Spin dynamics and thermal stability in L10 FePt

NASA Astrophysics Data System (ADS)

Chen, Tianran; Toomey, Wahida

Increasing the data storage density of hard drives remains one of the continuing goals in magnetic recording technology. A critical challenge for increasing data density is the thermal stability of the written information, which drops rapidly as the bit size gets smaller. To maintain good thermal stability in small bits, one should consider materials with high anisotropy energy such as L10 FePt. High anisotropy energy nevertheless implies high coercivity, making it difficult to write information onto the disk. This issue can be overcome by a new technique called heat-assisted magnetic recording, where a laser is used to locally heat the recording medium to reduce its coercivity while retaining relatively good thermal stability. Many of the microscopic magnetic properties of L10 FePt, however, have not been theoretically well understood. In this poster, I will focus on a single L10 FePt grain, typically of a few nanometers. Specifically, I will discuss its critical temperature, size effect and, in particular, spin dynamics in the writing process, a key to the success of heat-assisted magnetic recording. WCU URF16.

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.

In vitro corrosion behavior of cast iron-platinum magnetic alloys.

PubMed

Watanabe, I; Hai, K; Tanaka, Y; Hisatsune, K; Atsuta, M

2001-05-01

The objective of this study was to investigate the corrosion resistance of cast Fe-Pt alloys of varying compositions for use as attachment keepers and to make a comparison with the corrosion resistance of magnetic stainless steel. The corrosion behavior of cast Fe-Pt alloy keepers (Fe-40 at%Pt, Fe-38 at%Pt, Fe-37 at%Pt and Fe-36 at%Pt) was evaluated by means of an immersion test and an anodic polarization test. The solutions used were a 1.0% lactic acid aqueous solution (pH=2.3) (10 ml) and 0.9% NaCl solution (pH=7.3) (10 ml). As a control, the corrosion resistance of a magnetic stainless steel keeper (SUS 447J1: HICOREX) was also measured. Chromium and platinum ions were not detected in either the 1.0% lactic acid or 0.9% NaCl solutions. The only released ions detected were the Fe ions in the 1.0% lactic acid solution. The amounts of Fe ions released from the Fe-40 at%Pt and Fe-38 at%Pt alloys were significantly (p<0.05) lower than from the Fe-37at%Pt, Fe-36 at%Pt and SUS 447J1 alloys. In the anodic polarization test, the potentials at the beginning of passivation for the four Fe-Pt alloys were higher than for the SUS 447J1 alloy in both solutions. The Fe-Pt alloys, especially the alloys with higher Pt percentages (Fe-40 and 38 at%Pt), indicated a high corrosion resistance compared to the magnetic stainless steel keeper. A reduction in the Pt percentage may decrease the corrosion resistance in the oral environment.

Enhanced dielectric constant and fatigue-resistance of PbZr0.4Ti0.6O3 capacitor with magnetic intermetallic FePt top electrode

NASA Astrophysics Data System (ADS)

Liu, B. T.; Zhao, J. W.; Li, X. H.; Zhou, Y.; Bian, F.; Wang, X. Y.; Zhao, Q. X.; Wang, Y. L.; Guo, Q. L.; Wang, L. X.; Zhang, X. Y.

2010-06-01

Both FePt/PbZr0.4Ti0.6O3(PZT)/Pt and Pt/PZT/Pt ferroelectric capacitors have been fabricated on Si substrates. It is found that up to 109 switching cycles, the FePt/PZT/Pt capacitor, measured at 50 kHz, with polarization decreased by 57%, is superior to the Pt/PZT/Pt capacitor by 82%, indicating that an intermetallic FePt top electrode can also improve the fatigue-resistance of a PZT capacitor. Maximum dielectric constants are 980 and 770 for PZT capacitors with FePt and Pt, respectively. This is attributed to the interface effect between PZT film and the top electrode since the interfacial capacitance of FePt/PZT is 3.5 times as large as that of Pt/PZT interface.

Simple-Cubic Carbon Frameworks with Atomically Dispersed Iron Dopants toward High-Efficiency Oxygen Reduction.

PubMed

Wang, Biwei; Wang, Xinxia; Zou, Jinxiang; Yan, Yancui; Xie, Songhai; Hu, Guangzhi; Li, Yanguang; Dong, Angang

2017-03-08

Iron and nitrogen codoped carbons (Fe-N-C) have attracted increasingly greater attention as electrocatalysts for oxygen reduction reaction (ORR). Although challenging, the synthesis of Fe-N-C catalysts with highly dispersed and fully exposed active sites is of critical importance for improving the ORR activity. Here, we report a new type of graphitic Fe-N-C catalysts featuring numerous Fe single atoms anchored on a three-dimensional simple-cubic carbon framework. The Fe-N-C catalyst, derived from self-assembled Fe 3 O 4 nanocube superlattices, was prepared by in situ ligand carbonization followed by acid etching and ammonia activation. Benefiting from its homogeneously dispersed and fully accessible active sites, highly graphitic nature, and enhanced mass transport, our Fe-N-C catalyst outperformed Pt/C and many previously reported Fe-N-C catalysts for ORR. Furthermore, when used for constructing the cathode for zinc-air batteries, our Fe-N-C catalyst exhibited current and power densities comparable to those of the state-of-the-art Pt/C catalyst.

Magnetic characteristics and nanostructures of FePt granular films with GeO2 segregant

NASA Astrophysics Data System (ADS)

Ono, Takuya; Moriya, Tomohiro; Hatayama, Masatoshi; Tsumura, Kaoru; Kikuchi, Nobuaki; Okamoto, Satoshi; Kitakami, Osamu; Shimatsu, Takehito

2017-01-01

To realize a granular film composed of L10-FePt grains with high uniaxial magnetic anisotropy energy, Ku, and segregants for energy-assisted magnetic recording, a FePt-GeO2/FePt-C stacked film was investigated in the engineering process. The FePt-GeO2/FePt-C stacked film fabricated at a substrate temperature of 450 °C realized uniaxial magnetic anisotropy, Kugrain , of about 2.5 × 107 erg/cm3, which is normalized by the volume fraction of FePt grains, and a granular structure with an averaged grain size of 7.7 nm. As the thickness of the FePt-GeO2 upper layer was increased to 9 nm, the Ku values were almost constant. That result differs absolutely from the thickness dependences of the other oxide segregant materials such as SiO2 and TiO2. Such differences on the oxide segregant are attributed to their chemical bond. The strong covalent bond of GeO2 is expected to result in high Ku of the FePt-GeO2/FePt-C stacked films.

Electric-regulated enhanced in-plane uniaxial anisotropy in FeGa/PMN-PT composite using oblique pulsed laser deposition

NASA Astrophysics Data System (ADS)

Zhang, Yi; Huang, Chaojuan; Turghun, Mutellip; Duan, Zhihua; Wang, Feifei; Shi, Wangzhou

2018-04-01

The FeGa film with in-plane uniaxial magnetic anisotropy was fabricated onto different oriented single-crystal lead magnesium niobate-lead titanate using oblique pulsed laser deposition. An enhanced in-plane uniaxial magnetic anisotropy field of FeGa film can be adjusted from 18 Oe to 275 Oe by tuning the oblique angle and polarizing voltage. The competitive relationship of shape anisotropy and strain anisotropy has been discussed, which was induced by oblique angle and polarizing voltage, respectively. The (100)-oriented and (110)-oriented PMN-PT show completely different characters on voltage-dependent magnetic properties, which could be attributed to various anisotropy directions depended on different strain directions.

Sintering behavior of spin-coated FePt and FePtAu nanoparticles

NASA Astrophysics Data System (ADS)

Kang, Shishou; Jia, Zhiyong; Zoto, I.; Reed, D.; Nikles, David E.; Harrell, J. W.; Thompson, Gregory; Mankey, Gary; Krishnamurthy, Vemuru V.; Porcar, L.

2006-04-01

FePt and [FePt]95Au5 nanoparticles with an average size of about 4 nm were chemically synthesized and spin coated onto silicon substrates. Samples were subsequently thermally annealed at temperatures ranging from 250 to 500 °C for 30 min. Three-dimensional structural characterization was carried out with small-angle neutron scattering (SANS) and small-angle x-ray diffraction (SAXRD) measurements. For both FePt and [FePt]95Au5 particles before annealing, SANS measurements gave an in-plane coherence length parameter a=7.3 nm, while SAXRD measurements gave a perpendicular coherence length parameter c=12.0 nm. The ratio of c/a is about 1.64, indicating the as-made particle array has a hexagonal close-packed superstructure. For both FePt and FePtAu nanoparticles, the diffraction peaks shifted to higher angles and broadened with increasing annealing temperature. This effect corresponds to a shrinking of the nanoparticle array, followed by agglomeration and sintering of the nanoparticles, resulting in the eventual loss of positional order with increasing annealing temperature. The effect is more pronounced for FePtAu than for FePt. Dynamic coercivity measurements show that the FePtAu nanoparticles have both higher intrinsic coercivity and higher switching volume at the same annealing temperature. These results are consistent with previous studies that show that additive Au both lowers the chemical ordering temperature and promotes sintering.

The role of symmetry-breaking-induced interface anisotropy in [Fe/Pt]{sub n} multilayer films

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

Li Zhenghua; Center for Geo-environment Science, Faculty of Engineering and Resource Science, Akita University, Tegatagakuen-machi 1-1, Akita 010-8502; Xie Hailong

2011-04-01

The FePt films were deposited with [Fe/Pt]{sub n} multilayer structure on preheated Corning 1737F glass substrate using pure Fe and Pt target in a CMS-18 sputtering system. The dependence of FePt's texture and magnetic properties on the multilayer structure was investigated. The XRD patterns indicate that (111) texture is dominant for all [Fe/Pt]{sub n} (n = 8, 16, 20, 32) multilayer films. However, the measured M-H loops show that the perpendicular anisotropy is greatly enhanced in samples with n = 16, 20, and 32. The origin of the increased perpendicular anisotropy of [Fe/Pt]{sub n} multilayer films is related to themore » contributions of the interfaces, which will be analyzed using the micromagnetic models, with careful discussions of the crystalline and interface anisotropies. Finally, it is confirmed that the Fe/Pt interfaces favor the perpendicular orientation in the multilayer structure.« less

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.

Study the Polyol Process of Preparing the ru Doped FePt Nanoparticles

NASA Astrophysics Data System (ADS)

Lee, Chih-Hao; Hsu, Jen-Ho; Su, Hui-Chia; Huang, Tzu Wen

The structure of Ru doped FePt nanoparticles using polyol process was studied. The particle size grown is around 5 nm, and a shell structure might be formed. By selecting the time and temperature of adding the Ru precursors into solution, three different processes to synthesize the FePtRu particles were studied resulting in different growing mechanics. The possible models during the reaction process are also discussed. The phase transition temperature for the as-grown FCC FePt nanoparticle to transform into L10 FePt nanoparticle is about 823 K which is about the same as the one without doping Ru atoms. From the XAS study of each element, the possible scenario is that: although Ru atoms with the size close to the Pt, they do not totally replace the Pt sites in the FePt alloy. Instead, most of Ru formed a shell outside the FePt nanoparticles and Fe atoms are replaced.

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

Size-tunable drug-delivery capsules composed of a magnetic nanoshell.

PubMed

Fuchigami, Teruaki; Kitamoto, Yoshitaka; Namiki, Yoshihisa

2012-01-01

Nano-sized FePt capsules with two types of ultrathin shell were fabricated using a template method for use in a nano-scale drug delivery system. One capsule was composed of an inorganic-organic hybrid shell of a water-soluble polymer and FePt nanoparticles, and the other capsule was composed of a network of fused FePt nanoparticles. We demonstrated that FePt nanoparticles selectively accumulated on the polymer molecules adsorbed on the template silica particles, and investigated the morphologies of the particle accumulation by changing the concentration of the polymer solution with which the template particles were treated. Capsular size was reduced from 340 to less than 90 nm by changing the size of the silica template particles, and the shell thickness was controlled by changing the amount of FePt nanoparticles adsorbed on the template particles. The hybrid shell was maintained by the connection of FePt nanoparticles and polymer molecules, and the shell thickness was 10 nm at the maximum. The FePt network shell was fabricated by hydrothermal treatment of the FePt/polymer-modified silica composite particles. The FePt network shell was produced from only the FePt alloy, and the shell thickness was 3 nm. Water-soluble anti-cancer drugs could be loaded into the hollow space of FePt network capsules, and lipid-coated FePt network capsules loaded with anti-cancer drugs showed cellular toxicity. The nano-sized capsular structure and the ultrathin shell suggest applicability as a drug carrier in magnetically guided drug delivery systems.

Size-tunable drug-delivery capsules composed of a magnetic nanoshell

PubMed Central

Fuchigami, Teruaki; Kitamoto, Yoshitaka; Namiki, Yoshihisa

2012-01-01

Nano-sized FePt capsules with two types of ultrathin shell were fabricated using a template method for use in a nano-scale drug delivery system. One capsule was composed of an inorganic-organic hybrid shell of a water-soluble polymer and FePt nanoparticles, and the other capsule was composed of a network of fused FePt nanoparticles. We demonstrated that FePt nanoparticles selectively accumulated on the polymer molecules adsorbed on the template silica particles, and investigated the morphologies of the particle accumulation by changing the concentration of the polymer solution with which the template particles were treated. Capsular size was reduced from 340 to less than 90 nm by changing the size of the silica template particles, and the shell thickness was controlled by changing the amount of FePt nanoparticles adsorbed on the template particles. The hybrid shell was maintained by the connection of FePt nanoparticles and polymer molecules, and the shell thickness was 10 nm at the maximum. The FePt network shell was fabricated by hydrothermal treatment of the FePt/polymer-modified silica composite particles. The FePt network shell was produced from only the FePt alloy, and the shell thickness was 3 nm. Water-soluble anti-cancer drugs could be loaded into the hollow space of FePt network capsules, and lipid-coated FePt network capsules loaded with anti-cancer drugs showed cellular toxicity. The nano-sized capsular structure and the ultrathin shell suggest applicability as a drug carrier in magnetically guided drug delivery systems. PMID:23507895

Self-Supported Mesostructured Pt-Based Bimetallic Nanospheres Containing an Intermetallic Phase as Ultrastable Oxygen Reduction Electrocatalysts.

PubMed

Kim, Ho Young; Cho, Seonghun; Sa, Young Jin; Hwang, Sun-Mi; Park, Gu-Gon; Shin, Tae Joo; Jeong, Hu Young; Yim, Sung-Dae; Joo, Sang Hoon

2016-10-01

Developing highly active and stable cathode catalysts is of pivotal importance for proton exchange membrane fuel cells (PEMFCs). While carbon-supported nanostructured Pt-based catalysts have so far been the most active cathode catalysts, their durability and single-cell performance are yet to be improved. Herein, self-supported mesostructured Pt-based bimetallic (Meso-PtM; M = Ni, Fe, Co, Cu) nanospheres containing an intermetallic phase are reported, which can combine the beneficial effects of transition metals (M), an intermetallic phase, a 3D interconnected framework, and a mesoporous structure. Meso-PtM nanospheres show enhanced oxygen reduction reaction (ORR) activity, compared to Pt black and Pt/C catalysts. Notably, Meso-PtNi containing an intermetallic phase exhibits ultrahigh stability, showing enhanced ORR activity even after 50 000 potential cycles, whereas Pt black and Pt/C undergo dramatic degradation. Importantly, Meso-PtNi with an intermetallic phase also demonstrated superior activity and durability when used in a PEMFC single-cell, with record-high initial mass and specific activities. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Magnetic and superconducting nanowires.

PubMed

Piraux, L; Encinas, A; Vila, L; Mátéfi-Tempfli, S; Mátéfi-Tempfli, M; Darques, M; Elhoussine, F; Michotte, S

2005-03-01

This article is focused on the use of electrodeposition and of various nanoporous templates for the fabrication of metallic nanowires made from single metals (Ni, Co, Pb, Sn), alloys (NiFe, CoFe, CoPt), and multilayers (Co/Cu, NiFe/Cu). An overview is given of our recent studies performed on both magnetic and superconducting nanowires. Using different approaches entailing measurements on both single wires and arrays, numerous interesting physical properties have been identified in relation to the nanoscopic dimensions of these materials. Finally, various novel applications of the nanowires are also discussed.

Ternary Pt9RhFex Nanoscale Alloys as Highly Efficient Catalysts with Enhanced Activity and Excellent CO-Poisoning Tolerance for Ethanol Oxidation.

PubMed

Wang, Peng; Yin, Shibin; Wen, Ying; Tian, Zhiqun; Wang, Ningzhang; Key, Julian; Wang, Shuangbao; Shen, Pei Kang

2017-03-22

To address the problems of high cost and poor stability of anode catalysts in direct ethanol fuel cells (DEFCs), ternary nanoparticles Pt 9 RhFe x (x = 1, 3, 5, 7, and 9) supported on carbon powders (XC-72R) have been synthesized via a facile method involving reduction by sodium borohydride followed by thermal annealing in N 2 at ambient pressure. The catalysts are physically characterized by X-ray diffraction, scanning transmission electron microscopy, and X-ray photoelectron spectroscopy, and their catalytic performance for the ethanol oxidation reaction (EOR) is evaluated by cyclic and linear scan voltammetry, CO-stripping voltammograms, and chronopotentiometry. All the Pt 9 RhFe x /C catalysts of different atomic ratios produce high EOR catalytic activity. The catalyst of atomic ratio composition 9:1:3 (Pt/Rh/Fe) has the highest activity and excellent CO-poisoning tolerance. Moreover, the enhanced EOR catalytic activity on Pt 9 RhFe 3 /C when compared to Pt 9 Rh/C, Pt 3 Fe/C, and Pt/C clearly demonstrates the presence of Fe improves catalytic performance. Notably, the onset potential for CO oxidation on Pt 9 RhFe 3 /C (0.271 V) is ∼55, 75, and 191 mV more negative than on Pt 9 Rh/C (0.326 V), Pt 3 Fe/C (0.346 V), and Pt/C (0.462 V), respectively, which implies the presence of Fe atoms dramatically improves CO-poisoning tolerance. Meanwhile, compared to the commercial PtRu/C catalyst, the peak potential on Pt 9 RhFe 3 /C for CO oxidation was just slightly changed after several thousand cycles, which shows high stability against the potential cycling. The possible mechanism by which Fe and Rh atoms facilitate the observed enhanced performance is also considered herein, and we conclude Pt 9 RhFe 3 /C offers a promising anode catalyst for direct ethanol fuel cells.

Exchange coupled CoPt/FePtC media for heat assisted magnetic recording

NASA Astrophysics Data System (ADS)

Dutta, Tanmay; Piramanayagam, S. N.; Ru, Tan Hui; Saifullah, M. S. M.; Bhatia, C. S.; Yang, Hyunsoo

2018-04-01

L10 FePtC granular media are being studied as potential future magnetic recording media and are set to be used in conjunction with heat assisted magnetic recording (HAMR) to enable recording at write fields within the range of current day recording heads. Media structures based on a FePtC storage layer and a capping layer can alleviate the switching field distribution (SFD) requirements of HAMR and reduce the noise originating from the writing process. However, the current designs suffer from SFD issues due to high temperature writing. To overcome this problem, we study a CoPt/FePtC exchange coupled composite structure, where FePtC serves as the storage layer and CoPt (with higher Curie temperature, Tc) as the capping layer. CoPt remains ferromagnetic at near Tc of FePtC. Consequently, the counter exchange energy from CoPt would reduce the noise resulting from the adjacent grain interactions during the writing process. CoPt/FePtC bilayer samples with different thicknesses of CoPt were investigated. Our studies found that CoPt forms a continuous layer at a thickness of 6 nm and leads to considerable reduction in the saturation field and its distribution.

The role of the non-magnetic material in spin pumping and magnetization dynamics in NiFe and CoFeB multilayer systems

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

Ruiz-Calaforra, A., E-mail: ruiz@physik.uni-kl.de; Brächer, T.; Lauer, V.

2015-04-28

We present a study of the effective magnetization M{sub eff} and the effective damping parameter α{sub eff} by means of ferromagnetic resonance spectroscopy on the ferromagnetic (FM) materials Ni{sub 81}Fe{sub 19} (NiFe) and Co{sub 40}Fe{sub 40}B{sub 20} (CoFeB) in FM/Pt, FM/NM, and FM/NM/Pt systems with the non-magnetic (NM) materials Ru, Cr, Al, and MgO. Moreover, for NiFe layer systems, the influence of interface effects is studied by way of thickness dependent measurements of M{sub eff} and α{sub eff}. Additionally, spin pumping in NiFe/NM/Pt is investigated by means of inverse spin Hall effect (ISHE) measurements. We observe a large dependence ofmore » M{sub eff} and α{sub eff} of the NiFe films on the adjacent NM layer. While Cr and Al do not induce a large change in the magnetic properties, Ru, Pt, and MgO affect M{sub eff} and α{sub eff} in different degrees. In particular, NiFe/Ru and NiFe/Ru/Pt systems show a large perpendicular surface anisotropy and a significant enhancement of the damping. In contrast, the magnetic properties of CoFeB films do not have a large influence of the NM adjacent material and only CoFeB/Pt systems present an enhancement of α{sub eff}. However, this enhancement is much more pronounced in NiFe/Pt. By the introduction of the NM spacer material, this enhancement is reduced. Furthermore, a difference in symmetry between NiFe/NM/Pt and NiFe/NM systems in the output voltage signal from the ISHE measurements reveals the presence of spin pumping into the Pt layer in all-metallic NiFe/NM/Pt and NiFe/Pt systems.« less

Perpendicular magnetic anisotropy and spin reorientation transition in L1{sub 0} FePt films

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

Ahn, Jae Young; Lee, Nyun Jong; Kim, Tae Hee

2011-04-01

We investigated the thickness and composition dependence of perpendicular magnetic anisotropy (PMA) in L1{sub 0} Fe{sub 1-x}Pt{sub x} (x = 0.4, 0.5, and 0.55) films. The FePt films with different thicknesses of 35 and 70 A were grown at the substrate temperature T{sub s} = 300 deg. C by molecular beam epitaxy coevaporation technique. A (001)-oriented epitaxial L1{sub 0} FePt film was grown on the thin (001)-oriented fcc Pt layer, while a poorly crystallized FePt film was formed on the (111)-textured Pt layer. Our results showed that, at a fixed thickness of 70 A, the PMA of FePt alloy filmsmore » is enhanced as Pt content increases from 40% to 55%.« less

Shape-dependent surface magnetism of Co-Pt and Fe-Pt nanoparticles from first principles

NASA Astrophysics Data System (ADS)

Liu, Zhenyu; Wang, Guofeng

2017-12-01

In this paper, we have performed the first-principles density functional theory calculations to predict the magnetic properties of the CoPt and FePt nanoparticles in cuboctahedral, decahedral, and icosahedral shapes. The modeled alloy nanoparticles have a diameter of 1.1 nm and consist of 31 5 d Pt atoms and 24 3 d Co (or Fe) atoms. For both CoPt and FePt, we found that the decahedral nanoparticles had appreciably lower surface magnetic moments than the cuboctahedral and icosahedral nanoparticles. Our analysis indicated that this reduction in the surface magnetism was related to a large contraction of atomic spacing and high local Co (or Fe) concentration in the surface of the decahedral nanoparticles. More interestingly, we predicted that the CoPt and FePt cuboctahedral nanoparticles exhibited dramatically different surface spin structures when noncollinear magnetism was taken into account. Our calculation results revealed that surface anisotropy energy decided the fashion of surface spin canting in the CoPt and FePt nanoparticles, confirming previous predictions from atomistic Monte Carlo simulations.

Weathering of PGE sulfides and Pt-Fe alloys in the Freetown Layered Complex, Sierra Leone

NASA Astrophysics Data System (ADS)

Bowles, John F. W.; Suárez, Saioa; Prichard, Hazel M.; Fisher, Peter C.

2017-12-01

Fresh and weathered rocks and saprolite from Horizon B of the Freetown Layered Complex contain platinum-group minerals (PGM). The PGM in the fresh rocks are 1-7 μm across, including cooperite (PtS), isoferroplatinum (Pt3Fe), minor tetraferroplatinum (PtFe), tulameenite (Pt2FeCu), Os-bearing laurite (RuS2), and other base metal-sulfide (BMS)-bearing PGM. The weathered rocks contain fewer of those PGM but a high proportion of disordered Cu-(±Pd)-bearing Pt-Fe alloys. The saprolite hosts scarce, smaller (1-3 μm) ordered PtFe and disordered PtFe3. The Pt-Fe alloys became increasingly Fe rich as weathering proceeded. Pt-Fe oxides appeared during weathering. Copper sulfides associated with the primary PGM and cooperite (with <3% Pd) were destroyed to provide the minor Cu and Pd found in some of the disordered Pt-Fe alloys. Platinum- and Pd-bearing saprolites have retained the original rock fabric and, to a depth of about 2 m, surround residual rocks that show progressive weathering (corestones). Ground water passing through the saprolite has transported Pt and Pd (and probably Au) in solution down slope into saprolite over unmineralized rocks. Transport is marked by changes in the Pt/Pd ratio indicating that the metals have moved independently. Palladium is present in marginally higher concentrations in the deeper saprolite than in the corestones suggesting some retention of Pd in the deeper saprolite. Platinum and Pd are less concentrated in the upper saprolite than the deeper saprolite indicating surface leaching. Alteration occurred over a long period in an organic and microbial rich environment that may have contributed to the leaching and transport of PGE.

Physical properties of FePt nanocomposite doped with Ag atoms: First-principles study

NASA Astrophysics Data System (ADS)

Jia, Yong-Fei; Shu, Xiao-Lin; Xie, Yong; Chen, Zi-Yu

2014-07-01

L10 FePt nanocomposite with high magnetocrystalline anisotropy energy has been extensively investigated in the fields of ultra-high density magnetic recording media. However, the order—disorder transition temperature of the nanocomposite is higher than 600 °C, which is a disadvantage for the use of the material due to the sustained growth of FePt grain under the temperature. To address the problem, addition of Ag atoms has been proposed, but the magnetic properties of the doped system are still unclear so far. Here in this paper, we use first-principles method to study the lattice parameters, formation energy, electronic structure, atomic magnetic moment and order—disorder transition temperature of L10 FePt with Ag atom doping. The results show that the formation energy of a Ag atom substituting for a Pt site is 1.309 eV, which is lower than that of substituting for an Fe site 1.346 eV. The formation energy of substituting for the two nearest Pt sites is 2.560 eV lower than that of substituting for the further sites 2.621 eV, which indicates that Ag dopants tend to segregate L10 FePt. The special quasirandom structures (SQSs) for the pure FePt and the FePt doped with two Ag atoms at the stable Pt sites show that the order—disorder transition temperatures are 1377 °C and 600 °C, respectively, suggesting that the transition temperature can be reduced with Ag atom, and therefore the FePt grain growth is suppressed. The saturation magnetizations of the pure FePt and the two Ag atoms doped FePt are 1083 emu/cc and 1062 emu/cc, respectively, indicating that the magnetic property of the doped system is almost unchanged.

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

Ultra-thin L1{sub 0}-FePt for perpendicular anisotropy L1{sub 0}-FePt/Ag/[Co/Pd]{sub 30} pseudo spin valves

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

Ho, Pin; Chow, Gan Moog; Chen, Jing-Sheng, E-mail: msecj@nus.edu.sg

2014-05-07

Perpendicular anisotropy L1{sub 0}-FePt/Ag/[Co/Pd]{sub 30} pseudo spin valves (PSVs) with ultra-thin L1{sub 0}-FePt alloy free layer possessing high anisotropy and thermal stability have been fabricated and studied. The thickness of the L1{sub 0}-FePt layer was varied between 2 and 4 nm. The PSV became increasingly decoupled with reduced L1{sub 0}-FePt thickness due to the larger difference between the coercivity of the L1{sub 0}-FePt and [Co/Pd]{sub 30} films. The PSV with an ultra-thin L1{sub 0}-FePt free layer of 2 nm displayed a high K{sub u} of 2.21 × 10{sup 7} ergs/cm{sup 3}, high thermal stability of 84 and a largest giant magnetoresistance of 0.54%.

In vitro degradation and biocompatibility of Fe-Pd and Fe-Pt composites fabricated by spark plasma sintering.

PubMed

Huang, T; Cheng, J; Zheng, Y F

2014-02-01

In order to obtain biodegradable Fe-based materials with similar mechanical properties as 316L stainless steel and faster degradation rate than pure iron, Fe-5 wt.%Pd and Fe-5 wt.%Pt composites were prepared by spark plasma sintering with powders of pure Fe and Pd/Pt, respectively. The grain size of Fe-5 wt.%Pd and Fe-5 wt.%Pt composites was much smaller than that of as-cast pure iron. The metallic elements Pd and Pt were uniformly distributed in the matrix and the mechanical properties of these materials were improved. Uniform corrosion of Fe-Pd and Fe-Pt composites was observed in both electrochemical tests and immersion tests, and the degradation rates of Fe-Pd and Fe-Pt composites were much faster than that of pure iron. It was found that viabilities of mouse fibroblast L-929 cells and human umbilical vein endothelial cells (ECV304) cultured in extraction mediums of Fe-Pd and Fe-Pt composites were close to that of pure iron. After 4 days' culture, the viabilities of L-929 and ECV304 cells in extraction medium of experimental materials were about 80%. The result of direct contact cytotoxicity also indicated that experimental materials exhibited no inhibition on vascular endothelial process. Meanwhile, iron ions released from experimental materials could inhibit proliferation of vascular smooth muscle cells (VSMC), which may be beneficial for hindering vascular restenosis. Furthermore, compared with that of as-cast pure iron, the hemolysis rates of Fe-Pd and Fe-Pt composites were slightly higher, but still within the range of 5%, which is the criteria for good blood compatibility. The numbers of platelet adhered on the surface of Fe-Pd and Fe-Pt composites were lower than that of pure iron, and the morphology of platelets kept spherical. To sum up, the Fe-5 wt.%Pd and Fe-5 wt.%Pt composites exhibited good mechanical properties and degradation behavior, closely approaching the requirements for biodegradable metallic stents. © 2013.

Fe Stabilization by Intermetallic L1 0-FePt and Pt Catalysis Enhancement in L1 0-FePt/Pt Nanoparticles for Efficient Oxygen Reduction Reaction in Fuel Cells

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

Li, Junrui; Xi, Zheng; Pan, Yung -Tin

We report in this article a detailed study on how to stabilize a first-row transition metal (M) in an intermetallic L1 0-MPt alloy nanoparticle (NP) structure and how to surround the L1 0-MPt with an atomic layer of Pt to enhance the electrocatalysis of Pt for oxygen reduction reaction (ORR) in fuel cell operation conditions. Using 8 nm FePt NPs as an example, we demonstrate that Fe can be stabilized more efficiently in a core/shell structured L1 0-FePt/Pt with a 5 Å Pt shell. The presence of Fe in the alloy core induces the desired compression of the thin Ptmore » shell, especially the 2 atomic layers of Pt shell, further improving the ORR catalysis. This leads to much enhanced Pt catalysis for ORR in 0.1 M HClO 4 solution (both at room temperature and 60°C) and in the membrane electrode assembly (MEA) at 80°C. The L1 0-FePt/Pt catalyst has a mass activity of 0.7 A/mg Pt from the half-cell ORR test and shows no obvious mass activity loss after 30,000 potential cycles between 0.6 V and 0.95 V at 80°C in the MEA, meeting the DOE 2020 target (<40% loss in mass activity). Here, we are extending the concept and preparing other L1 0-MPt/Pt NPs, such as L1 0-CoPt/Pt NPs, with reduced NP size as a highly efficient ORR catalyst for automotive fuel cell applications.« less

Fe Stabilization by Intermetallic L1 0-FePt and Pt Catalysis Enhancement in L1 0-FePt/Pt Nanoparticles for Efficient Oxygen Reduction Reaction in Fuel Cells

DOE PAGES

Li, Junrui; Xi, Zheng; Pan, Yung -Tin; ...

2018-02-07

We report in this article a detailed study on how to stabilize a first-row transition metal (M) in an intermetallic L1 0-MPt alloy nanoparticle (NP) structure and how to surround the L1 0-MPt with an atomic layer of Pt to enhance the electrocatalysis of Pt for oxygen reduction reaction (ORR) in fuel cell operation conditions. Using 8 nm FePt NPs as an example, we demonstrate that Fe can be stabilized more efficiently in a core/shell structured L1 0-FePt/Pt with a 5 Å Pt shell. The presence of Fe in the alloy core induces the desired compression of the thin Ptmore » shell, especially the 2 atomic layers of Pt shell, further improving the ORR catalysis. This leads to much enhanced Pt catalysis for ORR in 0.1 M HClO 4 solution (both at room temperature and 60°C) and in the membrane electrode assembly (MEA) at 80°C. The L1 0-FePt/Pt catalyst has a mass activity of 0.7 A/mg Pt from the half-cell ORR test and shows no obvious mass activity loss after 30,000 potential cycles between 0.6 V and 0.95 V at 80°C in the MEA, meeting the DOE 2020 target (<40% loss in mass activity). Here, we are extending the concept and preparing other L1 0-MPt/Pt NPs, such as L1 0-CoPt/Pt NPs, with reduced NP size as a highly efficient ORR catalyst for automotive fuel cell applications.« less

Nanoscale variations in 187Os isotopic composition and HSE systematics in a Bultfontein peridotite

NASA Astrophysics Data System (ADS)

Wainwright, A. N.; Luguet, A.; Schreiber, A.; Fonseca, R. O. C.; Nowell, G. M.; Lorand, J.-P.; Wirth, R.; Janney, P. E.

2016-08-01

Understanding the mineralogical controls on radiogenic chronometers is a fundamental aspect of all geochronological tools. As with other common dating tools, it has become increasingly clear that the Re-Os system can be impacted by multiple mineral formation events. The accessory and micrometric nature of the Re-Os-bearing minerals has made assessing this influence complex. This is especially evident in cratonic peridotites, where long residence times and multiple metasomatic events have created a complex melting and re-enrichment history. Here we investigate a harzburgitic peridotite from the Bultfontein kimberlite (South Africa) which contains sub-micron Pt-Fe-alloy inclusions within base metal sulphides (BMS). Through the combination of the focused ion beam lift-out technique and low blank mass spectrometry we were able to remove and analyse the Pt-Fe-alloy inclusions for their Re-Os composition and highly siderophile element (HSE) systematics. Six repeats of the whole-rock yield 187Os/188Os compositions of 0.10893-0.10965, which correspond to Re depletion model ages (TRD) of 2.69-2.79 Ga. The Os, Ir and Pt concentrations are slightly variable across the different digestions, whilst Pd and Re remain constant. The resulting HSE pattern is typical of cratonic peridotites displaying depleted Pt and Pd. The Pt-Fe-alloys have PUM-like 187Os/188Os compositions of 0.1294 ± 24 (2-s.d.) and 0.1342 ± 38, and exhibit a saw-tooth HSE pattern with enriched Re and Pt. In contrast, their BMS hosts have unradiogenic 187Os/188Os of 0.1084 ± 6 and 0.1066 ± 3, with TRD ages of 2.86 and 3.09 Ga, similar to the whole-rock systematics. The metasomatic origin of the BMS is supported by (i) the highly depleted nature of the mantle peridotite and (ii) their Ni-rich sulphide assemblage. Occurrence of Pt-Fe-alloys as inclusions within BMS grains demonstrates the genetic link between the BMS and Pt-Fe-alloys and argues for formation during a single but continuous event of silicate melt percolation. While the high solubility of HSE within sulphide mattes rules out early formation of the alloys from a S-undersaturated silicate melt and subsequent scavenging in a sulphide matte, the alignment of the Pt-Fe-alloy inclusions attests that they are exsolutions formed during the sub-solidus re-equilibration of the high temperature sulphide phases. The significant difference in 187Os/188Os composition between the included Pt-Fe-alloys and their BMS host can only be accounted for by different Re/Os. This suggests that the formation of Pt-Fe-alloy inclusions within a BMS can result in the fractionation of Re from Os. A survey experiment examining the partitioning of Re and Os confirmed this observation, with the Re/Os of the Pt-Fe-alloy inclusion up to ten times higher than the co-existing BMS. This fractionation implies that, when Re is present in the sulphide melt, the TRD ages of BMS containing alloy inclusions do not date the loss of Re due to partial melting, but rather its fractionation into the Pt-Fe-alloys. As such, BMS ages should be used with caution when dating ancient partial melting events.

pH-Responsive, Self-Sacrificial Nanotheranostic Agent for Potential In Vivo and In Vitro Dual Modal MRI/CT Imaging, Real-Time, and In Situ Monitoring of Cancer Therapy.

PubMed

Yue, Ludan; Wang, Jinlong; Dai, Zhichao; Hu, Zunfu; Chen, Xue; Qi, Yafei; Zheng, Xiuwen; Yu, Dexin

2017-02-15

Multifunctional nanotheranostic agents have been highly commended due to the application to image-guided cancer therapy. Herein, based on the chemically disordered face centered cubic (fcc) FePt nanoparticles (NPs) and graphene oxide (GO), we develop a pH-responsive FePt-based multifunctional theranostic agent for potential in vivo and in vitro dual modal MRI/CT imaging and in situ cancer inhibition. The fcc-FePt will release highly active Fe ions due to the low pH in tumor cells, which would catalyze H 2 O 2 decomposition into reactive oxygen species (ROS) within the cells and further induce cancer cell apoptosis. Conjugated with folic acid (FA), the iron platinum-dimercaptosuccinnic acid/PEGylated graphene oxide-folic acid (FePt-DMSA/GO-PEG-FA) composite nanoassemblies (FePt/GO CNs) could effectively target and show significant toxicity to FA receptor-positive tumor cells, but no obvious toxicity to FA receptor-negative normal cells, which was evaluated by WST-1 assay. The FePt-based multifunctional nanoparticles allow real-time monitoring of Fe release by T 2 -weighted MRI, and the selective contrast enhancement in CT could be estimated in vivo after injection. The results showed that FePt-based NPs displayed excellent biocompatibility and favorable MRI/CT imaging ability in vivo and in vitro. Meanwhile, the decomposition of FePt will dramatically decrease the T 2 -weighted MRI signal and increase the ROS signal, which enables real-time and in situ visualized monitoring of Fe release in tumor cells. In addition, the self-sacrificial decomposition of fcc-FePt will be propitious to the self-clearance of the as-prepared FePt-based nanocomposite in vivo. Therefore, the FePt/GO CNs could serve as a potential multifunctional theranostic nanoplatform of MRI/CT imaging guided cancer diagnosis and therapy in the clinic.

Double enzymatic cascade reactions within FeSe-Pt@SiO2 nanospheres: synthesis and application toward colorimetric biosensing of H2O2 and glucose.

PubMed

Qiao, Fengmin; Wang, Zhenzhen; Xu, Ke; Ai, Shiyun

2015-10-07

A facile process was developed for the synthesis of FeSe-Pt@SiO2 nanospheres based on the hydrothermal treatment of FeCl3·6H2O, selenium and NaBH4 in ethanolamine solvent, followed by reducing HPtCl4 with NaBH4 in the presence of FeSe particles to obtain FeSe coated with Pt NPs (FeSe-Pt), ending with a surfactant assembled sol-gel process to obtain FeSe-Pt@SiO2. The morphology and composition of FeSe-Pt@SiO2 were characterized by transmission electron microscopy, high resolution TEM, X-ray diffraction and Fourier transform infrared spectroscopy. Structural analyses revealed that FeSe-Pt@SiO2 nanospheres were of regular spherical shape with smooth surfaces due to the SiO2 shells, compared with FeSe particles with 150 nm lateral diameter. The prepared FeSe-Pt@SiO2 nanospheres possessed both intrinsic glucose oxidase (GOx-) and peroxidase-mimic activities, and we engineered an artificial enzymatic cascade system with high activity and stability based on this nanostructure. The good catalytic performance of the composites could be attributed to the synergy between the functions of FeSe particles and Pt NPs. Significantly, the FeSe-Pt@SiO2 nanospheres as robust nanoreactors can catalyze a self-organized cascade reaction, which includes oxidation of glucose by oxygen to yield gluconic acid and H2O2, and then oxidation of 3,3,5,5-tetramethylbenzidine (TMB) by H2O2 to produce a colour change. Colorimetric detection of H2O2 and glucose using the FeSe-Pt@SiO2 nanospheres was conducted with high detection sensitivities, 0.227 nM and 1.136 nM, respectively, demonstrating the feasibility of practical sensing applications. It is therefore believed that our findings in this study could open up the possibility of utilizing FeSe-Pt@SiO2 nanospheres as enzymatic mimics in diagnostic and biotechnology fields.

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.

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

DFT calculations of strain and interface effects on electronic structures and magnetic properties of L10-FePt/Ag heterojunction of GMR applications

NASA Astrophysics Data System (ADS)

Pramchu, Sittichain; Jaroenjittichai, Atchara Punya; Laosiritaworn, Yongyut

2018-03-01

In this work, density functional theory (DFT) was employed to investigate the effect of strain and interface on electronic structures and magnetic properties of L10-FePt/Ag heterojunction. Two possible interface structures of L10-FePt(001)/Ag(001), that is, interface between Fe and Ag layers (Fe/Ag) and between Pt and Ag layers (Pt/Ag), were inspected. It was found that Pt/Ag interface is more stable than Fe/Ag interface due to its lower formation energy. Further, under the lattice mismatch induced tensile strain, the enhancement of magnetism for both Fe/Ag and Pt/Ag interface structures has been found to have progressed, though the magnetic moments of "interfacial" Fe and Pt atoms have been found to have decreased. To explain this further, the local density of states (LDOS) analysis suggests that interaction between Fe (Pt) and Ag near Fe/Ag (Pt/Ag) interface leads to spin symmetry breaking of the Ag atom and hence induces magnetism magnitude. In contrast, the magnetic moments of interfacial Fe and Pt atoms reduce because of the increase in the electronic states near the Fermi level of the minority-spin electrons. In addition, the significant enhancements of the LDOS near the Fermi levels of the minority-spin electrons signify the boosting of the transport properties of the minority-spin electrons and hence the spin-dependent electron transport at this ferromagnet/metal interface. From this work, it is expected that this clarification of the interfacial magnetism may inspire new innovation on how to improve spin-dependent electron transport for enhancing the giant magnetoresistance (GMR) ratio of potential GMR-based spintronic devices.

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.

Observation and elimination of broken symmetry in L1{sub 0} FePt nanostructures

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

Quarterman, P.; Wang, Hao; Qiu, Jiao-Ming

2015-12-07

An unexplained surface anisotropy effect was observed and confirmed in the magnetization reversal process of both L1{sub 0} phase FePt nanoparticles with octahedral shape and (001) textured L1{sub 0} FePt thin films with island nanostructures. We suggest that the nature of the observed surface effect is caused by broken symmetry on the FePt surface, which results in weakened exchange coupling for surface atoms. Furthermore, we propose, and experimentally demonstrate, a method to repair the broken symmetry by capping the FePt islands with a Pt layer, which could prove invaluable in understanding fundamental limitations of magnetic nanostructures.

Determination of intrinsic spin Hall angle in Pt

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

Wang, Yi; Deorani, Praveen; Qiu, Xuepeng

2014-10-13

The spin Hall angle in Pt is evaluated in Pt/NiFe bilayers by spin torque ferromagnetic resonance measurements and is found to increase with increasing the NiFe thickness. To extract the intrinsic spin Hall angle in Pt by estimating the total spin current injected into NiFe from Pt, the NiFe thickness dependent measurements are performed and the spin diffusion in the NiFe layer is taken into account. The intrinsic spin Hall angle of Pt is determined to be 0.068 at room temperature and is found to be almost constant in the temperature range of 13–300 K.

Texture formation in FePt thin films via thermal stress management

NASA Astrophysics Data System (ADS)

Rasmussen, P.; Rui, X.; Shield, J. E.

2005-05-01

The transformation variant of the fcc to fct transformation in FePt thin films was tailored by controlling the stresses in the thin films, thereby allowing selection of in- or out-of-plane c-axis orientation. FePt thin films were deposited at ambient temperature on several substrates with differing coefficients of thermal expansion relative to the FePt, which generated thermal stresses during the ordering heat treatment. X-ray diffraction analysis revealed preferential out-of-plane c-axis orientation for FePt films deposited on substrates with a similar coefficients of thermal expansion, and random orientation for FePt films deposited on substrates with a very low coefficient of thermal expansion, which is consistent with theoretical analysis when considering residual stresses.

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.

Effect of Ag addition to L1{sub 0} FePt and L1{sub 0} FePd films grown by molecular beam epitaxy

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

Tokuoka, Y.; Seto, Y.; Kato, T., E-mail: takeshik@nuee.nagoya-u.ac.jp

2014-05-07

L1{sub 0} ordered FePt-Ag (5 nm) and FePd-Ag (5 nm) films were grown on MgO (001) substrate at temperatures of 250–400 °C by using molecular beam epitaxy method, and their crystal and surface structures, perpendicular magnetic anisotropies and Curie temperatures were investigated. In the case of FePt-Ag, Ag addition with the amount of 10–20 at. % was effective to promote L1{sub 0} ordering and granular growth, resulting in the increase of the perpendicular magnetic anisotropy and coercivity of the FePt-Ag films. On the other hand, in the case of FePd-Ag, Ag addition changed the surface morphology from island to continuous film associated with themore » reductions of its coercivity and perpendicular anisotropy. The variations of lattice constants and Curie temperature with Ag addition were significantly different between FePt-Ag and FePd-Ag. For FePd-Ag, the c and a axes lattice spacings and Curie temperature gradually changed with increasing Ag content, while they unchanged for FePt-Ag. These results suggest the possibility of the formation of FePdAg alloy in FePd-Ag, while Ag segregation in FePt-Ag.« less

Monodisperse core/shell Ni/FePt nanoparticles and their con-version to Ni/Pt to catalyze oxygen reduction

DOE PAGES

Zhang, Sen; Hao, Yizhou; Su, Dong; ...

2014-10-28

We report a size-controllable synthesis of monodisperse core/shell Ni/FePt nanoparticles (NPs) via a seed-mediated growth and their subsequent conversion to Ni/Pt NPs. Preventing surface oxidation of the Ni seeds is essential for the growth of uniform FePt shells. These Ni/FePt NPs have a thin (≈ 1 nm) FePt shell, and can be converted to Ni/Pt by acetic acid wash to yield active catalysts for oxygen reduction reaction (ORR). Tuning the core size allow for optimization of their electrocatalytic activity. The specific activity and mass activity of 4.2 nm/0.8 nm core/shell Ni/FePt reach 1.95 mA/cm² and 490 mA/mg Pt at 0.9more » V ( vs. reversible hydrogen electrode, RHE), which are much higher than those of benchmark commercial Pt catalyst (0.34 mA/cm² and 92 mA/mg Pt at 0.9 V). Our studies provide a robust approach to monodisperse core/shell NPs with non-precious metal core, making it possible to develop advanced NP catalysts with ultralow Pt content for ORR and many other heterogeneous reactions.« less

Multicomponent Pt-Based Zigzag Nanowires as Selectivity Controllers for Selective Hydrogenation Reactions.

PubMed

Bai, Shuxing; Bu, Lingzheng; Shao, Qi; Zhu, Xing; Huang, Xiaoqing

2018-06-22

The selective hydrogenation of α, β-unsaturated aldehyde is an extremely important transformation, while developing efficient catalysts with desirable selectivity to highly value-added products is challenging, mainly due to the coexistence of two conjugated unsaturated functional groups. Herein, we report that a series of Pt-based zigzag nanowires (ZNWs) can be adopted as selectivity controllers for α, β-unsaturated aldehyde hydrogenation, where the excellent unsaturated alcohol (UOL) selectivity (>95%) and high saturated aldehyde (SA) selectivity (>94%) are achieved on PtFe ZNWs and PtFeNi ZNWs+AlCl 3 , respectively. The excellent UOL selectivity of PtFe ZNWs is attributed to the lower electron density of the surface Pt atoms, while the high SA selectivity of PtFeNi ZNWs+AlCl 3 is due to synergy between PtFeNi ZNWs and AlCl 3 , highlighting the importance of Pt-based NWs with precisely controlled surface and composition for catalysis and beyond.

Combining hard and soft magnetism into a single core-shell nanoparticle to achieve both hyperthermia and image contrast

PubMed Central

Yang, Qiuhong; Gong, Maogang; Cai, Shuang; Zhang, Ti; Douglas, Justin T; Chikan, Viktor; Davies, Neal M; Lee, Phil; Choi, In-Young; Ren, Shenqiang; Forrest, M Laird

2015-01-01

Background A biocompatible core/shell structured magnetic nanoparticles (MNPs) was developed to mediate simultaneous cancer therapy and imaging. Methods & results A 22-nm MNP was first synthesized via magnetically coupling hard (FePt) and soft (Fe3O4) materials to produce high relative energy transfer. Colloidal stability of the FePt@Fe3O4 MNPs was achieved through surface modification with silane-polyethylene glycol (PEG). Intravenous administration of PEG-MNPs into tumor-bearing mice resulted in a sustained particle accumulation in the tumor region, and the tumor burden of treated mice was a third that of the mice in control groups 2 weeks after a local hyperthermia treatment. In vivo magnetic resonance imaging exhibited enhanced T2 contrast in the tumor region. Conclusion This work has demonstrated the feasibility of cancer theranostics with PEG-MNPs. PMID:26606855

Reversible structural modulation of Fe-Pt bimetallic surfaces and its effect on reactivity.

PubMed

Ma, Teng; Fu, Qiang; Su, Hai-Yan; Liu, Hong-Yang; Cui, Yi; Wang, Zhen; Mu, Ren-Tao; Li, Wei-Xue; Bao, Xin-He

2009-05-11

Tunable surface: The surface structure of the Fe-Pt bimetallic catalyst can be reversibly modulated between the iron-oxide-rich Pt surface and the Pt-skin structure with subsurface Fe via alternating reduction and oxidation treatments (see figure). The regenerated active Pt-skin structure is active in reactions involving CO and/or O.

Reaction mechanism of WGS and PROX reactions catalyzed by Pt/oxide catalysts revealed by an FeO(111)/Pt(111) inverse model catalyst.

PubMed

Xu, Lingshun; Wu, Zongfang; Jin, Yuekang; Ma, Yunsheng; Huang, Weixin

2013-08-07

We have employed XPS and TDS to study the adsorption and surface reactions of H2O, CO and HCOOH on an FeO(111)/Pt(111) inverse model catalyst. The FeO(111)-Pt(111) interface of the FeO(111)/Pt(111) inverse model catalyst exposes coordination-unsaturated Fe(II) cations (Fe(II)CUS) and the Fe(II)CUS cations are capable of modifying the reactivity of neighbouring Pt sites. Water facilely dissociates on the Fe(II)CUS cations at the FeO(111)-Pt(111) interface to form hydroxyls that react to form both water and H2 upon heating. Hydroxyls on the Fe(II)CUS cations can react with CO(a) on the neighbouring Pt(111) sites to produce CO2 at low temperatures. Hydroxyls act as the co-catalyst in the CO oxidation by hydroxyls to CO2 (PROX reaction), while they act as one of the reactants in the CO oxidation by hydroxyls to CO2 and H2 (WGS reaction), and the recombinative reaction of hydroxyls to produce H2 is the rate-limiting step in the WGS reaction. A comparison of reaction behaviors between the interfacial CO(a) + OH reaction and the formate decomposition reaction suggest that formate is the likely surface intermediate of the CO(a) + OH reaction. These results provide some solid experimental evidence for the associative reaction mechanism of WGS and PROX reactions catalyzed by Pt/oxide catalysts.

Effect of interfacial structures on spin dependent tunneling in epitaxial L1 0-FePt/MgO/FePt perpendicular magnetic tunnel junctions

DOE PAGES

Yang, G.; Li, D. L.; Wang, S. G.; ...

2015-02-24

In this study, epitaxial FePt(001)/MgO/FePt magnetic tunnel junctions with L1 0-FePt electrodes showing perpendicular magnetic anisotropy were fabricated by molecular beam epitaxial growth. Tunnel magnetoresistance ratios of 21% and 53% were obtained at 300 K and 10 K, respectively. Our previous work, based on transmission electron microscopy, confirmed a semi-coherent interfacial structure with atomic steps (Kohn et al., APL 102, 062403 (2013)). Here, we show by x-ray photoemission spectroscopy and first-principles calculation that the bottom FePt/MgO interface is either Pt-terminated for regular growth or when an Fe layer is inserted at the interface, it is chemically bonded to O. Finally,more » both these structures have a dominant role in spin dependent tunneling across the MgO barrier resulting in a decrease of the tunneling magnetoresistance ratio compared with previous predictions.« less

Effect of interfacial structures on spin dependent tunneling in epitaxial L1{sub 0}-FePt/MgO/FePt perpendicular magnetic tunnel junctions

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

Yang, G.; Li, D. L.; Wang, S. G., E-mail: Sgwang@iphy.ac.cn

2015-02-28

Epitaxial FePt(001)/MgO/FePt magnetic tunnel junctions with L1{sub 0}-FePt electrodes showing perpendicular magnetic anisotropy were fabricated by molecular beam epitaxial growth. Tunnel magnetoresistance ratios of 21% and 53% were obtained at 300 K and 10 K, respectively. Our previous work, based on transmission electron microscopy, confirmed a semi-coherent interfacial structure with atomic steps (Kohn et al., APL 102, 062403 (2013)). Here, we show by x-ray photoemission spectroscopy and first-principles calculation that the bottom FePt/MgO interface is either Pt-terminated for regular growth or when an Fe layer is inserted at the interface, it is chemically bonded to O. Both these structures have a dominantmore » role in spin dependent tunneling across the MgO barrier resulting in a decrease of the tunneling magnetoresistance ratio compared with previous predictions.« less

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

Electric field control of magnetic properties in FeRh/PMN-PT heterostructures

NASA Astrophysics Data System (ADS)

Xie, Yali; Zhan, Qingfeng; Shang, Tian; Yang, Huali; Liu, Yiwei; Wang, Baomin; Li, Run-Wei

2018-05-01

We investigated electric control of magnetic properties in FeRh/PMN-PT heterostructures. An electric field of 1 kV/cm applied on the PMN-PT substrate could increase the coercivity of FeRh film from 60 to 161 Oe at 360 K where the FeRh antiferromagnetic to ferromagnetic phase transition occurs. The electric field dependent coercive field reveals a butterfly shape, indicating a strain-mediated magnetoelectric coupling across the FeRh/PMN-PT interface. However, the uniaxial magnetic anisotropy of FeRh is almost unchanged with the applied electric field on the PMN-PT substrate, which suggests the change of coercivity in FeRh films is mainly due to the shift of the magnetic transition temperature under the electric field.

From Metal-Organic Frameworks to Single-Atom Fe Implanted N-doped Porous Carbons: Efficient Oxygen Reduction in Both Alkaline and Acidic Media.

PubMed

Jiao, Long; Wan, Gang; Zhang, Rui; Zhou, Hua; Yu, Shu-Hong; Jiang, Hai-Long

2018-05-09

It remains highly desired but a great challenge to achieve atomically dispersed metals in high loadings for efficient catalysis. Now porphyrinic metal-organic frameworks (MOFs) have been synthesized based on a novel mixed-ligand strategy to afford high-content (1.76 wt %) single-atom (SA) iron-implanted N-doped porous carbon (Fe SA -N-C) via pyrolysis. Thanks to the single-atom Fe sites, hierarchical pores, oriented mesochannels and high conductivity, the optimized Fe SA -N-C exhibits excellent oxygen reduction activity and stability, surpassing almost all non-noble-metal catalysts and state-of-the-art Pt/C, in both alkaline and more challenging acidic media. More far-reaching, this MOF-based mixed-ligand strategy opens a novel avenue to the precise fabrication of efficient single-atom catalysts. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Modifying exchange-spring behavior of CoPt/NiFe bilayer by inserting a Pt or Ru spacer

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

Hsu, Jen-Hwa, E-mail: jhhsu@phys.ntu.edu.tw; Tsai, C. L.; Lee, C.-M.

2015-05-07

We herein explore the possibility of obtaining tunable tilted magnetic anisotropy in ordered-CoPt (5 nm)/NiFe(t{sub NiFe}) bilayers through modifying their exchange spring behavior by inserting Pt and Ru-spacers. The tuning process of tilt angle magnetization of NiFe-layer was systematically investigated by varying the Pt or Ru thickness (t{sub Pt} or t{sub Ru}) from 0 to 8 nm at different thicknesses of NiFe (t{sub NiFe} = 1.5, 4.0, and 6.0 nm). Polar magneto-optic Kerr effect (p-MOKE) studies reveal that the bilayers grown in absence of spacers exhibit almost a rectangular hysteresis loop. With the insertion of Pt-spacer, the loop becomes more and more tilted as t{submore » Pt} increases; whereas, in the case of Ru-spacer, the nature of the loops is not simply changing in one direction. The estimated SQR{sub ⊥} (= θ{sub r}/θ{sub s}) values from the p-MOKE loops are found to monotonically decrease with increasing t{sub Pt} when t{sub Pt} ≦ 4 nm. In contrast, in the case of Ru-spacer, an oscillatory behavior for the SQR{sub ⊥} values is apparent when t{sub Ru} ≦ 4 nm. As a result, an oscillatory tilted angle of NiFe spin configuration was obtained in the case of Ru-spacer; while a decoupling effect was prominent for the Pt-spacer. The results of present study reveal that the insertion of Pt and Ru-spacers as an appropriate means for realizing tunable tilted magnetic anisotropy in the CoPt/NiFe exchange springs.« less

Large magnetic penetration depth and thermal fluctuations in a superconducting Ca10(Pt3As8)[(Fe1 xPtx)2As2]5 (x = 0.097) single crystal

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

Kim J.; Nazaretski E.; Ronning, F.

2012-05-18

We have measured the temperature dependence of the absolute value of the magnetic penetration depth {lambda}(T) in a Ca{sub 10}(Pt{sub 3}As{sub 8})[(Fe{sub 1-x}Pt{sub x}){sub 2}As{sub 2}]{sub 5} (x = 0.097) single crystal using a low-temperature magnetic force microscope (MFM). We obtain {lambda}{sub ab}(0) {approx} 1000 nm via extrapolating the data to T = 0. This large {lambda} and pronounced anisotropy in this system are responsible for large thermal fluctuations and the presence of a liquid vortex phase in this low-temperature superconductor with a critical temperature of 11 K, consistent with the interpretation of the electrical transport data. The superconducting parametersmore » obtained from {lambda} and coherence length {zeta} place this compound in the extreme type II regime. Meissner responses (via MFM) at different locations across the sample are similar to each other, indicating good homogeneity of the superconducting state on a submicron scale.« less

Effect of atomic composition on the compressive strain and electrocatalytic activity of PtCoFe/sulfonated graphene

NASA Astrophysics Data System (ADS)

Lohrasbi, Elaheh; Javanbakht, Mehran; Mozaffari, Sayed Ahmad

2017-06-01

The aim of this work is improvement of the stability and durability of sulfonated graphene supported PtCoFe electrocatalyst (PtCoFe/SG) for application in proton exchange membrane fuel cells (PEMFCs). The durability investigation of PtCoFe/SG is evaluated by a repetitive potential cycling test. The compressive strain in the lattice of PtCoFe/SG towards the electrocatalytic oxygen reduction reaction is studied. The synthesized electrocatalysts are examined physically and electrochemically for their structure, morphology and electrocatalytic performance. It is shown that presence of SO3sbnd groups on the graphene cause better adsorption of PtCoFe nanoparticles on the support and increase stability of electrocatalysts. Also, it is shown that Co:Fe atomic ratio in the synthesized electrocatalysts plays important role in their electrocatalytic performance. In the optimum Co:Fe atomic ratio, the compressive strain goes through the ideal value of the binding energy; further increase in Co/Fe atomic fraction introduces the excessive compressive strain and the activity of electrocatalyst decreases. The electrocatalyst synthesized in the optimum conditions is utilized as cathode in PEMFC. The power density of the PEMFC in low metal loading (0.1 mg cm-2 Pt) reaches to a maximum of 530 mW cm-2 at 75 °C. It suggests that PtCoFe/SG with 7:3 Co:Fe atomic ratio promises to improve the power density of PEMFCs.

Microscopic, Transport and Thermodynamic properties of Ca10(Pt3As8)((Fe1-xTMx)2As2)5 (TM=Co, Ni) single crystals

NASA Astrophysics Data System (ADS)

Jiang, Shan; Ni, Ni

2015-03-01

Here we report detailed microscopic, transport and thermodynamic measurements on two series of high quality single crystals Ca10(Pt3As8)((Fe1-xTMx)2As2)5 (TM=Co, Ni). With electron doping on Fe sites, the structural/magnetic phase transitions in the parent compound were suppressed at a rate of roughly -7K per 0.01Co doping and -9K per 0.01Ni doping. Superconductivity emerges in the region of 0 . 048 < x < 0 . 20 for Co doping with optimal Tc of 13.5K (x = 0 . 11) while it occurs in the region of 0 . 035 < x < 0 . 11 for Ni doping with optimal Tc of 9.6K (x = 0 . 064). No coexistence of AFM and SC is observed, which is different from the well-studied 122 Fe-pnictides but reminiscent the one of La1111. The comparison of the effect between Co- and Ni- doping on 10-3-8 shows that rigid band approximation is likely working for these two dopants in this superconducting family.

A New Green Chemical Synthesis Strategy for Synthesis of L10 FePt Nanoparticles from Layered Precursor Fe(H2O)6PtCl6

NASA Astrophysics Data System (ADS)

Hadjipanayis, George; Hu, Xiaocao; Capobianchi, Aldo; Gallagher, Ryan

2014-03-01

In this work, a new green chemical strategy for the synthesis of L10 FePt nanoparticles is reported. The starting material is a polycrystalline molecular complex (Fe(H2O)6PtCl6) , in which Fe and Pt atoms are arranged on alternating planes. The starting compound was milled with crystalline NaCl and then annealed under forming gas (5 % H2 and 95 % Ar) at 450 °C for 2h. Finally, the mixture was washed with water to remove the NaCl and L10 FePt nanoparticles were obtained. Transmission electron microscopy (TEM) images revealed that this method is able to produce L10 nanoparticles with different average size varying from 13.9 nm to 5.4 nm depending on the (Fe(H2O)6PtCl6) /NaCl ratio. With smaller (Fe(H2O)6PtCl6) /NaCl ratio(10mg/20g) and longer milling time(15h), FePt nanoparticles had a smaller size and narrower size distribution. The X-Ray Diffraction (XRD) pattern showed the presence of the characteristic peaks of the fct phase. The hysteresis loop, measured both at room temperature and 50 K, shows a high coercivity of 7.6 kOe and 11.2 kOe, respectively as expected for the high anisotropy L10 phase. Larger precursor/NaCl ratio and shorter ball milling time led to larger coercivity.

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.

First-principles calculations of perpendicular magnetic anisotropy for spintronic applications

NASA Astrophysics Data System (ADS)

Ansarino, Masoud; Ravan, Bahram Abedi

2017-01-01

A combination of density functional theory and non-equilibrium Green’s function methods are used to simulate spin-dependent electronic transport in monatomic Au-nanowires sandwiched between ferromagnetic electrodes. Electrodes of the junction are in turn composed of tetragonal FeCo, FePd and FePt alloys. Magnetic anisotropy energies of the electrodes are calculated for different values of the c/a ratios of the electrode lattice constants and it is shown that at c/a = 1.05, the FePt electrodes gain a relatively large amount of magnetic anisotropy energy (MAE). Hence, it is concluded that the ferromagnetic FePt alloy can be used as a suitable type of electrode for applications in perpendicular magnetic tunnel junctions (MTJs). We observe that increasing the c/a ratio leads to notable improvements in the spin filtering of the FeCo and FePd MTJs while it only has a slight effect on the filtering of the FePt MTJ. Later, we show that by removing the interfacial Pt atoms of the FePt MTJ, we are able to enhance its filtering property.

Synergistic increase of oxygen reduction favourable Fe-N coordination structures in a ternary hybrid of carbon nanospheres/carbon nanotubes/graphene sheets.

PubMed

Zhang, Shiming; Liu, Bin; Chen, Shengli

2013-11-14

A Fe/N co-doped ternary nanocarbon hybrid, with uniform bamboo-like carbon nanotubes (CNTs) in situ grown on/between the single/few-layer graphene sheets interspaced by carbon nanosphere aggregates, was prepared through a one-pot heat treatment of a precursor mixture containing graphene oxide, Vulcan XC-72 carbon nanospheres, nitrogen rich melamine and small amounts of Fe ions. Physical characterization including electron microscopic images, N2 adsorption-desorption isotherms, pore size distribution, XPS, XRD, Mössbauer spectra, and EDX revealed that the 0-D/1-D/2-D ternary hybrid architecture not only offered an optimized morphology for high dispersion of each nanocarbon moiety, while the carbon nanosphere interspaced graphene sheets have provided a platform for efficient reaction between Fe ions and melamine molecules, resulting in uniform nucleation and growth of CNTs and formation of high density Fe-N coordination assemblies that have been believed to be the active centers for the oxygen reduction reaction (ORR) in carbon-based nonprecious metal electrocatalysts. In the absence of graphene oxides or carbon nanospheres, a similar heat treatment was found to result in large amounts of elemental Fe and Fe carbides and entangled CNTs with wide diameter distributions. As a result, the ternary Fe/N-doped nanocarbon hybrid exhibits ORR activity much higher than the Fe-N doped single or binary nanocarbon materials prepared under similar heat treatment conditions, and approaching that of the state-of-the-art carbon-supported platinum catalyst (Pt/C) in acidic media, as well as superior stability and methanol tolerance to Pt/C.

