl, A.; Doran, A.

2007-03-01

BiFeO3 is the only single phase room temperature multiferroic that is currently known. Not only does it have applications as a lead-free replacement for ferroelectric memory cells and piezoelectric sensors, but its interactions with other materials are now attracting a great deal of attention. Its multiferroic nature has potential in the field of exchange bias, where it could allow electric-field control of the ferromagnetic (FM) magnetization. In order to understand this coupling, an understanding of the magnetization in BiFeO3 is necessary. X-ray linear and circular dichroism images were obtained using a high spatial resolution photoelectron emission microscope (PEEM), allowing elemental specificity and surface sensitivity. A piezoelectric force microscope (PFM) was used to map the ferroelectric state in micron-sized regions of the films, which were then probed using crystallographic measurements and temperature dependent PEEM measurements. Temperature dependent structural measurements allow decoupling of the two order parameters, ferroelectric and magnetic, contributing to the photoemission signal. Careful analysis of linear and circular dichroism images allows determination of magnetic directions in BiFeO3 and FM layers.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Yong; Xing, Qingfeng; Straszheim, Warren E.

Here, we report how the superconducting phase forms in pseudo-single-crystal K xFe 2-ySe 2. In situ scanning electron microscopy (SEM) observation reveals that, as an order-disorder transition occurs, on cooling, most of the high-temperature iron-vacancy-disordered phase gradually changes into the iron-vacancy-ordered phase whereas a small quantity of the high-temperature phase retains its structure and aggregates to the stripes with more iron concentration but less potassium concentration compared to the iron-vacancy-ordered phase. The stripes that are generally recognized as the superconducting phase are actually formed as a remnant of the high-temperature phase with a compositional change after an “imperfect” order-disorder transition.more » It should be emphasized that the phase separation in pseudo-single-crystal K xFe 2-ySe 2 is caused by the iron-vacancy order-disorder transition. The shrinkage of the high-temperature phase and the expansion of the newly created iron-vacancy-ordered phase during the phase separation rule out the mechanism of spinodal decomposition proposed in an early report [Wang et al, Phys. Rev. B 91, 064513 (2015)]. Since the formation of the superconducting phase relies on the occurrence of the iron-vacancy order-disorder transition, it is impossible to synthesize a pure superconducting phase by a conventional solid state reaction or melt growth. By focused ion beam-scanning electron microscopy, we further demonstrate that the superconducting phase forms a contiguous three-dimensional architecture composed of parallelepipeds that have a coherent orientation relationship with the iron-vacancy-ordered phase.« less

Sound velocity measurements of dhcp-FeHx up to 70 GPa using inelastic X-ray scattering: Implications for the abundance of hydrogen in the Earth's core

NASA Astrophysics Data System (ADS)

Shibazaki, Y.; Ohtani, E.; Fukui, H.; Sakai, T.; Kamada, S.; Baron, A. Q.; Nishitani, N.; Hirao, N.; Takemura, K.

2011-12-01

The Earth's interior has been directly investigated by seismic wave propagation and normal mode oscillation. In particular, the distributions of density and sound velocity are available to study the Earth's core (e.g. PREM). The inner core, which is solid state, is approximately 3 % less dense than pure iron (a core density deficit), and it is considered that the core consists of iron and light elements, such as hydrogen, carbon, oxygen, silicon, and sulfur. In this work, in order to constrain the abundance of hydrogen in the Earth's core by matching the density and sound velocity of FeHx to those of PREM, we determined the compressional sound velocity of iron hydride at high pressure using inelastic X-ray scattering (IXS). The IXS experiments and in situ X-ray diffraction (XRD) experiments were conducted up to 70 GPa and room temperature. High-pressure conditions were generated using a symmetric diamond anvil cell (DAC) with tungsten gaskets. Hydrogen initially pressurized to 0.18 GPa was loaded to the sample chamber. The IXS experiments were performed at BL35XU of the SPring-8 facility in Japan. The XRD experiments at high pressure were carried out by the angle dispersive method at BL10XU of the SPring-8 facility in Japan. The each XRD pattern of FeHx was collected after each IXS measurement in order to obtain directly the density of FeHx. Over the range of pressure studied, the diffraction lines of double-hexagonal close-packed (dhcp)-FeHx were observed and there were no diffraction lines of iron. We show that FeHx follows Birch's law for Vp above 37 GPa, namely a linear dependence between velocity and density. The estimated Vp, extrapolated to core conditions, is compared with PREM. Our results provide that the Earth's inner core could contain about 0.2 wt% hydrogen.

N-doped graphene layers encapsulated NiFe alloy nanoparticles derived from MOFs with superior electrochemical performance for oxygen evolution reaction

NASA Astrophysics Data System (ADS)

Feng, Yi; Yu, Xin-Yao; Paik, Ungyu

2016-09-01

Water splitting, an efficient approach for hydrogen production, is often hindered by unfavorable kinetics of oxygen evolution reaction (OER). In order to reduce the overpotential, noble metal oxides-based electrocatalysts like RuO2 and IrO2 are usually utilized. However, due to their scarcity, the development of cost-effective non-precious OER electrocatalysts with high efficiency and good stability is urgently required. Herein, we report a facile one-step annealing of metal-organic frameworks (MOFs) strategy to synthesize N-doped graphene layers encapsulated NiFe alloy nanoparticles (NiFe@C). Through tuning the nanoparticle size and calcination temperature, NiFe@C with an average size of around 16 nm obtained at 700 °C exhibits superior OER performance with an overpotential of only 281 mV at 10 mA cm-2 and high durability. The facile synthesis method and excellent electrochemical performance show great potential of NiFe@C in replacing the precious metal-based electrocatalysts in the OER.

Molecular nanomagnets as contrast agents for Magnetic Resonance Imaging

NASA Astrophysics Data System (ADS)

Rodríguez, Elisenda; Roig, Anna; Molins, Elies; Arús, Carles; Cabañas, Miquel; Quintero, María Rosa; Cerdán, Sebastián; Sanfeliu, Coral

2003-03-01

Magnetic resonance imaging (MRI) is a non-invasive technique used in medicine to produce high quality images of human body slices. In order to enhance the contrast between different organs or to reveal altered portions of them such necrosis or tumors, the administration of a contrast agent is highly convenient. Currently Gd-DTPA, a paramagnetic complex, is the most widely administered compound. In this context, we have assayed molecular nanomagnets as MRI contrast agents. The complex [(tacn)_6Fe_8(μ_3-O)_2(μ_2-OH)_12]Br_8·9H_2O^1(Fe8 in brief) has been evaluated and shorter relaxation times, T1 and T_2, have been obtained for Fe8 than those obtained for the commercial Gd-DTPA. No toxic effects have been observed at concentrations up to 1 mM of Fe8 in cultured cells. Phantom studies with T_1-weighted MRI at 9.4 Tesla suggest that Fe8 can have potentiality as T_1-contrast agent. ^1Wieghardt K Angew Chem Intl Ed Engl 23 1 (1984) 77

High temperature calorimetry of sulfide systems

NASA Astrophysics Data System (ADS)

Cemič, L.; Kleppa, O. J.

1987-01-01

Enthalpies of solution of synthetic pentlandite Fe4.5Ni4.5S8, natural violarite (Fe0.2941Ni0.7059)3S4 from Vermillion mine, Sudbury, Ontario, synthetic pyrrhotite, FeS, synthetic high temperature NiS, synthetic vaesite, NiS2, synthetic pyrite, FeS2, Ni and Fe have been measured in a Ni0.6S0.4 melt at 1,100 K. Using these data and the standard enthalpies of formation of binary sulfides, given in literature, standard enthalpies of formation of pentlandite and violarite were calculated. The following values are reported: Δ H {f/o, Pent}=-837.37±14.59 kJ mol-1 and Δ H {f/o, Viol}=-378.02±11.81 kJ mol-1. While there are no thermo-chemical data for pentlandite with which our new value can be compared, an equilibrium investigation of stoichiometric violarite by Craig (1971) gives a significantly less negative enthalpy of formation. It is suggested that the difference may be due to the higher degree of order in the natural sample.

N-doped graphene layers encapsulated NiFe alloy nanoparticles derived from MOFs with superior electrochemical performance for oxygen evolution reaction

PubMed Central

Feng, Yi; Yu, Xin-Yao; Paik, Ungyu

2016-01-01

Water splitting, an efficient approach for hydrogen production, is often hindered by unfavorable kinetics of oxygen evolution reaction (OER). In order to reduce the overpotential, noble metal oxides-based electrocatalysts like RuO2 and IrO2 are usually utilized. However, due to their scarcity, the development of cost-effective non-precious OER electrocatalysts with high efficiency and good stability is urgently required. Herein, we report a facile one-step annealing of metal-organic frameworks (MOFs) strategy to synthesize N-doped graphene layers encapsulated NiFe alloy nanoparticles (NiFe@C). Through tuning the nanoparticle size and calcination temperature, NiFe@C with an average size of around 16 nm obtained at 700 °C exhibits superior OER performance with an overpotential of only 281 mV at 10 mA cm−2 and high durability. The facile synthesis method and excellent electrochemical performance show great potential of NiFe@C in replacing the precious metal-based electrocatalysts in the OER. PMID:27658968

Tuning magnetic spirals beyond room temperature with chemical disorder

NASA Astrophysics Data System (ADS)

Canevet, Emmanuel; Morin, Mickael; Raynaud, Adrien; Bartkowiak, Marek; Sheptyakov, Denis; Ban, Voraksmy; Kenzelmann, Michel; Pomjakushina, Ekaterina; Conder, Kazimierz; Medarde, Marisa

In the past years, magnetism-driven ferroelectricity and gigantic magnetoelectric effects have been reported for a number of frustrated magnets with spiral magnetic orders. Such materials are of high current interest due to their potential for spintronics and low-power magnetoelectric devices. However, their low magnetic order temperatures (typically lower than 100K) greatly restrict their fields of application. In this talk we will show that chemical disorder is a powerful tool that can be used to stabilize magnetic spiral phases at higher temperatures. To illustrate this mechanism, we will present our recent results obtain by neutron diffraction on the perovskyte YBaFeCuCuO5, where a controlled manipulation of the Cu/Fe chemical disorder was successfully used to increase the spiral order temperature from 154 to 310K.

Structural, chemical, and magnetic properties of Fe films grown on InAs(100)

NASA Astrophysics Data System (ADS)

Ruppel, L.; Witte, G.; Wöll, Ch.; Last, T.; Fischer, S. F.; Kunze, U.

2002-12-01

The structure of epitaxial Fe films grown on an InAs(100)-c(8×2)/(4×2) surface has been studied in situ by means of low-energy electron diffraction and x-ray photoelectron spectroscopy, while their magnetic properties were characterized ex situ by superconducting quantum interference device magnetometry at temperatures of 5 300 K. Deposition of iron at room temperature or below leads to the formation of a thin iron arsenide layer that floats on the Fe film upon further deposition. Postdeposition annealing causes no significant improvement of the film structure but activates a further arsenic diffusion through the Fe film. Significant exchange-bias effects were found at low temperatures for insufficiently capped and partially oxidized Fe films, and are attributed to noncollinear spin order at the Ag capping layer/Fe interface. For perfect, nonoxidized Fe films, such a noncollinear spin order at the Fe/InAs interface is excluded as no thermomagnetic irreversibilities were found. This indicates that the spin order at the Fe/InAs interface is suitable for spin injection.

Magnetic properties of nano-multiferroic materials

NASA Astrophysics Data System (ADS)

Ramam, Koduri; Diwakar, Bhagavathula S.; Varaprasad, Kokkarachedu; Swaminadham, Veluri; Reddy, Venu

2017-11-01

Latent magnetization in the multiferroics can be achieved via the structural distortion with respect to particle size and destroying the spiral spin structure, which plays the vital role in high-performance applications. In this investigation, multifunctional single phase Bi1-xLaxFe1-yCoyO3 nanomaterials were synthesized by co-precipitation technique. The chemical composition, phase genesis, morphology and thermal characteristics of the Bi1-xLaxFe1-yCoyO3 were studied by FTIR, XRD, SEM/EDS, TEM and TGA. XRD studies confirmed single phase distorted rhombohedral structure in Bi1-xLaxFe1-yCoyO3. The novelty in magnetic behavior of the Bi0.85La0.15Fe0.75Co0.25O3 multiferroic at room temperature showed both ferro and anti-ferromagnetic nature with higher order remanent magnetization among other nanocomposites in this study. This magnetic anomaly in Bi0.85La0.15Fe0.75Co0.25O3 is due to doping and size effects on the crystal structure that leads to spin-orbit interactions. Besides, Bi0.85La0.15Fe0.75Co0.25O3 integrated graphene oxide (GO) nanocomposite has shown the change in the magnetic hysteresis that indicates the effect of the semiconducting behavior of GO on the ordered magnetic moments in the multiferroic. This kind of magnetic anomaly could form advanced multiferroic devices.

Remanence carrying minerals in meteorites: a journey through an exotic jungle

NASA Astrophysics Data System (ADS)

Rochette, P.; Gattacceca, J.; Uehara, M.

2011-12-01

Well-known remanence carrying minerals in meteorites are magnetite and pyrrhotite, familiar on Earth, and Fe-Ni metal alloys. In Fe-Ni metal the difficulty in interpreting paleomagnetic data is due to the presence of multiple metastable phases which follow complex transformation paths during thermal treatment. A minor phase, tetrataenite (ordered Fe0.5Ni0.5), usually carries most of the remanence [1]. It is intimately mixed with high susceptibility phases (kamacite and taenite), implying strong interaction effects. FeNi phosphide and carbide (schreibersite and cohenite), often associated with metal, are usually overlooked although they may be responsible for the remanence of enstatite chondrites and some lunar basalts, with Tc around 200°C. They are also likely responsible for the claim of "magnetic carbon" found in Canyon Diablo meteorite [2]. Sulfides, a wide variety of which occurs in meteorites, provide even more thrill. Concerning pyrrhotite, there is still imperfect understanding of the observation that not monoclinic but hexagonal pyrrhotite is the ferromagnetic phase present in some martian meteorites and Rumuruti chondrites. The most common sulfide in meteorites, troilite (FeS), is an antiferromagnet (TN= 320°C), showing a susceptibility anomaly at 140°C. Recently a transition toward weak ferromagnetism has been proposed below 60-70 K [3]. However it has been shown subsequently that this weak ferromagnetism is due to impurities of chromite [4] an ubiquitous phase in meteorites that becomes ferromagnetic below a Tc of 40 to 150 K (a wide range linked to the various possible substitutions). Other sulfides found in meteorites show low temperature transitions. Alabandite ( (Fe,Mn)S) and Daubreelite (FeCr2S4) have been reviewed in [3]. Chalcopyrite (FeCuS2), an antiferromagnet at room temperature, shows magnetic ordering of Cu+ ions at 50 K with appearance of weak ferromagnetism [5]. Magnetic properties of cubanite (Fe2CuS3), a RT ferrimagnet found in CI chondrites and Martian meteorites will also be presented [6]. Most cited minerals exhibit high pressure phase transitions in the 3-5 GPa range and thus are remagnetized by moderate impact.

Magnetic Separation Using HTS Bulk Magnet for Cs-Bearing Fe precipitates

NASA Astrophysics Data System (ADS)

Oka, T.; Ichiju, K.; Sasaki, S.; Ogawa, J.; Fukui, S.; Sato, T.; Ooizumi, M.; Yokoyama, K.; Aoki, S.; Ohnishi, N.

2017-09-01

A peculiar magnetic separation technique has been examined in order to remove the Cs-bearing Fe precipitates formed of the waste ash from the withdrawn incinerator furnaces in Fukushima. The separation system was constructed in combination with high temperature superconducting bulk magnets which generates the intensive magnetic field over 2 T, which was activated by the pulsed field magnetization process. The separation experiment has been operated with use of the newly-built alternating channel type magnetic separating device, which followed the high-gradient magnetic separation technique. The magnetic stainless steel filters installed in the water channels are magnetized by the applied magnetic fields, and are capable of attracting the precipitates bearing the Fe compound and thin Cs contamination. The experimental results clearly exhibited the positive feasibility of HTS bulk magnets.

FAST TRACK COMMUNICATION: High pressure study of BaFe2As2—the role of hydrostaticity and uniaxial stress

NASA Astrophysics Data System (ADS)

Duncan, W. J.; Welzel, O. P.; Harrison, C.; Wang, X. F.; Chen, X. H.; Grosche, F. M.; Niklowitz, P. G.

2010-02-01

We investigate the evolution of the electrical resistivity of BaFe2As2 single crystals with pressure. The samples used were from the same batch, grown using a self-flux method, and showed properties that were highly reproducible. Samples were pressurized using three different pressure media: pentane-isopentane (in a piston-cylinder cell), Daphne oil (in an alumina anvil cell) and steatite (in a Bridgman cell). Each pressure medium has its own intrinsic level of hydrostaticity, which dramatically affects the phase diagram. An increasing uniaxial pressure component in this system quickly reduces the spin density wave order and favours the appearance of superconductivity, which is similar to what is seen in SrFe2As2.

A simple way to prepare Au@polypyrrole/Fe3O4 hollow capsules with high stability and their application in catalytic reduction of methylene blue dye

NASA Astrophysics Data System (ADS)

Yao, Tongjie; Cui, Tieyu; Wang, Hao; Xu, Linxu; Cui, Fang; Wu, Jie

2014-06-01

Metal nanoparticles are promising catalysts for dye degradation in treating wastewater despite the challenges of recycling and stability. In this study, we have introduced a simple way to prepare Au@polypyrrole (PPy)/Fe3O4 catalysts with Au nanoparticles embedded in a PPy/Fe3O4 capsule shell. The PPy/Fe3O4 capsule shell used as a support was constructed in one-step, which not only dramatically simplified the preparation process, but also easily controlled the magnetic properties of the catalysts through adjusting the dosage of FeCl2.4H2O. The component Au nanoparticles could catalyze the reduction of methylene blue dye with NaBH4 as a reducing agent and the reaction rate constant was calculated through the pseudo-first-order reaction equation. The Fe3O4 nanoparticles permitted quick recycling of the catalysts with a magnet due to their room-temperature superparamagnetic properties; therefore, the catalysts exhibited good reusability. In addition to catalytic activity and reusability, stability is also an important property for catalysts. Because both Au and Fe3O4 nanoparticles were wrapped in the PPy shell, compared with precursor polystyrene/Au composites and bare Fe3O4 nanoparticles, the stability of Au@PPy/Fe3O4 hollow capsules was greatly enhanced. Since the current method is simple and flexible to create recyclable catalysts with high stability, it would promote the practicability of metal nanoparticle catalysts in industrial polluted water treatment.Metal nanoparticles are promising catalysts for dye degradation in treating wastewater despite the challenges of recycling and stability. In this study, we have introduced a simple way to prepare Au@polypyrrole (PPy)/Fe3O4 catalysts with Au nanoparticles embedded in a PPy/Fe3O4 capsule shell. The PPy/Fe3O4 capsule shell used as a support was constructed in one-step, which not only dramatically simplified the preparation process, but also easily controlled the magnetic properties of the catalysts through adjusting the dosage of FeCl2.4H2O. The component Au nanoparticles could catalyze the reduction of methylene blue dye with NaBH4 as a reducing agent and the reaction rate constant was calculated through the pseudo-first-order reaction equation. The Fe3O4 nanoparticles permitted quick recycling of the catalysts with a magnet due to their room-temperature superparamagnetic properties; therefore, the catalysts exhibited good reusability. In addition to catalytic activity and reusability, stability is also an important property for catalysts. Because both Au and Fe3O4 nanoparticles were wrapped in the PPy shell, compared with precursor polystyrene/Au composites and bare Fe3O4 nanoparticles, the stability of Au@PPy/Fe3O4 hollow capsules was greatly enhanced. Since the current method is simple and flexible to create recyclable catalysts with high stability, it would promote the practicability of metal nanoparticle catalysts in industrial polluted water treatment. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr00023d

Low temperature magnetization and anomalous high temperature dielectric behaviour of (1-x) YMnO3/xZnFe2O4 composites

NASA Astrophysics Data System (ADS)

Kumar, Virendra; Gaur, Anurag

2018-04-01

We synthesized YMnO3 and ZnFe2O4 composites, (1-x)YMnO3/x(ZnFe2O4) with x = 0, 0.05, 0.10, and 0.15 by high temperature sintering. X-ray diffraction (XRD) patterns indicate the successful formation of composites. Weak ferromagnetism is manifested below Néel temperature (TN) for pristine YMnO3, according to (M-H) study performed at 10 K. For (1-x)YMnO3/xZnFe2O4 (x = 0.05, 0.10, 0.15) a thin coercivity is observed in all compositions, due to short range magnetic ordering at low temperature after the insertion of ZnFe2O4. For pristine YMnO3 explicit divarication between FC-ZFC curves is observed, with crimps observed in both FC and ZFC curves at 75 K, which is the TN of YMnO3. For 1-x(YMnO3)/x ZnFe2O4 composites (x = 0.05, 0.10, 0.15) crimps are perceived only in ZFC curves at slightly varying values of 39.8, 42.32 and 45.63 K respectively. Anomalous peaks are observed in high temperature dielectric curves above 400 K for 1-x(YMnO3)/xZnFe2O4 (x = 0, 0.05, 0.10, 0.15) composites due to Maxwell-Wagner relaxation effect.

SrFe1‑xMoxO2+δ : parasitic ferromagnetism in an infinite-layer iron oxide with defect structures induced by interlayer oxygen

NASA Astrophysics Data System (ADS)

Guo, Jianhui; Shi, Lei; Zhao, Jiyin; Wang, Yang; Yuan, Xueyou; Li, Yang; Wu, Liang

2018-04-01

The recent discovered compound SrFeO2 is an infinite-layer-structure iron oxide with unusual square-planar coordination of Fe2+ ions. In this study, SrFe1‑xMoxO2+δ (x < 0.12) is obtained by crystal transformation from SrFe1‑xMoxO3‑δ perovskite via low-temperature (≤380 °C) topotactic reduction. The parasitic ferromagnetism of the compound and its relationship to the defect structures are investigated. It is found that substitution of high-valent Mo6+ for Fe2+ results in excess oxygen anions O2‑ inserted at the interlayer sites for charge compensation, which further causes large atomic displacements along the c-axis. Due to the robust but flexible Fe-O-Fe framework, the samples are well crystallized within the ab-plane, but are significantly poorer crystallized along the c-axis. Defect structures including local lattice distortions and edge dislocations responsible for the lowered crystallinity are observed by high resolution transmission electron microscopy. Both the magnetic measurements and electron spin resonance spectra provide the evidence of a parasitic ferromagnetism (FM). The week FM interaction originated from the imperfect antiferromagnetic (AFM) ordering could be ascribed to the introduction of uncompensated magnetic moments due to substitution of Mo6+ (S = 0) for Fe2+ (S = 2) and the canted/frustrated spins resulted from defect structures.

In situ TEM study of electron-beam radiation induced boron diffusion and effects on phase and microstructure evolution in nanostructured CoFeB/SiO2 thin film

NASA Astrophysics Data System (ADS)

Liu, B. H.; Teo, H. W.; Mo, Z. H.; Mai, Z. H.; Lam, J.; Xue, J. M.; Zhao, Y. Z.; Tan, P. K.

2017-01-01

Using in situ transmission electron microscopy (TEM), we studied boron diffusion and segregation in CoFeB/SiO2 nanostructured thin film stacks. We also investigated how these phenomena affected the phase and microstructure of CoFeB thin films under electron beam irradiation at 300 kV. A unique phase transformation was observed in CoFeB thin films under high-dose electron irradiation, from a polycrystalline Co3Fe to a unilateral amorphous phase of Co3Fe and nanocrystalline FexCo23-xB6. The unilateral amorphization of the Co3Fe film showed an electron-dose-rate sensitivity with a threshold dose rate. Detailed in situ TEM studies revealed that the unilateral amorphization of the Co3Fe film arose from boron segregation at the bottom of the Co3Fe thin film induced by radiation-enhanced diffusion of boron atoms that were displaced by electron knock-on effects. The radiation-induced nanocrystallization of FexCo23-xB6 was also found to be dose-rate sensitive with a higher electron beam current leading to earlier nucleation and more rapid grain growth. The nanocrystallization of FexCo23-xB6 occurred preferentially at the CoFeB/SiO2 interface. Kinetic studies by in situ TEM revealed the surface crystallization and diffusion-controlled nucleation and grain growth mechanisms. The radiation-enhanced atomic diffusivity and high-concentration of radiation-induced point defects at the Co3Fe/SiO2 interface enhanced the local short-range ordering of Fe, Co, and B atoms, favoring nucleation and grain growth of FexCo23-xB6 at the interface.

Reinforced carbon fiber laminates with oriented carbon nanotube epoxy nanocomposites: Magnetic field assisted alignment and cryogenic temperature mechanical properties.

PubMed

He, Yuxin; Yang, Song; Liu, Hu; Shao, Qian; Chen, Qiuyu; Lu, Chang; Jiang, Yuanli; Liu, Chuntai; Guo, Zhanhu

2018-05-01

The epoxy nanocomposites with ordered multi-walled carbon nanotubes (MWCNTs) were used to influence the micro-cracks resistance of carbon fiber reinforced epoxy (CF/EP) laminate at 77 K, Oxidized MWCNTs functionalized with Fe 3 O 4 (Fe 3 O 4 /O-MWCNTs) with good magnetic properties were prepared by co-precipitation method and used to modify epoxy (EP) for cryogenic applications. Fe 3 O 4 /O-MWCNTs reinforced carbon fiber epoxy composites were also prepared through vacuum-assisted resin transfer molding (VARTM). The ordered Fe 3 O 4 /O-MWCNTs were observed to have effectively improved the mechanical properties of epoxy (EP) matrix at 77 K and reduce the coefficient of thermal expansion (CTE) of EP matrix. The ordered Fe 3 O 4 /O-MWCNTs also obviously improved the micro-cracks resistance of CF/EP composites at 77 K. Compared to neat EP, the CTE of ordered Fe 3 O 4 /O-MWCNTs modified CF/EP composites was decreased 37.6%. Compared to CF/EP composites, the micro-cracks density of ordered Fe 3 O 4 /O-MWCNTs modified CF/EP composites at 77 K was decreased 37.2%. Copyright © 2018 Elsevier Inc. All rights reserved.