Anomalous reduction in the long-time flux creep relaxation in superconducting Ca10(Pt4As8)((Fe1‑x Pt x )2As2)5 (x ≈ 0.05) single crystals

NASA Astrophysics Data System (ADS)

Haberkorn, N.; Huang, Silu; Jin, R.

2018-06-01

We report the vortex dynamics of superconducting a Ca10(Pt4As8)((Fe1‑x Pt x )2As2)5 (x ≈ 0.05) single crystal with T c = 26 K investigated by performing magnetic measurements. The field dependence of the magnetization displays a second peak (SPM), typically related to a crossover between elastic and plastic vortex relaxation in a weak pinning scenario. Long-time flux creep relaxation measurements for fields smaller that of the SPM show that the vortex dynamics can be separated in two different regions. For magnetic fields smaller than the lower end of the SPM, glassy relaxation (with a characteristic glassy exponent μ) is observed. For magnetic fields between the lower end and the SPM, the flux creep rate decreases systematically to values below to the ones predicted by the collective theory. This effect can be understood by considering a stable vortex lattice configuration. As the field position of the SPM can be adjusted by modifying the quenched potential, our results suggest that extremely low flux creep relaxation rate may be tuned in many other superconducting materials.

Absence of morphotropic phase boundary effects in BiFeO3-PbTiO3 thin films grown via a chemical multilayer deposition method

NASA Astrophysics Data System (ADS)

Gupta, Shashaank; Bhattacharjee, Shuvrajyoti; Pandey, Dhananjai; Bansal, Vipul; Bhargava, Suresh K.; Peng, Ju Lin; Garg, Ashish

2011-07-01

We report an unusual behavior observed in (BiFeO3)1- x -(PbTiO3) x (BF- xPT) thin films prepared using a multilayer chemical solution deposition method. Films of different compositions were grown by depositing several bilayers of BF and PT precursors of varying BF and PT layer thicknesses followed by heat treatment in air. X-ray diffraction showed that samples of all compositions show mixing of two compounds resulting in a single-phase mixture, also confirmed by transmission electron microscopy. In contrast to bulk compositions, samples show a monoclinic (MA-type) structure suggesting disappearance of the morphotropic phase boundary (MPB) at x=0.30 as observed in the bulk. This is accompanied by the lack of any enhancement of the remanent polarization at the MPB, as shown by the ferroelectric measurements. Magnetic measurements showed an increase in the magnetization of the samples with increasing BF content. Significant magnetization in the samples indicates melting of spin spirals in the BF- xPT films, arising from a random distribution of iron atoms. Absence of Fe2+ ions was corroborated by X-ray photoelectron spectroscopy measurements. The results illustrate that thin film processing methodology significantly changes the structural evolution, in contrast to predictions from the equilibrium phase diagram, besides modifying the functional characteristics of the BP- xPT system dramatically.

Synthesis of Cluster-Derived PtFe/SiO(2) Catalysts for the Oxidation of CO

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

Siani, A.; Alexeev, O.S.; Captain, B.

2009-05-27

Infrared (FTIR) and extended X-ray absorption fine structure (EXAFS) spectroscopy measurements were used to characterize the species formed after impregnation of Pt{sub 5}Fe{sub 2}(COD){sub 2}(CO){sub 12} onto silica, before and after removal of the organic ligands. The results indicate that the Pt{sub 5}Fe{sub 2}(COD){sub 2}(CO){sub 12} cluster adsorbs weakly on the SiO{sub 2} surface. Nevertheless, partial disintegration of the cluster was observed during aging even under He and at room temperature, related to the loss of CO ligands due to their interactions with silanol groups of the support. The organic ligands can be removed from a freshly impregnated cluster bymore » thermal treatment in either He or H{sub 2}, but the surface species formed in each case have different structures. Treatment in He at 350 {sup o}C leads to a complete disintegration of the Pt-Fe bimetallic core and results in the formation of highly dispersed Pt clusters with a nuclearity of six, along with surface Fe oxide-like species. In contrast, bimetallic PtFe nanoparticles with an average size of approximately 1 nm were formed when a similar H{sub 2} treatment was used. In this case, a greater degree of metal dispersion and a larger fraction of Pt-Fe interactions were observed compared to the PtFe/SiO{sub 2} samples prepared by co-impregnation of monometallic salt precursors. Electronic interactions between Pt and Fe atoms in such cluster-derived samples led to an increased electron density on platinum, as indicated by a red shift of the frequencies of FTIR bands for adsorbed NO and CO. These electronic interactions affect the strength of the CO adsorption on platinum. All bimetallic samples were found to be more active than Pt/SiO{sub 2} for the oxidation of CO in air; however, the activity depends strongly on the structure of the surface species, the fraction of Pt-Fe bimetallic contributions, the degree of electronic interactions between Pt and Fe, and the strength of the CO adsorption on platinum.« less

Orientation of FePt nanoparticles on top of a-SiO2/Si(001), MgO(001) and sapphire(0001): effect of thermal treatments and influence of substrate and particle size.

PubMed

Schilling, Martin; Ziemann, Paul; Zhang, Zaoli; Biskupek, Johannes; Kaiser, Ute; Wiedwald, Ulf

2016-01-01

Texture formation and epitaxy of thin metal films and oriented growth of nanoparticles (NPs) on single crystal supports are of general interest for improved physical and chemical properties especially of anisotropic materials. In the case of FePt, the main focus lies on its highly anisotropic magnetic behavior and its catalytic activity, both due to the chemically ordered face-centered tetragonal (fct) L10 phase. If the c-axis of the tetragonal system can be aligned normal to the substrate plane, perpendicular magnetic recording could be achieved. Here, we study the orientation of FePt NPs and films on a-SiO2/Si(001), i.e., Si(001) with an amorphous (a-) native oxide layer on top, on MgO(001), and on sapphire(0001) substrates. For the NPs of an approximately equiatomic composition, two different sizes were chosen: "small" NPs with diameters in the range of 2-3 nm and "large" ones in the range of 5-8 nm. The 3 nm thick FePt films, deposited by pulsed laser deposition (PLD), served as reference samples. The structural properties were probed in situ, particularly texture formation and epitaxy of the specimens by reflection high-energy electron diffraction (RHEED) and, in case of 3 nm nanoparticles, additionally by high-resolution transmission electron microscopy (HRTEM) after different annealing steps between 200 and 650 °C. The L10 phase is obtained at annealing temperatures above 550 °C for films and 600 °C for nanoparticles in accordance with previous reports. On the amorphous surface of a-SiO2/Si substrates we find no preferential orientation neither for FePt films nor nanoparticles even after annealing at 630 °C. On sapphire(0001) supports, however, FePt nanoparticles exhibit a clearly preferred (111) orientation even in the as-prepared state, which can be slightly improved by annealing at 600-650 °C. This improvement depends on the size of NPs: Only the smaller NPs approach a fully developed (111) orientation. On top of MgO(001) the effect of annealing on particle orientation was found to be strongest. From a random orientation in the as-prepared state observed for both, small and large FePt NPs, annealing at 650 °C for 30 min reorients the small particles towards a cube-on-cube epitaxial orientation with a minor fraction of (111)-oriented particles. In contrast, large FePt NPs keep their as-prepared random orientation even after doubling the annealing period at 650 °C to 60 min.

Orientation of FePt nanoparticles on top of a-SiO2/Si(001), MgO(001) and sapphire(0001): effect of thermal treatments and influence of substrate and particle size

PubMed Central

Schilling, Martin; Ziemann, Paul; Zhang, Zaoli; Biskupek, Johannes; Kaiser, Ute

2016-01-01

Summary Texture formation and epitaxy of thin metal films and oriented growth of nanoparticles (NPs) on single crystal supports are of general interest for improved physical and chemical properties especially of anisotropic materials. In the case of FePt, the main focus lies on its highly anisotropic magnetic behavior and its catalytic activity, both due to the chemically ordered face-centered tetragonal (fct) L10 phase. If the c-axis of the tetragonal system can be aligned normal to the substrate plane, perpendicular magnetic recording could be achieved. Here, we study the orientation of FePt NPs and films on a-SiO2/Si(001), i.e., Si(001) with an amorphous (a-) native oxide layer on top, on MgO(001), and on sapphire(0001) substrates. For the NPs of an approximately equiatomic composition, two different sizes were chosen: “small” NPs with diameters in the range of 2–3 nm and “large” ones in the range of 5–8 nm. The 3 nm thick FePt films, deposited by pulsed laser deposition (PLD), served as reference samples. The structural properties were probed in situ, particularly texture formation and epitaxy of the specimens by reflection high-energy electron diffraction (RHEED) and, in case of 3 nm nanoparticles, additionally by high-resolution transmission electron microscopy (HRTEM) after different annealing steps between 200 and 650 °C. The L10 phase is obtained at annealing temperatures above 550 °C for films and 600 °C for nanoparticles in accordance with previous reports. On the amorphous surface of a-SiO2/Si substrates we find no preferential orientation neither for FePt films nor nanoparticles even after annealing at 630 °C. On sapphire(0001) supports, however, FePt nanoparticles exhibit a clearly preferred (111) orientation even in the as-prepared state, which can be slightly improved by annealing at 600–650 °C. This improvement depends on the size of NPs: Only the smaller NPs approach a fully developed (111) orientation. On top of MgO(001) the effect of annealing on particle orientation was found to be strongest. From a random orientation in the as-prepared state observed for both, small and large FePt NPs, annealing at 650 °C for 30 min reorients the small particles towards a cube-on-cube epitaxial orientation with a minor fraction of (111)-oriented particles. In contrast, large FePt NPs keep their as-prepared random orientation even after doubling the annealing period at 650 °C to 60 min. PMID:27335749

Diffusion, phase equilibria and partitioning experiments in the Ni-Fe-Ru system

NASA Technical Reports Server (NTRS)

Blum, Joel D.; Wasserburg, G. J.; Hutcheon, I. D.; Beckett, J. R.; Stolper, E. M.

1989-01-01

Results are presented on thin-film diffusion experiments designed to investigate phase equilibria in systems containing high concentrations of Pt-group elements, such as Ni-Fe-Ru-rich systems containing Pt, at temperatures of 1273, 1073, and 873 K. The rate of Ru diffusion in Ni was determined as a function of temperature, and, in addition, the degree of Pt and Ir partitioning between phases in a Ni-Fe-Ru-rich system and of V between phases in a Ni-Fe-O-rich system at 873 were determined. It was found that Pt preferentially partitions into the (gamma)Ni-Fe phase, whereas Ir prefers the (epsilon)Ru-Fe phase. V partitions strongly into Fe oxides relative to (gamma)Ni-Fe. These results have direct application to the origin and thermal history of the alloys rich in Pt-group elements in meteorites.

Magnetic and electrical properties of Nd7Pt3 studied on single crystals

NASA Astrophysics Data System (ADS)

Tsutaoka, Takanori; Ueda, Koyo; Matsushita, Takuya

2018-07-01

Magnetic and electrical properties of Nd7Pt3 with the Th7Fe3 type hexagonal structure have been studied on single crystals by measuring magnetization, magnetic susceptibility and electrical resistivity. Nd7Pt3 possesses a ferromagnetic state below TC = 38 K; a canted antiferromagnetic state takes place at Tt2 = 34 K. Another magnetic phase transition has also been observed at Tt1 = 25 K. The magnetization curve along the a- and b-axes at 2 K shows anomalous first-order irreversible behavior. The direction of the magnetic moment in the canted state can be tilted from the c-plane. Electrical resistivity measurement results show metallic property; three anomalies were observed at Tt1, Tt2 and TC, respectively.

Development of iron platinum/oxide high anisotropy magnetic media

NASA Astrophysics Data System (ADS)

Yang, En

Because the size of magnetic grains is approaching the superparamagnetic limit in current perpendicular media, it is necessary to produce thin film media made with magnetic alloys with larger magneto-crystalline anisotropy energies to achieve higher recording densities. Due to its high anisotropy field and good environmental stability, FePt (L10) is the most promising media for achieving such ultra-high recording densities. However, there are several challenges associated with the development of FePt as a perpendicular media. As deposited FePt has disordered fee phase; either high deposition temperature, > 600 oC, or a high temperature post annealing process is required to obtain the ordered L10 structure, which is not desirable for manufacturing purposes. Therefore, techniques that enable ordering at significantly reduced temperatures are critically and urgently needed. Furthermore, in order to use it as a high density recording media, very small (less than 5 nm), uniform and fully-ordered, magnetically isolated FePt (L10) columnar grains with well defined grain boundaries, excellent perpendicular texture and high coercivity are desired. In this study, experiments and research have been mainly focused on the following aspects: (1) controlling of c axis orientation of FePt, (2) obtaining small columnar FePt grains, (3) improving order parameter and magnetic properties at lower ordering temperature. After a systematic experimental investigation, we have found an experimental approach for obtaining highly ordered L1 0 FePt-oxide thin film media at moderate deposition temperatures. In most previous studies, the FePt-Oxide layer is directly deposited on a textured MgO (001) layer. By introducing a double buffer layer in between the FePt-oxide layer and the MgO underlayer, we are able to substantially enhance the L1 0 ordering of the FePt-oxide layer while lowering the deposition temperature to 400oC. The buffer layers also yield a significantly enhanced (001) texture of the formed L10 FePt film. With the order parameter near unity, the coercivity of the resulting granular L10 FePt-oxide film exceeds Hc > 20 kOe with an average grain size about D = 8 nm. With the buffer layer technique, l8kOe coercivity has also been achieved for L10 FePt-oxide film at a grain size of about D = 4.5 nm, but it requires 35% of SiO2 in the magnetic layer. With 9% of Oxide in the film, excellent perpendicular texture, very high order parameter and small grain size of FePt can also be obtained by utilizing RuAl grain size defining layer along with TiN barrier layer. With the Ag buffer layer technique, the microstructure and magnetic properties of FePt films with RuAl grain size defining layer can be further improved.

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.

Synthesis and In Vitro Performance of Polypyrrole-Coated Iron-Platinum Nanoparticles for Photothermal Therapy and Photoacoustic Imaging

NASA Astrophysics Data System (ADS)

Phan, Thi Tuong Vy; Bui, Nhat Quang; Moorthy, Madhappan Santha; Lee, Kang Dae; Oh, Junghwan

2017-10-01

Multifunctional nano-platform for the combination of photo-based therapy and photoacoustic imaging (PAI) for cancer treatment has recently attracted much attention to nanotechnology development. In this study, we developed iron-platinum nanoparticles (FePt NPs) with the polypyrrole (PPy) coating as novel agents for combined photothermal therapy (PTT) and PAI. The obtained PPy-coated FePt NPs (FePt@PPy NPs) showed excellent biocompatibility, photothermal stability, and high near-infrared (NIR) absorbance for the combination of PTT and PAI. In vitro investigation experimentally demonstrated the effectiveness of FePt@PPy NPs in killing cancer cells with NIR laser irradiation. Moreover, the phantom test of PAI used in conjunction with FePt@PPy NPs showed a strong photoacoustic signal. Thus, the novel FePt@PPy NPs could be considered as promising multifunctional nanoparticles for further applications of photo-based diagnosis and treatment.

Temperature dependence of exchange anisotropy for (0 0 1) oriented Mn 89Pt 11/ferromagnetic bilayers

NASA Astrophysics Data System (ADS)

Yamato, T.; Kume, T.; Kato, T.; Tsunashima, S.; Iwata, S.

Temperature dependence of the exchange anisotropy was investigated for (0 0 1)-oriented top-type Mn 89Pt 11 ( tAF nm)/Ni 80Fe 20 (5 nm) and bottom-type Ni 80Fe 20 (3 nm)/Mn 89Pt 11 (30 nm) and Co 90Fe 10 (3 nm)/Mn 89Pt 11 (30 nm) bilayers. The top-type MnPt/NiFe bilayers exhibited both 1 and 4-fold anisotropies in their in-plane torque curves at 80 K. For tAF=3 nm, rapid decrease of 1-fold component and gradual decrease of 4-fold component were observed with increasing temperature. While for tAF=30 nm, the 1 and 4-fold anisotropies decreased similarly with temperature. In the bottom-type bilayers, by using CoFe ferromagnetic layer, the 4-fold anisotropy was found to become twice as that of the NiFe/MnPt bilayer.

Preparation and characterization of SiO2-coated submicron-sized L10 Fe-Pt particles

NASA Astrophysics Data System (ADS)

Hayashi, Yoshiaki; Ogawa, Tomoyuki; Ishiyama, Kazushi

2018-05-01

The development of magnets with higher performance is attracting increasing interest. The optimization of their microstructure is essential to enhance their properties, and a microstructure comprising magnetically isolated hard magnetic grains of a single-domain size has been proposed as an ideal structure for enhancing the coercivity of magnets. To obtain magnets with an ideal structure, we consider the fabrication of magnets by an approach based on core/shell nanoparticles with a hard magnetic core and a non-magnetic shell. In this study, to obtain particles for our proposed approach, we attempted to fabricate L10 Fe-Pt/SiO2-core/shell particles with submicron-sized cores less than the critical single-domain size. The fabrication of such core/shell particles was confirmed from morphology observations and XRD analysis of the particles. Although the formation of more desirable core/shell particles with submicron-sized single-crystal cores in the single-domain size range was not achieved, the fabricated core/shell particles showed a high coercivity of 25 kOe.

Lattice-Mismatch-Induced Oscillatory Feature Size and Its Impact on the Physical Limitation of Grain Size

NASA Astrophysics Data System (ADS)

Deng, Jinyu; Li, Huihui; Dong, Kaifeng; Li, Run-Wei; Peng, Yingguo; Ju, Ganping; Hu, Jiangfeng; Chow, Gan Moog; Chen, Jingsheng

2018-03-01

We find that the misfit strain may lead to the oscillatory size distributions of heteroepitaxial nanostructures. In heteroepitaxial FePt thin films grown on single-crystal MgO substrate, ⟨110 ⟩ -oriented mazelike and granular patterns with "quantized" feature sizes are realized in scanning-electron-microscope images. The physical mechanism responsible for the size oscillations is related to the oscillatory nature of the misfit strain energy in the domain-matching epitaxial FePt /MgO system, which is observed by transmission electron microscopy. Based on the experimental observations, a model is built and the results suggest that when the FePt island sizes are an integer times the misfit dislocation period, the misfit strain can be completely canceled by the misfit dislocations. With applying the mechanism, small and uniform grain is obtained on the TiN (200) polycrystalline underlayer, which is suitable for practical application. This finding may offer a way to synthesize nanostructured materials with well-controlled size and size distribution by tuning the lattice mismatch between the epitaxial-grown heterostructure.

Multi-photon excited luminescence of magnetic FePt core-shell nanoparticles.

PubMed

Seemann, K M; Kuhn, B

2014-07-01

We present magnetic FePt nanoparticles with a hydrophilic, inert, and biocompatible silico-tungsten oxide shell. The particles can be functionalized, optically detected, and optically manipulated. To show the functionalization the fluorescent dye NOPS was bound to the FePt core-shell nanoparticles with propyl-triethoxy-silane linkers and fluorescence of the labeled particles were observed in ethanol (EtOH). In aqueous dispersion the NOPS fluorescence is quenched making them invisible using 1-photon excitation. However, we observe bright luminescence of labeled and even unlabeled magnetic core-shell nanoparticles with multi-photon excitation. Luminescence can be detected in the near ultraviolet and the full visible spectral range by near infrared multi-photon excitation. For optical manipulation, we were able to drag clusters of particles, and maybe also single particles, by a focused laser beam that acts as optical tweezers by inducing an electric dipole in the insulated metal nanoparticles. In a first application, we show that the luminescence of the core-shell nanoparticles is bright enough for in vivo multi-photon imaging in the mouse neocortex down to cortical layer 5.

Thickness dependence of exchange anisotropy for (0 0 1) oriented Mn 89Pt 11/NiFe and Mn 80Ir 20/NiFe bilayers

NASA Astrophysics Data System (ADS)

Kume, T.; Yamato, T.; Kato, T.; Tsunashima, S.; Iwata, S.

2007-03-01

Antiferromagnetic layer thickness dependences of exchange anisotropy for (0 0 1) oriented Mn 89Pt 11 ( tAF nm)/Ni 80Fe 20 (5 nm) and Mn 80Ir 20 ( tAF nm)/Ni 80Fe 20 (5 nm) were investigated. For Mn 89Pt 11/NiFe, the exchange bias field appeared at tAF⩾5 nm. This critical thickness was found to be thicker than that of Mn 80Ir 20/NiFe ( tAF=3 nm). The thickness dependence of exchange bias field agreed well with that of 1-fold Fourier amplitude estimated from in-plane torque curves. The large coercivity of about 100 Oe was found for Mn 89Pt 11/NiFe at tAF=30 nm compared to that of Mn 80Ir 20/NiFe. The large coercivity in Mn 89Pt 11/NiFe bilayers seems to result from the large 4-fold anisotropy in their torque curve.

Nitrogen-Coordinated Single Cobalt Atom Catalysts for Oxygen Reduction in Proton Exchange Membrane Fuel Cells

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

Wang, Xiao Xia; Cullen, David A.; Pan, Yung-Tin

Due to the Fenton reaction, the presence of Fe and peroxide in electrodes generates free radicals causing serious degradation of the organic ionomer and the membrane. Pt-free and Fe-free cathode catalysts therefore are urgently needed for durable and inexpensive proton exchange membrane fuel cells (PEMFCs). In this paper, a high-performance nitrogen-coordinated single Co atom catalyst is derived from Co-doped metal-organic frameworks (MOFs) through a one-step thermal activation. Aberration-corrected electron microscopy combined with X-ray absorption spectroscopy virtually verifies the CoN 4 coordination at an atomic level in the catalysts. Through investigating effects of Co doping contents and thermal activation temperature, anmore » atomically Co site dispersed catalyst with optimal chemical and structural properties has achieved respectable activity and stability for the oxygen reduction reaction (ORR) in challenging acidic media (e.g., half-wave potential of 0.80 V vs reversible hydrogen electrode (RHE). The performance is comparable to Fe-based catalysts and 60 mV lower than Pt/C -60 μg Pt cm -2). Fuel cell tests confirm that catalyst activity and stability can translate to high-performance cathodes in PEMFCs. Finally, the remarkably enhanced ORR performance is attributed to the presence of well-dispersed CoN 4 active sites embedded in 3D porous MOF-derived carbon particles, omitting any inactive Co aggregates.« less

Nitrogen-Coordinated Single Cobalt Atom Catalysts for Oxygen Reduction in Proton Exchange Membrane Fuel Cells

DOE PAGES

Wang, Xiao Xia; Cullen, David A.; Pan, Yung-Tin; ...

2018-01-24

Due to the Fenton reaction, the presence of Fe and peroxide in electrodes generates free radicals causing serious degradation of the organic ionomer and the membrane. Pt-free and Fe-free cathode catalysts therefore are urgently needed for durable and inexpensive proton exchange membrane fuel cells (PEMFCs). In this paper, a high-performance nitrogen-coordinated single Co atom catalyst is derived from Co-doped metal-organic frameworks (MOFs) through a one-step thermal activation. Aberration-corrected electron microscopy combined with X-ray absorption spectroscopy virtually verifies the CoN 4 coordination at an atomic level in the catalysts. Through investigating effects of Co doping contents and thermal activation temperature, anmore » atomically Co site dispersed catalyst with optimal chemical and structural properties has achieved respectable activity and stability for the oxygen reduction reaction (ORR) in challenging acidic media (e.g., half-wave potential of 0.80 V vs reversible hydrogen electrode (RHE). The performance is comparable to Fe-based catalysts and 60 mV lower than Pt/C -60 μg Pt cm -2). Fuel cell tests confirm that catalyst activity and stability can translate to high-performance cathodes in PEMFCs. Finally, the remarkably enhanced ORR performance is attributed to the presence of well-dispersed CoN 4 active sites embedded in 3D porous MOF-derived carbon particles, omitting any inactive Co aggregates.« less

Nitrogen-Coordinated Single Cobalt Atom Catalysts for Oxygen Reduction in Proton Exchange Membrane Fuel Cells.

PubMed

Wang, Xiao Xia; Cullen, David A; Pan, Yung-Tin; Hwang, Sooyeon; Wang, Maoyu; Feng, Zhenxing; Wang, Jingyun; Engelhard, Mark H; Zhang, Hanguang; He, Yanghua; Shao, Yuyan; Su, Dong; More, Karren L; Spendelow, Jacob S; Wu, Gang

2018-03-01

Due to the Fenton reaction, the presence of Fe and peroxide in electrodes generates free radicals causing serious degradation of the organic ionomer and the membrane. Pt-free and Fe-free cathode catalysts therefore are urgently needed for durable and inexpensive proton exchange membrane fuel cells (PEMFCs). Herein, a high-performance nitrogen-coordinated single Co atom catalyst is derived from Co-doped metal-organic frameworks (MOFs) through a one-step thermal activation. Aberration-corrected electron microscopy combined with X-ray absorption spectroscopy virtually verifies the CoN 4 coordination at an atomic level in the catalysts. Through investigating effects of Co doping contents and thermal activation temperature, an atomically Co site dispersed catalyst with optimal chemical and structural properties has achieved respectable activity and stability for the oxygen reduction reaction (ORR) in challenging acidic media (e.g., half-wave potential of 0.80 V vs reversible hydrogen electrode (RHE). The performance is comparable to Fe-based catalysts and 60 mV lower than Pt/C -60 μg Pt cm -2 ). Fuel cell tests confirm that catalyst activity and stability can translate to high-performance cathodes in PEMFCs. The remarkably enhanced ORR performance is attributed to the presence of well-dispersed CoN 4 active sites embedded in 3D porous MOF-derived carbon particles, omitting any inactive Co aggregates. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Nano spin-diodes using FePt-NDs with huge on/off current ratio at room temperature

PubMed Central

Makihara, Katsunori; Kato, Takeshi; Kabeya, Yuuki; Mitsuyuki, Yusuke; Ohta, Akio; Oshima, Daiki; Iwata, Satoshi; Darma, Yudi; Ikeda, Mitsuhisa; Miyazaki, Seiichi

2016-01-01

Spin transistors have attracted tremendous interest as new functional devices. However, few studies have investigated enhancements of the ON/OFF current ratio as a function of the electron spin behavior. Here, we found a significantly high spin-dependent current ratio—more than 102 at 1.5 V—when changing the relative direction of the magnetizations between FePt nanodots (NDs) and the CoPtCr-coated atomic force microscope (AFM) probe at room temperature. This means that ON and OFF states were achieved by switching the magnetization of the FePt NDs, which can be regarded as spin-diodes. The FePt magnetic NDs were fabricated by exposing a bi-layer metal stack to a remote H2 plasma (H2-RP) on ~1.7 nm SiO2/Si(100) substrates. The ultrathin bi-layers with a uniform surface coverage are changed drastically to NDs with an areal density as high as ~5 × 1011 cm−2. The FePt NDs exhibit a large perpendicular anisotropy with an out-of-plane coercivity of ~4.8 kOe, reflecting the magneto-crystalline anisotropy of (001) oriented L10 phase FePt. We also designed and fabricated double-stacked FePt-NDs with low and high coercivities sandwiched between an ultra-thin Si-oxide interlayer, and confirmed a high ON/OFF current ratio when switching the relative magnetization directions of the low and high coercivity FePt NDs. PMID:27615374

Interplay between out-of-plane anisotropic L1{sub 1}-type CoPt and in-plane anisotropic NiFe layers in CoPt/NiFe exchange springs

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

Saravanan, P.; Defence Metallurgical Research Laboratory, Hyderabad 500058; Hsu, Jen-Hwa, E-mail: jhhsu@phys.ntu.edu.tw

2014-06-28

Films of L1{sub 1}-type CoPt/NiFe exchange springs were grown with different NiFe (Permalloy) layer thickness (t{sub NiFe} = 0–10 nm). X-ray diffraction analysis reveals that the characteristic peak position of NiFe(111) is not affected by the CoPt-layer—confirming the absence of any inter-diffusion between the CoPt and NiFe layers. Magnetic studies indicate that the magnetization orientation of NiFe layer can be tuned through varying t{sub NiFe} and the perpendicular magnetic anisotropy of L1{sub 1}-type CoPt/NiFe films cannot sustain for t{sub NiFe} larger than 3.0 nm due to the existence of exchange interaction at the interface of L1{sub 1}-CoPt and NiFe layers. Magnetic force microscopy analysismore » on the as-grown samples shows the changes in morphology from maze-like domains with good contrast to hazy domains when t{sub NiFe} ≥ 3.0 nm. The three-dimensional micro-magnetic simulation results demonstrate that the magnetization orientation in NiFe layer is not uniform, which continuously increases from the interface to the top of NiFe layer. Furthermore, the tilt angle of the topmost NiFe layers can be changed over a very wide range from a small number to about 75° by varying t{sub NiFe} from 1 to 10 nm. It is worth noting that there is an abrupt change in the magnetization direction at the interface, for all the t{sub NiFe} investigated. The results of present study demonstrate that the tunable tilted exchange springs can be realized with L1{sub 1}-type CoPt/NiFe bilayers for future applications in three-axis magnetic sensors or advanced spintronic devices demanding inclined magnetic anisotropy.« less

Design of N-Coordinated Dual-Metal Sites: A Stable and Active Pt-Free Catalyst for Acidic Oxygen Reduction Reaction.

PubMed

Wang, Jing; Huang, Zhengqing; Liu, Wei; Chang, Chunran; Tang, Haolin; Li, Zhijun; Chen, Wenxing; Jia, Chunjiang; Yao, Tao; Wei, Shiqiang; Wu, Yuen; Li, Yadong

2017-12-06

We develop a host-guest strategy to construct an electrocatalyst with Fe-Co dual sites embedded on N-doped porous carbon and demonstrate its activity for oxygen reduction reaction in acidic electrolyte. Our catalyst exhibits superior oxygen reduction reaction performance, with comparable onset potential (E onset , 1.06 vs 1.03 V) and half-wave potential (E 1/2 , 0.863 vs 0.858 V) than commercial Pt/C. The fuel cell test reveals (Fe,Co)/N-C outperforms most reported Pt-free catalysts in H 2 /O 2 and H 2 /air. In addition, this cathode catalyst with dual metal sites is stable in a long-term operation with 50 000 cycles for electrode measurement and 100 h for H 2 /air single cell operation. Density functional theory calculations reveal the dual sites is favored for activation of O-O, crucial for four-electron oxygen reduction.

Comparative study of different carbon-supported Fe2O3-Pt catalysts for oxygen reduction reaction.

PubMed

Tellez-Cruz, M M; Padilla-Islas, M A; Pérez-González, M; Solorza-Feria, O

2017-11-01

One of the challenges in electrocatalysis is the adequate dispersion of the catalyst on an appropriate porous support matrix, being up to now the most commonly used the carbon-based supports. To overcome this challenge, carbon supports must first be functionalized to guide the catalyst's nucleation, thereby, improving the dispersion and allowing the use of smaller amount of the catalyst material to achieve a higher electrochemically active surface area. This study present the effect of functionalized Vulcan carbon XC72 (FVC) and functionalized Black Pearl carbon (FBPC) as supports on the catalytic activity of decorated Fe 2 O 3 with Pt. Both carbons were functionalized with HNO 3 and subsequently treated with ethanolamine. Fe 2 O 3 nanoparticles were synthesized by chemical reduction and decorated with platinum by epitaxial growth. Pt and Fe 2 O 3 structural phases were identified by XRD and XPS; the Pt content was measured by XPS, and results showed to a high Pt content in Fe 2 O 3 -Pt/FBPC. TEM micrographs reveal nanoparticles with an average size of 2 nm in both supported catalysts. The Fe 2 O 3 -Pt/FVC catalyst presents the highest specific activity and mass activity, 0.21 mA cm -2 Pt and 140 mA mg Pt -1 , respectively, associated to the appropriate distribution of platinum on the Fe 2 O 3 nanoparticles.

Determination of the spin Hall angle in single-crystalline Pt films from spin pumping experiments

NASA Astrophysics Data System (ADS)

Keller, Sascha; Mihalceanu, Laura; Schweizer, Matthias R.; Lang, Philipp; Heinz, Björn; Geilen, Moritz; Brächer, Thomas; Pirro, Philipp; Meyer, Thomas; Conca, Andres; Karfaridis, Dimitrios; Vourlias, George; Kehagias, Thomas; Hillebrands, Burkard; Papaioannou, Evangelos Th

2018-05-01

We report on the determination of the spin Hall angle in ultra-clean, defect-reduced epitaxial Pt films. By applying vector network analyzer ferromagnetic resonance spectroscopy to a series of single crystalline Fe (12 nm) /Pt (t Pt) bilayers we determine the real part of the spin mixing conductance (4.4 ± 0.2) × 1019 m‑2 and reveal a very small spin diffusion length in the epitaxial Pt (1.1 ± 0.1) nm film. We investigate the spin pumping and ISHE in a stripe microstucture excited by a microwave coplanar waveguide antenna. By using their different angular dependencies, we distinguish between spin rectification effects and the inverse spin Hall effect. The relatively large value of the spin Hall angle (5.7 ± 1.4)% shows that ultra-clean e-beam evaporated non-magnetic materials can also have a comparable spin-to-charge current conversion efficiency as sputtered high resistivity layers.

Systems Ln-Fe-O ( Ln=Eu, Gd): thermodynamic properties of ternary oxides using solid-state electrochemical cells

NASA Astrophysics Data System (ADS)

Parida, S. C.; Rakshit, S. K.; Dash, S.; Singh, Ziley; Prasad, R.; Venugopal, V.

2003-05-01

The standard molar Gibbs energies of formation of LnFeO 3(s) and Ln3Fe 5O 12(s) where Ln=Eu and Gd have been determined using solid-state electrochemical technique employing different solid electrolytes. The reversible e.m.f.s of the following solid-state electrochemical cells have been measured in the temperature range from 1050 to 1255 K. Cell (I): (-)Pt / { LnFeO 3(s)+ Ln2O 3(s)+Fe(s)} // YDT/CSZ // {Fe(s)+Fe 0.95O(s)} / Pt(+); Cell (II): (-)Pt/{Fe(s)+Fe 0.95O(s)}//CSZ//{ LnFeO 3(s)+ Ln3Fe 5O 12(s)+Fe 3O 4(s)}/Pt(+); Cell (III): (-)Pt/{ LnFeO 3(s)+ Ln3Fe 5O 12(s)+Fe 3O 4(s)}//YSZ//{Ni(s)+NiO(s)}/Pt(+); and Cell(IV):(-)Pt/{Fe(s)+Fe 0.95O(s)}//YDT/CSZ//{ LnFeO 3(s)+ Ln3Fe 5O 12(s)+Fe 3O 4(s)}/Pt(+). The oxygen chemical potentials corresponding to the three-phase equilibria involving the ternary oxides have been computed from the e.m.f. data. The standard Gibbs energies of formation of solid EuFeO 3, Eu 3Fe 5O 12, GdFeO 3 and Gd 3Fe 5O 12 calculated by the least-squares regression analysis of the data obtained in the present study are given by Δ fG°m(EuFeO 3, s) /kJ mol -1 (± 3.2)=-1265.5+0.2687( T/K) (1050 ⩽ T/K ⩽ 1570), Δ fG°m(Eu 3Fe 5O 12, s)/kJ mol -1 (± 3.5)=-4626.2+1.0474( T/K) (1050 ⩽ T/K ⩽ 1255), Δ fG°m(GdFeO 3, s) /kJ mol -1 (± 3.2)=-1342.5+0.2539( T/K) (1050 ⩽ T/K ⩽ 1570), and Δ fG°m(Gd 3Fe 5O 12, s)/kJ·mol -1 (± 3.5)=-4856.0+1.0021( T/K) (1050 ⩽ T/K ⩽ 1255). The uncertainty estimates for Δ fG°m include the standard deviation in the e.m.f. and uncertainty in the data taken from the literature. Based on the thermodynamic information, oxygen potential diagrams for the systems Eu-Fe-O and Gd-Fe-O and chemical potential diagrams for the system Gd-Fe-O were computed at 1250 K.

STM/STS study of superconducting properties in Ca10(Pt4As8)(Fe2As2)5

NASA Astrophysics Data System (ADS)

Kim, Jisun; Nam, Hyoungdo; Li, Guorong; Karki, Amar; Shih, Chih-Kang; Zhang, Jiandi; Jin, Rongying; Plummer, E. W.

2014-03-01

Newly discovered iron-based superconductor, Ca10(Pt4As8)(Fe2As2)5 (Tc = 34 K) is studied using scanning tunneling microscopy/spectroscopy (STM/S). Given the symmetry of the crystal structure, several surface terminations are expected with roughly same probability: 1) Ca or partial Ca layer on top Fe2As2; 2) Ca or partial Ca layer on top Pt4As8 layer; 3) A Fe2As2 layer, and; 4) A Pt4As8layer.Surprisingly,Fe2As2 related layers (1 & 3) are rarely observed (less than 1%). Instead, we observe Pt4As8 layers separated by unit-cell-high (~ 1 nm) steps accompanied with Ca or partial Ca layer on top Pt4As8 layer (1 - 2 Å step height). Scanning tunneling spectroscopy reveals different spectra for each surface, with superconducting coherence peaks seen only on Ca layers. We argue that intermediary layers are proximity-coupled to superconducting Fe2As2 layers. The results from Ca10(Pt4As8)(Fe2As2)5 are discussed with the properties observed in other iron-based superconductors. Funded by NSF

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

Molecular dynamic simulation study of plasma etching L10 FePt media in embedded mask patterning (EMP) process

NASA Astrophysics Data System (ADS)

Zhu, Jianxin; Quarterman, P.; Wang, Jian-Ping

2017-05-01

Plasma etching process of single-crystal L10-FePt media [H. Wang et al., Appl. Phys. Lett. 102(5) (2013)] is studied using molecular dynamic simulation. Embedded-Atom Method [M. S. Daw and M. I. Baskes, Phy. Rev. B 29, 6443 (1984); X. W. Zhou, R. A. Johnson and H. N. G. Wadley, Phy. Rev. B 69, 144113 (2004)] is used to calculate the interatomic potential within atoms in FePt alloy, and ZBL potential [J.F. Ziegler, J. P. Biersack and U. Littmark, "The Stopping and Range of Ions in Matter," Volume 1, Pergamon,1985] in comparison with conventional Lennard-Jones "12-6" potential is applied to interactions between etching gas ions and metal atoms. It is shown the post-etch structure defects can include amorphized surface layer and lattice interstitial point defects that caused by etchant ions passed through the surface layer. We show that the amorphized or damaged FePt lattice surface layer (or "magnetic dead-layer") thickness after etching increases with ion energy for Ar ion impacts, but significantly small for He ions at up to 250eV ion energy. However, we showed that He sputtering creates more interstitial defects at lower energy levels and defects are deeper below the surface compared to Ar sputtering. We also calculate the interstitial defect level and depth as dependence on ion energy for both Ar and He ions. Media magnetic property loss due to these defects is also discussed.

Enhancement of spin-Seebeck effect by inserting ultra-thin Fe{sub 70}Cu{sub 30} interlayer

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

Kikuchi, D., E-mail: d.kikuchi@imr.tohoku.ac.jp; WPI Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577; Spin Quantum Rectification Project, ERATO, Japan Science and Technology Agency, Sendai 980-8577

2015-02-23

We report the longitudinal spin-Seebeck effects (LSSEs) for Pt/Fe{sub 70}Cu{sub 30}/BiY{sub 2}Fe{sub 5}O{sub 12} (BiYIG) and Pt/BiYIG devices. The LSSE voltage was found to be enhanced by inserting an ultra-thin Fe{sub 70}Cu{sub 30} interlayer. This enhancement decays sharply with increasing the Fe{sub 70}Cu{sub 30} thickness, suggesting that it is not due to bulk phenomena, such as a superposition of conventional thermoelectric effects, but due to interface effects related to the Fe{sub 70}Cu{sub 30} interlayer. Combined with control experiments using Pt/Fe{sub 70}Cu{sub 30} devices, we conclude that the enhancement of the LSSE voltage in the Pt/Fe{sub 70}Cu{sub 30}/BiYIG devices is attributedmore » to the improvement of the spin-mixing conductance at the Pt/BiYIG interfaces.« less

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.

Formation of metallic clusters in oxide insulators by means of ion beam mixing

NASA Astrophysics Data System (ADS)

Talut, G.; Potzger, K.; Mücklich, A.; Zhou, Shengqiang

2008-04-01

The intermixing and near-interface cluster formation of Pt and FePt thin films deposited on different oxide surfaces by means of Pt+ ion irradiation and subsequent annealing was investigated. Irradiated as well as postannealed samples were investigated using high resolution transmission electron microscopy. In MgO and Y :ZrO2 covered with Pt, crystalline clusters with mean sizes of 2 and 3.5nm were found after the Pt+ irradiations with 8×1015 and 2×1016cm-2 and subsequent annealing, respectively. In MgO samples covered with FePt, clusters with mean sizes of 1 and 2nm were found after the Pt+ irradiations with 8×1015 and 2×1016cm-2 and subsequent annealing, respectively. In Y :ZrO2 samples covered with FePt, clusters up to 5nm in size were found after the Pt+ irradiation with 2×1016cm-2 and subsequent annealing. In LaAlO3 the irradiation was accompanied by a full amorphization of the host matrix and appearance of embedded clusters of different sizes. The determination of the lattice constant and thus the kind of the clusters in samples covered by FePt was hindered due to strong deviation of the electron beam by the ferromagnetic FePt.

Epitaxial Fe{sub 3}Pt/FePt nanocomposites on MgO and SrTiO{sub 3}

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

Casoli, F., E-mail: casoli@imem.cnr.it; Nasi, L.; Cabassi, R.

We have exploited the pseudomorphic growth of the magnetically soft Fe{sub 3}Pt phase on top of L1{sub 0}-FePt to obtain fully epitaxial soft/hard nanocomposites on both MgO(100) and SrTiO{sub 3}(100). The magnetic properties of this new nanocomposite system, driven by the soft/hard exchange-coupling, can be tailored by varying soft phase thickness, soft phase magnetic anisotropy and substrate. Coercivity is strongly reduced by the addition of the soft phase, a reduction which is definitely affected by the nominal composition of the soft phase and by the substrate choice; similarly is the magnetic phase diagram of the composite system. Coercive field decreasesmore » down to 21% of the hard layer value for Fe{sub 3}Pt(5 nm)/FePt(3.55 nm) nanocomposites on SrTiO{sub 3}; this maximum coercivity reduction was obtained with a nominal atomic content of Fe in the soft phase of 80%.« less

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

Engineered Biocompatible Nanoparticles for in Vivo Imaging Applications

PubMed Central

2010-01-01

Iron−platinum alloy nanoparticles (FePt NPs) are extremely promising candidates for the next generation of contrast agents for magnetic resonance (MR) diagnostic imaging and MR-guided interventions, including hyperthermic ablation of solid cancers. FePt has high Curie temperature, saturation magnetic moment, magneto-crystalline anisotropy, and chemical stability. We describe the synthesis and characterization of a family of biocompatible FePt NPs suitable for biomedical applications, showing and discussing that FePt NPs can exhibit low cytotoxicity. The importance of engineering the interface of strongly magnetic NPs using a coating allowing free aqueous permeation is demonstrated to be an essential parameter in the design of new generations of diagnostic and therapeutic MRI contrast agents. We report effective cell internalization of FePt NPs and demonstrate that they can be used for cellular imaging and in vivo MRI applications. This opens the way for several future applications of FePt NPs, including regenerative medicine and stem cell therapy in addition to enhanced MR diagnostic imaging. PMID:20919679

Study of perpendicular anisotropy L1{sub 0}-FePt pseudo spin valves using a micromagnetic trilayer model

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

Ho, Pin, E-mail: hopin@mit.edu; Data Storage Institute, Agency of Science, Technology and Research - A*STAR, 117608 Singapore; Evans, Richard F. L.

2015-06-07

A trilayer micromagnetic model based on the Landau-Lifshitz-Bloch equation of motion is utilized to study the properties of L1{sub 0}-FePt/TiN/L1{sub 0}-FePt pseudo spin valves (PSVs) in direct comparison with experiment. Theoretical studies give an insight on the crystallographic texture, magnetic properties, reversal behavior, interlayer coupling effects, and magneto-transport properties of the PSVs, in particular, with varying thickness of the top L1{sub 0}-FePt and TiN spacer. We show that morphological changes in the FePt layers, induced by varying the FePt layer thickness, lead to different hysteresis behaviors of the samples, caused by changes in the interlayer and intralayer exchange couplings. Suchmore » effects are important for the optimization of the PSVs due to the relationship between the magnetic properties, domain structures, and the magnetoresistance of the device.« less

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.

Distinct local structure of superconducting Ca10M4As8(Fe2As2)5 (M =Pt ,Ir)

NASA Astrophysics Data System (ADS)

Paris, E.; Wakita, T.; Proux, O.; Yokoya, T.; Kudo, K.; Mitsuoka, D.; Kimura, T.; Fujimura, K.; Nishimoto, N.; Ioka, S.; Nohara, M.; Mizokawa, T.; Saini, N. L.

2017-12-01

We have studied the local structure of superconducting Ca10Pt4As8(Fe2As2)5 (Pt10418) and Ca10Ir4As8(Fe2As2)5 (Ir10418) iron arsenides, showing different transition temperatures (Tc=38 and 16 K, respectively), by polarized Fe K -edge extended x-ray absorption fine-structure measurements. Despite the similar average crystal structures, the local structures of the FeAs4 tetrahedra in the two compounds are found to be very different. The FeAs4 in Pt10418 is close to a regular tetrahedron, while it deviates largely in Ir10418. The Fe-Fe correlations in the two compounds are characterized by similar bond-length characteristics; however, the static disorder in Pt10418 is significantly lower than that in Ir10418. The results suggest that the optimized local structure and reduced disorder are the reasons for higher Tc and well-defined electronic states in Pt10418 unlike Ir10418 showing the coexistence of glassy and normal electrons at the Fermi surface, and hence provide direct evidence of the local-structure-driven optimization of the electronic structure and superconductivity in iron arsenides.

Activity and Stability of Dispersed Multi Metallic Pt-based Catalysts for CO Tolerance in Proton Exchange Membrane Fuel Cell Anodes.

PubMed

Hassan, Ayaz; Ticianelli, Edson A

2018-01-01

Studies aiming at improving the activity and stability of dispersed W and Mo containing Pt catalysts for the CO tolerance in proton exchange membrane fuel cell (PEMFC) anodes are revised for the following catalyst systems: (1) a carbon supported PtMo electrocatalyst submitted to heat treatments; (2) Pt and PtMo nanoparticles deposited on carbon-supported molybdenum carbides (Mo2C/C); (3) ternary and quaternary materials formed by PtMoFe/C, PtMoRu/C and PtMoRuFe/C and; (4) Pt nanoparticles supported on tungsten carbide/carbon catalysts and its parallel evaluation with carbon supported PtW catalyst. The heat-treated (600 oC) Pt-Mo/C catalyst showed higher hydrogen oxidation activity in the absence and in the presence of CO and better stability, compared to all other Mo-containing catalysts. PtMoRuFe, PtMoFe, PtMoRu supported on carbon and Pt supported on Mo2C/C exhibited similar CO tolerances but better stability, as compared to as-prepared PtMo supported on carbon. Among the tungsten-based catalysts, tungsten carbide supported Pt catalyst showed reasonable performance and reliable stability in comparison to simple carbon supported PtW catalyst, though an uneven level of catalytic activity towards H2 oxidation in presence of CO is observed for the former as compared to Mo containing catalyst. However, a small dissolution of Mo, Ru, Fe and W from the anodes and their migration toward cathodes during the cell operation is observed. These results indicate that the fuel cell performance and stability has been improved but not yet totally resolved.

Synthesis and Self-Assembly of fcc Phase FePt Nanorods

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

Chen, Min; Pica, Timothy; Jiang, Ying-Bing

2007-05-01

In this paper, we report a synthesis of FePt nanorods by confining decomposition of Fe(CO) 5 and reduction of Pt(caca) 2 in surfactant reverse cylindrical micelles. The controlled nucleation and growth kinetics in confined environment allows easy control over Fe/Pt composition, nanorod uniformity, and nanorod aspect ratio. The FePt nanorods tend to self-assemble into ordered arrays along three-dimensions. Directed assembly under external magnetic field leads to two-dimensional ordered arrays, parallel to the substrate magnetic field. We expect that with optimized external magnetic fields, we should be able to assemble these nanorods into orientated one or two-dimensional arrays, providing a uniformmore » anisotropic magnetic platform for varied applications in enhanced data storage, magneto-electron transport, etc.« less

Single Atomic Iron Catalysts for Oxygen Reduction in Acidic Media: Particle Size Control and Thermal Activation

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

Zhang, Hanguang; Hwang, Sooyeon; Wang, Maoyu

It remains a grand challenge to replace platinum group metal (PGM) catalysts with earth-abundant materials for the oxygen reduction reaction (ORR) in acidic media, which is crucial for large-scale deployment of proton exchange membrane fuel cells (PEMFCs). Here, we report a high-performance atomic Fe catalyst derived from chemically Fe-doped zeolitic imidazolate frameworks (ZIFs) by directly bonding Fe ions to imidazolate ligands within 3D frameworks. Although the ZIF was identified as a promising precursor, the new synthetic chemistry enables the creation of well-dispersed atomic Fe sites embedded into porous carbon without the formation of aggregates. The size of catalyst particles ismore » tunable through synthesizing Fe-doped ZIF nanocrystal precursors in a wide range from 20 to 1000 nm followed by one-step thermal activation. Similar to Pt nanoparticles, the unique size control without altering chemical properties afforded by this approach is able to increase the number of PGM-free active sites. The best ORR activity is measured with the catalyst at a size of 50 nm. Further size reduction to 20 nm leads to significant particle agglomeration, thus decreasing the activity. Using the homogeneous atomic Fe model catalysts, we elucidated the active site formation process through correlating measured ORR activity with the change of chemical bonds in precursors during thermal activation up to 1100 °C. The critical temperature to form active sites is 800 °C, which is associated with a new Fe species with a reduced oxidation number (from Fe3+ to Fe2+) likely bonded with pyridinic N (FeN4) embedded into the carbon planes. Further increasing the temperature leads to continuously enhanced activity, linked to the rise of graphitic N and Fe–N species. The new atomic Fe catalyst has achieved respectable ORR activity in challenging acidic media (0.5 M H2SO4), showing a half-wave potential of 0.85 V vs RHE and leaving only a 30 mV gap with Pt/C (60 μgPt/cm2). Enhanced stability is attained with the same catalyst, which loses only 20 mV after 10 000 potential cycles (0.6–1.0 V) in O2 saturated acid. The high-performance atomic Fe PGM-free catalyst holds great promise as a replacement for Pt in future PEMFCs.« less

Single Atomic Iron Catalysts for Oxygen Reduction in Acidic Media: Particle Size Control and Thermal Activation

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

Zhang, Hanguang; Hwang, Sooyeon; Wang, Maoyu

It remains a grand challenge to replace platinum group metal (PGM) catalysts with earth-abundant materials for the oxygen reduction reaction (ORR) in acidic media, which is crucial for large-scale deployment of proton exchange membrane fuel cells (PEMFCs). We report a high-performance atomic Fe catalyst derived from chemically Fe-doped zeolitic imidazolate frameworks (ZIFs) by directly bonding Fe ions to imidazolate ligands within 3D frameworks. Although the ZIF was identified as a promising precursor, the new synthetic chemistry enables the creation of well-dispersed atomic Fe sites embedded into porous carbon without the formation of aggregates. The size of catalyst particles is tunablemore » through synthesizing Fe-doped ZIF nanocrystal precursors in a wide range from 20 to 1000 nm followed by one-step thermal activation. Similar to Pt nanoparticles, the unique size control without altering chemical properties afforded by this approach is able to increase the number of PGM-free active sites. The best ORR activity is measured with the catalyst at a size of 50 nm. Further size reduction to 20 nm leads to significant particle agglomeration, thus decreasing the activity. In using the homogeneous atomic Fe model catalysts, we elucidated the active site formation process through correlating measured ORR activity with the change of chemical bonds in precursors during thermal activation up to 1100 °C. The critical temperature to form active sites is 800 °C, which is associated with a new Fe species with a reduced oxidation number (from Fe 3+ to Fe 2+) likely bonded with pyridinic N (FeN 4) embedded into the carbon planes. Further increasing the temperature leads to continuously enhanced activity, linked to the rise of graphitic N and Fe–N species. The new atomic Fe catalyst has achieved respectable ORR activity in challenging acidic media (0.5 M H 2SO 4), showing a half-wave potential of 0.85 V vs RHE and leaving only a 30 mV gap with Pt/C (60 μg Pt/cm 2). Finally, enhanced stability is attained with the same catalyst, which loses only 20 mV after 10 000 potential cycles (0.6–1.0 V) in O 2 saturated acid. The high-performance atomic Fe PGM-free catalyst holds great promise as a replacement for Pt in future PEMFCs.« less

Single Atomic Iron Catalysts for Oxygen Reduction in Acidic Media: Particle Size Control and Thermal Activation

DOE PAGES

Zhang, Hanguang; Hwang, Sooyeon; Wang, Maoyu; ...

2017-09-13

It remains a grand challenge to replace platinum group metal (PGM) catalysts with earth-abundant materials for the oxygen reduction reaction (ORR) in acidic media, which is crucial for large-scale deployment of proton exchange membrane fuel cells (PEMFCs). We report a high-performance atomic Fe catalyst derived from chemically Fe-doped zeolitic imidazolate frameworks (ZIFs) by directly bonding Fe ions to imidazolate ligands within 3D frameworks. Although the ZIF was identified as a promising precursor, the new synthetic chemistry enables the creation of well-dispersed atomic Fe sites embedded into porous carbon without the formation of aggregates. The size of catalyst particles is tunablemore » through synthesizing Fe-doped ZIF nanocrystal precursors in a wide range from 20 to 1000 nm followed by one-step thermal activation. Similar to Pt nanoparticles, the unique size control without altering chemical properties afforded by this approach is able to increase the number of PGM-free active sites. The best ORR activity is measured with the catalyst at a size of 50 nm. Further size reduction to 20 nm leads to significant particle agglomeration, thus decreasing the activity. In using the homogeneous atomic Fe model catalysts, we elucidated the active site formation process through correlating measured ORR activity with the change of chemical bonds in precursors during thermal activation up to 1100 °C. The critical temperature to form active sites is 800 °C, which is associated with a new Fe species with a reduced oxidation number (from Fe 3+ to Fe 2+) likely bonded with pyridinic N (FeN 4) embedded into the carbon planes. Further increasing the temperature leads to continuously enhanced activity, linked to the rise of graphitic N and Fe–N species. The new atomic Fe catalyst has achieved respectable ORR activity in challenging acidic media (0.5 M H 2SO 4), showing a half-wave potential of 0.85 V vs RHE and leaving only a 30 mV gap with Pt/C (60 μg Pt/cm 2). Finally, enhanced stability is attained with the same catalyst, which loses only 20 mV after 10 000 potential cycles (0.6–1.0 V) in O 2 saturated acid. The high-performance atomic Fe PGM-free catalyst holds great promise as a replacement for Pt in future PEMFCs.« less

Electric field induced reversible 180° magnetization switching through tuning of interfacial exchange bias along magnetic easy-axis in multiferroic laminates

PubMed Central

Xue, Xu; Zhou, Ziyao; Peng, Bin; Zhu, Mingmin; Zhang, Yijun; Ren, Wei; Ren, Tao; Yang, Xi; Nan, Tianxiang; Sun, Nian X.; Liu, Ming

2015-01-01

E-field control of interfacial exchange coupling and deterministic switching of magnetization have been demonstrated in two sets of ferromagnetic(FM)/antiferromagnetic(AFM)/ferroelectric(FE) multiferroic heterostructures, including NiFe/NiCoO/glass/PZN-PT (011) and NiFe/FeMn/glass/PZN-PT (011). We designed this experiment to achieve exchange bias tuning along the magnetic easy axis, which is critical for realizing reversible 180° magnetization deterministic switching at zero or small magnetic bias. Strong exchange coupling were established across AFM-FM interfaces, which plays an important role in voltage control of magnetization switching. Through the competition between the E-field induced uniaxial anisotropy in ferromagnetic layer and unidirectional anisotropy in antiferromagnetic layer, the exchange bias was significantly shifted by up to |∆Hex|/Hex = 8% in NiFe/FeMn/glass/PZN-PT (011) and 13% in NiFe/NiCoO/glass/PZN-PT (011). In addition, the square shape of the hysteresis loop, as well as a strong shape tunability of |∆Hex|/Hc = 67.5 ~ 125% in NiFe/FeMn/glass/PZN-PT and 30 ~ 38% in NiFe/NiCoO/glass/PZN-PT were achieved, which lead to a near 180° magnetization switching. Electrical tuning of interfacial exchange coupling in FM/AFM/FE systems paves a new way for realizing magnetoelectric random access memories and other memory technologies. PMID:26576658

Electric field induced reversible 180° magnetization switching through tuning of interfacial exchange bias along magnetic easy-axis in multiferroic laminates

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

Xue, Xu; Zhou, Ziyao; Peng, Bin

2015-11-18

E-field control of interfacial exchange coupling and deterministic switching of magnetization have been demonstrated in two sets of ferromagnetic(FM)/antiferromagnetic(AFM)/ferroelectric(FE) multiferroic heterostructures, including NiFe/NiCoO/glass/PZN-PT (011) and NiFe/FeMn/glass/PZN-PT (011). We designed this experiment to achieve exchange bias tuning along the magnetic easy axis, which is critical for realizing reversible 180° magnetization deterministic switching at zero or small magnetic bias. Strong exchange coupling were established across AFM-FM interfaces, which plays an important role in voltage control of magnetization switching. Through the competition between the E-field induced uniaxial anisotropy in ferromagnetic layer and unidirectional anisotropy in antiferromagnetic layer, the exchange bias was significantly shiftedmore » by up to |ΔH ex|/H ex=8% in NiFe/FeMn/glass/PZN-PT (011) and 13% in NiFe/NiCoO/glass/PZN-PT (011). In addition, the square shape of the hysteresis loop, as well as a strong shape tunability of |ΔH ex|/H c=67.5~125% in NiFe/FeMn/glass/PZN-PT and 30~38% in NiFe/NiCoO/glass/PZN-PT were achieved, which lead to a near 180° magnetization switching. Lastly, electrical tuning of interfacial exchange coupling in FM/AFM/FE systems paves a new way for realizing magnetoelectric random access memories and other memory technologies.« less

Electric field induced reversible 180° magnetization switching through tuning of interfacial exchange bias along magnetic easy-axis in multiferroic laminates

NASA Astrophysics Data System (ADS)

Xue, Xu; Zhou, Ziyao; Peng, Bin; Zhu, Mingmin; Zhang, Yijun; Ren, Wei; Ren, Tao; Yang, Xi; Nan, Tianxiang; Sun, Nian X.; Liu, Ming

2015-11-01

E-field control of interfacial exchange coupling and deterministic switching of magnetization have been demonstrated in two sets of ferromagnetic(FM)/antiferromagnetic(AFM)/ferroelectric(FE) multiferroic heterostructures, including NiFe/NiCoO/glass/PZN-PT (011) and NiFe/FeMn/glass/PZN-PT (011). We designed this experiment to achieve exchange bias tuning along the magnetic easy axis, which is critical for realizing reversible 180° magnetization deterministic switching at zero or small magnetic bias. Strong exchange coupling were established across AFM-FM interfaces, which plays an important role in voltage control of magnetization switching. Through the competition between the E-field induced uniaxial anisotropy in ferromagnetic layer and unidirectional anisotropy in antiferromagnetic layer, the exchange bias was significantly shifted by up to |ΔHex|/Hex = 8% in NiFe/FeMn/glass/PZN-PT (011) and 13% in NiFe/NiCoO/glass/PZN-PT (011). In addition, the square shape of the hysteresis loop, as well as a strong shape tunability of |ΔHex|/Hc = 67.5 ~ 125% in NiFe/FeMn/glass/PZN-PT and 30 ~ 38% in NiFe/NiCoO/glass/PZN-PT were achieved, which lead to a near 180° magnetization switching. Electrical tuning of interfacial exchange coupling in FM/AFM/FE systems paves a new way for realizing magnetoelectric random access memories and other memory technologies.

Electric field induced reversible 180° magnetization switching through tuning of interfacial exchange bias along magnetic easy-axis in multiferroic laminates.

PubMed

Xue, Xu; Zhou, Ziyao; Peng, Bin; Zhu, Mingmin; Zhang, Yijun; Ren, Wei; Ren, Tao; Yang, Xi; Nan, Tianxiang; Sun, Nian X; Liu, Ming

2015-11-18

E-field control of interfacial exchange coupling and deterministic switching of magnetization have been demonstrated in two sets of ferromagnetic(FM)/antiferromagnetic(AFM)/ferroelectric(FE) multiferroic heterostructures, including NiFe/NiCoO/glass/PZN-PT (011) and NiFe/FeMn/glass/PZN-PT (011). We designed this experiment to achieve exchange bias tuning along the magnetic easy axis, which is critical for realizing reversible 180° magnetization deterministic switching at zero or small magnetic bias. Strong exchange coupling were established across AFM-FM interfaces, which plays an important role in voltage control of magnetization switching. Through the competition between the E-field induced uniaxial anisotropy in ferromagnetic layer and unidirectional anisotropy in antiferromagnetic layer, the exchange bias was significantly shifted by up to |∆Hex|/Hex = 8% in NiFe/FeMn/glass/PZN-PT (011) and 13% in NiFe/NiCoO/glass/PZN-PT (011). In addition, the square shape of the hysteresis loop, as well as a strong shape tunability of |∆Hex|/Hc = 67.5 ~ 125% in NiFe/FeMn/glass/PZN-PT and 30 ~ 38% in NiFe/NiCoO/glass/PZN-PT were achieved, which lead to a near 180° magnetization switching. Electrical tuning of interfacial exchange coupling in FM/AFM/FE systems paves a new way for realizing magnetoelectric random access memories and other memory technologies.

Investigation of the annealing temperature dependence of the spin pumping in Co20Fe60B20/Pt systems

NASA Astrophysics Data System (ADS)

Belmeguenai, M.; Aitoukaci, K.; Zighem, F.; Gabor, M. S.; Petrisor, T.; Mos, R. B.; Tiusan, C.

2018-03-01

Co20Fe60B20/Pt systems with variable thicknesses of Co20Fe60B20 and of Pt have been sputtered and then annealed at various temperatures (Ta) up to 300 °C. Microstrip line ferromagnetic resonance (MS-FMR) has been used to investigate Co20Fe60B20 and Pt thickness dependencies of the magnetic damping enhancement due to the spin pumping. Using diffusion and ballistic models for spin pumping, the spin mixing conductance and the spin diffusion length have been deduced from the Co20Fe60B20 and the Pt thickness dependencies of the Gilbert damping parameter α of the Co20Fe60B20/Pt heterostructures, respectively. Within the ballistic simple model, both the spin mixing conductance at the CoFeB/Pt interface and the spin-diffusion length of Pt increase with the increasing annealing temperature and show a strong enhancement at 300 °C annealing temperature. In contrast, the spin mixing conductance, which increases with Ta, shows a different trend to the spin diffusion length when using the diffusion model. Moreover, MS-FMR measurements revealed that the effective magnetization varies linearly with the Co20Fe60B20 inverse thickness due to the perpendicular interface anisotropy, which is found to decrease as the annealing temperature increases. It also revealed that the angular dependence of the resonance field is governed by small uniaxial anisotropy which is found to vary linearly with the Co20Fe60B20 inverse thickness of the annealed films, in contrast to that of the as grown ones.

Surface structure of MgO underlayer with Ti diffusion for (002) oriented L10 FePt-based heat assisted magnetic recording media

NASA Astrophysics Data System (ADS)

Hinata, Sintaro; Jo, Shin; Saito, Shin

2018-05-01

Surface morphology of the MgO layer and magnetic properties of FePt-C layer deposited on the MgO were investigated for the FePt-based heat assisted magnetic recording media. Stacking structure of the underlayer for the FePt-C layer was MgO (0-5 nm)/Cr80Mn20 (0-30 nm)/Cr50Ti50 (0-50 nm)/glass sub.. Surface observation result for the MgO film by using an atomic force microscope revealed the existence of nodules with a height of about 2 nm and a network-like convex structure with a height difference of about sub nm (boundary wall, BW) on the MgO crystal grain boundary. Density of the nodules largely depends on the surface roughness of the CrTi layer, RaCrTi and it is suppressed from 10 to 2/0.5 μm2 by reducing RaCrTi from 420 to 260 pm. Height of the BW depends on thickness of the MgO layer, tMgO and it can be suppressed by reducing tMgO to less than 4 nm. From the cross-sectional energy dispersive x-ray mapping, it is clarified that the BW is formed by atomic diffusion of Ti atoms from CrTi layer due to the substrate heating process, and a compound consists of Mg, Ti and O atoms. This BW can be used as a template to magnetically isolate the FePt column in the FePt-based granular film, such as FePt-SiO2, if the size of the BW is reduced to less than 10 nm. M-H loop of the FePt-C granular film deposited on the underlayer showed that the nodule and BW induce oxidation of the FePt grains, and reduction of intergranular exchange coupling.