Investigations into Ti-(Nb,Ta)-Fe alloys for biomedical applications.

PubMed

Biesiekierski, Arne; Lin, Jixing; Li, Yuncang; Ping, Dehai; Yamabe-Mitarai, Yoko; Wen, Cuie

2016-03-01

In this study, a Ti-(Ta,Nb)-Fe system was investigated with aims toward the development of high strength, biocompatible titanium alloy suitable for the development of porous orthopedic biomaterials with minimal processing. Notable findings include yield strengths of 740, 1250 and 1360 MPa for the Ti-12Nb-5Fe, Ti-7Ta-5Fe and Ti-10Ta-4Fe alloys, respectively, with elastic moduli comparable to existing Ti-alloys, yielding admissible strains of 0.9 ± 0.3, 1.2 ± 0.2 and 1.13 ± 0.02% for the Ti-12Nb-5Fe, Ti-7Ta-5Fe and Ti-10Ta-4Fe alloys, respectively; more than twice that of human bone. Observed microstructure varied significantly depending on alloy; near pure β-phase was seen in Ti-12Nb-5Fe, β with some ω precipitation in Ti-10Ta-4Fe, and a duplex α+β structure was observed throughout the Ti-7Ta-5Fe. In addition to suitable mechanical parameters, all investigated alloys exhibited promising corrosion potentials on the order of -0.24 V SCE, equalling that seen for a C.P.-Ti control at -0.25V SCE, and substantially more noble than that seen for Ti-6Al-4V. Electrochemical corrosion rates of 0.5-3 μm/year were likewise seen to agree well with that measured for C.P.-Ti. Further, no statistically significant difference could be seen between any of the alloys relative to a C.P.-Ti control regards to cell proliferation, as investigated via MTS assay and confocal microscopy. As such, the combination of high admissible strain and low corrosion indicate all investigated alloys show significant promise as potential porous biomaterials while in the as-cast state, with the Ti-10Ta-4Fe alloy identified as the most promising composition investigated. The findings of this paper are of significance to the field of metallic biomaterials as they detail the development of alloys of satisfactory biocompatibility and electrochemical behaviour, that furthermore display exceptional mechanical properties. Notably, both extremely high compressive yield strengths and admissible strains, up to 1.36 GPa and 1.2% respectively, are reported, exceeding or rivalling that seen in traditional alloys such as Ti-6Al-4V, which typically displays compressive yield strengths and admissible strains on the order of 895 MPa and 0.81% respectively, as well as modern alloys such as Gum Metal or TNZT. That this is achieved in the absence of thermomechanical processing represents a significant and novel outcome of substantial benefit for application as a porous biomaterial. Copyright © 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The correlation of adsorption behavior between ciprofloxacin hydrochloride and the active sites of Fe-doped MCM-41

NASA Astrophysics Data System (ADS)

Wu, Ying; Tang, Yiming; Li, Laisheng; Liu, Peihong; Li, Xukai; Chen, Weirui; Xue, Ying

2018-02-01

Fe-MCM-41s with various molar ratios of silicon to iron (20, 40, 80 and 160) were prepared to investigate adsorption properties of ciprofloxacin hydrochloride (CPX) in aqueous solutions. Fe-MCM-41s were characterized by transmission electron microscope (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption/desorption isotherms and infrared spectroscopy (FT-IR). Effects of silicon–iron ratio, adsorbent dosage, pH and temperature were conducted to explore the adsorption mechanism of CPX on Fe-MCM-41. The results showed that the introduction of iron facilitated the absorption quantity for CPX from 20.04 to 83.33 mg g-1 at 120 min of reaction time, which was mainly attributed to surface complexation. The promotion of hydrophobic effect, electrostatic interactions and π-π electron donor–acceptor interaction also played coordinate roles in the adsorption process. The experimental kinetic data followed both the pseudo-second-order and intra-particle diffusion models, while the adsorption isotherm data fit well to Freundlich model at high temperature. Thermodynamic study showed that the adsorption was spontaneous. Under the effect of electrostatic interaction, pH of the solution strongly affected CPX adsorption. Five representative metal cations (Ca, Cu, Ni, Pb and Cd) were chosen to study the effects on CPX adsorption and their complexation. The inhibiting effect of metal cations on CPX adsorption was sequenced in the order of Cu > Ni > Pb > Cd > Ca, which followed the same order as the complexation stability constants between CPX and cations. The Fe-MCM-41 adsorbent possessed excellent reusability for 4 cycles use, suggesting a potential applicability of Fe-MCM-41 to remove CPX in water.

Application of x-ray absorption fine structure (XAFS) to local-order analysis in Fe-Cr maghemite-like materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Montero-Cabrera, M. E., E-mail: elena.montero@cimav.edu.mx; Fuentes-Cobas, L. E.; Macías-Ríos, E.

2015-07-23

The maghemite-like oxide system γ-Fe{sub 2-x}Cr{sub x}O{sub 3} (x=0.75, 1 and 1.25) was studied by X-ray absorption fine structure (XAFS) and by synchrotron radiation X-ray diffraction (XRD). Measurements were performed at the Stanford Synchrotron Radiation Lightsource at room temperature, at beamlines 2-1, 2-3 and 4-3. High-resolution XRD patterns were processed by means of the Rietveld method. In cases of atoms being neighbors in the Periodic Table, the order/disorder degree of the considered solutions is indiscernible by “normal” (absence of “anomalous scattering”) diffraction experiments. Thus, maghemite-like materials were investigated by XAFS in both Fe and Cr K-edges to clarify, via short-rangemore » structure characterization, the local ordering of the investigated system. Athena and Artemis graphic user interfaces for IFEFFIT and FEFF8.4 codes were employed for XAFS spectra interpretation. Pre-edge decomposition and theoretical modeling of X-ray absorption near edge structure (XANES) transitions were performed. By analysis of the Cr K-edge XANES, it has been confirmed that Cr is located in an octahedral environment. Fitting of the extended X-ray absorption fine structure (EXAFS) spectra was performed under the consideration that the central atom of Fe is allowed to occupy octa- and tetrahedral positions, while Cr occupies only octahedral ones. Coordination number of neighboring atoms, interatomic distances and their quadratic deviation average were determined for x=1, by fitting simultaneously the EXAFS spectra of both Fe and Cr K-edges. The results of fitting the experimental spectra with theoretical standards showed that the cation vacancies tend to follow a regular pattern within the structure of the iron-chromium maghemite (FeCrO{sub 3})« less

Comparison of magnetic properties and high-temperature phase stability of phosphate- and oleic acid-capped iron oxide nanoparticles

NASA Astrophysics Data System (ADS)

Muthukumaran, T.; Pati, S. S.; Singh, L. H.; de Oliveira, A. C.; Garg, V. K.; Philip, John

2018-03-01

We study the influence of dynamic capping of Fe3O4 nanoparticles with phosphate and oleic acid, on their structure, magnetic properties and thermal stability of magnetic nanoparticles. It is observed that the phosphate coating on iron oxide lowers the dipole-dipole interaction significantly, as compared to oleic acid capping. The Mössbauer results show that the spin canting order of oxidized shell and the mean hyperfine field values follow the order Fe0 (uncoated) > FeOA (oleic acid capped) > FP1 (phosphate capped). The uncoated Fe3O4 nanoparticle is non-stoichiometric in nature due to oxidation, whereas FP1 and FeOA are of the correct stoichiometry. Mössbauer and photoacoustic spectroscopic studies on air-annealed phosphate-coated magnetite nanoparticles confirm that the magnetic iron oxide phase is preserved up to 833 K and a complete conversion of Fe3O4 into the non-magnetic hematite phase occurs at 1173 K. The iron oxide air annealed at 833 K is found to have a shell of orthorhombic α-Fe2O3 over the magnetite core. However, in oleic acid-coated nanoparticles, the magnetic to non-magnetic phase transformation commences at 623 K and the conversion was complete at 823 K. The photoacoustic spectra of the air-annealed phosphate-coated Fe3O4 particles showed a flipping of the absorption intensity between 500-700 nm and 800-1000 nm, due to the conversion of Fe3O4 to γ-Fe2O3 at 923 and γ-Fe2O3 to α-Fe2O3 at 1173 K, respectively. The γ-Fe2O3 showed an intense absorption peak above 750 nm, whereas the α-Fe2O3 showed a peak broadening in the wavelength range of 600-700 nm, in addition to the strong peaks at a wavelength above 750 nm. This study suggests that the photoacoustic spectroscopy can distinguish clearly the three polymorphs of iron oxide i.e., Fe3O4, γ-Fe2O3 and α-Fe2O3. Our results confirm the ability of phosphate-capped iron oxide particles to retard the oxidation of Fe2+ contents during the crystal growth process.

An integrated approach to asses origin and mobilization of As, Fe and Mn in groundwater: the case study of Cremona (northern Italy)

NASA Astrophysics Data System (ADS)

Rotiroti, Marco; Bonomi, Tullia; Fumagalli, Letizia

2013-04-01

The present work concerns the analysis of the hydrogeology and the hydrogeochemistry of the As, Fe, Mn rich groundwater of the alluvial multi-layer aquifer in the lower Po Plain of Cremona (northern Italy). In this analysis, an integrated approach is applied in order to understand the origins (natural or anthropic) and chemical mechanisms of high groundwater As, Fe and Mn concentrations found in the study area. The study area covers a 50 km2 wide area around the urban territory of Cremona. It is located near the confluence between Adda and Po rivers. The multi-aquifer system which interests the first 200-250 m of depth is investigated. The integrated approach involves the (a) collection of historical data related to water quality, water levels and well logs; (b) storage of collected data in specific databases and geographical information systems; (c) design and execution of two field surveys of water levels and water quality, realized in July 2010 and July 2012, concerning also groundwater sampling for isotope and microbiological analysis; (d) construction of a 3D model of aquifer hydrogeological properties (deposits texture, hydraulic conductivity and effective porosity), built by means of ordinary kriging interpolation of numerical values derived from the coding of well logs; (e) analysis of the hydrodynamic properties of the system on the basis of the field measurements; (f) analysis of water quality data (both field and historical data) considering the hydrogeological and hydrodynamic properties of the aquifer system; (g) analysis of isotope and microbiological measurements; (h) implementation of a 1D reactive transport model in order to better understand the hydrogeochemical mechanisms in the system; (i) elaboration of a general hydrogeochemical conceptual model concerning possible origins and chemical mechanisms for the high groundwater As, Fe, Mn and NH4 concentrations, considering also possible anthropogenic influences; (j) development of management tools, as natural background levels (NBL) derivation, supporting groundwater resources protection by public authorities. This approach allows to assume the process of natural organic matter degradation (i.e. peat) as primary control factor on high As, Fe, Mn and NH4 concentrations. Degradation of peat is associated with the consecutive reduction of O2, NO3-, Mn(IV), Fe(III), SO42-, CO2. The reductive dissolution of Mn and Fe oxides (contained in the aquifer sediments) leads to high concentrations of dissolved Fe and Mn, but also to high concentrations of dissolved As, which is generally sorbed on Mn and Fe oxides. Dissolved As concentration can be also lowered by different processes (co-precipitation of As in iron sulfides, precipitation of arsenic sulfides, sorption of As on the remaining Fe-oxides and Mn-oxides, etc.). NH4 is released from the degradation of organic nitrogen of peat. Therefore, a natural origin of As, Fe, Mn and NH4 can be assumed. In addiction, anthropogenic influences on groundwater As, Fe, Mn and NH4 concentrations are locally identified in two sites located in the study area, that are affected by hydrocarbons and organic leachate pollution.

Phase stability and large in-plane resistivity anisotropy in the 112-type iron-based superconductor Ca 1 - x La x FeAs 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kang, Chang-Jong; Birol, Turan; Kotliar, Gabriel

The recently discovered high-T c superconductor Ca 1-xLa xFeAs 2 is a unique compound not just because of its low-symmetry crystal structure but also because of its electronic structure, which hosts Dirac-like metallic bands resulting from (spacer) zigzag As chains. We present a comprehensive first-principles theoretical study of the electronic and crystal structures of Ca 1-xLa xFeAs 2. After discussing the connection between the crystal structure of the 112 family, which Ca 1-xLa xFeAs 2 is a member of, with the other known structures of Fe pnictide superconductors, we check the thermodynamic phase stability of CaFeAs 2, and similar hyphotheticalmore » compounds SrFeAs 2 and BaFeAs 2 which, we find, are slightly higher in energy. We calculate the optical conductivity of Ca 1-xLa xFeAs 2 using the DFT+DMFT method and predict a large in-plane resistivity anisotropy in the normal phase, which does not originate from electronic nematicity, but is enhanced by the electronic correlations. In particular, we predict a 0.34 eV peak in the yy component of the optical conductivity of the 30% La-doped compound, which corresponds to coherent interband transitions within a fast-dispersing band arising from the zigzag As chains, which are unique to this compound. We also study the Landau free energy for Ca 1-xLa xFeAs 2 including the order parameter relevant for the nematic transition and find that the free energy does not have any extra terms that could induce ferro-orbital order. This explains why the presence of As chains does not broaden the nematic transition in Ca 1-xLa xFeAs 2.« less

Phase stability and large in-plane resistivity anisotropy in the 112-type iron-based superconductor Ca 1 - x La x FeAs 2

DOE PAGES

Kang, Chang-Jong; Birol, Turan; Kotliar, Gabriel

2017-01-17

The recently discovered high-T c superconductor Ca 1-xLa xFeAs 2 is a unique compound not just because of its low-symmetry crystal structure but also because of its electronic structure, which hosts Dirac-like metallic bands resulting from (spacer) zigzag As chains. We present a comprehensive first-principles theoretical study of the electronic and crystal structures of Ca 1-xLa xFeAs 2. After discussing the connection between the crystal structure of the 112 family, which Ca 1-xLa xFeAs 2 is a member of, with the other known structures of Fe pnictide superconductors, we check the thermodynamic phase stability of CaFeAs 2, and similar hyphotheticalmore » compounds SrFeAs 2 and BaFeAs 2 which, we find, are slightly higher in energy. We calculate the optical conductivity of Ca 1-xLa xFeAs 2 using the DFT+DMFT method and predict a large in-plane resistivity anisotropy in the normal phase, which does not originate from electronic nematicity, but is enhanced by the electronic correlations. In particular, we predict a 0.34 eV peak in the yy component of the optical conductivity of the 30% La-doped compound, which corresponds to coherent interband transitions within a fast-dispersing band arising from the zigzag As chains, which are unique to this compound. We also study the Landau free energy for Ca 1-xLa xFeAs 2 including the order parameter relevant for the nematic transition and find that the free energy does not have any extra terms that could induce ferro-orbital order. This explains why the presence of As chains does not broaden the nematic transition in Ca 1-xLa xFeAs 2.« less

Solitonic Spin-Liquid State Due to the Violation of the Lifshitz Condition in Fe(1+y)Te.

PubMed

Materne, Ph; Koz, C; Rössler, U K; Doerr, M; Goltz, T; Klauss, H H; Schwarz, U; Wirth, S; Rössler, S

2015-10-23

A combination of phenomenological analysis and Mössbauer spectroscopy experiments on the tetragonal Fe(1+y)Te system indicates that the magnetic ordering transition in compounds with higher Fe excess, y≥0.11, is unconventional. Experimentally, a liquidlike magnetic precursor with quasistatic spin order is found from significantly broadened Mössbauer spectra at temperatures above the antiferromagnetic transition. The incommensurate spin-density wave order in Fe(1+y)Te is described by a magnetic free energy that violates the weak Lifshitz condition in the Landau theory of second-order transitions. The presence of multiple Lifshitz invariants provides the mechanism to create multidimensional, twisted, and modulated solitonic phases.

Solitonic Spin-Liquid State Due to the Violation of the Lifshitz Condition in Fe1 +yTe

NASA Astrophysics Data System (ADS)

Materne, Ph.; Koz, C.; Rößler, U. K.; Doerr, M.; Goltz, T.; Klauss, H. H.; Schwarz, U.; Wirth, S.; Rößler, S.

2015-10-01

A combination of phenomenological analysis and Mössbauer spectroscopy experiments on the tetragonal Fe1 +yTe system indicates that the magnetic ordering transition in compounds with higher Fe excess, y ≥0.11 , is unconventional. Experimentally, a liquidlike magnetic precursor with quasistatic spin order is found from significantly broadened Mössbauer spectra at temperatures above the antiferromagnetic transition. The incommensurate spin-density wave order in Fe1 +yTe is described by a magnetic free energy that violates the weak Lifshitz condition in the Landau theory of second-order transitions. The presence of multiple Lifshitz invariants provides the mechanism to create multidimensional, twisted, and modulated solitonic phases.

Growth, structure, and magnetic properties of {gamma}-Fe{sub 2}O{sub 3} epitaxial films on MgO

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gao, Y.; Kim, Y.J.; Thevuthasan, S.

1997-04-01

Single-crystal epitaxial thin films of {gamma}-Fe{sub 2}O{sub 3}(001) have been grown on MgO(001) using oxygen-plasma-assisted molecular beam epitaxy. The structure and magnetic properties of these films have been characterized by a variety of techniques, including reflection high-energy electron diffraction (RHEED), low-energy electron diffraction (LEED), x-ray photoelectron spectroscopy and x-ray photoelectron/Auger electron diffraction (XPD/AED), vibrating sample magnetometry, and ferromagnetic resonance. Real-time RHEED reveals that the film growth occurs in a layer-by-layer fashion. The {gamma}-Fe{sub 2}O{sub 3}(001) film surface exhibits a (1{times}1) LEED pattern. The growth of {gamma}-Fe{sub 2}O{sub 3} films at 450 {degree}C is accompanied by significant Mg outdiffusion. AED ofmore » Mg KLL Auger emission reveals that Mg substitutionally incorporates in the {gamma}-Fe{sub 2}O{sub 3} lattice, occupying the octahedral sites. Magnetic moments are {approximately}2300 G and {approximately}4500 G for {gamma}-Fe{sub 2}O{sub 3} films grown at 250{degree}C and 450{degree}C, respectively. The high magnetic moment for the films grown at 450{degree}C could be attributed to the high degree of structural order of the films and Mg substitution at octahedral sites. {copyright} {ital 1997 American Institute of Physics.}« less

Effects of particle size and forming pressure on pore properties of Fe-Cr-Al porous metal by pressureless sintering

NASA Astrophysics Data System (ADS)

Koo, Bon-Uk; Yi, Yujeong; Lee, Minjeong; Kim, Byoung-Kee

2017-03-01

With increased hydrogen consumption in ammonia production, refining and synthesis, fuel cells and vehicle industries, development of the material components related to hydrogen production is becoming an important factor in industry growth. Porous metals for fabrication of hydrogen are commonly known for their relative excellence in terms of large area, lightness, lower heat capacity, high toughness, and permeability. Fe-Cr-Al alloys not only have high corrosion resistance, heat resistance, and chemical stability but also ductility, excellent mechanical properties. In order to control powder size and sintering temperature effects of Fe-Cr-Al porous metal fabrication, Fe-Cr-Al powder was classified into 25-35 μm, 35-45 μm, 45-75 μm using an auto shaking sieve machine and then classified Fe-Cr-Al powders were pressed into disk shapes using a uniaxial press machine and CIP. The pelletized Fe-Cr-Al specimens were sintered at various temperatures in high vacuum. Properties such as pore size, porosity, and air permeability were evaluated using perm-porosimetry. Microstructure and phase changes were observed with SEM and XRD. Porosity and relative density were proportionated to increasing sintering temperature. With sufficient sintering at increasing temperatures, the pore size is expected to be gradually reduced. Porosity decreased with increasing sintering temperature and gradually increased necking of the powder.

Highly Efficient, Low-Cost, and Magnetically Recoverable FePt⁻Ag Nanocatalysts: Towards Green Reduction of Organic Dyes.

PubMed

Liu, Yang; Zhang, Yuanyuan; Kou, Qiangwei; Chen, Yue; Sun, Yantao; Han, Donglai; Wang, Dandan; Lu, Ziyang; Chen, Lei; Yang, Jinghai; Xing, Scott Guozhong

2018-05-14

Nowadays, synthetic organic dyes and pigments discharged from numerous industries are causing unprecedentedly severe water environmental pollution, and conventional water treatment processes are hindered due to the corresponding sophisticated aromatic structures, hydrophilic nature, and high stability against light, temperature, etc. Herein, we report an efficient fabrication strategy to develop a new type of highly efficient, low-cost, and magnetically recoverable nanocatalyst, i.e., FePt⁻Ag nanocomposites, for the reduction of methyl orange (MO) and rhodamine B (RhB), by a facile seed deposition process. X-ray diffraction results elaborate that the as-synthesized FePt⁻Ag nanocomposites are pure disordered face-centered cubic phase. Transmission electron microscopy studies demonstrate that the amount of Ag seeds deposited onto the surfaces of FePt nanocrystals increases when increasing the additive amount of silver colloids. The linear correlation of the MO and RhB concentration versus reaction time catalyzed by FePt⁻Ag nanocatalysts is in line with pseudo-first-order kinetics. The reduction rate constants of MO and RhB increase with the increase of the amount of Ag seeds. FePt⁻Ag nanocomposites show good separation ability and reusability, and could be repeatedly applied for nearly complete reduction of MO and RhB for at least six successive cycles. Such cost-effective and recyclable nanocatalysts provide a new material family for use in environmental protection applications.

Petrographic Evidence for Rapid Heating and Cooling During Chrondrule Formation

NASA Technical Reports Server (NTRS)

Wasson, J. T.

2004-01-01

The chondrule cooling rates used in most chondrule-formation models appear to be too low. Recent petrographic evidence indicates that the amount of crystal (especially olivine) growth that occurred after the last melting event was about 30 smaller than the grain sizes simulated in order to estimate cooling rates. The smaller amount of growth leads to an upwards revision of cooling rates by about a factor of 1000. Most chondrules are porphyritic. They consist of large and small crystals of olivine and, less commonly, pyroxene immersed in a mesostasis having a plagioclase-rich composition. In the most primitive chondrites the mesostasis is often vitreous. Because the large majority of chondrules contain FeS, it is clear that the nebula had cooled below the FeS condensation temperature (ca. 650 K) before chondrule formation occurred. The high FeO/(FeO+MgO) ratios of some chondrules require still lower nebular temperatures (less than 500 K). The traditional view has been that porphyritic chondrules formed in a single heating/cooling event and many laboratory experiments have been carried out in various kinds of kinds of furnaces to try to simulate the formation of chondrules textures in a single heating/cooling cycle. These furnace experiments have been used to infer the cooling rates of chondrules during the temperature range at which olivine crystallized from the melt. Most of these inferred values are in the range 0.01-1 K per second. These low cooling rates are problematical because there is no long-term nebular environment that yields such values. In transparent regions chondrules would cool at rates orders of magnitude higher, whereas in an opaque nebular disk the cooling rates would be many orders of magnitude lower. And these latter conditions are not suitable locations for chondrule formation because such high temperatures would cause the complete evaporation of chondrules (which have melting temperatures about 600 K higher than their evaporation temperatures). During the last several years several kinds of petrographic evidence indicating rapid chondrule cooling have been recognized. These include thin overgrowths on relict grains, clusters of small crystals that grew following the most recent melting event, and fragments preserving shardlike shapes that would have been hidden had several tens of micrometers of new growth occurred following the last melting event. And there are other indications of rapid cooling including the preservation of volatiles such as FeS and one case where the modeling of O-isotopic and FeO/(FeO+MgO) gradients indicated a high cooling rate.

Enhanced spin-ordering temperature in ultrathin FeTe films grown on a topological insulator

NASA Astrophysics Data System (ADS)

Singh, Udai Raj; Warmuth, Jonas; Kamlapure, Anand; Cornils, Lasse; Bremholm, Martin; Hofmann, Philip; Wiebe, Jens; Wiesendanger, Roland

2018-04-01

We studied the temperature dependence of the diagonal double-stripe spin order in 1 and 2 unit cell thick layers of FeTe grown on the topological insulator B i2T e3 via spin-polarized scanning tunneling microscopy. The spin order persists up to temperatures which are higher than the transition temperature reported for bulk F e1 +yTe with lowest possible excess Fe content y . The enhanced spin order stability is assigned to a strongly decreased y with respect to the lowest values achievable in bulk crystal growth, and effects due to the interface between the FeTe and the topological insulator. The result is relevant for understanding the recent observation of a coexistence of superconducting correlations and spin order in this system.

First principles investigation of high pressure behavior of FeOOH-AlOOH-phase H (MgSiO4H2) system.

NASA Astrophysics Data System (ADS)

Tsuchiya, J.; Thompson, E. C.; Tsuchiya, T.; Nishi, M.; Kuwayama, Y.

2017-12-01

It has been believed that water is carried into the deep Earth's interior by hydrous minerals such as the dense hydrous magnesium silicates (DHMSs) in the descending cold plate. A numbers of researches have been conducted so far about the high pressure behaviors of DHMSs. In recent years, we found new DHMS, phase H, at lower mantle pressure condition and the solid solution between phase H and d-AlOOH has been proposed as the most important carrier of water in the deepest part of Earth's mantle (Tsuchiya 2013 GRL, Nishi et al. 2014 Nature Geo., Ohira et al. 2014 EPSL). However, those hydrous minerals are actually not denser than surrounding (dry) mantle minerals (Tsuchiya and Mookherjee 2015 Scientific Reports) and the gravitational stability in deeper part of the Earth is questionable. Therefore, the effects of denser element such as Fe on the stability of DHMS are intimately connected to the ability of transportation of water into Earth's deep interiors. In order to assess the effect of Fe on the phase relation of phase H and d-AlOOH, we first investigated the high pressure behavior of the end-member composition of this system, the e-FeOOH. We have found the new high pressure transformation of FeOOH in the lower mantle conditions both theoretically and experimentally(Nishi et al. 2017 Nature). Here we show high pressure structures and the physical properties of FeOOH-AlOOH-phase H system using first principles calculation and discuss the possible geophysical implications of these phases.

Oriented polyvinylidene fluoride–trifluoroethylene (P(VDF–TrFE)) films by Langmuir–Blodgett deposition: A synchrotron X-ray diffraction study

DOE PAGES

Lindemann, W. R.; Philiph, R. L.; Chan, D. W. W.; ...

2015-10-07

Langmuir–Blodgett films of polyvinylidene fluoride trifluoroethylene – P(VDF–TrFE)-copolymers possess substantially improved electrocaloric and pyroelectric properties, when compared with conventionally spin-cast films. In order to rationalize this, we prepared single-layered films of P(VDF–TrFE) (70:30) using both deposition techniques. Grazing incidence wide-angle X-ray scattering (GIWAXS), reveals that Langmuir–Blodgett deposited films have a higher concentration of the ferroelectric β-phase crystals, and that these films are highly oriented with respect to the substrate. Based on these observations, we suggest alternative means of deposition, which may substantially enhance the electrocaloric effect in P(VDF–TrFE) films. As a result, this development has significant implications for the potentialmore » use of P(VDF–TrFE) in solid-state refrigeration.« less

Effect of Heat Treatment on Microstructure and Magnetostrictive Property of Melt-Spun Fe85Ga15 Ribbons

NASA Astrophysics Data System (ADS)

Liu, Hao; Wang, Haiou; Cao, Mengxiong; Tan, Weishi; Shi, Yangguang; Chen, Yu; Huang, Yuying

2013-09-01

In order to study the microstructure of Fe-Ga alloy, Fe85Ga15 ribbons prepared with different wheel velocity were studied by high resolution X-ray diffraction (HRXRD) and extend X-ray absorption fine structure (EXAFS). HRXRD patterns showed that only disordered A2 phase was observed in as-cast Fe85Ga15 alloy. A modified-DO3 phase was detected in all of the melt spun samples. The HRXRD associated with EXAFS results indicated that Ga atoms were located as second-nearest neighbor along [100] orientation. A little DO3 phase was found in ribbons annealed at 1000°C under 0.06 MPa Ar atmosphere. The result of magnetostriction measurement revealed that in the ribbon prepared with higher wheel velocity, more modified-DO3 phase will enhance the magnetostriction. DO3 phase in the annealed sample will deteriorate the magnetostrictive properties of Fe-Ga ribbons.

Spherical V-Fe-MCM-48: The Synthesis, Characterization and Hydrothermal Stability.

PubMed

Qian, Wang; Wang, Haiqing; Chen, Jin; Kong, Yan

2015-04-14

Spherical MCM-48 mesoporous sieve co-doped with vanadium and iron was successfully synthesized via one-step hydrothermal method. The material was characterized by X-ray diffraction (XRD), nitrogen adsorption-desorption isotherms, inductively coupled plasma (ICP), scanning electron microscopy (SEM), transmission electron microscopy (TEM), diffuse reflectance UV-vis spectra, and X-ray photoelectron spectra (XPS) techniques. Results indicated that the V-Fe-MCM-48 showed an ordered 3D cubic mesostructure with spherical morphology, narrow pore size distribution and high specific surface area. Most of vanadium and iron atoms existing as tetrahedral V 4+ and Fe 3+ species were co-doped into the silicate framework. The particle sizes of V-Fe-MCM-48 were smaller and the specific area was much higher than those of of V-MCM-48. Additionally, the synthesized V-Fe-MCM-48 exhibited improved hydrothermal stability compared with the pure MCM-48.

Spherical V-Fe-MCM-48: The Synthesis, Characterization and Hydrothermal Stability

PubMed Central

Qian, Wang; Wang, Haiqing; Chen, Jin; Kong, Yan

2015-01-01

Spherical MCM-48 mesoporous sieve co-doped with vanadium and iron was successfully synthesized via one-step hydrothermal method. The material was characterized by X-ray diffraction (XRD), nitrogen adsorption-desorption isotherms, inductively coupled plasma (ICP), scanning electron microscopy (SEM), transmission electron microscopy (TEM), diffuse reflectance UV-vis spectra, and X-ray photoelectron spectra (XPS) techniques. Results indicated that the V-Fe-MCM-48 showed an ordered 3D cubic mesostructure with spherical morphology, narrow pore size distribution and high specific surface area. Most of vanadium and iron atoms existing as tetrahedral V4+ and Fe3+ species were co-doped into the silicate framework. The particle sizes of V-Fe-MCM-48 were smaller and the specific area was much higher than those of of V-MCM-48. Additionally, the synthesized V-Fe-MCM-48 exhibited improved hydrothermal stability compared with the pure MCM-48. PMID:28788030

Nature of ferroelectric to paraelectric phase transition in multiferroic 0.8BiFeO3-0.2Pb(Fe1/2Nb1/2)O3 ceramics

NASA Astrophysics Data System (ADS)

Patel, Jay Prakash; Singh, Anar; Pandey, Dhananjai

2010-05-01

We present here the results of high temperature powder x-ray diffraction study on 0.8BiFeO3-0.2Pb(Fe1/2Nb1/2)O3, which is isostructural with the well known multiferroic BiFeO3 (BF). It is shown that the room temperature ferroelectric phase of 0.8BF-0.2PFN in the R3c space group transforms to the paraelectric/paraelastic cubic (Pm3¯m) phase directly without any intermediate "β" phase reported in the literature for pure BF. This transition is of first order type as confirmed by the coexistence of R3c and Pm3¯m phases over a 100 K range and discontinuous change in the unit cell volume.

Dislocations and deformation microstructure in a B2-ordered Al28Co20Cr11Fe15Ni26 high-entropy alloy

NASA Astrophysics Data System (ADS)

Feuerbacher, Michael

2016-07-01

High-entropy alloys are multicomponent metallic materials currently attracting high research interest. They display a unique combination of chemical disorder and crystalline long-range order, and due to their attractive properties are promising candidates for technological application. Many high-entropy alloys possess surprisingly high strength, occasionally in combination with high ductility and low density. The mechanisms effecting these attractive mechanical properties are not understood. This study addresses the deformation mechanism of a Al28Co20Cr11Fe15Ni26 high-entropy alloy, which is a two-phase material, consisting of a B2-ordered matrix and disordered body-centred inclusions. We quantitatively analyse the microstructure and dislocations in deformed samples by transmission-electron-microscopic methods including weak-beam imaging and convergent-beam electron diffraction. We find that the deformation process in the B2 phase is dominated by heterogeneous slip of screw dislocations gliding on planes. The dislocations are perfect superdislocations of the B2 lattice and show no dissociation. This indicates that the antiphase-boundary energy in the structure is very high, inhibiting spread of the dislocation core. Along with the observation of a widely extending strain field associated to the dislocations, our results provide a possible explanation for the high strength of this high-entropy alloy as a direct consequence of its dislocation structure.

Fe-MoS4: An Effective and Stable LDH-Based Adsorbent for Selective Removal of Heavy Metals.

PubMed

Jawad, Ali; Liao, Zhuwei; Zhou, Zhihua; Khan, Aimal; Wang, Ting; Ifthikar, Jerosha; Shahzad, Ajmal; Chen, Zhulei; Chen, Zhuqi

2017-08-30

It has always been a serious challenge to design efficient, selective, and stable absorbents for heavy-metal removal. Herein, we design layered double hydroxide (LDH)-based Fe-MoS 4 , a highly efficient adsorbent, for selective removal of heavy metals. We initially synthesized FeMgAl-LDH and then enriched its protective layers with MoS 4 2- anions as efficient binding sites for heavy metals. Various characterization tools, such as X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, scanning electron microscopy, energy-dispersive X-ray, X-ray photoelectron spectroscopy (XPS), CHN analysis, and inductively coupled plasma analysis, were applied to confirm structural and compositional changes during the synthesis of Fe-MoS 4 as final product. The prepared Fe-MoS 4 offered excellent attraction for heavy metals, such as Hg 2+ , Ag + , Pb 2+ , and Cu 2+ , and displayed selectivity in the order Hg 2+ ∼ Ag + > Pb 2+ > Cu 2+ > Cr 6+ > As 3+ > Ni 2+ ∼ Zn 2+ ∼ Co 2+ . The immense capacities of Hg 2+ , Ag + , and Pb 2+ (583, 565, and 346 mg/g, respectively), high distribution coefficient (K d ∼ 10 7 -10 8 ), and fast kinetics place Fe-MoS 4 on the top of materials list known for removal of such metals. The sorption kinetics and isothermal studies conducted on Hg 2+ , Ag + , Pb 2+ , and Cu 2+ suit well pseudo-second-order kinetics and Langmuir model, suggesting monolayer chemisorption mechanism through M-S linkages. XRD and FTIR studies suggested that adsorbed metals could result as coordinated complexes in LDH interlayer region. More interestingly, LDH structure offers protective space for MoS 4 2- anions to avoid oxidation under ambient environments, as confirmed by XPS studies. These features provide Fe-MoS 4 with enormous capacity, good reusability, and excellent selectivity even in the presence of huge concentration of common cations.

Coexistence of ferromagnetism and spin glass freezing in the site-disordered kagome ferrite SrSn2Fe4O11

NASA Astrophysics Data System (ADS)

Shlyk, Larysa; Strobel, S.; Farmer, B.; De Long, L. E.; Niewa, R.

2018-05-01

Single-crystal x-ray diffraction refinements indicate SrSn2Fe4O11 crystallizes in the hexagonal R-type ferrite structure with non-centrosymmetric space group P63mc and lattice parameters a = 5.9541(2) Å, c = 13.5761(5) Å, Z = 2 (R(F) = 0.034). Octahedrally coordinated sites are randomly occupied by Sn and Fe; whereas tetrahedrally coordinated sites are exclusively occupied by Fe, whose displacement from ideal trigonal-bipyramidal coordination causes the loss of inversion symmetry. DC magnetization data indicate SrSn2Fe4O11 single crystals undergo ferro- or ferri-magnetic order below a transition temperature TC = 630 K with very low coercive fields Hc ⊥ = 0.27 Oe and Hc// = 1.5 Oe at 300 K, for applied fields perpendicular and parallel to the c-axis, respectively. The value for TC is exceptionally high, and the coercive fields exceptionally low, among the known R-type ferrites. Enhanced coercivity and thermomagnetic hysteresis suggest the onset of short-range, spin glass order occurs below Tf = 35 K. Optical measurements indicate a band gap of 0.8 eV, consistent with wide-gap semiconducting behavior and a previously established empirical correlation between the semiconducting gap and TC for R-type ferrites based upon Ru.

Elevated concentrations of dissolved Ba, Fe and Mn in a mangrove subterranean estuary: Consequence of sea level rise?

NASA Astrophysics Data System (ADS)

Sanders, Christian J.; Santos, Isaac R.; Barcellos, Renato; Silva Filho, Emmanoel V.

2012-07-01

Groundwater underlying a mangrove habitat was studied to determine the geochemical nature of Ba, Fe and Mn as related to dissolved organic carbon (DOC), SO4 and salinity (Sepetiba Bay, Brazil). Wells were placed across geobotanic facies and sampled monthly for a year. We observed non-conservative behavior and elevated concentrations of dissolved metals relative to local end-members (i.e., fresh river water and seawater). Average Ba concentrations were near 2000 nM in an area with low salinity (˜5.3). Dissolved Fe (up to 654 μM) was two orders of magnitude greater in fresh groundwater than in the seaward sampling stations. Manganese concentrations were greatest (112 μM) in the high salinity (˜65) zone, being directly influenced by salinity. Groundwater Ba, Fe and Mn showed differing site specific concentrations, likely related to ion exchange processes and redox-controlled cycling along distinct mangrove facies. The results of this work show that metal concentrations are altered relative to conservative mixing between terrestrial and marine endmembers, illustrating the importance of mangrove subterranean estuaries as biogeochemical reactors. Roughly-estimated submarine groundwater discharge-derived dissolved Ba, Fe and Mn fluxes were at least one order of magnitude greater than river-derived fluxes into Sepetiba Bay.

Synthesis of core-shell iron nanoparticles via a new (novel) approach

NASA Astrophysics Data System (ADS)

Chaudhary, Rakesh P.; Koymen, Ali R.

2014-03-01

Carbon-encapsulated iron (Fe) nanoparticles were synthesized by a newly developed method in toluene. Transmission Electron Microscopy (TEM) and High Resolution Transmission Electron Microscopy (HRTEM) of the as prepared sample reveal that core-shell nanostructures have been formed with Fe as core and graphitic carbon as shell. Fe nanoparticles with diameter 11nm to 102 nm are encapsulated by 6-8 nm thick graphitic carbon layers. There was no iron carbide formation observed between the Fe core and the graphitic shell. The Fe nanoparticles have body centered cubic (bcc) crystal structure. The magnetic hysteresis loop of the as synthesized powder at room temperature showed a saturation magnetization of 9 Am2 kg-1. After thermal treatment crystalline order of the samples improved and hence saturation magnetization increased to 24 Am2kg-1. We foresee that the carbon-encapsulated Fe nanoparticles are biologically friendly and could have potential applications in Magnetic Resonance Imaging (MRI) and Photothermal cancer therapy.

Preparation of carbon coated Fe3O4 nanoparticles for magnetic separation of uranium

NASA Astrophysics Data System (ADS)

Zhang, Xiaofei; Wang, Jun

2018-01-01

Uranium(VI) was removed from aqueous solutions using carbon coated Fe3O4 nanoparticles (Fe3O4@C). Batch experiments were conducted to study the effects of initial pH, shaking time and temperature on uranium sorption efficiency. It was found that the maximum adsorption capacity of the Fe3O4@C toward uranium(VI) was ∼120.20 mg g-1 when the initial uranium(VI) concentration was 100 mg L-1, displaying a high efficiency for the removal of uranium(VI) ions. Kinetics of the uranium(VI) removal is found to follow pseudo-second-order rate equation. In addition, the uranium(VI)-loaded Fe3O4@C nanoparticles can be recovered easily from aqueous solution by magnetic separation and regenerated by acid treatment. Present study suggested that magnetic Fe3O4@C composite particles can be used as an effective and recyclable adsorbent for the removal of uranium(VI) from aqueous solutions.

Solid iron-hydrogen alloys under high pressure by first principles

NASA Astrophysics Data System (ADS)

Umemoto, K.; Hirose, K.

2016-12-01

Hydrogen and iron are two of major constituents of the Earth and planetary interiors. The crystal structure of solid FeHx is one of the most fundamental information in order to understand properties of planetary cores. It is well known that FeH takes closed-packed structures: dhcp, hcp, and fcc. Recently, hydrogen-rich phases, FeH2 and FeH3, were experimentally synthesized [1]. Although a tetragonal structure of FeH2 was proposed, it could not explain experimental observations, energetic stability and compression curve. Here we propose a new crystal structure of FeH2. The symmetry of the new structure is completely identical to that in originally proposed one, but the hydrogen sublattice which cannot be directly determined by XRD experiments is different. It will be demonstrated by first principles that the new structure can be fully consistent with experimental observations. [1] C. M. Pépin, A. Dewaele, G. Geneste, P. Loubeyre, and M. Mezouar, Phys. Rev. Lett. 113, 265504 (2014).

Atomically engineered ferroic layers yield a room-temperature magnetoelectric multiferroic

NASA Astrophysics Data System (ADS)

Mundy, Julia A.; Brooks, Charles M.; Holtz, Megan E.; Moyer, Jarrett A.; Das, Hena; Rébola, Alejandro F.; Heron, John T.; Clarkson, James D.; Disseler, Steven M.; Liu, Zhiqi; Farhan, Alan; Held, Rainer; Hovden, Robert; Padgett, Elliot; Mao, Qingyun; Paik, Hanjong; Misra, Rajiv; Kourkoutis, Lena F.; Arenholz, Elke; Scholl, Andreas; Borchers, Julie A.; Ratcliff, William D.; Ramesh, Ramamoorthy; Fennie, Craig J.; Schiffer, Peter; Muller, David A.; Schlom, Darrell G.

2016-09-01

Materials that exhibit simultaneous order in their electric and magnetic ground states hold promise for use in next-generation memory devices in which electric fields control magnetism. Such materials are exceedingly rare, however, owing to competing requirements for displacive ferroelectricity and magnetism. Despite the recent identification of several new multiferroic materials and magnetoelectric coupling mechanisms, known single-phase multiferroics remain limited by antiferromagnetic or weak ferromagnetic alignments, by a lack of coupling between the order parameters, or by having properties that emerge only well below room temperature, precluding device applications. Here we present a methodology for constructing single-phase multiferroic materials in which ferroelectricity and strong magnetic ordering are coupled near room temperature. Starting with hexagonal LuFeO3—the geometric ferroelectric with the greatest known planar rumpling—we introduce individual monolayers of FeO during growth to construct formula-unit-thick syntactic layers of ferrimagnetic LuFe2O4 (refs 17, 18) within the LuFeO3 matrix, that is, (LuFeO3)m/(LuFe2O4)1 superlattices. The severe rumpling imposed by the neighbouring LuFeO3 drives the ferrimagnetic LuFe2O4 into a simultaneously ferroelectric state, while also reducing the LuFe2O4 spin frustration. This increases the magnetic transition temperature substantially—from 240 kelvin for LuFe2O4 (ref. 18) to 281 kelvin for (LuFeO3)9/(LuFe2O4)1. Moreover, the ferroelectric order couples to the ferrimagnetism, enabling direct electric-field control of magnetism at 200 kelvin. Our results demonstrate a design methodology for creating higher-temperature magnetoelectric multiferroics by exploiting a combination of geometric frustration, lattice distortions and epitaxial engineering.

Amperometric hydrogen peroxide and glucose biosensor based on NiFe2/ordered mesoporous carbon nanocomposites.

PubMed

Xiang, Dong; Yin, Longwei; Ma, Jingyun; Guo, Enyan; Li, Qun; Li, Zhaoqiang; Liu, Kegao

2015-01-21

Nanocomposites of NiFex embedded in ordered mesoporous carbon (OMC) (x = 0, 1, 2) were prepared by a wet impregnation and hydrogen reduction process and were used to construct electrochemical biosensors for the amperometric detection of hydrogen peroxide (H2O2) or glucose. The NiFe2/OMC nanocomposites were demonstrated to have a large surface area, suitable mesoporous channels, many edge-plane-like defective sites, and a good distribution of alloyed nanoparticles. The NiFe2/OMC and Nafion modified glass carbon electrode (GCE) exhibited excellent electrocatalytic activities toward the reduction of H2O2 as well. By utilizing it as a bioplatform, GOx (glucose oxidase) cross-linked with Nafion was immobilized on the surface of the electrode for the construction of an amperometric glucose biosensor. Our results indicated that the amperometric hydrogen peroxide biosensor (NiFe2/OMC + Nafion + GCE) showed good analytical performances in term of a high sensitivity of 4.29 μA mM(-1) cm(-2), wide linearity from 6.2 to 42,710 μM and a low detection limit of 0.24 μM at a signal-to-noise ratio of 3 (S/N = 3). This biosensor exhibited excellent selectivity, high stability and negligible interference for the detection of H2O2. In addition, the immobilized enzyme on NiFe2/OMC + Nafion + GCE, retaining its bioactivity, exhibited a reversible two-proton and two-electron transfer reaction, a fast heterogeneous electron transfer rate and an effective Michaelis-Menten constant (K) (3.18 mM). The GOx + NiFe2/OMC + Nafion + GCE could be used to detect glucose based on the oxidation of glucose catalyzed by GOx and exhibited a wide detection range of 48.6-12,500 μM with a high sensitivity of 6.9 μA mM(-1) cm(-2) and a low detection limit of 2.7 μM (S/N = 3). The enzymic biosensor maintained a high selectivity and stability features, and shows great promise for application in the detection of glucose.

Molecular Beam Epitaxial Growth of Iron Nitrides on Zinc-Blende Gallium Nitride(001)

NASA Astrophysics Data System (ADS)

Pak, Jeongihm; Lin, Wenzhi; Chinchore, Abhijit; Wang, Kangkang; Smith, Arthur R.

2008-03-01

Iron nitrides are attractive materials for their high magnetic moments, corrosion, and oxidation resistance. We present the successful epitaxial growth of iron nitride on zinc-blende gallium nitride (c-GaN) in order to develop a novel magnetic transition metal nitride/semiconductor system. First, GaN is grown on magnesium oxide (MgO) substrates having (001) orientation using rf N2-plasma molecular beam epitaxy. Then we grow FeN at substrate temperature of ˜ 210 ^oC up to a thickness of ˜ 10.5 nm. In-situ reflection high-energy electron diffraction (RHEED) is used to monitor the surface during growth. Initial results suggest that the epitaxial relationship is FeN[001] || GaN[001] and FeN[100] || GaN[100]. Work in progress is to investigate the surface using in-situ scanning tunneling microscopy (STM) to reveal the surface structure at atomic scale, as well as to explore more Fe-rich magnetic phases.

Spiral pattern in a radial displacement in a Hele-Shaw cell

NASA Astrophysics Data System (ADS)

Ban, Mitsumasa; Nagatsu, Yuichiro; Hayashi, Atsushi; Kato, Yoshihiro; Tada, Yutaka

2008-11-01

When a reactive and miscible less-viscous liquid displaces a more-viscous liquid in a Hele-Shaw cell, reactive miscible viscous fingering takes place. We have experimentally shown that the pattern created by the displacement of a more-viscous fluid by a less-viscous one in a radial Hele-Shaw cell develops not radially but spirally when a more-viscous sodium polyacrylate solution is displaced by a less-viscous trivalent iron ion (Fe^3+) solution with a sufficiently high concentration of Fe^3+. Another experiment in order to investigate the mechanism of spiral pattern formation revealed that an instantaneous chemical reaction takes place between the two fluids and at high Fe^3+ concentrations it produces a film of the gel at the contact plane. The gel is formed by three-dimensional network structures between the polyacrylate solution and the trivalent iron ion (Fe^3+) solution. We have proposed a physical model that the gel's film is responsible for the form of the spiral pattern.

First-principles study of high spin-polarization and thermoelectric efficiency of ferromagnetic CoFeCrAs quaternary Heusler alloy

NASA Astrophysics Data System (ADS)

Bhat, Tahir Mohiuddin; Gupta, Dinesh C.

2018-03-01

The ground state properties along with thermodynamic and thermoelectric properties of quaternary CoFeCrAs alloy within the ordered LiMgPdSn-type structure have been investigated by employing first-principles calculations. The alloy offers half-metallic ferromagnet character with an indirect band gap of 1.12 eV in the minority spin state with total spin magnetic moment of 4μB and follows Slater-Pauling relation. Effects on various properties of the material has been studied by the variation of the pressure and temperature. CoFeCrAs tenders large value of the Grüneisen parameter and small value for the thermal expansion coefficient. The materials present high Seebeck coefficient and huge power factor with the room temperature value of ∼-40 μV/K and 18 (1014 μWcm-1 K-2 s-1) respectively, which make CoFeCrAs promising candidate for efficient thermoelectric material.

Off-plane polarization ordering in metal chalcogen diphosphates from bulk to monolayer

NASA Astrophysics Data System (ADS)

Song, Wenshen; Fei, Ruixiang; Yang, Li

2017-12-01

Vertically (off-plane) ferroelectric ordering in ultrathin films has been pursued for decades. We predict the existence of intrinsic vertical polarization orderings in ultrathin metal chalcogen-diphosphates (MCDs). Taking CuInP2Se6 as an example, the first-principles calculation and electrostatic-energy model show that, under the open-circuit boundary condition, the ground state of bulk CuInP2Se6 is ferroelectric (FE) while that of monolayer is antiferroelectric (AFE), and the critical thickness for this FE/AFE transition is around six layers. Interestingly, under the closed-circuit boundary condition, the FE state can hold even for monolayer. Particularly, because of the small energy difference but the large barrier between FE and AFE orderings, the FE state can be stabilized in a free-standing monolayer, giving rise to intrinsic, off-plane two-dimensional ferroelectrics. Applying Monte Carlo simulations, we further calculate the ferroelectric Curie temperature (Tc) and electric hysteresis.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jesche, A.; Förster, T.; Spehling, J.