Giant Electric Field Control of Magnetism and Narrow Ferromagnetic Resonance Linewidth in FeCoSiB/Si/SiO2/PMN PT Multiferroic Heterostructures (Open Access Author’s Manuscript)

DTIC Science & Technology

2016-06-06

the widely used lead zirconate titanate ceramics which have a typical piezoelectric coefficient d31 of ~- 200pC/N, PMN-PT single crystals used in...substrate clamping effect, therefore, a relatively giant tunability can be obtained. However, the normally large roughness of piezoelectric layer...is the saturation magnetostriction constant, Y the Young’s modulus of the magnetic film, deff the effective piezoelectric coefficient, E

First-Principles Study on the Gilbert Damping Constants of Transition Metal Alloys, Fe--Ni and Fe--Pt Systems

NASA Astrophysics Data System (ADS)

Sakuma, Akimasa

2012-08-01

We adapt the tight-binding linear muffin-tin orbital (TB-LMTO) method to the torque-correlation model for the Gilbert damping constant α and perform the first-principles calculation for disordered transition metal alloys, Fe--Ni and Fe--Pt systems, within the framework of the CPA. Quantitatively, the calculated α values are about one-half of the experimental values, whereas the variations in the Fermi level dependence of α are much larger than these discrepancies. As expected, we confirm in the (Fe--Ni)1-XPtX and FePt systems that Pt atoms certainly enhance α owing to their large spin--orbit coupling. For the disordered alloys, we find that α decreases with increasing chemical degree of order in a wide range.

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

Optimization of L1{sub 0} FePt/Fe{sub 45}Co{sub 55} thin films for rare earth free permanent magnet applications

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

Giannopoulos, G., E-mail: g.giannopoulos@inn.demokritos.gr; Psycharis, V.; Niarchos, D.

The magnetic properties of magnetron sputtered bilayers consisting of Fe{sub 45}Co{sub 55} ultrathin layers on top of L1{sub 0} FePt films epitaxially grown on MgO substrates are studied in view of their possible application as rare earth free permanent magnets. It is found that FePt layers induce a tetragonal distortion to the Fe-Co layers which leads to increased anisotropy. This allows to take advantage of the Fe-Co high magnetic moment with less significant loss of the coercivity compared to a typical hard/soft exchange spring system. A maximum energy product approaching 50 MGOe is obtained for a FePt(7 ML)/FeCo/(5 ML) sample.more » The results are in accordance with first-principles computational methods, which predict that even higher energy products are possible for micromagnetically optimized microstructures.« less

Universal Strategy for Ultrathin Pt-M (M = Fe, Co, Ni) Nanowires for Efficient Catalytic Hydrogen Generation.

PubMed

Bai, Shuxing; Huang, Bolong; Shao, Qi; Huang, Xiaoqing

2018-06-25

Methanol (CH 3 OH) reformation with water (H 2 O) to in situ release hydrogen (H 2 ) is regarded as a hopeful H 2 production approach for polymer electrolyte membrane fuel cells, while developing highly efficient CH 3 OH reformation catalysts still remains a great challenge. Herein, a series of Pt-based ultrafine nanowires (UNWs) with high surface atom ratio are used as highly active and stable catalysts for CH 3 OH reformation to H 2 . By tuning Pt 3 M (M = Fe, Co, Ni), support and the composition of the Pt x Fe UNWs, the optimized Pt 4 Fe UNWs/Al 2 O 3 exhibits excellent catalytic behaviors with the high H 2 turnover frequency reaching to 2035.8 h -1 , more than 4 times higher than that of Pt UNWs/Al 2 O 3 . The reaction mechanism investigated by diffuse reflectance infrared Fourier transform spectroscopy turns out that the production of H 2 undergoes the CH 3 OH decomposition to *CO and gas-shift reaction of *CO with H 2 O. Combing with the XPS result and the density functional theory calculations, the high CH 3 OH reformation activity of Pt 4 Fe UNWs/Al 2 O 3 is attributable to synergism between Pt and Fe, which facilitates H 2 desorption and intermediate HCOO* and *COO formations via the reaction between *CO and OH - .

Impact of active phase chemical composition and dispersity on catalytic behavior in PROX reaction

NASA Astrophysics Data System (ADS)

Cherkezova-Zheleva, Z.; Paneva, D.; Todorova, S.; Kolev, H.; Shopska, M.; Yordanova, I.; Mitov, I.

2014-04-01

Iron and iron-platinum catalysts supported on activated carbon have been successfully synthesized by wet impregnation method and low-temperature treatment in inert atmosphere. The content of the supported phases corresponds to 10 wt % Fe and 0.5 wt % Pt. Four catalytic samples were synthesized: Sample A—activated carbon impregnated with Fe nitrate; Sample B—activated carbon impregnated with Pt salt; Sample C—activated carbon impregnated consequently with Fe and Pt salts; Sample D—activated carbon impregnated simultaneously with Fe and Pt salts. The as-prepared materials were characterized by Mössbauer spectroscopy, X-ray diffraction, infrared and X-ray photoelectron spectroscopy. The spectra show that the activated carbon support and the preparation procedure give rise to the synthesis of isolated metal Pt ions and ultradispersed Fe and Pt oxide species. Probably the presence of different functional groups of activated carbon gives rise to registered very high dispersion of loaded species on support. The catalytic tests were carried out in PROX reaction. A lower activity of bimetallic Pt-Fe samples was explained with the increase in surface oxygen species as a result of predomination of iron oxide on the support leading to the increase in selectivity to the H2 oxidation. Partial agglomeration of supported iron oxide phase was registered after catalytic tests.

Thin films sputtered from Ba{sub 2}NdFeNb{sub 4}O{sub 15} multiferroic targets on BaFe{sub 12}O{sub 19} coated substrates

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

Bodeux, Romain; Univ. Bordeaux, ICMCB, UPR 9048, F-33600 Pessac; Michau, Dominique, E-mail: dominique.michau@icmcb.cnrs.fr

2016-09-15

Highlights: • Synthesis of Ba{sub 2}NdFeNb{sub 4}O{sub 15}/BaFe{sub 12}O{sub 19} (BaM) heterostructures by RF magnetron sputtering. • Growth of TTB layer were retained regardless of the underlayer (Pt bottom electrode or BaM). • Dielectric and magnetic properties were obtained from the Pt/TTB/BaM/Pt stacks. - Abstract: Ba{sub 2}NdFeNb{sub 4}O{sub 15} tetragonal tungsten bronze (TTB)/BaFe{sub 12}O{sub 19} (BaM) hexaferrite bilayers have been grown by RF magnetron sputtering on Pt/TiO{sub 2}/SiO{sub 2}/Si (PtS) substrates. The BaM layer is textured along (0 0 1) while the TTB layer is multioriented regardless of the PtS or BaM/PtS substrate. Dielectric properties of TTB films are similarmore » to those of bulk, i.e., ε ∼ 150 and a magnetic hysteresis loop is obtained from TTB/BaM bilayers, thanks to the BaM component. This demonstrates the possibility of transferring to 2 dimensional structures the composite multiferroic system TTB/BaM previously identified in 3 dimensional bulk ceramics.« less

Large lattice mismatch effects on the epitaxial growth and magnetic properties of FePt films

NASA Astrophysics Data System (ADS)

Deng, Jinyu; Dong, Kaifeng; Yang, Ping; Peng, Yingguo; Ju, Ganping; Hu, Jiangfeng; Chow, Gan Moog; Chen, Jingsheng

2018-01-01

Heteroepitaxial film growth is crucial for magnetic and electronic devices. In this work, we reported the effects of the large lattice mismatch and film thickness on the epitaxial growth and magnetic properties of FePt films on ZrxTi1-xN (0 0 1) intermediate layer. FePt films with different thickness were deposited on ZrTiN intermediate layers with various doping concentration of TiN in ZrN. The increase in doping concentration of TiN caused a decrease in the lattice parameters of ZrTiN intermediate layer. It was found that (0 0 1) epitaxy of FePt 10 nm films was only achieved on ZrTiN intermediate layer when the TiN composition was ≥25 vol%, while (0 0 1) texture of 5 nm films was achieved on ZrTiN intermediate layer with a minimum of 50 vol% TiN composition. The in-plane lattice constants of FePt and Zr0.70Ti0.30N (25 vol% TiN) were 3.870 Å and 4.476 Å, respectively, which resulted in a lattice mismatch as large as 15.7%. These large lattice mismatch heterostructures adopted 7/6 domain matching epitaxy. The magneto-crystalline anisotropy of FePt films was improved with the increase in lattice mismatch. Intrinsic magnetic properties were extrapolated for FePt (30 nm)/Zr0.70Ti0.30N (30 nm)/TaN (30 nm)/MgO, and the Ms(0 K) and K1(0 K) were 1042 emu/cc and 5.10 × 107 erg/cc, respectively, which is comparable to that of bulk L10 FePt.

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.

A Comparative Study of Hydrodeoxygenation of Furfural Over Fe/Pt(111) and Fe/Mo 2C Surfaces

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

Wan, Weiming; Jiang, Zhifeng; Chen, Jingguang G.

It is desirable to convert biomass-derived furfural to 2-methylfuran through the hydrodeoxygenation (HDO) reaction using an inexpensive catalyst with high stability. In this work, Mo 2C was used as an alternative substrate to replace precious Pt to support monolayer Fe for the HDO reaction of furfural. The HDO activity and stability of Fe/Pt(111) and Fe/Mo 2C/Mo(110) surfaces were compared. Density functional theory calculations and vibrational spectroscopy results indicated that both surfaces bonded to furfural with similar adsorption geometries and should be active toward the furfural HDO reaction. Temperature programmed desorption experiments confirmed a similar HDO activity between the two surfaces,more » with Fe/Mo 2C/Mo(110) being more thermally stable than Fe/Pt(111). As a result, the combined theoretical and experimental results demonstrated that Fe/Mo 2C should be a promising non-precious metal catalyst for the HDO reaction of furfural to produce 2-methylfuran.« less

A Comparative Study of Hydrodeoxygenation of Furfural Over Fe/Pt(111) and Fe/Mo 2C Surfaces

DOE PAGES

Wan, Weiming; Jiang, Zhifeng; Chen, Jingguang G.

2018-01-19

It is desirable to convert biomass-derived furfural to 2-methylfuran through the hydrodeoxygenation (HDO) reaction using an inexpensive catalyst with high stability. In this work, Mo 2C was used as an alternative substrate to replace precious Pt to support monolayer Fe for the HDO reaction of furfural. The HDO activity and stability of Fe/Pt(111) and Fe/Mo 2C/Mo(110) surfaces were compared. Density functional theory calculations and vibrational spectroscopy results indicated that both surfaces bonded to furfural with similar adsorption geometries and should be active toward the furfural HDO reaction. Temperature programmed desorption experiments confirmed a similar HDO activity between the two surfaces,more » with Fe/Mo 2C/Mo(110) being more thermally stable than Fe/Pt(111). As a result, the combined theoretical and experimental results demonstrated that Fe/Mo 2C should be a promising non-precious metal catalyst for the HDO reaction of furfural to produce 2-methylfuran.« less

Study of interlayer coupling between FePt and FeCoB thin films through MgO spacer layer

NASA Astrophysics Data System (ADS)

Singh, Sadhana; Kumar, Dileep; Gupta, Mukul; Reddy, V. Raghvendra

2017-05-01

Interlayer exchange coupling between hard-FePt and soft-FeCoB magnetic layers has been studied with increasing thickness of insulator MgO spacer layer in FePt/MgO/FeCoB sandwiched structure. A series of the samples were prepared in identical condition using ion beam sputtering method and characterized for their magnetic and structural properties using magneto-optical Kerr effect (MOKE) and X-ray reflectivity measurements. The nature of coupling between FePt and FeCoB was found to be ferromagnetic which decreases exponentially with increasing thickness of MgO layer. At very low thickness of MgO layer, both layers were found strongly coupled thus exhibiting coherent magnetization reversal. At higher thickness, both layers were found decoupled and magnetization reversal occurred at different switching fields. Strong coupling at very low thickness is attributed to pin holes in MgO layer which lead to direct coupling whereas on increasing thickness, coupling may arise due to magneto-static interactions.

On the advantages of spring magnets compared to pure FePt: Strategy for rare-earth free permanent magnets following a bottom-up approach

NASA Astrophysics Data System (ADS)

Pousthomis, M.; Garnero, C.; Marcelot, C. G.; Blon, T.; Cayez, S.; Cassignol, C.; Du, V. A.; Krispin, M.; Arenal, R.; Soulantica, K.; Viau, G.; Lacroix, L.-M.

2017-02-01

Nanostructured magnets benefiting from efficient exchange-coupling between hard and soft grains represent an appealing approach for integrated miniaturized magnetic power sources. Using a bottom-up approach, nanostructured materials were prepared from binary assemblies of bcc FeCo and fcc FePt nanoparticles and compared with pure L10-FePt materials. The use of a bifunctional mercapto benzoic acid yields homogeneous assemblies of the two types of particles while reducing the organic matter amount. The 650 °C thermal annealing, mandatory to allow the L10-FePt phase transition, led to an important interdiffusion and thus decreased drastically the amount of soft phase present in the final composites. The analysis of recoil curves however evidenced the presence of an efficient interphase exchange coupling, which allows obtaining better magnetic performances than pure L10 FePt materials, energy product above 100 kJ m-3 being estimated for a Pt content of only 33%. These results clearly evidenced the interest of chemically grown nanoparticles for the preparation of performant spring-magnets, opening promising perspective for integrated subcentimetric magnets with optimized properties.

Optimizing the ORR activity of Pd based nanocatalysts by tuning their strain and particle size

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

Xiao, Weiping; Liutheviciene Cordeiro, Marco Aurelio; Gong, Mingxing

Controlling of the particle size and surface strain is the key to tuning the surface chemistry and optimizing the catalytic performance of electrocatalysts. In this study, we show that by introducing both Fe and Co into Pd lattices, the surface strain of Pd nanocatalysts can be tuned to optimize their oxygen reduction activity in both fuel cells and Zn–air batteries. The Pd 2FeCo/C alloy particles are uniquely coated with an ultrathin Fe 2O 3 shell which is in situ formed during a thermal annealing treatment. The thin shell acts as an effective barrier that prevents the coalescence and ripening ofmore » Pd 2FeCo/C nanoparticles. Compared with Pd/C, Pd 2FeCo/C exhibits higher catalytic activity and long-term stability for the ORR, signifying changes in catalytic behavior due to particle sizes and strain effects. Moreover, by spontaneous decoration of Pt on the surface of Pd 2FeCo/C, the Pd 2FeCo@Pt/C core@shell structure was formed and the Pt mass activity was about 37.6 and 112.5 times higher than that on Pt/C in a 0.1 M HClO 4 and KOH solution at 0.9 V, respectively, suggesting an enhanced ORR performance after Pt decoration. More interestingly, Pd 2FeCo@Pt/C also shows a power density of ~308 mW cm -2, which is much higher than that of Pt/C (175 mW cm -2), and excellent durability in a home-made Zn–air battery.« less

Optimizing the ORR activity of Pd based nanocatalysts by tuning their strain and particle size

DOE PAGES

Xiao, Weiping; Liutheviciene Cordeiro, Marco Aurelio; Gong, Mingxing; ...

2017-04-18

Controlling of the particle size and surface strain is the key to tuning the surface chemistry and optimizing the catalytic performance of electrocatalysts. In this study, we show that by introducing both Fe and Co into Pd lattices, the surface strain of Pd nanocatalysts can be tuned to optimize their oxygen reduction activity in both fuel cells and Zn–air batteries. The Pd 2FeCo/C alloy particles are uniquely coated with an ultrathin Fe 2O 3 shell which is in situ formed during a thermal annealing treatment. The thin shell acts as an effective barrier that prevents the coalescence and ripening ofmore » Pd 2FeCo/C nanoparticles. Compared with Pd/C, Pd 2FeCo/C exhibits higher catalytic activity and long-term stability for the ORR, signifying changes in catalytic behavior due to particle sizes and strain effects. Moreover, by spontaneous decoration of Pt on the surface of Pd 2FeCo/C, the Pd 2FeCo@Pt/C core@shell structure was formed and the Pt mass activity was about 37.6 and 112.5 times higher than that on Pt/C in a 0.1 M HClO 4 and KOH solution at 0.9 V, respectively, suggesting an enhanced ORR performance after Pt decoration. More interestingly, Pd 2FeCo@Pt/C also shows a power density of ~308 mW cm -2, which is much higher than that of Pt/C (175 mW cm -2), and excellent durability in a home-made Zn–air battery.« less

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.

Catalysts synthesized by selective deposition of Fe onto Pt for the water-gas shift reaction

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

Aragao, Isaias Barbosa; Ro, Insoo; Liu, Yifei

FePt bimetallic catalysts with intimate contact between the two metals were synthesized by controlled surface reactions (CSR) of (cyclohexadiene)iron tricarbonyl with hydrogen-treated supported Pt nanoparticles. Adsorption of the iron precursor on a Pt/SiO 2 catalyst was studied, showing that the Fe loading could be increased by performing multiple CSR cycles, and the efficiency of this process was linked to the renewal of adsorption sites by a reducing pretreatment. Here, the catalytic activity of these bimetallic catalysts for the water gas shift reaction was improved due to promotion by iron, likely linked to H 2O activation on FeO x species atmore » or near the Pt surface, mostly in the (II) oxidation state.« less

Catalysts synthesized by selective deposition of Fe onto Pt for the water-gas shift reaction

DOE PAGES

Aragao, Isaias Barbosa; Ro, Insoo; Liu, Yifei; ...

2017-10-04

FePt bimetallic catalysts with intimate contact between the two metals were synthesized by controlled surface reactions (CSR) of (cyclohexadiene)iron tricarbonyl with hydrogen-treated supported Pt nanoparticles. Adsorption of the iron precursor on a Pt/SiO 2 catalyst was studied, showing that the Fe loading could be increased by performing multiple CSR cycles, and the efficiency of this process was linked to the renewal of adsorption sites by a reducing pretreatment. Here, the catalytic activity of these bimetallic catalysts for the water gas shift reaction was improved due to promotion by iron, likely linked to H 2O activation on FeO x species atmore » or near the Pt surface, mostly in the (II) oxidation state.« less

Supergene neoformation of Pt-Ir-Fe-Ni alloys: multistage grains explain nugget formation in Ni-laterites

NASA Astrophysics Data System (ADS)

Aiglsperger, Thomas; Proenza, Joaquín A.; Font-Bardia, Mercè; Baurier-Aymat, Sandra; Galí, Salvador; Lewis, John F.; Longo, Francisco

2017-10-01

Ni-laterites from the Dominican Republic host rare but extremely platinum-group element (PGE)-rich chromitites (up to 17.5 ppm) without economic significance. These chromitites occur either included in saprolite (beneath the Mg discontinuity) or as `floating chromitites' within limonite (above the Mg discontinuity). Both chromitite types have similar iridium-group PGE (IPGE)-enriched chondrite normalized patterns; however, chromitites included in limonite show a pronounced positive Pt anomaly. Investigation of heavy mineral concentrates, obtained via hydroseparation techniques, led to the discovery of multistage PGE grains: (i) Os-Ru-Fe-(Ir) grains of porous appearance are overgrown by (ii) Ni-Fe-Ir and Ir-Fe-Ni-(Pt) phases which are overgrown by (iii) Pt-Ir-Fe-Ni mineral phases. Whereas Ir-dominated overgrowths prevail in chromitites from the saprolite, Pt-dominated overgrowths are observed within floating chromitites. The following formation model for multistage PGE grains is discussed: (i) hypogene platinum-group minerals (PGM) (e.g. laurite) are transformed to secondary PGM by desulphurization during serpentinization; (ii) at the stages of serpentinization and/or at the early stages of lateritization, Ir is mobilized and recrystallizes on porous surfaces of secondary PGM (serving as a natural catalyst) and (iii) at the late stages of lateritization, biogenic mediated neoformation (and accumulation) of Pt-Ir-Fe-Ni nanoparticles occurs. The evidence presented in this work demonstrates that in situ growth of Pt-Ir-Fe-Ni alloy nuggets of isometric symmetry is possible within Ni-laterites from the Dominican Republic.

Enhanced Performance of Photoelectrochemical Water Splitting with ITO@α-Fe2O3 Core-Shell Nanowire Array as Photoanode.

PubMed

Yang, Jie; Bao, Chunxiong; Yu, Tao; Hu, Yingfei; Luo, Wenjun; Zhu, Weidong; Fu, Gao; Li, Zhaosheng; Gao, Hao; Li, Faming; Zou, Zhigang

2015-12-09

Hematite (α-Fe2O3) is one of the most promising candidates for photoelectrodes in photoelectrochemical water splitting system. However, the low visible light absorption coefficient and short hole diffusion length of pure α-Fe2O3 limits the performance of α-Fe2O3 photoelectrodes in water splitting. Herein, to overcome these drawbacks, single-crystalline tin-doped indium oxide (ITO) nanowire core and α-Fe2O3 nanocrystal shell (ITO@α-Fe2O3) electrodes were fabricated by covering the chemical vapor deposited ITO nanowire array with compact thin α-Fe2O3 nanocrystal film using chemical bath deposition (CBD) method. The J-V curves and IPCE of ITO@α-Fe2O3 core-shell nanowire array electrode showed nearly twice as high performance as those of the α-Fe2O3 on planar Pt-coated silicon wafers (Pt/Si) and on planar ITO substrates, which was considered to be attributed to more efficient hole collection and more loading of α-Fe2O3 nanocrystals in the core-shell structure than planar structure. Electrochemical impedance spectra (EIS) characterization demonstrated a low interface resistance between α-Fe2O3 and ITO nanowire arrays, which benefits from the well contact between the core and shell. The stability test indicated that the prepared ITO@α-Fe2O3 core-shell nanowire array electrode was stable under AM1.5 illumination during the test period of 40,000 s.

High Performance Fe- and N- Doped Carbon Catalyst with Graphene Structure for Oxygen Reduction

NASA Astrophysics Data System (ADS)

Peng, Hongliang; Mo, Zaiyong; Liao, Shijun; Liang, Huagen; Yang, Lijun; Luo, Fan; Song, Huiyu; Zhong, Yiliang; Zhang, Bingqing

2013-05-01

Proton exchange membrane fuel cells are promising candidates for a clean and efficient energy conversion in the future, the development of carbon based inexpensive non-precious metal ORR catalyst has becoming one of the most attractive topics in fuel cell field. Herein we report a Fe- and N- doped carbon catalyst Fe-PANI/C-Mela with graphene structure and the surface area up to 702 m2 g-1. In 0.1 M HClO4 electrolyte, the ORR onset potential for the catalyst is high up to 0.98 V, and the half-wave potential is only 60 mV less than that of the Pt/C catalyst (Loadings: 51 μg Pt cm-2). The catalyst shows high stability after 10,000 cyclic voltammetry cycles. A membrane electrode assembly made with the catalyst as a cathode is tested in a H2-air single cell, the maximum power density reached ~0.33 W cm2 at 0.47 V.

Exchange-coupled hard magnetic Fe-Co/CoPt nanocomposite films fabricated by electro-infiltration

NASA Astrophysics Data System (ADS)

Wen, Xiao; Andrew, Jennifer S.; Arnold, David P.

2017-05-01

This paper introduces a potentially scalable electro-infiltration process to produce exchange-coupled hard magnetic nanocomposite thin films. Fe-Co/CoPt nanocomposite films are fabricated by deposition of CoFe2O4 nanoparticles onto Si substrate, followed by electroplating of CoPt. Samples are subsequently annealed under H2 to reduce the CoFe2O4 to magnetically soft Fe-Co and also induce L10 ordering in the CoPt. Resultant films exhibit 0.97 T saturation magnetization, 0.70 T remanent magnetization, 127 kA/m coercivity and 21.8 kJ/m3 maximum energy density. First order reversal curve (FORC) analysis and δM plot are used to prove the exchange coupling between soft and hard magnetic phases.

Fe Isolated Single Atoms on S, N Codoped Carbon by Copolymer Pyrolysis Strategy for Highly Efficient Oxygen Reduction Reaction.

PubMed

Li, Qiheng; Chen, Wenxing; Xiao, Hai; Gong, Yue; Li, Zhi; Zheng, Lirong; Zheng, Xusheng; Yan, Wensheng; Cheong, Weng-Chon; Shen, Rongan; Fu, Ninghua; Gu, Lin; Zhuang, Zhongbin; Chen, Chen; Wang, Dingsheng; Peng, Qing; Li, Jun; Li, Yadong

2018-06-01

Heteroatom-doped Fe-NC catalyst has emerged as one of the most promising candidates to replace noble metal-based catalysts for highly efficient oxygen reduction reaction (ORR). However, delicate controls over their structure parameters to optimize the catalytic efficiency and molecular-level understandings of the catalytic mechanism are still challenging. Herein, a novel pyrrole-thiophene copolymer pyrolysis strategy to synthesize Fe-isolated single atoms on sulfur and nitrogen-codoped carbon (Fe-ISA/SNC) with controllable S, N doping is rationally designed. The catalytic efficiency of Fe-ISA/SNC shows a volcano-type curve with the increase of sulfur doping. The optimized Fe-ISA/SNC exhibits a half-wave potential of 0.896 V (vs reversible hydrogen electrode (RHE)), which is more positive than those of Fe-isolated single atoms on nitrogen codoped carbon (Fe-ISA/NC, 0.839 V), commercial Pt/C (0.841 V), and most reported nonprecious metal catalysts. Fe-ISA/SNC is methanol tolerable and shows negligible activity decay in alkaline condition during 15 000 voltage cycles. X-ray absorption fine structure analysis and density functional theory calculations reveal that the incorporated sulfur engineers the charges on N atoms surrounding the Fe reactive center. The enriched charge facilitates the rate-limiting reductive release of OH* and therefore improved the overall ORR efficiency. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Magnetic moment in single crystalline BaFe2-xZnxAs2

NASA Astrophysics Data System (ADS)

Guo, Yanfeng; Wang, Xia; Li, Jun; Yamaura, Kazunari; Takayama-Muromachi, Eiji

2012-02-01

Nature of the magnetism for iron-based superconductors (FeSCs) has been actively studied since the discovery of this new family of compounds in 2008, largely owing to its significance for interpreting the paring mechanism. The approach through impurity substitution to shed light into this issue is always one of major ways. The substitution shows distinct responses to species of impurities, where partially replacement of Fe in parent FeSCs with a variety of d-metals like Co, Ni Ru, Rh, Pd, Ir, and Pt generally results in superconductivity, while recent progress in Zn doped FeSCs gives rather contrary result, where Zn severely degenerates the TC. Herein we show the magnetic and electrical studies on BaFe2-xZnxAs2 single crystals. Nonmagnetic Zn doping progressively suppresses the SDW without resulting in superconductivity, while it alternatively develops the spin-glass state, possibly suggestive of local magnetic moment around the Fe sites induced by Zn. The characterizations by X-ray diffraction, magnetic and electrical transport properties, specific heat capacity, and Hall coefficient have been done and the results will be discussed in detail.

Size-depressed critical temperatures for the order-disorder transition of FePt, CoPt, FePb, Cu2S, and ZnS nanostructures

NASA Astrophysics Data System (ADS)

Jiang, R.; Zhou, Z. F.; Yang, X. X.; Guo, N. G.; Qi, W. H.; Sun, C. Q.

2013-01-01

The size dependency of the critical temperature (TC) for the order-disorder phase transitions of both the bimetallic and the chalcogenide nanoclusters is shown to follow the rule of bond order-length-strength correlation. The loss of the cohesive energy of the undercoordinated atoms in the surface skin dictates the structural stability. Theoretical reproduction of the size TC trends of FePt, CoPt, FePb, Cu2S, and ZnS nanostructures not only confirms our expectations without involving the concepts of surface energy or entropy used for continuum bulk materials but also provides guideline for engineering nanostructured alloys or compounds.

Enhanced catalytic performance for methane combustion of 3DOM CoFe2O4 by co-loading MnOx and Pd-Pt alloy nanoparticles

NASA Astrophysics Data System (ADS)

Li, Xiangyu; Liu, Yuxi; Deng, Jiguang; Xie, Shaohua; Zhao, Xingtian; Zhang, Yang; Zhang, Kunfeng; Arandiyan, Hamidreza; Guo, Guangsheng; Dai, Hongxing

2017-05-01

Three-dimensionally ordered macroporous (3DOM) CoFe2O4, zMnOx/3DOM CoFe2O4 (z = 4.99-12.30 wt%), and yPd-Pt/6.70 wt% MnOx/3DOM CoFe2O4 (y = 0.44-1.81 wt%; Pd/Pt molar ratio = 2.1-2.2) have been prepared using the polymethyl methacrylate microspheres-templating, incipient wetness impregnation, and bubble-assisted polyvinyl alcohol-protected reduction strategies, respectively. All of the samples were characterized by means of various techniques. Catalytic performance of the samples was measured for methane combustion. It is shown that the as-prepared samples exhibited a high-quality 3DOM structure (103 ± 20 nm in pore size) and a surface area of 19-28 m2/g, and the noble metal or alloy nanoparticles (NPs) with a size of 2.2-3.0 nm were uniformly dispersed on the macropore wall surface of 3DOM CoFe2O4. The loading of MnOx on CoFe2O4 gave rise to a slight increase in activity, however, the dispersion of Pd-Pt NPs on 6.70MnOx/3DOM CoFe2O4 significantly enhanced the catalytic performance, with the 1.81Pd2.1Pt/6.70MnOx/3DOM CoFe2O4 sample showing the highest activity (T10% = 255 °C, T50% = 301 °C, and T90% = 372 °C at a space velocity of 20,000 mL/(g h)). We believe that the excellent catalytic activity of 1.81Pd2.1Pt/6.70MnOx/3DOM CoFe2O4 was related to its well-dispersed Pd-Pt alloy NPs, high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interaction between MnOx or Pd-Pt NPs and 3DOM CoFe2O4.

Effect of atomic monolayer insertions on electric-field-induced rotation of magnetic easy axis

NASA Astrophysics Data System (ADS)

Tsujikawa, M.; Haraguchi, S.; Oda, T.

2012-04-01

We have investigated the electric field (EF) effect on the magnetic anisotropy energy (MAE) in the thin films MgO/M/Fe/Au(001) and MgO/Fe/M(001) (M = Pd, Pt, and Au) by means of first-principles density-functional calculations. We find that the MAE varies linearly with the EF and investigate the change in slope of the MAE as a function of the EF as the buffer layer is changed. We find that a single monatomic buffer layer may be useful for devices that use EF-modified MAE. We simulate the critical EF for easy-axis rotation and discuss interface effects of Mg/Fe and Fe/Au on MAE.

Preparation and characterization of Fe3O4-Pt nanoparticles

NASA Astrophysics Data System (ADS)

Andrade, Ângela Leão; Cavalcante, Luis Carlos Duarte; Fabris, José Domingos; Pereira, Márcio César; Ardisson, José Domingos; Domingues, Rosana Zacarias

2017-11-01

Pt and Pt-based nanomaterials are active anticancer drugs for their ability to inhibit the division of living cells. Nanoparticles of magnetite containing variable proportions of platinum were prepared in the laboratory. The magnetite nanoparticles with platinum (Pt-Fe3O4) were obtained by reducing the Fe3+ of the maghemite ( γ Fe2O3) mixed with platinum (II) acetylacetonate and sucrose in two inversely coupled ceramic crucibles and heated in a furnace at 400 °C for 20 min. The formed carbon during this preparation acts to chemically reduce the ferric iron in maghemite. Moreover, its residual layer on the particle surface prevents the forming magnetite from oxidizing in air and helps retain the platinum in the solid mixture. The produced Pt-magnetite samples were characterized by 57Fe-Mössbauer spectroscopy, powder X-ray diffraction, scanning electron microscopy, and magnetization measurements. Measurements of AC magnetic-field-induced heating properties of the obtained nanocomposites, in aqueous solution, showed that they are suitable as a hyperthermia agent for biological applications.

Magnetic anisotropy of Fe{sub 1−y}X{sub y}Pt-L1{sub 0} [X = Cr, Mn, Co, Ni, Cu] bulk alloys

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

Cuadrado, R.; Chantrell, R. W.; Klemmer, Timothy J.

2014-10-13

We demonstrate by means of fully relativistic first principles calculations that, by substitution of Fe by Cr, Mn, Co, Ni, or Cu in FePt-L1{sub 0} bulk alloys, with fixed Pt content, it is possible to tune the magnetocrystalline anisotropy energy by adjusting the content of the non-magnetic species in the material. The changes in the geometry due to the inclusion of each element induces different values of the tetragonality and hence changes in the magnetic anisotropy and in the net magnetic moment. The site resolved magnetic moments of Fe increase with the X content while those of Pt and Xmore » are simultaneously reduced. The calculations are in good quantitative agreement with experimental data and demonstrate that models with fixed band structure but varying numbers of electrons per unit cell are insufficient to describe the experimental data for doped FePt-L1{sub 0} alloys.« less

Metallic State FeS Anchored (Fe)/Fe3O4/N-Doped Graphitic Carbon with Porous Spongelike Structure as Durable Catalysts for Enhancing Bioelectricity Generation.

PubMed

Xu, Xin; Dai, Ying; Yu, Jia; Hao, Liang; Duan, Yaqiang; Sun, Ye; Zhang, Yanhong; Lin, Yuhui; Zou, Jinlong

2017-03-29

The critical issues in practical application of microbial fuel cells (MFCs) for wastewater treatment are the high cost and poor activity and durability of precious metal catalysts. To alleviate the activity loss and kinetic barriers for oxygen reduction reaction (ORR) on cathode, (Fe)/Fe 3 O 4 /FeS/N-doped graphitic carbon ((Fe)/Fe 3 O 4 /FeS/NGC) is prepared as ORR catalyst through a one-step method using waste pomelo skins as carbon source. Various characterization techniques and electrochemical analyses are conducted to illustrate the correlation between structural characteristics and catalytic activity. MFCs with Fe/Fe 3 O 4 /FeS/NGC (900 °C) cathode produces the maximum power density of 930 ± 10 mW m -2 (Pt/C of 489 mW m -2 ) and maintains a good long-term durability, which only declines 18% after 90 day operation. Coulombic efficiency (22.2%) obtained by Fe/Fe 3 O 4 /FeS/NGC (900 °C) cathode is significantly higher than that of Pt/C (17.3%). Metallic state FeS anchored in porous NGC skeleton can boost electron transport through the interconnected channels in spongelike structure to improve catalytic activity. Charge delocalization of C atoms can be strengthened by N atoms incorporation into carbon skeleton, which correspondingly contributes to the O 2 chemisorptions and O-O bond weakening during ORR. Energetically existed active components (Fe and N species) are more efficient than Pt to trap and consume electrons in catalyzing ORR in wastewater containing Pt-poisoning substances (bacterial metabolites). (Fe)/Fe 3 O 4 /FeS/NGC catalysts with the advantages of durable power outputs and environmental-friendly raw material can cover the shortages of Pt/C and provide an outlook for further applications of these catalysts.

Monolayer-directed Assembly and Magnetic Properties of FePt Nanoparticles on Patterned Aluminum Oxide

PubMed Central

Yildirim, Oktay; Gang, Tian; Kinge, Sachin; Reinhoudt, David N.; Blank, Dave H.A.; van der Wiel, Wilfred G.; Rijnders, Guus; Huskens, Jurriaan

2010-01-01

FePt nanoparticles (NPs) were assembled on aluminum oxide substrates, and their ferromagnetic properties were studied before and after thermal annealing. For the first time, phosph(on)ates were used as an adsorbate to form self-assembled monolayers (SAMs) on alumina to direct the assembly of NPs onto the surface. The Al2O3 substrates were functionalized with aminobutylphosphonic acid (ABP) or phosphonoundecanoic acid (PNDA) SAMs or with poly(ethyleneimine) (PEI) as a reference. FePt NPs assembled on all of these monolayers, but much less on unmodified Al2O3, which shows that ligand exchange at the NPs is the most likely mechanism of attachment. Proper modification of the Al2O3 surface and controlling the immersion time of the modified Al2O3 substrates into the FePt NP solution resulted in FePt NPs assembly with controlled NP density. Alumina substrates were patterned by microcontact printing using aminobutylphosphonic acid as the ink, allowing local NP assembly. Thermal annealing under reducing conditions (96%N2/4%H2) led to a phase change of the FePt NPs from the disordered FCC phase to the ordered FCT phase. This resulted in ferromagnetic behavior at room temperature. Such a process can potentially be applied in the fabrication of spintronic devices. PMID:20480007

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

Ledge-type Co/L1{sub 0}-FePt exchange-coupled composites

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

Speliotis, Th.; Giannopoulos, G.; Niarchos, D.

2016-06-21

FePt-based exchange-coupled composites consisting of a magnetically hard L1{sub 0}-FePt phase exchange-coupled with a soft ferromagnetic material are promising candidates for future ultra-high density (>1 Tbit/in{sup 2}) perpendicular magnetic recording media, also being of interest for other applications including spin torque oscillators and micro-electro-mechanical systems, among others. In this paper, the effect of the thickness of a soft Co layer (3 < th{sub Co} < 20 nm) on the magnetic behavior of ledge-type fcc(100)-Co/L1{sub 0}(001)-FePt composites deposited on an MgO (100) substrate is systematically studied by combining morpho-structural analyses and angular magnetization measurements. Starting from a film consisting of isolated L1{submore » 0}(001)–FePt islands, the ledge-type structure was obtained by depositing a Co layer that either covered the FePt islands or filled-up the inter-island region, gradually forming a continuous layer with increasing Co thickness. A perpendicular anisotropy was maintained up to th{sub Co} ∼ 9.5 nm and a significant reduction in the coercivity (about 50% for th{sub Co} ∼ 3 nm) with the increase in th{sub Co} was observed, indicating that, by coupling hard FePt and soft Co phases in a ledge-type configuration, the writability can be greatly improved. Recoil loops' measurements confirmed the exchange-coupled behavior, reinforcing a potential interest in these systems for future magnetic recording media.« less

Gate control of spin-polarized conductance in alloyed transitional metal nanocontacts

NASA Astrophysics Data System (ADS)

Sivkov, Ilia N.; Brovko, Oleg O.; Rungger, Ivan; Stepanyuk, Valeri S.

2017-03-01

To date, endeavors in nanoscale spintronics are dominated by the use of single-electron or single-spin transistors having at their heart a semiconductor, metallic, or molecular quantum dot whose localized states are non-spin-degenerate and can be controlled by an external bias applied via a gate electrode. Adjusting the bias of the gate one can realign those states with respect to the chemical potentials of the leads and thus tailor the spin-polarized transmission properties of the device. Here we show that similar functionality can be achieved in a purely metallic junction comprised of a metallic magnetic chain attached to metallic paramagnetic leads and biased by a gate electrode. Our ab initio calculations of electron transport through mixed Pt-Fe (Fe-Pd and Fe-Rh) atomic chains suspended between Pt (Pd and Rh) electrodes show that spin-polarized confined states of the chain can be shifted by the gate bias causing a change in the relative contributions of majority and minority channels to the nanocontact's conductance. As a result, we observe strong dependence of conductance spin polarization on the applied gate potential. In some cases the spin polarization of conductance can even be reversed in sign upon gate potential application, which is a remarkable and promising trait for spintronic applications.

Self-Assembled Fe-N-Doped Carbon Nanotube Aerogels with Single-Atom Catalyst Feature as High-Efficiency Oxygen Reduction Electrocatalysts

DOE PAGES

Zhu, Chengzhou; Fu, Shaofang; Song, Junhua; ...

2017-02-06

In this study, self-assembled M–N-doped carbon nanotube aerogels with single-atom catalyst feature are for the first time reported through one-step hydrothermal route and subsequent facile annealing treatment. By taking advantage of the porous nanostructures, 1D nanotubes as well as single-atom catalyst feature, the resultant Fe–N-doped carbon nanotube aerogels exhibit excellent oxygen reduction reaction electrocatalytic performance even better than commercial Pt/C in alkaline solution.

Pt-Doped NiFe₂O₄ Spinel as a Highly Efficient Catalyst for H₂ Selective Catalytic Reduction of NO at Room Temperature.

PubMed

Sun, Wei; Qiao, Kai; Liu, Ji-Yuan; Cao, Li-Mei; Gong, Xue-Qing; Yang, Ji

2016-04-11

H2 selective catalytic reduction (H2-SCR) has been proposed as a promising technology for controlling NOx emission because hydrogen is clean and does not emit greenhouse gases. We demonstrate that Pt doped into a nickel ferrite spinel structure can afford a high catalytic activity of H2-SCR. A superior NO conversion of 96% can be achieved by employing a novel NiFe1.95Pt0.05O4 spinel-type catalyst at 60 °C. This novel catalyst is different from traditional H2-SCR catalysts, which focus on the role of metallic Pt species and neglect the effect of oxidized Pt states in the reduction of NO. The obtained Raman and XPS spectra indicate that Pt in the spinel lattice has different valence states with Pt(2+) occupying the tetrahedral sites and Pt(4+) residing in the octahedral ones. These oxidation states of Pt enhance the back-donation process, and the lack of filling electrons of the 5d band causes Pt to more readily hybridize with the 5σ orbital of the NO molecule, especially for octahedral Pt(4+), which enhances the NO chemisorption on the Pt sites. We also performed DFT calculations to confirm the enhancement of adsorption of NO onto Pt sites when doped into the Ni-Fe spinel structure. The prepared Pt/Ni-Fe catalysts indicate that increasing the dispersity of Pt on the surfaces of the individual Ni-Fe spinel-type catalysts can efficiently promote the H2-SCR activity. Our demonstration provides new insight into designing advanced catalysts for H2-SCR.

Oxygen Fugacity in Large Metal Capsules

NASA Astrophysics Data System (ADS)

Faul, U.; Cline, C. J., II; Jackson, I.; Berry, A.

2016-12-01

During experiments with iron bearing silicates, equilibration between metal capsules and sample interior depends on diffusion of Fe if the capsule composition is not initially in equilibrium with the sample composition. For example, placing Pt or Ni capsules in contact with Fe-bearing olivine leads to Fe-loss from the olivine. In a fully equilibrated system the Fe contents of coexisting metal capsule and olivine reflect the oxygen fugacity (fO2) of the system. Experiments were conducted with olivine encapsulated or wrapped in four different metals (Fe, Ni70Fe30, Ni and Pt) to determine the fO2 in the cm-sized samples used for deformation and seismic property experiments. Small Pt particles mixed with olivine powder were used as fO2 sensors in the interior of the capsules. The results show an ordering of the fO2 in the interior that is consistent with the enclosing metals, i.e. the fO2 is lowest in a Fe capsule and highest in a Pt capsule. However, fO2 values in the more oxidizing metal capsules are substantially below their respective metal-oxide buffers. For example, solgel olivine encapsulated in Ni has an oxygen fugacity that is more than three orders of magnitude below Ni-NiO at 1200C and 0.3 GPa. The fO2 in a capsule interior is therefore to some extent self-buffering and only moderately influenced by the composition of the capsule. While the Pt particles in the interior are equilibrated, Fe gradients from the interior up to the Pt and Ni sample-capsule interfaces show that Fe loss into the capsules is diffusion limited. The fO2 at the interface also has implications for the water retention in unbuffered capsules. We infer that relatively high fO2 and hence fH2O observed adjacent to Pt capsules enables retention of water in these capsules, but the fO2 adjacent to Ni capsules is too low and water is lost.

Effect of interlayer coupling on the coexistence of antiferromagnetism and superconductivity in Fe pnictide superconductors: A study of Ca0.74 (1 )La0.26 (1 )(Fe1 -xCox)As2 single crystals

NASA Astrophysics Data System (ADS)

Jiang, Shan; Liu, Lian; Schütt, Michael; Hallas, Alannah M.; Shen, Bing; Tian, Wei; Emmanouilidou, Eve; Shi, Aoshuang; Luke, Graeme M.; Uemura, Yasutomo J.; Fernandes, Rafael M.; Ni, Ni

2016-05-01

We report the transport, thermodynamic, muon spin relaxation, and neutron study of the Ca0.74 (1 )La0.26 (1 ) (Fe1 -xCox )As2 single crystals, mapping out the temperature-doping level phase diagram. Upon Co substitution on the Fe site, the structural and magnetic phase transitions in this 112 compound are suppressed and superconductivity up to 20 K occurs. Our measurements of the superconducting and magnetic volume fractions show that these two phases coexist microscopically in the underdoped region, in contrast to the related Ca10(Pt3As8 )((Fe1 -xPtx )2As2 )5 (10-3-8) compound, where coexistence is absent. Supported by model calculations, we discuss the differences in the phase diagrams of the 112 and 10-3-8 compounds in terms of the FeAs interlayer coupling, whose strength is affected by the character of the spacer layer, which is metallic in the 112 compound and insulating in the 10-3-8 compound.

The role of Pt underlayer on the magnetization dynamics of perpendicular magnetic anisotropy Pt/Co{sub 2}FeAl{sub 0.5}Si{sub 0.5}/MgO

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

Besbas, Jean; Loong, Li Ming; Wu, Yang

2016-06-06

We investigate the role of Pt on the magnetization dynamics of Pt/Co{sub 2}FeAl{sub 0.5}Si{sub 0.5}/MgO with perpendicular magnetic anisotropy using the time resolved magneto-optic Kerr effect. Pt/Co{sub 2}FeAl{sub 0.5}Si{sub 0.5}/MgO shows ultrafast magnetization dynamics comparable to 3d ferromagnets and can be fully demagnetized. The demagnetization time τ{sub d} ∼ 0.27 ps and magnetic heat capacity are independent of the Pt underlayer, whereas the value of the electron-phonon coupling time τ{sub e} ∼ 0.77 ps depends on the presence of the Pt layer. We further measure the effective damping α{sub eff} ∼ 1 that does not scale as the inverse demagnetizationmore » time (1/τ{sub d}), but is strongly affected by the Pt layer.« less

Large enhancement of magnetic moment in L1(0) ordered FePt thin films by Nd substitutional doping

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

Xu, D. B.; Sun, C J; Chen, J. S.

2015-07-01

We studied L1(0) ordered Fe50Pt50-xNdx alloy films, which showed a large enhancement (similar to 18.4% at room temperature and similar to 11.7% at 10 K) of magnetic moment with 6 atomic % of Nd. Analysis of the x-ray magnetic circular dichroism spectra at the Fe L-3,L-2 edges and Nd M-5,M-4 edges in Fe50Pt44Nd6 films indicated a significant contribution of the Nd orbital moment. The origin of the large enhancement of magnetic moment was attributed to the effect of ferromagnetic coupling of the total magnetic moments between Fe and Nd. Density functional theory based first principles calculations supported the experimental observationsmore » of increasing moment due to Nd substitution of Pt.« less

Constructing hierarchical interfaces: TiO 2-supported PtFe-FeO x nanowires for room temperature CO oxidation

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

Zhu, Huiyuan; Wu, Zili; Dong, Su

2015-08-05

This is a report of a facile approach to constructing catalytic active hierarchical interfaces in one-dimensional (1D) nanostructure, exemplified by the synthesis of TiO 2-supported PtFe–FeO x nanowires (NWs). The hierarchical interface, constituting atomic level interactions between PtFe and FeO x within each NW and the interactions between NWs and support (TiO 2), enables CO oxidation with 100% conversion at room temperature. We identify the role of the two interfaces by probing the CO oxidation reaction with isotopic labeling experiments. Both the oxygen atoms (Os) in FeO x and TiO 2 participate in the initial CO oxidation, facilitating the reactionmore » through a redox pathway. Moreover, the intact 1D structure leads to the high stability of the catalyst. After 30 h in the reaction stream, the PtFe–FeO x/TiO2 catalyst exhibits no activity decay. These results provide a general approach and new insights into the construction of hierarchical interfaces for advanced catalysis.« less

Influence of ball milling and annealing conditions on the properties of L10 FePt nanoparticles fabricated by a new green chemical synthesis method

NASA Astrophysics Data System (ADS)

Hu, X. C.; Capobianchi, A.; Gallagher, R.; Hadjipanayis, G. C.

2014-05-01

In this work, a new green chemical strategy for the synthesis of L10 FePt alloy nanoparticles is reported. The precursor is a polycrystalline molecular complex (Fe(H2O)6PtCl6), in which Fe and Pt atoms are arranged on alternating planes and milled with NaCl to form nanocrystals. Then the mixture was annealed under reducing atmosphere (5% H2 and 95% Ar) at temperatures varying from 350 °C to 500 °C for 2 h with a heating rate of 5 °C/min. After the reduction, the mixture was washed with water to remove the NaCl and L10 FePt nanoparticles were obtained. The X-Ray Diffraction pattern showed the presence of the characteristic peaks of the fct phase of FePt nanoparticles. Influence of precursor/NaCl ratio and ball milling time on particle size was investigated. Transmission electron microscopy images revealed that smaller precursor/NaCl ratio (10 mg/20 g) and longer milling time (15 h) lead to smaller particle size and narrower size distribution. Milling time does not influence the coercivity much but the decrease of the amount of precursor leads to a decrease of coercivity from 10.8 kOe to 4.8 kOe.

Influence of chemical ordering on the thermal conductivity and electronic relaxation in FePt thin films in heat assisted magnetic recording applications

DOE PAGES

Giri, Ashutosh; Wee, Sung Hun; Jain, Shikha; ...

2016-08-26

Here, we report on the out-of-plane thermal conductivities of tetragonal L1 0 FePt (001) easy-axis and cubic A1 FePt thin films via time-domain thermoreflectance over a temperature range from 133 K to 500 K. The out-of-plane thermal conductivity of the chemically ordered L10 phase with alternating Fe and Pt layers is ~23% greater than the thermal conductivity of the disordered A1 phase at room temperature and below. However, as temperature is increased above room temperature, the thermal conductivities of the two phases begin to converge. Molecular dynamics simulations on model FePt structures support our experimental findings and help shed moremore » light into the relative vibrational thermal transport properties of the L1 0 and A1 phases. Furthermore, unlike the varying temperature trends in the thermal conductivities of the two phases, the electronic scattering rates in the out-of-plane direction of the two phases are similar for the temperature range studied in this work.« less

Catalysts synthesized by selective deposition of Fe onto Pt for the water-gas shift reaction

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

Aragao, Isaias Barbosa; Ro, Insoo; Liu, Yifei

FePt bimetallic catalysts with intimate contact between the two metals were synthesized by controlled surface reactions (CSR) of (cyclohexadiene)iron tricarbonyl with hydrogen-treated supported Pt nanoparticles. Adsorption of the iron precursor on a Pt/SiO2 catalyst was studied, showing that the Fe loading could be increased by performing multiple CSR cycles, and the efficiency of this process was linked to the renewal of adsorption sites by a reducing pretreatment. The catalytic activity of these bimetallic catalysts for the water gas shift reaction was improved due to promotion by iron, likely linked to H2O activation on FeOx species at or near the Ptmore » surface, mostly in the (II) oxidation state.« less

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.

Enhancement of electrical properties in polycrystalline BiFeO3 thin films

NASA Astrophysics Data System (ADS)

Yun, Kwi Young; Ricinschi, Dan; Kanashima, Takeshi; Okuyama, Masanori

2006-11-01

Ferroelectric BiFeO3 thin films were grown on Pt /TiO2/SiO2/Si substrates by pulsed-laser deposition. From the x-ray diffraction analysis, the BiFeO3 thin films consist of perovskite single phase, and the crystal structure shows the tetragonal structure with a space group P4mm. The BiFeO3 thin films show enhanced electrical properties with low leakage current density value of ˜10-4A /cm2 at a maximum applied voltage of 31V. This enhanced electrical resistivity allowed the authors to obtain giant ferroelectric polarization values such as saturation polarizations of 110 and 166μC/cm2 at room temperature and 80K, respectively.

Bimetallic magnetic PtPd-nanoparticles as efficient catalyst for PAH removal from liquid media

NASA Astrophysics Data System (ADS)

Zanato, A. F. S.; Silva, V. C.; Lima, D. A.; Jacinto, M. J.

2017-11-01

Monometallic Pd- and bimetallic PtPd-nanoparticles supported on a mesoporous magnetic magnetite@silica matrix resembling a core-shell structure (Fe3O4@mSiO2) have been fabricated. The material was characterized by transmission electron microscope (TEM), high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM), X-ray photoelectron spectra (XPS), energy dispersive spectroscopy (EDS) and inductively coupled plasma mass spectrometry (ICP-MS). The catalysts were applied in the removal of anthracene from liquid phase via catalytic hydrogenation. It was found that anthracene as a model compound could be completely converted into the partially hydrogenated species by the monometallic and bimetallic solids. However, during the recycling study the bimetallic material (Fe3O4@mSiO2PtPd-) showed an enhanced activity towards anthracene removal compared with the monometallic materials. A single portion of the PtPd-based catalyst can be used up to 11 times in the hydrogenation of anthracene under mild conditions (6 atm of H2, 75 °C, 20 min). Thanks to the presence of a dense magnetic core, the catalysts were capable of responding to an applied external magnetic field and once the reaction was completed, catalyst/product separation was straightforward.

Synergistically Enhanced Electrochemical Performance of Ni3S4-PtX (X = Fe, Ni) Heteronanorods as Heterogeneous Catalysts in Dye-Sensitized Solar Cells.

PubMed

Huang, Shoushuang; Ma, Dui; Hu, ZhangJun; He, Qingquan; Zai, Jiantao; Chen, Dayong; Sun, Huai; Chen, Zhiwen; Qiao, Qiquan; Wu, Minghong; Qian, Xuefeng

2017-08-23

Platinum (Pt)-based alloys are considerably promising electrocatalysts for the reduction of I - /I 3 - and Co 2+ /Co 3+ redox couples in dye-sensitized solar cells (DSSCs). However, it is still challenging to minimize the dosage of Pt to achieve comparable or even higher catalytic efficiency. Here, by taking full advantages of the Mott-Schottky (M-S) effect at the metal-semiconductor interface, we successfully strategize a low-Pt-based M-S catalyst with enhanced electrocatalytic performance and stability for the large-scale application of DSSCs. The optimized M-S electrocatalyst of Ni 3 S 4 -Pt 2 X 1 (X = Fe, Ni) heteronanorods is constructed by rationally controlling the ratio of Pt to transition metal in the hybrids. It was found that the electrons transferred from Ni 3 S 4 to Pt 2 X 1 at their interface under the Mott-Schottky effect result in the concentration of electrons onto Pt 2 X 1 domains, which subsequently accelerates the regeneration of both I - /I 3 - and Co 2+ /Co 3+ redox shuttles in DSSCs. As a result, the DSSC with Ni 3 S 4 -Pt 2 Fe 1 manifests an impressive power conversion efficiency (PCE) of 8.79% and 5.56% for iodine and cobalt-based electrolyte under AM1.5G illumination, respectively. These PCEs are obviously superior over those with Ni 3 S 4 -Pt, PtFe, Ni 3 S 4 , and pristine Pt electrodes. The strategy reported here is able to be further expanded to fabricate other low-Pt-alloyed M-S catalysts for wider applications in the fields of photocatalysis, water splitting, and heterojunction solar cells.

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

Magnetization reversal process and evaluation of thermal stability factor in Cu doped granular L10 FePt films

NASA Astrophysics Data System (ADS)

Jain, S.; Papusoi, C.; Admana, R.; Yuan, H.; Acharya, R.

2018-05-01

Curie temperature TC distributions and magnetization reversal mechanism in Cu doped L10 FePt granular films is investigated as a function of film thickness in the range of ˜5-12 nm with Cu mol. % varying in the range of 0%-6%. It is shown that Cu doping increases the FePt tetragonality and chemical ordering. For Cu doped FePt-X films, coercivity (HC) exhibits a non-monotonic behavior with increasing film thickness, i.e., HC increases initially up to tcr ˜ 7 nm, and decreases thereafter. We attribute this behavior to the change in magnetization reversal mechanism from coherent to an incoherent (domain-wall driven) mode. While in un-doped films, the domain-walls nucleate at the grain boundaries, in doped films the Cu atoms may act as domain-wall nucleation and pinning sites, isolating magnetic spin clusters of reduced dimensionality with respect to the physical grain size. This is experimentally supported by a much poorer dependence of the AC susceptibility (both, real and imaginary components) on the film thickness above 7 nm than in the case of un-doped films. The formation of magnetic spin clusters inside the grains as a consequence of the reduced coupling between Fe-Fe and Fe-Pt-Fe atoms with increasing Cu doping can explain the experimentally evidenced reduction of both, the film Curie temperature, TC, and intrinsic anisotropy energy density, KC, with increasing Cu doping.

Kerr microscopy study of exchange-coupled FePt/Fe exchange spring magnets

NASA Astrophysics Data System (ADS)

Hussain, Zaineb; Kumar, Dileep; Reddy, V. Raghavendra; Gupta, Ajay

2017-05-01

Magnetization reversal and magnetic microstructure of top soft magnetic layer (Fe) in exchange spring coupled L10 FePt/Fe is studied using high resolution Kerr microscopy. With remnant state of the hard magnetic layer (L10 FePt) as initial condition, magnetization loops along with magnetic domains are recorded for the top soft magnetic layer (Fe) using Kerr microscopy. Considerable shifting of Fe layer hysteresis loop from center which is similar to exchange bias phenomena is observed. It is also observed that one can tune the magnitude of hysteresis shift by reaching the remanent state from different saturating fields (HSAT) and also by varying the angle between measuring field and HSAT. The hysteresis loops and magnetic domains of top soft Fe layer demonstrate unambiguously that soft magnetic layer at remanent state in such exchange coupled system is having unidirectional anisotropy. An analogy is drawn and the observations are explained in terms of established model of exchange bias phenomena framed for field-cooled ferromagnetic - antiferromagnetic bilayer systems.

Simple preparations of Pd6Cl12, Pt6Cl12, and Qn[Pt2Cl8+n], n=1, 2 (Q=TBA+, PPN+) and structural characterization of [TBA][Pt2Cl9] and [PPN]2[Pt2Cl10].C7H8.

PubMed

Dell'Amico, Daniela Belli; Calderazzo, Fausto; Marchetti, Fabio; Ramello, Stefano; Samaritani, Simona

2008-02-04

The hexanuclear Pd6Cl12, i.e., the crystal phase classified as beta-PdCl2, was obtained by reacting [TBA]2[Pd2Cl6] with AlCl3 (or FeCl3) in CH2Cl2. The action of AlCl3 on PtCl42-, followed by digestion of the resulting solid in 1,2-C2H4Cl2 (DCE), CHCl3, or benzene, produced Pt6Cl12.DCE, Pt6Cl12.CHCl3, or Pt6Cl12.C6H6, respectively. Treating [TBA]2[PtCl6] with a slight excess of AlCl3 afforded [TBA][Pt2Cl9], whose anion was established crystallographically to be constituted by two "PtCl6" octahedra sharing a face. Dehydration of H2PtCl6.nH2O with SOCl2 gave an amorphous compound closely analyzing as PtCl4, reactive with [Q]Cl in SOCl2 to yield [Q][Pt2Cl9] or [Q]2[Pt2Cl10], depending on the [Q]Cl/Pt molar ratio (Q=TBA+, PPN+). A single-crystal X-ray diffraction study has shown [PPN]2[Pt2Cl10].C7H8 to contain dinuclear anions formed by two edge-sharing PtCl6 octahedra.

Converse magnetoelectric coupling in NiFe/Pb(Mg{sub 1/3}Nb{sub 2/3})O{sub 3}–PbTiO{sub 3} nanocomposite thin films grown on Si substrates

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

Feng, Ming; Key Laboratory of Functional Materials Physics and Chemistry of the Ministry of Education, Jilin Normal University, Siping 136000; Hu, Jiamian

2013-11-04

Multiferroic NiFe (∼30 nm)/Pb(Mg{sub 1/3}Nb{sub 2/3})O{sub 3}–PbTiO{sub 3}(PMN–PT, ∼220 nm) bilayered thin films were grown on common Pt/Ti/SiO{sub 2}/Si substrates by a combination of off-axis magnetron sputtering and sol-gel spin-coating technique. By using AC-mode magneto-optical Kerr effect technique, the change in the Kerr signal (magnetization) of the NiFe upon applying a low-frequency AC voltage to the PMN–PT film was in situ acquired at zero magnetic field. The obtained Kerr signal versus voltage loop essentially tracks the electromechanical strain curve of the PMN–PT thin film, clearly demonstrating a strain-mediated converse magnetoelectric coupling, i.e., voltage-modulated magnetization, in the NiFe/PMN–PT nanocomposite thin films.

Evidence of spin phonon coupling in magnetoelectric NiFe{sub 2}O{sub 4}/PMN-PT composite

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

Ahlawat, Anju; Satapathy, S., E-mail: srinu73@rrcat.gov.in, E-mail: srinusatapathy@gmail.com; Gupta, P. K.

2013-12-16

The coupling of phonon with spin in strain coupled magnetoelectric NiFe{sub 2}O{sub 4} (NFO)/0.65Pb(Mg{sub 1/3}Nb{sub 2/3})O{sub 3}–0.35PbTiO{sub 3} (PMN-PT) composite was investigated by temperature-dependent Raman spectroscopy and magnetic measurements in the range 30–350 °C. Pure NFO shows usual ferromagnetic behaviour in this temperature range while NFO/PMN-PT composite show dramatic change in magnetic moment across ferroelectric transition temperature (T{sub c} ∼ 180 °C) of PMN-PT. The temperature evolution of the Raman spectra for the composite shows significant phonon anomalies in T-site (Fe-O) and O-site (Ni/Fe-O) phonon modes at ferroelectric transition temperature is attributed to spin phonon coupling in NFO/PMN-PT composite. The strain mediated magnetoelectric couplingmore » mechanism in this composite is apparent from the observed spin phonon interaction.« less

Degradation of pharmaceutical beta-blockers by electrochemical advanced oxidation processes using a flow plant with a solar compound parabolic collector.

PubMed

Isarain-Chávez, Eloy; Rodríguez, Rosa María; Cabot, Pere Lluís; Centellas, Francesc; Arias, Conchita; Garrido, José Antonio; Brillas, Enric

2011-08-01

The degradation of the beta-blockers atenolol, metoprolol tartrate and propranolol hydrochloride was studied by electro-Fenton (EF) and solar photoelectro-Fenton (SPEF). Solutions of 10 L of 100 mg L⁻¹ of total organic carbon of each drug in 0.1 M Na₂SO₄ with 0.5 mM Fe²⁺ of pH 3.0 were treated in a recirculation flow plant with an electrochemical reactor coupled with a solar compound parabolic collector. Single Pt/carbon felt (CF) and boron-doped diamond (BDD)/air-diffusion electrode (ADE) cells and combined Pt/ADE-Pt/CF and BDD/ADE-Pt/CF cells were used. SPEF treatments were more potent with the latter cell, yielding 95-97% mineralization with 100% of maximum current efficiency and energy consumptions of about 0.250 kWh g TOC⁻¹. However, the Pt/ADE-Pt/CF cell gave much lower energy consumptions of about 0.080 kWh g TOC⁻¹ with slightly lower mineralization of 88-93%, then being more useful for its possible application at industrial level. The EF method led to a poorer mineralization and was more potent using the combined cells by the additional production of hydroxyl radicals (•OH) from Fenton's reaction from the fast Fe²⁺ regeneration at the CF cathode. Organics were also more rapidly destroyed at BDD than at Pt anode. The decay kinetics of beta-blockers always followed a pseudo first-order reaction, although in SPEF, it was accelerated by the additional production of •OH from the action of UV light of solar irradiation. Aromatic intermediates were also destroyed by hydroxyl radicals. Ultimate carboxylic acids like oxalic and oxamic remained in the treated solutions by EF, but their Fe(III) complexes were photolyzed by solar irradiation in SPEF, thus explaining its higher oxidation power. NO₃⁻ was the predominant inorganic ion lost in EF, whereas the SPEF process favored the production of NH₄⁺ ion and volatile N-derivatives. Copyright © 2011 Elsevier Ltd. All rights reserved.

Composition distributions in FePt(Au) nanoparticles

NASA Astrophysics Data System (ADS)

Srivastava, C.; Nikles, D. E.; Harrell, J. W.; Thompson, G. B.

2010-08-01

Ternary alloy FePt(Au) nanoparticles were prepared by the co-reduction of platinum(II) acetylacetonate and gold(III) acetate and the thermal decomposition of iron pentacarbonyl in hot phenyl ether in the presence of oleic acid and oleylamine ligands. This gave spherical particles with an average diameter of 4.4 nm with a range of diameters from approximately 1.6-9 nm. The as-synthesized particles had a solid solution, face-centered-cubic structure. Though the average composition of the particles was Fe44Pt45Au11, individual particle analysis by Scanning Transmission Electron Microscopy-X-ray Energy Dispersive Spectroscopy showed a broad distribution in composition. In general, smaller-sized particles tended to have a lower amount of Au as compared to larger-sized particles. As the Au content increased, the ratio of Fe/Pt widened.

Longitudinal spin Seebeck effect in various garnet ferrites

NASA Astrophysics Data System (ADS)

Uchida, K.; Nonaka, T.; Kikkawa, T.; Kajiwara, Y.; Saitoh, E.

2013-03-01

The longitudinal spin Seebeck effect (LSSE) is investigated in various garnet ferrites Y3-xRxFe5-yMyO12 (R=Gd, Ca; M=Al, Mn, V, In, Zr) by means of the inverse spin Hall effect in Pt films. The magnitude of the LSSE voltage in the Pt/Y3-xRxFe5-yMyO12 samples is found to be enhanced with increasing concentration of Fe in the garnet ferrites, which can be explained by a change in the spin-mixing conductance at the Pt/Y3-xRxFe5-yMyO12 interfaces. We also investigate the dependence of the LSSE voltage on macroscopic magnetic parameters of Y3-xRxFe5-yMyO12. The experimental results show that the LSSE voltage in the Pt/Y3-xRxFe5-yMyO12 samples has a positive correlation with the Curie temperature and the saturation magnetization, but no clear correlation with the gyromagnetic ratio and the Gilbert damping constant of the samples.

Fundamental limits in heat-assisted magnetic recording and methods to overcome it with exchange spring structures

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

Suess, D.; Abert, C.; Bruckner, F.

2015-04-28

The switching probability of magnetic elements for heat-assisted recording with pulsed laser heating was investigated. It was found that FePt elements with a diameter of 5 nm and a height of 10 nm show, at a field of 0.5 T, thermally written-in errors of 12%, which is significantly too large for bit-patterned magnetic recording. Thermally written-in errors can be decreased if larger-head fields are applied. However, larger fields lead to an increase in the fundamental thermal jitter. This leads to a dilemma between thermally written-in errors and fundamental thermal jitter. This dilemma can be partly relaxed by increasing the thickness of the FePtmore » film up to 30 nm. For realistic head fields, it is found that the fundamental thermal jitter is in the same order of magnitude of the fundamental thermal jitter in conventional recording, which is about 0.5–0.8 nm. Composite structures consisting of high Curie top layer and FePt as a hard magnetic storage layer can reduce the thermally written-in errors to be smaller than 10{sup −4} if the damping constant is increased in the soft layer. Large damping may be realized by doping with rare earth elements. Similar to single FePt grains in composite structure, an increase of switching probability is sacrificed by an increase of thermal jitter. Structures utilizing first-order phase transitions breaking the thermal jitter and writability dilemma are discussed.« less

Visualization of anomalous Ettingshausen effect in a ferromagnetic film: Direct evidence of different symmetry from spin Peltier effect

NASA Astrophysics Data System (ADS)

Seki, T.; Iguchi, R.; Takanashi, K.; Uchida, K.

2018-04-01

Spatial distribution of temperature modulation due to the anomalous Ettingshausen effect (AEE) is visualized in a ferromagnetic FePt thin film with in-plane and out-of-plane magnetizations using the lock-in thermography technique. Comparing the AEE of FePt with the spin Peltier effect (SPE) of a Pt/yttrium iron garnet junction provides direct evidence of different symmetries of AEE and SPE. Our experiments and numerical calculations reveal that the distribution of heat sources induced by AEE strongly depends on the direction of magnetization, leading to the remarkable different temperature profiles in the FePt thin film between the in-plane and perpendicularly magnetized configurations.

In-plane/out-of-plane disorder influence on the magnetic anisotropy of Fe{sub 1−y}Mn{sub y}Pt-L1{sub 0} bulk alloy

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

Cuadrado, R.; Catalan Institute of Nanoscience and Nanotechnology; Liu, Kai

2016-03-21

The random substitution of a non-magnetic species instead of Fe atoms in FePt-L1{sub 0} bulk alloy will permit to tune the magnetic anisotropy energy of this material. We have performed by means of first principles calculations a study of Fe{sub 1−y}Mn{sub y}Pt-L1{sub 0} (y = 0.0, 0.08, 0.12, 0.17, 0.22, and 0.25) bulk alloy for a fixed Pt concentration when the Mn species have ferro-/antiferromagnetic (FM,AFM) alignment at the same(different) atomic plane(s). This substitution will promote several in-plane lattice values for a fixed amount of Mn. Charge hybridization will change compared to the FePt-L1{sub 0} bulk due to this lattice variation leadingmore » to a site resolved magnetic moment modification. We demonstrate that this translates into a total magnetic anisotropy reduction for the AFM phase and an enhancement for the FM alignment. Several geometric configurations were taken into account for a fixed Mn concentration because of different possible Mn positions in the simulation cell.« less

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

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

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

Zuo, Zhiqi

The Full Potential Linear Augmented Plane Wave (FPLAPW or FLAPW) method is used for a spin-polarized band calculation for ordered Fe 3Pt. As major purpose, the momentum distributions of the spin-polarized electrons are calculated and compared with results from a magnetic Compton scattering measurement. To get related information, the electronic behavior is also analyzed by examining the partial densities of states and the spatial electron distributions; the role of alloying effects is then explored by studying the electrons in some related alloys: Fe 3Ni, Fe 3Pd, Ni 3Pt and Co 3Pt.

Local environment effects in the magnetic properties and electronic structure of disordered FePt

NASA Astrophysics Data System (ADS)

Khan, Saleem Ayaz; Minár, Ján; Ebert, Hubert; Blaha, Peter; Šipr, Ondřej

2017-01-01

Local aspects of magnetism of disordered FePt are investigated by ab initio fully relativistic full-potential calculations, employing the supercell approach and the coherent potential approximation (CPA). The focus is on trends of the spin and orbital magnetic moments with chemical composition and with bond lengths around the Fe and Pt atoms. A small but distinct difference between average magnetic moments obtained when using the supercells and when relying on the CPA is identified and linked to the neglect of the Madelung potential in the CPA.

Sputtering growth of Y3Fe5O12/Pt bilayers and spin transfer at Y3Fe5O12/Pt interfaces

NASA Astrophysics Data System (ADS)

Chang, Houchen; Liu, Tao; Reifsnyder Hickey, Danielle; Janantha, P. A. Praveen; Mkhoyan, K. Andre; Wu, Mingzhong

2017-12-01

For the majority of previous work on Y3Fe5O12 (YIG)/normal metal (NM) bi-layered structures, the YIG layers were grown on Gd3Ga5O12 first and were then capped by an NM layer. This work demonstrates the sputtering growth of a Pt/YIG structure where the Pt layer was grown first and the YIG layer was then deposited on the top. The YIG layer shows well-oriented (111) texture, a surface roughness of 0.15 nm, and an effective Gilbert damping constant less than 4.7 × 10-4, and the YIG/Pt interface allows for efficient spin transfers. This demonstration indicates the feasibility of fabricating high-quality NM/YIG/NM tri-layered structures for new physics studies.

Time-domain detection of current controlled magnetization damping in Pt/Ni{sub 81}Fe{sub 19} bilayer and determination of Pt spin Hall angle

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

Ganguly, A.; Haldar, A.; Sinha, J.

2014-09-15

The effect of spin torque from the spin Hall effect in Pt/Ni{sub 81}Fe{sub 19} rectangular bilayer film was investigated using time-resolved magneto-optical Kerr microscopy. Current flow through the stack resulted in a linear variation of effective damping up to ±7%, attributed to spin current injection from the Pt into the Ni{sub 81}Fe{sub 19}. The spin Hall angle of Pt was estimated as 0.11 ± 0.03. The modulation of the damping depended on the angle between the current and the bias magnetic field. These results demonstrate the importance of optical detection of precessional magnetization dynamics for studying spin transfer torque due to spinmore » Hall effect.« less

Optical and thermal charge-transfer processes occurring in a series of three-centered, cyanide-bridged intervalent charge-transfer complexes

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

Pfennig, B.W.; Bocarsly, A.B.

1992-01-09

The mixed-valent compound (Pt(NH{sub 3}){sub 4}){sub 2}((NC){sub 5}Fe-CN-Pt(NH{sub 3}){sub 4}-NC-Fe(CN){sub 5} was used as the starting point for the synthesis and characterization of two series of trinuclear {open_quotes}M-Pt-M{close_quotes} compounds. The first group of complexes have the general formula Na{sub 2}(L(NC){sub 4}Fe-CN-Pt(NH{sub 3}){sub 4}-NC-Fe(CN){sub 4}L) (where the sixth coordination site on the terminal iron units has been varied using six different substituted pyridine or pyrazine ligands, L), and the secondary group of compounds have the general formula (Pt(NH){sub 3}){sub 4}){sub 2}((NC){sub 5}M-CN-Pt(NH{sub 3}){sub 4}-NC-M(CN){sub 5}) (where M = Fe, Ru, and Os). All of the compounds yielded an absorption spectrum containingmore » an intervalent charge-transfer (IT) band in the visible. Both series of complexes were modeled using Marcus-Hush theory to estimate the reorganization energies for the optical electron-transfer processes, electron-transfer rate constants, thermal-activation barriers, and the degrees of delocalization of these species. In addition, the kinetics of formation, photochemical decomposition, and a novel solvent-gated charge-transfer process are discussed. 26 refs., 10 figs., 4 tabs.« less

Chemical synthesis of L10 Fe-Pt-Ni alloy nanoparticles

NASA Astrophysics Data System (ADS)

Deepchand, Vimal; Abel, Frank M.; Tzitzios, Vasileios; Hadjipanayis, George C.

2018-05-01

This work focuses on the study of the magnetic and structural properties of chemically synthesized FePt1-xNix nanoparticles, with Ni content x in the range 0.2-0.4. We report the effect of Ni substitution on the L10 structure, on both the as-synthesized and annealed nanoparticles. A decrease in nanoparticle size as well as in chemical order is observed with an increase in Ni content, for both the as-made and annealed nanoparticles. The results also show that the post annealing procedure at 700oC significantly enhanced the L10 ordering of the nanoparticles. Substitution of nickel leads to a decrease in coercivity from 14.9 kOe in FePt to 0.8 kOe for FePt0.6Ni0.4 alloy, while the magnetization at 3 T is increased from 48 emu/g to 88 emu/g.

[μ-Bis(diphenyl­phosphan­yl)methane]­tricarbon­yl(μ-p-toluene­sulfonyl­meth­yl isocyanato)(triphenyl­phosphane)ironplatinum(Fe—Pt)

PubMed Central

Jourdain, Isabelle; Knorr, Michael; Koller, Stephan G.; Strohmann, Carsten

2012-01-01

The title compound, [FePt(C9H9NO2S)(C18H15P)(C25H22P2)(CO)3], represents a rare example of an isonitrile-bridged heterobimetallic complex (here Pt and Fe) and is an inter­esting precursor for the preparation of heterodinuclear μ-amino­carbyne complexes, since the basic imine-type N atom of the μ2-C=N–R ligand readily undergoes addition with various electrophiles to afford iminium-like salts. In the crystal, the almost symmetrically bridging μ2-C=N-R ligand (neglecting the different atomic radii of Fe and Pt) is strongly bent towards the Fe(CO)3 fragment, with a C=N-R angle of only 121.1 (4)°. PMID:22412466

Resistive switching properties and physical mechanism of cobalt ferrite thin films

NASA Astrophysics Data System (ADS)

Hu, Wei; Zou, Lilan; Chen, Ruqi; Xie, Wei; Chen, Xinman; Qin, Ni; Li, Shuwei; Yang, Guowei; Bao, Dinghua

2014-04-01

We report reproducible resistive switching performance and relevant physical mechanism of sandwiched Pt/CoFe2O4/Pt structures in which the CoFe2O4 thin films were fabricated by a chemical solution deposition method. Uniform switching voltages, good endurance, and long retention have been demonstrated in the Pt/CoFe2O4/Pt memory cells. On the basis of the analysis of current-voltage characteristic and its temperature dependence, we suggest that the carriers transport through the conducting filaments in low resistance state with Ohmic conduction behavior, and the Schottky emission and Poole-Frenkel emission dominate the conduction mechanism in high resistance state. From resistance-temperature dependence of resistance states, we believe that the physical origin of the resistive switching refers to the formation and rupture of the oxygen vacancies related filaments. The nanostructured CoFe2O4 thin films can find applications in resistive random access memory.

Preparation and characterization of supported magnetic nanoparticles prepared by reverse micelles

PubMed Central

Han, Luyang; Biskupek, Johannes; Kaiser, Ute; Ziemann, Paul

2010-01-01

Summary Monatomic (Fe, Co) and bimetallic (FePt and CoPt) nanoparticles were prepared by exploiting the self-organization of precursor loaded reverse micelles. Achievements and limitations of the preparation approach are critically discussed. We show that self-assembled metallic nanoparticles can be prepared with diameters d = 2–12 nm and interparticle distances D = 20–140 nm on various substrates. Structural, electronic and magnetic properties of the particle arrays were characterized by several techniques to give a comprehensive view of the high quality of the method. For Co nanoparticles, it is demonstrated that magnetostatic interactions can be neglected for distances which are at least 6 times larger than the particle diameter. Focus is placed on FePt alloy nanoparticles which show a huge magnetic anisotropy in the L10 phase, however, this is still less by a factor of 3–4 when compared to the anisotropy of the bulk counterpart. A similar observation was also found for CoPt nanoparticles (NPs). These results are related to imperfect crystal structures as revealed by HRTEM as well as to compositional distributions of the prepared particles. Interestingly, the results demonstrate that the averaged effective magnetic anisotropy of FePt nanoparticles does not strongly depend on size. Consequently, magnetization stability should scale linearly with the volume of the NPs and give rise to a critical value for stability at ambient temperature. Indeed, for diameters above 6 nm such stability is observed for the current FePt and CoPt NPs. Finally, the long-term conservation of nanoparticles by Au photoseeding is presented. PMID:21977392

Key concepts behind forming-free resistive switching incorporated with rectifying transport properties

PubMed Central

Shuai, Yao; Ou, Xin; Luo, Wenbo; Mücklich, Arndt; Bürger, Danilo; Zhou, Shengqiang; Wu, Chuangui; Chen, Yuanfu; Zhang, Wanli; Helm, Manfred; Mikolajick, Thomas; Schmidt, Oliver G.; Schmidt, Heidemarie

2013-01-01

This work reports the effect of Ti diffusion on the bipolar resistive switching in Au/BiFeO3/Pt/Ti capacitor-like structures. Polycrystalline BiFeO3 thin films are deposited by pulsed laser deposition at different temperatures on Pt/Ti/SiO2/Si substrates. From the energy filtered transmission electron microscopy and Rutherford backscattering spectrometry it is observed that Ti diffusion occurs if the deposition temperature is above 600°C. The current-voltage (I–V) curves indicate that resistive switching can only be achieved in Au/BiFeO3/Pt/Ti capacitor-like structures where this Ti diffusion occurs. The effect of Ti diffusion is confirmed by the BiFeO3 thin films deposited on Pt/sapphire and Pt/Ti/sapphire substrates. The resistive switching needs no electroforming process, and is incorporated with rectifying properties which is potentially useful to suppress the sneak current in a crossbar architecture. Those specific features open a promising alternative concept for nonvolatile memory devices as well as for other memristive devices like synapses in neuromorphic circuits. PMID:23860408

Enhancement of oxygen reduction reaction activities by Pt nanoclusters decorated on ordered mesoporous porphyrinic carbons

DOE PAGES

Sun-Mi Hwang; Choi, YongMan; Kim, Min Gyu; ...

2016-03-08

The high cost of Pt-based membrane electrode assemblies (MEAs) is a critical hurdle for the commercialization of polymer electrolyte fuel cells (PEFCs). Recently, non-precious metal-based catalysts (NPMCs) have demonstrated much enhanced activity but their oxygen reduction reaction (ORR) activity is still inferior to that of Pt-based catalysts resulting in a much thicker electrode in the MEA. For the reduction of mass transport and ohmic overpotential we adopted a new concept of catalyst that combines an ultra-low amount of Pt nanoclusters with metal–nitrogen (M–Nx) doped ordered mesoporous porphyrinic carbon (FeCo–OMPC(L)). The 5 wt% Pt/FeCo–OMPC(L) showed a 2-fold enhancement in activities comparedmore » to a higher loading of Pt. Our experimental results supported by first-principles calculations indicate that a trace amount of Pt nanoclusters on FeCo–OMPC(L) significantly enhances the ORR activity due to their electronic effect as well as geometric effect from the reduced active sites. Finally, in terms of fuel cell commercialization, this class of catalysts is a promising candidate due to the limited use of Pt in the MEA.« less

Synthesis of an excellent electrocatalyst for oxygen reduction reaction with supercritical fluid: Graphene cellular monolith with ultrafine and highly dispersive multimetallic nanoparticles

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

Zhou, Yazhou; Cheng, Xiaonong; Yen, Clive H.

Graphene cellular monolith (GCM) can be used as an excellent support for nanoparticles in widespread applications. However, it's still a great challenge to deposit the desirable nanoparticles in GCM that have small size, controllable structure, composition, and high dispersion using the current methods. Here we demonstrate a green, efficient and large-scale method to address this challenge using supercritical fluid (SCF). By this superior method, graphene hydrogel can be transferred into GCM while being deposited with ultrafine and highly dispersive nanoparticles. Specifically, the bimetallic PtFe/GCM and the trimetallic PtFeCo/GCM catalysts are successfully synthesized, and their electrocatalytic performances toward oxygen reduction reactionmore » (ORR) are also studied. The resultant PtFe/GCM shows the significant enhancement in ORR activity, including a factor of 8.47 enhancement in mass activity (0.72 A mgPt-1), and a factor of 7.67 enhancement in specific activity (0.92 mA cm-2), comparing with those of the commercial Pt/C catalyst (0.085 A mgPt-1, 0.12 mA cm-2). Importantly, by introducing the Co, the trimetallic PtFeCo/GCM exhibits the further improved ORR activities (1.28 A mgPt-1, 1.80 mA cm-2). The high ORR activity is probably attributed to the alloying structure, ultrafine size, highly dispersive, well-defined, and a better interface with 3D porous graphene support.« less

Synthesis of an excellent electrocatalyst for oxygen reduction reaction with supercritical fluid: Graphene cellular monolith with ultrafine and highly dispersive multimetallic nanoparticles

NASA Astrophysics Data System (ADS)

Zhou, Yazhou; Cheng, Xiaonong; Yen, Clive H.; Wai, Chien M.; Wang, Chongmin; Yang, Juan; Lin, Yuehe

2017-04-01

Graphene cellular monolith (GCM) can be used as an excellent support for nanoparticles in widespread applications. However, it's still a great challenge to deposit the desirable nanoparticles in GCM that have small size, controllable structure, composition, and high dispersion using the current methods. Here we demonstrate a green, efficient and large-scale method to address this challenge using supercritical fluid (SCF). By this superior method, graphene hydrogel can be transferred into GCM while being deposited with ultrafine and highly dispersive nanoparticles. Specifically, the bimetallic PtFe/GCM and the trimetallic PtFeCo/GCM catalysts are successfully synthesized, and their electrocatalytic performances toward oxygen reduction reaction (ORR) are also studied. The resultant PtFe/GCM shows the significant enhancement in ORR activity, including a factor of 8.47 enhancement in mass activity (0.72 A mgPt-1), and a factor of 7.67 enhancement in specific activity (0.92 mA cm-2), comparing with those of the commercial Pt/C catalyst (0.085 A mgPt-1, 0.12 mA cm-2). Importantly, by introducing the Co, the trimetallic PtFeCo/GCM exhibits the further improved ORR activities (1.28 A mgPt-1, 1.80 mA cm-2). The high ORR activity is probably attributed to the alloying structure, ultrafine size, highly dispersive, well-defined, and a better interface with 3D porous graphene support.

Phonons of Fe-based superconductor Ca 10Pt 4As 8(Fe 1-xPt xAs) 10

DOE PAGES

Ikeuchi, K.; Kobayashi, Y.; Suzuki, K.; ...

2015-10-28

In this paper, we report the results of inelastic neutron scattering measurements on particular phonons of a superconducting (SC) Ca10Pt 4As 8(Fe 1-xPt xAs) 10 with the onset transition temperature T c ~ 33 K to investigate mainly what roles orbital fluctuation plays in Cooper pairing, where we observed a slight softening of the in-plane transverse acoustic mode corresponding to the elastic constant C 66. This softening starts at temperature T well above the superconducting T c, as T decreases. An anomalously strong change of the scattering intensity of in-plane optical modes was observed at the M point of themore » pseudo tetragonal reciprocal space in the range of 35 < ω < 40 meV with decreasing T from far above T c. Finally, because this ω region mainly corresponds to the motion of Fe and As atoms in the FeAs planes, the finding presents information on the coupling between the orbital fluctuation of Fe 3d electrons and the lattice system, useful for studying the possible roles of orbital fluctuation in the pairing mechanism and/or the appearance of the so-called nematic phase.« less

Platinum-free catalysts for low temperature fuel cells

NASA Astrophysics Data System (ADS)

Lastovina, Tatiana; Pimonova, Julia; Budnyk, Andriy

2017-04-01

In this work, we have successfully prepared Zn/Co-N/C and Zn/Co-Fe/N/C composites, both derived from single zeolitic imidazolate framework (ZIF) precursor Zn/Co-ZIF containing equivalent quantities of Zn and Co metal sites. The composites were formed by pyrolysis of the precursor at 700 °C in inert gas atmosphere as such and after mixing it with Fe(II) salt and 1,10-phenontraline in ethanol. Catalytic tests for oxygen reduction reaction (ORR) in electrochemical cell demonstrated promising results allowing us to consider these composites as potential Pt-free catalysts for low temperature fuel cells.

Bottom-up meets top-down: tailored raspberry-like Fe 3 O 4 –Pt nanocrystal superlattices

DOE PAGES

Qiu, Fen; Vervuurt, René H. J.; Verheijen, Marcel A.; ...

2018-01-01

Bottom up colloidal synthesis is combined with top down atomic layer deposition to achieve raspberry-like Pt-decorated Fe 3 O 4 nanoparticle superlattices with good metal–oxide–metal contact for photoelectrocatalysis.

Bottom-up meets top-down: tailored raspberry-like Fe 3 O 4 –Pt nanocrystal superlattices

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

Qiu, Fen; Vervuurt, René H. J.; Verheijen, Marcel A.

Bottom up colloidal synthesis is combined with top down atomic layer deposition to achieve raspberry-like Pt-decorated Fe 3 O 4 nanoparticle superlattices with good metal–oxide–metal contact for photoelectrocatalysis.

Patterned FePt nanostructures using ultrathin self-organized templates

NASA Astrophysics Data System (ADS)

Deng, Chen Hua; Zhang, Min; Wang, Fang; Xu, Xiao Hong

2018-02-01

Patterned magnetic thin films are both scientifically interesting and technologically useful. Ultrathin self-organized anodic aluminum oxide (AAO) template can be used to fabricate large area nanodot and antidot arrays. The magnetic properties of these nanostructures may be tuned by the morphology of the AAO template, which in turn can be controlled by synthetic parameters. In this work, ultrathin AAO templates were used as etching masks for the fabrication of both FePt nanodot and antidot arrays with high areal density. The perpendicular magnetic anisotropy of L10 FePt thin films are preserved in the nanostructures.

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.

Phase investigation in Pt supported off-stoichiometric iron-platinum thin films

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

Gupta, Rekha; Medwal, Rohit; Annapoorni, S., E-mail: annapoornis@yahoo.co.in

2013-10-15

Graphical abstract: - Highlights: • Low temperature FePt L1{sub 0} phase transformation using Pt/Fe{sub 3}Pt/Pt structure. • Temperature dependent FCC to FCT phase investigation using Rietveld refinement. • Estimation of soft and hard ferromagnetic contribution from demagnetization curve. • Interlayer diffusion and stoichiometry conformation of L1{sub 0} phase using RBS. • Correlation of structural, magnetic and RBS studies were successfully understood. - Abstract: The structural and magnetic phase transformation of Pt/Fe{sub 3}Pt/Pt films on Si <1 0 0> substrates prepared by DC magnetron sputtering is investigated as a function of annealing temperature. Pt diffusion driven low temperature phase transformation frommore » A1 to L1{sub 0} phase is achieved at 300 °C, attaining a very high coercivity of 9 kOe. At 300 °C, 85% L1{sub 0} phase transformation is observed using the X-ray diffraction profile fitting. The estimated phase content is also further verified by fitting the demagnetization curve. The underlayer promotes the ordering at lower temperature while overlayer induces growth along (0 0 1) preferred orientation. Rutherford back scattering study reveals interlayer diffusion and confirms the desired stoichiometry for L1{sub 0} phase. The presence of Pt under-overlayer provides the Pt source and further facilitates the Pt diffusion, which makes it effective in promoting the phase ordering at a lower temperature.« less

Nanostructured double-layer FeO as nanotemplate for tuning adsorption of titanyl phthalocyanine molecules

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

Lu, Shuangzan; University of Chinese Academy of Sciences, Beijing 100049; Qin, Zhihui, E-mail: zhqin@wipm.ac.cn

2014-06-23

The growth, structure of Pt(111) supported double-layer FeO and the adsorption of titanyl phthalocyanine (TiOPc) molecules with tunable site and orientation were presented. According to the atomic-resolution STM image, the structure was rationalized as (8√3 × 8√3) R30°/Pt(111) nanostructure constructed by Fe species coordinated with different number of oxygen on top of non-rotated (8 × 8) FeO /Pt(111) structure. Due to the modulation of the stacking of Fe atoms in the second layer relative to the O atoms in the second layer and the underlying layer, the interface and total dipole moment periodically vary within (8√3 × 8√3) R30°/Pt(111) structure. The resulted periodically distributed dipole-dipole interactionmore » benefits the growth of TiOPc molecules with area-selective sites and molecular orientations. Thus, this study provides a reliable method to govern the adsorption process of the polar molecules for potential applications in future functional molecular devices.« less

Self-current induced spin-orbit torque in FeMn/Pt multilayers

NASA Astrophysics Data System (ADS)

Xu, Yanjun; Yang, Yumeng; Yao, Kui; Xu, Baoxi; Wu, Yihong

2016-05-01

Extensive efforts have been devoted to the study of spin-orbit torque in ferromagnetic metal/heavy metal bilayers and exploitation of it for magnetization switching using an in-plane current. As the spin-orbit torque is inversely proportional to the thickness of the ferromagnetic layer, sizable effect has only been realized in bilayers with an ultrathin ferromagnetic layer. Here we demonstrate that, by stacking ultrathin Pt and FeMn alternately, both ferromagnetic properties and current induced spin-orbit torque can be achieved in FeMn/Pt multilayers without any constraint on its total thickness. The critical behavior of these multilayers follows closely three-dimensional Heisenberg model with a finite Curie temperature distribution. The spin torque effective field is about 4 times larger than that of NiFe/Pt bilayer with a same equivalent NiFe thickness. The self-current generated spin torque is able to switch the magnetization reversibly without the need for an external field or a thick heavy metal layer. The removal of both thickness constraint and necessity of using an adjacent heavy metal layer opens new possibilities for exploiting spin-orbit torque for practical applications.

Ni doping dependent dielectric, leakage, ferroelectric and magnetic properties in Bi7Fe3-xNixTi3O21 thin films

NASA Astrophysics Data System (ADS)

Yang, B. B.; Song, D. P.; Wei, R. H.; Tang, X. W.; Hu, L.; Yang, J.; Song, W. H.; Dai, J. M.; Zhu, X. B.; Sun, Y. P.

2018-05-01

Bi7Fe3-xNixTi3O21 thin films were prepared by chemical solution deposition on Pt/Ti/SiO2/Si substrates. The Ni doping effects on the dielectric, leakage, ferroelectric and magnetic properties were investigated. Coexistence of ferroelectric and ferromagnetic properties at room-temperature was observed in the Bi7Fe2NiTi3O21 thin film with a remnant polarization 2Pr of 36.4 μC/cm2 and a remnant magnetization 2Mr of 3.9 emu/cm3. The dielectric and leakage properties were discussed in detailed. The results will provide important information to explore single-phase multiferroic materials.

Colloidal strategies for controlling the morphology, composition, and crystal structure of inorganic nanoparticles

NASA Astrophysics Data System (ADS)

Hodges, James M.

Emerging applications and fundamental studies require nanomaterials with increasingly sophisticated architectures that have precise composition, morphology, and crystal structure. Colloidal nanochemistry has emerged as one of the most effective methods for generating high quality, monodisperse nanoparticles with diverse structural features and highly complex geometries. These wet-chemical approaches offer an array of synthetic levers that can be used to tailor nanoparticles for targeted applications, and deliver solution-dispersible solids that are easily integrated onto device architectures. Additionally, colloidal nanoparticles can be used as building blocks for constructing periodic superlattices and multicomponent hybrid nanoparticles, which offer unique properties that can support next-generation technologies. As the applications for colloidal nanoparticles continue to expand, the architectural and compositional requirements for these materials are becoming increasingly rigid. Conventional colloidal methods are effective for generating diverse nanoparticle systems, but rely on complex nucleation and growth processes, which are often poorly understood and difficult to control in dynamic reaction environments. For these reasons, there are a number of high profile nanoparticle targets that remain out of reach. Accordingly, new approaches are needed that can circumvent these synthetic bottlenecks and narrow the growing disconnect between nano-design and synthetic capability. In this dissertation, I present several colloidal strategies for engineering synthetically challenging nanomaterials using multistep reaction sequences that, in many ways, parallel the total-synthesis framework that organic chemists use to access complex molecules. A variety of approaches are discussed, including nanoscale ion exchange transformations and seeded-growth protocol for constructing multicomponent hybrid nanoparticles. First, I demonstrate that solution-mediated anion and cation exchange can be integrated into one multistep reaction sequence, which leads to a complete material transformation of a pre-synthesized nanotemplate. Importantly, although the final product does not contain any of the original elements, the morphology is retained, effectively decoupling morphology and composition control. Next, I demonstrate that both anion and cation sublattice features of preformed Cu2-xS nanocrystals can be retained during cation exchange with Co2+ and Mn2+, yielding wurtzite-type CoS and MnS polymorphs that are metastable in bulk systems. This study was enabled by new cation exchange chemistry with previously unexplored 3d transition metal systems, and offers new guidelines for predictably targeting sublattice features in colloidal nanomaterials. To conclude the dissertation, I offer two studies investigating the seeded-growth synthesis of three-component Ag-Pt-Fe3O4 heterotrimer nanoparticles, which are generated by adding a Ag domain to preformed Pt-Fe 3O4 heterodimers. First, to gain access to the alternate Pt-Fe3O4-Ag configuration, I demonstrate that a thin iron oxide shell can be applied to the Pt surface of the Pt-Fe3O 4 seeds, which acts as a solid-state protecting group that can direct Ag growth onto the Fe3O4 domain, producing the otherwise inaccessible Pt-Fe3O4-Ag architecture. This strategy is inspired by similar techniques used in organic synthesis, and represents an important addition to the 'total synthesis toolbox' used to construct colloidal hybrid nanoparticles. Finally, I offer an in-depth microscopic investigation that probes the chemoselective addition of Ag to Pt-Fe 3O4 to form the Ag-Pt-Fe3O4 heterotrimer product. This study reveals that Ag indiscriminately nucleates on both the Pt and Fe3O4 domains of the Pt-Fe3O 4 seeds during the early stages of the reaction, followed by a surface-mediated coalescence of Ag onto the Pt domain to yield the Ag-Pt-Fe3O 4 configuration. The mechanistic insights gained in this work provide new design criteria for synthesizing multicomponent hybrid nanoparticle systems with targeted configurations.

Dependence of magnetic properties on different buffer layers of Mn3.5Ga thin films

NASA Astrophysics Data System (ADS)

Takahashi, Y.; Sato, K.; Shima, T.; Doi, M.

2018-05-01

D022-Mn3.5Ga thin films were prepared on MgO (100) single crystalline substrates with different buffer layer (Cr, Fe, Cr/Pt and Cr/Au) using an ultra-high-vacuum electron beam vapor deposition system. From XRD patterns, a fundamental (004) peak has clearly observed for all samples. The relatively low saturation magnetization (Ms) of 178 emu/cm3, high magnetic anisotropy (Ku) of 9.1 Merg/cm3 and low surface roughness (Ra) of 0.30 nm were obtained by D022-Mn3.5Ga film (20 nm) on Cr/Pt buffer layer at Ts = 300 °C, Ta = 400 °C (3h). These findings suggest that MnGa film on Cr/Pt buffer layer is a promising PMA layer for future spin electronics devices.

Re-evaluation of the impact of ternary additions of Ni and Cu on the A1 to L1{sub 0} transformation in FePt films

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

Wang, B.; Barmak, K.

2011-06-15

The impact of ternary additions of Ni (1.6-21.5 at. %) and Cu (1.3-17.3 at. %) on the A1 (face centered cubic, fcc) to L1{sub 0} phase transformation in FePt films has been re-evaluated based on compositions obtained using energy dispersive x-ray spectrometry (EDS). The data presented here serve as corrections to results reported in six previous studies [D. C. Berry and K. Barmak, J. Appl. Phys. 102, 024912 (2007); 101, 014905 (2007); 99, 08G901 (2006); D. C. Berry, J. Kim, K. Barmak, K. Wierman, E. B. Svedberg, and J. K. Howard, Scr. Mater. 53, 423 (2005); K. Barmak, J. Kim,more » D. C. Berry, W. N. Hanani, K. Wierman, E. B. Svedberg, and J. K. Howard, J. Appl. Phys. 97, 024902 (2005); K. Barmak, J. Kim, D. C. Berry, K. W. Wierman, E. B. Svedberg, and J. K. Howard, ibid. 95, 7486 (2004)]. The new EDS compositions do not change the following conclusions of these previous studies: (i) when ternary FeNiPt and FeCuPt alloys are compared with binary FePt alloys with the same Pt content, it is seen that additions of Ni slow the transformation kinetics, whereas additions of Cu have no measurable impact on the kinetics, (ii) the Curie temperature of the L1{sub 0} phase is lowered by additions of Ni or Cu, (iii) the Curie temperature of the A1 phase is increased by additions of Ni, but lowered by additions of Cu, and (iv) the transformation enthalpy is lowered by large additions of Ni, but is unaffected by additions of Cu. The ordering behavior of FeCuPt alloys as evidenced by the kinetic ordering temperature is compared with other reports in the literature based on magnetic measurements.« less

Feasibilty of a Multi-bit Cell Perpendicular Magnetic Tunnel Junction Device

NASA Astrophysics Data System (ADS)

Kim, Chang Soo

The ultimate objective of this research project was to explore the feasibility of making a multi-bit cell perpendicular magnetic tunnel junction (PMTJ) device to increase the storage density of spin-transfer-torque random access memory (STT-RAM). As a first step toward demonstrating a multi-bit cell device, this dissertation contributed a systematic and detailed study of developing a single cell PMTJ device using L10 FePt films. In the beginning of this research, 13 up-and-coming non-volatile memory (NVM) technologies were investigated and evaluated to see whether one of them might outperform NAND flash memories and even HDDs on a cost-per-TB basis in 2020. This evaluation showed that STT-RAM appears to potentially offer superior power efficiency, among other advantages. It is predicted that STTRAM's density could make it a promising candidate for replacing NAND flash memories and possibly HDDs if STTRAM could be improved to store multiple bits per cell. Ta/Mg0 under-layers were used first in order to develop (001) L1 0 ordering of FePt at a low temperature of below 400 °C. It was found that the tradeoff between surface roughness and (001) L10 ordering of FePt makes it difficult to achieve low surface roughness and good perpendicular magnetic properties simultaneously when Ta/Mg0 under-layers are used. It was, therefore, decided to investigate MgO/CrRu under-layers to simultaneously achieve smooth films with good ordering below 400°C. A well ordered 4 nm L10 FePt film with RMS surface roughness close to 0.4 nm, perpendicular coercivity of about 5 kOe, and perpendicular squareness near 1 was obtained at a deposition temperature of 390 °C on a thermally oxidized Si substrate when MgO/CrRu under-layers are used. A PMTJ device was developed by depositing a thin MgO tunnel barrier layer and a top L10 FePt film and then being postannealed at 450 °C for 30 minutes. It was found that the sputtering power needs to be minimized during the thin MgO tunnel barrier deposition because the high sputtering power can degrade perpendicular magnetic anisotropy of the bottom L1 0 FePt film and also increase RMS film surface roughness of the MgO tunnel barrier layer. From a lithographically unpatterned PMTJ sample, MR ratio and RA were measured at room temperature by the CIPT method and found to be 138% and 6.4 kOmicrom2, respectively. A completed PMTJ test pattern with a junction size of 80x40 microm2 was fabricated and showed a measured MR ratio and RA product of 108% and 4~6 kOmicrom 2, respectively. These values agree relatively well with the corresponding values of 138% and 6.4 kOmicrom2 obtained from the unpatterned PMTJ sample measured by a current-in-plane tunneling (CIPT) method.

Influence of antisite defects and stacking faults on the magnetocrystalline anisotropy of FePt

NASA Astrophysics Data System (ADS)

Wolloch, M.; Suess, D.; Mohn, P.

2017-09-01

We present density functional theory (DFT) calculations of the magnetic anisotropy energy (MAE) of FePt, which is of great interest for magnetic recording applications. Our data, and the majority of previously calculated results for perfectly ordered crystals, predict a MAE of ˜3.0 meV per formula unit, which is significantly larger than experimentally measured values. Analyzing the effects of disorder by introducing stacking faults (SFs) and antisite defects (ASDs) in varying concentrations we are able to reconcile calculations with experimental data and show that even a low concentration of ASDs are able to reduce the MAE of FePt considerably. Investigating the effect of exact exchange and electron correlation within the adiabatic-connection dissipation fluctuation theorem in the random phase approximation (ACDFT-RPA) reveals a significantly smaller influence on the MAE. Thus the effect of disorder, and more specifically ASDs, is the crucial factor in explaining the deviation of common DFT calculations of FePt to experimental measurements.

Grindability of dental magnetic alloys.

PubMed

Hayashi, Eisei; Kikuchi, Masafumi; Okuno, Osamu; Kimura, Kohei

2005-06-01

In this study, the grindability of cast magnetic alloys (Fe-Pt-Nb magnetic alloy and magnetic stainless steel) was evaluated and compared with that of conventional dental casting alloys (Ag-Pd-Au alloy, Type 4 gold alloy, and cobalt-chromium alloy). Grindability was evaluated in terms of grinding rate (i.e., volume of metal removed per minute) and grinding ratio (i.e., volume ratio of metal removed compared to wheel material lost). Solution treated Fe-Pt-Nb magnetic alloy had a significantly higher grinding rate than the aged one at a grinding speed of 750-1500 m x min(-1). At 500 m x min(-1), there were no significant differences in grinding rate between solution treated and aged Fe-Pt-Nb magnetic alloys. At a lower speed of 500 m x min(-1) or 750 m x min(-1), it was found that the grinding rates of aged Fe-Pt-Nb magnetic alloy and stainless steel were higher than those of conventional casting alloys.

Polarization fatigue of BiFeO3 films with ferromagnetic metallic electrodes

NASA Astrophysics Data System (ADS)

Chen, Chen; Wang, Ji; Li, Chen; Wen, Zheng; Xu, Qingyu; Du, Jun

2017-05-01

BiFeO3 (BFO) thin films were epitaxially grown on (001) SrTiO3 substrates using LaNiO3 as bottom electrode by pulsed laser deposition. The ferroelectric properties of BFO layer with ferromagnetic Ni21Fe79 (NiFe) or non-magnetic Pt electrode are investigated. Well saturated polarization-electric field (P-E) hysteresis loops are observed. Significant fatigue and associated drastic decrease in switchable polarization have been observed with cycling number exceeds 106, which can be explained by the domain wall pinning due to the oxygen vacancies trapping. With increasing cycle number to above 107, the polarization is rejuvenated. The polarization for BFO layer with NiFe electrode recovers to the initial value, while only about 75% of initial polarization is recovered for BFO layer with Pt electrode. Furthermore, the imprint is alleviated and the P-E hysteresis loops become more symmetric after the polarization recovery. The difference can be understood by the different interface state of NiFe/BFO and Pt/BFO.

Fabrication of superhydrophobic Pt3Fe/Fe surface for its application

NASA Astrophysics Data System (ADS)

Cui, Shuo; Lu, Shixiang; Xu, Wenguo; Wu, Bei

2017-10-01

Well-defined Pt3Fe/Fe superhydrophobic materials on iron sheet with special properties, such as corrosion resistance, superhydrophobicity and superoleophilicity, was fabricated. The fabrication process involved etching in hydrochloric acid aqueous solution and simple replacement deposition process without using any seed and organic solvent, and then annealing. The electrochemical measurements show that the resultant surface in 3.5% sodium chloride solution displays good corrosion resistance. Also, it is proved that the obtained surface has better mechanical abrasion resistance via scratch test. The superoleophilicity and low water adhesion force of the obtained surface endow it high oil/water separation capacity. The as-prepared nanocomposites display enhanced catalytic activity and kinetics toward degradation of methyl orange. In particular, it possesses the most efficient degradation capacity (95%) towards methyl orange at a high concentration (17.5 mg/L) in 80 min. The improved stability and excellent catalytic activity of the Pt3Fe/Fe nanocomposites promise new opportunities for the development of waste water treatment.

Direct Visualization of Catalytically Active Sites at the FeO–Pt(111) Interface

DOE PAGES

Kudernatsch, Wilhelmine; Peng, Guowen; Zeuthen, Helene; ...

2015-05-31

Within the area of surface science, one of the “holy grails” is to directly visualize a chemical reaction at the atomic scale. Whereas this goal has been reached by high-resolution scanning tunneling microscopy (STM) in a number of cases for reactions occurring at flat surfaces, such a direct view is often inhibited for reaction occurring at steps and interfaces. Here we have studied the CO oxidation reaction at the interface between ultrathin FeO islands and a Pt(111) support by in situ STM and density functional theory (DFT) calculations. Time-lapsed STM imaging on this inverse model catalyst in O 2 andmore » CO environments revealed catalytic activity occurring at the FeO–Pt(111) interface and directly showed that the Fe-edges host the catalytically most active sites for the CO oxidation reaction. This is an important result since previous evidence for the catalytic activity of the FeO–Pt(111) interface is essentially based on averaging techniques in conjunction with DFT calculations. As a result, the presented STM results are in accord with DFT+U calculations, in which we compare possible CO oxidation pathways on oxidized Fe-edges and O-edges. We found that the CO oxidation reaction is more favorable on the oxidized Fe-edges, both thermodynamically and kinetically.« less

Synthesis of Pt-Ni-Fe/CNT/CP nanocomposite as an electrocatalytic electrode for PEM fuel cell cathode

NASA Astrophysics Data System (ADS)

Litkohi, Hajar Rajaei; Bahari, Ali; Ojani, Reza

2017-08-01

In order to use carbon nanotube (CNT)-supported catalyst as fuel cell electrodes, Pt-Ni-Fe/CNT/carbon paper (CP) electrode was prepared using an ethylene glycol reduction method. CNTs were directly synthesized on Ni-impregnated carbon paper, plain carbon cloth, and Teflonized carbon cloth using chemical vapor deposition. FESEM and TEM images and thermogravimetric analysis indicated that in situ CNT on carbon paper (ICNT/CP) possesses more appropriate structural quality and stronger adhesion to the substrate than other substrates. The contact angle analysis demonstrated that the degree of ICNT/CP surface hydrophobicity encountered a 24% increase in comparison to CP and promoted to superhydrophobicity from hydrophobicity. The polarization curves and electrochemical impedance spectroscopy results of the loaded Pt-Ni-Fe on in situ and ex situ CNT/CP illustrated that the power density increased and charge transfer resistance reduced compared to commercial Pt/C loaded on CP. The results can be attributed to the outstanding properties of CNTs and high catalytic activity of triple catalysts causing alloying of Pt with Ni and Fe, which makes them a proper candidate to be used as cathode electrodes in proton exchange membrane fuel cells.

Iron-platinum-coated carbon nanocone probes on tipless cantilevers for high resolution magnetic force imaging.

PubMed

Chen, I-Chen; Chen, Li-Han; Gapin, Andrew; Jin, Sungho; Yuan, Lu; Liou, Sy-Hwang

2008-02-20

High coercivity iron-platinum-coated carbon nanocones (CNCs) have been fabricated for magnetic force microscopy (MFM) by direct-current plasma-enhanced chemical vapor deposition growth of nanocones on tipless cantilevers followed by sputtering and annealing of the FePt film. The FePt-coated CNC probe has many localized magnetic stray fields due to the high-aspect-ratio geometry and small radius of the tip. The MFM imaging on magnetic recording media was performed using CNC probes and compared with the imaging by FePt-coated silicon probes. An image with 20 nm lateral resolution has been demonstrated.

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.

Electric-field tunable spin diode FMR in patterned PMN-PT/NiFe structures

NASA Astrophysics Data System (ADS)

Zietek, Slawomir; Ogrodnik, Piotr; Skowroński, Witold; Stobiecki, Feliks; van Dijken, Sebastiaan; Barnaś, Józef; Stobiecki, Tomasz

2016-08-01

Dynamic properties of NiFe thin films on PMN-PT piezoelectric substrate are investigated using the spin-diode method. Ferromagnetic resonance (FMR) spectra of microstrips with varying width are measured as a function of magnetic field and frequency. The FMR frequency is shown to depend on the electric field applied across the substrate, which induces strain in the NiFe layer. Electric field tunability of up to 100 MHz per 1 kV/cm is achieved. An analytical model based on total energy minimization and the Landau-Lifshitz-Gilbert equation, taking into account the magnetostriction effect, is used to explain the measured dynamics. Based on this model, conditions for optimal electric-field tunable spin diode FMR in patterned NiFe/PMN-PT structures are derived.

The role of phase separation for self-organized surface pattern formation by ion beam erosion and metal atom co-deposition

NASA Astrophysics Data System (ADS)

Hofsäss, H.; Zhang, K.; Pape, A.; Bobes, O.; Brötzmann, M.

2013-05-01

We investigate the ripple pattern formation on Si surfaces at room temperature during normal incidence ion beam erosion under simultaneous deposition of different metallic co-deposited surfactant atoms. The co-deposition of small amounts of metallic atoms, in particular Fe and Mo, is known to have a tremendous impact on the evolution of nanoscale surface patterns on Si. In previous work on ion erosion of Si during co-deposition of Fe atoms, we proposed that chemical interactions between Fe and Si atoms of the steady-state mixed Fe x Si surface layer formed during ion beam erosion is a dominant driving force for self-organized pattern formation. In particular, we provided experimental evidence for the formation of amorphous iron disilicide. To confirm and generalize such chemical effects on the pattern formation, in particular the tendency for phase separation, we have now irradiated Si surfaces with normal incidence 5 keV Xe ions under simultaneous gracing incidence co-deposition of Fe, Ni, Cu, Mo, W, Pt, and Au surfactant atoms. The selected metals in the two groups (Fe, Ni, Cu) and (W, Pt, Au) are very similar regarding their collision cascade behavior, but strongly differ regarding their tendency to silicide formation. We find pronounced ripple pattern formation only for those co deposited metals (Fe, Mo, Ni, W, and Pt), which are prone to the formation of mono and disilicides. In contrast, for Cu and Au co-deposition the surface remains very flat, even after irradiation at high ion fluence. Because of the very different behavior of Cu compared to Fe, Ni and Au compared to W, Pt, phase separation toward amorphous metal silicide phases is seen as the relevant process for the pattern formation on Si in the case of Fe, Mo, Ni, W, and Pt co-deposition.

Nanocrystalline Fe-Fe2O3 particle-deposited N-doped graphene as an activity-modulated Pt-free electrocatalyst for oxygen reduction reaction

NASA Astrophysics Data System (ADS)

Dhavale, Vishal M.; Singh, Santosh K.; Nadeema, Ayasha; Gaikwad, Sachin S.; Kurungot, Sreekumar

2015-11-01

The size-controlled growth of nanocrystalline Fe-Fe2O3 particles (2-3 nm) and their concomitant dispersion on N-doped graphene (Fe-Fe2O3/NGr) could be attained when the mutually assisted redox reaction between NGr and Fe3+ ions could be controlled within the aqueous droplets of a water-in-oil emulsion. The synergistic interaction existing between Fe-Fe2O3 and NGr helped the system to narrow down the overpotential for the oxygen reduction reaction (ORR) by bringing a significant positive shift to the reduction onset potential, which is just 15 mV higher than its Pt-counterpart. In addition, the half-wave potential (E1/2) of Fe-Fe2O3/NGr is found to be improved by a considerable amount of 135 mV in comparison to the system formed by dispersing Fe-Fe2O3 nanoparticles on reduced graphene oxide (Fe-Fe2O3/RGO), which indicates the presence of a higher number of active sites in Fe-Fe2O3/NGr. Despite this, the ORR kinetics of Fe-Fe2O3/NGr are found to be shifted significantly to the preferred 4-electron-transfer pathway compared to NGr and Fe-Fe2O3/RGO. Consequently, the H2O2% was found to be reduced by 78.3% for Fe-Fe2O3/NGr (13.0%) in comparison to Fe-Fe2O3/RGO (51.2%) and NGr (41.0%) at -0.30 V (vs. Hg/HgO). This difference in the yield of H2O2 formed between the systems along with the improvements observed in terms of the oxygen reduction onset and E1/2 in the case of Fe-Fe2O3/NGr reveals the activity modulation achieved for the latter is due to the coexistence of factors such as the presence of the mixed valancies of iron nanoparticles, small size and homogeneous distribution of Fe-Fe2O3 nanoparticles and the electronic modifications induced by the doped nitrogen in NGr. A controlled interplay of these factors looks like worked favorably in the case of Fe-Fe2O3/NGr. As a realistic system level validation, Fe-Fe2O3/NGr was employed as the cathode electrode of a single cell in a solid alkaline electrolyte membrane fuel cell (AEMFC). The system could display an open circuit voltage (OCV) of 0.73 V and maximum power and current densities of 54.40 mW cm-2 and 200 mA cm-2, respectively, which are comparable to the performance characteristics of a similar system derived by using 40 wt% Pt/C as the cathode electrode.The size-controlled growth of nanocrystalline Fe-Fe2O3 particles (2-3 nm) and their concomitant dispersion on N-doped graphene (Fe-Fe2O3/NGr) could be attained when the mutually assisted redox reaction between NGr and Fe3+ ions could be controlled within the aqueous droplets of a water-in-oil emulsion. The synergistic interaction existing between Fe-Fe2O3 and NGr helped the system to narrow down the overpotential for the oxygen reduction reaction (ORR) by bringing a significant positive shift to the reduction onset potential, which is just 15 mV higher than its Pt-counterpart. In addition, the half-wave potential (E1/2) of Fe-Fe2O3/NGr is found to be improved by a considerable amount of 135 mV in comparison to the system formed by dispersing Fe-Fe2O3 nanoparticles on reduced graphene oxide (Fe-Fe2O3/RGO), which indicates the presence of a higher number of active sites in Fe-Fe2O3/NGr. Despite this, the ORR kinetics of Fe-Fe2O3/NGr are found to be shifted significantly to the preferred 4-electron-transfer pathway compared to NGr and Fe-Fe2O3/RGO. Consequently, the H2O2% was found to be reduced by 78.3% for Fe-Fe2O3/NGr (13.0%) in comparison to Fe-Fe2O3/RGO (51.2%) and NGr (41.0%) at -0.30 V (vs. Hg/HgO). This difference in the yield of H2O2 formed between the systems along with the improvements observed in terms of the oxygen reduction onset and E1/2 in the case of Fe-Fe2O3/NGr reveals the activity modulation achieved for the latter is due to the coexistence of factors such as the presence of the mixed valancies of iron nanoparticles, small size and homogeneous distribution of Fe-Fe2O3 nanoparticles and the electronic modifications induced by the doped nitrogen in NGr. A controlled interplay of these factors looks like worked favorably in the case of Fe-Fe2O3/NGr. As a realistic system level validation, Fe-Fe2O3/NGr was employed as the cathode electrode of a single cell in a solid alkaline electrolyte membrane fuel cell (AEMFC). The system could display an open circuit voltage (OCV) of 0.73 V and maximum power and current densities of 54.40 mW cm-2 and 200 mA cm-2, respectively, which are comparable to the performance characteristics of a similar system derived by using 40 wt% Pt/C as the cathode electrode. Electronic supplementary information (ESI) available: Experimental, deconvulated XPS of C 1s, and O 1s of Fe-Fe2O3/RGO, Fe-Fe2O3/NGr, RGO and NGr. Deconvoluted N 1s of Fe-Fe2O3/NGr and NGr, formulae, CV, LSV at different rpm, and K-L plots. See DOI: 10.1039/c5nr04929f

A simple route to diverse noble metal-decorated iron oxide nanoparticles for catalysis

NASA Astrophysics Data System (ADS)

Walker, Joan M.; Zaleski, Jeffrey M.

2016-01-01

Developing facile synthetic routes to multifunctional nanoparticles combining the magnetic properties of iron oxides with the optical and catalytic utility of noble metal particles remains an important goal in realizing the potential of hybrid nanomaterials. To this end, we have developed a single route to noble metal-decorated magnetic nanoparticles (Fe3O4@SiO2-M M = Au, Pd, Ag, and PtAg) and characterized them by HRTEM and STEM/EDX imaging to reveal their nanometer size (16 nm Fe3O4 and 1-5 nm M seeds) and uniformity. This represents one of the few examples of genuine multifunctional particles on the nanoscale. We show that these hybrid structures have excellent catalytic activity for the reduction of 4-nitrophenol (knorm = 2 × 107 s-1 mol(Pd)-1 5 × 106 s-1 mol(Au)-1 5 × 105 s-1 mol(PtAg)-1 7 × 105 s-1 mol(Ag)-1). These rates are the highest reported for nano-sized comparables, and are competitive with mesoparticles of similar composition. Due to their magnetic response, the particles are also suitable for magnetic recovery and maintain >99% conversion for at least four cycles. Using this synthetic route, Fe3O4@SiO2-M particles show great promise for further development as a precursor to complicated anisotropic materials or for applications ranging from nanocatalysis to biomedical sensing.Developing facile synthetic routes to multifunctional nanoparticles combining the magnetic properties of iron oxides with the optical and catalytic utility of noble metal particles remains an important goal in realizing the potential of hybrid nanomaterials. To this end, we have developed a single route to noble metal-decorated magnetic nanoparticles (Fe3O4@SiO2-M M = Au, Pd, Ag, and PtAg) and characterized them by HRTEM and STEM/EDX imaging to reveal their nanometer size (16 nm Fe3O4 and 1-5 nm M seeds) and uniformity. This represents one of the few examples of genuine multifunctional particles on the nanoscale. We show that these hybrid structures have excellent catalytic activity for the reduction of 4-nitrophenol (knorm = 2 × 107 s-1 mol(Pd)-1 5 × 106 s-1 mol(Au)-1 5 × 105 s-1 mol(PtAg)-1 7 × 105 s-1 mol(Ag)-1). These rates are the highest reported for nano-sized comparables, and are competitive with mesoparticles of similar composition. Due to their magnetic response, the particles are also suitable for magnetic recovery and maintain >99% conversion for at least four cycles. Using this synthetic route, Fe3O4@SiO2-M particles show great promise for further development as a precursor to complicated anisotropic materials or for applications ranging from nanocatalysis to biomedical sensing. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr06700f

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.

Tailoring the composition of ultrathin, ternary alloy PtRuFe nanowires for the methanol oxidation reaction and formic acid oxidation reaction

DOE PAGES

Scofield, Megan E.; Koenigsmann, Christopher; Wang, Lei; ...

2014-11-25

In the search for alternatives to conventional Pt electrocatalysts, we have synthesized ultrathin, ternary PtRuFe nanowires (NW), possessing different chemical compositions in order to probe their CO tolerance as well as electrochemical activity as a function of composition for both (i) the methanol oxidation reaction (MOR) and (ii) the formic acid oxidation reaction (FAOR). As-prepared ‘multifunctional’ ternary NW catalysts exhibited both higher MOR and FAOR activity as compared with binary Pt₇Ru₃ NW, monometallic Pt NW, and commercial catalyst control samples. In terms of synthetic novelty, we utilized a sustainably mild, ambient wet-synthesis method never previously applied to the fabrication ofmore » crystalline, pure ternary systems in order to fabricate ultrathin, homogeneous alloy PtRuFe NWs with a range of controlled compositions. Thus, these NWs were subsequently characterized using a suite of techniques including XRD, TEM, SAED, and EDAX in order to verify not only the incorporation of Ru and Fe into the Pt lattice but also their chemical homogeneity, morphology, as well as physical structure and integrity. Lastly, these NWs were electrochemically tested in order to deduce the appropriateness of conventional explanations such as (i) the bi-functional mechanism as well as (ii) the ligand effect to account for our MOR and FAOR reaction data. Specifically, methanol oxidation appears to be predominantly influenced by the Ru content, whereas formic acid oxidation is primarily impacted by the corresponding Fe content within the ternary metal alloy catalyst itself.« less

Synthesis, characterization, and photophysical properties of a series of supramolecular mixed-valence compounds.

PubMed

Pfennig, B W; Fritchman, V A; Hayman, K A

2001-01-15

The synthesis and characterization of 10 cyano-bridged trinuclear mixed-valence compounds of the form [(NH3)5M-NC-FeII(CN)4-CN-M'(NH3)5]n+ (M = RuIII, OsIII, CrIII, or PtIV; n = 2, 3, or 4) is reported. The electronic spectra of these supramolecular compounds exhibit a single intervalent (IT) absorption band for each nondegenerate Fe-->M/M' transition. The redox potential of the Fe(II) center is shifted more positive with the addition of each coordinated metal complex, while the redox potentials of the pendant metals vary only slightly from their dinuclear counterparts. As a result, the Fe-->M IT bands are blue-shifted from those in the corresponding dinuclear mixed-valence compounds. The energies of these IT bands show a linear correlation with the ground-state thermodynamic driving force, as predicted by classical electron transfer theory. Estimates of the degree of electronic coupling (Hab) between the metal centers using a theoretical analysis of the IT band shapes indicate that most of these values are similar to those for the corresponding dinuclear species. Notable exceptions occur for the Fe-->M IT transitions in Os-Fe-M (M = Cr or Pt). The enhanced electronic coupling in these two species can be explained as a result of excited state mixing between electron transfer and/or ligand-based charge transfer states and an intensity-borrowing mechanism. Additionally, the possibility of electronic coupling between the remote metal centers in the Ru-Fe-Ru species is discussed in order to explain the observation of two closely spaced redox waves for the degenerate Ru(III) acceptors.

A General Strategy for the Synthesis of PtM (M=Fe, Co, Ni) Decorated Three-Dimensional Hollow Graphene Nanospheres for Efficient Methanol Electrooxidation.

PubMed

Qiu, Xiaoyu; Li, Tiancheng; Deng, Sihui; Cen, Ke; Xu, Lin; Tang, Yawen

2018-01-26

A universal sacrificial template-based synthesis strategy was reported to prepare three dimensional (3D) reduced oxide graphene supported PtM (M=Fe, Co, Ni) hollow nanospheres (PtM/RGO HNSs). The inner 3D wrinkle-free graphene skeleton can promote electron and ion kinetics, resulting in enhancement for the permeation of small organic molecule in fuel cells. As inspired by this, the 3D PtM (M=Fe, Co, Ni)/RGO HNSs exhibit clearly enhanced electrocatalytic activity and durability towards the methanol oxidation reaction (MOR) in acidic medium compared with a commercial Pt/C catalyst. This study provides a versatile approach of realizing controlled synthesis of 3D graphene-metal hybrid nanostructures irrespective of the components of the metal domains, and will pave the way for the design of hetero-nanostructures with optimized morphologies and functions. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ferroelectric enhancement in heterostructured ZnO /BiFeO3-PbTiO3 film

NASA Astrophysics Data System (ADS)

Yu, Shengwen; Chen, Rui; Zhang, Guanjun; Cheng, Jinrong; Meng, Zhongyan

2006-11-01

The authors have prepared heterostructured ZnO /BiFeO3-PbTiO3 (BFO-PT) composite film and BFO-PT film on Pt /Ti/SiO2/Si substrates by pulsed-laser deposition. The structure and morphologies of the films were characterized by x-ray diffraction (XRD) and scanning electron microscope. XRD results show that both films are perovskite structured last with different orientations. The leakage current density in the ZnO /BFO-PT film was found to be nearly two orders of magnitude lower. This could be due to the introduced ZnO layer behaving as a Schottky barrier between the BFO-PT film and top electrodes. The dramatic ferroelectric enhancement in ZnO /BFO-PT film is mostly ascribed to the improved insulation.

Self-current induced spin-orbit torque in FeMn/Pt multilayers

PubMed Central

Xu, Yanjun; Yang, Yumeng; Yao, Kui; Xu, Baoxi; Wu, Yihong

2016-01-01

Extensive efforts have been devoted to the study of spin-orbit torque in ferromagnetic metal/heavy metal bilayers and exploitation of it for magnetization switching using an in-plane current. As the spin-orbit torque is inversely proportional to the thickness of the ferromagnetic layer, sizable effect has only been realized in bilayers with an ultrathin ferromagnetic layer. Here we demonstrate that, by stacking ultrathin Pt and FeMn alternately, both ferromagnetic properties and current induced spin-orbit torque can be achieved in FeMn/Pt multilayers without any constraint on its total thickness. The critical behavior of these multilayers follows closely three-dimensional Heisenberg model with a finite Curie temperature distribution. The spin torque effective field is about 4 times larger than that of NiFe/Pt bilayer with a same equivalent NiFe thickness. The self-current generated spin torque is able to switch the magnetization reversibly without the need for an external field or a thick heavy metal layer. The removal of both thickness constraint and necessity of using an adjacent heavy metal layer opens new possibilities for exploiting spin-orbit torque for practical applications. PMID:27185656

Platinum stable isotopes in ferromanganese crust and nodules

NASA Astrophysics Data System (ADS)

Corcoran, Loretta; Seward, Terry; Handler, Monica R.

2015-04-01

Hydrogenetic ferromanganese (Fe-Mn) crust and nodules are slow-growing chemical sediments that form by direct precipitation from seawater, resulting in a record of changing seawater chemistry. These sediments are the primary sink for platinum in the modern oxic marine environment, hosting well-documented enrichments over other platinum-group elements (PGEs): the Pt anomaly [1]. Platinum is a non-bio-essential, highly siderophile, transition metal with six stable isotopes (190Pt, 192Pt, 194Pt, 195Pt, 196Pt, and 198Pt) with several oxidation states (Pt0, Pt2+ and Pt4+). Platinum is generally considered to exist in the hydrosphere as Pt2+ although its behaviour in the marine environment is poorly constrained, and Pt4+may also be present. Variations in ocean redox state, together with changes in source fluxes to the oceans, may therefore lead to small variations (< ±1) in the stable isotopic composition of marine platinum, raising the potential of adding platinum to the growing arsenal of paleoceanographic tracers. A method has been developed to measure the platinum isotopic composition using double spike MC-ICPMS analysis [2]and applied to a global suite of modern Fe-Mn crust and nodules. Combining synchrotron XAFS analyses of platinum adsorbed onto Fe-Mn oxide and oxyhydroxide surfaces to determine oxidation state and bonding environment, with platinum stable isotopic measurements allowing us to evaluate both platinum incorporation onto these sediments and the associated degree of platinum isotopic fractionation. Leaching experiments conducted on platinum rich terrestrial materials underwent platinum stable isotopic measurement as an analogue for the Pt isotopic fractionation associated with continental weathering. [1] Hodge, V.F. et al. (1985) Earth and Planetary Science Letters, 72, 158-162. [2] Creech, J. et al. (2013) Journal of Analytical Atomic Spectrometry, 28. 853-865.

Highly (001) oriented L1{sub 0}-CoPt/TiN multilayer films on glass substrates with perpendicular magnetic anisotropy

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

An, Hongyu; Sannomiya, Takumi; Muraishi, Shinji

2015-03-15

To obtain strong perpendicular magnetic anisotropy (PMA) based on L1{sub 0} structure for magnetic storage devices, costly single crystalline substrates are generally required to achieve (001) texture. Recently, various studies also have focused on depositing different kinds of seed layers on glass or other amorphous substrates to promote (001) preferred orientation of L1{sub 0} CoPt and FePt. TiN is a very promising seed layer material because of its cubic crystalline structure (similar to MgO) and excellent diffusion barring property even at high temperatures. In the present work, highly (001) oriented L1{sub 0}-CoPt/TiN multilayer films have been successfully deposited on glassmore » substrates. After annealing at 700 °C, the film exhibits PMA, and a strong (001) peak is detected from the x-ray diffraction profiles, indicating the ordering transformation of CoPt layers from fcc (A1) to L1{sub 0} structure. It also is found that alternate deposition of cubic TiN and CoPt effectively improves the crystallinity and (001) preferred orientation of CoPt layers. This effect is verified by the substantial enhancement of (001) reflection and PMA with increasing the period number of the multilayer films.« less

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.