We report on superconductivity in CeFeAs 1-xP xO and the possible coexistence with Ce ferromagnetism (FM) in a small homogeneity range around x=30% with ordering temperatures of T SC≅T C≅4 K. The antiferromagnetic (AFM) ordering temperature of Fe at this critical concentration is suppressed to Tmore » $$Fe\\atop{N}$$≈40 K and does not shift to lower temperatures with a further increase of the P concentration. Therefore, a quantum-critical-point scenario with T$$Fe\\atop{N}$$→0 K which is widely discussed for the iron based superconductors can be excluded for this alloy series. Surprisingly, thermal expansion and x-ray powder diffraction indicate the absence of an orthorhombic distortion despite clear evidence for short-range AFM Fe ordering from muon-spin-rotation measurements. Furthermore, we discovered the formation of a sharp electron spin resonance signal unambiguously connected with the emergence of FM ordering.« less

Anion ordering, magnetic structure and properties of the vacancy ordered perovskite Ba{sub 3}Fe{sub 3}O{sub 7}F

DOE Office of Scientific and Technical Information (OSTI.GOV)

Clemens, Oliver, E-mail: oliver.clemens@nano.tu-darmstadt.de; Karlsruher Institut für Technologie, Institut für Nanotechnologie, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen; University of Birmingham, School of Chemistry, Birmingham B152TT

2016-11-15

This article describes a detailed investigation of the crystallographic and magnetic structure of perovskite type Ba{sub 3}Fe{sub 3}O{sub 7}F by a combined analysis of X-ray and neutron powder diffraction data. Complete ordering of vacancies within the perovskite lattice could be confirmed. In addition, the structure of the anion sublattice was studied by means of the valence bond method, which suggested partial ordering of the fluoride ions on two of the six crystallographically different anion sites. Moreover, the compound was found to show G-type antiferromagnetic ordering of Fe moments, in agreement with magnetometric measurements as well as previously recorded {sup 57}Femore » Mössbauer spectroscopy data. - Graphical abstract: The vacancy and anion ordered structure of Ba{sub 3}Fe{sub 3}O{sub 7}F is described together with its magnetic properties. - Highlights: • Ba{sub 3}Fe{sub 3}O{sub 7}F possesses a unique vacancy order not found for other perovskite type compounds. • The valence bond method was used to locate oxide and fluoride ions. • Fluoride ions are distributed only on two of the six anion sites in Ba{sub 3}Fe{sub 3}O{sub 7}F. • The compound shows G-type antiferromagnetic ordering of magnetic moments. • The magnetic structure could be refined in one of the maximal magnetic subgroups of the nuclear structure.« less

The metamorphosis of heterometallic trinuclear antiferromagnetic complexes into nano-sized superparamagnetic spinels.

PubMed

Vasylenko, Inna V; Gavrylenko, Konstiantyn S; Il'yin, Vladimir G; Golub, Vladimir; Goloverda, Galina; Kolesnichenko, Vladimir; Addison, Anthony W; Pavlishchuk, Vitaly V

2010-05-15

Thermal decomposition of the trinuclear heterometallic oxoacetates [Fe(2)M(μ(3)-O)(CH(3)COO)(6)(H(2)O)(3)] has been used as a single-precursor method for synthesis of the spinel-structured ternary oxides MFe(2)O(4) (M = Mn(II), Co(II), and Ni(II)). This facile process occurring at 320 °C results in the formation of nanocrystalline, (7-20 nm) highly pure stoichiometric ferrites in quantitative yield. The magnetic properties of these nanoparticulate ferrites were studied in the 10-300 K temperature range, revealing superparamagnetic behaviour for the Ni and Mn particles and ferromagnetic behavior for the Co ones at room temperature. Their blocking temperatures follow the order: CoFe(2)O(4) > MnFe(2)O(4) > NiFe(2)O(4).

Graphene oxide/ferroferric oxide/polyethylenimine nanocomposites for Congo red adsorption from water.

PubMed

Wang, Lina; Mao, Changming; Sui, Ning; Liu, Manhong; Yu, William W

2017-04-01

Graphene oxide/ferroferric oxide/polyethylenimine (GO/Fe 3 O 4 /PEI) nanocomposites were synthesized by an in situ growth of Fe 3 O 4 nanoparticles on GO sheets, and then modified by PEI. The GO/Fe 3 O 4 /PEI nanocomposites showed extremely high removal efficiency for anionic dye Congo Red (CR) due to the positively charged PEI molecules (methylene blue was also tested but with low adsorption capacity due to its cationic property). The CR removal capacity was 574.7 mg g -1 , higher than most of reported results. The adsorption kinetics could be well described by a pseudo-second-order model. Furthermore, GO/Fe 3 O 4 /PEI nanocomposites could be easily recycled by magnetic separation. The removal efficiency remained above 70% after five cycles.

Critical switching fluence of L10-FePt nanoparticles with practical size to ultrafast all-optical polarization switching

NASA Astrophysics Data System (ADS)

Huang, Tao; Wang, Haiwei; Cheng, Weiming; Zou, Yuhao; Xie, Changsheng

2017-06-01

The magnetic storage industry will be pushed into a new era by emerging magnetic materials and ingenious read/write techniques. Recently, L10-FePt nanoparticles with exceptionally high uniaxial anisotropy, combined with the technique of all-optical magnetic switching, have increasingly drawn the attention of researchers. Focusing on L10-FePt nanoparticles, we report the superparamagnetic size limits and three elaborate stages of magnetic orientation switching, which demonstrate that in terms of the opto-magnetic responses of L10-FePt nanoparticles with the size of 6 nm, the fluence of an ultrashort laser pulse should not be larger than the level of 40 mJ/cm2 in order to achieve the helicity-dependent all-optical switching.

Ferro and antiferro orbital ordering in Fe{sub 0.5}Mn{sub 0.5}V{sub 2}O{sub 4}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dey, Dibyendu, E-mail: dibyendu@phy.iitkgp.ernet.in; Taraphder, A.; Maitra, T.

2016-05-23

Using density functional theory calculations, we have investigated the orbital ordering in Fe{sub 0.5}Mn{sub 0.5}V{sub 2}O{sub 4} where Fe and V sites are orbitally active. Our first principles study within GGA+U and GGA+U+SO shows ferro-orbital ordering of d{sub x2−y2} orbital at all Fe sites, whereas A-type antiferro-orbital ordering at V sites where one 3d electron occupies d{sub xy} orbital at every V site and another electron occupies either 1/√2 (d{sub xz} + d{sub yz}) or 1/√2 (d{sub xz} - d{sub yz}) orbital alternatively along c axis. Insulating nature and the orbital ordering of this compound are found to be correlationmore » driven while the effect of spin-orbit interaction on orbital ordering is not significant.« less

Effect of chitosan coating on the structural and magnetic properties of MnFe2O4 and Mn0.5Co0.5Fe2O4 nanoparticles

NASA Astrophysics Data System (ADS)

Mdlalose, W. B.; Mokhosi, S. R.; Dlamini, S.; Moyo, T.; Singh, M.

2018-05-01

We report the influence of polymer coatings on structural and magnetic properties of MnFe2O4 and Mn0.5Co0.5Fe2O4 nanoferrites synthesized by glycol thermal technique and then coated with chitosan viz. CHI-MnFe2O4 and CHI-Mn0.5Co0.5Fe2O4. The compounds were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), high-resolution scanning electron microscopy (HRSEM), Mössbauer spectroscopy and magnetization measurements. The powder XRD patterns of naked nanoferrites confirmed single-phase spinel cubic structure with an average crystallite size of 13 nm, while the coated samples exhibited an average particle size of 15 nm. We observed a reduction in lattice parameters with coating. HRTEM results correlated well with XRD results. 57Fe Mössbauer spectra showed ordered magnetic spin states in both nanoferrites. This study shows that coatings have significant effects on the structural and magnetic properties of Mn-nanoferrites. Magnetization studies performed at room temperature in fields up to 14 kOe revealed the superparamagnetic nature of both naked and coated nanoparticles with spontaneous magnetizations at room temperature of 49.2 emu/g for MnFe2O4, 23.6 emu/g for coated CHI-MnFe2O4 nanoparticles, 63.2 emu/g for Mn0.5Co0.5Fe2O4 and 33.2 emu/g for coated CHI-Mn0.5Co0.5Fe2O4 nanoparticles. We observed reduction in coercive fields due to coating. Overall, chitosan-coated manganese and manganese-cobalt nanoferrites present as suitable candidates for biomedical applications owing to physicochemical, and magnetic properties exhibited.

A new solution method for wheel/rail rolling contact.

PubMed

Yang, Jian; Song, Hua; Fu, Lihua; Wang, Meng; Li, Wei

2016-01-01

To solve the problem of wheel/rail rolling contact of nonlinear steady-state curving, a three-dimensional transient finite element (FE) model is developed by the explicit software ANSYS/LS-DYNA. To improve the solving speed and efficiency, an explicit-explicit order solution method is put forward based on analysis of the features of implicit and explicit algorithm. The solution method was first applied to calculate the pre-loading of wheel/rail rolling contact with explicit algorithm, and then the results became the initial conditions in solving the dynamic process of wheel/rail rolling contact with explicit algorithm as well. Simultaneously, the common implicit-explicit order solution method is used to solve the FE model. Results show that the explicit-explicit order solution method has faster operation speed and higher efficiency than the implicit-explicit order solution method while the solution accuracy is almost the same. Hence, the explicit-explicit order solution method is more suitable for the wheel/rail rolling contact model with large scale and high nonlinearity.

Coincident structural and magnetic order in BaFe 2 ( As 1 - x P x ) 2 revealed by high-resolution neutron diffraction

DOE PAGES

Allred, J. M.; Taddei, K. M.; Bugaris, D. E.; ...

2014-09-19

We present neutron dffraction analysis of BaFe 2(As 1-xP x) 2 over a wide temperature (10 to 300 K) and compositional (0.11 < x < 0.79) range, including the normal state, the magnetically ordered state, and the superconducting state. The paramagnetic to spin-density wave and orthorhombic to tetragonal transitions are first order and coincident within the sensitivity of our measurements (~ 0:5 K). Extrapolation of the orthorhombic order parameter down to zero suggests that structural quantum criticality cannot exist at compositions higher than x = 0.28, which is much lower than values determined using other methods, but in good agreementmore » with our observations of the actual phase stability range. Lastly, the onset of spin-density wave order shows a stronger structural anomaly than the charge-doped system in the form of an enhancement of the c/a ratio below the transition.« less

Phase Coexistence and Kinetic Arrest in the Magnetostructural Transition of the Ordered Alloy FeRh

DOE PAGES

Keavney, David J.; Choi, Yongseong; Holt, Martin V.; ...

2018-01-29

In materials where two or more ordering degrees of freedom are closely matched in their free energies, coupling between them, or multiferroic behavior can occur. These phenomena can produce a very rich phase behavior, as well as emergent phases that offer useful properties and opportunities to reveal novel phenomena in phase transitions. The ordered alloy FeRh undergoes an antiferromagnetic to ferromagnetic phase transition at ~375 K, which illustrates the interplay between structural and magnetic order mediated by a delicate energy balance between two configurations. We have examined this transition using a combination of high-resolution x-ray structural and magnetic imaging andmore » comprehensive x-ray magnetic circular dichroism spectroscopy. We find that the transition proceeds via a defect-driven domain nucleation and growth mechanism, with significant return point memory in both the structural and magnetic domain configurations. In conclusion, the domains show evidence of inhibited growth after nucleation, resulting in a quasi- 2nd order temperature behavior.« less

In situ growth of well-ordered NiFe-MOF-74 on Ni foam by Fe2+ induction as an efficient and stable electrocatalyst for water oxidation.

PubMed

Xing, Jiale; Guo, Kailu; Zou, Zehua; Cai, Minmin; Du, Jing; Xu, Cailing

2018-06-06

Well-ordered NiFe-MOF-74 is in situ grown on Ni foam by the induction of Fe2+ and directly used as an OER electrocatalyst. Benefited from the intrinsic open porous structure of MOF-74, the in situ formed MOF arrays and the synergistic effect of Ni and Fe, outstanding water oxidation activity is obtained in alkaline electrolytes with an overpotential of 223 mV at 10 mA cm-2.

Suppression of magnetic order in CaCo1.86As2 with Fe substitution: Magnetization, neutron diffraction, and x-ray diffraction studies of Ca (Co1-xFex) yAs2

NASA Astrophysics Data System (ADS)

Jayasekara, W. T.; Pandey, Abhishek; Kreyssig, A.; Sangeetha, N. S.; Sapkota, A.; Kothapalli, K.; Anand, V. K.; Tian, W.; Vaknin, D.; Johnston, D. C.; McQueeney, R. J.; Goldman, A. I.; Ueland, B. G.

2017-02-01

Magnetization, neutron diffraction, and high-energy x-ray diffraction results for Sn-flux grown single-crystal samples of Ca (Co1-xFex) yAs2 , 0 ≤x ≤1 , 1.86 ≤y ≤2 , are presented and reveal that A-type antiferromagnetic order, with ordered moments lying along the c axis, persists for x ≲0.12 (1 ) . The antiferromagnetic order is smoothly suppressed with increasing x , with both the ordered moment and Néel temperature linearly decreasing. Stripe-type antiferromagnetic order does not occur for x ≤0.25 , nor does ferromagnetic order for x up to at least x =0.104 , and a smooth crossover from the collapsed-tetragonal (cT) phase of CaCo1.86As2 to the tetragonal (T) phase of CaFe2As2 occurs. These results suggest that hole doping CaCo1.86As2 has a less dramatic effect on the magnetism and structure than steric effects due to substituting Sr for Ca.

Tuning the magnetism of the top-layer FeAs on BaFe2As2 (001): First-principles study

NASA Astrophysics Data System (ADS)

Zhang, Bing-Jing; Liu, Kai; Lu, Zhong-Yi

2018-04-01

Magnetism may play an important role in inducing the superconductivity in iron-based superconductors. As a prototypical system, the surface of BaFe2As2 provides a good platform for studying related magnetic properties. We have designed systematic first-principles calculations to clarify the surface magnetism of BaFe2As2 (001), which previously has received little attention in comparison with surface structures and electronic states. We find that the surface environment has an important influence on the magnetic properties of the top-layer FeAs. For As-terminated surfaces, the magnetic ground state of the top-layer FeAs is in the staggered dimer antiferromagnetic (AFM) order, distinct from that of the bulk, while for Ba-terminated surfaces the collinear (single-stripe) AFM order is the most stable, the same as that in the bulk. When a certain coverage of Ba or K atoms is deposited onto the As-terminated surface, the calculated energy differences among different AFM orders for the top-layer FeAs on BaFe2As2 (001) can be much reduced, indicating enhanced spin fluctuations. To compare our results with available scanning tunneling microscopy (STM) measurements, we have simulated the STM images of several structural/magnetic terminations. Astonishingly, when the top-layer FeAs is in the staggered dimer AFM order, a stripe pattern appears in the simulated STM image even when the surface Ba atoms adopt a √{2 }×√{2 } structure, while a √{2 }×√{2 } square pattern comes out for the 1 ×1 full As termination. Our results suggest: (i) the magnetic state at the BaFe2As2 (001) surface can be quite different from that in the bulk; (ii) the magnetic properties of the top-layer FeAs can be tuned effectively by surface doping, which may likely induce superconductivity at the surface layer; (iii) both the surface termination and the AFM order in the top-layer FeAs can affect the STM image of BaFe2As2 (001), which needs to be taken into account when identifying the surface termination.

Nematicity and magnetism in LaFeAsO single crystals probed by 75As nuclear magnetic resonance

NASA Astrophysics Data System (ADS)

Ok, J. M.; Baek, S.-H.; Efremov, D. V.; Kappenberger, R.; Aswartham, S.; Kim, J. S.; van den Brink, Jeroen; Büchner, B.

2018-05-01

We report a 75As nuclear magnetic resonance study in LaFeAsO single crystals, which undergoes nematic and antiferromagnetic transitions at Tnem˜156 K and TN˜138 K, respectively. Below Tnem, the 75As spectrum splits sharply into two for an external magnetic field parallel to the orthorhombic a or b axis in the FeAs planes. Our analysis of the data demonstrates that the NMR line splitting arises from an electronically driven rotational symmetry breaking. The 75As spin-lattice relaxation rate as a function of temperature shows that spin fluctuations are strongly enhanced just below Tnem. These NMR findings indicate that nematic order promotes spin fluctuations in magnetically ordered LaFeAsO, as observed in nonmagnetic and superconducting FeSe. We conclude that the origin of nematicity is identical in both FeSe and LaFeAsO regardless of whether or not a long-range magnetic order develops in the nematic state.

Fe doped TiO2 nanofibers on the surface of graphene sheets for photovoltaics applications

NASA Astrophysics Data System (ADS)

Farhangi, Nasrin; Medina-Gonzalez, Yaocihuatl; Charpentier, Paul A.

2011-08-01

Highly ordered, visible light driven TiO2 nanowire arrays doped with Fe photocatalysts were grown on the surface of functionalized graphene sheets (FGSs) using a sol-gel method with titanium isopropoxide (TIP) monomer, acetic acid (HAc) as the polycondensation agent and iron chloride in the green solvent, supercritical carbon dioxide (scCO2). The morphology of the synthesized materials was studied by SEM and TEM, which showed uniform formation of Fe doped TiO2 nanofibers on the surface of graphene sheets, which acted as a template for nanowire growth through surface -COOH functionalities. Increasing Fe content in the nanowires did not change the morphology significantly. Optical properties of the synthesized composites were examined by UV spectroscopy which showed a significant reduction in band gap with increasing Fe content, i.e. 2.25 eV at 0.6% Fe. The enhancement of the optical properties of synthesized materials was confirmed by photocurrent measurement. The optimum sample containing 0.6% Fe doped TiO2 on the graphene sheets increased the power conversation efficiency by 6-fold in comparison to TiO2 alone.

Exchange spring in A1/L1{sub 0} FePt composite and its application in magnetic force microscope

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Guoqing, E-mail: gqli@swu.edu.cn; Zhu, Yanyan, E-mail: zhubai@swu.edu.cn; Zhang, Yong

2015-02-23

This paper reported fabrication of Fe{sub x}Pt{sub 100-x} films with (001) epitaxy on MgO(100) substrates. The atomic percentage of Fe was changed within the range of x = 10–85 in order to search the optimal atomic ratio for achieving both high and isotropic-like coercivity. It was found that the Fe{sub 60}Pt{sub 40} film exhibited large coercivities exceeding 5 kOe along both in-plane and out-of-plane directions due to the formation of A1/L1{sub 0} FePt composite. A penta-domain model for hard/soft/hard exchange spring system was proposed to interpret the anomalous magnetization behaviors observed in Fe{sub 60}Pt{sub 40} sample. By using Fe{sub 60}Pt{sub 40} asmore » the magnetic coating layer on a probe of magnetic force microscope, the flux changes at a linear density of 1000 kfci could be readily observed at a resolution of ∼13 nm.« less

Thermoelastic properties of γ-Fe and γ- Fe64Ni36 alloys

NASA Astrophysics Data System (ADS)

Tsujino, N.; Nishihara, Y.; Nakajima, Y.; Takahashi, E.; Funakoshi, K.

2009-12-01

The Earth’s core consists mainly of Fe-Ni alloy. Therefore the physical property of Fe-Ni alloy is a key issue to understand the planetary core. At 1 bar, γ-Fe is known as Anti-Invar alloy which shows anomalously high thermal expansivity, while γ-Fe64Ni36 is as a typical Inver-alloy. In addition, previous studies on γ-Fe-Ni Invar-alloys reported an anomalous pressure dependence of compression behavior (e.g., Dubrovinsky et al., 2001, Nataf et al., 2006, Matsushita et al., 2008). However, these studies were conducted at limited pressure range (> 6 GPa) or low temperature (30-300 K) conditions to identify physical properties of those alloys in the planetary interior. Therefore, we performed pressure-volume-temperature (P-V-T) measurements on γ-Fe and γ-Fe-Ni alloys at a wide P-T range of 0-23 GPa and 773-1873 K using the SPEED- Mk.II kawai-type multi-anvil apparatus at the SPring-8 synchrotron facility. On the basis of 2-γ state model by Weiss (1963), the thermal expansivity of γ-Fe can be decreased significantly with pressure. Our data, however, show no anomalous variation in the thermal expansion coefficient relative to pressure up to 23 GPa. In addition, anomalous pressure dependence on volume of γ-Fe64Ni36 reported by Matsushita et al. (2008) was not observed. Fitting 3rd order Birch-Murnaghan EOS and Mie-Grüneisen-Debye EOS to the P-V-T data of γ-Fe yielded V 0 = 49.028 ± 0.027 Å 3 , K T 0 = 111.2 ± 1.8 GPa, K ’ T = 5.2 ± 0.2, γ 0 = 2.30 ± 0.04 and q = -0.09 ± 0.21 with the fixed value of θ 0 = 340 K. The P-V data of γ- Fe64Ni36 was fittied using the 3rd order Birch-Marnagan, which yields V 0 = 48.85 ± 0.06 Å 3 , K T 0 = 88.1 ± 3.4 GPa, and K ’ 0 = 8.6± 0.5 at 1273 K.

Corrosion Behavior of High Nitrogen Nickel-Free Fe-16Cr-Mn-Mo-N Stainless Steels

NASA Astrophysics Data System (ADS)

Chao, K. L.; Liao, H. Y.; Shyue, J. J.; Lian, S. S.

2014-04-01

The purpose of the current study is to develop austenitic nickel-free stainless steels with lower chromium content and higher manganese and nitrogen contents. In order to prevent nickel-induced skin allergy, cobalt, manganese, and nitrogen were used to substitute nickel in the designed steel. Our results demonstrated that manganese content greater than 14 wt pct results in a structure that is in full austenite phase. The manganese content appears to increase the solubility of nitrogen; however, a lower corrosion potential was found in steel with high manganese content. Molybdenum appears to be able to increase the pitting potential. The effects of Cr, Mn, Mo, and N on corrosion behavior of Fe-16Cr-2Co-Mn-Mo-N high nitrogen stainless steels were evaluated with potentiodynamic tests and XPS surface analysis. The results reveal that anodic current and pits formation of the Fe-16Cr-2Co-Mn-Mo-N high nitrogen stainless steels were smaller than those of lower manganese and nitrogen content stainless steel.

High energy density rechargeable magnesium battery using earth-abundant and non-toxic elements

PubMed Central

Orikasa, Yuki; Masese, Titus; Koyama, Yukinori; Mori, Takuya; Hattori, Masashi; Yamamoto, Kentaro; Okado, Tetsuya; Huang, Zhen-Dong; Minato, Taketoshi; Tassel, Cédric; Kim, Jungeun; Kobayashi, Yoji; Abe, Takeshi; Kageyama, Hiroshi; Uchimoto, Yoshiharu

2014-01-01

Rechargeable magnesium batteries are poised to be viable candidates for large-scale energy storage devices in smart grid communities and electric vehicles. However, the energy density of previously proposed rechargeable magnesium batteries is low, limited mainly by the cathode materials. Here, we present new design approaches for the cathode in order to realize a high-energy-density rechargeable magnesium battery system. Ion-exchanged MgFeSiO4 demonstrates a high reversible capacity exceeding 300 mAh·g−1 at a voltage of approximately 2.4 V vs. Mg. Further, the electronic and crystal structure of ion-exchanged MgFeSiO4 changes during the charging and discharging processes, which demonstrates the (de)insertion of magnesium in the host structure. The combination of ion-exchanged MgFeSiO4 with a magnesium bis(trifluoromethylsulfonyl)imide–triglyme electrolyte system proposed in this work provides a low-cost and practical rechargeable magnesium battery with high energy density, free from corrosion and safety problems. PMID:25011939

High energy density rechargeable magnesium battery using earth-abundant and non-toxic elements

NASA Astrophysics Data System (ADS)

Orikasa, Yuki; Masese, Titus; Koyama, Yukinori; Mori, Takuya; Hattori, Masashi; Yamamoto, Kentaro; Okado, Tetsuya; Huang, Zhen-Dong; Minato, Taketoshi; Tassel, Cédric; Kim, Jungeun; Kobayashi, Yoji; Abe, Takeshi; Kageyama, Hiroshi; Uchimoto, Yoshiharu

2014-07-01

Rechargeable magnesium batteries are poised to be viable candidates for large-scale energy storage devices in smart grid communities and electric vehicles. However, the energy density of previously proposed rechargeable magnesium batteries is low, limited mainly by the cathode materials. Here, we present new design approaches for the cathode in order to realize a high-energy-density rechargeable magnesium battery system. Ion-exchanged MgFeSiO4 demonstrates a high reversible capacity exceeding 300 mAh.g-1 at a voltage of approximately 2.4 V vs. Mg. Further, the electronic and crystal structure of ion-exchanged MgFeSiO4 changes during the charging and discharging processes, which demonstrates the (de)insertion of magnesium in the host structure. The combination of ion-exchanged MgFeSiO4 with a magnesium bis(trifluoromethylsulfonyl)imide-triglyme electrolyte system proposed in this work provides a low-cost and practical rechargeable magnesium battery with high energy density, free from corrosion and safety problems.

Perspective for using Nd-Fe-B magnets as a tool for the improvement of the production and transportation of Vietnamese crude oil with high paraffin content

NASA Astrophysics Data System (ADS)

Tung, N. P.; Vinh, N. Q.; Phong, N. T. P.; Long, B. Q. K.; Hung, P. V.

2003-04-01

Controlling the paraffin deposition is one of the most serious and costly problems for high-paraffin crude-oil production and transportation. This holds especially for offshore, deep-water wells and pipelines, like in Vietnam. For finding solutions for these problems, a series of experiments has been performed in order to study the effects of a magnetic field on the rheology of two often produced crude oil samples, using the high and variable magnetic-flux density of a Nd-Fe-B magnet. The resulting changes in the essential characteristics of the magnetically treated (MT) crude oils, like form and size of the paraffin clusters as well as the rheology parameters, have definitely proved the possibility to use a Nd-Fe-B magnetic tool as an environmentally friendly and effective method to control the paraffin deposition in crude oils of Vietnam that have a high paraffin content.

The Iron Project & Iron Opacity Project: Updates on Photoionization, Electron-Ion Recombination of Fe XVII and Ca XV

NASA Astrophysics Data System (ADS)

Eissner, W.; Nahar, S.; Pradhan, A.; Hala, H.; Zhao, L.; Bailey, J.

2016-05-01

We have carried out converged close coupling (CCC) calculations for photoionization of Ne-like Fe XVII and demonstrate orders-of-magnitude enhancements in cross section due to successive core excitations. Convergence criteria are: (i) inclusion of sufficient number of residual ion Fe XVIII core states and (ii) high-resolution of myriad autoionizing resonances. We discuss verification of the conventional oscillator strength sum-rule in limited energy regions for bound-free plasma opacity. We will also report preliminary results from a larger R-matrix calculations of photoionization cross sections and electron-ion recombination rates of Ca XV where Rydberg series of resonances are included for core excitations to 28 states of n=2,3 complexes in contrast to previous 7 states of n=2 complex. The new results show existence of high-peak resonances of n=3 complex and enhanced background in high energy photoionization and a corresponding enhancement in the recombination in the high temperature region. Partial support: NSF, DOE, Ohio Supercomputer Center.

Electrochemical CO 2 Reduction with Atomic Iron-Dispersed on Nitrogen-Doped Graphene

DOE PAGES

Zhang, Chenhao; Yang, Shize; Wu, Jingjie; ...

2018-03-25

Electrochemical reduction of CO 2 provides an opportunity to reach a carbon-neutral energy recycling regime, in which CO 2 emissions from fuel use are collected and converted back to fuels. The reduction of CO 2 to CO is the first step toward the synthesis of more complex carbon-based fuels and chemicals. Therefore, understanding this step is crucial for the development of high-performance electrocatalyst for CO 2 conversion to higher order products such as hydrocarbons. In this paper, atomic iron dispersed on nitrogen-doped graphene (Fe/NG) is synthesized as an efficient electrocatalyst for CO 2 reduction to CO. Fe/NG has a lowmore » reduction overpotential with high Faradic efficiency up to 80%. The existence of nitrogen-confined atomic Fe moieties on the nitrogen-doped graphene layer is confirmed by aberration-corrected high-angle annular dark-field scanning transmission electron microscopy and X-ray absorption fine structure analysis. The Fe/NG catalysts provide an ideal platform for comparative studies of the effect of the catalytic center on the electrocatalytic performance. Finally, the CO 2 reduction reaction mechanism on atomic Fe surrounded by four N atoms (Fe–N 4) embedded in nitrogen-doped graphene is further investigated through density functional theory calculations, revealing a possible promotional effect of nitrogen doping on graphene.« less

Electrochemical CO 2 Reduction with Atomic Iron-Dispersed on Nitrogen-Doped Graphene

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Chenhao; Yang, Shize; Wu, Jingjie

Electrochemical reduction of CO 2 provides an opportunity to reach a carbon-neutral energy recycling regime, in which CO 2 emissions from fuel use are collected and converted back to fuels. The reduction of CO 2 to CO is the first step toward the synthesis of more complex carbon-based fuels and chemicals. Therefore, understanding this step is crucial for the development of high-performance electrocatalyst for CO 2 conversion to higher order products such as hydrocarbons. In this paper, atomic iron dispersed on nitrogen-doped graphene (Fe/NG) is synthesized as an efficient electrocatalyst for CO 2 reduction to CO. Fe/NG has a lowmore » reduction overpotential with high Faradic efficiency up to 80%. The existence of nitrogen-confined atomic Fe moieties on the nitrogen-doped graphene layer is confirmed by aberration-corrected high-angle annular dark-field scanning transmission electron microscopy and X-ray absorption fine structure analysis. The Fe/NG catalysts provide an ideal platform for comparative studies of the effect of the catalytic center on the electrocatalytic performance. Finally, the CO 2 reduction reaction mechanism on atomic Fe surrounded by four N atoms (Fe–N 4) embedded in nitrogen-doped graphene is further investigated through density functional theory calculations, revealing a possible promotional effect of nitrogen doping on graphene.« less

High pressure floating zone growth and structural properties of ferrimagnetic quantum paraelectric BaFe 12O 19

DOE PAGES

Cao, Huibo B.; Zhao, Zhiying Y.; Lee, Minseong; ...

2015-06-24

High quality single crystals of BaFemore » $$_{12}$$O$$_{19}$$ were grown with the floating zone technique in flowing oxygen atmosphere of 100 atm. BaFe$$_{12}$$O$$_{19}$$ melts incongruently in atmospheric oxygen. High oxygen pressure above 50 atm modifies the melting behavior to be congruent, which allows for the crystal growth with the crucible-free floating zone technique. Single crystal neutron diffraction were measured to determine the nuclear and magnetic structures at 4 K and 295 K. At both temperatures, there exist local electric dipoles formed by the off-mirror-plane displacements of magnetic Fe$$^{3+}$$ ions at the bypyramidal sites. The displacement at 4 K is about half of that at room temperature. The temperature dependence of specific heat shows no anomaly associated with the long range polar ordering in the temperature range of 1.90-300~K. The inverse dielectric constant along the c-axis shows a $T^2$ temperature dependence below 20 K and then following by a plateau below 10 K, recognized as quantum paraelectric features. Further cooling below 1.4 K, the upturn region was clearly revealed and indicates BaFe$$_{12}$$O$$_{19}$$ is a critical quantum paraelectric system with Fe$$^{3+}$$ ions playing roles for both magnetic and electric dipoles.« less

Ultrahigh Tunneling-Magnetoresistance Ratios in Nitride-Based Perpendicular Magnetic Tunnel Junctions from First Principles

NASA Astrophysics Data System (ADS)

Yang, Baishun; Tao, Lingling; Jiang, Leina; Chen, Weizhao; Tang, Ping; Yan, Yu; Han, Xiufeng

2018-05-01

We report a first-principles study of electronic structures, magnetic properties, and the tunneling-magnetoresistance (TMR) effect of a series of ferromagnetic nitride M4N (M =Fe , Co, Ni)-based magnetic tunnel junctions (MTJs). It is found that bulk Fe4 N reveals a half-metal nature in terms of the Δ1 state. A perpendicular magnetic anisotropy is observed in the periodic system Fe4 N /MgO . In particular, the ultrahigh TMR ratio of over 24 000% is predicted in the Fe4 N /MgO /Fe4N MTJ due to the interface resonance tunneling and relatively high transmission for states of other symmetry. Besides, the large TMR can be maintained with the change of atomic details at the interface, such as the order-disorder interface, the change of thickness of the MgO barrier, and different in-plane lattice constants of the MTJ. The physical origin of the TMR effect can be well understood by analyzing the band structure and transmission channel of bulk Fe4 N as well as the transmission in momentum space of Fe4 N /MgO /Fe4N . Our results suggest that the Fe4 N /MgO /Fe4N MTJ is a benefit for spintronic applications.

In-Situ Fixation of All-Inorganic Mo-Fe-S Clusters for the Highly Selective Removal of Lead(II).

PubMed

Zhang, Wentao; Shi, Shuo; Zhu, Wenxin; Yang, Chengyuan; Li, Sihang; Liu, Xinnan; Hu, Na; Huang, Lunjie; Wang, Rong; Suo, Yourui; Li, Zhonghong; Wang, Jianlong

2017-09-27

The selective adsorption by suitable substrate materials is considered one of the most economical methods. In this work, an all-inorganic bimetallic Mo-Fe-S cluster is facilely achieved through in situ chemical fixation of tetrathiomolybdate (TTM) on Fe 3 O 4 nanoparticles (NPs) at room temperature (donated as FeMoS NPs). The bimetallic building blocks on the obtained FeMoS NPs possess a monovacancy species of sulfur, endowing FeMoS NPs with a selectivity order of Zn 2+ , Mn 2+ , Ni 2+ < Cd 2+ ≪ Cu 2+ < Pb 2+ for metal-ion adsorption, a novel application for the Mo-Fe-S clusters. Particularly, with the highest selectivity for Pb 2+ (K d ≈ 10 7 ), which is about 3 × 10 3 -1 × 10 6 times higher than those for other ions and has exceeded that of a series of outstanding sorbents reported for Pb 2+ , FeMoS NPs can efficiently reduce the concentration of Pb 2+ from ∼10 ppm to an extremely low level of ∼1 ppb. This facile and rational fabrication of the Mo-Fe-S cluster with Fe 3 O 4 represents a feasible approach to cheaply develop novel and efficient materials for the selective removal of lead(II).

Catalytic Oxidation of Vanillyl Alcohol Using FeMCM-41 Nanoporous Tubular Reactor

NASA Astrophysics Data System (ADS)

Elamathi, P.; Kolli, Murali Krishna; Chandrasekar, G.

Iron containing nanoporous MCM-41 (FeMCM-41) with different Si/Fe ratios of 50, 100 and 150 was synthesized by hydrothermal synthesis process. The materials obtained from hydrothermal synthesis were characterized by various physico chemical techniques such as XRD, N2 adsorption, DR UV-vis, EPR and FTIR spectroscopy. XRD analyses of FeMCM-41 materials confirmed the presence of well-ordered crystalline structure. N2 isotherm of FeMCM-41 materials showed type IV adsorption isotherm. EPR and DR UV-vis analysis of FeMCM-41 samples indicates the presence of high tetrahedral coordination at the Si/Fe ratios of 100 and 150. The catalytic performance of FeMCM-41 nano tubular reactor was tested in the liquid phase oxidation of vanillyl alcohol into vanillin using H2O2 (50wt% in water). The reaction products were analyzed by gas chromatography in DB-5 capillary column with flame ionization detector. The products were confirmed by 1H NMR, 13C NMR and LC-Mass spectroscopy. The maximum conversion of vanillyl alcohol (85%) and selectivity towards vanillin (82%) were observed using the catalyst FeMCM-41(100) in 30min at 60∘C. The influence of reaction temperature, reaction time, reactants molar ratio, Si/Fe ratio and amount of catalyst were investigated.

Beating the macroscopic quantum tunneling limit by man-made magnetic dead layers

NASA Astrophysics Data System (ADS)

Ma, Ji; Chen, Kezheng

2018-05-01

Magnetic dead layers (MDLs) are always undesirable in practical applications due to their highly frustrated spin configurations and severe degradation of host magnetism. Here we provide new insights in MDLs and unravel their attractive prospect for ferrimagnetic hybrid of Fe3O4 and γ-Fe2O3 (denoted as Fe3O4@γ-Fe2O3 in the main text) to exhibit macroscopic quantum tunneling (MQT) phenomena in measureable kelvin range. The 3 nm-sized negatively-charged Fe3O4@γ-Fe2O3 nanoparticles were immersed in various metal chloride solutions containing Mn2+, Co2+, Ni2+, Fe3+, and Fe2+ cations to form cationic MDLs via electrostatic attraction. These man-made MDLs, if being of positive enough zeta potentials, greatly disordered the magnetic dipole interactions among Fe3O4@γ-Fe2O3 nanoparticles and induce extra energy barrier to yield pronounced MQT effect in Fe3O4@γ-Fe2O3 nanoparticles even though they were dispersed neither in water nor in oil. Their crossover temperatures dividing MQT and purely thermal relaxation were found to be one order of magnitude higher than reported values in other MQT systems, and more strikingly, they could be tailored by altering the soak period in our facile and scalable route.

Static compression of Fe 0.83Ni 0.09Si 0.08 alloy to 374 GPa and Fe 0.93Si 0.07 alloy to 252 GPa: Implications for the Earth's inner core

NASA Astrophysics Data System (ADS)

Asanuma, Hidetoshi; Ohtani, Eiji; Sakai, Takeshi; Terasaki, Hidenori; Kamada, Seiji; Hirao, Naohisa; Ohishi, Yasuo

2011-10-01

The pressure-volume equations of state of iron-nickel-silicon alloy Fe 0.83Ni 0.09Si 0.08 (Fe-9.8 wt.% Ni-4.0 wt.% Si) and iron-silicon alloy Fe 0.93Si 0.07 (Fe-3.4 wt.% Si) have been investigated up to 374 GPa and 252 GPa, respectively. The present compression data covered pressures of the Earth's core. We confirmed that both Fe 0.83Ni 0.09Si 0.08 and Fe 0.93Si 0.07 alloys remain in the hexagonal close packed structure at all pressures studied. We obtained the density of these alloys at the pressure of the inner core boundary (ICB), 330 GPa at 300 K by fitting the compression data to the third order Birch-Murnaghan equation of state. Using these density values combined with the previous data for hcp-Fe, hcp-Fe 0.8Ni 0.2, and hcp-Fe 0.84Si 0.16 alloys and comparing with the density of the PREM inner core, we estimated the Ni and Si contents of the inner core. The Si content of the inner core estimated here is slightly greater than that estimated previously based on the sound velocity measurement of the hcp-Fe-Ni-Si alloy at high pressure.

Kinetics of Fe2+-Mg order-disorder in orthopyroxene: experimental studies and applications to cooling rates of rocks

NASA Astrophysics Data System (ADS)

Stimpfl, M.; Ganguly, J.; Molin, G.

2005-10-01

We determined the forward rate constant (K+) for the Fe2+-Mg order-disorder between the M2 and M1 sites of orthopyroxene (OPx), which is described by the homogeneous reaction Fe2+ (M2) + Mg(M1) ↔ Mg(M2) + Fe2+ (M1), by both ordering and disordering experiments at isothermal condition and also by continuous cooling experiments. The rate constant was determined as a function of temperature in the range of 550-750°C, oxygen fugacity between quartz-fayalite-iron and Ni-NiO buffers, and at compositions of 16 and 50 mol% ferrosilite component. The K+ value derived from disordering experiment was found to be larger than that derived from ordering experiment at 550°C, while at T>580°C, these two values are essentially the same. The fO2 dependence of the rate constant can be described by the relation K+ α (fO2) n with n=5.5-6.5, which is compatible with the theoretically expected relation. The Arrhenius relation at the WI buffer condition is given by ln (C_{text{o}} {text{K}}^+) = - {41511 - 12600{text{X}}_{{text{Fe}}} }/{{T({text{K}})}} + 28.26 + 5.27{text{X}}_{{text{Fe}}}, min^{-1} where C o represents the total number of M2 + M1 sites occupied by Fe2+ and Mg per unit volume of the crystal. The above relation can be used to calculate the cooling rates of natural OPx crystals around the closure temperature ( T c) of Fe-Mg ordering, which are usually below 300°C for slowly cooled rocks. We determined the Fe-Mg ordering states of several OPx crystals (˜ Fs50) from the Central Gneissic Complex (Khtada Lake), British Columbia, which yields T c ˜290°C. Numerical simulation of the change of Fe2+-Mg ordering in OPx as a function of temperature using the above expression of rate constant and a non-linear cooling model yields quenched values of ordering states that are in agreement with the observed values for cooling rates of 11-17°C/Myr below 300°C. The inferred cooling rate is in agreement with the available geochronological constraints.

Kinetics and Equilibrium of Fe3+ Ions Adsorption on Carbon Nanofibers

NASA Astrophysics Data System (ADS)

Alimin; Agusu, La; Ahmad, L. O.; Kadidae, L. O.; Ramadhan, L.; Nurdin, M.; Isdayanti, N.; Asria; Aprilia M, P.; Hasrudin

2018-05-01

Generally, the interaction between metal ions and adsorbent is governed by many factors including; concentration of metal ions, interaction time and solution pH. In this work, we applied liquid phase adsorption for studying the interaction between Fe3+ ions and Carbon Nanofibers (CNFs) irradiated by ultrasonic waves. Kinetics and isotherms model of the Fe3+ ion adsorption was investigated by varying contact time and pH. We found that the Fe3+ ions were efficiently adsorbed on CNFs for 0.5 h in acidic pH of around 5. In order to obtain the best-fitted isotherms model, Langmuir and Freundlich’s isotherms were used in this work. The adsorption equilibrium Fe3+ metal ions on CNFs tend to follow Langmuir. Adsorption kinetics of Fe3+ ions on CNFs were investigated by using both pseudo-first and pseudo-second orders. The adsorption kinetics coincided well with the pseudo-second-order.

Seasonal changes in Fe species and soluble Fe concentration in the atmosphere in the Northwest Pacific region based on the analysis of aerosols collected in Tsukuba, Japan

NASA Astrophysics Data System (ADS)

Takahashi, Y.; Furukawa, T.; Kanai, Y.; Uematsu, M.; Zheng, G.; Marcus, M. A.

2013-08-01

Atmospheric iron (Fe) can be a significant source of nutrition for phytoplankton inhabiting remote oceans, which in turn has a large influence on the Earth's climate. The bioavailability of Fe in aerosols depends mainly on the fraction of soluble Fe (= [FeSol]/[FeTotal], where [FeSol] and [FeTotal] are the atmospheric concentrations of soluble and total Fe, respectively). However, the numerous factors affecting the soluble Fe fraction have not been fully understood. In this study, the Fe species, chemical composition, and soluble Fe concentrations in aerosols collected in Tsukuba, Japan were investigated over a year (nine samples from December 2002 to October 2003) to identify the factors affecting the amount of soluble Fe supplied into the ocean. The soluble Fe concentration in aerosols is correlated with those of sulfate and oxalate originated from anthropogenic sources, suggesting that soluble Fe is mainly derived from anthropogenic sources. Moreover, the soluble Fe concentration is also correlated with the enrichment factors of vanadium and nickel emitted by fossil fuel combustion. These results suggest that the degree of Fe dissolution is influenced by the magnitude of anthropogenic activity, such as fossil fuel combustion. X-ray absorption fine structure (XAFS) spectroscopy was performed in order to identify the Fe species in aerosols. Fitting of XAFS spectra coupled with micro X-ray fluorescence analysis (μ-XRF) showed the main Fe species in aerosols in Tsukuba to be illite, ferrihydrite, hornblende, and Fe(III) sulfate. Moreover, the soluble Fe fraction in each sample measured by leaching experiments is closely correlated with the Fe(III) sulfate fraction determined by the XAFS spectrum fitting, suggesting that Fe(III) sulfate is the main soluble Fe in the ocean. Another possible factor that can control the amount of soluble Fe supplied into the ocean is the total Fe(III) concentration in the atmosphere, which was high in spring due to the high mineral dust concentrations during spring in East Asia. However, this factor does not contribute to the amount of soluble Fe to a larger degree than the effect of Fe speciation, or more strictly speaking the presence of Fe(III) sulfate. Therefore, based on these results, the most significant factor influencing the amount of soluble Fe in the North Pacific region is the concentration of anthropogenic Fe species such as Fe(III) sulfate that can be emitted from megacities in Eastern Asia.

Trends in activity for the oxygen evolution reaction on transition metal (M = Fe, Co, Ni) phosphide pre-catalysts† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c7sc05033j

PubMed Central

Xu, Junyuan; Li, Junjie; Xiong, Dehua; Zhang, Bingsen; Liu, Yuefeng; Wu, Kuang-Hsu; Amorim, Isilda; Li, Wei

2018-01-01

Transition metal phosphides (TMPs) have recently emerged as a new class of pre-catalysts that can efficiently catalyze the oxygen evolution reaction (OER). However, how the OER activity of TMPs varies with the catalyst composition has not been systematically explored. Here, we report the alkaline OER electrolysis of a series of nanoparticulate phosphides containing different equimolar metal (M = Fe, Co, Ni) components. Notable trends in OER activity are observed, following the order of FeP < NiP < CoP < FeNiP < FeCoP < CoNiP < FeCoNiP, which indicate that the introduction of a secondary metal(s) to a mono-metallic TMP substantially boosts the OER performance. We ascribe the promotional effect to the enhanced oxidizing power of bi- and tri-metallic TMPs that can facilitate the formation of MOH and chemical adsorption of OH– groups, which are the rate-limiting steps for these catalysts according to our Tafel analysis. Remarkably, the tri-metallic FeCoNiP pre-catalyst exhibits exceptionally high apparent and intrinsic OER activities, requiring only 200 mV to deliver 10 mA cm–2 and showing a high turnover frequency (TOF) of ≥0.94 s–1 at the overpotential of 350 mV. PMID:29780476

Modification of the structural and magnetic properties of granular FePt films by seed layer conditioning

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wicht, S., E-mail: s.wicht@ifw-dresden.de; TU Dresden, Institut für Werkstoffwissenschaft, Helmholtzstraße 10, D-01069 Dresden; Neu, V.

2015-01-07

The steadily increasing amount of digital information necessitates the availability of reliable high capacity magnetic data storage. Here, future hard disk drives with extended areal storage densities beyond 1.0 Tb/in{sup 2} are envisioned by using high anisotropy granular and chemically L1{sub 0}-ordered FePt (002) perpendicular media within a heat-assisted magnetic recording scheme. Perpendicular texturing of the [001] easy axes of the individual grains can be achieved by using MgO seed layers. It is therefore investigated, if and how an Ar{sup +} ion irradiation of the MgO seed layer prior to the deposition of the magnetic material influences the MgO surfacemore » properties and hereby the FePt [001] texture. Structural investigations reveal a flattening of the seed layer surface accompanied by a change in the morphology of the FePt grains. Moreover, the fraction of small second layer particles and the degree of coalescence of the primarily deposited FePt grains strongly increases. As for the magnetic performance, this results in a reduced coercivity along the magnetic easy axis (out of plane) and in enhanced hard axis (in-plane) remanence values. The irradiation induced changes in the magnetic properties of the granular FePt-C films are traced back to the accordingly modified atomic structure of the FePt-MgO interface region.« less

Elemental Mercury Oxidation over Fe-Ti-Mn Spinel: Performance, Mechanism, and Reaction Kinetics.

PubMed

Xiong, Shangchao; Xiao, Xin; Huang, Nan; Dang, Hao; Liao, Yong; Zou, Sijie; Yang, Shijian

2017-01-03

The design of a high-performance catalyst for Hg 0 oxidation and predicting the extent of Hg 0 oxidation are both extremely limited due to the uncertainties of the reaction mechanism and the reaction kinetics. In this work, Fe-Ti-Mn spinel was developed as a high-performance catalyst for Hg 0 oxidation, and the reaction mechanism and the reaction kinetics of Hg 0 oxidation over Fe-Ti-Mn spinel were studied. The reaction orders of Hg 0 oxidation over Fe-Ti-Mn spinel with respect to gaseous Hg 0 concentration and gaseous HCl concentration were approximately 1 and 0, respectively. Therefore, Hg 0 oxidation over Fe-Ti-Mn spinel mainly followed the Eley-Rideal mechanism (i.e., the reaction of gaseous Hg 0 with adsorbed HCl), and the rate of Hg 0 oxidation mainly depended on Cl • concentration on the surface. As H 2 O, SO 2 , and NO not only inhibited Cl • formation on the surface but also interfered with the interface reaction between gaseous Hg 0 and Cl • on the surface, Hg 0 oxidation over Fe-Ti-Mn spinel was obviously inhibited in the presence of H 2 O, SO 2 , and NO. Furthermore, the extent of Hg 0 oxidation over Fe-Ti-Mn spinel can be predicted according to the kinetic parameter k E-R , and the predicted result was consistent with the experimental result.

Spin-orbit driven phenomena in the isoelectronic L 10 -Fe(Pd,Pt) alloys from first principles

NASA Astrophysics Data System (ADS)

Kudrnovský, J.; Drchal, V.; Turek, I.

2017-12-01

The anomalous Hall effect (AHE) and the Gilbert damping (GD) are studied theoretically for the partially ordered L 10 -Fe(Pd,Pt) alloys. The varying alloy order and the spin-orbit coupling, which are due to the change in the Pd/Pt composition, allow for a chemical tuning of both phenomena which play an important role in the spintronic applications. The impact of the antisite disorder on the residual resistivity, AHE, and GD is studied from first principles using recently developed methods employing the Kubo-Bastin approach and the nonlocal torque operator method. The most interesting result is a different behavior of samples with low and high chemical orders. Good agreement between calculated and measured concentration trends is obtained for all quantities studied, while the absolute GD values are underestimated.

Doping evolution of spin fluctuations and their peculiar suppression at low temperatures in Ca(Fe 1 -xCox)2As2

NASA Astrophysics Data System (ADS)

Sapkota, A.; Das, P.; Böhmer, A. E.; Ueland, B. G.; Abernathy, D. L.; Bud'ko, S. L.; Canfield, P. C.; Kreyssig, A.; Goldman, A. I.; McQueeney, R. J.

2018-05-01

Results of inelastic neutron scattering measurements are reported for two annealed compositions of Ca(Fe 1 -xCox)2As2,x =0.026 and 0.030, which possess stripe-type antiferromagnetically ordered and superconducting ground states, respectively. In the AFM ground state, well-defined and gapped spin waves are observed for x =0.026 , similar to the parent CaFe2As2 compound. We conclude that the well-defined spin waves are likely to be present for all x corresponding to the AFM state. This behavior is in contrast to the smooth evolution to overdamped spin dynamics observed in Ba(Fe 1 -xCox)2As2 , wherein the crossover corresponds to microscopically coexisting AFM order and SC at low temperature. The smooth evolution is likely absent in Ca(Fe 1 -xCox)2As2 due to the mutual exclusion of AFM ordered and SC states. Overdamped spin dynamics characterize paramagnetism of the x =0.030 sample and high-temperature x =0.026 sample. A sizable loss of magnetic intensity is observed over a wide energy range upon cooling the x =0.030 sample, at temperatures just above and within the superconducting phase. This phenomenon is unique amongst the iron-based superconductors and is consistent with a temperature-dependent reduction in the fluctuating moment. One possible scenario ascribes this loss of moment to a sensitivity to the c -axis lattice parameter in proximity to the nonmagnetic collapsed tetragonal phase and another scenario ascribes the loss to a formation of a pseudogap.