Time-Dependent Density Functional Theory Analysis of Triphenylamine-Functionalized Graphene Doped with Transition Metals for Photocatalytic Hydrogen Production.

PubMed

Mota, Elder A V; Neto, Abel F G; Marques, Francisco C; Mota, Gunar V S; Martins, Marcelo G; Costa, Fabio L P; Borges, Rosivaldo S; Neto, Antonio M J C

2018-07-01

The electronic structures and optical properties of triphenylamine-functionalized graphene (G-TPA) doped with transition metals, using water as a solvent, were theoretically investigated to verify the efficiency of photocatalytic hydrogen production with the use of transition metals. This study was performed by Density Functional Theory and Time-dependent Density Functional Theory through Gaussian 09W software, adopting the B3LYP functional for all structures. The 6-31g(d) basis set was used for H, C and N atoms, and the LANL2DZ basis set for transition metals using the Effective Core Potentials method. Two approaches were adopted: (1) using single metallic dopants (Ni, Pd, Fe, Os and Pt) and (2) using combinations of Ni with the other dopants (NiPd, NiPt, NiFe and NiOs). The DOS spectra reveal an increase of accessible states in the valence shell, in addition to a gap decrease for all dopants. This doping also increases the absorption in the visible region of solar radiation where sunlight is most intense (400 nm to 700 nm), with additional absorption peaks. The results lead us to propose the G-TPA structures doped with Ni, Pd, Pt, NiPt or NiPd to be novel catalysts for the conversion of solar energy for photocatalytic hydrogen production, since they improve the absorption of solar energy in the range of interest for solar radiation; and act as reaction centers, reducing the required overpotential for hydrogen production from water.

Electric-field tunable spin diode FMR in patterned PMN-PT/NiFe structures

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

Ziętek, Slawomir, E-mail: zietek@agh.edu.pl; Skowroński, Witold; Stobiecki, Tomasz

Dynamic properties of NiFe thin films on PMN-PT piezoelectric substrate are investigated using the spin-diode method. Ferromagnetic resonance (FMR) spectra of microstrips with varying width are measured as a function of magnetic field and frequency. The FMR frequency is shown to depend on the electric field applied across the substrate, which induces strain in the NiFe layer. Electric field tunability of up to 100 MHz per 1 kV/cm is achieved. An analytical model based on total energy minimization and the Landau-Lifshitz-Gilbert equation, taking into account the magnetostriction effect, is used to explain the measured dynamics. Based on this model, conditions formore » optimal electric-field tunable spin diode FMR in patterned NiFe/PMN-PT structures are derived.« less

Effect of the spin-twist structure on the spin-wave dynamics in Fe{sub 55}Pt{sub 45}/Ni{sub 80}Fe{sub 20} exchange coupled bi-layers with varying Ni{sub 80}Fe{sub 20} thickness

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

Pal, Semanti; Barman, Saswati, E-mail: saswati@bose.res.in; Barman, Anjan, E-mail: abarman@bose.res.in

2014-05-07

We have investigated optically induced ultrafast magnetization dynamics of a series of Fe{sub 55}Pt{sub 45}/Ni{sub 80}Fe{sub 20} exchange spring bi-layers with varying Ni{sub 80}Fe{sub 20} thickness. Rich spin-wave spectra are observed; whose frequency shows a strong dependence on the Ni{sub 80}Fe{sub 20} layer thickness. Micromagnetic simulations based on a simplified magnetic microstructure were able to reproduce the experimental data qualitatively. The spin twist structure introduced in the Ni{sub 80}Fe{sub 20} layer gives rise to new modes in the composite system as opposed to the bare Ni{sub 80}Fe{sub 20} films.

Magnetic Fe, Si, Al-Rich Impact Spherules from the P-T Boundary Layer at Graphite Peak, Antarctica

NASA Technical Reports Server (NTRS)

Petaev, M. I.; Jacobsen, S. B.; Basu, A. R.; Becker, L.

2004-01-01

The geological boundary between Triassic and Permian strata coincides with the greatest life extinction in the Earth's history. Although the cause of the extinction is still the subject of intense debates, recent discoveries in the P-T boundary layer of shocked quartz grains, fullerenes with the extraterrestrial noble gases, Fe metal nuggets, and chondritic meteorite fragments all point to a powerful collision of Earth with a celestial body in the late Permian. Here we report the discovery of magnetic Fe, Si, Al-rich impact spherules which accompany the chondritic meteorite fragments in some samples from the P-T boundary layer at Graphite Peak, Antarctica.

Pd-Pt and Fe-Ni nanoparticles formed by covalent molecular assembly in supercritical carbon dioxide.

PubMed

Puniredd, Sreenivasa Reddy; Weiyi, Seah; Srinivasan, M P

2008-04-01

We report the formation of Pd-Pt nanoparticles within a dendrimer-laden ultrathin film matrix immobilized on a solid support and constructed by covalent layer-by-layer (LbL) assembly using supercritical carbon dioxide (SCCO2) as the processing medium. Particle size distribution and composition were controlled by precursor composition. The precursor compositions are optimized for Pd-Pt nanoparticles and later extended to the formation of Fe-Ni nanoparticles. As an example of the application of nanoparticles in tribology, Fe-Ni nanoparticle-laden films were observed to exhibit better tribological properties than those containing the monometallic species, thereby suggesting that combination of nanoparticles can be used to derive greater benefits.

Interfacial perpendicular magnetic anisotropy in CoFeB/MgO structure with various underlayers

NASA Astrophysics Data System (ADS)

Oh, Young-Wan; Lee, Kyeong-Dong; Jeong, Jong-Ryul; Park, Byong-Guk

2014-05-01

Interfacial perpendicular magnetic anisotropy (PMA) in CoFeB/MgO structures was investigated and found to be critically relied on underlayer material and annealing temperature. With Ta or Hf underlayer, clear PMA is observed in as-deposited samples while no PMA was shown in those with Pt or Pd. This may be attributed to smaller saturation magnetization of the films with Ta or Hf underlayer, which makes the PMA of CoFeB/MgO interface dominates over demagnetization field. On the contrary, samples with Pt or Pd demonstrate PMA only after annealing, which might be due to the CoPt (or CoPd) alloy formation that enhances PMA.

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.

About some processes of replacement of PGM from the placers of Southern Siberia

NASA Astrophysics Data System (ADS)

Shvedov, G. I.; Knyazev, V. N.; Nekos, V. V.

2003-04-01

Authors observed a series of replacement (conversions) in PGM from gold-bearing placers of southern part of Krasnoyarsk region. These facts have mineralogical and genetic interest. In researched placers primary PGM are presented by solid solutions Os-Ir-Ru with different ratios of main elements from osmium to iridium (by classification of D. Harris and L. Cabri /5 /. At smaller amounts Pt-Fe and sperrylite are presented, and other PGM were found in single cases. In minerals of Os-Ir-Ru system the main typical replacement is the forming of edgings of phase (Os,Ir,Ru)S_2 upon the edges of native Os, Ir, Ru or rutheniridosmine. Usually, the process of transformation takes place in grains in a direction of the best permeability, i.e. along deformational gaps or along planes of cleavage, because the phases of this system are chemically stable. The structures of replacements are diversified: fulfillment of gaps, formation of edgings around the grains, selective replacement, forming of metacrystalls or metagrains. The thickness of forming edgings is not stable; boundaries have corrosion textures with penetration inside of replaced grain. The chemical composition of cations of forming disulfides depends upon the composition of primary mineral first of all, but it cannot be subject to this rule. For example, grains from placer of Bolshoy Khailyk river (Western Sayan) have a composition adequate to ruthenium (tab., No. 1) and are replaced by laurite more often (tab., No. 1-1). In Kuznetsky Alatau (placer of Talanovaya river) authors observed simultaneous replacement of osmium (with admixtures of Ru and Ir) (tab., No. 2) by laurite (tab., No. 2-1) and irarsite (tab., No. 2-2) along gaps. This fact is explained by more affinity of ruthenium to sulfur, then iridium and osmium to sulfur /2/. In conditions of low fugitivity of sulfur the edgings with more rare composition (Ir,Os,Ru)_3S_2 (tab., No. 3-1) are formed. It was observed by the authors on iridium (tab., No. 3) from placer of Sysim river (Eastern Sayan). The similar composition of phase was described by S.A.Toma and S.Murphy /6/. In placer of Talanovaya river (Kuznetsky Alatau) the edging of idealized composition Os_2S (tab., No. 4-1) are develops on the grain of Os-Ir-ruthenium (tab., No.4). It indicates deficit of sulfur in a solution. In case of increased concentration of arsenic the minerals of Os-Ir-Ru system (tab., No. 5) are replaced by diarsenides (anduoite - omeiite series) (tab., No. 5-1) or sulfoarsenides of these elements as it was observed in PGM from placer of Rudnaya river (Western Sayan). In the extremely rare cases at superposition of sulfurless and arsenicless solutions the replacement of alloys Os-Ir-Ru by exotic phases can happen. For example, authors find the grain of native iridium, which was heavily deformed and impregnated on microgaps by phases of generalized composition from Pt(Ni,Cu,Fe)_2 to Ir(Ni,Fe,Cu)_3 in placer of Bolshoy Khaylik river /7/. The forming of similar phases can be initiated by very specific conditions: the extremely reducing conditions, very low fugitivity of sulfur and oxygen, absence of other anion-forming elements, high activity of a nickel, iron and cooper. The similar phases were found in streak-schlieren chromitic ores in one massif of alpine-type ultramafic rocks of Koryak Highland /3/. Also rather rare replacement of platinum with the high contents of ruthenium and iridium (platruthenosmiridium by old nomenclature) (tab., No.6) by Pt-Fe alloys (tab., No.6-1). It was observed by authors in PGM from placer of Talanovaya river (Kuznetsky Alatau). In the system Pt-Fe most widespread placer-forming minerals are ferriferous platinum, tetraferroplatinum and isoferroplatinum. In placers that were investigated by the authors the Pt-Fe alloys most frequently is replaced by cuperite, which forms the various thickness edgings. It usual phenomenon in some cases becomes complicated by forming of narrow (first microns) intermittent band of high-standard gold on the boundary of cuperite and Pt-Fe alloy. Same edgings of gold round the grains of alloys with consequent overlap by a more broad band of cuperite were observed by S.A. Shcheka with the co-authors in PGM from placers of Far East /4/. According to these authors the forming of edgings of gold is connected to effect of gold-bearing solutions with low fugitivity of S and As on the Pt-Fe alloy. Hereinafter under the opinion of the quoted authors the concentrations of S and As have increased and cuperite or arsenides (sulfoarsenides) of platinum were formed. On ours opinion the forming of edgings of gold between PtS and Pt-Fe alloy may occur by two ways. At the first, the allocation of the bands of high-standard gold on the boundary Pt-Fe alloy and PtS was simultaneously with replacement. It is connected that the gold and silver was included in the crystalline of Pt-Fe alloys primary and at the time of replacement of this mineral these elements reduced to native phase because the entry to the lattice of cuperite is impossible. Such process can be presented as the following equation: (Pt,Pd,Au,Ag)_3Fe + 2S_2 =3(Pt,Pd)S + 3(Au,Ag)^0 + FeS There aren't crystallochemical prohibitions for such process. At the second, the gold from later solutions may penetrate deep into the grain through porous edging of cuperite and locate at the boundary of PtS and Pt-Fe alloy. Probability of these processes must be test by experiments. The cuperite edgings on Pt-Fe alloys are acquired by the band or metacrystalls of sperrilite later. It is connected to occurrence of arsenic in the system. A feature of the composition of these sperrylites is increased contents of those elements, which originally were included in the lattice of Pt-Fe alloys (Rh, Ir, Os). The complex replacements of Pt-Fe alloys were observed by the authors in placer Sysim river. Pt-Fe alloys from this placer are presented by small-sized isomeric grains and contain increased contents of rhodium (tab., No.7). This feature was reflected in phases of replacement. In one case the edgings of Rh-sperrylite thickness 15-30 microns rounds the grain of Pt-Fe alloy and between these minerals the thin intermittent band of mineral with adequate RhAs (cherepanovite?) composition is situated (tab., No.7-1). This association is complicated by formation of small-sized selections hollingworthite (tab., No.7-2). In the near-drift placers sperrylite occurs frequently. This mineral is brittle and havn't transported on distant distances, but it is chemically very stable phase. Nevertheless, it mineral is replaced by native platinum on the edgings frequently, that was observed by authors in placers of the rivers Coloromo, Danilovsky (Yenisei Ridge), Caragan (East Sayan) etc. This process can be finished by formation of the native platinum. According to T.L. Evstigneeva with co-authors /1/ the de-arsenization of sperrylite can happen only at rather high temperatures more 400^oC;. Therefore it cannot be attributed to process of low-temperature replacement in solid condition, and it is necessary to connect with temperature burning of sperrylite. The native platinum which was formed in it process differs from primary magmatic in high cleanness of composition and absence of any admixtures, except for As (tab., No.8, 8-1). References: 1.T.L.Evstigneeva, A.A.Kim, I.Ay.Nekrasov (1990) //About de-arsenization of sperrylite in nature. Mineralogical Zhurnal, vol.12, No3, pp.90-96 (in Russian). 2. A.A.Marakushev, N.I.Bezmen Thermodynamics of sulfides and oxides in connection with problems of ore-forming. - M., Nauka, 1972. - 230p (in Russian). 3. A.G.Mochalov, G.G.Dmitrenko, I.V.Zhernovskii, N.S.Rudashevskii (1985) New iridium-osmium-ruthenium type (solid solutions of rare platinum-group elements with iron) of platinum-group mineralization in chromium spinel-group minerals of alpine-type ultramafic rocks of Koryak Highland. - Zapiski Vses. Mineral. Obshch., 114, pp.544-554 (in Russian). 4. S.A.Shcheka, A.A.Vrzhosek, V.I. Sapin, N.I.Kiryukhina (1991) Trasformations of platinum-group minerals from Primor'ye placers. - Mineralogical Zhurnal, vol.13, No1, pp.31-40 (in Russian). 5. D.C.Harris, L.J.Cabri (1991) Nomenclature of platinum-group-element alloys: review and revision. - Canadian Mineralogist, vol.29, pp.231-237. 6. L.J.Cabri (ed.) (1978) Unnamed platinum-group minerals. In: Platinum-group elements: mineralogy, geology, recovery. - Canadian Institute of Mining and Metallurgy, Montreal, pp.177-195. 7. G.I.Shvedov, V.N.Knyazev Unnamed PGE Phases from Gold Placer Deposits of South Siberia, Russia. - 9th International Platinum Symposium, July 21-25, Billings, Montana, USA, 2002 (http://www.duke.edu/˜boudreau/IPS_Abstracts.htm).

Enhanced activity and stability of binuclear iron (III) phthalocyanine on graphene nanosheets for electrocatalytic oxygen reduction in acid

NASA Astrophysics Data System (ADS)

Li, Tengfei; Peng, Yingxiang; Li, Kai; Zhang, Rui; Zheng, Lirong; Xia, Dingguo; Zuo, Xia

2015-10-01

Binuclear iron (III) phthalocyanine (bi-FePc) and iron (III) phthalocyanine (FePc) are synthesized in situ on graphene nanosheets (GNS) by a microwave-assisted method. TEM, ultraviolet-visible spectroscopy and Raman spectroscopy confirm that bi-FePc is supported on GNS through π-π interactions. The catalytic activity of the bi-FePc/GNS and FePc/GNS composites in the oxygen reduction reaction (ORR) is investigated by CV and RDE measurements. The bi-FePc/GNS composite shows a more positive onset potential (0.12 V vs. Hg/Hg2SO4) for the ORR than FePc/GNS (-0.02 V vs. Hg/Hg2SO4), and a four-electron mechanism similar to commercial Pt/C (0.22 V vs. Hg/Hg2SO4). Moreover, bi-FePc/GNS exhibits good stability with 100% retention after 36,000 s, while Pt/C has a retention of only 50% after the same period. Additionally, bi-FePc/GNS shows higher tolerance toward methanol than the Pt/C catalyst. XPS and X-ray absorption fine structure spectroscopy demonstrate that compared with FePc/GNS, bi-FePc/GNS possesses a higher concentration of Fe3+ and smaller skeleton radius of the phthalocyanine ring, which has a square-planar structure that evidently favors the ORR. Thus, bi-FePc/GNS is a promising candidate as a cathode catalyst in direct methanol fuel cells.

Non-Aqueous Sol-Gel Synthesis of FePt Nanoparticles in the Absence of In Situ Stabilizers

PubMed Central

Preller, Tobias; Knickmeier, Saskia; Porsiel, Julian Cedric; Temel, Bilal

2018-01-01

The synthesis of FePt nanocrystals is typically performed in an organic solvent at rather high temperatures, demanding the addition of the in situ stabilizers oleic acid and oleylamine to produce monomodal particles with well-defined morphologies. Replacing frequently-used solvents with organic media bearing functional moieties, the use of the stabilizers can be completely circumvented. In addition, various morphologies and sizes of the nanocrystals can be achieved by the choice of organic solvent. The kinetics of particle growth and the change in the magnetic behavior of the superparamagnetic FePt nanocrystals during the synthesis with a set of different solvents, as well as the resulting morphologies and stoichiometries of the nanoparticles were determined by powder X-ray diffraction (PXRD), small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), inductively coupled plasma optical emission spectroscopy (ICP-OES)/mass spectrometry (ICP-MS), and superconducting quantum interference device (SQUID) measurements. Furthermore, annealing of the as-prepared FePt nanoparticles led to the ordered L10 phase and, thus, to hard magnetic materials with varying saturation magnetizations and magnetic coercivities. PMID:29751508

Standard Gibbs energy of formation of Mo 3Te 4 by emf measurements

NASA Astrophysics Data System (ADS)

Mallika, C.; Sreedharan, O. M.

1990-03-01

The emf of the galvanic cells Pt, Mo, MoO 2¦8 YSZ¦'FeO', Fe, Pt (I) and Pt, Fe,'FeO' ¦8 YSZ¦MoO 2, Mo 3Te 4, MoTe 2(α), C, Pt (II) were measured over the temperature ranges 837 to 1151 K and 775 to 1196 K, respectively, using 8 mass% yttria-stabilized zirconia (8 YSZ) as the solid electrolyte. From the emf values, the partial molar Gibbs energy of solution of molybdenum in Mo 3Te 4/MoTe 2(α), Δ ḠMo was found to be Δ ḠMo ± 1.19 ( kJ/mol) = -025.08 + 0.00420T(K) . Using the literature data for the Gibbs energy of formation of MoTe 2(α). the expression ΔG° f( Mo3Te4, s) ± 5.97 (kj/mol) = -253.58 + 0.09214 T( K) was derived for the range 775 to 1196 K. A third-law analysis yielded a value of -209 ± 10 kJ/mol for ΔH° f.298o of Mo 3Te 4(s).

Ionic Liquid Gating Control of RKKY Interaction in FeCoB/Ru/FeCoB and (Pt/Co) 2/Ru/(Co/Pt) 2 Multilayers.

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

Yang, Qu; Wang, Lei; Zhou, Ziyao

To overcome the fundamental challenge of the weak natural response of antiferromagnetic materials under a magnetic field, voltage manipulation of antiferromagnetic interaction is developed to realize ultrafast, high-density, and power efficient antiferromagnetic spintronics. Here, we report a low voltage modulation of Ruderman–Kittel–Kasuya–Yosida (RKKY) interaction via ionic liquid gating in synthetic antiferromagnetic multilayers of FeCoB/Ru/FeCoB and (Pt/Co) 2/Ru/(Co/Pt) 2. At room temperature, the distinct voltage control of transition between antiferromagnetic and ferromagnetic ordering is realized and up to 80% of perpendicular magnetic moments manage to switch with a small-applied voltage bias of 2.5 V. We related this ionic liquid gating-induced RKKYmore » interaction modification to the disturbance of itinerant electrons inside synthetic antiferromagnetic heterostructure and the corresponding change of its Fermi level. Voltage tuning of RKKY interaction may enable the next generation of switchable spintronics between antiferromagnetic and ferromagnetic modes with both fundamental and practical perspectives.« less

Electrical control of antiferromagnetic metal up to 15 nm

NASA Astrophysics Data System (ADS)

Zhang, PengXiang; Yin, GuFan; Wang, YuYan; Cui, Bin; Pan, Feng; Song, Cheng

2016-08-01

Manipulation of antiferromagnetic (AFM) spins by electrical means is on great demand to develop the AFM spintronics with low power consumption. Here we report a reversible electrical control of antiferromagnetic moments of FeMn up to 15 nm, using an ionic liquid to exert a substantial electric-field effect. The manipulation is demonstrated by the modulation of exchange spring in [Co/Pt]/FeMn system, where AFM moments in FeMn pin the magnetization rotation of Co/Pt. By carrier injection or extraction, the magnetic anisotropy of the top layer in FeMn is modulated to influence the whole exchange spring and then passes its influence to the [Co/Pt]/FeMn interface, through a distance up to the length of exchange spring that fully screens electric field. Comparing FeMn to IrMn, despite the opposite dependence of exchange bias on gate voltages, the same correlation between carrier density and exchange spring stiffness is demonstrated. Besides the fundamental significance of modulating the spin structures in metallic AFM via all-electrical fashion, the present finding would advance the development of low-power-consumption AFM spintronics.

X-ray structural study of intermetallic alloys RT{sub 2}Si and RTSi{sub 2} (R=rare earth, T=noble metal)

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

Gribanov, Alexander, E-mail: avgri@mail.r; Chemistry Department of the Moscow State University, Leninskie Gory, GSP-1, 119991 Moscow; Grytsiv, Andriy

Two series of intermetallic alloys, RT{sub 2}Si and RTSi{sub 2}, have been synthesized from stoichiometric compositions. The crystal structures of EuPt{sub 1+x}Si{sub 2-x} (CeNiSi{sub 2}-type), CeIr{sub 2}Si (new structure type), YbPd{sub 2}Si and YbPt{sub 2}Si (both YPd{sub 2}Si-type) have been elucidated from X-ray single crystal CCD data, which were confirmed by XPD experiments. The crystal structures of LaRh{sub 2}Si and LaIr{sub 2}Si (CeIr{sub 2}Si-type), {l_brace}La,Ce,Pr,Nd{r_brace}AgSi{sub 2} (all TbFeSi{sub 2}-type), and EuPt{sub 2}Si (inverse CeNiSi{sub 2}-type) were characterized by XPD data. RT{sub 2}Si/RTSi{sub 2} compounds were neither detected in as-cast alloys Sc{sub 25}Pt{sub 50}Si{sub 25}, Eu{sub 25}Os{sub 25}Si{sub 50} and Eu{submore » 25}Rh{sub 25}Si{sub 50} nor after annealing at 900 {sup o}C. Instead, X-ray single crystal data prompted Eu{sub 2}Os{sub 3}Si{sub 5} (Sc{sub 2}Fe{sub 3}Si{sub 5}-type) and EuRh{sub 2+x}Si{sub 2-x} (x=0.04, ThCr{sub 2}Si{sub 2}-type) as well as a new structure type for Sc{sub 2}Pt{sub 3}Si{sub 2} (own type). - Graphical abstract: Two series of the intermetallic compounds, RT{sub 2}Si and RTSi{sub 2}, have been investigated by X-ray diffraction methods. The new tetragonal CeIr{sub 2}Si-type of the crystal structure was described and the interrelation between orthorhombic CeNiSi{sub 2} and tetragonal CeIr{sub 2}Si had been discussed as a similar packing of the BaAl{sub 4} and AlB{sub 2} slabs.« less

Porous Pt-Ni Nanowires within In Situ Generated Metal-Organic Frameworks for Highly Chemoselective Cinnamaldehyde Hydrogenation.

PubMed

Zhang, Nan; Shao, Qi; Wang, Pengtang; Zhu, Xing; Huang, Xiaoqing

2018-05-01

Although chemoselective hydrogenation of unsaturated aldehydes is the major route to highly valuable industrially demanded unsaturated alcohols, it is still challenging, as the production of saturated aldehydes is more favorable over unsaturated alcohols from the view of thermodynamics. By combining the structural features of porous nanowires (NWs) and metal-organic frameworks (MOFs), a unique class of porous Pt-Ni NWs in situ encapsuled by MOFs (Pt-Ni NWs@Ni/Fex-MOFs) is designed to enhance the unsaturated alcohols selectivity in the cinnamaldehyde (CAL) hydrogenation. A detailed catalytic study shows that the porous Pt-Ni NWs@Ni/Fe x -MOFs exhibit volcano-type activity and selectivity in CAL hydrogenation as a function of Fe content. The optimized porous PtNi 2.20 NWs@Ni/Fe 4 -MOF is highly active and selective with 99.5% CAL conversion and 83.3% cinnamyl alcohol selectivity due to the confinement effect, appropriate thickness of MOF and its optimized electronic structure, and excellent durability with negligible activity and selectivity loss after five runs. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Fe local structure in Pt-free nitrogen-modified carbon based electrocatalysts: XAFS study

NASA Astrophysics Data System (ADS)

Witkowska, Agnieszka; Giuli, Gabriele; Renzi, Marco; Marzorati, Stefania; Yiming, Wubulikasimu; Nobili, Francesco; Longhi, Mariangela

2016-05-01

The paper presents a new results on the bonding environment (coordination number and geometry) and on oxidation states of Fe in nitrogen-modified Fe/C composites used as Pt-free catalysts for oxygen reduction in Direct Hydrogen Fuel Cells. Starting from glucose or fructose, two catalysts displaying different electrochemical performance were prepared and studied in the form of pristine powder and thin catalytic layer of electrode by Fe K-edge XAFS spectroscopy. The results show how the Fe local structure varies as a function of different synthesis conditions and how changes in the structural properties of the catalysts are related to fuel cell electrochemical performance increase during a cell activation period.

Electrochemically deposited cobalt/platinum (Co/Pt) film into porous silicon: Structural investigation and magnetic properties

NASA Astrophysics Data System (ADS)

Harraz, F. A.; Salem, A. M.; Mohamed, B. A.; Kandil, A.; Ibrahim, I. A.

2013-01-01

A nanostructured CoPt magnetic film was deposited from a single electrolyte into porous silicon layer by an electrochemical technique, followed by annealing at 600 °C in Ar atmosphere during which the CoPt alloy was converted to L10 ordered phase. Porous silicon with pore diameter between 5 and 100 nm was firstly fabricated by galvanostatic anodization of n-type silicon wafer in the presence of CrO3 as oxidizing agent and ethanol or sodium lauryl sulfate as surfactants. The role of the surfactant on the produced pore size and morphology was investigated by means of UV-vis spectra. As-formed porous silicon was consequently used as a template for the electrodeposition of magnetic CoPt film. The phase formation, microstructure and the magnetic properties were fully analyzed by XRD, FE-SEM, EDS and VSM measurements. It was found that, upon annealing the coercivity was significantly increased due to the transformation to the L10 ordered structure. The saturation magnetization and remanence ratio were also found to increase, indicating no loss of Co content or oxidation reaction after the annealing. Results of synthesis and characterization of CoPt/porous silicon nanocomposite are addressed and thoroughly discussed.

Ultrafast Magnetism of Multi-component Ferromagnets and Ferrimagnets on the Time Scale of the Exchange Interaction

NASA Astrophysics Data System (ADS)

Radu, Ilie

2012-02-01

Revealing the ultimate speed limit at which magnetic order can be controlled, is a fundamental challenge of modern magnetism having far reaching implications for the magnetic recording industry [1]. Exchange interaction is the strongest force in magnetism, being ultimately responsible for ferromagnetic or antiferromagnetic spin order. How do spins react after being optically excited on a timescale of or even faster than the exchange interaction? Here, we demonstrate that femtosecond (fs) measurements of ferrimagnetic and ferromagnetic alloys using X-ray magnetic circular dichroism provide revolutionary new insights into the problem of ultrafast magnetism on timescales pertinent to the exchange interaction. In particular, we show that upon fs optical excitation the ultrafast spin reversal of GdFeCo - a material with antiferromagnetic coupling of spins - occurs via a transient ferromagnetic state [2]. The latter emerges due to different dynamics of the Gd and Fe magnetic moments: Gd switches within 1.5 ps while it takes only 300 fs for Fe. Thus, by using a single fs laser pulse one can force the spin system to evolve via an energetically unfavorable way and temporarily switch from an antiferromagnetic to a ferromagnetic type of ordering. In order to understand whether the observation of this temporarily decoupled and element-specific dynamics is a general phenomenon or just something strictly related to the case of ferrimagnetic GdFeCo, we have investigated the demagnetization of the archetypal ferromagnetic NiFe alloys. Essentially, we observe the same distinct magnetization dynamics of the constituent magnetic moments: Ni demagnetizes within ˜300 fs being much faster than the demagnetization of Fe of ˜800 fs. This distinct demagnetization behavior leads to an apparent decoupling of the Fe and Ni magnetic moments on a few hundreds of fs time scale, despite the strong exchange interaction of 260meV (˜16 fs) that couples them. These observations supported by atomistic simulations, present a novel concept of manipulating magnetic order on different classes of magnetic materials on timescales of the exchange interaction [3]. [4pt] [1] A. Kirilyuk, A.V. Kimel and Th. Rasing, Rev. Mod. Phys. 82, 2731 (2010). [0pt] [2] I. Radu et al., Nature 472, 205 (2011). [0pt] [3] I. Radu et al., submitted (2011).

Quantification of strain and charge co-mediated magnetoelectric coupling on ultra-thin Permalloy/PMN-PT interface.

PubMed

Nan, Tianxiang; Zhou, Ziyao; Liu, Ming; Yang, Xi; Gao, Yuan; Assaf, Badih A; Lin, Hwaider; Velu, Siddharth; Wang, Xinjun; Luo, Haosu; Chen, Jimmy; Akhtar, Saad; Hu, Edward; Rajiv, Rohit; Krishnan, Kavin; Sreedhar, Shalini; Heiman, Don; Howe, Brandon M; Brown, Gail J; Sun, Nian X

2014-01-14

Strain and charge co-mediated magnetoelectric coupling are expected in ultra-thin ferromagnetic/ferroelectric multiferroic heterostructures, which could lead to significantly enhanced magnetoelectric coupling. It is however challenging to observe the combined strain charge mediated magnetoelectric coupling, and difficult in quantitatively distinguish these two magnetoelectric coupling mechanisms. We demonstrated in this work, the quantification of the coexistence of strain and surface charge mediated magnetoelectric coupling on ultra-thin Ni0.79Fe0.21/PMN-PT interface by using a Ni0.79Fe0.21/Cu/PMN-PT heterostructure with only strain-mediated magnetoelectric coupling as a control. The NiFe/PMN-PT heterostructure exhibited a high voltage induced effective magnetic field change of 375 Oe enhanced by the surface charge at the PMN-PT interface. Without the enhancement of the charge-mediated magnetoelectric effect by inserting a Cu layer at the PMN-PT interface, the electric field modification of effective magnetic field was 202 Oe. By distinguishing the magnetoelectric coupling mechanisms, a pure surface charge modification of magnetism shows a strong correlation to polarization of PMN-PT. A non-volatile effective magnetic field change of 104 Oe was observed at zero electric field originates from the different remnant polarization state of PMN-PT. The strain and charge co-mediated magnetoelectric coupling in ultra-thin magnetic/ferroelectric heterostructures could lead to power efficient and non-volatile magnetoelectric devices with enhanced magnetoelectric coupling.

Partitioning of Pd Between Fe-S-C and Mantle Liquids at High Pressure and Temperature: Implications for Core Formation

NASA Technical Reports Server (NTRS)

Righter, K.; Humayun, M.; Danielson, L.

2007-01-01

One of the most elusive geochemical aspects of the early Earth has been explaining the near chondritic relative abundances of the highly siderophile elements (HSE; Au, Re and the platinum group elements) in Earth's primitive upper mantle (PUM). Perhaps they were delivered to the Earth after core formation, by late addition of carbonaceous chondrite material. However, the recognition that many moderately siderophile elements can be explained by high pressure and temperature (PT) metal-silicate equilibrium, leads to the question whether high PT equilibrium can also explain the HSE concentrations. Answers to this question have been slowed by experimental difficulties (nugget effect and very low solubilities). But two different perspectives have emerged from recent studies. One perspective is that D(M/S) for HSE at high PT are not low enough to explain terrestrial mantle depletions of these elements (for Pd and Pt). A second perspective is D(M/S) are reduced substantially at high PT and even low enough to explain terrestrial mantle depletions (for Au and Pt). Issues complicating interpretation of all experiments include use of MgO- and FeO-free silicate melts, and S-free and FeNi metal-free systems. In addition, conclusions for Pt rest on an interpretation that the tiny metallic nuggets plaguing many such experiments, were formed upon quench. There is not agreement on this issue, and the general question of HSE solubility at high PT remains unresolved

A density functional theory study of self-regenerating catalysts LaFe(1-x)M(x)O(3-y) (M = Pd, Rh, Pt).

PubMed

Hamada, Ikutaro; Uozumi, Akifumi; Morikawa, Yoshitada; Yanase, Akira; Katayama-Yoshida, Hiroshi

2011-11-23

Periodic density functional theory was used to investigate the stability and electronic structures of precious-metal atoms in the vicinity of LaFe(1-x)M(x)O(3) (M = Pd, Rh, Pt) perovskite catalyst surfaces. It was found that the surface segregation of Pd and Pt is significantly stabilized by the introduction of O vacancies, whereas the solid-solution phase is favorable for Rh, suggesting an important role of O vacancies in the self-regeneration of Pd and Pt. On the basis of the results, we propose a possible scenario for the self-regeneration of the precious metal in the perovskite catalyst.

Understanding the Role of M/Pt(111) (M = Fe, Co, Ni, Cu) Bimetallic Surfaces for Selective Hydrodeoxygenation of Furfural

DOE PAGES

Jiang, Zhifeng; Wan, Weiming; Lin, Zhexi; ...

2017-07-24

Selectively cleaving the C=O bond of the aldehyde group in furfural is critical for converting this biomass-derived platform chemical to an important biofuel molecule, 2-methylfuran. This work combined density functional theory (DFT) calculations and temperature-programmed desorption (TPD) and high-resolution electron energy loss spectroscopy (HREELS) measurements to investigate the hydrodeoxygenation (HDO) activity of furfural on bimetallic surfaces prepared by modifying Pt(111) with 3d transition metals (Cu, Ni, Fe, and Co). The stronger binding energy of furfural and higher tilted degree of the furan ring on the Co-terminated bimetallic surface resulted in a higher activity for furfural HDO to produce 2-methylfuran inmore » comparison to that on either Pt(111) or Pt-terminated PtCoPt(111). The 3d-terminated bimetallic surfaces with strongly oxophilic 3d metals (Co and Fe) showed higher 2-methylfuran yield in comparison to those surfaces modified with weakly oxophilic 3d metals (Cu and Ni). The effect of oxygen on the HDO selectivity was also investigated on oxygen-modified bimetallic surfaces, revealing that the presence of surface oxygen resulted in a decrease in 2-methylfuran yield. Furthermore, the combined theoretical and experimental results presented here should provide useful guidance for designing Pt-based bimetallic HDO catalysts.« less

Understanding the Role of M/Pt(111) (M = Fe, Co, Ni, Cu) Bimetallic Surfaces for Selective Hydrodeoxygenation of Furfural

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

Jiang, Zhifeng; Wan, Weiming; Lin, Zhexi

Selectively cleaving the C=O bond of the aldehyde group in furfural is critical for converting this biomass-derived platform chemical to an important biofuel molecule, 2-methylfuran. This work combined density functional theory (DFT) calculations and temperature-programmed desorption (TPD) and high-resolution electron energy loss spectroscopy (HREELS) measurements to investigate the hydrodeoxygenation (HDO) activity of furfural on bimetallic surfaces prepared by modifying Pt(111) with 3d transition metals (Cu, Ni, Fe, and Co). The stronger binding energy of furfural and higher tilted degree of the furan ring on the Co-terminated bimetallic surface resulted in a higher activity for furfural HDO to produce 2-methylfuran inmore » comparison to that on either Pt(111) or Pt-terminated PtCoPt(111). The 3d-terminated bimetallic surfaces with strongly oxophilic 3d metals (Co and Fe) showed higher 2-methylfuran yield in comparison to those surfaces modified with weakly oxophilic 3d metals (Cu and Ni). The effect of oxygen on the HDO selectivity was also investigated on oxygen-modified bimetallic surfaces, revealing that the presence of surface oxygen resulted in a decrease in 2-methylfuran yield. Furthermore, the combined theoretical and experimental results presented here should provide useful guidance for designing Pt-based bimetallic HDO catalysts.« less

Core/shell face-centered tetragonal FePd/Pd nanoparticles as an efficient non-Pt catalyst for the oxygen reduction reaction

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

Zhu, Huiyuan; Jiang, Guangming; Zhang, Xu

We report the synthesis of core/shell face-centered tetragonal (fct)-FePd/Pd nanoparticles (NPs) via reductive annealing of core/shell Pd/Fe 3O 4 NPs followed by temperature-controlled Fe etching in acetic acid. Among three different kinds of core/shell FePd/Pd NPs studied (FePd core at similar to 8 nm and Pd shell at 0.27, 0.65, or 0.81 nm), the fct-FePd/Pd-0.65 NPs are the most efficient catalyst for the oxygen reduction reaction (ORR) in 0.1 M HClO 4 with Pt-like activity and durability. This enhanced ORR catalysis arises from the desired Pd lattice compression in the 0.65 nm Pd shell induced by the fct-FePd core. Lastly,more » our study offers a general approach to enhance Pd catalysis in acid for ORB.« less

Core/shell face-centered tetragonal FePd/Pd nanoparticles as an efficient non-Pt catalyst for the oxygen reduction reaction

DOE PAGES

Zhu, Huiyuan; Jiang, Guangming; Zhang, Xu; ...

2015-10-04

We report the synthesis of core/shell face-centered tetragonal (fct)-FePd/Pd nanoparticles (NPs) via reductive annealing of core/shell Pd/Fe 3O 4 NPs followed by temperature-controlled Fe etching in acetic acid. Among three different kinds of core/shell FePd/Pd NPs studied (FePd core at similar to 8 nm and Pd shell at 0.27, 0.65, or 0.81 nm), the fct-FePd/Pd-0.65 NPs are the most efficient catalyst for the oxygen reduction reaction (ORR) in 0.1 M HClO 4 with Pt-like activity and durability. This enhanced ORR catalysis arises from the desired Pd lattice compression in the 0.65 nm Pd shell induced by the fct-FePd core. Lastly,more » our study offers a general approach to enhance Pd catalysis in acid for ORB.« less

Extraordinary Hall resistance and unconventional magnetoresistance in Pt/LaCoO 3 hybrids

NASA Astrophysics Data System (ADS)

Shang, T.; Zhan, Q. F.; Yang, H. L.; Zuo, Z. H.; Xie, Y. L.; Zhang, Y.; Liu, L. P.; Wang, B. M.; Wu, Y. H.; Zhang, S.; Li, Run-Wei

2015-10-01

We report an investigation of transverse Hall resistance and longitudinal resistance on Pt thin films sputtered on epitaxial LaCoO3 (LCO) ferromagnetic insulator films. The LaCoO3 films were deposited on several single crystalline substrates [LaAlO3,(La,Sr)(Al,Ta)O3, and SrTiO3] with (001) orientation. The physical properties of LaCoO3 films were characterized by the measurements of magnetic and transport properties. The LaCoO3 films undergo a paramagnetic to ferromagnetic (FM) transition at Curie temperatures ranging from 40 to 85 K, below which the Pt/LCO hybrids exhibit significant extraordinary Hall resistance up to 50 m Ω and unconventional magnetoresistance ratio Δ ρ /ρ0 about 1.2 ×10-4 , accompanied by the conventional magnetoresistance. The observed spin transport properties share some common features as well as some unique characteristics when compared with well-studied Y3Fe5O12 -based Pt thin films. Our findings call for new theories since the extraordinary Hall resistance and magnetoresistance cannot be consistently explained by the existing theories.

Static magnetism and thermal switching in randomly oriented L10 FePt thin films

NASA Astrophysics Data System (ADS)

Lisfi, A.; Pokharel, S.; Alqarni, A.; Akioya, O.; Morgan, W.; Wuttig, M.

2018-05-01

Static magnetism and thermally activated magnetic relaxation were investigated in granular FePt films (20 nm-200 nm thick) with random magnetic anisotropy through hysteresis loop, torque curve and magnetization time dependence measurements. While the magnetism of thicker film (200 nm thick) is dominated by a single switching of the ordered L10 phase, thinner film (20 nm) displays a double switching, which is indicative of the presence of the disordered cubic phase. The pronounced behavior of double switching in thinner film suggests that the film grain boundary is composed of soft cubic magnetic phase. The magnetic relaxation study reveals that magnetic viscosity S of the films is strongly dependent on the external applied field and exhibits a maximum value (12 kAm) around the switching field and a vanishing behavior at low (1 kOe) and large (12 kOe) fields. The activation volume of the thermal switching was found to be much smaller than the physical volume of the granular structure due to the incoherent rotation mode of the magnetization reversal mechanism, which is established to be domain wall nucleation.

Crystal growth and electrical properties of CuFeO 2 single crystals

NASA Astrophysics Data System (ADS)

Dordor, P.; Chaminade, J. P.; Wichainchai, A.; Marquestaut, E.; Doumerc, J. P.; Pouchard, M.; Hagenmuller, P.; Ammar, A.

1988-07-01

Delafossite-type CuFeO 2 single crystals have been prepared by a flux method: crystals obtained in a Cu crucible with LiBO 2 as flux are n-type whereas those prepared in a Pt crucible with a Cu 2O flux are p-type. Electrical measurements have revealed that n-type crystals exhibit weak anisotropic conductivities with large activation energies and small mobilities (r.t. values perpendicular and parallel to the c-axis: μ⊥ = 5 × 10 -5 and μ‖ = 10 -7 cm -2 V -1 sec -1). p-type crystals, less anisotropic, are characterized by low activation energies and higher mobilities ( μ⊥ = 34 and μ‖ = 8.9 cm 2 V -1 sec -1). A two -conduction-band model is proposed to account for the difference observed between the energy gap value deduced from photoelectrochemical measurements and the activation energy of the electrical conductivity in the intrinsic domain.

PREPARATION OF NOVEL METALLIC AND BIMETALLIC CROSS-LINKED POLY (VINYL ALCOHOL) NANOCOMPOSITES UNDER MICROWAVE IRRADIATION

EPA Science Inventory

A facile method utilizing microwave irradiation is described that accomplishes the cross-linking reaction of PVA with metallic and bimetallic systems. Nanocomposites of PVA-cross-linked metallic systems such as Pt, Cu, and In and bimetallic systems such as Pt-In, Ag-Pt, Pt-Fe, Cu...

Role of crystal orientation on electrical tuning of dynamic permeability in strain-mediated multiferroic structures

NASA Astrophysics Data System (ADS)

Phuoc, Nguyen N.; Ong, C. K.

2017-06-01

Multiferroic structures of FeCo/NiFe/[Pb(Mg1/3Nb2/3)O3]0.68-[PbTiO3]0.32 (PMN-PT) with three different crystal orientations of PMN-PT(0 1 1), PMN-PT(0 0 1) and PMN-PT(1 1 1) were fabricated by a sputtering deposition system. Their dynamic magnetic properties were characterized under various applied electrical fields. The sample with PMN-PT(0 1 1) orientation shows a large tuning of the permeability spectra while the ones with PMN-PT(0 0 1) and PMN-PT(1 1 1) orientations exhibit a moderate and little change in the permeability spectra, respectively. The result can be explained via the magnetoelectric effect by considering the role of the piezoelectric coefficients being highly dependent on the crystal orientation along which the PMN-PT is poled. This explanation is consistent with the static magnetic characteristics of the samples before and after poling.

Tunneling-Magnetoresistance Ratio Comparison of MgO-Based Perpendicular-Magnetic-Tunneling-Junction Spin Valve Between Top and Bottom Co2Fe6B2 Free Layer Structure.

PubMed

Lee, Du-Yeong; Lee, Seung-Eun; Shim, Tae-Hun; Park, Jea-Gun

2016-12-01

For the perpendicular-magnetic-tunneling-junction (p-MTJ) spin valve with a nanoscale-thick bottom Co2Fe6B2 free layer ex situ annealed at 400 °C, which has been used as a common p-MTJ structure, the Pt atoms of the Pt buffer layer diffused into the MgO tunneling barrier. This transformed the MgO tunneling barrier from a body-centered cubic (b.c.c) crystallized layer into a mixture of b.c.c, face-centered cubic, and amorphous layers and rapidly decreased the tunneling-magnetoresistance (TMR) ratio. The p-MTJ spin valve with a nanoscale-thick top Co2Fe6B2 free layer could prevent the Pt atoms diffusing into the MgO tunneling barrier during ex situ annealing at 400 °C because of non-necessity of a Pt buffer layer, demonstrating the TMR ratio of ~143 %.

The partitioning of Fe, Ni, Cu, Pt, and Au between sulfide, metal, and fluid phases: A pilot study

NASA Astrophysics Data System (ADS)

Ballhaus, C.; Ryan, C. G.; Mernagh, T. P.; Green, D. H.

1994-01-01

This paper describes new experimental and analytical techniques to study element partitioning behavior between crystalline material and a late- to post-magmatic fluid phase. Samples of the fluid phase are isolated at experimental run conditions as synthetic fluid in quartz. Individual fluid inclusions are later analyzed for dissolved metals using Proton Induced X-ray Emission (PIXE). Back reactions between fluid and solid phases during quenching are prevented because the fluid is isolated at the experimental pressure, temperature ( P, T) conditions before quenching occurs. The technique is applied to study the partitioning of chalcophile elements (Fe, Ni, Cu, Pt and Au) between sulfide phases, metal alloys and supercritical SiO 2-NaCl-saturated H2O ± CH4- CO2- H2S fluids. Synthetic Ni-Cu-rich monosulfide solid solution (mss) doped with PtS or Au is packed in a quartz capsule and, together with a hydrogen buffer capsule and compounds to generate a fluid phase, welded shut in an outer Pt or Au metal capsule. The fluid phase is generated by combustion and reaction of various C-H-O fluid components during heating. Depending on capsule material and sample composition, the run products consist of platiniferous or auriferous mss, Pt-Fe, or ( Au, Cu) alloy phases, PtS, Fe 3O 4, sometimes a Cu-rich sulfide melt, and a fluid phase. Samples of the fluid are trapped in the walls of the quartz sample capsule as polyphase fluid inclusions. All phases are now available for analysis: fluid speciation is analyzed by piercing the outer metal capsule under vacuum and feeding the released fluid into a mass spectrometer. Phases and components within fluid inclusions are identified with Raman spectroscopy. Platinum and gold in solid solution in mss are determined with a CAMECA SX50 electron microanalyser. Metal contents trapped in selected fluid inclusions are determined quantitatively by in situ analysis with a proton microprobe using PIXE and a correction procedure specifically developed for quantitative fluid inclusion analysis. Initial results of metal solubilities in the fluid are as follows. Iron decreases from above 6,000 ppm under reduced conditions in the presence of H 2S in the fluid, to less than 1,000 ppm if hematite is stable in the crystalline run product. Copper and gold concentrations in the fluid range from about 600 to over 1200 and from 150 to about 270 ppm, respectively. The solubilities of these two metals in NaCl-saturated fluids are apparently independent of fluid speciations covered here. Nickel is mostly below detection limit (<10 ppm) and apparently poorly soluble in high-temperature fluid phases. Platinum concentrations in fluid inclusions are highly variable even among fluid inclusions of single runs, possibly because Pt tends to form multi-atom complexes in fluid phases.

Cryomagnetic Point-Contact Andreev Reflection Spectroscopy on Single Crystal Iron-Chalcogenide Superconductors

NASA Astrophysics Data System (ADS)

Yen, Y. T.; Hu, Rongwei; Petrovic, C.; Yeh, K. W.; Wu, M. K.; Wei, J. Y. T.

2012-02-01

We report on cryomagnetic point-contact Andreev reflection spectroscopy performed on single crystals of superconducting FeTe1-xSx and FeTe1-xSex. The samples are cleaved in-situ and the measurements are carried out at temperatures down to 4.2K and in a field up to 9T. At base temperature and zero field, we observe a cone-shaped hump at lower voltages in the conductance spectra with no dips at zero bias and a linear background at higher voltages. The spectral evolution of gap size, zero-bias conductance, and excess spectral area are analyzed as a function of temperature and field. Further spectral analysis is carried out using theoretical models of conductance spectra in multiband superconductors [1,2] and of gap symmetry in Fe-based superconductors [3]. The role of interstitial iron is also considered, by comparison with atomically-resolved scanning tunneling spectroscopy data.[4pt] [1] V. Lukic and E.J. Nicol, PRB 76, 144508 (2007) [2] A. Golubov et al., PRL 103, 077003 (2009) [3] P.J. Hirschfeld et al., RPP 74, 124508 (2011)

Improvement in surface conditions of electroplated Fe-Pt thick-film magnets

NASA Astrophysics Data System (ADS)

Yanai, T.; Honda, J.; Hamamura, R.; Omagari, Y.; Yamada, H.; Fujita, N.; Takashima, K.; Nakano, M.; Fukunaga, H.

2018-05-01

Fe-Pt thick-films were electroplated on Ta, Ti, Co, Ni, and Cu plates (substrates) using a direct current, and the surface morphology, the magnetic properties, and the crystal structure of the films were evaluated. The films plated on the Co, Ni, and Cu substrates showed much smooth surface compared with those for the Ta and Ti ones, and we confirmed that the Cu plate was the most attractive substrate due to very small cracks after an annealing for L10 ordering. High coercivity (>800 kA/m) for the Cu substrate is almost the same as that for our previous study in which we employed the Ta substrate, and we found that the Cu plate is a hopeful substrate to improve the surface conditions of electroplated Fe-Pt thick-film magnets.

Temperature dependence of the superconducting energy gaps in Ca9.35La0.65(Pt3As8)(Fe2As2)5 single crystal.

PubMed

Seo, Yu-Il; Choi, Woo-Jae; Ahmad, D; Kimura, Shin-Ichi; Kwon, Yong Seung

2018-06-05

We measured the optical reflectivity R(ω) for an underdoped (Ca 0.935 La 0.065 ) 10 (Pt 3 As 8 )(Fe 2 As 2 ) 5 single crystal and obtained the optical conductivity [Formula: see text] using the K-K transformation. The normal state [Formula: see text] at 30 K is well fitted by a Drude-Lorentz model with two Drude components (ω p1  = 1446 cm -1 and ω p2  = 6322 cm -1 ) and seven Lorentz components. Relative reflectometry was used to accurately determine the temperature dependence of the superconducting gap at various temperatures below T c . The results clearly show the opening of a superconducting gap with a weaker second gap structure; the magnitudes for the gaps are estimated from the generalized Mattis-Bardeen model to be Δ 1  = 30 and Δ 2  = 50 cm -1 , respectively, at T = 8 K, which both decrease with increasing temperature. The temperature dependence of the gaps was not consistent with one-band BCS theory but was well described by a two-band (hence, two gap) BCS model with interband interactions. The temperature dependence of the superfluid density is flat at low temperatures, indicating an s-wave full-gap superconducting state.

INVESTIGATION OF LEAKAGE CURRENT BEHAVIOR OF Pt/Bi0.975La0.025Fe0.975Ni0.025O3/Pt CAPACITOR MEASURED AT DIFFERENT TEMPERATURES

NASA Astrophysics Data System (ADS)

Dai, Xiu Hong; Zhao, Hong Dong; Zhang, Lei; Zhu, Hui Juan; Li, Xiao Hong; Zhao, Ya Jun; Guo, Jian Xin; Zhao, Qing Xun; Wang, Ying Long; Liu, Bao Ting; Ma, Lian Xi

2014-03-01

Polycrystalline Bi0.975La0.025Fe0.975Ni0.025O3 (BLFNO) film is fabricated on Pt/Ti/SiO2/Si(111) substrate by sol-gel method. It is found that the well-crystallized BLFNO film is polycrystalline, and the Pt/BLFNO/Pt capacitor possesses good ferroelectric properties with remnant polarization of 74 μC/cm2 at electric field of 833 kV/cm. Moreover, it is also found that the leakage current density of the Pt/BLFNO/Pt capacitor increases with the increase of measurement temperature ranging from 100 to 300 K. The leakage density of the Pt/BLFNO/Pt capacitor satisfies space-charge-limited conduction (SCLC) at higher electric field and shows little dependence on voltage polarity and temperature, but shows polarity and temperature dependence at lower applied electric field. With temperature increasing from 100 to 300 K at lower applied electric field, the most likely conduction mechanism is from Ohmic behavior to SCLC for positive biases, but no clear dominant mechanism for negative biases is shown.

Reduced carbonic fluid at magmatic PT conditions: new experimental data.

NASA Astrophysics Data System (ADS)

Simakin, Alexander; Salova, Tamara; Rinat, Gabitov; Sergey, Isaenko

2017-04-01

We study properties of the dry fluid of C-O-S composition at P=2000 bar and T=900-1000oC. Dry carbonic fluid was generated at the thermal decomposition of FeCO3 and (Fe,Mg)CO3. At the decomposition of pure FeCO3 assemblages of Wus-Mt and pure Mt was recognized. Wus-Mt corresponds to the fO2 on the level around QFM-2. Native carbon was formed from the fluid when CO concentration was above constrained by CCO buffer. Generated fluid was trapped as the bubbles within welded albite glass matrix. Micro-Raman study yields around 15 vol.% of CO in the mixture with CO2. The glass trap composition was interpreted to estimate the minimum solubilities of different elements in the studied fluid: Pt - 15 ppm, Mn - 262 ppm, P - 4100 ppm, Ce -22 ppm, S- 3400 ppm, Sr - 3300 ppm (Simakin et al., 2016). We add sulfur to the system in the form of FeS2, thermally decomposing after carbonates. Fluid interaction with platinum capsule walls to form PtS leads to the fast removal of sulfur. Analysis of the interaction products provides preliminary estimate of the Pt solubility. We observe transformation of magnetite to FeS at the reaction with COS. Pyrrhotite formed from oxide contains in average 1.5 wt.% of Pt. Assuming that at the reaction 1/3Fe3O4+COS+1/3CO = FeS +CO2 all dissolved in the fluid platinum was incorporated into the sulfide we get minimum Pt solubility of about 5000 ppm. To capture fluid composition we perform experiments in the Au capsules with sodium-silicate glass trap. Micro-Raman shows that presence of water in sodium-silicate leads to the partial COS decomposition to thiols and H2S, however, COS still was prevailing form of sulfur in the fluid as predicted theoretically (Simakin, 2014). Transport of siderophile (Ni, Cr, PGE, Au), LILE (Ba, Cs, Rb, Sr), LREE and chalcophile (Ag, Zn, Cu) elements by the dry fluid of C-O-S composition can be decisive during the formation of different volcanic aerosol phases. Study was partially supported by RFBR-DFG grant # 16-55-12040. References. Simakin AG, Salova TP, Gabitov RI and Isaenko SI. Dry CO2-CO fluid as an important potential deep Earth solvent. Geofluids (2016, online). Simakin AG (2014) Peculiarities of the fluid composition in the dry C-O-S system at PT parameters of the low crust by the data of the thermodynamic modeling. Petrology, 22, 50-59.

Switching times of nanoscale FePt: Finite size effects on the linear reversal mechanism

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

Ellis, M. O. A.; Chantrell, R. W.

2015-04-20

The linear reversal mechanism in FePt grains ranging from 2.316 nm to 5.404 nm has been simulated using atomistic spin dynamics, parametrized from ab-initio calculations. The Curie temperature and the critical temperature (T{sup *}), at which the linear reversal mechanism occurs, are observed to decrease with system size whilst the temperature window T{sup *}

Platinum group elements and gold in ferromanganese crusts from Afanasiy-Nikitin seamount, equatorial Indian Ocean: Sources and fractionation

USGS Publications Warehouse

Banakar, V.K.; Hein, J.R.; Rajani, R.P.; Chodankar, A.R.

2007-01-01

The major element relationships in ferromanganese (Fe-Mn) crusts from Afanasiy-Nikitin seamount (ANS), eastern equatorial Indian Ocean, appear to be atypical. High positive correlations (r = 0.99) between Mn/Co and Fe/Co ratios, and lack of correlation of those ratios with Co, Ce, and Ce/Co, indicate that the ANS Fe-Mn crusts are distinct from Pacific seamount Fe-Mn crusts, and reflect region-specific chemical characteristics. The platinum group elements (PGE: Ir, Ru, Rh, Pt, and Pd) and Au in ANS Fe-Mn crusts are derived from seawater and are mainly of terrestrial origin, with a minor cosmogenic component. The Ru/Rh (0.5-2) and Pt/Ru ratios (7-28) are closely comparable to ratios in continental basalts, whereas Pd/Ir ratios exhibit values ( 0.75) correlations between water depth and Mn/Co, Fe/Co, Ce/Co, Co, and the PGEs. Fractionation of the PGE-Au from seawater during colloidal precipitation of the major-oxide phases is indicated by well-defined linear positive correlations (r > 0.8) of Co and Ce with Ir, Ru, Rh, and Pt; Au/Co with Mn/Co; and by weak or no correlations of Pd with water depth, Co-normalized major-element ratios, and with the other PGE (r < 0.5). The strong enrichment of Pt (up to 1 ppm) relative to the other PGE and its positive correlations with Ce and Co demonstrate a common link for the high concentrations of all three elements, which likely involves an oxidation reaction on the Mn-oxide and Fe-oxyhydroxide surfaces. The documented fractionation of PGE-Au and their positive association with redox sensitive Co and Ce may have applications in reconstructing past-ocean redox conditions and water masses.

Electrical detection of microwave assisted magnetization reversal by spin pumping

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

Rao, Siddharth; Subhra Mukherjee, Sankha; Elyasi, Mehrdad

2014-03-24

Microwave assisted magnetization reversal has been investigated in a bilayer system of Pt/ferromagnet by detecting a change in the polarity of the spin pumping signal. The reversal process is studied in two material systems, Pt/CoFeB and Pt/NiFe, for different aspect ratios. The onset of the switching behavior is indicated by a sharp transition in the spin pumping voltage. At a threshold value of the external field, the switching process changes from partial to full reversal with increasing microwave power. The proposed method provides a simple way to detect microwave assisted magnetization reversal.

Advanced bifunctional electrocatalyst generated through cobalt phthalocyanine tetrasulfonate intercalated Ni2Fe-layered double hydroxides for a laminar flow unitized regenerative micro-cell

NASA Astrophysics Data System (ADS)

Zhong, Haihong; Tian, Ran; Gong, Xiaoman; Li, Dianqing; Tang, Pinggui; Alonso-Vante, Nicolas; Feng, Yongjun

2017-09-01

We fabricated a NiFeOx/CoNy-C nanocomposite derived from CoPcTs-intercalated Ni2Fe-layered double hydroxides (Ni2Fe-CoPcTs-LDH), which served as high-efficiency, low-cost, and long-durability bifunctional oxygen electrocatalyst in half-cell, and a H2-O2 laminar flow unitized regenerative micro-cell (LFURMC) in alkaline media. Based on the synergistic effect between Co-Ny and NiFeOx centers, the non-noble hybrid catalyst NiFeOx/CoNy-C achieves a ΔE (η@jOER,10 - η@jORR,-3) = 0.84 V in alkaline solution, outperforming the commercial Pt/C, and very close to that of IrOx/C. In the fuel cell mode, the performance of NiFeOx/CoNy-C with the maximum power density of 56 mW cm-2 is similar to that of Pt/C (63 mW cm-2) and IrOx/C (58 mW cm-2); in the electrolysis mode, the calculated maximum electrical power consumed on NiFeOx/CoNy-C (237 mW cm-2) is more than 3 times that on Pt/C (73 mW cm-2), similar with that of IrOx/C. More importantly, the NiFeOx/CoNy-C shows a remarkable stability in alternating modes in a LFURMC system.

The iron-nickel-phosphorus system: Effects on the distribution of trace elements during the evolution of iron meteorites

NASA Astrophysics Data System (ADS)

Corrigan, Catherine M.; Chabot, Nancy L.; McCoy, Timothy J.; McDonough, William F.; Watson, Heather C.; Saslow, Sarah A.; Ash, Richard D.

2009-05-01

To better understand the partitioning behavior of elements during the formation and evolution of iron meteorites, two sets of experiments were conducted at 1 atm in the Fe-Ni-P system. The first set examined the effect of P on solid metal/liquid metal partitioning behavior of 22 elements, while the other set explored the effect of the crystal structures of body-centered cubic (α)- and face-centered cubic (γ)-solid Fe alloys on partitioning behavior. Overall, the effect of P on the partition coefficients for the majority of the elements was minimal. As, Au, Ga, Ge, Ir, Os, Pt, Re, and Sb showed slightly increasing partition coefficients with increasing P-content of the metallic liquid. Co, Cu, Pd, and Sn showed constant partition coefficients. Rh, Ru, W, and Mo showed phosphorophile (P-loving) tendencies. Parameterization models were applied to solid metal/liquid metal results for 12 elements. As, Au, Pt, and Re failed to match previous parameterization models, requiring the determination of separate parameters for the Fe-Ni-S and Fe-Ni-P systems. Experiments with coexisting α and γ Fe alloy solids produced partitioning ratios close to unity, indicating that an α versus γ Fe alloy crystal structure has only a minor influence on the partitioning behaviors of the trace element studied. A simple relationship between an element's natural crystal structure and its α/γ partitioning ratio was not observed. If an iron meteorite crystallizes from a single metallic liquid that contains both S and P, the effect of P on the distribution of elements between the crystallizing solids and the residual liquid will be minor in comparison to the effect of S. This indicates that to a first order, fractional crystallization models of the Fe-Ni-S-P system that do not take into account P are appropriate for interpreting the evolution of iron meteorites if the effects of S are appropriately included in the effort.