Study on Composition, Microstructure and Wear Behavior of Fe-B-C Wear-Resistant Surfacing Alloys

NASA Astrophysics Data System (ADS)

Zhuang, Minghui; Li, Muqin; Wang, Jun; Ma, Zhen; Yuan, Shidan

2017-12-01

Fe-B-C alloy layers with various microstructures were welded on Q235 steel plates using welding powders/H08Mn2Si and welding wires composite surfacing technology. The relationship existing between the chemical composition, microstructure and wear resistance of the surfacing alloy layers was investigated by scanning electron microscopy, x-ray diffraction, electron backscatter diffraction and wear tests. The results demonstrated that the volume fractions and morphologies of the microstructures in the surfacing alloy layers could be controlled by adjusting the boron and carbon contents in the welding powders, which could further regulate the wear resistance of the surfacing alloy layers. The typical microstructures of the Fe-B-C surfacing alloy layers included dendritic Fe, rod-like Fe2B, fishbone-like Fe2B and daisy-like Fe3(C, B). The wear resistance of the alloy layers with various morphologies differed. The wear resistance order of the different microstructures was: rod-like Fe2B > fishbone-like Fe2B > daisy-like Fe3(C, B) > dendritic Fe. A large number of rod-like Fe2B with high microhardness could be obtained at the boron content of 5.70 5.90 wt.% and the carbon content of 0.50 0.60wt.%. The highest wear resistance of the Fe-B-C alloy layers reached the value of 24.1 g-1, which demonstrates the main microscopic cutting wear mechanism of the Fe-B-C alloy layers.

Probing the unconventional superconducting state of LiFeAs by quasiparticle interference.

PubMed

Hänke, Torben; Sykora, Steffen; Schlegel, Ronny; Baumann, Danny; Harnagea, Luminita; Wurmehl, Sabine; Daghofer, Maria; Büchner, Bernd; van den Brink, Jeroen; Hess, Christian

2012-03-23

A crucial step in revealing the nature of unconventional superconductivity is to investigate the symmetry of the superconducting order parameter. Scanning tunneling spectroscopy has proven a powerful technique to probe this symmetry by measuring the quasiparticle interference (QPI) which sensitively depends on the superconducting pairing mechanism. A particularly well-suited material to apply this technique is the stoichiometric superconductor LiFeAs as it features clean, charge neutral cleaved surfaces without surface states and a relatively high T(c)∼18  K. Our data reveal that in LiFeAs the quasiparticle scattering is governed by a van Hove singularity at the center of the Brillouin zone which is in stark contrast to other pnictide superconductors where nesting is crucial for both scattering and s(±) superconductivity. Indeed, within a minimal model and using the most elementary order parameters, calculations of the QPI suggest a dominating role of the holelike bands for the quasiparticle scattering. Our theoretical findings do not support the elementary singlet pairing symmetries s(++), s(±), and d wave. This brings to mind that the superconducting pairing mechanism in LiFeAs is based on an unusual pairing symmetry such as an elementary p wave (which provides optimal agreement between the experimental data and QPI simulations) or a more complex order parameter (e.g., s+id wave symmetry).

Structural transitions and multiferroic properties of high Ni-doped BiFeO3

NASA Astrophysics Data System (ADS)

Betancourt-Cantera, L. G.; Bolarín-Miró, A. M.; Cortés-Escobedo, C. A.; Hernández-Cruz, L. E.; Sánchez-De Jesús, F.

2018-06-01

Nickel doped bismuth ferrite powders, BiFe1-x NixO3 (0 ≤ x ≤ 0.5), were synthesized by high-energy ball milling followed by an annealing at 700 °C. A detailed study about the substitution of Fe3+ by Ni2+ on the crystal structure and multiferroic properties is presented. The X-ray diffraction patterns reveal the formation of rhombohedral structure with small amounts of Bi2Fe4O9 as a secondary phase for x < 0.1. Also it is inferred the stabilization of a Bi25FeO40, sillenite phase, as the amount of Ni2+ substitution increases, reaching up 95.23% of sillenite for x = 0.5. The magnetic behavior indicates the frustration of the G-antiferromagnetic order typical of the un-doped BiFeO3, caused by the presence of small amounts of Ni2+ (x < 0.1) on the structure. The DC conductivity exhibited a little increment with increasing Ni content (up to x = 0.1). Although the conductivity increases, for nickel concentrations of 0.2-0.5, the bismuth ferrites doped with nickel retain their property of being an electrical insulating material. Behavior modifications of electrical conductivity, permittivity and dielectric loss versus frequency are related with crystal structure transformations, when nickel concentration is increased.

Rapid and efficient uranium(VI) capture by phytic acid/polyaniline/FeOOH composites.

PubMed

Wei, Xintao; Liu, Qi; Zhang, Hongsen; Liu, Jingyuan; Chen, Rongrong; Li, Rumin; Li, Zhangshuang; Liu, Peili; Wang, Jun

2018-02-01

Uranium plays an indispensable role in nuclear energy, but there are limited land resources to meet the ever growing demand; therefore, a need exists to develop efficient materials for capturing uranium from water. Herein, we synthesize a promising adsorbent of phytic acid/polyaniline/FeOOH composites (PA/PANI/FeOOH) by oxidative polymerization. Phytic acid, acting asa gelator and dopant, plays an important role in the formation of polyaniline (PANI). The PA/PANI/FeOOH exhibites high adsorption capacity (q m =555.8mgg -1 , T=298K), rapid adsorption rate (within 5min), excellent selectivity and cyclic stability. In addition, the results show that the adsorption isotherm is well fitted to the Langmuir isotherm model, and the adsorption kinetics agree with a pseudo-second order model. XPS analysis indicates that the removal of uranium is mainly attributed to abundant amine and imine groups on the surface of PA/PANI/FeOOH. Importantly, the removal of uranium from low concentrations of simulated seawater is highly efficient with a removal rate exceeding 92%. From our study, superior adsorption capacities, along with a low-cost, environmentally friendly and facile synthesis, reveal PA/PANI/FeOOH asa promising material for uranium capture. Copyright © 2017. Published by Elsevier Inc.

Density functional theory study of small X-doped Mg(n) (X = Fe, Co, Ni, n = 1-9) bimetallic clusters: equilibrium structures, stabilities, electronic and magnetic properties.

PubMed

Kong, Fanjie; Hu, Yanfei

2014-03-01

The geometries, stabilities, and electronic and magnetic properties of Mg(n) X (X = Fe, Co, Ni, n = 1-9) clusters were investigated systematically within the framework of the gradient-corrected density functional theory. The results show that the Mg(n)Fe, Mg(n)Co, and Mg(n)Ni clusters have similar geometric structures and that the X atom in Mg(n)X clusters prefers to be endohedrally doped. The average atomic binding energies, fragmentation energies, second-order differences in energy, and HOMO-LUMO gaps show that Mg₄X (X = Fe, Co, Ni) clusters possess relatively high stability. Natural population analysis was performed and the results showed that the 3s and 4s electrons always transfer to the 3d and 4p orbitals in the bonding atoms, and that electrons also transfer from the Mg atoms to the doped atoms (Fe, Co, Ni). In addition, the spin magnetic moments were analyzed and compared. Several clusters, such as Mg₁,₂,₃,₄,₅,₆,₈,₉Fe, Mg₁,₂,₄,₅,₆,₈,₉Co, and Mg₁,₂,₅,₆,₇,₉Ni, present high magnetic moments (4 μ(B), 3 μ(B), and 2 μ(B), respectively).

Observation of magnetization and exchange bias reversals in NdFe0.5Cr0.5O3

NASA Astrophysics Data System (ADS)

Sharannia, M. P.; De, Santanu; Singh, Ripandeep; Das, A.; Nirmala, R.; Santhosh, P. N.

2017-05-01

Polycrystalline NdFe0.5Cr0.5O3 has orthorhombic structure with Pnma space group and is magnetically ordered at room temperature as confirmed by neutron diffraction. The magnetic structure involves CxGyFz type ordering of Fe3+/Cr3+ ions. NdFe0.5Cr0.5O3 shows magnetization reversal and sign reversal of exchange bias at 16 K. Nd3+ moments that get induced by the internal field of |Fe+Cr| sublattice couple antiferromagnetically with the ferromagnetic component of |Fe+Cr| sublattice. Nd3+ moments overcome the |Fe+Cr| moments at 16 K below which the material shows negative magnetization and positive exchange bias.

Mineralogical, geochemical, and magnetic signatures of surface sediments from the Canadian Beaufort Shelf and Amundsen Gulf (Canadian Arctic)

NASA Astrophysics Data System (ADS)

Gamboa, Adriana; Montero-Serrano, Jean-Carlos; St-Onge, Guillaume; Rochon, André; Desiage, Pierre-Arnaud

2017-02-01

Mineralogical, geochemical, magnetic, and siliciclastic grain-size signatures of 34 surface sediment samples from the Mackenzie-Beaufort Sea Slope and Amundsen Gulf were studied in order to better constrain the redox status, detrital particle provenance, and sediment dynamics in the western Canadian Arctic. Redox-sensitive elements (Mn, Fe, V, Cr, Zn) indicate that modern sedimentary deposition within the Mackenzie-Beaufort Sea Slope and Amundsen Gulf took place under oxic bottom-water conditions, with more turbulent mixing conditions and thus a well-oxygenated water column prevailing within the Amundsen Gulf. The analytical data obtained, combined with multivariate statistical (notably, principal component and fuzzy c-means clustering analyses) and spatial analyses, allowed the division of the study area into four provinces with distinct sedimentary compositions: (1) the Mackenzie Trough-Canadian Beaufort Shelf with high phyllosilicate-Fe oxide-magnetite and Al-K-Ti-Fe-Cr-V-Zn-P contents; (2) Southwestern Banks Island, characterized by high dolomite-K-feldspar and Ca-Mg-LOI contents; (3) the Central Amundsen Gulf, a transitional zone typified by intermediate phyllosilicate-magnetite-K-feldspar-dolomite and Al-K-Ti-Fe-Mn-V-Zn-Sr-Ca-Mg-LOI contents; and (4) mud volcanoes on the Canadian Beaufort Shelf distinguished by poorly sorted coarse-silt with high quartz-plagioclase-authigenic carbonate and Si-Zr contents, as well as high magnetic susceptibility. Our results also confirm that the present-day sedimentary dynamics on the Canadian Beaufort Shelf is mainly controlled by sediment supply from the Mackenzie River. Overall, these insights provide a basis for future studies using mineralogical, geochemical, and magnetic signatures of Canadian Arctic sediments in order to reconstruct past variations in sediment inputs and transport pathways related to late Quaternary climate and oceanographic changes.

Weldability of a high entropy CrMnFeCoNi alloy

DOE PAGES

Wu, Zhenggang; David, Stan A.; Feng, Zhili; ...

2016-07-19

We present the high-entropy alloys are unique alloys in which five or more elements are all in high concentrations. In order to determine its potential as a structural alloy, a model face-centered-cubic CrMnFeCoNi alloy was selected to investigate its weldability. Welds produced by electron beam welding show no cracking. The grain structures within the fusion zone (FZ) are controlled by the solidification behavior of the weld pool. The weldment possesses mechanical properties comparable to those of the base metal (BM) at both room and cryogenic temperatures. Finally, compared with the BM, deformation twinning was more pronounced in the FZ ofmore » the tested alloy.« less

Fabry-Perot magnonic ballistic coherent transport across ultrathin ferromagnetic lamellar bcc Ni nanostructures between Fe leads

NASA Astrophysics Data System (ADS)

Khater, A.; Saim, L.; Tigrine, R.; Ghader, D.

2018-06-01

We propose thermodynamically stable systems of ultrathin lamellar bcc Ni nanostructures between bcc Fe leads, sbnd Fe[Ni(n)]Fesbnd , based on the available literature for bcc Ni overlayers on Fe(001) surfaces, and establish the necessary criteria for their structural and ferromagnetic order, for thicknesses n ≤ 6 bcc Ni monatomic layers. The system is globally ferromagnetic. A theoretical model is presented to investigate and understand the ballistic coherent scattering of Fe spin-waves, incident from the leads, at the ferromagnetic bcc Ni nanostructure. The Nisbnd Ni and Nisbnd Fe exchange are computed using the Ising effective field theory (EFT), and the magnetic ground state of the system is constructed in the Heisenberg representation. We compute the spin-wave eigenmodes localized on the bcc Ni nanostructure, using the phase field matching theory (PFMT), illustrating the effects of symmetry breaking on the confinement of localized spin excitations. The reflection and transmission scattering properties of spin-waves incident from the Fe leads, across the embedded Ni nanostructures are investigated within the framework of the same PFMT methodology. A highly refined Fabry-Perot magnonic ballistic coherent transmission spectra is observed for these sbnd Fe[Ni(n)]Fesbnd systems.

Accurate solid solution range of BiMnxFe3-xO6 and low temperature magnetism

NASA Astrophysics Data System (ADS)

Jiang, Pengfei; Yue, Mufei; Cong, Rihong; Gao, Wenliang; Yang, Tao

2017-11-01

BiMnxFe3-xO6 (x = 1) represents a new type of oxide structure containing Bi3+ and competing magnetic super-exchanges. In literature, multiple magnetic states were realized at low temperatures in BiMnFe2O6, and the hypothetical parent compounds (BiMn3O6, BiFe3O6) were predicted to be different in magnetism. Herein, we performed a careful study on the syntheses of BiMnxFe3-xO6 at ambient pressure, and the solid solution range was determined to be 0.9 ≤ x ≤ 1.3 by Rietveld refinements on high-quality powder X-ray diffraction data. Due to the very similar cationic size of Mn3+ and Fe3+, and possibly the structural rigidity, there was no significant structure change in the whole range of solid solution. The magnetic behavior of BiMnxFe3-xO6 (x = 1.2, 1.22, 1.26, 1.28 and 1.3) was generally similar to BiMnFe2O6, while the relative higher concentration of Mn3+ led to the decreasing of the antiferromagnetic ordering temperature.

Monte Carlo Simulation Study of Atomic Structure of alnico Permanent Magnets

NASA Astrophysics Data System (ADS)

Nguyen, Manh Cuong; Wang, Cai-Zhuang; Ho, Kai-Ming

Lattice Monte Carlo simulation based on quinternary cluster expansion energy model is used to investigate nano-scale structure of alnico alloy, which is considered as a candidate material for rare-earth free high performance permanent magnets, especially for high or elevated temperature applications such as electric motor for vehicles. We observe phase decomposition of the master alnico alloy into FeCo-rich magnetic (α1) and NiAl-rich matrix (α2) phases. Concentrations of Fe and Co in α1 phase and Ni and Al in α2 phase are higher for lower annealing temperature. Ti is residing mostly in the α2 phase. The phase boundary between α1 and α2 phases are quite sharp with only few atomic layers. The α1 phase is in B2 ordering with Fe and Al occupying the α-site and Ni and Co occupying the β-site. The α2 phase is in L21 ordering with Al occupying the 4a-site. The phase composition profile again annealing temperature suggests that lower annealing temperature would improve the magnetism of α2 and diminish the magnetism of α2 phase, hence improve shape anisotropy of α1 phase rods and that of alnico.

Laser surface alloying of FeCoCrAlNi high-entropy alloy on 304 stainless steel to enhance corrosion and cavitation erosion resistance

NASA Astrophysics Data System (ADS)

Zhang, S.; Wu, C. L.; Zhang, C. H.; Guan, M.; Tan, J. Z.

2016-10-01

FeCoCrAlNi high-entropy alloy coating was synthesized with premixed high-purity Co, Cr, Al and Ni powders on 304 stainless steel by laser surface alloying, aiming at improving corrosion and cavitation erosion resistance. Phase constituents, microstructure and microhardness were investigated using XRD, SEM, and microhardness tester, respectively. The cavitation erosion and electrochemical corrosion behavior of FeCoCrAlNi coating in 3.5% NaCl solution were also evaluated using an ultrasonic vibrator and potentiodynamic polarization measurement. Experimental results showed that with appropriate laser processing parameters, FeCoCrAlNi coating with good metallurgical bonding to the substrate could be achieved. FeCoCrAlNi coating was composed of a single BCC solid solution. The formation of simple solid solutions in HEAs was the combined effect of mixing entropy (ΔSmix), mixing enthalpy (ΔHmix), atom-size difference (δ) and valence electron concentration (VEC), and the effect of ΔSmix was much larger than that of the other factors. The microhardness of the FeCoCrAlNi coating was ~3 times that of the 304 stainless steel. Both the corrosion and cavitation erosion resistance of the coating were improved. The cavitation erosion resistance for FeCoCrAlNi HEA coating was ~7.6 times that of 304 stainless steel. The corrosion resistance was also improved as reflected by a reduction in the current density of one order of magnitude as compared with 304 stainless steel.

High throughput light absorber discovery, Part 2: Establishing structure–band gap energy relationships

DOE PAGES

Suram, Santosh K.; Newhouse, Paul F.; Zhou, Lan; ...

2016-09-23

Combinatorial materials science strategies have accelerated materials development in a variety of fields, and we extend these strategies to enable structure-property mapping for light absorber materials, particularly in high order composition spaces. High throughput optical spectroscopy and synchrotron X-ray diffraction are combined to identify the optical properties of Bi-V-Fe oxides, leading to the identification of Bi 4V 1.5Fe 0.5O 10.5 as a light absorber with direct band gap near 2.7 eV. Here, the strategic combination of experimental and data analysis techniques includes automated Tauc analysis to estimate band gap energies from the high throughput spectroscopy data, providing an automated platformmore » for identifying new optical materials.« less

High throughput light absorber discovery, Part 2: Establishing structure–band gap energy relationships

DOE Office of Scientific and Technical Information (OSTI.GOV)

Suram, Santosh K.; Newhouse, Paul F.; Zhou, Lan

Combinatorial materials science strategies have accelerated materials development in a variety of fields, and we extend these strategies to enable structure-property mapping for light absorber materials, particularly in high order composition spaces. High throughput optical spectroscopy and synchrotron X-ray diffraction are combined to identify the optical properties of Bi-V-Fe oxides, leading to the identification of Bi 4V 1.5Fe 0.5O 10.5 as a light absorber with direct band gap near 2.7 eV. Here, the strategic combination of experimental and data analysis techniques includes automated Tauc analysis to estimate band gap energies from the high throughput spectroscopy data, providing an automated platformmore » for identifying new optical materials.« less

High Throughput Light Absorber Discovery, Part 2: Establishing Structure-Band Gap Energy Relationships.

PubMed

Suram, Santosh K; Newhouse, Paul F; Zhou, Lan; Van Campen, Douglas G; Mehta, Apurva; Gregoire, John M

2016-11-14

Combinatorial materials science strategies have accelerated materials development in a variety of fields, and we extend these strategies to enable structure-property mapping for light absorber materials, particularly in high order composition spaces. High throughput optical spectroscopy and synchrotron X-ray diffraction are combined to identify the optical properties of Bi-V-Fe oxides, leading to the identification of Bi 4 V 1.5 Fe 0.5 O 10.5 as a light absorber with direct band gap near 2.7 eV. The strategic combination of experimental and data analysis techniques includes automated Tauc analysis to estimate band gap energies from the high throughput spectroscopy data, providing an automated platform for identifying new optical materials.

Spin density wave instability in a ferromagnet.

PubMed

Wu, Yan; Ning, Zhenhua; Cao, Huibo; Cao, Guixin; Benavides, Katherine A; Karna, S; McCandless, Gregory T; Jin, R; Chan, Julia Y; Shelton, W A; DiTusa, J F

2018-03-27

Due to its cooperative nature, magnetic ordering involves a complex interplay between spin, charge, and lattice degrees of freedom, which can lead to strong competition between magnetic states. Binary Fe 3 Ga 4 is one such material that exhibits competing orders having a ferromagnetic (FM) ground state, an antiferromagnetic (AFM) behavior at intermediate temperatures, and a conspicuous re-entrance of the FM state at high temperature. Through a combination of neutron diffraction experiments and simulations, we have discovered that the AFM state is an incommensurate spin-density wave (ISDW) ordering generated by nesting in the spin polarized Fermi surface. These two magnetic states, FM and ISDW, are seldom observed in the same material without application of a polarizing magnetic field. To date, this unusual mechanism has never been observed and its elemental origins could have far reaching implications in many other magnetic systems that contain strong competition between these types of magnetic order. Furthermore, the competition between magnetic states results in a susceptibility to external perturbations allowing the magnetic transitions in Fe 3 Ga 4 to be controlled via temperature, magnetic field, disorder, and pressure. Thus, Fe 3 Ga 4 has potential for application in novel magnetic memory devices, such as the magnetic components of tunneling magnetoresistance spintronics devices.

Real-time subject-specific monitoring of internal deformations and stresses in the soft tissues of the foot: a new approach in gait analysis.

PubMed

Yarnitzky, G; Yizhar, Z; Gefen, A

2006-01-01

No technology is presently available to provide real-time information on internal deformations and stresses in plantar soft tissues of individuals during evaluation of the gait pattern. Because internal deformations and stresses in the plantar pad are critical factors in foot injuries such as diabetic foot ulceration, this severely limits evaluation of patients. To allow such real-time subject-specific analysis, we developed a hierarchal modeling system which integrates a two-dimensional gross structural model of the foot (high-order model) with local finite element (FE) models of the plantar tissue padding the calcaneus and medial metatarsal heads (low-order models). The high-order whole-foot model provides real-time analytical evaluations of the time-dependent plantar fascia tensile forces during the stance phase. These force evaluations are transferred, together with foot-shoe local reaction forces, also measured in real time (under the calcaneus, medial metatarsals and hallux), to the low-order FE models of the plantar pad, where they serve as boundary conditions for analyses of local deformations and stresses in the plantar pad. After careful verification of our custom-made FE solver and of our foot model system with respect to previous literature and against experimental results from a synthetic foot phantom, we conducted human studies in which plantar tissue loading was evaluated in real time during treadmill gait in healthy individuals (N = 4). We concluded that internal deformations and stresses in the plantar pad during gait cannot be predicted from merely measuring the foot-shoe force reactions. Internal loading of the plantar pad is constituted by a complex interaction between the anatomical structure and mechanical behavior of the foot skeleton and soft tissues, the body characteristics, the gait pattern and footwear. Real-time FE monitoring of internal deformations and stresses in the plantar pad is therefore required to identify elevated deformation/stress exposures toward utilizing it in gait laboratories to protect feet that are susceptible to injury.

Magnetic State of Quasiordered Fe-Al Alloys Doped with Ga and B: Magnetic Phase Separation and Spin Order

NASA Astrophysics Data System (ADS)

Voronina, E. V.; Ivanova, A. G.; Arzhnikov, A. K.; Chumakov, A. I.; Chistyakova, N. I.; Pyataev, A. V.; Korolev, A. V.

2018-04-01

Results of structural, magnetic, and Mössbauer studies of quasi ordered alloys Fe65Al35 - x M x ( M x = Ga, B; x = 0, 5 at %) are presented. The magnetic state of examined structurally-single-phase alloys at low temperatures is interpreted from the viewpoint of magnetic phase separation. An explanation is proposed for the observed behavior of magnetic characteristics of Fe65Al35 and Fe65Al30Ga5 in the framework of the model of two magnetic phases, a ferromagnetic-type one and a spin density wave. The boron-doped alloy Fe65Al30B5 is shown to demonstrate behavior that is typical of materials with the ferromagnetic type of ordering.

Plastic dynamics of the Al0.5CoCrCuFeNi high entropy alloy at cryogenic temperatures: Jerky flow, stair-like fluctuation, scaling behavior, and non-chaotic state

NASA Astrophysics Data System (ADS)

Guo, Xiaoxiang; Xie, Xie; Ren, Jingli; Laktionova, Marina; Tabachnikova, Elena; Yu, Liping; Cheung, Wing-Sum; Dahmen, Karin A.; Liaw, Peter K.

2017-12-01

This study investigates the plastic behavior of the Al0.5CoCrCuFeNi high-entropy alloy at cryogenic temperatures. The samples are uniaxially compressed at 4.2 K, 7.5 K, and 9 K. A jerky evolution of stress and stair-like fluctuation of strain are observed during plastic deformation. A scaling relationship is detected between the released elastic energy and strain-jump sizes. Furthermore, the dynamical evolution of serrations is characterized by the largest Lyapunov exponent. The largest Lyapunov exponents of the serrations at the three temperatures are all negative, which indicates that the dynamical regime is non-chaotic. This trend reflects an ordered slip process, and this ordered slip process exhibits a more disordered slip process, as the temperature decreases from 9 K to 4.2 K or 7.5 K.

Laboratory calibration of density-dependent lines in the extreme ultraviolet spectral region

NASA Astrophysics Data System (ADS)

Lepson, J. K.; Beiersdorfer, P.; Gu, M. F.; Desai, P.; Bitter, M.; Roquemore, L.; Reinke, M. L.

2012-05-01

We have been making spectral measurements in the extreme ultraviolet (EUV) from different laboratory sources in order to investigate the electron density dependence of various astrophysically important emission lines and to test the atomic models underlying the diagnostic line ratios. The measurement are being performed at the Livermore EBIT-I electron beam ion trap, the National Spherical Torus Experiment (NSTX) at Princeton, and the Alcator C-Mod tokamak at the Massachusetts Institute of Technology, which together span an electron density of four orders of magnitude and which allow us to test the various models at high and low density limits. Here we present measurements of Fe XXII and Ar XIV, which include new data from an ultra high resolution (λ/Δλ >4000) spectrometer at the EBIT-I facility. We found good agreement between the measurements and modeling calculations for Fe XXII, but poorer agreement for Ar XIV.

Oxidation of nickel-aluminum and iron-aluminum alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cathcart, J.V.

1985-01-01

The high-temperature oxidation behavior of several ordered alloys in the Ni-Al and Fe-Al systems is reviewed with special emphasis on Ni/sub 3/Al and NiAl. Ordering influences oxidation through its effect on the activities of the alloy components and by changing the point defect concentration in an alloy. Three categories of Ni-Al alloys are distinguished based on Al content and oxidation behavior. A characteristic feature of the oxidation of high-aluminum Ni-Al and Fe-Al alloys is the formation of voids in the substrate at the oxidate-metal interface. The mechanism of void formation and its suppression by minor additions of oxygen-active elements ismore » discussed. A brief description of the effect of preoxidation on the reactions of Ni/sub 3/Al-base alloys in SO/sub 2//O/sub 2/ environments is also included. 51 references, 14 figures, 1 table.« less

Oxidation of nickel-aluminum and iron-aluminum alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cathcart, J.V.

1984-01-01

The high-temperature oxidation behavior of several ordered alloys in the Ni-Al and Fe-Al systems is reviewed with special emphasis on Ni/sub 3/Al and NiAl. Ordering influences oxidation through its effect on the activities of the alloy components and by changing the point defect concentration in an alloy. Three categories of Ni-Al alloys are distinguished based on Al content and oxidation behavior. A characteristic feature of the oxidation of high-aluminum Ni-Al and Fe-Al alloys is the formation of voids in the substrate at the oxide-metal interface. The mechanism of void formation and its suppression by minor additions of oxygen-active elements aremore » discussed. A brief description of the effect of pre-oxidation on the reactions of Ni/sub 3/Al-base alloys in SO/sub 2//O/sub 2/ environments is also included.« less

Optimizing the coupled effects of Hall-Petch and precipitation strengthening in a Al 0.3 CoCrFeNi high entropy alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gwalani, B.; Soni, Vishal; Lee, Michael

2017-05-01

A successful demonstration of applying integrated strengthening using Hall-Petch strengthening (grains size effect) and precipitation strengthening is shown in the fcc based high entropy alloy (HEA) Al0.3CoCrFeNi, leading to quantitative determinations of the Hall-Petch coefficients for both hardness and tensile yield strength, aswell as the enhancements in the yield strength fromtwo distinct types of ordered precipitates, L12 and B2. An excellent combination of yield strength (~490MPa), ultimate tensile strength (~850MPa), and ductility (~45% elongation) was achieved by optimizing and coupling both strengtheningmechanisms, resulting from a refined grain size as well as both L12 and B2 ordered precipitates. This opens upmore » new avenues for the future development of HEAs, with the appropriate balance of properties required for engineering applications.« less

Spin scattering asymmetric coefficients and enhanced specific interfacial resistance of fully epitaxial current-perpendicular-to-plane giant magnetoresistance spin valves using alternate monatomic layered [Fe/Co]n and a Ag spacer layer

NASA Astrophysics Data System (ADS)

Jung, J. W.; Shiozaki, R.; Doi, M.; Sahashi, M.

2011-04-01

Using current-perpendicular-to-plane (CPP) giant magnetoresistance (GMR) measurement, we have evaluated the bulk and interface spin scattering asymmetric coefficients, βF and γF/N and the specific interfacial resistance, AR*F/N, for exchange-biased spin-valves consisting of artificially ordered B2 structure Fe50Co50 and Ag spacer layer. Artificially epitaxial ordered Fe50Co50 superlattices have been successfully fabricated on MgO (001) substrate by alternate monatomic layer (AML) deposition at a substrate temperature of 75 °C. The structural properties of the full epitaxial trilayer, AML[Fe/Co]n/Ag/AML[Fe/Co]n, on the Ag electrode have been confirmed by in situ reflection high-energy electron diffraction and transmission electron diffraction microscopy. A considerably large resistance-area product change and MR ratio (ΔRA > 3 mΩμm2 and MR ratio ˜5%) were confirmed even at thin AML[Fe/Co]n layer at room temperature (RT) in our spin-valve elements. The estimated values of βF and γF/N were 0.80 and 0.84 ± 0.02, respectively, from the Valet-Fert theory analysis of ΔRA as a function of thickness of the ferromagnetic layer (3, 4, and 5 nm) on the basis of the two-current model.

Evidence for negative thermal expansion in the superconducting precursor phase SmFeAsO

NASA Astrophysics Data System (ADS)

Zhou, H. D.; Sarte, P. M.; Conner, B. S.; Balicas, L.; Wiebe, C. R.; Chen, X. H.; Wu, T.; Wu, G.; Liu, R. H.; Chen, H.; Fang, D. F.

2018-03-01

The fluorine-doped rare-earth iron oxypnictide series SmFeAsO1-x F x (0 ≤slant x ≤slant 0.10) was investigated with high resolution powder x-ray scattering. In agreement with previous studies (Margadonna et al 2009 Phys. Rev. B. 79 014503), the parent compound SmFeAsO exhibits a tetragonal-to-orthorhombic structural distortion at T{S}   =  130 K which is rapidly suppressed by x ≃ 0.10 deep within the superconducting dome. The change in unit cell symmetry is followed by a previously unreported magnetoelastic distortion at 120 K. The temperature dependence of the thermal expansion coefficient αV reveals a rich phase diagram for SmFeAsO: (i) a global minimum at 125 K corresponds to the opening of a spin-density wave instability as measured by pump-probe femtosecond spectroscopy (Mertelj et al 2010 Phys. Rev. B 81 224504) whilst (ii) a global maximum at 110 K corresponds to magnetic ordering of the Sm and Fe sublattices as measured by magnetic x-ray scattering (Nandi et al 2011 Phys. Rev. B 84 055419). At much lower temperatures than T{N} , SmFeAsO exhibits a significant negative thermal expansion on the order of  -40 ppm · K-1 in contrast to the behaviour of other rare-earth oxypnictides such as PrFeAsO (Kimber et al 2008 Phys. Rev. B 78 140503) and the actinide oxypnictide NpFeAsO (Klimczuk et al 2012 Phys. Rev. B 85 174506) where the onset of αV < 0 only appears in the vicinity of magnetic ordering. Correlating this feature with the temperature and doping dependence of the resistivity and the unit cell parameters, we interpret the negative thermal expansion as being indicative of the possible condensation of itinerant electrons accompanying the opening of a SDW gap, consistent with transport measurements (Tropeano et al 2009 Supercond. Sci. Technol. 22 034004).

Chemical projectile-target interaction and liquid immiscibility in impact glass from the Wabar craters, Saudi Arabia

NASA Astrophysics Data System (ADS)

Hamann, Christopher; Hecht, Lutz; Ebert, Matthias; Wirth, Richard

2013-11-01

Impact glasses are usually strongly affected by secondary alteration and chemical weathering. Thus, in order to understand relevant formation processes, detailed petrographic studies on unweathered impact glasses are necessary as preserved heterogeneities in quenched impact glasses may serve as a tool to better understand their genesis. Here, we report on petrography and microchemistry of impact glasses from the Wabar impact craters (Saudi Arabia) that, with an age of ∼300 years, are among the youngest terrestrial impact craters. The fact that parts of the IIIAB iron meteorite have survived impact and subsequent weathering is granting Wabar a special role among the presently 184 confirmed terrestrial impact structures. Electron microprobe analysis (EMPA) and transmission electron microscopy (TEM) obtained on the black impact melt/glass variety at Wabar suggest that meteoritic Fe was selectively mixed with high-silica target melt at high temperatures due to selective oxidation, resulting in high Fe/Ni ratios for the black melt (37 on average, individual values range from 13 to 449) and low Fe/Ni ratios for projectile droplets ("FeNi spheres" with a Fe/Ni ratio of 3 on average; Fe/Ni ratio for the meteorite is ∼12). The black melt shows emulsion textures that are the result of silicate liquid immiscibility. Liquid-liquid phase-separation resulted in the formation of a poorly polymerized, ultrabasic melt (Lfe) rich in divalent cations like Fe2+, Ca2+, or Mg2+, that is dispersed in a highly polymerized, high-silica melt (Lsi) matrix. The typical Wabar black melt emulsion displays a spheres-in-a-matrix texture of ∼10-20% Lfe homogeneously dispersed in the form of two sets of spheres and droplets (10-30 nm and 0.1-0.4 μm in diameter) in ∼80-90% Lsi matrix, plus occasionally disseminated FeNi spheres. Around large (>10 μm) FeNi spheres, however, the typical emulsion texture changes to ∼21% Lsi dispersed in ∼79% Lfe. This change of texture is interpreted as evidence for the transfer of meteoritic Fe from the meteoritic FeNi spheres into the target melt due to selective oxidation of Fe over Ni and Co. Variations in the bulk composition of Wabar black melt largely depend on the volume ratios between immiscible ultrabasic Lfe, felsic Lsi, and remains of meteoritic FeNi spheres. Based on natural occurrences of phase-separated glasses (this work and literature) and quenching experiments (literature), there is growing evidence that liquid immiscibility is a major process in the formation of glassy impactites.

High-Field Superconductivity on Iron Chalcogenide FeSe

NASA Astrophysics Data System (ADS)

Shi, Anlu; Kitagawa, Shunsaku; Ishida, Kenji; Böhmer, Anna E.; Meingast, Christoph; Wolf, Thomas

2018-06-01

We have performed ac-susceptibility and 77Se-NMR measurements on single-crystal FeSe in the field range from 12.5 to 14.75 T below 1.6 K in order to investigate the superconducting properties of the B phase. Our results show that although superconductivity persists beyond the A-B transition line (H*), the broadening of the 77Se-NMR linewidth arising from the superconducting diamagnetic effect decreases at around H*, suggesting that superconducting character is changed at H*.

Using electron irradiation to probe iron-based superconductors

NASA Astrophysics Data System (ADS)

Cho, Kyuil; Kończykowski, M.; Teknowijoyo, S.; Tanatar, M. A.; Prozorov, R.

2018-06-01

High-energy electron irradiation at low temperatures is an efficient and controlled way to create vacancy–interstitial Frenkel pairs in a crystal lattice, thereby inducing nonmagnetic point-like scattering centers. In combination with London penetration depth and resistivity measurements, the electron irradiation was used as a phase-sensitive probe to study the superconducting order parameter in iron-based superconductors (FeSCs), lending strong support to sign-changing s ± pairing. Here, we review the key results of the effect of electron irradiation in FeSCs.

Enhanced Column Filtration for Arsenic Removal from Water: Polymer-Templated Iron Oxide Nanoparticles Immobilized on Sand via Layer-by-Layer Deposition

NASA Astrophysics Data System (ADS)

Cheng, Calvin Chia-Hung

Arsenic is ubiquitous in water sources around the world and is highly toxic. While precipitation and membrane filtration techniques are successfully implemented in developed cities, they are unsuitable for rural and low-resource settings lacking centralized facilities. This thesis presents the use of ultra-small iron oxide (Fe2O3) nanoparticles functionalized on sand granules for use as a house-hold scale adsorption filter. Water-stable alpha-Fe2O3 (hematite) nanoparticles (<10 nm) were synthesized via a collapsed-polymer approach using poly(acrylic acid) and Fe3+ ions. The nanoparticles exhibited high arsenic adsorption, with 147 +/- 2 mg As(III) per g Fe2O3 and 91 +/- 10 mg As(V) per g Fe2O3. The platform was also used to synthesize iron-based composites, including magnetite (Fe 3O4) and Fe-Cu oxide nanoparticles. For use as a column filter, Fe2O3-PAA nanoparticles were functionalized on sand granules using a layer-by-layer deposition method, with the nanoparticles embedded in the negative layer. The removal of As(III) by the Fe2O 3-PAA functionalized column was described by reversible 1st order kinetics where the forward and reverse rate constants were 0.31 hr -1 and 0.097 hr-1, respectively. Implemented as a passive water filter with 30 x 30 x 50 cm3 dimensions, the filter has an expected lifetime in the order of many years. By controlling the flow rate of the column depending on contamination levels, the filter effectively removes arsenic down to the safety limit of 0.01 mg/L. In a parallel project, the layer-by-layer deposition of Poly(diallydimethyl ammonium chloride) (PDDA) and poly(sodium 5-styrenesulfonate) (PSS) was exploited for a highly practical synthesis of discrete gradient surfaces. By independently controlling the concentration of NaCl in PDDA and PSS deposition solutions, a 2-dimensional matrix of surfaces was created in 96-well microtiter plates. Distinct non-monotonic dye adsorption patterns on the gradient surfaces was observed. Practical knowledge from this project was also used to enhance the nanoparticle surface functionalization described above. In all, a practical, no expertise-needed passive water filtration unit was described in this thesis. The unit makes use of hardware available in existing sand-based water filters, and is designed to address the unmet need of arsenic removal from drinking water in low-resource or rural settings.

Morphology, stability, and X-ray absorption spectroscopic study of iron oxide (Hematite) nanoparticles prepared by micelle nanolithography

NASA Astrophysics Data System (ADS)

Bera, Anupam; Bhattacharya, Atanu; Tiwari, N.; Jha, S. N.; Bhattacharyya, D.

2018-03-01

Currently, considerable effort is being made towards synthesis and characterization of iron oxide nanoparticles. In this article, we report on the preparation and characterization of iron oxide nanoparticle (NP) arrays supported on natively oxidized Si(100) surface. The NPs are synthesized by reverse micelle nanolithography technique and are then deposited onto natively oxidized Si(100) surface via spin-coating. Plasma oxidation followed by high temperature annealing results in a unimodal size distribution of pseudohexagonally-ordered array of iron oxide NPs (with ∼14 nm mean diameter and ∼5 nm mean height). High temperature annealing does not fragment the NPs. Particles are sinter-resistant: the unimodal arrays are robust with respect to thermal treatment. X-ray absorption spectroscopy (XAS), including X-ray Absorption Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS), reveals that structure of the iron oxide particle resembles closely the hematite α-Fe2O3 structure. Furthermore, with the help of EXAFS spectra, we eliminate the possibility of γ-Fe2O3, Fe3O4, FeO and FeO(OH) structures for the NPs.

Magnetism and electronic structure of CoFeCrX (X = Si, Ge) Heusler alloys

NASA Astrophysics Data System (ADS)

Jin, Y.; Kharel, P.; Lukashev, P.; Valloppilly, S.; Staten, B.; Herran, J.; Tutic, I.; Mitrakumar, M.; Bhusal, B.; O'Connell, A.; Yang, K.; Huh, Y.; Skomski, R.; Sellmyer, D. J.

2016-08-01

The structural, electronic, and magnetic properties of CoFeCrX (X = Si, Ge) Heusler alloys have been investigated. Experimentally, the alloys were synthesized in the cubic L21 structure with small disorder. The cubic phase of CoFeCrSi was found to be highly stable against heat treatment, but CoFeCrGe disintegrated into other new compounds when the temperature reached 402 °C (675 K). Although the first-principle calculation predicted the possibility of tetragonal phase in CoFeCrGe, the tetragonal phase could not be stabilized experimentally. Both CoFeCrSi and CoFeCrGe compounds showed ferrimagnetic spin order at room temperature and have Curie temperatures (TC) significantly above room temperature. The measured TC for CoFeCrSi is 790 K but that of CoFeCrGe could not be measured due to its dissociation into new compounds at 675 K. The saturation magnetizations of CoFeCrSi and CoFeCrGe are 2.82 μB/f.u. and 2.78 μB/f.u., respectively, which are close to the theoretically predicted value of 3 μB/f.u. for their half-metallic phases. The calculated band gaps for CoFeCrSi and CoFeCrGe are, respectively, 1 eV and 0.5 eV. These materials have potential for spintronic device applications, as they exhibit half-metallic electronic structures with large band gaps, and Curie temperatures significantly above room temperature.

Solid-state reactions during mechanical alloying of ternary Fe-Al-X (X=Ni, Mn, Cu, Ti, Cr, B, Si) systems: A review

NASA Astrophysics Data System (ADS)

Hadef, Fatma

2016-12-01

The last decade has witnessed an intensive research in the field of nanocrystalline materials due to their enhanced properties. A lot of processing techniques were developed in order to synthesis these novel materials, among them mechanical alloying or high-energy ball milling. In fact, mechanical alloying is one of the most common operations in the processing of solids. It can be used to quickly and easily synthesize a variety of technologically useful materials which are very difficult to manufacture by other techniques. One advantage of MA over many other techniques is that is a solid state technique and consequently problems associated with melting and solidification are bypassed. Special attention is being paid to the synthesis of alloys through reactions mainly occurring in solid state in many metallic ternary Fe-Al-X systems, in order to improve mainly Fe-Al structural and mechanical properties. The results show that nanocrystallization is the common result occurring in all systems during MA process. The aim of this work is to illustrate the uniqueness of MA process to induce phase transformation in metallic Fe-Al-X (X=Ni, Mn, Cu, Ti, Cr, B, Si) systems.

Controlled Phase and Tunable Magnetism in Ordered Iron Oxide Nanotube Arrays Prepared by Atomic Layer Deposition

DOE PAGES

Zhang, Yijun; Liu, Ming; Peng, Bin; ...

2016-01-27

Highly-ordered and conformal iron oxide nanotube arrays on an atomic scale are successfully prepared by atomic layer deposition (ALD) with controlled oxidization states and tunable magnetic properties between superparamagnetism and ferrimagnetism. Non-magnetic α-Fe 2O 3 and superparamagnetic Fe 2O 3with a blocking temperature of 120 K are in-situ obtained by finely controlling the oxidation reaction. Both of them exhibit a very small grain size of only several nanometers due to the nature of atom-by-atom growth of the ALD technique. Post-annealing α-Fe 2O 3 in a reducing atmosphere leads to the formation of the spinel Fe 3O 4 phase which displaysmore » a distinct ferrimagnetic anisotropy and the Verwey metal-insulator transition that usually takes place only in single crystal magnetite or thick epitaxial films at low temperatures. Finally, the ALD deposition of iron oxide with well-controlled phase and tunable magnetism demonstrated in this work provides a promising opportunity for the fabrication of 3D nano-devices to be used in catalysis, spintronics, microelectronics, data storages and bio-applications.« less

Metastable phase formation in undercooled Fe-Co melts under terrestrial and parabolic flight conditions

NASA Astrophysics Data System (ADS)

Hermann, R.; Löser, W.; Lindenkreuz, H. G.; Yang-Bitterlich, W.; Mickel, Ch.; Diefenbach, A.; Schneider, S.; Dreier, W.

2007-12-01

Soft magnetic Fe-Co alloys display primary fcc phase solidification for>19,5 at% Co in conventional near-equilibrium solidification processes. Undercooled Fe-Co melt drops within the composition range of 30 to 50 at% Co have been investigated with the electromagnetic levitation technique. The solidification kinetics was measured in situ using a high-resolution Siphotodiode. Melt drops were undercooled up to 263 K below the liquidus temperature and subsequently quenched onto a chill substrate in order to characterize the solidification sequence and microstructure. The transition from stable fcc phase to metastable bcc primary phase solidification has been observed after reaching a critical undercooling level. The critical undercooling increases with rising Co content. The growth velocity drops obviously after transition to metastable bcc phase formation. Parabolic flight experiments were performed in order to study the phase selection under reduced gravity conditions. Under microgravity conditions, a much smaller critical undercooling and an increased life time of the metastable bcc phase were obtained. This result was validated with TEM investigations. The appearance of Fe-O particles gives an indirect hint for an intermediate fcc phase formation from the metastable bcc phase at elevated temperature.

Reduction of CO2 to low carbon alcohols on CuO FCs/Fe2O3 NTs catalyst with photoelectric dual catalytic interfaces

NASA Astrophysics Data System (ADS)

Li, Peiqiang; Wang, Huying; Xu, Jinfeng; Jing, Hua; Zhang, Jun; Han, Haixiang; Lu, Fusui

2013-11-01

In this paper, the CuO FCs/Fe2O3 NTs catalyst was obtained after Fe2O3 nanotubes (Fe2O3 NTs) were decorated with CuO flower clusters (CuO FCs) by the pulse electrochemical deposition method. The in situ vertically aligned Fe2O3 NTs were prepared on the ferrous substrate by a potentiostatic anodization method. The SEM result showed the volcano-like Fe2O3 NTs were arranged in order and the CuO FCs constituted of flaky CuO distributed on the Fe2O3 NTs surface uniformly. After CuO FCs were loaded on Fe2O3 NTs, the absorption of visible light was enhanced noticeably, and its band gap narrowed to 1.78 eV from 2.03 eV. The conduction band and valence band locating at -0.73 eV and 1.05 eV, respectively were further obtained. In the PEC reduction of CO2 process, methanol and ethanol were two major products identified by chromatography. Their contents reached 1.00 mmol L-1 cm-2 and 107.38 μmol L-1 cm-2 after 6 h, respectively. This high-efficiency catalyst with photoelectric dual catalytic interfaces has a great guidance and reference significance for CO2 reduction to liquid carbon fuels.In this paper, the CuO FCs/Fe2O3 NTs catalyst was obtained after Fe2O3 nanotubes (Fe2O3 NTs) were decorated with CuO flower clusters (CuO FCs) by the pulse electrochemical deposition method. The in situ vertically aligned Fe2O3 NTs were prepared on the ferrous substrate by a potentiostatic anodization method. The SEM result showed the volcano-like Fe2O3 NTs were arranged in order and the CuO FCs constituted of flaky CuO distributed on the Fe2O3 NTs surface uniformly. After CuO FCs were loaded on Fe2O3 NTs, the absorption of visible light was enhanced noticeably, and its band gap narrowed to 1.78 eV from 2.03 eV. The conduction band and valence band locating at -0.73 eV and 1.05 eV, respectively were further obtained. In the PEC reduction of CO2 process, methanol and ethanol were two major products identified by chromatography. Their contents reached 1.00 mmol L-1 cm-2 and 107.38 μmol L-1 cm-2 after 6 h, respectively. This high-efficiency catalyst with photoelectric dual catalytic interfaces has a great guidance and reference significance for CO2 reduction to liquid carbon fuels. Electronic supplementary information (ESI) available: Reduction of CO2 to low carbon alcohols on CuO FCs/Fe2O3 NTs catalyst with photoelectric dual catalytic interfaces. See DOI: 10.1039/c3nr03352j

Neutron-scattering measurements of spin excitations in LaFeAsO and Ba(Fe 0.953Co 0.047)2As 2: Evidence for a sharp enhancement of spin fluctuations by nematic order [Sharp enhancement of spin fluctuations by nematic order in iron pnictides

DOE PAGES

Zhang, Qiang; Fernandes, Rafael M.; Lamsal, Jagat; ...

2015-02-04

Inelastic neutron scattering is employed to investigate the impact of electronic nematic order on the magnetic spectra of LaFeAsO and Ba(Fe 0.953Co 0.047) 2As 2. These materials are ideal to study the paramagnetic-nematic state, since the nematic order, signaled by the tetragonal-to-orthorhombic transition at T S, sets in well above the stripe antiferromagnetic ordering at T N. We find that the temperature-dependent dynamic susceptibility displays an anomaly at T S followed by a sharp enhancement in the spin-spin correlation length, revealing a strong feedback effect of nematic order on the low-energy magnetic spectrum. As a result, our findings can bemore » consistently described by a model that attributes the structural or nematic transition to magnetic fluctuations, and unveils the key role played by nematic order in promoting the long-range stripe antiferromagnetic order in iron pnictides.« less

Neutron-scattering measurements of spin excitations in LaFeAsO and Ba(Fe 0.953Co 0.047)2As 2: Evidence for a sharp enhancement of spin fluctuations by nematic order [Sharp enhancement of spin fluctuations by nematic order in iron pnictides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Qiang; Fernandes, Rafael M.; Lamsal, Jagat

Inelastic neutron scattering is employed to investigate the impact of electronic nematic order on the magnetic spectra of LaFeAsO and Ba(Fe 0.953Co 0.047) 2As 2. These materials are ideal to study the paramagnetic-nematic state, since the nematic order, signaled by the tetragonal-to-orthorhombic transition at T S, sets in well above the stripe antiferromagnetic ordering at T N. We find that the temperature-dependent dynamic susceptibility displays an anomaly at T S followed by a sharp enhancement in the spin-spin correlation length, revealing a strong feedback effect of nematic order on the low-energy magnetic spectrum. As a result, our findings can bemore » consistently described by a model that attributes the structural or nematic transition to magnetic fluctuations, and unveils the key role played by nematic order in promoting the long-range stripe antiferromagnetic order in iron pnictides.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Biendicho, J.J.; The ISIS Facility, STFC Rutherford Appleton Laboratory, Didcot, OX11 0QX Oxfordshire; Shafeie, S.