Hierarchically porous Fe-N-C derived from covalent-organic materials as a highly efficient electrocatalyst for oxygen reduction

NASA Astrophysics Data System (ADS)

Zuo, Quan; Zhao, Pingping; Luo, Wei; Cheng, Gongzhen

2016-07-01

Developing high-performance non-precious catalysts to replace platinum as oxygen reduction reaction (ORR) catalysts is still a big scientific and technological challenge. Herein, we report a simple method for the synthesis of a FeNC catalyst with a 3D hierarchically micro/meso/macro porous network and high surface area through a simple carbonization method by taking the advantages of a high specific surface area and diverse pore dimensions in 3D porous covalent-organic material. The resulting FeNC-900 electrocatalyst with improved reactant/electrolyte transport and sufficient active site exposure, exhibits outstanding ORR activity with a half-wave potential of 0.878 V, ca. 40 mV more positive than Pt/C for ORR in alkaline solution, and a half-wave potential of 0.72 V, which is comparable to that of Pt/C in acidic solution. In particular, the resulting FeNC-900 exhibits a much higher stability and methanol tolerance than those of Pt/C, which makes it among the best non-precious catalysts ever reported for ORR.Developing high-performance non-precious catalysts to replace platinum as oxygen reduction reaction (ORR) catalysts is still a big scientific and technological challenge. Herein, we report a simple method for the synthesis of a FeNC catalyst with a 3D hierarchically micro/meso/macro porous network and high surface area through a simple carbonization method by taking the advantages of a high specific surface area and diverse pore dimensions in 3D porous covalent-organic material. The resulting FeNC-900 electrocatalyst with improved reactant/electrolyte transport and sufficient active site exposure, exhibits outstanding ORR activity with a half-wave potential of 0.878 V, ca. 40 mV more positive than Pt/C for ORR in alkaline solution, and a half-wave potential of 0.72 V, which is comparable to that of Pt/C in acidic solution. In particular, the resulting FeNC-900 exhibits a much higher stability and methanol tolerance than those of Pt/C, which makes it among the best non-precious catalysts ever reported for ORR. Electronic supplementary information (ESI) available: Fig. S1-S12 and Tables S1 and S2. See DOI: 10.1039/c6nr03273g

Quantum Mechanics Studies of Fuel Cell Catalysts and Proton Conducting Ceramics with Validation by Experiment

NASA Astrophysics Data System (ADS)

Tsai, Ho-Cheng

We carried out quantum mechanics (QM) studies aimed at improving the performance of hydrogen fuel cells. In part I, The challenge was to find a replacement for the Pt cathode that would lead to improved performance for the Oxygen Reduction Reaction (ORR) while remaining stable under operational conditions and decreasing cost. Our design strategy was to find an alloy with composition Pt3M that would lead to surface segregation such that the top layer would be pure Pt, with the second and subsequent layers richer in M. Under operating conditions we expect the surface to have significant O and/or OH chemisorbed on the surface; we searched for M that would remain segregated under these conditions. Using QM we examined surface segregation for 28 Pt3M alloys, where M is a transition metal. We found that only Pt3Os and Pt3Ir showed significant surface segregation when O and OH are chemisorbed on the catalyst surfaces. This result indicates that Pt3Os and Pt 3Ir favor formation of a Pt-skin surface layer structure that would resist the acidic electrolyte corrosion during fuel cell operation environments. We chose to focus on Os because the phase diagram for Pt-Ir indicated that Pt-Ir could not form a homogeneous alloy at lower temperature. To determine the performance for ORR, we used QM to examine intermediates, reaction pathways, and reaction barriers involved in the processes for which protons from the anode reactions react with O2 to form H2O. These QM calculations used our Poisson-Boltzmann implicit solvation model include the effects of the solvent (water with dielectric constant 78 with pH 7 at 298K). We also carried out similar QM studies followed by experimental validation for the Os/Pt core-shell catalyst fabricated by the underpotential deposition (UPD) method. The QM results indicated that the RDS for ORR is a compromise between the OOH formation step (0.37 eV for Pt, 0.23 eV for Pt2ML/Os core-shell) and H2O formation steps (0.32 eV for Pt, 0.22 eV for Pt2ML /Os core-shell). We found that Pt2ML/Os has the highest activity (compared to pure Pt and to the Pt3Os alloy) because the 0.37 eV barrier decreases to 0.23 eV. To understand what aspects of the core shell structure lead to this improved performance, we considered the effect on ORR of compressing the alloy slab to the dimensions of pure Pt. However this had the same RDS barrier 0.37 eV. Experimental materials characterization proves the core-shell feature of our catalyst. In part II, we used QM calculations to study methane stream reforming on a Ni-alloy catalyst surfaces for solid oxide fuel cell (SOFC) application. SOFC has wide fuel adaptability but the coking and sulfur poisoning will reduce its stability. We carried out QM calculations on surface segregation and found that the most stable configuration for Ni4Fe has a Fe atom distribution of (0%, 50%, 25%, 25%, 0%) starting at the bottom layer. We calculated that the binding of C atoms on the Ni4Fe surface is 142.9 Kcal/mol, which is about 10 Kcal/mol weaker compared to the pure Ni surface. This result confirms the experimental observation. The reaction energy barriers for CH x decomposition and C binding on various alloy surface, Ni4X (X=Fe, Co, Mn, and Mo), showed Ni4Fe, Ni4Co, and Fe4Mn all have better coking resistance than pure Ni, but that only Ni4Fe and Fe4Mn have (slightly) improved activity compared to pure Ni. In part III, we used QM to examine the proton transport in doped perovskite-ceramics. Here we used a 2x2x2 supercell of perovskite with composition Ba8X 7M1(OH)1O23 where X=Ce or Zr and M=Y, Gd, or Dy. Thus in each case a 4+ X is replace by a 3 + M plus a proton on one O. Here we predicted the barriers for proton diffusion allowing both includes intra-octahedron and inter-octahedra proton transfer. Without any restriction, we only observed the inter-octahedra proton transfer with similar energy barrier as previous computational work but 0.2 eV higher than experimental result for Y doped zirconate. For one restriction in our calculations is that the Odonor-Oacceptor atoms were kept at fixed distances, we found that the barrier difference between cerates/zirconates with various dopants are only 0.02~0.03 eV. To fully address performance one would need to examine proton transfer at grain boundaries, which will require larger scale ReaxFF reactive dynamics for systems with millions of atoms. The QM calculations used here will be used to train the ReaxFF force field. (Abstract shortened by UMI.).

Thermal dewetting with a chemically heterogeneous nano-template for self-assembled L1(0) FePt nanoparticle arrays.

PubMed

Wang, Liang-Wei; Cheng, Chung-Fu; Liao, Jung-Wei; Wang, Chiu-Yen; Wang, Ding-Shuo; Huang, Kuo-Feng; Lin, Tzu-Ying; Ho, Rong-Ming; Chen, Lih-Juann; Lai, Chih-Huang

2016-02-21

A design for the fabrication of metallic nanoparticles is presented by thermal dewetting with a chemically heterogeneous nano-template. For the template, we fabricate a nanostructured polystyrene-b-polydimethylsiloxane (PS-b-PDMS) film on a Si|SiO2 substrate, followed by a thermal annealing and reactive ion etching (RIE) process. This gives a template composed of an ordered hexagonal array of SiOC hemispheres emerging in the polystyrene matrix. After the deposition of a FePt film on this template, we utilize the rapid thermal annealing (RTA) process, which provides in-plane stress, to achieve thermal dewetting and structural ordering of FePt simultaneously. Since the template is composed of different composition surfaces with periodically varied morphologies, it offers more tuning knobs to manipulate the nanostructures. We show that both the decrease in the area of the PS matrix and the increase in the strain energy relaxation transfer the dewetted pattern from the randomly distributed nanoparticles into a hexagonal periodic array of L10 FePt nanoparticles. Transmission electron microscopy with the in situ heating stage reveals the evolution of the dewetting process, and confirms that the positions of nanoparticles are aligned with those of the SiOC hemispheres. The nanoparticles formed by this template-dewetting show an average diameter and center-to-center distance of 19.30 ± 2.09 nm and 39.85 ± 4.80 nm, respectively. The hexagonal array of FePt nanoparticles reveals a large coercivity of 1.5 T, much larger than the nanoparticles fabricated by top-down approaches. This approach offers an efficient pathway toward self-assembled nanostructures in a wide range of material systems.

Dual role of CO in the stability of subnano Pt clusters at the Fe3O4(001) surface

PubMed Central

Bliem, Roland; van der Hoeven, Jessi E. S.; Hulva, Jan; Pavelec, Jiri; Gamba, Oscar; de Jongh, Petra E.; Schmid, Michael; Blaha, Peter; Diebold, Ulrike; Parkinson, Gareth S.

2016-01-01

Interactions between catalytically active metal particles and reactant gases depend strongly on the particle size, particularly in the subnanometer regime where the addition of just one atom can induce substantial changes in stability, morphology, and reactivity. Here, time-lapse scanning tunneling microscopy (STM) and density functional theory (DFT)-based calculations are used to study how CO exposure affects the stability of Pt adatoms and subnano clusters at the Fe3O4(001) surface, a model CO oxidation catalyst. The results reveal that CO plays a dual role: first, it induces mobility among otherwise stable Pt adatoms through the formation of Pt carbonyls (Pt1–CO), leading to agglomeration into subnano clusters. Second, the presence of the CO stabilizes the smallest clusters against decay at room temperature, significantly modifying the growth kinetics. At elevated temperatures, CO desorption results in a partial redispersion and recovery of the Pt adatom phase. PMID:27457953

Single Atomic Iron Catalysts for Oxygen Reduction in Acidic Media: Particle Size Control and Thermal Activation

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

Zhang, Hanguang; Hwang, Sooyeon; Wang, Maoyu

To significantly reduce the cost of proton exchange membrane (PEM) fuel cells, current Pt must be replaced by platinum-metal-group (PGM)-free catalysts for the oxygen reduction reaction (ORR) in acid. We report here a new class of high-performance atomic iron dispersed carbon catalysts through controlled chemical doping of iron ions into zinc-zeolitic imidazolate framework (ZIF), a type of metal-organic framework (MOF). The novel synthetic chemistry enables accurate size control of Fe-doped ZIF catalyst particles with a wide range from 20 to 1000 nm without changing chemical properties, which provides a great opportunity to increase the density of active sites that ismore » determined by the particle size. We elucidated the active site formation mechanism by correlating the chemical and structural changes with thermal activation process for the conversion from Fe-N4 complex containing hydrocarbon networks in ZIF to highly active FeNx sites embedded into carbon. A temperature of 800oC was identified as the critical point to start forming pyridinic nitrogen doping at the edge of the graphitized carbon planes. Further increasing heating temperature to 1100oC leads to increase of graphitic nitrogen, generating possible synergistic effect with FeNx sites to promote ORR activity. The best performing catalyst, which has well-defined particle size around 50 nm and abundance of atomic FeNx sites embedded into carbon structures, achieve a new performance milestone for the ORR in acid including a half-wave potential of 0.85 V vs RHE and only 20 mV loss after 10,000 cycles in O2 saturated H2SO4 electrolyte. The new class PGM-free catalyst with approaching activity to Pt holds great promise for future PEM fuel cells.« less

Ferromagnetic alloy material CoFeC with high thermal tolerance in MgO/CoFeC/Pt structure and comparable intrinsic damping factor with CoFeB

NASA Astrophysics Data System (ADS)

Chen, Shaohai; Zhou, Jing; Lin, Weinan; Yu, Jihang; Guo, Rui; Poh, Francis; Shum, Danny; Chen, Jingsheng

2018-02-01

The thermal tolerance and perpendicular magnetic anisotropy (PMA) of ferromagnetic alloy Co40Fe40C20 in the structure MgO/CoFeC/Pt (or Ta) were investigated and compared with the commonly used CoFeB alloy. It is found that the PMA of CoFeC with {{K}i,CoFeC}=2.21 erg c{{m}-2} , which is 59% higher than that of CoFeB, can be obtained after proper post-annealing treatment. Furthermore, CoFeC alloy provides better thermal tolerance to temperature of 400 °C than CoFeB. The studies on ferromagnetic resonance show that the intrinsic damping constant α in of Co40Fe40C20 alloy is 0.0047, which is similar to the reported value of 0.004 for Co40Fe40B20 alloy. The comprehensive comparisons indicate that CoFeC alloy is a promising candidate for the application of the integration of spin torque transfer magnetic random access memory with complementary metal-oxide semiconductor processes.

Superconductivity by rare earth doping in the 1038-type compounds (Ca1-xREx) 10(FeAs)10(Pt3As8) with RE=Y, La-Nd, Sm-Lu

NASA Astrophysics Data System (ADS)

Stürzer, Tobias; Derondeau, Gerald; Bertschler, Eva-Maria; Johrendt, Dirk

2015-01-01

We report superconductivity in polycrystalline samples of the 1038-type compounds (Ca1-xREx) 10(FeAs)10(Pt3As8) up to Tc=35 K with RE=Y, La-Nd, Sm, Gd-Lu. The critical temperatures are nearly independent of the trivalent rare earth element used, yielding a common Tc(xRE) phase diagram for electron doping in all these systems. The absence of superconductivity in Eu2+ doped samples, as well as the close resemblance of (Ca1-xREx) 10(FeAs)10(Pt3As8) to the 1048 compound substantiate that the electron doping scenario in the RE-1038 and 1048 phases is analogous to other iron-based superconductors with simpler crystal structures.

Elasticity of Single-Crystal Phase D across the Spin Transitions of Ferrous and Ferric Iron in the Lower Mantle

NASA Astrophysics Data System (ADS)

Wu, X.; Lin, J. F.; Liu, J.; Mao, Z.; Guo, X.; Yoshino, T.; McCammon, C. A.; Xiao, Y.; Prakapenka, V.

2014-12-01

Phase D, the densest hydrous magnesium silicate synthesized at the Earth's mantle P-T conditions thus far, has been proposed to be a potential candidate for transportation of H2O into the lower mantle by subduction of the hydrated oceanic lithosphere. A certain amount of iron, the most abundant transition metal element in the Earth's interior, is expected to be incorporated into the phase D. Here we synthesized high-quality single-crystal Fe,Al-bearing Phase D (Mg0.89Fe0.11Al0.37Si1.55H2.65O6, ~13.3wt% H2O) with grain sizes of ~200 micron using the Kawai multianvil apparatus at 21 GPa and 1200 °C at the Institute for Study of the Earth's Interior, University of Oakayama, Japan. Conventional Mössbauer results indicate that the sample contains both ferrous and ferric iron that occupy the octahedral sites of the hexagonal structure. In situ high-pressure single crystal XRD and NFS experiments were performed up to megabar pressures at 13IDD beamline (GSECARS) and 16IDD beamline (HPCAT) of the Advanced Photon Source, respectively. Both experimental results clearly show that both Fe2+ and Fe3+ undergo a HS-LS transition at high pressures. High-resolution XRD results further indicate an abnormal compression behavior at approximately 37 GPa that can be linked with the previously proposed hydrogen bond symmetrization. Elasticity of phase D has a marked influence by the two-step spin transitions of both Fe2+ and Fe3+ and the hydrogen bond symmetrization, presenting in the seismic wave model, which is of implication for our understanding of the deep-Earth geophysics and geochemistry especially along the subducted slabs.

Large enhancement of Blocking temperature by control of interfacial structures in Pt/NiFe/IrMn/MgO/Pt multilayers

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

Chen, Xi; Wang, Shouguo, E-mail: sgwang@ustb.edu.cn; Han, Gang

2015-09-15

The Blocking temperature (T{sub B}) of Pt/NiFe/IrMn/MgO/Pt multilayers was greatly enhanced from far below room temperature (RT) to above RT by inserting 1 nm thick Mg layer at IrMn/MgO interface. Furthermore, the exchange bias field (H{sub eb}) was increased as well by the control of interfacial structures. The evidence for a significant fraction of Mn-O bonding at IrMn/MgO interface without Mg insertion layer was provided by X-ray photoelectron spectroscopy. The bonding between Mn and O can decrease the antiferromagnetism of IrMn film, leading to lower value of T{sub B} in Pt/NiFe/IrMn/MgO/Pt multilayers. Ultrathin Mg film inserted at IrMn/MgO interface actingmore » as an oxygen sinking layer can suppress the oxidation reactions between Mn and O and reduce the formation of Mn-O bonding greatly. The oxidation suppression results in the recovery of the antiferromagnetism of IrMn film, which can enhance T{sub B} and H{sub eb}. Furthermore, the high resolution transmission electron microscopy demonstrates that the Mg insertion layer can efficiently promote a high-quality MgO (200) texture. This study will enhance the understanding of physics in antiferromagnet-based spintronic devices.« less

Comparison of platinum, palladium, and rhodium distributions in some layered intrusions with special reference to the late differentiates (upper zone) of the Bushveld complex, South Africa.

USGS Publications Warehouse

Page, N.J.; Von Gruenewaldt, G.; Haffty, J.; Aruscavage, P. J.

1982-01-01

The Stillwater, Fiskenaesset and Bushveld complexes have many similarities. The trends of the Pt/(Pt + Pd) and its correlation with Mg/(Mg + Fe2+) are presented. Presumably the Pt/(Pt + Pd) variations are related to changes in major mineral compositions. -K.A.R.

High-Performance Direct Methanol Fuel Cells with Precious-Metal-Free Cathode.

PubMed

Li, Qing; Wang, Tanyuan; Havas, Dana; Zhang, Hanguang; Xu, Ping; Han, Jiantao; Cho, Jaephil; Wu, Gang

2016-11-01

Direct methanol fuel cells (DMFCs) hold great promise for applications ranging from portable power for electronics to transportation. However, apart from the high costs, current Pt-based cathodes in DMFCs suffer significantly from performance loss due to severe methanol crossover from anode to cathode. The migrated methanol in cathodes tends to contaminate Pt active sites through yielding a mixed potential region resulting from oxygen reduction reaction and methanol oxidation reaction. Therefore, highly methanol-tolerant cathodes must be developed before DMFC technologies become viable. The newly developed reduced graphene oxide (rGO)-based Fe-N-C cathode exhibits high methanol tolerance and exceeds the performance of current Pt cathodes, as evidenced by both rotating disk electrode and DMFC tests. While the morphology of 2D rGO is largely preserved, the resulting Fe-N-rGO catalyst provides a more unique porous structure. DMFC tests with various methanol concentrations are systematically studied using the best performing Fe-N-rGO catalyst. At feed concentrations greater than 2.0 m, the obtained DMFC performance from the Fe-N-rGO cathode is found to start exceeding that of a Pt/C cathode. This work will open a new avenue to use nonprecious metal cathode for advanced DMFC technologies with increased performance and at significantly reduced cost.

Self-Propelled Soft Protein Microtubes with a Pt Nanoparticle Interior Surface.

PubMed

Kobayakawa, Satoshi; Nakai, Yoko; Akiyama, Motofusa; Komatsu, Teruyuki

2017-04-11

Human serum albumin (HSA) microtubes with an interior surface composed of Pt nanoparticles (PtNPs) are self-propelled in aqueous H 2 O 2 medium. They can capture cyanine dye and Escherichia coli (E. coli) efficiently. Microtubes were prepared by wet templating synthesis by using a track-etched polycarbonate (PC) membrane with alternate filtrations of aqueous HSA, poly-l-arginine (PLA), and citrate-PtNPs. Subsequent dissolution of the PC template yielded uniform hollow cylinders made of (PLA/HSA) 8 PLA/PtNP stacking layers (1.16±0.02 μm outer diameter, ca. 23 μm length). In aqueous H 2 O 2 media, the soft protein microtubes are self-propelled by jetting O 2 bubbles from the open-end terminus. The effects of H 2 O 2 and surfactant concentrations on the velocity were investigated. The swimming microtube captured cyanine dye in the HSA component of the wall. Addition of an intermediate γ-Fe 3 O 4 layer allowed manipulation of the direction of movement of the tubule by using a magnetic field. Because the exterior surface is positively charged, the bubble-propelled microtubes adsorbed E. coli with high efficiency. The removal ratio of E. coli by a single treatment reached 99 %. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Interface perpendicular magnetic anisotropy in ultrathin Ta/NiFe/Pt layered structures

NASA Astrophysics Data System (ADS)

Hirayama, Shigeyuki; Kasai, Shinya; Mitani, Seiji

2018-01-01

Interface perpendicular magnetic anisotropy (PMA) in ultrathin Ta/NiFe/Pt layered structures was investigated through magnetization measurements. Ta/NiFe/Pt films with NiFe layer thickness (t) values of 2 nm or more showed typical in-plane magnetization curves, which was presumably due to the dominant contribution of the shape magnetic anisotropy. The thickness dependence of the saturation magnetization of the entire NiFe layer (M s) was well analyzed using the so-called dead-layer model, showing that the magnetically active part of the NiFe layer has saturation magnetization (M\\text{s}\\text{act}) independent of t and comparable to the bulk value. In the perpendicular direction, the saturation field H k was found to clearly decrease with decreasing t, while the effective field of shape magnetic anisotropy due to the active NiFe saturation magnetization M\\text{s}\\text{act} should be independent of t. These observations show that there exists interface PMA in the layered structures. The interface PMA energy density was determined to be ∼0.17 erg/cm2 using the dead-layer model. Motivated by the correlation observed between M s and H k, we also attempted to interpret the experimental results using an alternative approach beyond the dead-layer model; however, it gives only implications on the incomplete validity of the dead-layer model and no better understanding.

FePO4 based single chamber air-cathode microbial fuel cell for online monitoring levofloxacin.

PubMed

Zeng, Libin; Li, Xinyong; Shi, Yueran; Qi, Yefei; Huang, Daqiong; Tadé, Moses; Wang, Shaobin; Liu, Shaomin

2017-05-15

A bio-electrochemical strategy was developed for constructing a simple and sensitive levofloxacin (LEV) sensor based on a single chamber microbial fuel cell (SC-MFC) using FePO 4 nanoparticles (NPs) as the cathode catalyst instead of traditional Pt/C. In this assembled sensor device, FePO 4 NPs dramatically promoted the electrooxidation of oxygen on the cathode, which helps to accelerate the voltage output from SC-MFC and can provide a powerful guarantee for LEV detection. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to fully characterize the FePO 4 NPs. Under the optimized COD condition (3mM), the LEV with a concentration range of 0.1-1000µg/L could be detected successfully, and exhibited the excellent linear interval in the concentration range of 0.1-100µg/L. During this range of concentrations of LEV, a temporary effect on the anode of exoelectrogenic bacterial in less than 10min could occur, and then came back to the normal. It exhibited a long-term stability, maintaining the stable electricity production for 14 months of continuous running. Besides, the detection mechanism was investigated by quantum chemical calculation using density functional theory (DFT). Copyright © 2016. Published by Elsevier B.V.

Modulated spin orbit torque in a Pt/Co/Pt/YIG multilayer by nonequilibrium proximity effect

NASA Astrophysics Data System (ADS)

Liu, Q. B.; Meng, K. K.; Cai, Y. Z.; Qian, X. H.; Wu, Y. C.; Zheng, S. Q.; Jiang, Y.

2018-01-01

We have compared the spin orbit torque (SOT) induced magnetization switching in Pt/Co/Pt/Y3Fe5O12 (YIG) and Pt/Co/Pt/SiO2 multilayers. The critical switching current in Pt/Co/Pt/YIG is almost half of that in Pt/Co/Pt/SiO2. Through harmonic measurements, we demonstrated the enhancement of the effective spin Hall angle in Pt/Co/Pt/YIG. The increased efficiency of SOT is ascribed to the nonequilibrium proximity effect at the Pt/YIG interface, which suppresses the spin current reflection and enhances the effective spin accumulation at the Co/Pt interface. Our method can effectively reduce the switching current density and provide another way to modulate SOT.

Platinum and Palladium Exsolution Textures in Quenched Sulfide Melts

NASA Astrophysics Data System (ADS)

Reo, G.; Frank, M. R.; Loocke, M. P.; Macey, C. J.

2017-12-01

Magmatic sulfide ore deposits account for over 80% of the world's platinum group element (PGE) reserves. Layered mafic intrusions (LMIs), a type of magmatic sulfide ore deposit, contain alternating layers of silicate and sulfide mineralization that are thought to have coexisted as an immiscible silicate + sulfide melt pair. Platinum and palladium, the most common PGEs found in LMIs, heavily favor the sulfide melt. Nernst partition coefficients for Pt (D = wt% of Pt in sulfide/wt% of Pt in silicate) range from 102 to 109. This study examined the Pt- and Pd-bearing phases that formed from the quenched sulfide melts to better constrain the PGE-rich sulfide layers of LMIs system. Experiments were conducted with a basalt melt, sulfide melt, and Pt-Pd metal in a vertical tube furnace at 1100°C and 1 atm and with oxygen fugacity buffered to QFM (quartz-fayalite-magnetite). Following the experiments, run products containing both sulfide and silicate glasses (quenched melts) were analyzed by a Shimadzu EPMA-1720HT Electron Probe Microanalyzer. The focus here is on the quenched Fe-rich sulfides whereas data on the partitioning of Pt and Pd between the coexisting silicate and sulfide melts will be presented in the future. The sulfide samples were imaged in back-scattering mode and major and trace element concentrations of separate metal-rich phases in the sulfide matrix were ascertained through wavelength-dispersive x-ray spectroscopy. Three discernable PGE-rich phases were found to have exsolved from the sulfide matrix upon quenching of the sulfide melt. All of these phases had Fe and S of 21-24 and 16-22 wt.%, respectively. An irregularly shaped Pd- and Cu-rich sulfide phase ( 36 and 14 wt.%, respectively) makes up the majority of the exsolution product. A separate Pd- and Ni-rich phase ( 22 and 14 wt%, respectively) can be found as grains or rims adjacent to the exsolved Pd- and Cu-rich phase. A third Pd- and Pt-rich phase ( 26 and 18 wt.%, respectively) exhibits a dendritic quench texture and is usually surrounded by the sulfide matrix. These data indicate that multiple phases, each with a different Pt:Pd ratio can form upon quench of a homogenous sulfide melt. Thus, the analysis of PGE-rich sulfide domains within LMI may be best considered as a single phase when conducting exploration efforts.

Controlling the anomalous Hall effect by electric-field-induced piezo-strain in Fe40Pt60/(001)-Pb(Mg1/3Nb2/3)0.67Ti0.33O3 multiferroic heterostructures

NASA Astrophysics Data System (ADS)

Yang, Yuanjun; Yao, Yingxue; Chen, Lei; Huang, Haoliang; Zhang, Benjian; Lin, Hui; Luo, Zhenlin; Gao, Chen; Lu, Y. L.; Li, Xiaoguang; Xiao, Gang; Feng, Ce; Zhao, Y. G.

2018-01-01

Electric-field control of the anomalous Hall effect (AHE) was investigated in Fe40Pt60/(001)-Pb(Mg1/3Nb2/3)0.67Ti0.33O3 (FePt/PMN-PT) multiferroic heterostructures at room temperature. It was observed that a very large Hall resistivity change of up to 23.9% was produced using electric fields under a magnetic field bias of 100 Oe. A pulsed electric field sequence was used to generate nonvolatile strain to manipulate the Hall resistivity. Two corresponding nonvolatile states with distinct Hall resistivities were achieved after the electric fields were removed, thus enabling the encoding of binary information for memory applications. These results demonstrate that the Hall resistivity can be reversibly switched in a nonvolatile manner using programmable electric fields. Two remanent magnetic states that were created by electric-field-induced piezo-strain from the PMN-PT were attributed to the nonvolatile and reversible properties of the AHE. This work suggests that a low-energy-consumption-based approach can be used to create nonvolatile resistance states for spintronic devices based on electric-field control of the AHE.

Durability enhancement of intermetallics electrocatalysts via N-anchor effect for fuel cells.

PubMed

Li, Xiang; An, Li; Chen, Xin; Zhang, Nanlin; Xia, Dingguo; Huang, Weifeng; Chu, Wangsheng; Wu, Ziyu

2013-11-18

Insufficient durability and catalytic activity of oxygen reduction reaction (ORR) electrocatalyst are key issues that have to be solved for the practical application of low temperature fuel cell. This paper introduces a new catalyst design strategy using N-anchor to promote the corrosion resistance of electrocatalyst. The as-synthesized N-Pt3Fe1/C shows a high electrocatalytic activity and a superior durability towards ORR. The kinetic current density of N-Pt3Fe1/C as normalized by ECSA is still as high as 0.145 mA cm(-2) and only 7% loss after 20,000 potential cycles from 0.6 to 1.2 V (vs. NHE) in O2-bubbling perchloric acid solution, whereas Pt3Fe1/C shows 49% loss under the same tests. The N-anchor approach offers novel opportunities for the development of ORR catalyst with excellent electrochemical properties.

Giant Magnetoelectric Energy Conversion Utilizing Inter-Ferroelectric Phase Transformations in Ferroics

NASA Astrophysics Data System (ADS)

Finkel, Peter; Staruch, Margo

Phase transition-based electromechanical transduction permits achieving a non-resonant broadband mechanical energy conversion see (Finkel et al Actuators, 5 [1] 2. (2015)) , the idea is based on generation high energy density per cycle , at least 100x of magnitude larger than linear piezoelectric type generators in stress biased [011]cut relaxor ferroelectric Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) single crystal can generate reversible strain >0.35% at remarkably low fields (0.1 MV/m) for tens of millions of cycles. Recently we demonstrated that large strain and polarization rotation can be generated for over 40 x 106cycles with little fatigue by realization of reversible ferroelectric-ferroelectric phase transition in [011] cut PIN-PMN-PT relaxor ferroelectric single crystal while sweeping through the transition with a low applied electric field <0.18 MV/m under mechanical stress. This methodology was extended in the present work to propose magnetoelectric (ME) composite hybrid system comprised of highly magnetostrictive alloymFe81.4Ga18.6 (Galfenol), and lead indium niobate-lead magnesium niobate-lead titanate (PIN-PMN-PT) domain engineered relaxor ferroelectric single crystal. A small time-varying magnetic field applied to this system causes the magnetostrictive element to expand, and the resulting stress forces the phase change in the relaxor ferroelectric single crystal. ME coupling coefficient was fond to achieve 80 V/cm Oe near the FR-FO phase transition that is at least 100X of magnitude higher than any currently reported values.

Spin Hall magnetoresistance in CoFe 2O 4/Pt films

DOE PAGES

Wu, Hao; Qintong, Zhang; Caihua, Wan; ...

2015-05-13

Pulse laser deposition and magnetron sputtering techniques have been employed to prepare MgO(001)//CoFe 2O 4/Pt samples. Cross section transmission electron microscope results prove that the CoFe 2O 4 film epitaxially grew along (001) direction. X-ray magnetic circular dichroism results show that magnetic proximity effect in this sample is negligible. Magnetoresistance (MR) properties confirm that spin Hall MR (SMR) dominates in this system. Spin Hall effect-induced anomalous Hall voltage was also observed in this sample. Lastly, these results not only demonstrate the universality of SMR effect but also demonstrate the utility in spintronics of CoFe 2O 4 as a new typemore » of magnetic insulator.« less

System DyFeO: thermodynamic properties of ternary oxides using Calvet calorimetry and solid-state electrochemical cell

NASA Astrophysics Data System (ADS)

Parida, S. C.; Jacob, K. T.; Venugopal, V.

2002-10-01

The enthalpy increments and the standard molar Gibbs energies of formation of DyFeO 3(s) and Dy 3Fe 5O 12(s) have been measured using a Calvet micro-calorimeter and a solid oxide galvanic cell, respectively. A co-operative phase transition, related to anti-ferromagnetic to paramagnetic transformation, is apparent from the heat capacity data for DyFeO 3 at ˜648 K. A similar type of phase transition has been observed for Dy 3Fe 5O 12 at ˜560 K which is related to ferrimagnetic to paramagnetic transformation. Enthalpy increment data for DyFeO 3(s) and Dy 3Fe 5O 12(s), except in the vicinity of the second-order transition, can be represented by the following polynomial expressions: {H 0m(T)-H 0m(298.15 K)} ( J mol-1) (±1.1%)=-52754+142.9×(T ( K))+2.48×10 -3×(T ( K)) 2+2.951×10 6×(T ( K)) -1;(298.15⩽ T ( K)⩽1000) for DyFeO 3(s), and {H 0m(T)-H 0m(298.15 K)} ( J mol-1) (±1.2%)=-191048+545.0×(T ( K))+2.0×10 -5×(T ( K)) 2+8.513×10 6×(T ( K)) -1;(298.15⩽T ( K)⩽1000) for Dy 3Fe 5O 12(s). The reversible emfs of the solid-state electrochemical cells: (-)Pt/{DyFeO 3(s) + Dy 2O 3(s) + Fe(s)}//YDT/CSZ//{Fe(s) + Fe 0.95O(s)}/Pt(+) and (-)Pt/{Fe(s) + Fe 0.95O(s)}//CSZ//{DyFeO 3(s) + Dy 3Fe 5O 12(s) + Fe 3O 4(s)}/Pt(+), were measured in the temperature range from 1021 to 1250 K and 1035 to 1250 K, respectively. The standard Gibbs energies of formation of solid DyFeO 3 and Dy 3Fe 5O 12 calculated by the least squares regression analysis of the data obtained in the present study, and data for Fe 0.95O and Dy 2O 3 from the literature, are given by: Δ fG 0m( DyFeO3, s) ( kJ mol-1) (±3.2)=-1339.9+0.2473×(T ( K));(1021⩽T ( K)⩽1548) and Δ fG 0m( Dy3Fe5O12, s) ( kJ mol-1) (±3.5)=-4850.4+0.9846×(T ( K));(1035⩽T ( K)⩽1250). The uncertainty estimates for Δ fG 0m include the standard deviation in the emf and uncertainty in the data taken from the literature. Based on the thermodynamic information, oxygen potential diagram and chemical potential diagrams for the system DyFeO were developed at 1250 K.

N/S/B-doped graphitized carbon encased Fe species as a highly active and durable catalyst towards oxygen reduction reaction.

PubMed

Li, Guang-Lan; Cheng, Guang-Chun; Chen, Wen-Wen; Liu, Cai-Di; Yuan, Li-Fang; Yang, Bei-Bei; Hao, Ce

2018-03-15

Exploring cost-effective, high-performance and durable non-precious metal catalysts is of great significance for the acceleration of sluggish oxygen reduction reaction (ORR). Here, we report an intriguing heteroatom-doped graphitized carbon encased Fe species composite by introducing N, S and B sequentially. The experimental approach was designed ingeniously for that the FeCl 3 ·6H 2 O could catalyze thiourea to synthesize N, S co-doped carbon materials which would further react with H 3 BO 3 and NH 3 (emerged at the heat-treatment process) to prepare N, S and B co-doped carbon materials (Fe-N/S/B-C). The Fe-N/S/B-C exhibits an impressive ORR activity for its half-wave potential of -0.1 V, which is 36 mV or 19 mV higher than that of the corresponding single or dual doped counterparts (Fe-N-C or Fe-N/S-C) and 31 mV positive than that of Pt/C catalyst, respectively. Further chronoamperometric measurement and accelerated aging test confirm the excellent electrochemical durability of Fe-N/S/B-C with the stable core-shell structure. The remarkable ORR performance and facile preparation method enable Fe-N/S/B-C as a potential candidate in electrochemical energy devices. Copyright © 2017 Elsevier Inc. All rights reserved.

A new member of ferrous sulfates, FeSO{sub 4}·2H{sub 2}O with PtS topology showing spin-canted long-range antiferromagnetic ordering

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

Zhao, Long; Liu, Wei, E-mail: weiliu@ouc.edu.cn; Cao, Lixin

2015-11-15

A sanderite ferrous sulfate FeSO{sub 4}·2H{sub 2}O has been synthesized by the hydro/solvothermal method. Its crystal structure (Pccn, a=6.3160 Å, b=7.7550 Å, c=8.9880 Å, V=440.2 Å{sup 3}, Z=4) can be regarded as the condensation of alternately corner-shared FeO{sub 4}(H{sub 2}O){sub 2} octahedra and SO{sub 4} tetrahedra with a similar topology of PtS. By structural comparison with the known hydrated ferrous sulfates, the structural relation among them has been noted and discussed in detail. A variable temperature magnetic study shows a spin-canted long-range antiferromagnetic ordering in the low temperature regime, which might result from a possible phase transition during the coolingmore » from the high temperature. - Graphical abstract: As a new number of ferrous sulfates, sanderite FeSO{sub 4}·2H{sub 2}O has been synthesized under hydro/solvothermal conditions, which exhibits a similar topology of PtS. - Highlights: • Sanderite ferrous sulfate has been synthesized. • The topology of its structure is similar to that of PtS. • A structural relation between these hydrated ferrous sulfates is discovered.« less

Ensemble averaged structure–function relationship for nanocrystals: effective superparamagnetic Fe clusters with catalytically active Pt skin [Ensemble averaged structure-function relationship for composite nanocrystals: magnetic bcc Fe clusters with catalytically active fcc Pt skin

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

Petkov, Valeri; Prasai, Binay; Shastri, Sarvjit

Practical applications require the production and usage of metallic nanocrystals (NCs) in large ensembles. Besides, due to their cluster-bulk solid duality, metallic NCs exhibit a large degree of structural diversity. This poses the question as to what atomic-scale basis is to be used when the structure–function relationship for metallic NCs is to be quantified precisely. In this paper, we address the question by studying bi-functional Fe core-Pt skin type NCs optimized for practical applications. In particular, the cluster-like Fe core and skin-like Pt surface of the NCs exhibit superparamagnetic properties and a superb catalytic activity for the oxygen reduction reaction,more » respectively. We determine the atomic-scale structure of the NCs by non-traditional resonant high-energy X-ray diffraction coupled to atomic pair distribution function analysis. Using the experimental structure data we explain the observed magnetic and catalytic behavior of the NCs in a quantitative manner. Lastly, we demonstrate that NC ensemble-averaged 3D positions of atoms obtained by advanced X-ray scattering techniques are a very proper basis for not only establishing but also quantifying the structure–function relationship for the increasingly complex metallic NCs explored for practical applications.« less

In-plane current-driven spin-orbit torque switching in perpendicularly magnetized films with enhanced thermal tolerance

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

Wu, Di; Department of Optical Science and Engineering, Key Laboratory of Micro and Nano Photonic Structures; Yu, Guoqiang, E-mail: guoqiangyu@ucla.edu

2016-05-23

We study spin-orbit-torque (SOT)-driven magnetization switching in perpendicularly magnetized Ta/Mo/Co{sub 40}Fe{sub 40}B{sub 20} (CoFeB)/MgO films. The thermal tolerance of the perpendicular magnetic anisotropy (PMA) is enhanced, and the films sustain the PMA at annealing temperatures of up to 430 °C, due to the ultra-thin Mo layer inserted between the Ta and CoFeB layers. More importantly, the Mo insertion layer also allows for the transmission of the spin current generated in the Ta layer due to spin Hall effect, which generates a damping-like SOT and is able to switch the perpendicular magnetization. When the Ta layer is replaced by a Pt layer,more » i.e., in a Pt/Mo/CoFeB/MgO multilayer, the direction of the SOT-induced damping-like effective field becomes opposite because of the opposite sign of spin Hall angle in Pt, which indicates that the SOT-driven switching is dominated by the spin current generated in the Ta or Pt layer rather than the Mo layer. Quantitative characterization through harmonic measurements reveals that the large SOT effective field is preserved for high annealing temperatures. This work provides a route to applying SOT in devices requiring high temperature processing steps during the back-end-of-line processes.« less

Pt-Au/MOx-CeO₂ (M = Mn, Fe, Ti) Catalysts for the Co-Oxidation of CO and H₂ at Room Temperature.

PubMed

Hong, Xiaowei; Sun, Ye; Zhu, Tianle; Liu, Zhiming

2017-02-27

A series of nanostructured Pt-Au/MO x -CeO₂ (M = Mn, Fe, Ti) catalysts were prepared and their catalytic performance for the co-oxidation of carbon monoxide (CO) and hydrogen (H₂) were evaluated at room temperature. The results showed that MO x promoted the CO oxidation of Pt-Au/CeO₂, but only the TiO₂ could enhance co-oxidation of CO and H₂ over Pt-Au/CeO₂. Related characterizations were conducted to clarify the promoting effect of MO x . Temperature-programmed reduction of hydrogen (H₂-TPR) and X-ray photoelectron spectroscopy (XPS) results suggested that MO x could improve the charge transfer from Au sites to CeO₂, resulting in a high concentration of Ce 3+ and cationic Au species which benefits for the CO oxidation. In-situ diffuse reflectance infrared Fourier transform spectroscopy (In-situ DRIFTS) results indicated that TiO₂ could facilitate the oxidation of H₂ over the Pt-Au/TiO₂-CeO₂ catalyst.

Tuning electrocatalytic activity of Pt monolayer shell by bimetallic Ir-M (M=Fe, Co, Ni or Cu) cores for the oxygen reduction reaction

DOE PAGES

Kuttiyiel, Kurian A.; Choi, YongMan; Sasaki, Kotaro; ...

2016-05-18

Here, platinum monolayer electrocatalyst are known to exhibit excellent oxygen reduction reaction (ORR) activity depending on the type of substrate used. Here we demonstrate a relationship between the ORR electrocatalytic activity and the surface electronic structure of Pt monolayer shell induced by various IrM bimetallic cores (M=Fe, Co, Ni or Cu). The relationship is rationalized by comparing density functional theory calculations and experimental results. For an efficient Pt monolayer electrocatalyst, the core should induce sufficient contraction to the Pt shell leading to a downshift of the d-band center with respect to the Fermi level. Depending on the structure of themore » IrM, relative to that of pure Ir, this interaction not only alters the electronic and geometric structure but also induces segregation effects. Combined these effects significantly enhance the ORR activities of the Pt monolayer shell on bimetallic Ir cores electrocatalysts.« less

Effect of annealing on magnetic properties of Ni80Fe20 permalloy nanoparticles prepared by polyol method.

PubMed

Qin, G W; Pei, W L; Ren, Y P; Shimada, Y; Endo, Y; Yamaguchi, M; Okamoto, S; Kitakami, O

2011-12-01

Ni80Fe20 permalloy nanoparticles with narrow size distribution and homogeneous composition have been prepared by the polyol processing at 180 degrees C for 2 h and their particle sizes can be tunable in the size range of 20-440 nm by proper addition of K2PtCI4 agent. X-ray diffraction results show that the NiFe nanoparticles are of face centered cubic structure. The addition of K2PtCl4 does not affect the composition of NiFe NPs but decreases the particle size remarkably. Both saturation magnetization and coercivity of the as-prepared NiFe nanoparticles decrease with decreasing particle size. Annealed at 280 degrees C, however, the saturation magnetization of various sized NiFe nanoparticles increases drastically and approaches to the bulk for the -440 nm NiFe particles, and a maximum coercivity (-270 Oe) happens at a critical size of -50 nm. The magnetic property dependency of these NiFe nanoparticles on annealing has been discussed by considering the surface chemistry.

Sensitivity analysis of pars-tensa young's modulus estimation using inverse finite-element modeling

NASA Astrophysics Data System (ADS)

Rohani, S. Alireza; Elfarnawany, Mai; Agrawal, Sumit K.; Ladak, Hanif M.

2018-05-01

Accurate estimates of the pars-tensa (PT) Young's modulus (EPT) are required in finite-element (FE) modeling studies of the middle ear. Previously, we introduced an in-situ EPT estimation technique by optimizing a sample-specific FE model to match experimental eardrum pressurization data. This optimization process requires choosing some modeling assumptions such as PT thickness and boundary conditions. These assumptions are reported with a wide range of variation in the literature, hence affecting the reliability of the models. In addition, the sensitivity of the estimated EPT to FE modeling assumptions has not been studied. Therefore, the objective of this study is to identify the most influential modeling assumption on EPT estimates. The middle-ear cavity extracted from a cadaveric temporal bone was pressurized to 500 Pa. The deformed shape of the eardrum after pressurization was measured using a Fourier transform profilometer (FTP). A base-line FE model of the unpressurized middle ear was created. The EPT was estimated using golden section optimization method, which minimizes the cost function comparing the deformed FE model shape to the measured shape after pressurization. The effect of varying the modeling assumptions on EPT estimates were investigated. This included the change in PT thickness, pars flaccida Young's modulus and possible FTP measurement error. The most influential parameter on EPT estimation was PT thickness and the least influential parameter was pars flaccida Young's modulus. The results of this study provide insight into how different parameters affect the results of EPT optimization and which parameters' uncertainties require further investigation to develop robust estimation techniques.

Role of magnetic exchange interaction due to magnetic anisotropy on inverse spin Hall voltage at FeSi3%/Pt thin film bilayer interface

NASA Astrophysics Data System (ADS)

Shah, Jyoti; Ahmad, Saood; Chaujar, Rishu; Puri, Nitin K.; Negi, P. S.; Kotnala, R. K.

2017-12-01

In our recent studies inverse spin Hall voltage (ISHE) was investigated by ferromagnetic resonance (FMR) using bilayer FeSi3%/Pt thin film prepared by pulsed laser deposition (PLD) technique. In ISHE measurement microwave signal was applied on FeSi3% film along with DC magnetic field. Higher magnetization value along the film-plane was measured by magnetic hysteresis (M-H) loop. Presence of magnetic anisotropy has been obtained by M-H loop which showed easy direction of magnetization when applied magnetic field is parallel to the film plane. The main result of this study is that FMR induced inverse spin Hall voltage 12.6 μV at 1.0 GHz was obtained across Pt layer. Magnetic exchange field at bilayer interface responsible for field torque was measured 6 × 1014 Ω-1 m-2 by spin Hall magnetoresistance. The damping torque and spin Hall angle have been evaluated as 0.084 and 0.071 respectively. Presence of Si atom in FeSi3% inhomogenize the magnetic exchange field among accumulated spins at bilayer interface and feebly influenced by spin torque of FeSi3% layer. Weak field torque suppresses the spin pumping to Pt layer thus low value of inverse spin Hall voltage is obtained. This study provides an excellent opportunity to investigate spin transfer torque effect, thus motivating a more intensive experimental effort for its utilization at maximum potential. The improvement in spin transfer torque may be useful in spin valve, spin battery and spin transistor application.

Synthesis of ferromagnetic nanoparticles, formic acid oxidation catalyst nanocomposites, and late-transition metal-boride intermetallics by unique synthetic methods and single-source precursors

NASA Astrophysics Data System (ADS)

Wellons, Matthew S.

The design, synthesis, and characterization of magnetic alloy nanoparticles, supported formic acid oxidation catalysts, and superhard intermetallic composites are presented. Ferromagnetic equatomic alloy nanoparticles of FePt, FePd, and CoPt were synthesized utilizing single-source heteronuclear organometallic precursors supported on an inert water-soluble matrix. Direct conversion of the precursor-support composite to supported ferromagnetic nanoparticles occurs under elevated temperatures and reducing conditions with metal-ion reduction and minimal nanoparticle coalescence. Nanoparticles were easily extracted from the support by addition of water and characterized in structure and magnetic properties. Palladium and platinum based nanoparticles were synthesized with microwave-based and chemical metal-ion reduction strategies, respectively, and tested for catalytic performance in a direct formic acid fuel cell (DFAFC). A study of palladium carbide nanocomposites with various carbonaceous supports was conducted and demonstrated strong activity comparable to commercially available palladium black, but poor catalytic longevity. Platinum-lead alloy nanocomposites synthesized with chemical reduction and supported on Vulcan carbon demonstrated strong activity, excellent catalytic longevity, and were subsequently incorporated into a prototype DFAFC. A new method for the synthesis of superhard ceramics on polymer substrates called Confined Plasma Chemical Deposition (CPCD) was developed. The CPCD method utilizes a tuned Free Electron Laser to selectively decompose the single-source precursor, Re(CO)4(B3H8), in a plasma-like state resulting in the superhard intermetallic ReB2 deposited on polymer substrates. Extension of this method to the synthesis of other hard of superhard ceramics; WB4, RuB2, and B4C was demonstrated. These three areas of research show new synthetic methods and novel materials of technological importance, resulting in a substantial advance in their respective fields.

Exchange coupling in permalloy/BiFeO3 heterostructures

NASA Astrophysics Data System (ADS)

Heron, John; Wang, Chen; Carlton, David; Nowakowski, Mark; Gajek, Martin; Awschalom, David; Bokor, Jeff; Ralph, Dan; Ramesh, R.

2010-03-01

BiFeO3 is a ferroelectric and antiferromagnetic multiferroic with the ferroelectric and antiferromagnetic order parameters coupled at room temperature. This coupling results in the reorientation of the ferroelectric and magnetic domains as applied voltages switch the electric polarization. Previous studies using ferromagnet/BiFeO3 heterostructures have shown that the anisotropy of the ferromagnetic layer can be tuned by the ferroelectric domain structure of the BiFeO3 film [1, 2]. The physical mechanism driving this exchange bias with BiFeO3 is still under investigation. We use patterned permalloy structures, with varying aspect ratios, on BiFeO3 thin films to investigate the physics of this interaction. The results of our studies using MFM, PEEM, and MOKE to understand this mechanism as a means to electric field control of magnetic structures will be presented. [4pt] [1] H. Bea et al., Physical Review Letters 100, 017204 (2008).[0pt] [2] L.W. Martin et al., Nanoletters 8, 2050 (2008).

Single-reactor process for producing liquid-phase organic compounds from biomass

DOEpatents

Dumesic, James A.; Simonetti, Dante A.; Kunkes, Edward L.

2015-12-08

Disclosed is a method for preparing liquid fuel and chemical intermediates from biomass-derived oxygenated hydrocarbons. The method includes the steps of reacting in a single reactor an aqueous solution of a biomass-derived, water-soluble oxygenated hydrocarbon reactant, in the presence of a catalyst comprising a metal selected from the group consisting of Cr, Mn, Fe, Co, Ni, Cu, Mo, Tc, Ru, Rh, Pd, Ag, W, Re, Os, Ir, Pt, and Au, at a temperature, and a pressure, and for a time sufficient to yield a self-separating, three-phase product stream comprising a vapor phase, an organic phase containing linear and/or cyclic mono-oxygenated hydrocarbons, and an aqueous phase.

Single-reactor process for producing liquid-phase organic compounds from biomass

DOEpatents

Dumesic, James A [Verona, WI; Simonetti, Dante A [Middleton, WI; Kunkes, Edward L [Madison, WI

2011-12-13

Disclosed is a method for preparing liquid fuel and chemical intermediates from biomass-derived oxygenated hydrocarbons. The method includes the steps of reacting in a single reactor an aqueous solution of a biomass-derived, water-soluble oxygenated hydrocarbon reactant, in the presence of a catalyst comprising a metal selected from the group consisting of Cr, Mn, Fe, Co, Ni, Cu, Mo, Tc, Ru, Rh, Pd, Ag, W, Re, Os, Ir, Pt, and Au, at a temperature, and a pressure, and for a time sufficient to yield a self-separating, three-phase product stream comprising a vapor phase, an organic phase containing linear and/or cyclic mono-oxygenated hydrocarbons, and an aqueous phase.

High P-T experiments and first principles calculations of the diffusion of Si and Cr in liquid iron

NASA Astrophysics Data System (ADS)

Posner, Esther S.; Rubie, David C.; Frost, Daniel J.; Vlček, Vojtěch; Steinle-Neumann, Gerd

2017-04-01

Chemical diffusion rates of Si and Cr in liquid iron have been measured over the P-T range of 1-18 GPa and 1873-2428 K. The experiments were performed using a multi-anvil apparatus with diffusion couples comprised of pure iron and iron alloy placed end to end in a vertical orientation. In order to extend our dataset to the Earth's core-mantle boundary and to compare experimental data with theoretical diffusion rates calculated under laboratory-accessible conditions, we have also performed first principles molecular dynamic simulations (FP-MD) and calculated self-diffusion coefficients and activation parameters for Si, Cr, and Fe diffusion in liquid Fe, Fe0.92Si0.08 and Fe0.92Cr0.08 compositions over the P-T range of 1 bar-135 GPa and 2200-5500 K. Over the entire range of pressures and temperatures studied using both methods, diffusion coefficients are described well using an exponential function of the homologous temperature relation, D = Dhexp(-gTh), where Th = Tm/T, Tm is the melting temperature at the pressure of interest and g and Dh are constants. Our findings indicate constant diffusivities of approximately 4 × 10-9 m2 s-1 for Si and Cr and 5 × 10-9 m2 s-1 for Fe along the melting curve from ambient to core pressures in all liquid compositions studied, with an increase of ∼0.8 log units at T = 2Tm. Differences between experimental data and computational results are less than 0.1 log units. Structural properties of liquid iron alloys analyzed using partial radial distribution functions (RDFs) show the average distance between two Fe atoms, rFe-Fe, is identical to that of rFe-Si and rFe-Cr over the entire P-T range of study, which supports that the diffusion of Si and Cr (and thus likely other species of similar atomic radii) occurs via direct substitution with Fe. Diffusion coefficients and interatomic distances used to calculate liquid viscosities via the Stokes-Einstein relation yield constant viscosity along the melting curve of ∼6 mPa s for liquid Fe, ∼7 mPa s for liquid Fe0.92Cr0.08, and ∼8 mPa s for liquid Fe0.92Si0.08, with a decrease of ∼0.8 log units at T = 2Tm. The data can also be reproduced within <10% using the Arrhenian model with derivatives of the activation parameters determined over a very wide range of P-T conditions. Verification of a homologous temperature dependence of diffusion in liquid metals, as well as the excellent agreement between experimental results and FP-MD simulations, provides a new and simple framework for interpreting and modeling mass transport processes of liquid iron alloys in all planetary bodies regardless of size. Our results are used to evaluate the kinetics of metal-silicate chemical equilibration during core formation and diffusivity contrasts across a solid-liquid metal interface, i.e. at the inner core boundary.

Multiferroic and magnetoelectric nanocomposites for data processing

NASA Astrophysics Data System (ADS)

Kleemann, Wolfgang

2017-06-01

Recent progress in preparing and understanding composite magnetoelectrics is highlighted. Apart from optimized standard solutions novel methods of switching magnetism with electric fields and vice versa with focus on magnetoelectric (ME) data processing in multiferroic and magnetoelectric nanocomposites deserve particular interest. First, we report on the patented MERAM, which uses the electric field control of exchange bias in a layered composite via an epitaxial magnetoelectric Cr2O3 layer exchange coupled to a Pt/Co/Pt trilayer. It promises to crucially reduce Joule energy losses in RAM devices. Second, magnetic switching of the electric polarization by a transverse magnetic field in a composite of CoFe2O4 nanopillars embedded in a vertically poled BaTiO3 thick film produces a regular surface polarization pattern with rectangular local symmetry. Its possible use for data processing is discussed. Third, in the relaxor ferroelectric single-phase compound (BiFe0.9Co0.1O3)0.4-(Bi1/2K1/2TiO3)0.6 polar nanoregions emerging from ferrimagnetic Bi(Fe,Co)O3 regions embedded in a Bi1/2K1/2TiO3 relaxor component transform into ferroelectric clusters and simultaneously enable congruent magnetic clusters. The local polarization and magnetization couple with record-high direct and converse magnetoelectric coupling coefficients, α  ≈  1.0  ×  10-5 s m-1. These ‘multiferroic’ clusters are promising for applications in data storage or processing devices.

3D polymer hydrogel for high-performance atomic iron-rich catalysts for oxygen reduction in acidic media

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

Qiao, Zhi; Zhang, Hanguang; Karakalos, Stavros

Current platinum group metal (PGM)-free carbon nanocomposite catalysts for the oxygen reduction reaction (ORR) in acidic electrolyte often suffer from rapid degradation associated with carbon corrosion due to the use of large amount of amorphoous carbon black supports. Here, we developed a new concept of using freestanding 3D hydrogel to design support-free Fe-N-C catalysts. A 3D polyaniline (PANI)-based hydrogel was used for preparing a new type of single atomic iron site-rich catalyst, which has exhibited exceptionally enhanced activity and stability compared to conventional Fe-N-C catalysts supported on amorphous carbon blacks. The achieved performance metric on the hydrogel PANI-Fe catalysts ismore » one of the best ever reported PGM-free catalysts, reaching a half-wave potential up to 0.83 V vs. RHE and only leaving 30 mV gap with Pt/C catalysts (60 μgPt/cm2) in challenging acidic media. Remarkable ORR stability was accomplished as well on the same catalyst evidenced by using harsh potential cycling tests. The well dispersion of atomic iron into partially graphitized carbon, featured with dominance of micropores and porous network structures, is capable of accommodating increased number of active sites, strengthening local bonding among iron, nitrogen and carbon, and facilitating mass transfer. The 3D polymer hydrogel approach would be a new pathway to advance PGM-free catalysts.« less

3D polymer hydrogel for high-performance atomic iron-rich catalysts for oxygen reduction in acidic media

DOE PAGES

Qiao, Zhi; Zhang, Hanguang; Karakalos, Stavros; ...

2017-08-03

Current platinum group metal (PGM)-free carbon nanocomposite catalysts for the oxygen reduction reaction (ORR) in acidic electrolyte often suffer from rapid degradation associated with carbon corrosion due to the use of large amount of amorphoous carbon black supports. Here, we developed a new concept of using freestanding 3D hydrogel to design support-free Fe-N-C catalysts. A 3D polyaniline (PANI)-based hydrogel was used for preparing a new type of single atomic iron site-rich catalyst, which has exhibited exceptionally enhanced activity and stability compared to conventional Fe-N-C catalysts supported on amorphous carbon blacks. The achieved performance metric on the hydrogel PANI-Fe catalysts ismore » one of the best ever reported PGM-free catalysts, reaching a half-wave potential up to 0.83 V vs. RHE and only leaving 30 mV gap with Pt/C catalysts (60 μgPt/cm2) in challenging acidic media. Remarkable ORR stability was accomplished as well on the same catalyst evidenced by using harsh potential cycling tests. The well dispersion of atomic iron into partially graphitized carbon, featured with dominance of micropores and porous network structures, is capable of accommodating increased number of active sites, strengthening local bonding among iron, nitrogen and carbon, and facilitating mass transfer. The 3D polymer hydrogel approach would be a new pathway to advance PGM-free catalysts.« less

Selective field evaporation in field-ion microscopy for ordered alloys

NASA Astrophysics Data System (ADS)

Ge, Xi-jin; Chen, Nan-xian; Zhang, Wen-qing; Zhu, Feng-wu

1999-04-01

Semiempirical pair potentials, obtained by applying the Chen-inversion technique to a cohesion equation of Rose et al. [Phys. Rev. B 29, 2963 (1984)], are employed to assess the bonding energies of surface atoms of intermetallic compounds. This provides a new calculational model of selective field evaporation in field-ion microscopy (FIM). Based on this model, a successful interpretation of FIM image contrasts for Fe3Al, PtCo, Pt3Co, Ni4Mo, Ni3Al, and Ni3Fe is given.

Noise Reduction Based on an Fe -Rh Interlayer in Exchange-Coupled Heat-Assisted Recording Media

NASA Astrophysics Data System (ADS)

Vogler, Christoph; Abert, Claas; Bruckner, Florian; Suess, Dieter

2017-11-01

High storage density and high data rate are two of the most desired properties of modern hard disk drives. Heat-assisted magnetic recording (HAMR) is believed to achieve both. Recording media, consisting of exchange-coupled grains with a high and a low TC part, were shown to have low dc noise—but increased ac noise—compared to hard magnetic single-phase grains like FePt. We extensively investigate the influence of an Fe -Rh interlayer on the magnetic noise in exchange-coupled grains. We find an optimal grain design that reduces the jitter in the down-track direction by up to 30% and in the off-track direction by up to 50%, depending on the head velocity, compared to the same structures without FeRh. Furthermore, the mechanisms causing this jitter reduction are demonstrated. Additionally, we show that, for short heat pulses and low write temperatures, the switching-time distribution of the analyzed grain structure is reduced by a factor of 4 compared to the same structure without an Fe -Rh layer. This feature could be interesting for HAMR use with a pulsed laser spot and could encourage discussion of this HAMR technique.

Thermal stability of bubble domains in ferromagnetic discs

NASA Astrophysics Data System (ADS)

Hrkac, G.; Bance, S.; Goncharov, A.; Schrefl, T.; Suess, D.

2007-05-01

The transition and thermal stability of disc-shaped ferromagnetic particles at the temperature of T = 300 K with a uniaxial anisotropy along the symmetry axis from a bi-domain to a single domain state has been studied. The nudge elastic band method was used to map the energy landscape and to calculate the energy barrier between the transition states. For single FePt disc-shaped particles with perpendicular anisotropy three transition configurations have been found: single domain, stripe- and stable bubble domains at zero applied field. The single domain configuration along the positive anisotropy axis is reached by an annihilation process of the domain wall and the all-down state by a complex domain expansion process. Magnetization configurations in two interacting discs show an increase in thermal stability compared with single disc systems, which is attributed to the interacting magnetostatic energy between the two particles.

Nanofabrication and ion milling introduced effects on magnetic properties in magnetic recording

NASA Astrophysics Data System (ADS)

Sun, Zhenzhong

Perpendicular magnetic nanostructures have played an important role in magnetic recording technologies. In this dissertation, a systematic study on the CoPt magnetic nanostructures from fabrication, characterization to computer simulation has been performed. During the fabrication process, ion irradiation/bombardment in ion mill can cause physical damage to the magnetic nanostructures and degrade their magnetic properties. To study the effect of ion damage on CoPt nanostructures, different degrees of ion damage are introduced into CoPt nanopillars by varying the accelerating voltage in ion mill. The results demonstrate that the ion damage can reduce the coercivity by softening circumferential edge, and therefore changes the switching mechanism from coherent rotation to nucleation followed by rapid domain wall propagation. The SFD of CoPt nanostructures is independent of ion damage and is mainly determined by the intrinsic anisotropy distribution of the film rather than the nanostructure size distribution. Anisotropy-graded bit-patterned media are fabricated and studied based on high anisotropy L10-FePt material system. L10-FePt thin films with linearly and quadratically distributed anisotropy are achieved by varying substrate temperature during film growth. After patterning, the anisotropy-graded L10-FePt nanopillars display a reduced switching field and maintain a good thermal stability compared to the non-graded one. Experimental investigation and comparison further prove the concept of "anisotropy-graded" bit-patterned media and their potential application in the future magnetic recording. During magnetic write head fabrication, ion-beam damage may degrade the performance of the magnetic write pole. A surface sensitive MOKE is used to characterize the magnetic properties of these etched FeCo films. MOKE measurement shows a hard axis hysteresis loop with a high Mr in the high power etched film due to the ion beam introduced defects. The high power etched film also shows the highest RMS by AFM measurement. The geometric peaks at the top surface may have shape anisotropy and serve as the pinning sites. These magnetic pinning sites can prevent the nucleation center forming at the top surface during the switching process and lead to a high Mr in the top surface region.

Cumulative effect of transition metals on nitrogen and fluorine co-doped graphite nanofibers: an efficient and highly durable non-precious metal catalyst for the oxygen reduction reaction.

PubMed

Peera, S Gouse; Arunchander, A; Sahu, A K

2016-08-14

Nitrogen and fluorine co-doped graphite nanofibers (N/F-GNF) and their cumulative effect with Fe and Co have been developed as an alternative non-precious metal catalyst for efficient oxygen reduction reaction (ORR) in acidic media. The synergistic effect between the doped hetero atoms and the co-ordinated Fe and Co towards ORR activity and durability of the catalyst is deeply investigated. A high ORR onset potential comparable with commercial Pt/C catalyst is observed with the Fe-Co/NF-GNF catalyst, which indicates that this catalyst is a potential alternative to Pt/C. A fivefold increase in mass activity is achieved by the Fe-Co/NF-GNF catalyst compared to the simple N/F-GNF catalyst, which endorses the significant role of transition metal atoms in enhancing ORR activity. The advanced Fe-Co/NF-GNF catalyst also exhibits complete tolerance to CH3OH and CO. The Fe-Co/NF-GNF catalyst also exhibits excellent durability towards the ORR with only a 10 mV negative shift in its half wave potential after a 10 000 repeated potential cycling test, whereas in the case of a commercial Pt/C catalyst there was an ∼110 mV negative shift under similar environmental conditions. More stringent corrosive test cycles were also performed by maintaining the cell as high as 1.4 V with a later decrease to 0.6 V vs. RHE for 300 cycles, which showed the excellent durability of the Fe-Co/NF-GNF catalyst in comparison with the Pt/C catalyst. XPS analysis of the Fe-Co/NF-GNF catalyst presents the ORR active chemical states of N (pyridinic-N and graphitic-N) and F (semi-ionic-F) and the co-ordinated sites of Fe and Co species with the dopants. The excellent performance and durability of the Fe-Co/NF-GNF catalyst is due to the synergistic effect between the hetero atoms dopants (N and F) and strong co-ordinating bonds of M-N-C, which protect the graphene layers around the metallic species and greatly mitigates the leaching of Co and Fe during the long term cycling test. The high activity and long term durability of the Fe-Co/NF-GNF catalyst make it a promising ORR electrocatalyst for the fuel cell cathode reaction.

Microstructure and mechanical properties of a Ti-microalloyed low-carbon stainless steel treated by quenching-partitioning-tempering process

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

Xie, S.T., E-mail: xst-2007@163.com; Liu, Z.Y.; Wang, Z.

Quenching-partitioning-tempering (Q-P-T) process was used to treat a Ti-microalloyed low-carbon stainless steel after cold rolling. In addition to martensite, ferrite and retained austenite, TiN, coarse TiC, fine TiC, (Fe,Cr){sub 3}C and ultra-fine TiC precipitates were formed after the Q-P-T treatment. Based on field emission-scanning electron microscope (FESEM) and transmission electron microscope (TEM) observations, thermodynamic, crystallographic and statistical analyses were used to reveal the precipitation behaviors of these particles. The effects of partitioning-tempering (P-T) temperature and time on the microstructure and mechanical properties of Q-P-T treated specimens were specially studied. The coarsening and spheroidization of (Fe,Cr){sub 3}C particles during P-T stagemore » were obviously retarded by large Cr addition. The retained austenite was obtained significantly with appropriate P-T parameters. The precipitation of ultra-fine TiC particles in the martensite during the P-T stage at 500 °C induced a secondary hardening. - Highlights: • Some fine TiC with 30–70 nm precipitated in austenite during partial austenization. • A part of fine TiC had K-S OR with martensite after Q-P-T treatment. • A part of fine TiC had a OR specially deviating from K-S OR with martensite. • Coarsening and spheroidization of (Fe,Cr){sub 3}C were retarded during P-T stage. • Ultra-fine TiC with < 10 nm precipitated in martensite during P-T stage at 500 °C.« less

Influence of piezoelectric strain on the Raman spectra of BiFeO 3 films deposited on PMN-PT substrates

DOE PAGES

Himcinschi, Cameliu; Guo, Er -Jia; Talkenberger, Andreas; ...

2016-01-27

In this study, BiFeO 3 epitaxial thin films were deposited on piezoelectric 0.72Pb(Mg 1/3Nb 2/3)O 3-0.28PbTiO 3 (PMN-PT) substrates with a conductive buffer layer (La 0.7Sr 0.3MnO 3 or SrRuO 3) using pulsed laser deposition. The calibration of the strain values induced by the electric field applied on the piezoelectric PMN-PT substrates was realised using X-Ray diffraction measurements. The method of piezoelectrically induced strain allows to obtain a quantitative correlation between strain and the shift of the Raman-active phonons, ruling out the influence of extrinsic factors, such as growth conditions, crystalline quality of substrates, or film thickness. Using the Poissonmore » number for BiFeO 3 one can determine the volume change induced by strain, and therefore the Gr neisen parameters for specific phonon modes.« less

Grain growth mechanism and magnetic properties in L10-FePt thin films

NASA Astrophysics Data System (ADS)

Li, W.; Chen, L.