Oxygen-deficient ferrates with the cubic perovskite structure Sr{sub x}Y{sub 1−x}FeO{sub 3−δ} were prepared in air (0.71≤x≤0.91) as well as in N{sub 2} (x=0.75 and 0.79) at 1573 K. The oxygen content of the compounds prepared in air increases with increasing strontium content from 3−δ=2.79(2) for x=0.75 to 3−δ=2.83(2) for x=0.91. Refinement of the crystal structure of Sr{sub 0.75}Y{sub 0.25}FeO{sub 2.79} using TOF neutron powder diffraction (NPD) data shows high anisotropic atomic displacement parameter (ADP) for the oxygen atom resulting from a substantial cation and anion disorder. Electron diffraction (ED) and high-resolution electron microscopy (HREM) studies of Sr{sub 0.75}Y{sub 0.25}FeO{sub 2.79}more » reveal a modulation along 〈1 0 0〉{sub p} with G± ∼0.4〈1 0 0〉{sub p} indicating a local ordering of oxygen vacancies. Magnetic susceptibility measurements at 5–390 K show spin-glass behaviour with dominating antiferromagnetic coupling between the magnetic moments of Fe cations. Among the studied compositions, Sr{sub 0.75}Y{sub 0.25}FeO{sub 2.79} shows the lowest thermal expansion coefficient (TEC) of 10.5 ppm/K in air at 298–673 K. At 773–1173 K TEC increases up to 17.2 ppm/K due to substantial reduction of oxygen content. The latter also results in a dramatic decrease of the electrical conductivity in air above 673 K. Partial substitution of Fe by Cr, Mn and Ni according to the formula Sr{sub 0.75}Y{sub 0.25}Fe{sub 1−y}M{sub y}O{sub 3−δ} (y=0.2, 0.33, 0.5) leads to cubic perovskites for all substituents with y=0.2. Their TECs are higher in comparison with un-doped Sr{sub 0.75}Y{sub 0.25}FeO{sub 2.79}. Only M=Ni has increased electrical conductivity compared to un-doped Sr{sub 0.75}Y{sub 0.25}FeO{sub 2.79}. - Graphical abstract: Oxygen-deficient ferrates with the cubic perovskite structure Sr{sub x}Y{sub 1−x}FeO{sub 3−δ} were prepared both in air (0.71≤x≤0.91) and N{sub 2} (x=0.75 and 0.79) at 1573 K. Refinement of the crystal structure of Sr{sub 0.75}Y{sub 0.25}FeO{sub 2.79} using TOF neutron powder diffraction (NPD) data (S.G. Pm-3m, a=3.86455(3) Å; χ{sup 2}=6.71, R{sub p}=0.03; R{sub wp}=0.04) confirmed the cubic perovskite structure. The observed high anisotropic atomic displacement parameter for the oxygen atom indicates a substantial anion sublattice disorder. Electron diffraction (ED) and high-resolution electron microscopy (HREM) studies of Sr{sub 0.75}Y{sub 0.25}FeO{sub 2.79} show compositional modulation along 〈1 0 0〉{sub p} with G± ∼0.4〈1 0 0〉{sub p} indicating ordering of oxygen vacancies at the local scale. Highlights: ► Cubic perovskites Sr{sub x}Y{sub 1−x}FeO{sub 3−δ} (0.71≤x<0.91) were synthesized. ► Sr{sub 0.75}Y{sub 0.25}Fe{sub 1−y}M{sub y}O{sub 3−δ}, M=Cr, Mn, Ni were prepared. ► High-temperature conductivity properties and crystal structure were studied. ► High-temperature thermal expansion behavior was investigated.« less

Kinetics of abiotic nitrous oxide production via oxidation of hydroxylamine by particulate metals in seawater

NASA Astrophysics Data System (ADS)

Cavazos, A. R.; Taillefert, M.; Glass, J. B.

2016-12-01

The oceans are a significant of nitrous oxide (N2O) to the atmosphere. Current models of global oceanic N2­O flux focus on microbial N2O cycling and often ignore abiotic reactions, such as the thermodynamically favorable oxidation of the nitrification intermediate hydroxylamine (NH2OH) by Mn(IV) or Fe(III). At circumneutral pH, NH2OH oxidation is more thermodynamically favorable via Mn(IV) than Fe(III) reduction. We characterized the kinetics of NH2OH oxidation in synthetic ocean water at pH 5.1-8.8 using microsensor electrodes to measure real-time N2O production. N2O production rates and yield were greater when NH2OH was oxidized by Mn(IV) than Fe(III). Accordingly, the reduction of Mn(IV) was first order with respect to NH2OH whereas the reduction of Fe(III) was zero order with respect to NH2OH. Interestingly, the order of the reaction with respect to Mn(IV) appears to be negative whereas the reaction is second order with respect to Fe(III). The inverse order with respect to Mn(IV) may be due to the aggregation of particles in seawater, which decreases their surface area and changes their reactivity. Finally, the reaction is first order with respect to protons with Fe(III) as the oxidant but zero order with Mn(IV). The stronger effect of the pH on the reaction with Fe(III) as the oxidant compared to Mn(IV) reflects the stoichiometry of these two reactions, as each mole of N2O produced by Fe(III) reduction consumes eight protons while each mole of N2O produced with Mn(IV) as the oxidant requires only four protons. Our data show that abiotic NH2OH oxidation by Mn(IV) or Fe(III) particles may represent a significant source of N2O in seawater. These findings suggest that abiotic N2O production in marine waters may be significant in areas of the oceans where particulate metals originating from aerosols, dust, or rivers may react with NH2OH released from ammonia-oxidizing microorganisms.

Switching Magnetism and Superconductivity with Spin-Polarized Current in Iron-Based Superconductor.

PubMed

Choi, Seokhwan; Choi, Hyoung Joon; Ok, Jong Mok; Lee, Yeonghoon; Jang, Won-Jun; Lee, Alex Taekyung; Kuk, Young; Lee, SungBin; Heinrich, Andreas J; Cheong, Sang-Wook; Bang, Yunkyu; Johnston, Steven; Kim, Jun Sung; Lee, Jhinhwan

2017-12-01

We explore a new mechanism for switching magnetism and superconductivity in a magnetically frustrated iron-based superconductor using spin-polarized scanning tunneling microscopy (SPSTM). Our SPSTM study on single-crystal Sr_{2}VO_{3}FeAs shows that a spin-polarized tunneling current can switch the Fe-layer magnetism into a nontrivial C_{4} (2×2) order, which cannot be achieved by thermal excitation with an unpolarized current. Our tunneling spectroscopy study shows that the induced C_{4} (2×2) order has characteristics of plaquette antiferromagnetic order in the Fe layer and strongly suppresses superconductivity. Also, thermal agitation beyond the bulk Fe spin ordering temperature erases the C_{4} state. These results suggest a new possibility of switching local superconductivity by changing the symmetry of magnetic order with spin-polarized and unpolarized tunneling currents in iron-based superconductors.

Switching Magnetism and Superconductivity with Spin-Polarized Current in Iron-Based Superconductor

NASA Astrophysics Data System (ADS)

Choi, Seokhwan; Choi, Hyoung Joon; Ok, Jong Mok; Lee, Yeonghoon; Jang, Won-Jun; Lee, Alex Taekyung; Kuk, Young; Lee, SungBin; Heinrich, Andreas J.; Cheong, Sang-Wook; Bang, Yunkyu; Johnston, Steven; Kim, Jun Sung; Lee, Jhinhwan

2017-12-01

We explore a new mechanism for switching magnetism and superconductivity in a magnetically frustrated iron-based superconductor using spin-polarized scanning tunneling microscopy (SPSTM). Our SPSTM study on single-crystal Sr2VO3FeAs shows that a spin-polarized tunneling current can switch the Fe-layer magnetism into a nontrivial C4 (2 ×2 ) order, which cannot be achieved by thermal excitation with an unpolarized current. Our tunneling spectroscopy study shows that the induced C4 (2 ×2 ) order has characteristics of plaquette antiferromagnetic order in the Fe layer and strongly suppresses superconductivity. Also, thermal agitation beyond the bulk Fe spin ordering temperature erases the C4 state. These results suggest a new possibility of switching local superconductivity by changing the symmetry of magnetic order with spin-polarized and unpolarized tunneling currents in iron-based superconductors.

Thermo-induced modifications and selective accumulation of glucose-conjugated magnetic nanoparticles in vivo in rats - increasing the effectiveness of magnetic-assisted therapy - pilot study.

PubMed

Traikov, L; Antonov, I; Gerou, A; Vesselinova, L; Hadjiolova, R; Raynov, J

2015-09-01

Ferro-Magnetic nanoparticles (Fe-MNP) have gained a lot of attention in biomedical and industrial applications due to their biocompatibility, ease of surface modification and paramagnetic properties. The basic idea of our study is whether it is possible to use glucose-conjugate Fe-MNP (Glc-Fe-MNP) for targeting and more accurate focusing in order to increase the effect of high-frequency electromagnetic fields induced hyperthermia in solid tumors. Tumors demonstrate high metabolic activity for glucose in comparison with other somatic cells.Increasing of accumulation of glucose conjugated (Glc)-Fe-MNP on tumor site and precision of radio frequency electro-magnetic field (RF-EMF) energy absorption in solid tumors, precede RF-EMF induced hyperthermia. Rat model for monitoring the early development of breast cancer. Twenty female Wistar rats (MU-line-6171) were divided into two groups of 10 rats that were either treated with N-methyl-N-nitrosourea to induce breast cancer and 10 with carrageenan to induce inflammation (control). Glc-Fe-MNP can offer a solution to increase hyperthermia effect to the desired areas in the body by accumulation and increasing local concentration due to high tissue metabolic assimilation. In this condition, it is considered that the magnetization of the nanoparticles is a single-giant magnetic moment, the sum of all the individual magnetic moments and is proportional to the concentration of Glc-Fe-MNP.

Characterisation of the Microstructure of Fe–Al/Cr3C2 Composite Coatings

NASA Astrophysics Data System (ADS)

Liu, Xiaoming; JunhuiDong; Yang, Yuehong; Sun, Changming; Tuo, Ya; Li, Yanwei

2018-03-01

An Fe-Al/Cr3C2 composite coating is investigated to assess its suitability for treating high-temperature components in a power plant. The coating exhibits excellent high- temperature properties including good corrosion, erosion and friction-wear resistance at high temperatures. To deduce the formation of the Fe-Al/Cr3C2 composite coating and to provide an adequate theoretical basis for its extensive application, its structures and microstructures are investigated. Scanning electronic microscopy (SEM)is used along with energy-dispersive X-ray analysis (EDAX) to analyse the surface of the coating. Energy-dispersive spectroscopy (EDS) is used to analyse the cross-section of the coating. Further, X-ray diffraction (XRD) and transmission electron microscopy (TEM) are used to analyse the phases and micro structural features within the coating. The results reveal that the basic phases are two orderly inter metallic compounds (Fe3Al and FeAl) and that the reinforcement includes two oxides (Al2O3 and Cr2O3) as well as substantial quantities of Cr3C2. Al2O3is formed using two mechanisms: oxidation of aluminium in the coating and separation of Al2O3crystals from Fe3Al and FeAl. The grain size of Al2O3 and Cr2O3 in the coatings is nanometric. These two oxides may increase the corrosion-erosion and wear resistances of the coating when they are used as reinforcements.

Metagenomic and PCR-Based Diversity Surveys of [FeFe]-Hydrogenases Combined with Isolation of Alkaliphilic Hydrogen-Producing Bacteria from the Serpentinite-Hosted Prony Hydrothermal Field, New Caledonia.

PubMed

Mei, Nan; Postec, Anne; Monnin, Christophe; Pelletier, Bernard; Payri, Claude E; Ménez, Bénédicte; Frouin, Eléonore; Ollivier, Bernard; Erauso, Gaël; Quéméneur, Marianne

2016-01-01

High amounts of hydrogen are emitted in the serpentinite-hosted hydrothermal field of the Prony Bay (PHF, New Caledonia), where high-pH (~11), low-temperature (< 40°C), and low-salinity fluids are discharged in both intertidal and shallow submarine environments. In this study, we investigated the diversity and distribution of potentially hydrogen-producing bacteria in Prony hyperalkaline springs by using metagenomic analyses and different PCR-amplified DNA sequencing methods. The retrieved sequences of hydA genes, encoding the catalytic subunit of [FeFe]-hydrogenases and, used as a molecular marker of hydrogen-producing bacteria, were mainly related to those of Firmicutes and clustered into two distinct groups depending on sampling locations. Intertidal samples were dominated by new hydA sequences related to uncultured Firmicutes retrieved from paddy soils, while submarine samples were dominated by diverse hydA sequences affiliated with anaerobic and/or thermophilic submarine Firmicutes pertaining to the orders Thermoanaerobacterales or Clostridiales. The novelty and diversity of these [FeFe]-hydrogenases may reflect the unique environmental conditions prevailing in the PHF (i.e., high-pH, low-salt, mesothermic fluids). In addition, novel alkaliphilic hydrogen-producing Firmicutes (Clostridiales and Bacillales) were successfully isolated from both intertidal and submarine PHF chimney samples. Both molecular and cultivation-based data demonstrated the ability of Firmicutes originating from serpentinite-hosted environments to produce hydrogen by fermentation, potentially contributing to the molecular hydrogen balance in situ.

Tuning magnetic spirals beyond room temperature with chemical disorder

NASA Astrophysics Data System (ADS)

Morin, Mickaël; Canévet, Emmanuel; Raynaud, Adrien; Bartkowiak, Marek; Sheptyakov, Denis; Ban, Voraksmy; Kenzelmann, Michel; Pomjakushina, Ekaterina; Conder, Kazimierz; Medarde, Marisa

2016-12-01

In the past years, magnetism-driven ferroelectricity and gigantic magnetoelectric effects have been reported for a number of frustrated magnets featuring ordered spiral magnetic phases. Such materials are of high-current interest due to their potential for spintronics and low-power magnetoelectric devices. However, their low-magnetic ordering temperatures (typically <100 K) greatly restrict their fields of application. Here we demonstrate that the onset temperature of the spiral phase in the perovskite YBaCuFeO5 can be increased by more than 150 K through a controlled manipulation of the Fe/Cu chemical disorder. Moreover, we show that this novel mechanism can stabilize the magnetic spiral state of YBaCuFeO5 above the symbolic value of 25 °C at zero magnetic field. Our findings demonstrate that the properties of magnetic spirals, including its wavelength and stability range, can be engineered through the control of chemical disorder, offering a great potential for the design of materials with magnetoelectric properties beyond room temperature.

Tuning magnetic spirals beyond room temperature with chemical disorder

PubMed Central

Morin, Mickaël; Canévet, Emmanuel; Raynaud, Adrien; Bartkowiak, Marek; Sheptyakov, Denis; Ban, Voraksmy; Kenzelmann, Michel; Pomjakushina, Ekaterina; Conder, Kazimierz; Medarde, Marisa

2016-01-01

In the past years, magnetism-driven ferroelectricity and gigantic magnetoelectric effects have been reported for a number of frustrated magnets featuring ordered spiral magnetic phases. Such materials are of high-current interest due to their potential for spintronics and low-power magnetoelectric devices. However, their low-magnetic ordering temperatures (typically <100 K) greatly restrict their fields of application. Here we demonstrate that the onset temperature of the spiral phase in the perovskite YBaCuFeO5 can be increased by more than 150 K through a controlled manipulation of the Fe/Cu chemical disorder. Moreover, we show that this novel mechanism can stabilize the magnetic spiral state of YBaCuFeO5 above the symbolic value of 25 °C at zero magnetic field. Our findings demonstrate that the properties of magnetic spirals, including its wavelength and stability range, can be engineered through the control of chemical disorder, offering a great potential for the design of materials with magnetoelectric properties beyond room temperature. PMID:27982127

H T P21/ c- C2/ c phase transition and kinetics of Fe2+-Mg order-disorder of an Fe-poor pigeonite: implications for the cooling history of ureilites

NASA Astrophysics Data System (ADS)

Alvaro, Matteo; Cámara, Fernando; Domeneghetti, M. Chiara; Nestola, Fabrizio; Tazzoli, Vittorio

2011-09-01

A natural Ca-poor pigeonite (Wo6En76Fs18) from the ureilite meteorite sample PCA82506-3, free of exsolved augite, was studied by in situ high-temperature single-crystal X-ray diffraction. The sample, monoclinic P21/ c, was annealed up to 1,093°C to induce a phase transition from P21/ c to C2/ c symmetry. The variation with increasing temperature of the lattice parameters and of the intensity of the b-type reflections ( h + k = 2 n + 1, present only in the P21/ c phase) showed a displacive phase transition P21/ c to C2/ c at a transition temperature T Tr = 944°C, first order in character. The Fe-Mg exchange kinetics was studied by ex situ single-crystal X-ray diffraction in a range of temperatures between the closure temperature of the Fe-Mg exchange reaction and the transition temperature. Isothermal disordering annealing experiments, using the IW buffer, were performed on three crystals at 790, 840 and 865°C. Linear regression of ln k D versus 1/ T yielded the following equation: ln k_{{D}} = - 3717( ± 416)/T(K) + 1.290( ± 0.378);quad (R2 = 0.988) . The closure temperature ( T c) calculated using this equation was ˜740(±30)°C. Analysis of the kinetic data carried out taking into account the e.s.d.'s of the atomic fractions used to define the Fe-Mg degree of order, performed according to Mueller's model, allowed us to retrieve the disordering rate constants C 0 K {dis/+} for all three temperatures yielding the following Arrhenius relation: ln ( {C0 K_{{dis}}^{ + } } ) = ln K0 - Q/(RT) = 20.99( ± 3.74) - 26406( ± 4165)/T(K);quad (R2 = 0.988) . An activation energy of 52.5(±4) kcal/mol for the Fe-Mg exchange process was obtained. The above relation was used to calculate the following Arrhenius relation modified as a function of X Fe (in the range of X Fe = 0.20-0.50): ln ( {C0 K_{{dis}}^{ + } } ) = (21.185 - 1.47X_{{Fe}} ) - {{(27267 - 4170X_{{Fe}} )}/T(K)} . The cooling time constant, η = 6 × 10-1 K-1 year-1 calculated on the PCA82506-3 sample, provided a cooling rate of the order of 1°C/min consistent with the extremely fast late cooling history of the ureilite parent body after impact excavation.

Direct Measurement of the Magnetocaloric Effect in La(Fe,Si,Co) 13 Compounds in Pulsed Magnetic Fields

DOE PAGES

Zavareh, M. Ghorbani; Skourski, Y.; Skokov, K. P.; ...

2017-07-28

We report on magnetization, magnetostriction, and magnetocaloric-effect measurements of polycrystal-line LaFe 11.74Co 0.13Si 1.13 and LaFe 11.21Co 0.65Si 1.11 performed in both pulsed and static magnetic fields. Although the two compounds behave rather differently at low fields (~ 5 T), they show quite similar values of the magnetocaloric effect, namely a temperature increases of about 20 K at high fields (50-60 T). The magnetostriction and magnetization also reach very similar values here. We are able to quantify the magnetoelastic coupling and, based on that, apply the Bean-Rodbell criterion distinguishing first- and second-order transitions.

Direct Measurement of the Magnetocaloric Effect in La(Fe,Si,Co) 13 Compounds in Pulsed Magnetic Fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zavareh, M. Ghorbani; Skourski, Y.; Skokov, K. P.

We report on magnetization, magnetostriction, and magnetocaloric-effect measurements of polycrystal-line LaFe 11.74Co 0.13Si 1.13 and LaFe 11.21Co 0.65Si 1.11 performed in both pulsed and static magnetic fields. Although the two compounds behave rather differently at low fields (~ 5 T), they show quite similar values of the magnetocaloric effect, namely a temperature increases of about 20 K at high fields (50-60 T). The magnetostriction and magnetization also reach very similar values here. We are able to quantify the magnetoelastic coupling and, based on that, apply the Bean-Rodbell criterion distinguishing first- and second-order transitions.

Magnetic superlattices and their nanoscale phase transition effects

PubMed Central

Cheon, Jinwoo; Park, Jong-Il; Choi, Jin-sil; Jun, Young-wook; Kim, Sehun; Kim, Min Gyu; Kim, Young-Min; Kim, Youn Joong

2006-01-01

The systematic assembly of nanoscale constituents into highly ordered superlattices is of significant interest because of the potential of their multifunctionalities and the discovery of new collective properties. However, successful observations of such superlattice-associated nanoscale phenomena are still elusive. Here, we present magnetic superlattices of Co and Fe3O4 nanoparticles with multidimensional symmetry of either AB (NaCl) or AB2 (AlB2). The discovery of significant enhancement (≈25 times) of ferrimagnetism is further revealed by forming previously undescribed superlattices of magnetically soft–hard Fe3O4@CoFe2O4 through the confined geometrical effect of thermally driven intrasuperlattice phase transition between the nanoparticulate components. PMID:16492783

The cooling rate dependence of cation distributions in CoFe2O4

NASA Technical Reports Server (NTRS)

De Guire, Mark R.; O'Handley, Robert C.; Kalonji, Gretchen

1989-01-01

The room-temperature cation distributions in bulk CoFe2O4 samples, cooled at rates between less than 0.01 and about 1000 C/sec, have been determined using Mossbauer spectroscopy in an 80-kOe magnetic field. With increasing cooling rate, the quenched structure departs increasingly from the mostly ordered cation distribution ordinarily observed at room temperature. However, the cation disorder appears to saturate just short of a random distribution at very high cooling rates. These results are interpreted in terms of a simple relaxation model of cation redistribution kinetics. The disordered cation distributions should lead to increased magnetization and decreased coercivity in CoFe2O4.

Thermal expansion and specific heat of Cr2TeO6 and Fe2TeO6 by first principles calculations

NASA Astrophysics Data System (ADS)

Mishra, Vinayak

2018-05-01

Cr2TeO6 and Fe2TeO6 crystallize in tetragonal structure. These compounds are formed in nuclear reactors. Therefore, study of thermal expansion of these compounds is important. In this paper, using WIEN2k code we have calculated the volume dependent total energies E(V) of these materials at zero kelvin. Subsequently, we have applied the quasi harmonic approximation, in order to include the thermal effects. Using our calculations, we have predicted the thermal expansion and specific heat at high temperatures. The calculated properties for Fe2TeO6 are in very good agreement with the reported experimental results.

Ordered vs. disordered perovskites; structural studies of Fe-doped SrIrO{sub 3} and SrRuO{sub 3}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qasim, Ilyas; Blanchard, Peter E.R.; Liu, Samuel

2013-10-15

The structures of the two Fe containing perovskites Sr{sub 2}IrFeO{sub 6} and SrRu{sub 0.5}Fe{sub 0.5}O{sub 3} have been established using a combination of synchrotron and neutron diffraction methods. Sr{sub 2}IrFeO{sub 6} and SrRu{sub 0.5}Fe{sub 0.5}O{sub 3} are shown to be monoclinic I2/m and tetragonal I4/mcm respectively The former exhibits a rock-salt like ordering of the Fe and Ir cations and displays a sequence of phase transitions associated with the loss of the octahedral tilts upon heating; 12/m→I4/m→Fm3{sup ¯}m. The Fe and Ru cations are disordered in SrRu{sub 0.5}Fe{sub 0.5}O{sub 3} and this shows a single structural phase transition upon heatingmore » due to the loss of the in-phase tilts, viz. I4/mcm→Pm3{sup ¯}m. In both cases XANES measurements show partial oxidation of the Fe{sup 3+} to Fe{sup 4+}. The difference in the structures between the two is remarkable given the similar size of Ir{sup 5+} and Ru{sup 5+}, and this is reflected in their magnetic properties. - Graphical abstract: Sr{sub 2}IrFeO{sub 6} and SrRu{sub 0.5}Fe{sub 0.5}O{sub 3} are shown, using a combination of synchrotron and neutron diffraction, to be monoclinic I2/m with cation ordering and tetragonal I4/mcm with disordered Fe and Ir, respectively. Both undergo phase transitions upon heating due to the loss of the octahedral tilts. Display Omitted - Highlights: • Sr{sub 2}IrFeO{sub 6} shown to be monoclinic and shows the transitions upon heating I2/m→I4/m→ Fm3{sup ¯}m. • SrRu{sub 0.5}Fe{sub 0.5}O{sub 3} is tetragonal and shows a single I4/mcm→Pm3m transition upon heating. • The Fe and Ru cations are disordered in SrRu{sub 0.5}Fe{sub 0.5}O{sub 3} but ordered in Sr{sub 2}FeIrO{sub 6}. • XANES measurements show partial oxidation of the Fe{sup 3+} to Fe{sup 4+}.« less

Magnetic domain observation of FeCo thin films fabricated by alternate monoatomic layer deposition

NASA Astrophysics Data System (ADS)

Ohtsuki, T.; Kojima, T.; Kotsugi, M.; Ohkochi, T.; Mizuguchi, M.; Takanashi, K.

2014-01-01

FeCo thin films are fabricated by alternate monoatomic layer deposition method on a Cu3Au buffer layer, which in-plane lattice constant is very close to the predicted value to obtain a large magnetic anisotropy constant. The variation of the in-plane lattice constant during the deposition process is investigated by reflection high-energy electron diffraction. The magnetic domain images are also observed by a photoelectron emission microscope in order to microscopically understand the magnetic structure. As a result, element-specific magnetic domain images show that Fe and Co magnetic moments align parallel. A series of images obtained with various azimuth reveal that the FeCo thin films show fourfold in-plane magnetic anisotropy along ⟨110⟩ direction, and that the magnetic domain structure is composed only of 90∘ wall.

Relationship between the structure of Fe-MCM-48 and its activity in catalytic ozonation for diclofenac mineralization.

PubMed

Li, Xukai; Chen, Weirui; Tang, Yiming; Li, Laisheng

2018-05-12

Fe-MCM-48 catalyst with a three-dimensional cubic pore structure was directly synthesized via a hydrothermal method, and the mineralization efficiency of diclofenac (DCF) in the catalytic ozonation process (Fe-MCM-48/O 3 ) was assessed. X-ray diffraction (XRD), N 2 adsorption desorption, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) characterizations revealed that Fe existed in the framework of MCM-48, and Fe-MCM-48 possessed a large surface area and a highly ordered cubic mesoporous structure, which could accelerate reactants and products diffusion. Regarding mineralization efficiency, the addition of Fe-MCM-48 significantly improved total organic carbon (TOC) removal, and approximately 49.9% TOC were removed through the Fe-MCM-48/O 3 process at 60 min, which was 2.0 times higher than that in single ozonation. Due to this catalyst's superior structure, Fe-MCM-48 showed the better catalytic activity compared with Fe-MCM-41 and Fe loaded MCM-48 (Fe/MCM-48, Fe existed on the surface of MCM-48). DCF removal in the Fe-MCM-48/O 3 process was primarily based on ozone direct oxidation. The improvement of mineralization efficiency was attributed to the function of generated hydroxyl radicals (•OH), which indicated that the presence of Fe-MCM-48 accelerated ozone decomposition. Moreover, the negatively charged surface of Fe-MCM-48 and the proper pH value of the DCF solution played an essential role in OH generation. Copyright © 2018 Elsevier Ltd. All rights reserved.