2017-08-01

This paper focuses on the grain growth mechanisms and magnetic properties of FePt thin films during an annealing process. The grain size and grain orientation distribution have been quantitatively investigated by electron backscatter diffraction (EBSD), and the grain growth kinetics of thin films were described by the phenomenological kinetic grain growth model. The results show that the grain growth exponent and activation energy of the FePt thin films were 4.26 and 136 kJ/mol respectively, indicating that the grain growth mechanism is mainly controlled by the stochastic jumping of atoms crossing the grain boundaries. X-ray diffraction (XRD) results show that disorder-order transformation was concurrent with grain growth during the annealing process, slowing down the velocity of grain growth. The hysteresis loops reveal that the out-of-plane coercivity and squareness is enhanced with increasing annealing temperature and this can be attributed to the improvement of L10-ordered phase volume fraction and texture intensity.

Atomistic modeling of L10 FePt: path to HAMR 5Tb/in2

NASA Astrophysics Data System (ADS)

Chen, Tianran; Benakli, Mourad; Rea, Chris

2015-03-01

Heat assisted magnetic recording (HAMR) is a promising approach for increasing the storage density of hard disk drives. To increase data density, information must be written in small grains, which requires materials with high anisotropy energy such as L10 FePt. On the other hand, high anisotropy implies high coercivity, making it difficult to write the data with existing recording heads. This issue can be overcome by the technique of HAMR, where a laser is used to heat the recording medium to reduce its coercivity while retaining good thermal stability at room temperature due to the large anisotropy energy. One of the keys to the success of HAMR is the precise control of writing process. In this talk, I will propose a Monte Carlo simulation, based on an atomistic model, that would allow us to study the magnetic properties of L10 FePt and dynamics of spin reversal for the writing process in HAMR.

Single-crystal structure determination of hydrous minerals and insights into a wet deep lower mantle

NASA Astrophysics Data System (ADS)

Zhang, L.; Yuan, H.; Meng, Y.; Popov, D.

2017-12-01

Water enters the Earth's interior through hydrated subducting slabs. How deep within the lower mantle (670-2900 km depth) can water be transported down and stored depends upon the availability of hydrous phases that is thermodynamically stable under the high P-T conditions and have a sufficiently high density to sink through the lower mantle. Phase H [MgSiH2O4] (1) and the δ-AlOOH (2) form solid solutions that are stable in the deep lower mantle (3), but the solid solution phase is 10% lighter than the corresponding lower mantle. Recent experimental discoveries of the pyrite (Py) structured FeO2 and FeOOH (4-6) suggest that these Fe-enriched phases can be transported to the deepest lower mantle owing to their high density. We have further discovered a very dense hydrous phase in (Fe,Al)OOH with a previously unknown hexagonal symmetry and this phase is stable relative to the Py-phase under extreme high P-T conditions in the deep lower mantle. Through in situ multigrain analysis (7) and single-crystal structure determination of the hydrous minerals at P-Tconditions of the deep lower mantle, we can obtain detailed structure information of the hydrous phases and therefore provide insights into the hydration mechanism in the deep lower mantle. These highly stable hydrous minerals extend the water cycle at least to the depth of 2900 km. 1. M. Nishi et al., Nature Geoscience 7, 224-227 (2014). 2. E. Ohtani, K. Litasov, A. Suzuki, T. Kondo, Geophysical Research Letters 28, 3991-3993 (2001). 3. I. Ohira et al., Earth and Planetary Science Letters 401, 12-17 (2014). 4. Q. Hu et al., Proceedings of the National Academy of Sciences of the United States of America 114, 1498-1501 (2017). 5. M. Nishi, Y. Kuwayama, J. Tsuchiya, T. Tsuchiya, Nature 547, 205-208 (2017). 6. Q. Hu et al., Nature 534, 241-244 (2016). 7. L. Zhang et al., American Mineralogist 101, 231-234 (2016).

Electric field poling induced self-biased converse magnetoelectric response in PMN-PT/NiFe2O4 nanocomposites

NASA Astrophysics Data System (ADS)

Ahlawat, Anju; Satapathy, S.; Deshmukh, Pratik; Shirolkar, M. M.; Sinha, A. K.; Karnal, A. K.

2017-12-01

In this letter, studies on structural transitions and the effect of electric field poling on magnetoelectric (ME) properties in 0.65Pb (Mg1/3Nb2/3)O3-0.35PbTiO3 (PMN-PT)/NiFe2O4 (NFO) nanocomposites are reported. The composite illustrates dramatic changes in the NFO crystal structure across ferroelectric transition temperature [Curie temperature (Tc) ˜ 450 K] of PMN-PT, while pure NFO does not exhibit any structural change in the temperature range (300 K-650 K). Synchrotron based X-ray diffraction analysis revealed the splitting of NFO peaks across the Tc of PMN-PT in the PMN-PT/NFO composite. Consequently, the anomalies are observed in temperature dependent magnetization of the NFO phase at the Tc of PMN-PT, establishing ME coupling in the PMN-PT/NFO composite. Furthermore, the composite exhibits drastic modification in ME coupling under electrically poled and unpoled conditions. A large self-biased ME effect characterized by non-zero ME response at zero Hbias was observed in electrically poled composites, which was not observed in unpoled PMN-PT/NFO. These results propose an alternative mechanism for intrinsic converse ME effects. The maximum magnetoelectric output was doubled after electrical poling. The observed self-biased converse magnetoelectric effect at room temperature provides potential applications in electrically controlled memory devices and magnetic flux control devices.

The spin-Hall effect and spin-orbit torques in epitaxial Co2FeAl/platinum bilayers

NASA Astrophysics Data System (ADS)

Peterson, T. A.; Liu, C.; McFadden, T.; Palmstrøm, C. J.; Crowell, P. A.

We have performed magnetoresistance measurements on epitaxially grown Co2FeAl/platinum (CFA/Pt) ultrathin ferromagnet/heavy metal bilayers to study the spin-Hall effect in Pt and the accompanying spin-orbit torque (SOT) exerted on the magnetic CFA layer. Specifically, we measure the spin-Hall magnetoresistance in the Pt layer by changing the orientation of the CFA magnetization with respect to the spin current orientation created in the Pt, and we determine the SOT efficiency using a second-harmonic detection technique. Because the latter of the two measurements is proportional to the spin-Hall ratio θSHE while the former is proportional to θSHE2, we are able to extract the bare Pt spin-Hall ratio with no assumptions about the CFA/Pt interface spin mixing conductance. Furthermore, by varying the Pt thickness we show that the results are consistent with resistivity-independent spin-Hall conductivity. Finally, the two measurements in combination allow us to infer a spin-mixing conductance at the CFA/Pt interface of 2 +/- 1 ×1015Ω-1m-2 . The combination of spin-Hall magnetoresistance and SOT measurements allows for a determination of the spin-mixing conductance using only low-frequency transport techniques. This work was supported by STARnet, a Semiconductor Research Corporation program, sponsored by MARCO and DARPA.

Platinum complexes of a borane-appended analogue of 1,1'-bis(diphenylphosphino)ferrocene: flexible borane coordination modes and in situ vinylborane formation.

PubMed

Cowie, Bradley E; Emslie, David J H

2014-12-15

A bis(phosphine)borane ambiphilic ligand, [Fe(η(5) -C5 H4 PPh2 )(η(5) -C5 H4 PtBu{C6 H4 (BPh2 )-ortho})] (FcPPB), in which the borane occupies a terminal position, was prepared. Reaction of FcPPB with tris(norbornene)platinum(0) provided [Pt(FcPPB)] (1) in which the arylborane is η(3) BCC-coordinated. Subsequent reaction with CO and CNXyl (Xyl=2,6-dimethylphenyl) afforded [PtL(FcPPB)] {L=CO (2) and CNXyl (3)} featuring η(2) BC- and η(1) B-arylborane coordination modes, respectively. Reaction of 1 or 2 with H2 yielded [PtH(μ-H)(FcPPB)] in which the borane is bound to a hydride ligand on platinum. Addition of PhC2 H to [Pt(FcPPB)] afforded [Pt(C2 Ph)(μ-H)(FcPPB)] (5), which rapidly converted to [Pt(FcPPB')] (6; FcPPB'=[Fe(η(5) -C5 H4 PPh2 )(η(5) -C5 H4 PtBu{C6 H4 (BPh-CPh=CHPh-Z)-ortho}]) in which the newly formed vinylborane is η(3) BCC-coordinated. Unlike arylborane complex 1, vinylborane complex 6 does not react with CO, CNXyl, H2 or HC2 Ph at room temperature. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Self-Assembled Fe-N-Doped Carbon Nanotube Aerogels with Single-Atom Catalyst Feature as High-Efficiency Oxygen Reduction Electrocatalysts

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

Zhu, Chengzhou; Fu, Shaofang; Song, Junhua

Finely controlled synthesis of high active and robust non-precious metal catalysts with excellent electrocatalytic efficiency towards oxygen reduction reaction is extremely vital for successful implementation of fuel cells and metal batteries. Unprecedented oxygen reduction reaction electrocatalytic performances and the diversified synthetic procedure in term of favorable structure/morphology characteristics make transition metals-derived M–N–C (M=Fe, Co) structures the most promising nanocatalysts. Herein, using the nitrogen-containing small molecular and inorganic salt as precursors and ultrathin tellurium nanowires as templates, we successfully synthesized a series of well-defined M-N-doped hollow carbon nanowire aerogels through one step hydrothermal route and subsequent facile annealing treatment. Taking advantagemore » of the porous nanostructures, one-dimensional building block as well as homogeneity of active sites, the resultant Fe-N-doped carbon hollow nanowire aerogels exhibited excellent ORR electrocatalytic performance even better than commercial Pt/C in alkaline solution, holding great potential in fuel cell applications.« less

UV-Vis-Induced Degradation of Phenol over Magnetic Photocatalysts Modified with Pt, Pd, Cu and Au Nanoparticles

PubMed Central

Wysocka, Izabela; Trzciński, Konrad; Łapiński, Marcin; Nowaczyk, Grzegorz; Zielińska-Jurek, Anna

2018-01-01

The combination of TiO2 photocatalyst and magnetic oxide nanoparticles enhances the separation and recoverable properties of nanosized TiO2 photocatalyst. Metal-modified (Me = Pd, Au, Pt, Cu) TiO2/SiO2@Fe3O4 nanocomposites were prepared by an ultrasonic-assisted sol-gel method. All prepared samples were characterized by X-ray powder diffraction (XRD) analysis, Brunauer-Emmett-Teller (BET) method, X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM), Mott-Schottky analysis and photoluminescence spectroscopy (PL). Phenol oxidation pathways of magnetic photocatalysts modified with Pt, Pd, Cu and Au nanoparticles proceeded by generation of reactive oxygen species, which oxidized phenol to benzoquinone, hydroquinone and catechol. Benzoquinone and maleic acid were products, which were determined in the hydroquinone oxidation pathway. The highest mineralization rate was observed for Pd-TiO2/SiO2@Fe3O4 and Cu-TiO2/SiO2@Fe3O4 photocatalysts, which produced the highest concentration of catechol during photocatalytic reaction. For Pt-TiO2/SiO2@Fe3O4 nanocomposite, a lack of catechol after 60 min of irradiation resulted in low mineralization rate (CO2 formation). It is proposed that the enhanced photocatalytic activity of palladium and copper-modified photocatalysts is related to an increase in the amount of adsorption sites and efficient charge carrier separation, whereas the keto-enol tautomeric equilibrium retards the rate of phenol photomineralization on Au-TiO2/SiO2@Fe3O4. The magnetization hysteresis loop indicated that the obtained hybrid photocatalyst showed magnetic properties and therefore could be easily separated after treatment process. PMID:29316667

Effect of magnetism and atomic order on static atomic displacements in the Invar alloy Fe-27 at.% Pt

NASA Astrophysics Data System (ADS)

Sax, C. R.; Schönfeld, B.; Ruban, A. V.

2015-08-01

Fe-27 at.% Pt was aged at 1123 K and quenched to room temperature (RT) to set up a state of thermal equilibrium. The local atomic arrangement was studied by diffuse x-ray scattering above (at 427 K) and below (at RT) the Curie temperature as well as at RT under a saturating magnetic field. The separated short-range order scattering remained unchanged for all three states, with maxima at 100 positions. Effective pair interaction parameters determined by the inverse Monte Carlo method gave an order-disorder transition temperature of about 1088 K, close to direct experimental findings. The species-dependent static atomic displacements for the first two shells show large differences, with a strong increase in magnitude from the state at 427 K over RT to the state under saturating magnetic field. This outcome is in agreement with an increase in atomic volume of Fe with increasing local magnetic moment. Electronic-structure calculations closely reproduce the values for the static atomic displacements in the ferromagnetic state, and predict their dependence on the atomic configuration. They also reveal a strong dependence of the magnetic exchange interactions in Fe-Pt on the atomic configuration state and lattice parameter. In particular, the increase of the Curie temperature in a random state relative to that in the ordered one is demonstrated to be related to the corresponding change of the magnetic exchange interactions due to the different local atomic chemical environment. There exists a similar strong concentration dependence of the chemical interactions as in the case of magnetic exchange interactions. Theoretical effective interactions for Fe-27 at.% Pt alloy are in good agreement with experimental results, and they also reproduce well the L1 2-A1 transition temperature.

Highly (002) textured large grain bcc Cr{sub 80}Mn{sub 20} seed layer on Cr{sub 50}Ti{sub 50} amorphous layer for FePt-C granular film

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

Jeon, Seong-Jae, E-mail: jsjigst@ecei.tohoku.ac.jp; Saito, Shin; Hinata, Shintaro

Effect of bcc Cr{sub 80}Mn{sub 20} seed layer and Cr{sub 50}Ti{sub 50} amorphous texture inducing layer on the heteroepitaxy system in FePt-C granular film was studied by introducing a new concept of the layered structure. The concept suggested that the large grain seed layer in which the crystallographic texture was initially formed on an amorphous layer in the layered structure can reduce the angular distribution of (002) c-axis crystal orientation in the FePt-C granular film owing to heteroepitaxial growth. Structure analysis by X-ray diffraction revealed that (1) when the substrate heating temperature was elevated from 300 °C to 500 °C, grain sizemore » in the seed layer increased from 9.8 nm to 11.6 nm, and then decreased with further increasing the substrate temperature. The reduction of the grain size over 500 °C corresponds to the crystallization of the amorphous texture inducing layer, (2) when the grain size increased from 9.8 nm to 11.6 nm, the angular distribution of the (002) orientation in the seed layer dramatically decreased from 13.7° to 4.1°. It was shown that the large grain seed layer increased the perpendicular hysteresis in FePt-C granular film.« less

Superoxo, μ-peroxo, and μ-oxo complexes from heme/O2 and heme-Cu/O2 reactivity: Copper ligand influences in cytochrome c oxidase models

PubMed Central

Kim, Eunsuk; Helton, Matthew E.; Wasser, Ian M.; Karlin, Kenneth D.; Lu, Shen; Huang, Hong-wei; Moënne-Loccoz, Pierre; Incarvito, Christopher D.; Rheingold, Arnold L.; Honecker, Marcus; Kaderli, Susan; Zuberbühler, Andreas D.

2003-01-01

The O2-reaction chemistry of 1:1 mixtures of (F8)FeII (1; F8 = tetrakis(2,6-diflurorophenyl)porphyrinate) and [(LMe2N)CuI]+ (2; LMe2N = N,N-bis{2-[2-(N′,N′-4-dimethylamino)pyridyl]ethyl}methylamine) is described, to model aspects of the chemistry occurring in cytochrome c oxidase. Spectroscopic investigations, along with stopped-flow kinetics, reveal that low-temperature oxygenation of 1/2 leads to rapid formation of a heme-superoxo species (F8)FeIII-(O\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\setlength{\\oddsidemargin}{-69pt} \\begin{document} \\begin{equation*}{\\mathrm{_{2}^{-}}}\\end{equation*}\\end{document}) (3), whether or not 2 is present. Complex 3 subsequently reacts with 2 to form [(F8)FeIII–(O\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\setlength{\\oddsidemargin}{-69pt} \\begin{document} \\begin{equation*}{\\mathrm{_{2}^{2-}}}\\end{equation*}\\end{document})–CuII(LMe2N)]+ (4), which thermally converts to [(F8)FeIII–(O)–CuII(LMe2N)]+ (5), which has an unusually bent (Fe–O–Cu) bond moiety. Tridentate chelation, compared with tetradentate, is shown to dramatically lower the ν(O–O) values observed in 4 and give rise to the novel structural features in 5. PMID:12655050

A new trinuclear complex of platinum and iron efficiently promotes cleavage of plasmid DNA.

PubMed Central

Lempers, E L; Bashkin, J S; Kostić, N M

1993-01-01

The compound [[Pt(trpy)]2Arg-EDTA]+ is synthesized in five steps, purified, and characterized by 1H, 13C, and 195Pt NMR spectroscopy, mass spectrometry, UV-vis spectrophotometry, and elemental analysis. The binuclear [[(Pt(trpy)]2Arg]3+ moiety binds to double-stranded DNA, and the chelating EDTA moiety holds metal cations. In the presence of ferrous ions and the reductant dithiothreitol, the new compound cleaves DNA. It cleaves a single strand in the pBR322 plasmid nearly as efficiently as methidiumrpropyl-EDTA (MPE), and it cleaves a restriction fragment of the XP10 plasmid nonselectively and more efficiently than [Fe(EDTA)]2-. The mechanism of cleavage was studied in control experiments involving different transition-metal ions, superoxide dismutase, catalase, glucose oxidase with glucose, metal-sequestering agents, and deaeration. These experiments indicate that adventitious iron and copper ions, superoxide anion, and hydrogen peroxide are not involved and that dioxygen is required. The cleavage apparently is done by hydroxyl radicals generated in the vicinity of the DNA molecule. The reagent [[Pt(trypy)]2Arg-EDTA]+ differs from methidiumpropyl-EDTA in not containing an intercalator. This difference in binding modes between the binuclear platinum(II) complex and the planar heterocycle may cause useful differences between the two reagents in cleavage of nucleic acids. Images PMID:8493109

Low-temperature conducting state in two candidate topological Kondo insulators: SmB 6 and Ce 3 Bi 4 Pt 3

DOE PAGES

Wakeham, N.; Rosa, P. F. S.; Wang, Y. Q.; ...

2016-07-12

We have investigated the low temperature conducting state of two Kondo insulators, SmB 6 and Ce 3Bi 4Pt 3, which have been theoretically predicted to host topological surface states. Through comparison of the speci c heat of as-grown and powdered single crystals of SmB 6, we show that the residual term that is linear in temperature is not dominated by any surface state contribution, but rather is a bulk property. In Ce 3Bi 4Pt 3, we find that the Hall coefficient is independent of sample thickness, which indicates that conduction at low temperatures is dominated by the bulk of themore » sample, and not by a surface state. The low temperature resistivity of Ce 3Bi 4Pt 3 is found to monotonically decrease with low concentrations of disorder introduced through ion-irradiation. This is in contrast to SmB 6, which is again indicative of the contrasting origins of the low temperature conduction. In SmB 6, we also show that the effect of low concentrations of irradiation damage of the surface with Fe + ions is qualitatively consistent with damage with non-magnetic ions.« less

A GREEN CHEMISTRY APPROACH TO PREPARATION OF CORE (FE OR CU)-SHELL (NOBLE METALS) NANOCOMPOSITES USING AQUEOUS ASCORBIC ACID

EPA Science Inventory

A greener method to fabricate novel core (Fe or Cu)-shell (noble metals) nanocomposites of transition metals such as Fe and Cu and noble metals such as Au, Pt, Pd, and Ag using aqueous ascorbic acid is described. Transition metal salts such as Cu and Fe were reduced using ascor...

London penetration depth measurements in Ba (Fe 1-xT x) 2As 2(T=Co,Ni,Ru,Rh,Pd,Pt,Co+Cu) superconductors

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

Gordon, Ryan T.

2011-01-01

The London penetration depth has been measured in various doping levels of single crystals of Ba(Fe 1-xT x) 2As 2 (T=Co,Ni,Ru,Rh,Pd,Pt,Co+Cu) superconductors by utilizing a tunnel diode resonator (TDR) apparatus. All in-plane penetration depth measurements exhibit a power law temperature dependence of the form Δλ ab(T) = CT n, indicating the existence of low-temperature, normal state quasiparticles all the way down to the lowest measured temperature, which was typically 500 mK. Several different doping concentrations from the Ba(Fe 1-xT x) 2As 2 (T=Co,Ni) systems have been measured and the doping dependence of the power law exponent, n, is compared tomore » results from measurements of thermal conductivity and specific heat. In addition, a novel method has been developed to allow for the measurement of the zero temperature value of the in-plane penetration depth, λ ab(0), by using TDR frequency shifts. By using this technique, the doping dependence of λ ab(0) has been measured in the Ba(Fe 1-xCo x) 2As 2 series, which has allowed also for the construction of the doping-dependent superfluid phase stiffness, ρ s(T) = [λ(0)/λ(T)] 2. By studying the effects of disorder on these superconductors using heavy ion irradiation, it has been determined that the observed power law temperature dependence likely arises from pair-breaking impurity scattering contributions, which is consistent with the proposed s±-wave symmetry of the superconducting gap in the dirty scattering limit. This hypothesis is supported by the measurement of an exponential temperature dependence of the penetration depth in the intrinsically clean LiFeAs, indicative of a nodeless superconducting gap.« less

Temperature dependence of the enhanced inverse spin Hall voltage in Pt/Antiferromagnetic/ Y3Fe5O12

NASA Astrophysics Data System (ADS)

Brangham, J. T.; Lee, A. J.; Cheng, Y.; Yu, S. S.; Dunsiger, S. R.; Page, M. R.; Hammel, P. C.; Yang, F. Y.

The generation, propagation, and detection of spin currents are of intense interest in the field of spintronics. Spin current generation by FMR spin pumping using Y3Fe5O12 (YIG) and spin current detection by the inverse spin Hall effect (ISHE) in metals such as Pt have been well studied. This is due to YIG's exceptionally low damping and insulating behavior and the large spin Hall angle of Pt. Previously, our group showed that the ISHE voltages are significantly enhanced by adding a thin intermediate layer of an antiferromagnet (AFM) between Pt and YIG at room temperature. Recent theoretical work predicts a mechanism for this enhancement as well as the temperature dependence of the ISHE voltages of metal/AFM/YIG trilayers. The predictions show a maximum in the ISHE voltages for these systems near the magnetic phase transition temperature of the AFM. Here we present experimental results showing the temperature dependence for Pt/AFM/YIG structures with various AFMs. DOE Grant No. DE-SC0001304.

Crystal structure of tricarbon­yl(μ-di­phenyl­phosphido-κ2 P:P)(methyl­diphenyl­silyl-κSi)bis(tri­phenyl­phosphane-κP)iron(II)platinum(0)(Fe—Pt)

PubMed Central

Mohamed, Ahmed Said; Jourdain, Isabelle; Knorr, Michael; Rousselin, Yoann; Kubicki, Marek M.

2015-01-01

The title compound, [FePt(C12H10P)(C13H13Si)(C18H15P)2(CO)3]·0.5CH2Cl2, represents an example of a phosphido-bridged heterobimetallic silyl complex; these are inter­esting precursors for the coordination and activation of small unsaturated organic mol­ecules. The μ2-PPh2 ligand spans the iron and platinum atoms, which are connected via a metal–metal bond of 2.7738 (4) Å. In contrast to most other complexes of the [(OC)3Fe(SiR 3)(μ-PR 2)PtL 2] family, where the iron-bound SiR 3 group is trans-arranged with respect to the μ2-PPh2 ligand, the SiPh2Me ligand is roughly collinear with the Fe–Pt vector [Si—Fe—Pt = 169.07 (3)°]. PMID:25878830

Imaging Magnetization Structure and Dynamics in Ultrathin Y3Fe5O12/Pt Bilayers with High Sensitivity Using the Time-Resolved Longitudinal Spin Seebeck Effect

NASA Astrophysics Data System (ADS)

Bartell, Jason M.; Jermain, Colin L.; Aradhya, Sriharsha V.; Brangham, Jack T.; Yang, Fengyuan; Ralph, Daniel C.; Fuchs, Gregory D.

2017-04-01

We demonstrate an instrument for time-resolved magnetic imaging that is highly sensitive to the in-plane magnetization state and dynamics of thin-film bilayers of yttrium iron garnet [Y3Fe5O12(YIG )]/Pt : the time-resolved longitudinal spin Seebeck (TRLSSE) effect microscope. We detect the local in-plane magnetic orientation within the YIG by focusing a picosecond laser to generate thermally driven spin current from the YIG into the Pt by the spin Seebeck effect and then use the inverse spin Hall effect in the Pt to transduce this spin current to an output voltage. To establish the time resolution of TRLSSE, we show that pulsed optical heating of patterned YIG (20 nm )/Pt (6 nm )/Ru (2 nm ) wires generates a magnetization-dependent voltage pulse of less than 100 ps. We demonstrate TRLSSE microscopy to image both static magnetic structure and gigahertz-frequency magnetic resonance dynamics with submicron spatial resolution and a sensitivity to magnetic orientation below 0.3 °/√{H z } in ultrathin YIG.

Simulations of magnetic hysteresis loops at high temperatures

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

Plumer, M. L.; Whitehead, J. P.; Fal, T. J.

2014-09-28

The kinetic Monte-Carlo algorithm as well as standard micromagnetics are used to simulate MH loops of high anisotropy magnetic recording media at both short and long time scales over a wide range of temperatures relevant to heat-assisted magnetic recording. Microscopic parameters, common to both methods, were determined by fitting to experimental data on single-layer FePt-based media that uses the Magneto-Optic Kerr effect with a slow sweep rate of 700 Oe/s. Saturation moment, uniaxial anisotropy, and exchange constants are given an intrinsic temperature dependence based on published atomistic simulations of FePt grains with an effective Curie temperature of 680 K. Ourmore » results show good agreement between micromagnetics and kinetic Monte Carlo results over a wide range of sweep rates. Loops at the slow experimental sweep rates are found to become more square-shaped, with an increasing slope, as temperature increases from 300 K. These effects also occur at higher sweep rates, typical of recording speeds, but are much less pronounced. These results demonstrate the need for accurate determination of intrinsic thermal properties of future recording media as input to micromagnetic models as well as the sensitivity of the switching behavior of thin magnetic films to applied field sweep rates at higher temperatures.« less

Hemoglobin-carbon nanotube derived noble-metal-free Fe5C2-based catalyst for highly efficient oxygen reduction reaction

NASA Astrophysics Data System (ADS)

Vij, Varun; Tiwari, Jitendra N.; Lee, Wang-Geun; Yoon, Taeseung; Kim, Kwang S.

2016-02-01

High performance non-precious cathodic catalysts for oxygen reduction reaction (ORR) are vital for the development of energy materials and devices. Here, we report an noble metal free, Fe5C2 nanoparticles-studded sp2 carbon supported mesoporous material (CNTHb-700) as cathodic catalyst for ORR, which was prepared by pyrolizing the hybrid adduct of single walled carbon nanotubes (CNT) and lyophilized hemoglobin (Hb) at 700 °C. The catalyst shows onset potentials of 0.92 V in 0.1 M HClO4 and in 0.1 M KOH which are as good as commercial Pt/C catalyst, giving very high current density of 6.34 and 6.69 mA cm-2 at 0.55 V vs. reversible hydrogen electrode (RHE), respectively. This catalyst has been confirmed to follow 4-electron mechanism for ORR and shows high electrochemical stability in both acidic and basic media. Catalyst CNTHb-700 possesses much higher tolerance towards methanol than the commercial Pt/C catalyst. Highly efficient catalytic properties of CNTHb-700 could lead to fundamental understanding of utilization of biomolecules in ORR and materialization of proton exchange membrane fuel cells for clean energy production.

Platinum-TM (TM = Fe, Co) alloy nanoparticles dispersed nitrogen doped (reduced graphene oxide-multiwalled carbon nanotube) hybrid structure cathode electrocatalysts for high performance PEMFC applications.

PubMed

Vinayan, B P; Ramaprabhu, S

2013-06-07

The efforts to push proton exchange membrane fuel cells (PEMFC) for commercial applications are being undertaken globally. In PEMFC, the sluggish kinetics of oxygen reduction reactions (ORR) at the cathode can be improved by the alloying of platinum with 3d-transition metals (TM = Fe, Co, etc.) and with nitrogen doping, and in the present work we have combined both of these aspects. We describe a facile method for the synthesis of a nitrogen doped (reduced graphene oxide (rGO)-multiwalled carbon nanotubes (MWNTs)) hybrid structure (N-(G-MWNTs)) by the uniform coating of a nitrogen containing polymer over the surface of the hybrid structure (positively surface charged rGO-negatively surface charged MWNTs) followed by the pyrolysis of these (rGO-MWNTs) hybrid structure-polymer composites. The N-(G-MWNTs) hybrid structure is used as a catalyst support for the dispersion of platinum (Pt), platinum-iron (Pt3Fe) and platinum-cobalt (Pt3Co) alloy nanoparticles. The PEMFC performances of Pt-TM alloy nanoparticle dispersed N-(G-MWNTs) hybrid structure electrocatalysts are 5.0 times higher than that of commercial Pt-C electrocatalysts along with very good stability under acidic environment conditions. This work demonstrates a considerable improvement in performance compared to existing cathode electrocatalysts being used in PEMFC and can be extended to the synthesis of metal, metal oxides or metal alloy nanoparticle decorated nitrogen doped carbon nanostructures for various electrochemical energy applications.

Stray field signatures of Néel textured skyrmions in Ir/Fe/Co/Pt multilayer films

NASA Astrophysics Data System (ADS)

Yagil, A.; Almoalem, A.; Soumyanarayanan, Anjan; Tan, Anthony K. C.; Raju, M.; Panagopoulos, C.; Auslaender, O. M.

2018-05-01

Skyrmions are nanoscale spin configurations with topological properties that hold great promise for spintronic devices. Here, we establish their Néel texture, helicity, and size in Ir/Fe/Co/Pt multilayer films by constructing a multipole expansion to model their stray field signatures and applying it to magnetic force microscopy images. Furthermore, the demonstrated sensitivity to inhomogeneity in skyrmion properties, coupled with a unique capability to estimate the pinning force governing dynamics, portend broad applicability in the burgeoning field of topological spin textures.

Chemiluminescence analyzer of NOx as a high-throughput screening tool in selective catalytic reduction of NO

PubMed Central

Oh, Kwang Seok; Woo, Seong Ihl

2011-01-01

A chemiluminescence-based analyzer of NOx gas species has been applied for high-throughput screening of a library of catalytic materials. The applicability of the commercial NOx analyzer as a rapid screening tool was evaluated using selective catalytic reduction of NO gas. A library of 60 binary alloys composed of Pt and Co, Zr, La, Ce, Fe or W on Al2O3 substrate was tested for the efficiency of NOx removal using a home-built 64-channel parallel and sequential tubular reactor. The NOx concentrations measured by the NOx analyzer agreed well with the results obtained using micro gas chromatography for a reference catalyst consisting of 1 wt% Pt on γ-Al2O3. Most alloys showed high efficiency at 275 °C, which is typical of Pt-based catalysts for selective catalytic reduction of NO. The screening with NOx analyzer allowed to select Pt-Ce(X) (X=1–3) and Pt–Fe(2) as the optimal catalysts for NOx removal: 73% NOx conversion was achieved with the Pt–Fe(2) alloy, which was much better than the results for the reference catalyst and the other library alloys. This study demonstrates a sequential high-throughput method of practical evaluation of catalysts for the selective reduction of NO. PMID:27877438

Novel anode catalyst for direct methanol fuel cells.

PubMed

Basri, S; Kamarudin, S K; Daud, W R W; Yaakob, Z; Kadhum, A A H

2014-01-01

PtRu catalyst is a promising anodic catalyst for direct methanol fuel cells (DMFCs) but the slow reaction kinetics reduce the performance of DMFCs. Therefore, this study attempts to improve the performance of PtRu catalysts by adding nickel (Ni) and iron (Fe). Multiwalled carbon nanotubes (MWCNTs) are used to increase the active area of the catalyst and to improve the catalyst performance. Electrochemical analysis techniques, such as energy dispersive X-ray spectrometry (EDX), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and X-ray photoelectron spectroscopy (XPS), are used to characterize the kinetic parameters of the hybrid catalyst. Cyclic voltammetry (CV) is used to investigate the effects of adding Fe and Ni to the catalyst on the reaction kinetics. Additionally, chronoamperometry (CA) tests were conducted to study the long-term performance of the catalyst for catalyzing the methanol oxidation reaction (MOR). The binding energies of the reactants and products are compared to determine the kinetics and potential surface energy for methanol oxidation. The FESEM analysis results indicate that well-dispersed nanoscale (2-5 nm) PtRu particles are formed on the MWCNTs. Finally, PtRuFeNi/MWCNT improves the reaction kinetics of anode catalysts for DMFCs and obtains a mass current of 31 A g(-1) catalyst.

Novel Anode Catalyst for Direct Methanol Fuel Cells

PubMed Central

Basri, S.; Kamarudin, S. K.; Daud, W. R. W.; Yaakob, Z.; Kadhum, A. A. H.

2014-01-01

PtRu catalyst is a promising anodic catalyst for direct methanol fuel cells (DMFCs) but the slow reaction kinetics reduce the performance of DMFCs. Therefore, this study attempts to improve the performance of PtRu catalysts by adding nickel (Ni) and iron (Fe). Multiwalled carbon nanotubes (MWCNTs) are used to increase the active area of the catalyst and to improve the catalyst performance. Electrochemical analysis techniques, such as energy dispersive X-ray spectrometry (EDX), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and X-ray photoelectron spectroscopy (XPS), are used to characterize the kinetic parameters of the hybrid catalyst. Cyclic voltammetry (CV) is used to investigate the effects of adding Fe and Ni to the catalyst on the reaction kinetics. Additionally, chronoamperometry (CA) tests were conducted to study the long-term performance of the catalyst for catalyzing the methanol oxidation reaction (MOR). The binding energies of the reactants and products are compared to determine the kinetics and potential surface energy for methanol oxidation. The FESEM analysis results indicate that well-dispersed nanoscale (2–5 nm) PtRu particles are formed on the MWCNTs. Finally, PtRuFeNi/MWCNT improves the reaction kinetics of anode catalysts for DMFCs and obtains a mass current of 31 A g−1 catalyst. PMID:24883406

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

Potential of transition metal atoms embedded in buckled monolayer g-C3N4 as single-atom catalysts.

PubMed

Li, Shu-Long; Yin, Hui; Kan, Xiang; Gan, Li-Yong; Schwingenschlögl, Udo; Zhao, Yong

2017-11-15

We use first-principles calculations to systematically explore the potential of transition metal atoms (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Ir, Pt, and Au) embedded in buckled monolayer g-C 3 N 4 as single-atom catalysts. We show that clustering of Sc and Ti on g-C 3 N 4 is thermodynamically impeded and that V, Cr, Mn, and Cu are much less susceptible to clustering than the other TM atoms under investigation. Strong bonding of the transition metal atoms in the cavities of g-C 3 N 4 and high diffusion barriers together are responsible for single-atom fixation. Analysis of the CO oxidation process indicates that embedding of Cr and Mn in g-C 3 N 4 gives rise to promising single-atom catalysts at low temperature.

Carbon-supported bimetallic Pd–Fe catalysts for vapor-phase hydrodeoxygenation of guaiacol

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

Sun, Junming; Karim, Ayman M.; Zhang, He

2013-10-01

Abstract Carbon supported metal catalysts (Cu/C, Fe/C, Pd/C, Pt/C, PdFe/C and Ru/C) have been prepared, characterized and tested for vapor-phase hydrodeoxygenation (HDO) of guaiacol (GUA) at atmospheric pressure. Phenol was the major intermediate on all catalysts. Over the noble metal catalysts saturation of the aromatic ring was the major pathway observed at low temperature (250 °C), forming predominantly cyclohexanone and cyclohexanol. Substantial ring opening reaction was observed on Pt/C and Ru/C at higher reaction temperatures (e.g., 350 °C). Base metal catalysts, especially Fe/C, were found to exhibit high HDO activity without ring-saturation or ring-opening with the main products being benzene,more » phenol along with small amounts of cresol, toluene and trimethylbenzene (TMB). A substantial enhancement in HDO activity was observed on the PdFe/C catalysts. Compared with Fe/C, the yield to oxygen-free aromatic products (i.e., benzene/toluene/TMB) on PdFe/C increased by a factor of four at 350 °C, and by approximately a factor of two (83.2% versus 43.3%) at 450 °C. The enhanced activity of PdFe/C is attributed to the formation of PdFe alloy as evidenced by STEM, EDS and TPR.« less

A GREENER SYNTHESIS OF CORE (FE, CU)-SHELL (AU, PT, PD AND AG) NANOCRYSTALS USING AQUEOUS VITAMIN C

EPA Science Inventory

A greener method to fabricate the novel core (Fe and Cu)-shell (noble metals) metal nanocrystals using aqueous ascorbic acid (vitamin C) is described. Transition metal salts such as Cu and Fe were reduced using ascorbic acid, a benign naturally available antioxidant, and then add...

Tungsten carbide encapsulated in nitrogen-doped carbon with iron/cobalt carbides electrocatalyst for oxygen reduction reaction

NASA Astrophysics Data System (ADS)

Zhang, Jie; Chen, Jinwei; Jiang, Yiwu; Zhou, Feilong; Wang, Gang; Wang, Ruilin

2016-12-01

This work presents a type of hybrid catalyst prepared through an environmental and simple method, combining a pyrolysis of transition metal precursors, a nitrogen-containing material, and a tungsten source to achieve a one-pot synthesis of N-doping carbon, tungsten carbides, and iron/cobalt carbides (Fe/Co/WC@NC). The obtained Fe/Co/WC@NC consists of uniform Fe3C and Co3C nanoparticles encapsulated in graphitized carbon with surface nitrogen doping, closely wrapped around a plate-like tungsten carbide (WC) that functions as an efficient oxygen reduction reaction (ORR) catalyst. The introduction of WC is found to promote the ORR activity of Fe/Co-based carbide electrocatalysts, which is attributed to the synergistic catalysts of WC, Fe3C, and Co3C. Results suggest that the composite exhibits comparable electrocatalytic activity, higher durability, and ability for methanol tolerance compared with commercial Pt/C for ORR in alkaline electrolyte. These advantages make Fe/Co/WC@NC a promising ORR electrocatalyst and a cost-effective alternative to Pt/C for practical application as fuel cell.

2D Nanoporous Fe-N/C Nanosheets as Highly Efficient Non-Platinum Electrocatalysts for Oxygen Reduction Reaction in Zn-Air Battery.

PubMed

Yang, Zheng Kun; Lin, Ling; Xu, An-Wu

2016-11-01

It is an ongoing challenge to fabricate nonprecious oxygen reduction reaction (ORR) catalysts that can be comparable to or exceed the efficiency of platinum. A highly active non-platinum self-supporting Fe-N/C catalyst has been developed through the pyrolysis of a new type of precursor of iron coordination complex, in which 1,4-bis(1H-1,3,7,8-tetraazacyclopenta(1)phenanthren-2-yl)benzene (btcpb) functions as a ligand complexing Fe(II) ions. The optimal catalyst pyrolyzed at 700 °C (Fe-N/C-700) shows the best ORR activity with a half-wave potential (E 1/2 ) of 840 mV versus reversible hydrogen electrode (RHE) in 0.1 m KOH, which is more positive than that of commercial Pt/C (E 1/2 : 835 mV vs RHE). Additionally, the Fe-N/C-700 catalyst also exhibits high ORR activity in 0.1 m HClO 4 with the onset potential and E 1/2 comparable to those of the Pt/C catalyst. Notably, the Fe-N/C-700 catalyst displays superior durability (9.8 mV loss in 0.1 m KOH and 23.6 mV loss in 0.1 m HClO 4 for E 1/2 after 8000 cycles) and better tolerance to methanol than Pt/C. Furthermore, the Fe-N/C-700 catalyst can be used for fabricating the air electrode in Zn-air battery with a specific capacity of 727 mA hg -1 at 5 mA cm -2 and a negligible voltage loss after continuous operation for 110 h. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Fe2SiO4-rich spinel as mineral in a shocked meteorite - constraints on P-T conditions during shock

NASA Astrophysics Data System (ADS)

Tschauner, O.; Ma, C.; Asimow, P. D.; Kostandova, N.

2008-12-01

We report the occurrence of a spinel phase (Fe0.8, Mg0.2)2(Si0.9, Fe0.1)O4 in veins of the L4 chondrite Laundry West, Nullarbor, Australia. While Fe2SiO4-rich spinel has been reported from the Umbarger meteorite earlier (Xie et al. Am .Min. 87, 1257, 2002), the present study is the first to present complete structural and chemical information. We collected powder diffraction, EBSD, and EMP data, all confirming structure and chemistry of this new mineral, the Fe-endmember analog of Mg2SiO4 ringwoodite. The observation of this spinel phase, which forms at pressures of a few GPa under static conditions, in a shocked meteorite is a contribution to a finer shock metamorphic scale. The vicinity of these FeSi-spinel grains to melted (Fe,Ni)S in combination with modeling of shock reverberation in a FeS-silicate system allows for estimating a lower limit of the peak shock pressure and temperature: The fayalite-spinel P-T phase boundary and the melting curve of (Fe,Ni)S determine a fixed point in P-T space of 5-6 GPa and 1500 - 1600 K. However, the bulk shock pressure (and temperature) was lower and can be calculated by impedance match. Acknowledgements: We dedicate this work to our friend and collaborator Thomas J. Ahrens. We are particularly grateful to Dr. Zhongwu Wang, CHESS, for providing beamtime and support at station B2. This work was supported by NNSA Cooperative Agreement DOE-FC88-01NV14049 and NASA/Goddard grants under awards NNG04GP57G and NNG04GI07G. Participation by NK was supported by the Caltech SURF program and in particular by Mr. and Mrs. Robert E. Anderson.

Dual role of TiO2 buffer layer in Pt catalyzed BiFeO3 photocathodes: Efficiency enhancement and surface protection

NASA Astrophysics Data System (ADS)

Shen, Huanyu; Zhou, Xiaoxue; Dong, Wen; Su, Xiaodong; Fang, Liang; Wu, Xi; Shen, Mingrong

2017-09-01

Polycrystalline ferroelectric BiFeO3 (BFO) films deposited on transparent indium tin oxide (ITO) electrodes have shown to be an interesting photocathode for photoelectrochemical (PEC) water splitting; however, its PEC performance and stability are far from perfection. Herein, we reported an amorphous TiO2 buffer layer, inserted between BFO and Pt catalyst, improves significantly both its PEC activity and stability. A photocathodic current density of -460 μA/cm2 at 0 V vs. reversible hydrogen electrode (RHE) and an onset potential of 1.25 V vs. RHE were obtained in ITO/BFO/TiO2/Pt photocathode under 100 mW/cm2 Xe-lamp illumination. TiO2 functions as a buffer layer to remove the upward barrier between BFO and Pt, and makes the photogenerated carriers separate efficiently. The photocathode also shows high stability in acid solution after a 10-h PEC continuous testing.

Opportunity of spinel ferrite materials in nonvolatile memory device applications based on their resistive switching performances.

PubMed

Hu, Wei; Qin, Ni; Wu, Guangheng; Lin, Yanting; Li, Shuwei; Bao, Dinghua

2012-09-12

The opportunity of spinel ferrites in nonvolatile memory device applications has been demonstrated by the resistive switching performance characteristics of a Pt/NiFe(2)O(4)/Pt structure, such as low operating voltage, high device yield, long retention time (up to 10(5) s), and good endurance (up to 2.2 × 10(4) cycles). The dominant conduction mechanisms are Ohmic conduction in the low-resistance state and in the lower-voltage region of the high-resistance state and Schottky emission in the higher-voltage region of the high-resistance state. On the basis of measurements of the temperature dependence of the resistances and magnetic properties in different resistance states, we explain the physical mechanism of resistive switching of Pt/NiFe(2)O(4)/Pt devices using the model of formation and rupture of conducting filaments by considering the thermal effect of oxygen vacancies and changes in the valences of cations due to the redox effect.

Sign reversal of Hall signals in Tm3Fe5O12 /Pt with perpendicular magnetic anisotropy

NASA Astrophysics Data System (ADS)

Liu, Yawen; Tang, Chi; Xu, Yadong; Shi, Zhong; Shi, Jing

Robust interface strain-induced perpendicular magnetic anisotropy is produced in atomically flat ferromagnetic insulator Tm3Fe5O12 (TIG) films grown with pulsed laser deposition on both substituted-Gd3Ga5O12 and Nd3Ga5O12 (NGG). In TIG/Pt bilayers, we observe large hysteresis loops over a wide range of Pt thicknesses and temperatures. Both the ordinary Hall effect and anomalous Hall effect undergo a sign reversal as the temperature is lowered. The temperature dependence of the Hall signals in bilayers with different thickness of Pt indicates the existence of exchange interaction at the interface. Our results provide a clue to further understand the origin of the anomalous Hall effect in ferromagnetic insulator/normal metal bilayer systems. The work was supported as part of the SHINES, an Energy Frontier Research Center funded by the US Department of Energy, BES under Award No. SC0012670.

Microstructure and magnetic properties of (001) textured L1(0) FePt films on amorphous glass substrate

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

Speliotis, T; Varvaro, G; Testa, AM

2015-05-15

L1(0) FePt thin films with an island-like morphology and magnetic perpendicular anisotropy were grown at low temperature (300 < T-dep< 375 degrees C) by magnetron sputtering on Hoya glass substrates using a 30-nm thick Cr (2 0 0) underlayer. An MgO buffer layer with a thickness of 2 nm was used to inhibit the diffusion from the Cr underlayer and promote the growth of (0 0 1) oriented L1(0) FePt films by inducing an in-plane lattice distortion. By varying the substrate temperature and the Ar sputter pressure (3.5 < P-Ar< 15 mTorr) during the deposition, the degree of chemical order,more » the microstructure and the magnetic properties were tuned and the best properties in term of squareness ratio (M-r/M-s similar to 0.95) and coercive field (H-c similar to 14 kOe) were observed for films deposited at T-dep = 350 degrees C and P-Ar= 5 mTorr, due to the appearance of a tensile strain, which favors the perpendicular anisotropy. The analysis of the angular dependence of remanent magnetization curves on the optimized sample suggests that the magnetization reversal is highly incoherent due to the inter-island interactions. Our results provide useful information on the low temperature growth of FePt films with perpendicular anisotropy onto glass substrates, which are relevant for a variety of technological applications, such as magnetic recording and spintronic devices. (C) 2015 Elsevier B.V. All rights reserved.« less

Mass and number size distributions of particulate matter components: comparison of an industrial site and an urban background site.

PubMed

Taiwo, Adewale M; Beddows, David C S; Shi, Zongbo; Harrison, Roy M

2014-03-15

Size-resolved composition of particulate matter (PM) sampled in the industrial town of Port Talbot (PT), UK was determined in comparison to a typical urban background site in Birmingham (EROS). A Micro-Orifice Uniform Deposit Impactor (MOUDI) sampler was deployed for two separate sampling campaigns with the addition of a Grimm optical spectrometer at the PT site. MOUDI samples were analysed for water-soluble anions (Cl(-), NO₃(-) and SO₄(2-)) and cations (Na(+), NH4(+), K(+), Mg(2+) and Ca(2+)) and trace metals (Al, V, Cr, Mn, Fe, Cu, Zn, Sb, Ba and Pb). The PM mass distribution showed a predominance of fine particle (PM₂.₅) mass at EROS whereas the PT samples were dominated by the coarse fraction (PM₂.₅₋₁₀). SO₄(2-), Cl(-), NH4(+), Na(+), NO₃(-), and Ca(2+) were the predominant ionic species at both sites while Al and Fe were the metals with highest concentrations at both sites. Mean concentrations of Cl(-), Na(+), K(+), Ca(2+), Mg(2+), Cr, Mn, Fe and Zn were higher at PT than EROS due to industrial and marine influences. The contribution of regional pollution by sulphate, ammonium and nitrate was greater at EROS relative to PT. The traffic signatures of Cu, Sb, Ba and Pb were particularly prominent at EROS. Overall, PM at EROS was dominated by secondary aerosol and traffic-related particles while PT was heavily influenced by industrial activities and marine aerosol. Profound influences of wind direction are seen in the 72-hour data, especially in relation to the PT local sources. Measurements of particle number in 14 separate size bins plotted as a function of wind direction and speed are highly indicative of contributing sources, with local traffic dominant below 0.5 μm, steelworks emissions from 0.5 to 15 μm, and marine aerosol above 15 μm. Copyright © 2013 Elsevier B.V. All rights reserved.

Evaluation of thermal barrier coating systems on novel substrates

NASA Astrophysics Data System (ADS)

Pint, B. A.; Wright, I. G.; Brindley, W. J.

2000-06-01

Testing was conducted on both plasma-sprayed (PS) and electron beam-physical vapor deposited (EB-PVD) Y2O3-stabilized ZrO2 (YSZ) thermal barrier coatings (TBCs) applied directly to oxidation-resistant substrates such as β-NiAl, oxide-dispersed FeCrAl, and NiCr. On an alloy that forms a very adherent alumina scale, β-NiAl+Zr, the coating lifetime of YSZ in furnace cyclic tests was 6 or more times longer than on state-of-the-art, YSZ coatings on single-crystal Ni-base superalloys with MCrAlY or Pt aluminide bond coats. Coatings on FeCrAl alloys appear to be a viable option for applications such as the external skin of the X-33, single stage to orbit, reusable launch vehicle. Model chromia-forming bond coat compositions also show promise for power generation applications at temperatures where hot corrosion may be a major problem. In general, while this work examined unique materials systems, many of the same fundamental failure mechanisms observed in conventional TBCs were observed.

5-aminoisoquinoline improves renal function and fibrosis during recovery phase of cisplatin-induced acute kidney injury in rats.

PubMed

Quesada, Andrés; O'Valle, Francisco; Montoro-Molina, Sebastián; Gómez-Morales, Mercedes; Caba-Molina, Mercedes; González, Juan Francisco; de Gracia, María C; Osuna, Antonio; Vargas, Félix; Wangensteen, Rosemary

2018-04-27

The aim of the present study is to analyze the effects of 5-aminoisoquinoline (5-AIQ), a poly(ADP-ribose) polymerase-1 (PARP1) inhibitor, over renal dysfunction and fibrosis during recovery phase of cisplatin (CisPt)-induced acute kidney injury (AKI) in rats. Male Wistar rats were distributed in three groups ( n =8 each group): control, CisPt, and CisPt + 5-AIQ. Control and CisPt groups received a subcutaneous injection of either saline or 7 mg/kg CisPt, respectively. CisPt + 5-AIQ group received two intraperitoneal injections of 10 mg/kg 5-AIQ 2 h before and 24 h after CisPt treatment. Thirteen days after the treatment, rats were housed in metabolic cages and 24-h urine collection was made. At day 14, CisPt-treated rats showed increased diuresis, N-acetyl-β-d-glucosaminidase (NAG) excretion, glucosuria and sodium fractional excretion (NaFE), and decreased creatinine clearance (CrCl). 5-AIQ significantly increased CrCl and decreased NAG excretion, glucosuria, and NaFE. In plasma, CisPt increased sodium, urea, and creatinine concentrations, while 5-AIQ treatment decreased these variables to the levels of control group. 5-AIQ completely prevented the body weight loss evoked by CisPt treatment. CisPt also induced an increased renal expression of PAR polymer, α-smooth muscle actin (α-SMA), transforming growth factor-β1 (TGF-β1), and collagen-IV. These variables were decreased in CisPt + 5-AIQ group. Tubular lesions and renal fibrosis were also decreased by 5-AIQ treatment. We conclude that inhibition of PARP1 with 5-AIQ can attenuate long-term nephrotoxic effects associated with the CisPt treatment, preventing renal dysfunction and body weight decrease and ameliorating tubular lesions and collagen deposition. © 2018 The Author(s).

5-aminoisoquinoline improves renal function and fibrosis during recovery phase of cisplatin-induced acute kidney injury in rats

PubMed Central

Quesada, Andrés; O’Valle, Francisco; Montoro-Molina, Sebastián; Gómez-Morales, Mercedes; Caba-Molina, Mercedes; González, Juan Francisco; de Gracia, María C.; Osuna, Antonio; Vargas, Félix; Wangensteen, Rosemary

2018-01-01

The aim of the present study is to analyze the effects of 5-aminoisoquinoline (5-AIQ), a poly(ADP-ribose) polymerase-1 (PARP1) inhibitor, over renal dysfunction and fibrosis during recovery phase of cisplatin (CisPt)-induced acute kidney injury (AKI) in rats. Male Wistar rats were distributed in three groups (n=8 each group): control, CisPt, and CisPt + 5-AIQ. Control and CisPt groups received a subcutaneous injection of either saline or 7 mg/kg CisPt, respectively. CisPt + 5-AIQ group received two intraperitoneal injections of 10 mg/kg 5-AIQ 2 h before and 24 h after CisPt treatment. Thirteen days after the treatment, rats were housed in metabolic cages and 24-h urine collection was made. At day 14, CisPt-treated rats showed increased diuresis, N-acetyl-β-d-glucosaminidase (NAG) excretion, glucosuria and sodium fractional excretion (NaFE), and decreased creatinine clearance (CrCl). 5-AIQ significantly increased CrCl and decreased NAG excretion, glucosuria, and NaFE. In plasma, CisPt increased sodium, urea, and creatinine concentrations, while 5-AIQ treatment decreased these variables to the levels of control group. 5-AIQ completely prevented the body weight loss evoked by CisPt treatment. CisPt also induced an increased renal expression of PAR polymer, α-smooth muscle actin (α-SMA), transforming growth factor-β1 (TGF-β1), and collagen-IV. These variables were decreased in CisPt + 5-AIQ group. Tubular lesions and renal fibrosis were also decreased by 5-AIQ treatment. We conclude that inhibition of PARP1 with 5-AIQ can attenuate long-term nephrotoxic effects associated with the CisPt treatment, preventing renal dysfunction and body weight decrease and ameliorating tubular lesions and collagen deposition. PMID:29599129

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

Jungfleisch, Matthias B.; Ding, Junjia; Zhang, Wei

Magnetic insulators, such as yttrium iron garnet (Y 3Fe 5O 12), are ideal materials for ultra-low power spintronics applications due to their low energy dissipation and efficient spin current generation and transmission. Recently, it has been realized that spin dynamics can be driven very effectively in micrometer-sized Y 3Fe 5O 12/Pt heterostructures by spin-Hall effects. We demonstrate here the excitation and detection of spin dynamics in Y 3Fe 5O 12/Pt nanowires by spin-torque ferromagnetic resonance. The nanowires defined via electron-beam lithography are fabricated by conventional room temperature sputtering deposition on Gd 3Ga 5O 12 substrates and lift-off. We observe field-likemore » and anti-damping-like torques acting on the magnetization precession, which are due to simultaneous excitation by Oersted fields and spin-Hall torques. The Y 3Fe 5O 12/Pt nanowires are thoroughly examined over a wide frequency and power range. We observe a large change in the resonance field at high microwave powers, which is attributed to a decreasing effective magnetization due to microwave absorption. By comparing different nanowire widths, the importance of geometrical confinements for magnetization dynamics becomes evident. In conclusion, our results are the first stepping stones toward the realization of integrated magnonic logic devices based on insulators, where nanomagnets play an essential role.« less

Influence of piezoelectric strain on the Raman spectra of BiFeO{sub 3} films deposited on PMN-PT substrates

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

Himcinschi, Cameliu, E-mail: himcinsc@physik.tu-freiberg.de; Talkenberger, Andreas; Kortus, Jens

2016-01-25

BiFeO{sub 3} epitaxial thin films were deposited on piezoelectric 0.72Pb(Mg{sub 1/3}Nb{sub 2/3})O{sub 3}-0.28PbTiO{sub 3} (PMN-PT) substrates with a conductive buffer layer (La{sub 0.7}Sr{sub 0.3}MnO{sub 3} or SrRuO{sub 3}) using pulsed laser deposition. The calibration of the strain values induced by the electric field applied on the piezoelectric PMN-PT substrates was realised using X-Ray diffraction measurements. The method of piezoelectrically induced strain allows one to directly obtain a quantitative correlation between the strain and the shift of the Raman-active phonons. This is a prerequisite for making Raman scattering a strong tool to probe the strain coupling in multiferroic nanostructures. Using themore » Poisson's number for BiFeO{sub 3}, one can determine the volume change induced by strain, and therefore the Grüneisen parameters for specific phonon modes.« less

Synthesis and characterization of potential iron–platinum drugs and supplements by laser liquid photolysis

PubMed Central

Nkosi, Steven S; Mwakikunga, Bonex W; Sideras-Haddad, Elias; Forbes, Andrew

2012-01-01

Highly crystalline nanospherical iron–platinum systems were produced by 248 nm laser irradiation of a liquid precursor at different laser fluences, ranging from 100–375 mJ/cm2. The influence of laser intensity on particle size, iron composition, and structure was systematically investigated. Different nanostructures of iron–platinum alloy and chemically disordered iron–platinum L10 phase were obtained without annealing. The prepared precursor solution underwent deep photolysis to polycrystalline iron–platinum nanoalloys through Fe(III) acetylacetonate and Pt(II) acetylacetonate. Fe(II) and Pt(I) acetylacetone decomposed into Fe0 and Pt0 nanoparticles. We found that the (001) diffraction peak shifted linearly to a lower angle, with the last peak shifting in opposition to the others. This caused the face-centered cubic L10 structure to change its composition according to laser fluence. The nanostructures were shown to contain iron and platinum only by energy-dispersive spectroscopy at several spots. The response of these iron–platinum nanoparticles to infrared depends on their stoichiometric composition, which is controlled by laser fluence. PMID:24198494

Measurement of magnetic property of FePt granular media at near Curie temperature

NASA Astrophysics Data System (ADS)

Yang, H. Z.; Chen, Y. J.; Leong, S. H.; An, C. W.; Ye, K. D.; Hu, J. F.

2017-02-01

The characterization of the magnetic switching behavior of heat assisted magnetic recording (HAMR) media at near Curie temperature (Tc) is important for high density recording. In this study, we measured the magnetic property of FePt granular media (with room temperature coercivity 25 kOe) at near Tc with a home built HAMR testing instrument. The local area of HAMR media is heated to near Tc by a flat-top optical heating beam. The magnetic property in the heated area was in-situ measured by a magneto-optic Kerr effect (MOKE) testing beam. The switching field distribution (SFD) and coercive field (Hc) of the FePt granular media and their dependence on the optical heating power at near Tc were studied. We measured the DC demagnetization (DCD) signal with pulsed laser heating at different optical powers. We also measured the Tc distribution of the media by measuring the AC magnetic signal as a function of optical heating power. In a summary, we studied the SFD, Hc of the HAMR media at near Tc in a static manner. The present methodology will facilitate the HAMR media testing.

Investigating vibrational relaxation in cyanide-bridged transition metal mixed-valence complexes using two-dimensional infrared and infrared pump-probe spectroscopies

PubMed Central

Slenkamp, Karla M.; Lynch, Michael S.; Brookes, Jennifer F.; Bannan, Caitlin C.; Daifuku, Stephanie L.; Khalil, Munira

2016-01-01

Using polarization-selective two-dimensional infrared (2D IR) and infrared pump-probe spectroscopies, we study vibrational relaxation of the four cyanide stretching (νCN) vibrations found in [(NH3)5RuIIINCFeII(CN)5]− (FeRu) dissolved in D2O or formamide and [(NC)5FeIICNPtIV(NH3)4NCFeII(CN)5]4− (FePtFe) dissolved in D2O. These cyanide-bridged transition metal complexes serve as models for understanding the role high frequency vibrational modes play in metal-to-metal charge transfers over a bridging ligand. However, there is currently little information about vibrational relaxation and dephasing dynamics of the anharmonically coupled νCN modes in the electronic ground state of these complexes. IR pump-probe experiments reveal that the vibrational lifetimes of the νCN modes are ∼2 times faster when FeRu is dissolved in D2O versus formamide. They also reveal that the vibrational lifetimes of the νCN modes of FePtFe in D2O are almost four times as long as for FeRu in D2O. Combined with mode-specific relaxation dynamics measured from the 2D IR experiments, the IR pump-probe experiments also reveal that intramolecular vibrational relaxation is occurring in all three systems on ∼1 ps timescale. Center line slope dynamics, which have been shown to be a measure of the frequency-frequency correlation function, reveal that the radial, axial, and trans νCN modes exhibit a ∼3 ps timescale for frequency fluctuations. This timescale is attributed to the forming and breaking of hydrogen bonds between each mode and the solvent. The results presented here along with our previous work on FeRu and FePtFe reveal a picture of coupled anharmonic νCN modes where the spectral diffusion and vibrational relaxation dynamics depend on the spatial localization of the mode on the molecular complex and its specific interaction with the solvent. PMID:27158634

Investigating vibrational relaxation in cyanide-bridged transition metal mixed-valence complexes using two-dimensional infrared and infrared pump-probe spectroscopies.

PubMed

Slenkamp, Karla M; Lynch, Michael S; Brookes, Jennifer F; Bannan, Caitlin C; Daifuku, Stephanie L; Khalil, Munira

2016-03-01

Using polarization-selective two-dimensional infrared (2D IR) and infrared pump-probe spectroscopies, we study vibrational relaxation of the four cyanide stretching (νCN) vibrations found in [(NH3)5Ru(III)NCFe(II)(CN)5](-) (FeRu) dissolved in D2O or formamide and [(NC)5Fe(II)CNPt(IV)(NH3)4NCFe(II)(CN)5](4-) (FePtFe) dissolved in D2O. These cyanide-bridged transition metal complexes serve as models for understanding the role high frequency vibrational modes play in metal-to-metal charge transfers over a bridging ligand. However, there is currently little information about vibrational relaxation and dephasing dynamics of the anharmonically coupled νCN modes in the electronic ground state of these complexes. IR pump-probe experiments reveal that the vibrational lifetimes of the νCN modes are ∼2 times faster when FeRu is dissolved in D2O versus formamide. They also reveal that the vibrational lifetimes of the νCN modes of FePtFe in D2O are almost four times as long as for FeRu in D2O. Combined with mode-specific relaxation dynamics measured from the 2D IR experiments, the IR pump-probe experiments also reveal that intramolecular vibrational relaxation is occurring in all three systems on ∼1 ps timescale. Center line slope dynamics, which have been shown to be a measure of the frequency-frequency correlation function, reveal that the radial, axial, and trans νCN modes exhibit a ∼3 ps timescale for frequency fluctuations. This timescale is attributed to the forming and breaking of hydrogen bonds between each mode and the solvent. The results presented here along with our previous work on FeRu and FePtFe reveal a picture of coupled anharmonic νCN modes where the spectral diffusion and vibrational relaxation dynamics depend on the spatial localization of the mode on the molecular complex and its specific interaction with the solvent.

Dimensionality effects on magnetic properties of FexCo1-x nanoclusters on Pt(1 1 1)

NASA Astrophysics Data System (ADS)

Miranda, I. P.; Igarashi, R. N.; Klautau, A. B.; Petrilli, H. M.

2017-11-01

The behavior of local magnetic moments and exchange coupling parameters of FexCo1-x nanostructures (nanowires and compact clusters) on the fcc Pt(1 1 1) surface is here investigated using the first-principles real-space RS-LMTO-ASA method, in the framework of the DFT. Different configurations of FexCo1-x trimers and heptamers on Pt(1 1 1) are considered, varying the positions and the concentration of Fe or Co atoms. We discuss the influence of dimensionality and stoichiometry changes on the magnetic properties, specially on the orbital moments, which are very important in establishing a nanoscopic understanding of delocalized electron systems. We demonstrate the existence of a strictly decreasing nonlinear trend of the average orbital moments with the Fe concentration for the compact clusters, different from what was found for FexCo1-x nanowires on Pt(1 1 1) and also for corresponding higher-dimensional systems (FexCo1-x monolayer on Pt(1 1 1) and FexCo1-x bulk). The average spin moments, however, are invariably described by a linear function with respect to stoichiometry. In all studied cases, the nearest neighbors exchange couplings have shown to be strongly ferromagnetic.

Strong Enhancement of the Spin Hall Effect by Spin Fluctuations near the Curie Point of FexPt1 -x Alloys

NASA Astrophysics Data System (ADS)

Ou, Yongxi; Ralph, D. C.; Buhrman, R. A.

2018-03-01

Robust spin Hall effects (SHE) have recently been observed in nonmagnetic heavy metal systems with strong spin-orbit interactions. These SHE are either attributed to an intrinsic band-structure effect or to extrinsic spin-dependent scattering from impurities, namely, side jump or skew scattering. Here we report on an extraordinarily strong spin Hall effect, attributable to spin fluctuations, in ferromagnetic FexPt1 -x alloys near their Curie point, tunable with x . This results in a dampinglike spin-orbit torque being exerted on an adjacent ferromagnetic layer that is strongly temperature dependent in this transition region, with a peak value that indicates a lower bound 0.34 ±0.02 for the peak spin Hall ratio within the FePt. We also observe a pronounced peak in the effective spin-mixing conductance of the FM /FePt interface, and determine the spin diffusion length in these FexPt1 -x alloys. These results establish new opportunities for fundamental studies of spin dynamics and transport in ferromagnetic systems with strong spin fluctuations, and a new pathway for efficiently generating strong spin currents for applications.

Pt Single Atoms Embedded in the Surface of Ni Nanocrystals as Highly Active Catalysts for Selective Hydrogenation of Nitro Compounds.

PubMed

Peng, Yuhan; Geng, Zhigang; Zhao, Songtao; Wang, Liangbing; Li, Hongliang; Wang, Xu; Zheng, Xusheng; Zhu, Junfa; Li, Zhenyu; Si, Rui; Zeng, Jie

2018-06-13

Single-atom catalysts exhibit high selectivity in hydrogenation due to their isolated active sites, which ensure uniform adsorption configurations of substrate molecules. Compared with the achievement in catalytic selectivity, there is still a long way to go in exploiting the catalytic activity of single-atom catalysts. Herein, we developed highly active and selective catalysts in selective hydrogenation by embedding Pt single atoms in the surface of Ni nanocrystals (denoted as Pt 1 /Ni nanocrystals). During the hydrogenation of 3-nitrostyrene, the TOF numbers based on surface Pt atoms of Pt 1 /Ni nanocrystals reached ∼1800 h -1 under 3 atm of H 2 at 40 °C, much higher than that of Pt single atoms supported on active carbon, TiO 2 , SiO 2 , and ZSM-5. Mechanistic studies reveal that the remarkable activity of Pt 1 /Ni nanocrystals derived from sufficient hydrogen supply because of spontaneous dissociation of H 2 on both Pt and Ni atoms as well as facile diffusion of H atoms on Pt 1 /Ni nanocrystals. Moreover, the ensemble composed of the Pt single atom and nearby Ni atoms in Pt 1 /Ni nanocrystals leads to the adsorption configuration of 3-nitrostyrene favorable for the activation of nitro groups, accounting for the high selectivity for 3-vinylaniline.

Electric-Field-Induced Amplitude Tuning of Ferromagnetic Resonance Peak in Nano-granular Film FeCoB-SiO2/PMN-PT Composites.

PubMed

Luo, Mei; Zhou, Peiheng; Liu, Yunfeng; Wang, Xin; Xie, Jianliang

2016-12-01

One of the challenges in the design of microwave absorbers lies in tunable amplitude of dynamic permeability. In this work, we demonstrate that electric-field-induced magnetoelastic anisotropy in nano-granular film FeCoB-SiO 2 /PMN-PT (011) composites can be used to tune the amplitude of ferromagnetic resonance peak at room temperature. The FeCoB magnetic particles are separated from each other by SiO 2 insulating matrix and present slightly different in-plane anisotropy fields. As a result, multi-resonances appear in the imaginary permeability (μ″) curve and mixed together to form a broadband absorption peak. The amplitude of the resonance peak could be modulated by external electric field from 118 to 266.

Determination of the electrostatic potential distribution in Pt/Fe:SrTiO3/Nb:SrTiO3 thin-film structures by electron holography

NASA Astrophysics Data System (ADS)

Marchewka, Astrid; Cooper, David; Lenser, Christian; Menzel, Stephan; Du, Hongchu; Dittmann, Regina; Dunin-Borkowski, Rafal E.; Waser, Rainer

2014-11-01

We determined the electrostatic potential distribution in pristine Pt/Fe:SrTiO3/Nb:SrTiO3 structures by electron holography experiments, revealing the existence of a depletion layer extending into the Nb-doped bottom electrode. Simulations of potential profiles in metal-insulator-metal structures were conducted assuming different types and distributions of dopants. It is found that the presence of acceptor-type dopant concentrations at the Fe:SrTiO3/Nb:SrTiO3 interface with a donor-doped insulating layer provides a good match to the measured profile. Such acceptor-type interface concentrations may be associated with Sr vacancies on the Nb:SrTiO3 side of the bottom interface.

Determination of the electrostatic potential distribution in Pt/Fe:SrTiO₃/Nb:SrTiO₃ thin-film structures by electron holography.

PubMed

Marchewka, Astrid; Cooper, David; Lenser, Christian; Menzel, Stephan; Du, Hongchu; Dittmann, Regina; Dunin-Borkowski, Rafal E; Waser, Rainer

2014-11-10

We determined the electrostatic potential distribution in pristine Pt/Fe:SrTiO3/Nb:SrTiO3 structures by electron holography experiments, revealing the existence of a depletion layer extending into the Nb-doped bottom electrode. Simulations of potential profiles in metal-insulator-metal structures were conducted assuming different types and distributions of dopants. It is found that the presence of acceptor-type dopant concentrations at the Fe:SrTiO3/Nb:SrTiO3 interface with a donor-doped insulating layer provides a good match to the measured profile. Such acceptor-type interface concentrations may be associated with Sr vacancies on the Nb:SrTiO3 side of the bottom interface.

Biaxially strained PtPb/Pt core/shell nanoplate boosts oxygen reduction catalysis

DOE PAGES

Bu, Lingzheng; Zhang, Nan; Guo, Shaojun; ...

2016-12-16

Compressive surface strains have been necessary to boost oxygen reduction reaction (ORR) activity in core/shell M/Pt catalysts (where M can be Ni, Co, Fe). We report a class of PtPb/Pt core/shell nanoplate catalysts that exhibit large biaxial tensile strains. The stable Pt (110) facets of the nanoplates have high ORR specific and mass activities that reach 7.8 milliampere per centimeter square and 4.3 ampere per milligram of platinum at 0.9 volts versus the reversible hydrogen electrode (RHE), respectively. Density functional theory calculations revealed that the edge-­Pt and top (bottom)-Pt (110) facets undergo large tensile strains that help optimize the Pt-­Omore » bond strength. The intermetallic core and uniform 4 layers of Pt shell of the PtPb/Pt nanoplates appear to underlie the high endurance of these catalysts, which can undergo 50,000 voltage cycles with negligible activity decay and no apparent structure and composition changes.« less

Biaxially strained PtPb/Pt core/shell nanoplate boosts oxygen reduction catalysis

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

Bu, Lingzheng; Zhang, Nan; Guo, Shaojun

Compressive surface strains have been necessary to boost oxygen reduction reaction (ORR) activity in core/shell M/Pt catalysts (where M can be Ni, Co, Fe). We report a class of PtPb/Pt core/shell nanoplate catalysts that exhibit large biaxial tensile strains. The stable Pt (110) facets of the nanoplates have high ORR specific and mass activities that reach 7.8 milliampere per centimeter square and 4.3 ampere per milligram of platinum at 0.9 volts versus the reversible hydrogen electrode (RHE), respectively. Density functional theory calculations revealed that the edge-­Pt and top (bottom)-Pt (110) facets undergo large tensile strains that help optimize the Pt-­Omore » bond strength. The intermetallic core and uniform 4 layers of Pt shell of the PtPb/Pt nanoplates appear to underlie the high endurance of these catalysts, which can undergo 50,000 voltage cycles with negligible activity decay and no apparent structure and composition changes.« less

Controls on ferromanganese crust composition and reconnaissance resource potential, Ninetyeast Ridge, Indian Ocean

USGS Publications Warehouse

Hein, James; Conrad, Tracey A.; Mizell, Kira; Banakar, Virupaxa K.; Frey, Frederick A.; Sager, William W.

2016-01-01

The southern third of NER has Fe-Mn crusts with the highest Co (0.91%), Ni (0.43%), ΣREY (0.33%), Cu (0.22%), Te (146 ppm), Pt (1.5 ppm), Ru (52 ppb), and Rh (99 ppb) contents. These are among the highest Pt, Ru, and Rh concentrations measured in marine Fe-Mn deposits. Because of these high metal concentrations, exploration is warranted for the southern sector of the NER, especially at shallower-water sites where the platinum group elements (PGE) and Co are likely to be even more enriched.

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.

Investigating and engineering spin-orbit torques in heavy metal/Co{sub 2}FeAl{sub 0.5}Si{sub 0.5}/MgO thin film structures

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

Loong, Li Ming; Deorani, Praveen; Qiu, Xuepeng

2015-07-13

Current-induced spin-orbit torques (SOTs) have the potential to revolutionize magnetization switching technology. Here, we investigate SOT in a heavy metal (HM)/Co{sub 2}FeAl{sub 0.5}Si{sub 0.5} (CFAS)/MgO thin film structure with perpendicular magnetic anisotropy (PMA), where the HM is either Pt or Ta. Our results suggest that both the spin Hall effect and the Rashba effect contribute significantly to the effective fields in the Pt underlayer samples. Moreover, after taking the PMA energies into account, current-induced SOT-based switching studies of both the Pt and Ta underlayer samples suggest that the two HM underlayers yield comparable switching efficiency in the HM/CFAS/MgO material system.

Effect of substitutional defects on Kambersky damping in L10 magnetic materials

NASA Astrophysics Data System (ADS)

Qu, T.; Victora, R. H.

2015-02-01

Kambersky damping, representing the loss of magnetic energy from the electrons to the lattice through the spin orbit interaction, is calculated for L10 FePt, FePd, CoPt, and CoPd alloys versus chemical degree of order. When more substitutional defects exist in the alloys, damping is predicted to increase due to the increase of the spin-flip channels allowed by the broken symmetry. It is demonstrated that this corresponds to an enhanced density of states (DOS) at the Fermi level, owing to the rounding of the DOS with loss of long-range order. Both the damping and the DOS of the Co-based alloy are found to be less affected by the disorder. Pd-based alloys are predicted to have lower damping than Pt-based alloys, making them more suitable for high density spintronic applications.

Activation of surface lattice oxygen in single-atom Pt/CeO 2 for low-temperature CO oxidation

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

Nie, Lei; Mei, Donghai; Xiong, Haifeng

While single-atom catalysts can provide high catalytic activity and selectivity, application in industrial catalysts demands long term performance and the ability to regenerate the catalysts. We have investigated the factors that lead to improved catalytic activity of a Pt/CeO2 catalyst for low temperature CO oxidation. Single-atom Pt/CeO2 becomes active for CO oxidation under lean condition only at elevated temperatures, because CO is strongly bound to ionic Pt sites. Reducing the catalyst, even under mild conditions, leads to onset of CO oxidation activity even at room temperature. This high activity state involves the transformation of mononuclear Pt species to sub-nanometer sizedmore » Pt particles. Under oxidizing conditions, the Pt can be restored to its stable, single-atom state. The key to facile regeneration is the ability to create mobile Pt species and suitable trapping sites on the support, making this a prototypical catalyst system for industrial application of single-atom catalysis.« less

Identification of O-rich structures on platinum(111)-supported ultrathin iron oxide films

DOE PAGES

Merte, Lindsay R.; Bai, Yunhai; Zeuthen, Helene; ...

2016-01-06

Using high-resolution scanning tunneling microscopy (STM) we have studied the oxidation of ultrathin FeO films grown on Pt(111). At the initial stage of the FeO film oxidation by atomic oxygen exposure, we identified three distinct types of line defects, all of which form boundaries between FeO domains of opposite orientation. Two types of line defects appearing bright ( type-i) and dark ( type-ii) in the STM images at typical scanning parameters are “metallic”, whereas the third line defect exhibits nonmetallic behavior ( type-iii). Atomic-scale structure models of these line defects are proposed, with type-i defects exhibiting 4-fold coordinated Fe atoms,more » type-ii exhibiting 2-fold coordinated O atoms, and type-iii exhibiting tetrahedrally-coordinated Fe atoms. In addition, FeO 2 trilayer islands are formed upon oxidation, which appear at FCC-type domains of the moiré structure. At high scanning bias, distinct protrusions on the trilayer islands are observed over surface O ions, which are assigned to H adatoms. The experimental data are supported by density functional theory (DFT) calculations, in which bare and hydroxylated FeO 2 trilayer islands are compared. Finally, we compare the formation of O-rich features on continuous FeO films using atomic oxygen with the oxidation of Pt(111)-supported FeO islands accomplished by O 2 exposure.« less

Electrodeposited-film electrodes derived from a precursor dinitrosyl iron complex for electrocatalytic water splitting.

PubMed

Li, Wei-Liang; Chiou, Tzung-Wen; Chen, Chien-Hong; Yu, Yi-Ju; Chu, Li-Kang; Liaw, Wen-Feng

2018-05-29

In artificial photosynthesis, water splitting plays an important role for the conversion and storage of renewable energy sources. Here, we report a study on the electrocatalytic properties of the electrodeposited-film electrodes derived from irreversible electro-reduction/-oxidation of a molecular dinitrosyl iron complex (DNIC) {Fe(NO)2}9 [(Me6tren)Fe(NO)2]+ (Me6tren = tris[2-(dimethylamino)ethyl]amine) for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) in alkaline solution, individually. For HER, the overpotential and Tafel slope for the electrodeposited-film cathode are lower than those of the equiv.-weight Pt/C electrode. The electrodeposited-film anode for the OER is stable for 139 h. Integration of the electrodeposited-film cathode and anode into a single electrode-pair device for electrocatalytic water splitting exhibits an onset voltage of 1.77 V, achieving a geometrical current density of 10 mA cm-2.

Enhanced magnetoelectric response in 2-2 bilayer 0.50Pb(Ni1/3Nb2/3)O3-0.35PbTiO3-0.15PbZrO3/NiFe2O4 thin films

NASA Astrophysics Data System (ADS)

Ade, Ramesh; Sambasiva, V.; Kolte, Jayant; Karthik, T.; Kulkarni, Ajit R.; Venkataramani, N.

2018-03-01

In this work, room temperature magnetoelectric (ME) properties of 0.50Pb(Ni1/3Nb2/3)O3-0.35PbTiO3-0.15PbZrO3 (PNNZT)/NiFe2O4 (NFO) 2-2 bilayer thin films grown on Pt/Ti/SiO2/Si substrate, using pulsed laser deposition technique, are reported. Structural studies confirm single phase PNNZT/NFO 2-2 bilayer structure formation. PNNZT/NFO 2-2 bilayer thin film shows a maximum ME voltage coefficient (α E ) of ~0.70 V cm-1. Oe-1 at a frequency of 1 kHz. The present study reveals that PNNZT/NFO bilayer thin film can be a potential candidate for technological applications.

Single Pt Atoms Confined into a Metal-Organic Framework for Efficient Photocatalysis.

PubMed

Fang, Xinzuo; Shang, Qichao; Wang, Yu; Jiao, Long; Yao, Tao; Li, Yafei; Zhang, Qun; Luo, Yi; Jiang, Hai-Long

2018-02-01

It is highly desirable yet remains challenging to improve the dispersion and usage of noble metal cocatalysts, beneficial to charge transfer in photocatalysis. Herein, for the first time, single Pt atoms are successfully confined into a metal-organic framework (MOF), in which electrons transfer from the MOF photosensitizer to the Pt acceptor for hydrogen production by water splitting under visible-light irradiation. Remarkably, the single Pt atoms exhibit a superb activity, giving a turnover frequency of 35 h -1 , ≈30 times that of Pt nanoparticles stabilized by the same MOF. Ultrafast transient absorption spectroscopy further unveils that the single Pt atoms confined into the MOF provide highly efficient electron transfer channels and density functional theory calculations indicate that the introduction of single Pt atoms into the MOF improves the hydrogen binding energy, thus greatly boosting the photocatalytic H 2 production activity. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Can we judge an oxide by its cover? The case of the metal/oxide interface from first principles

NASA Astrophysics Data System (ADS)

Caspary Toroker, Maytal

Metal/metal-oxide interfaces appear in a wide variety of disciplines including electronics, corrosion, electrochemistry, and catalysis. Specifically, covering a metal-oxide with a metal is often thought to enhance solar energy absorption and to improve photocatalytic activity. For example, the platinum/hematite (Pt/ α-Fe2O3) interface has demonstrated improved functionality. In order to advance our understanding of how metal coverage over an oxide helps performance, we characterize the geometry and electronic structure of the Pt/ α-Fe2O3 interface. We investigate the interface using density functional theory +U, and find a stable crystallographic orientation relationship that agrees with experiment. Furthermore, there are significant changes in the electronic structure of α-Fe2O3 as a result of Pt coverage. We therefore suggest the concept of ``judging'' the electronic properties of an oxide only with its cover. Specifically, covering Fe2O3 with Pt reduces carrier effective mass and creates a continuum of states in the band gap. The former could be beneficial for catalytic activity, while the latter may cause surface recombination. In order to circumvent this problem, we suggest putting metal coverage behind the oxide and far from the electrolyte in a photoelectrochemical device in order to quickly collect electron carriers and avoid recombination with vulnerable holes accumulating as a result of catalysis at the surface. Reference: O. Neufeld and M. Caspary Toroker, ``Can we judge an oxide by its cover? The case of platinum over alpha-Fe2O3 from first principles'', Phys. Chem. Chem. Phys. 17, 24129 (2015). This research was supported by the Morantz Energy Research Fund, the Nancy and Stephen Grand Technion Energy Program, the I-CORE Program of the Planning and Budgeting Committee, and The Israel Science Foundation (Grant No. 152/11).

Sigmoid sinus cortical plate dehiscence induces pulsatile tinnitus through amplifying sigmoid sinus venous sound.

PubMed

Tian, Shan; Wang, Lizhen; Yang, Jiemeng; Mao, Rui; Liu, Zhaohui; Fan, Yubo

2017-02-08

Sigmoid sinus cortical plate dehiscence (SSCPD) is common in pulsatile tinnitus (PT) patients, and is treated through SSCPD resurfacing surgery in clinic, but the bio-mechanism is not clear as so far. This study aimed to clarify the bio-mechanism of PT sensation induced by SSCPD, and quantify the relationship of cortical plate (CP) thickness and PT sensation intensity. It was hypothesized that SSCPD would induce PT through significantly amplifying sigmoid sinus (SS) venous sound in this study. Finite element (FE) analysis based on radiology data of typical patient was used to verify this hypothesis, and was validated with clinical reports. In cases with different CP thickness, FE simulations of SS venous sound generation and propagation procedure were performed, involving SS venous flow field, vibration response of tissue overlying dehiscence area (including SS vessel wall and CP) and sound propagation in temporal bone air cells. It was shown in results that SS venous sound at tympanic membrane was 56.9dB in SSCPD case and -45.2dB in intact CP case, and was inaudible in all thin CP cases. It was concluded that SSCPD would directly induce PT through significantly amplifying SS venous sound, and thin CP would not be the only pathophysiology of PT. This conclusion would provide a theoretical basis for the design of SSCPD resurfacing surgery for PT patients with SSCPD or thin CP. Copyright © 2017 Elsevier Ltd. All rights reserved.

Experimental Studies of Phase Equilibria of Meteorites and Planetary Bodies

NASA Technical Reports Server (NTRS)

Stolper, Edward M.

2005-01-01

The primary theme of this project was the application of experimental petrology and geochemistry to a variety of problems in meteoritics and planetary geology. The studies were designed to help develop constraints on the histories of primitive meteorites and their components, the environments in which they formed and evolved, and to understand quantitatively the processes involved in the evolution of igneous rocks on the earth and other planetary bodies. We undertook several projects relating to the origin of CAIs and chondrules. Systematics in the thermodynamic properties of CAI-like liquids were investigated and used to elucidate speciation of multi-valent cations and sulfide capacity of silicate melts and to constrain redox conditions and the vapor pressures of volatile species over molten chondrules. We experimentally determined vanadium speciation in meteoritic pyroxenes and in pyroxenes crystallized from CAI-like melts under very reducing conditions. We also found that bulk oxygen isotope compositions of chondrules in the moderately unequilibrated LL chondrites are related to the relative timing of plagioclase crystallization. We completed an experimental study on the vaporization of beta-SiC and SiO2 (glass or cristobalite) in reducing gases and established the conditions under which these presolar grains could have survived in the solar nebula. We expanded our technique for determining the thermodynamic properties of minerals and liquids to iron-bearing systems. We determined activity-composition relationships in Pt-Fe, Pt-Cr and Pt-Fe-Cr alloys. Results were used to determine the thermodynamic properties of chromite-picrochromite spinels including the free energy of formation of end-member FeCr2O4. We also established a new approach for evaluating Pt-Fe saturation experiments. We calculated the T-fO2 relationships in equilibrated ordinary chondrites and thereby constrained the conditions of metamorphism in their parent bodies.

Energy scavenging based on a single-crystal PMN-PT nanobelt

NASA Astrophysics Data System (ADS)

Wu, Fan; Cai, Wei; Yeh, Yao-Wen; Xu, Shiyou; Yao, Nan

2016-03-01

Self-powered nanodevices scavenging mechanical energy require piezoelectric nanostructures with high piezoelectric coefficients. Here we report the fabrication of a single-crystal (1 - x)Pb(Mg1/3Nb2/3)O3 - xPbTiO3 (PMN-PT) nanobelt with a superior piezoelectric constant (d33 = ~550 pm/V), which is approximately ~150%, 430%, and 2100% of the largest reported values for previous PMN-PT, PZT and ZnO nanostructures, respectively. The high d33 of the single-crystalline PMN-PT nanobelt results from the precise orientation control during its fabrication. As a demonstration of its application in energy scavenging, a piezoelectric nanogenerator (PNG) is built on the single PMN-PT nanobelt, generating a maximum output voltage of ~1.2 V. This value is ~4 times higher than that of a single-CdTe PNG, ~13 times higher than that of a single-ZnSnO3 PNG, and ~26 times higher than that of a single-ZnO PNG. The profoundly increased output voltage of a lateral PNG built on a single PMN-PT nanobelt demonstrates the potential application of PMN-PT nanostructures in energy harvesting, thus enriching the material choices for PNGs.

Energy scavenging based on a single-crystal PMN-PT nanobelt.

PubMed

Wu, Fan; Cai, Wei; Yeh, Yao-Wen; Xu, Shiyou; Yao, Nan

2016-03-01

Self-powered nanodevices scavenging mechanical energy require piezoelectric nanostructures with high piezoelectric coefficients. Here we report the fabrication of a single-crystal (1 - x)Pb(Mg1/3Nb2/3)O3 - xPbTiO3 (PMN-PT) nanobelt with a superior piezoelectric constant (d33 = ~550 pm/V), which is approximately ~150%, 430%, and 2100% of the largest reported values for previous PMN-PT, PZT and ZnO nanostructures, respectively. The high d33 of the single-crystalline PMN-PT nanobelt results from the precise orientation control during its fabrication. As a demonstration of its application in energy scavenging, a piezoelectric nanogenerator (PNG) is built on the single PMN-PT nanobelt, generating a maximum output voltage of ~1.2 V. This value is ~4 times higher than that of a single-CdTe PNG, ~13 times higher than that of a single-ZnSnO3 PNG, and ~26 times higher than that of a single-ZnO PNG. The profoundly increased output voltage of a lateral PNG built on a single PMN-PT nanobelt demonstrates the potential application of PMN-PT nanostructures in energy harvesting, thus enriching the material choices for PNGs.

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

Xiong, Haifeng; Lin, Sen; Goetze, Joris

CeO2 supports are unique in their ability to trap ionic Pt, providing exceptional stability for isolated single atoms of Pt. Here, we explore the reactivity and stability of single atom Pt species for the industrially important reaction of light alkane dehydrogenation. The single atom Pt/CeO2 catalysts are stable during propane dehydrogenation, but we observe no selectivity towards propene. DFT calculations show strong adsorption of the olefin produced, leading to further unwanted reactions. In contrast, when Sn is added to ceria, the single atom Pt catalyst undergoes an activation phase where it transforms into Pt-Sn clusters under reaction conditions. Formation ofmore » small Pt-Sn clusters allows the catalyst to achieve high selectivity towards propene, due to facile desorption of the product. The CeO2-supported Pt-Sn clusters are very stable, even during extended reaction at 680 °C. By adding water vapor to the feed, coke formation can almost completely be suppressed. Furthermore, the Pt-Sn clusters can be readily transformed back to the atomically dispersed species on ceria via oxidation, making Pt-Sn/CeO2 a fully regenerable catalyst.« less

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.

Enhanced electrocatalytic activity of PANI and CoFe2O4/PANI composite supported on graphene for fuel cell applications

NASA Astrophysics Data System (ADS)

Mohanraju, Karuppannan; Sreejith, Vasudevan; Ananth, Ramaiyan; Cindrella, Louis

2015-06-01

New catalysts of reduced graphene oxide (rGO) with poly aniline (PANI) and cobalt ferrite (CF) have been successfully prepared by simple chemical reduction method. Their electrocatalytic activity for oxygen reduction reaction (ORR) was evaluated. Semi-crystalline nature of CF was analyzed by X-ray diffraction (XRD) study. Surface morphology by HR-SEM showed features of CF particles and PANI film on graphene sheets. FT-IR studies revealed changes in C-N and Cdbnd N stretching vibrations of PANI confirming bonding of PANI to graphene sheets. Raman spectrum showed presence of PANI on distorted graphene layers. TG/DTA revealed thermal stability and extent of loading of CF in composite. ORR performance was studied using catalyst modified rotating disc electrode (RDE). A maximum kinetic current density of -3.46 mA cm-2 at -0.2 V was obtained for CF/PANI/rGO. Tafel slope, onset and half wave potentials for the catalyst were obtained from ORR response. Durability studies showed that synthesized electrocatalyst has better stability and methanol tolerance than commercial Pt/C catalyst. To the best of our knowledge, this is the first study aiming enhancement of ORR activity using PANI and CoFe2O4 on graphene support. A trace amount of Pt in the composite boosted the performance of single PEM fuel cell.

Size-dependent effects in supported highly dispersed Fe2O3 catalysts, doped with Pt and Pd

NASA Astrophysics Data System (ADS)

Cherkezova-Zheleva, Zara; Shopska, Maya; Mitov, Ivan; Kadinov, Georgi

2010-06-01

Series of Fe and Fe-Me (Me = Pt or Pd) catalyst supported on γ-Al2O3, TiO2 (anatase) or diatomite were prepared by the incipient wetness impregnation method. The metal loading was 8 wt.% Fe and 0.7 wt.% noble metal. The preparation and pretreatment conditions of all studied samples were kept to be the same. X-ray diffraction, Moessbauer spectroscopy, X-ray photoelectron spectroscopy and temperature-programmed reduction are used for characterization of the supports and the samples at different steps during their treatment and catalytic tests. The catalytic activity of the samples was tested in the reaction of total benzene oxidation. The physicochemical and catalytic properties of the obtained materials are compared with respect of the different chemical composition, dispersion of used carriers and of the supported phases. Samples with the same composition prepared by mechanical mixing are studied as catalysts for comparison and for clearing up the presence of size-dependent effect, also.

Control of Ferromagnetic Resonance Frequency and Frequency Linewidth by Electrical Fields in FeCo/[Pb(Mg1/3Nb2/3)O3]0.68-[PbTiO3]0.32(011) Heterostructures

NASA Astrophysics Data System (ADS)

Phuoc, Nguyen N.; Ong, C. K.

2016-10-01

We report our detailed investigation of the electrical tuning of the ferromagnetic resonance frequency and frequency linewidth in multiferroic heterostructures consisting of FeCo thin films grown onto [Pb(Mg1/3Nb2/3) O3]0.68-[PbTiO3]0.32 (PMN-PT) substrates with NiFe underlayers. Our study shows that the electrical tuning range of both ferromagnetic resonance frequency and frequency linewidth in this FeCo/PMN-PT heterostructure can be very large. Specifically, the resonance frequency can be tuned from 1.8 GHz to 10.3 GHz, and the frequency linewidth can be changed from 1.6 GHz to 7.3 GHz. The electrical tuning of these microwave properties is discussed in conjunction with the result from the static magnetic characterization and is explained based on the strain-driven magnetoelectric heterostructured effect.

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

Li, Peng; Liu, Tao; Chang, Houchen

As an in-plane charge current flows in a heavy metal film with spin-orbit coupling, it produces a torque on and thereby switches the magnetization in a neighbouring ferromagnetic metal film. Such spin-orbit torque (SOT)-induced switching has been studied extensively in recent years and has shown higher efficiency than switching using conventional spin-transfer torque. Here we report the SOT-assisted switching in heavy metal/magnetic insulator systems. The experiments used a Pt/BaFe 12O 19 bilayer where the BaFe 12O 19 layer exhibits perpendicular magnetic anisotropy. As a charge current is passed through the Pt film, it produces a SOT that can control themore » up and down states of the remnant magnetization in the BaFe 12O 19 film when the film is magnetized by an in-plane magnetic field. Furthermore, it can reduce or increase the switching field of the BaFe 12O 19 film by as much as about 500 Oe when the film is switched with an out-of-plane field.« less

Insulating nanomagnets driven by spin torque

DOE PAGES

Jungfleisch, Matthias B.; Ding, Junjia; Zhang, Wei; ...

2016-11-29

Magnetic insulators, such as yttrium iron garnet (Y 3Fe 5O 12), are ideal materials for ultra-low power spintronics applications due to their low energy dissipation and efficient spin current generation and transmission. Recently, it has been realized that spin dynamics can be driven very effectively in micrometer-sized Y 3Fe 5O 12/Pt heterostructures by spin-Hall effects. We demonstrate here the excitation and detection of spin dynamics in Y 3Fe 5O 12/Pt nanowires by spin-torque ferromagnetic resonance. The nanowires defined via electron-beam lithography are fabricated by conventional room temperature sputtering deposition on Gd 3Ga 5O 12 substrates and lift-off. We observe field-likemore » and anti-damping-like torques acting on the magnetization precession, which are due to simultaneous excitation by Oersted fields and spin-Hall torques. The Y 3Fe 5O 12/Pt nanowires are thoroughly examined over a wide frequency and power range. We observe a large change in the resonance field at high microwave powers, which is attributed to a decreasing effective magnetization due to microwave absorption. By comparing different nanowire widths, the importance of geometrical confinements for magnetization dynamics becomes evident. In conclusion, our results are the first stepping stones toward the realization of integrated magnonic logic devices based on insulators, where nanomagnets play an essential role.« less

Spin caloritronic nano-oscillator

DOE PAGES

Safranski, C.; Barsukov, I.; Lee, H. K.; ...

2017-07-18

Energy loss due to ohmic heating is a major bottleneck limiting down-scaling and speed of nano-electronic devices, and harvesting ohmic heat for signal processing is a major challenge in modern electronics. Here, we demonstrate that thermal gradients arising from ohmic heating can be utilized for excitation of coherent auto-oscillations of magnetization and for generation of tunable microwave signals. The heat-driven dynamics is observed in Y 3Fe 5O 12/Pt bilayer nanowires where ohmic heating of the Pt layer results in injection of pure spin current into the Y 3Fe 5O 12 layer. This leads to excitation of auto-oscillations of the Ymore » 3Fe 5O 12 magnetization and generation of coherent microwave radiation. Thus, our work paves the way towards spin caloritronic devices for microwave and magnonic applications.« less

Spin caloritronic nano-oscillator

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

Safranski, C.; Barsukov, I.; Lee, H. K.

Energy loss due to ohmic heating is a major bottleneck limiting down-scaling and speed of nano-electronic devices, and harvesting ohmic heat for signal processing is a major challenge in modern electronics. Here, we demonstrate that thermal gradients arising from ohmic heating can be utilized for excitation of coherent auto-oscillations of magnetization and for generation of tunable microwave signals. The heat-driven dynamics is observed in Y 3Fe 5O 12/Pt bilayer nanowires where ohmic heating of the Pt layer results in injection of pure spin current into the Y 3Fe 5O 12 layer. This leads to excitation of auto-oscillations of the Ymore » 3Fe 5O 12 magnetization and generation of coherent microwave radiation. Thus, our work paves the way towards spin caloritronic devices for microwave and magnonic applications.« less

3D Polymer Hydrogel for High-Performance Atomic Fe and Mn Catalysts for Oxygen Reduction in Challenging Acids

NASA Astrophysics Data System (ADS)

Qiao, Zhi

Current platinum group metal (PGM)-free carbon nanocomposite catalysts for the oxygen reduction reaction (ORR) in acidic electrolyte often suffer from rapid degradation associated with carbon corrosion due to the use of large amount of the amorphoous carbon black supports. Here, we developed a new concept of using freestanding 3D hydrogel to design support-free Fe-N-C catalysts. A 3D polyaniline (PANI)-based hydrogel approach was used for preparing a new type of single atomic iron site-rich catalyst, which has exhibited exceptionally enhanced activity and stability compared to conventional Fe-N-C catalysts supported on amorphous carbon blacks. The achieved performance metric on the hydrogel PANI-Fe catalysts is one of the best ever reported PGM-free catalysts, reaching a half-wave potential up to 0.83 V vs. RHE and only leaving 30 mV gap with Pt/C catalysts (60mugPt/cm 2) in challenging acidic media. Remarkable ORR stability was accomplished as well on the same catalyst evidenced by using harsh potential cycling tests. The well dispersion of atomic iron into partially graphitized carbon, featured with dominance of micropores and porous network structures, is capable of accommodating increased number of active sites, strengthening local bonding among iron, nitrogen and carbon, and facilitating mass transfer. On the other hand, in order to decrease the produced Fenton reagent, which will oxidize the proton exchange membrane and ionomer in membrane electrode assembly (MEA), we produce Mn-based catalysts by this novel hydrogel method. This is the first time that Mn-based catalysts can show such outstanding performance in acid media, whose half-wave potential is up to 0.80 V vs. RHE. The work related to the performance improvement is still in processing. We believe the 3D polymer hydrogel approach would be a new pathway to advance PGM-free catalysts.

Doping-evolution of the superconducting gap in single crystals of (Ca 1-x La x ) 10 (Pt 3 As 8 )(Fe 2 As 2 ) 5 superconductor from London penetration depth measurements

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

Cho, K.; Tanatar, M. A.; Ni, N.

2014-09-19

The doping-evolution of the superconducting gap structure in iron-based superconductor (Ca 1-xLax)10(Pt3As8)(Fe2As2)5(x = 0.04, 0.06, 0.09, 0.11, and 0.18) was probed by high-resolution measurements of the London penetration depth, λ(T). The samples spanned compositions from underdoped to slightly overdoped with superconducting critical temperatures, Tc, from 12.7 K (x = 0.04) through (optimal) 23.3 K (x = 0.11) to 21.9 K (x = 0.18). The low-temperature variation (up to 0.3 Tc ) of λ(T) was analysed using a power-law function, Δλ = ATn. For compositions close to the optimal doping, (x = 0.09, 0.11, and 0.18), characterized by Tc > 20K,more » Δλ(T) shows a tendency to saturation, indicative of a full gap on the Fermi surface. Fitting over the lowest temperature range (T < 0.1 Tc) gives n = 2.6. This value is well outside the range 1 ≤ n ≤ 2 expected for the line-nodal superconductor. The exponent n decreased to n ~ 2 in the two most underdoped compositions x = 0.04 (Tc = 12.7 K) and 0.06 (Tc = 18.2 K), implying the development of a notable gap anisotropy revealed by the enhanced influence of pair-breaking scattering. This decrease is accompanied by a significant increase of the total variation of the penetration depth Δλ in a fixed temperature interval (e.g., Tmin - 0.3Tc). Both the decrease of the exponent and the increase of the absolute value of Δλ in the underdoped regime are similar to the observations in other charge-doped iron-based superconductors, such as doped BaFe2As2 and NaFeAs, suggesting a universal behavior in iron-based superconductors.« less

A Polycarboxyl-Decorated FeIII -Based Xerogel-Derived Multifunctional Composite (Fe3 O4 /Fe/C) as an Efficient Electrode Material towards Oxygen Reduction Reaction and Supercapacitor Application.

PubMed

Devi, Bandhana; Venkateswarulu, Mangili; Kushwaha, Himmat Singh; Halder, Aditi; Koner, Rik Rani

2018-05-02

Low cost, non-noble metal catalysts with a good oxygen reduction reaction (ORR) activity comparable to that of platinum and also having good energy storage properties are highly desirable but challenging. Several challenges are associated with the development of such materials. Herein, we demonstrate a new polycarboxyl-functionalised Fe III -based gel material, synthesised following a solvothermal method and the development of its composite (Fe 3 O 4 /Fe/C) by annealing at optimised temperature. The developed composite displayed excellent electrocatalytic activity for the oxygen reduction reaction with an onset potential of 0.87 V (vs. RHE) and a current density value of -5 mA cm -2 , which are comparable with commercial 20 wt % Pt/C. In addition, as one of the most desirable properties, the composite exhibits a better methanol tolerance and greater durability than Pt/C. The same material was explored as an energy storage material for supercapacitors, which showed a specific capacitance of 245 F g -1 at a current density of 1 A g -1 . It is expected that this Fe 3 O 4 /Fe/C composite with a disordered graphitised carbon matrix will pave a horizon for developing energy conversion and energy storage devices. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Nonvolatile resistive switching in metal/La-doped BiFeO3/Pt sandwiches.

PubMed

Li, Mi; Zhuge, Fei; Zhu, Xiaojian; Yin, Kuibo; Wang, Jinzhi; Liu, Yiwei; He, Congli; Chen, Bin; Li, Run-Wei

2010-10-22

The resistive switching (RS) characteristics of a Bi(0.95)La(0.05)FeO(3) (La-BFO) film sandwiched between a Pt bottom electrode and top electrodes (TEs) made of Al, Ag, Cu, and Au have been studied. Devices with TEs made of Ag and Cu showed stable bipolar RS behaviors, whereas those with TEs made of Al and Au exhibited unstable bipolar RS. The Ag/La-BFO/Pt structure showed an on/off ratio of 10(2), a retention time > 10(5) s, and programming voltages < 1 V. The RS effect can be attributed to the formation/rupture of nanoscale metal filaments due to the diffusion of the TEs under a bias voltage. The maximum current before the reset process (on-to-off switching) was found to increase linearly with the current compliance applied during the set process (off-to-on switching).

Pure spin-Hall magnetoresistance in Rh/Y3Fe5O12 hybrid

NASA Astrophysics Data System (ADS)

Shang, T.; Zhan, Q. F.; Ma, L.; Yang, H. L.; Zuo, Z. H.; Xie, Y. L.; Li, H. H.; Liu, L. P.; Wang, B. M.; Wu, Y. H.; Zhang, S.; Li, Run-Wei

2015-12-01

We report an investigation of anisotropic magnetoresistance (AMR) and anomalous Hall resistance (AHR) of Rh and Pt thin films sputtered on epitaxial Y3Fe5O12 (YIG) ferromagnetic insulator films. For the Pt/YIG hybrid, large spin-Hall magne toresistance (SMR) along with a sizable conventional anisotropic magnetoresistance (CAMR) and a nontrivial temperature dependence of AHR were observed in the temperature range of 5-300 K. In contrast, a reduced SMR with negligible CAMR and AHR was found in Rh/YIG hybrid. Since CAMR and AHR are characteristics for all ferromagnetic metals, our results suggest that the Pt is likely magnetized by YIG due to the magnetic proximity effect (MPE) while Rh remains free of MPE. Thus the Rh/YIG hybrid could be an ideal model system to explore physics and devices associated with pure spin current.

Effect of substitutional defects on Kambersky damping in L1{sub 0} magnetic materials

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

Qu, T.; Victora, R. H., E-mail: victora@umn.edu; Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, Minnesota 55455

2015-02-16

Kambersky damping, representing the loss of magnetic energy from the electrons to the lattice through the spin orbit interaction, is calculated for L1{sub 0} FePt, FePd, CoPt, and CoPd alloys versus chemical degree of order. When more substitutional defects exist in the alloys, damping is predicted to increase due to the increase of the spin-flip channels allowed by the broken symmetry. It is demonstrated that this corresponds to an enhanced density of states (DOS) at the Fermi level, owing to the rounding of the DOS with loss of long-range order. Both the damping and the DOS of the Co-based alloymore » are found to be less affected by the disorder. Pd-based alloys are predicted to have lower damping than Pt-based alloys, making them more suitable for high density spintronic applications.« less

Magneto-optical Kerr effect in L1{sub 0} FePdPt ternary alloys: Experiments and first-principles calculations

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

Ma, L.; Shi, Z.; Zhou, S. M., E-mail: wur@uci.edu, E-mail: shiming@tongji.edu.cn

2014-05-14

We have studied the magneto-optical Kerr effect (MOKE) of L1{sub 0} Fe{sub 0.5}(Pd{sub 1−x}Pt{sub x}){sub 0.5} alloy films with both experiments and first-principles calculations. In the visible region, negative Kerr rotation and ellipticity peaks are, respectively, observed in the regions of 1.5–2.0 eV and 1.7–2.6 eV. These peaks are shifted towards higher energies, and their magnitudes are enhanced for larger x. The MOKE evolution is mainly ascribed to the anomalous Hall conductivity contributed by the spin-down d{sub ↓,x{sup 2}−y{sup 2}} bands from Pd and Pt. We established a close correlation among the MOKE spectra, the spin orbit coupling strength, andmore » the band feature for this prototypical system.« less

49 CFR Appendix B to Part 20 - Disclosure Form To Report Lobbying

Code of Federal Regulations, 2013 CFR

2013-10-01

... 49 Transportation 1 2013-10-01 2013-10-01 false Disclosure Form To Report Lobbying B Appendix B to Part 20 Transportation Office of the Secretary of Transportation NEW RESTRICTIONS ON LOBBYING Pt. 20, App. B Appendix B to Part 20—Disclosure Form To Report Lobbying EC02FE91.097 EC02FE91.098 EC02FE91.099 ...

49 CFR Appendix B to Part 20 - Disclosure Form To Report Lobbying

Code of Federal Regulations, 2011 CFR

2011-10-01

... 49 Transportation 1 2011-10-01 2011-10-01 false Disclosure Form To Report Lobbying B Appendix B to Part 20 Transportation Office of the Secretary of Transportation NEW RESTRICTIONS ON LOBBYING Pt. 20, App. B Appendix B to Part 20—Disclosure Form To Report Lobbying EC02FE91.097 EC02FE91.098 EC02FE91.09...

49 CFR Appendix B to Part 20 - Disclosure Form To Report Lobbying

Code of Federal Regulations, 2010 CFR

2010-10-01

... 49 Transportation 1 2010-10-01 2010-10-01 false Disclosure Form To Report Lobbying B Appendix B to Part 20 Transportation Office of the Secretary of Transportation NEW RESTRICTIONS ON LOBBYING Pt. 20, App. B Appendix B to Part 20—Disclosure Form To Report Lobbying EC02FE91.097 EC02FE91.098 EC02FE91.09...

The effect of sediment mixing on mercury dynamics in two intertidal mudflats at Great Bay Estuary, New Hampshire, USA

PubMed Central

Brown, Lauren E.; Chen, Celia Y.; Voytek, Mary A.; Amirbahman, Aria

2016-01-01

Estuarine sediments store particulate contaminants including mercury (Hg). We studied Hg sediment dynamics in two intertidal mudflats at Great Bay estuary, NH, over multiple years. Sediments at both mudflats were physically mixed down to ~10 cm, as determined by 7Be measurements, albeit via different mechanisms. Portsmouth mudflat (PT) sediments were subject to bioturbation by infaunal organisms and Squamscott mudflat (SQ) sediments were subject to erosion and redeposition. The presence of higher concentrations of fresh Fe(III) hydroxide at PT suggested bioirrigation by the polychaetes (Nereis virens). At depths where infaunal bioirrigation was observed, pore-water inorganic Hg (Hgi) and methylmercury (MeHg) were lower potentially due to their interaction with Fe(III) hydroxide. Methylmercury concentrations increased immediately below this zone in some samples, suggesting that the observed increase in material flux in bioirrigated sediments may initiate from lower depths. Pore water in sediment at PT also had higher fractions of more protein-like and labile DOC than those at SQ that can lead to increased MeHg production in PT, especially at depths where Hgi is not removed from solution by Fe(III) hydroxide. Where sediment erosion and redeposition were observed at SQ, Hg species distribution was extended deeper into the sediment column. Moreover, methyl coenzyme M reductase (MCR) and mercury reductase (mer-A) genes were higher at SQ than PT suggesting differences in conditions for Hg cycling. Results showed that the near-surface region of high MeHg concentrations commonly observed in unmixed sediments does not exist in physically mixed sediments that are common in many estuarine environments. PMID:26924879

The effect of sediment mixing on mercury dynamics in two intertidal mudflats at Great Bay Estuary, New Hampshire, USA.

PubMed

Brown, Lauren E; Chen, Celia Y; Voytek, Mary A; Amirbahman, Aria

2015-12-01

Estuarine sediments store particulate contaminants including mercury (Hg). We studied Hg sediment dynamics in two intertidal mudflats at Great Bay estuary, NH, over multiple years. Sediments at both mudflats were physically mixed down to ~10 cm, as determined by 7 Be measurements, albeit via different mechanisms. Portsmouth mudflat (PT) sediments were subject to bioturbation by infaunal organisms and Squamscott mudflat (SQ) sediments were subject to erosion and redeposition. The presence of higher concentrations of fresh Fe(III) hydroxide at PT suggested bioirrigation by the polychaetes ( Nereis virens ). At depths where infaunal bioirrigation was observed, pore-water inorganic Hg (Hg i ) and methylmercury (MeHg) were lower potentially due to their interaction with Fe(III) hydroxide. Methylmercury concentrations increased immediately below this zone in some samples, suggesting that the observed increase in material flux in bioirrigated sediments may initiate from lower depths. Pore water in sediment at PT also had higher fractions of more protein-like and labile DOC than those at SQ that can lead to increased MeHg production in PT, especially at depths where Hg i is not removed from solution by Fe(III) hydroxide. Where sediment erosion and redeposition were observed at SQ, Hg species distribution was extended deeper into the sediment column. Moreover, methyl coenzyme M reductase (MCR) and mercury reductase ( mer -A) genes were higher at SQ than PT suggesting differences in conditions for Hg cycling. Results showed that the near-surface region of high MeHg concentrations commonly observed in unmixed sediments does not exist in physically mixed sediments that are common in many estuarine environments.

Surfaces and Interfaces of Magnetoelectric Oxide Systems

NASA Astrophysics Data System (ADS)

Cao, Shi

Magnetoelectric materials Cr2O3, hexagonal LuFeO 3 and YbFeO3 are studied in this thesis. The surface of chromia (Cr2O3) has a surface electronic structure distinct from the bulk. Our work shows that placing a Cr2O3 single crystal into a single domain state will result in net Cr2O 3 spin polarization at the boundary, even in the presence of a gold overlayer. From the Cr 2p3/2 X-ray magnetic circular dichroism signal, there is clear evidence of interface polarization with overlayers of both Pd and Pt on chromia. Cobalt thin films on Cr2O3(0001) show larger magnetic contrast in magnetic force microscopy indicating enhancement of perpendicular anisotropy induced by Cr2O3. The interfacial charge transfer between mechanically exfoliated few-layer graphene and Cr2O3(0001) surfaces has been investigated showing hole doping of few-layer graphene. Density functional theory calculations furthermore confirm the p-type nature of the graphene on top of chromia, and suggest that the chromia is able to induce a significant carrier spin polarization in the graphene layer. The surface termination and the nominal valence states for hexagonal LuFeO3 thin films were characterized. The stable surface terminates in a Fe-O layer. This is consistent wit the results of density functional calculations. The structural transition at about 1000 °C, from the hexagonal to the orthorhombic phase of LuFeO3, has been investigated in thin films of LuFeO3. The electronic structure for the conduction bands of both hexagonal and orthorhombic LuFeO3 thin films have been measured. Dramatic differences in both the spectral features and the linear dichroism are observed. We have also studied the ferrimagnetism in h-YbFeO3 by measuring the magnetization of Fe and Yb separately. The results directly show antialignment of magnetization of Yb and Fe ions in h-YbFeO3 at low temperature, with an exchange field on Yb of about 17 kOe. All ferrimagnets, by default, are magnetoelectrics. These findings directly demonstrate that ferrimagnetic order exists in h-YbFeO3.

Quantitative analysis of the protein corona on FePt nanoparticles formed by transferrin binding

PubMed Central

Jiang, Xiue; Weise, Stefan; Hafner, Margit; Röcker, Carlheinz; Zhang, Feng; Parak, Wolfgang J.; Nienhaus, G. Ulrich

2010-01-01

Nanoparticles are finding a rapidly expanding range of applications in research and technology, finally entering our daily life in medical, cosmetic or food products. Their ability to invade all regions of an organism including cells and cellular organelles offers new strategies for medical diagnosis and therapy (nanomedicine), but their safe use requires a deep knowledge about their interactions with biological systems at the molecular level. Upon incorporation, nanoparticles are exposed to biological fluids from which they adsorb proteins and other biomolecules to form a ‘protein corona’. These nanoparticle–protein interactions are still poorly understood and quantitative studies to characterize them remain scarce. Here we have quantitatively analysed the adsorption of human transferrin onto small (radius approx. 5 nm) polymer-coated FePt nanoparticles by using fluorescence correlation spectroscopy. Transferrin binds to the negatively charged nanoparticles with an affinity of approximately 26 µM in a cooperative fashion and forms a monolayer with a thickness of 7 nm. By using confocal fluorescence microscopy, we have observed that the uptake of FePt nanoparticles by HeLa cells is suppressed by the protein corona compared with the bare nanoparticles. PMID:19776149

Experimental partitioning of Zr, Ti, and Nb between silicate liquid and a complex noble metal alloy and the partitioning of Ti between perovskite and platinum metal

NASA Technical Reports Server (NTRS)

Jurewicz, Stephen R.; Jones, John H.

1993-01-01

El Goresy et al.'s observation of Nb, Zr, and Ta in refractory platinum metal nuggets (RPMN's) from Ca-Al-rich inclusions (CAI's) in the Allende meteorite led them to propose that these lithophile elements alloyed in the metallic state with noble metals in the early solar nebula. However, Grossman pointed out that the thermodynamic stability of Zr in the oxide phase is vastly greater than metallic Zr at estimated solar nebula conditions. Jones and Burnett suggested this discrepancy may be explained by the very non-ideal behavior of some lithophile transition elements in noble metal solutions and/or intermetallic compounds. Subsequently, Fegley and Kornacki used thermodynamic data taken from the literature to predict the stability of several of these intermetallic compounds at estimated solar nebula conditions. Palme and Schmitt and Treiman et al. conducted experiments to quantify the partitioning behavior of certain lithophile elements between silicate liquid and Pt-metal. Although their results were somewhat variable, they did suggest that Zr partition coefficients were too small to explain the observed 'percent' levels in some RPMN's. Palme and Schmitt also observed large partition coefficients for Nb and Ta. No intermetallic phases were identified. Following the work of Treiman et al., Jurewicz and Jones performed experiments to examine Zr, Nb, and Ti partitioning near solar nebula conditions. Their results showed that Zr, Nb, and Ti all have an affinity for the platinum metal, with Nb and Ti having a very strong preference for the metal. The intermetallic phases (Zr,Fe)Pt3, (Nb,Fe)Pt3, and (Ti,Fe)Pt3 were identified. Curiously, although both experiments and calculations indicate that Ti should partition strongly into Pt-metal (possibly as TiPt3), no Ti has ever been observed in any RPMN's. Fegley and Kornacki also noticed this discrepancy and hypothesized that the Ti was stabilized in perovskite which is a common phase in Allende CAI's.

Conformation-related exciton localization and charge-pair formation in polythiophenes: ensemble and single-molecule study.

PubMed

Sugimoto, Toshikazu; Habuchi, Satoshi; Ogino, Kenji; Vacha, Martin

2009-09-10

We study conformation-dependent photophysical properties of polythiophene (PT) by molecular dynamics simulations and by ensemble and single-molecule optical experiments. We use a graft copolymer consisting of a polythiophene backbone and long polystyrene branches and compare its properties with those obtained on the same polythiophene derivative without the side chains. Coarse-grain molecular dynamics simulations show that in a poor solvent, the PT without the side chains (PT-R) forms a globulelike conformation in which distances between any two conjugated segments on the chain are within the Forster radius for efficient energy transfer. In the PT with the polystyrene branches (PT-PS), the polymer main PT chain retains an extended coillike conformation, even in a poor solvent, and the calculated distances between conjugated segments favor energy transfer only between a few neighboring chromophores. The theoretical predictions are confirmed by measurements of fluorescence anisotropy and fluorescence blinking of the polymers' single chains. High anisotropy ratios and two-state blinking in PT-R are due to localization of the exciton on a single conjugated segment. These signatures of exciton localization are absent in single chains of PT-PS. Electric-field-induced quenching measured as a function of concentration of PT dispersed in an inert matrix showed that in well-isolated chains of PT-PS, the exciton dissociation is an intrachain process and that aggregation of the PT-R chains causes an increase in quenching due to the onset of interchain interactions. Measurements of the field-induced quenching on single chains indicate that in PT-R, the exciton dissociation is a slower process that takes place only after the exciton is localized on one conjugated segment.

Performance comparison of low-temperature direct alcohol fuel cells with different anode catalysts

NASA Astrophysics Data System (ADS)

Zhou, W. J.; Zhou, B.; Li, W. Z.; Zhou, Z. H.; Song, S. Q.; Sun, G. Q.; Xin, Q.; Douvartzides, S.; Goula, M.; Tsiakaras, P.

Low-temperature polymer electrolyte membrane fuel cells directly fed by methanol and ethanol were investigated employing carbon supported Pt, PtSn and PtRu as anode catalysts, respectively. Employing Pt/C as anode catalyst, both direct methanol fuel cell (DMFC) and direct ethanol fuel cell (DEFC) showed poor performances even in presence of high Pt loading on anode. It was found that the addition of Ru or Sn to the Pt dramatically enhances the electro-oxidation of both methanol and ethanol. It was also found that the single cell adopting PtRu/C as anode shows better DMFC performance, while PtSn/C catalyst shows better DEFC performance. The single fuel cell using PtSn/C as anode catalyst at 90 °C shows similar power densities whenever fueled by methanol or ethanol. The cyclic voltammetry (CV) and single fuel cell tests indicated that PtRu is more suitable for DMFC while PtSn is more suitable for DEFC.

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

Mukerjee, S.; McBreen, J.; Srinivasan, S.

Electrocatalysis for the oxygen reduction reaction (ORR) on five binary Pt alloy electrocatalysts (PtCr/C, PtMn/C, PtFe/C, PtCo/C and PtNi/C) supported on carbon have been investigated. The electrochemical characteristics for ORR in a proton conducting fuel cell environment has been correlated with the electronic and structural parameters determined under in situ conditions using XANES and EXAFS technique respectively. Results indicate that all the alloys possess higher Pt 5d band vacancies as compared to Pt/C. There is also evidence of lattice contraction in the alloys (supported by XRD results). Further, the Pt/C shows increase in Pt 5 d band vacancies during potentialmore » transitions from 0.54 to 0.84 V vs. RHE, which has been ration@ on the basis of OH type adsorption. In contrast to this, the alloys do not exhibit such an enhancement. Detailed EXAFS analysis supports the presence of OH species on Pt/C and its relative absence in the alloys. Correlation of the electrochemical results with bond distances and d-band vacancies show a volcano type behavior with the PtCr/C on top of the curve.« less

Metal-organic framework derived Fe/Fe3C@N-doped-carbon porous hierarchical polyhedrons as bifunctional electrocatalysts for hydrogen evolution and oxygen-reduction reactions.

PubMed

Song, Chunsen; Wu, Shikui; Shen, Xiaoping; Miao, Xuli; Ji, Zhenyuan; Yuan, Aihua; Xu, Keqiang; Liu, Miaomiao; Xie, Xulan; Kong, Lirong; Zhu, Guoxing; Ali Shah, Sayyar

2018-08-15

The development of simple and cost-effective synthesis methods for electrocatalysts of hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) is critical to renewable energy technologies. Herein, we report an interesting bifunctional HER and ORR electrocatalyst of Fe/Fe 3 C@N-doped-carbon porous hierarchical polyhedrons (Fe/Fe 3 C@N-C) by a simple metal-organic framework precursor route. The Fe/Fe 3 C@N-C polyhedrons consisting of Fe and Fe 3 C nanocrystals enveloped by N-doped carbon shells and accompanying with some carbon nanotubes on the surface were prepared by thermal annealing of Zn 3 [Fe(CN) 6 ] 2 ·xH 2 O polyhedral particles in nitrogen atmosphere. This material exhibits a large specific surface area of 182.5 m 2  g -1 and excellent ferromagnetic property. Electrochemical tests indicate that the Fe/Fe 3 C@N-C hybrid has apparent HER activity with a relatively low overpotential of 236 mV at the current density of 10 mA cm -2 and a small Tafel slope of 59.6 mV decade -1 . Meanwhile, this material exhibits excellent catalytic activity toward ORR with an onset potential (0.936 V vs. RHE) and half-wave potential (0.804 V vs. RHE) in 0.1 M KOH, which is comparable to commercial 20 wt% Pt/C (0.975 V and 0.820 V), and shows even better stability than the Pt/C. This work provides a new insight to developing multi-functional materials for renewable energy application. Copyright © 2018 Elsevier Inc. All rights reserved.

Homogeneous deposition-assisted synthesis of iron-nitrogen composites on graphene as highly efficient non-precious metal electrocatalysts for microbial fuel cell power generation

NASA Astrophysics Data System (ADS)

Liu, Yuan; Jin, Xiao-Jun; Dionysiou, Dionysios D.; Liu, Hong; Huang, Yu-Ming

2015-03-01

This work proposed a novel strategy for synthesizing highly efficient non-precious metal oxygen reduction reaction (ORR) electrocatalysts. Fe complexes were homogeneously deposited (HD) on graphene oxide through in situ hydrolysis of urea, followed by two-step pyrolysis under Ar and NH3 atmospheres, resulting in formation of Fe- and N-functionalized graphene (HD-FeN/G). The morphology, crystalline structure and elemental composition of HD-FeN/G were characterized. ORR activity was evaluated by using a rotary disk electrode (RDE) electrochemical system. HD improved the loading and distribution of the Fe-Nx composites on graphene. The ORR activity of the as-prepared HD-FeN/G in neutral medium was comparable to that of the state-of-the-art commercial Pt/C and significantly superior to a FeN/G counterpart produced via traditional approach. The ORR electron transfer number of HD-FeN/G was as high as 3.83 ± 0.08, which suggested that ORR catalysis proceeds through a four-electron pathway. HD-FeN/G was used as a cathodic electrocatalyst in microbial fuel cells (MFCs), and the resultant HD-FeN/G-MFC showed comparable voltage output and maximum power density to those of Pt/C-MFC. The HD-FeN/G-MFC achieved a maximum power density of 885 mW m-2, which was much higher than that of FeN/G-MFC (708 mW m-2). These findings demonstrate that HD-FeN/G produced through the novel synthesis strategy proposed in this work would be a good candidate as cathodic electrocatalyst in MFCs.

Size, shape, and compositional effects on the order-disorder phase transitions in Au-Cu and Pt-M (M = Fe, Co, and Ni) nanocluster alloys.

PubMed

Kaatz, Forrest H; Bultheel, Adhemar

2018-08-24

Au-Cu and Pt-M (M = Fe, Co, and Ni) nanocluster alloys are currently being investigated world-wide by many researchers for their interesting catalytic and nanophase properties. The low temperature behavior of the phase diagrams is not well understood for alloys with nanometer sizes and shapes. We consider two models for low temperature ordering in the phase diagrams of Au-Cu and Pt-M nanocluster alloys. These models are valid for sizes ∼5 nm and approach bulk values for sizes ∼20 nm. We study the phase transitions in nanoclusters with cubic, octahedral, and cuboctahedral shapes, covering the compositions of interest. These models are based on studying the melting temperatures in nanoclusters using the regular solution, mixing model for alloys. From our data, experiments on nanocubes about 5 nm in size, of stoichiometric AuCu and PtM composition, could help differentiate between the models. Dispersion data shows that for the three shapes considered, octahedra have the highest percentage of surface atoms for the same relative diameter. We summarize the effects of structural ordering on the catalytic activity and suggest a method to avoid sintering during annealing of Pt-M alloys.

An electrochemical immunoassay for Escherichia coli O157:H7 using double functionalized Au@Pt/SiO2 nanocomposites and immune magnetic nanoparticles.

PubMed

Ye, Lingxian; Zhao, Guangying; Dou, Wenchao

2018-05-15

A sensitive Point-of-Care Testing (POCT) with Au-Pt bimetallic nanoparticles (Au@Pt) functionalized silica nanoparticle (SiO 2 NPs) and Fe 3 O 4 magnetic nanoparticles (Fe 3 O 4 NPs) was designed for the quantitative detection of Escherichia coli O157:H7 (E. coli O157:H7). The poly-(4-styrenesulfonic acid-co-maleic acid) (PSSMA) as a negatively charged polyelectrolyte can be easily coated on surface of the amino group modified SiO 2 NPs via electrostatic force. PSSMA is also a good stabilizer for water-soluble bimetallic nanostructures. The PSSMA is first time used as a "bridge" to connect the negative charge Au@Pt NPs to the SiO 2 NPs, forming Au@Pt/SiO 2 NPs. Antibody and invertase conjugated Au@Pt/SiO 2 NPs (denoted as Ab/invertase-Au@Pt/SiO 2 NPs) were used as signal labels. Monoclonal antibody against E. coli O157:H7 (Ab) functionalized magnetic nanoparticles (denoted as Ab-Fe 3 O 4 @SiO 2 NPs) were used to enrich and capture the E. coli O157:H7 in positive sample. The immunosensing platform also composed of a personal glucometer (PGM) using for signal readout. Based on this sandwich-type immunoassay, the invertase in the final formed sandwich immunocomplex catalyzed the hydrolysis of sucrose to produce a large amount of glucose for quantitative readout by the PGM. Under optimal conditions, a linear relationship between the glucose concentration and the logarithm of E. coli O157:H7 concentration was obtained in the concentration range from 3.5 × 10 2 to 3.5 × 10 8 CFU mL -1 with a detection limit of 1.83 × 10 2 CFU mL -1 (3σ). This method was used to detect E. coli O157:H7 in spiked milk samples, indicating its potential practical application. This protocol can be applied in various fields of study. Copyright © 2018 Elsevier B.V. All rights reserved.

Catalyst Architecture for Stable Single Atom Dispersion Enables Site-Specific Spectroscopic and Reactivity Measurements of CO Adsorbed to Pt Atoms, Oxidized Pt Clusters, and Metallic Pt Clusters on TiO2.

PubMed

DeRita, Leo; Dai, Sheng; Lopez-Zepeda, Kimberly; Pham, Nicholas; Graham, George W; Pan, Xiaoqing; Christopher, Phillip

2017-10-11

Oxide-supported precious metal nanoparticles are widely used industrial catalysts. Due to expense and rarity, developing synthetic protocols that reduce precious metal nanoparticle size and stabilize dispersed species is essential. Supported atomically dispersed, single precious metal atoms represent the most efficient metal utilization geometry, although debate regarding the catalytic activity of supported single precious atom species has arisen from difficulty in synthesizing homogeneous and stable single atom dispersions, and a lack of site-specific characterization approaches. We propose a catalyst architecture and characterization approach to overcome these limitations, by depositing ∼1 precious metal atom per support particle and characterizing structures by correlating scanning transmission electron microscopy imaging and CO probe molecule infrared spectroscopy. This is demonstrated for Pt supported on anatase TiO 2 . In these structures, isolated Pt atoms, Pt iso , remain stable through various conditions, and spectroscopic evidence suggests Pt iso species exist in homogeneous local environments. Comparing Pt iso to ∼1 nm preoxidized (Pt ox ) and prereduced (Pt metal ) Pt clusters on TiO 2 , we identify unique spectroscopic signatures of CO bound to each site and find CO adsorption energy is ordered: Pt iso ≪ Pt metal < Pt ox . Pt iso species exhibited a 2-fold greater turnover frequency for CO oxidation than 1 nm Pt metal clusters but share an identical reaction mechanism. We propose the active catalytic sites are cationic interfacial Pt atoms bonded to TiO 2 and that Pt iso exhibits optimal reactivity because every atom is exposed for catalysis and forms an interfacial site with TiO 2 . This approach should be generally useful for studying the behavior of supported precious metal atoms.

ELECTRODE MEASUREMENT OF REDOX POTENTIAL IN ANAEROBIC FERRIC/FERROUS CHLORIDE SYSTEMS

EPA Science Inventory

The behaviour of two inert redox electrodes (Pt and wax-impregnated graphite) was investigated in anaerobic ferrous and ferric chloride solutions in order to establish if these electrodes respond to the Fe³⁺/Fe²⁺ couple in a Nernstian manner. A new method fo...

Microwave-assisted synthesis of Pt/CNT nanocomposite electrocatalysts for PEM fuel cells.

PubMed

Zhang, Weimin; Chen, Jun; Swiegers, Gerhard F; Ma, Zi-Feng; Wallace, Gordon G

2010-02-01

Microwave-assisted heating of functionalized, single-wall carbon nanotubes (FCNTs) in ethylene glycol solution containing H(2)PtCl(6), led to the reductive deposition of Pt nanoparticles (2.5-4 nm) over the FCNTs, yielding an active catalyst for proton-exchange membrane fuel cells (PEMFCs). In single-cell testing, the Pt/FCNT composites displayed a catalytic performance that was superior to Pt nanoparticles supported by raw (unfunctionalized) CNTs (RCNTs) or by carbon black (C), prepared under identical conditions. The supporting single-wall carbon nanotubes (SWNTs), functionalized with carboxyl groups, were studied by thermogravimetric analysis (TGA), cyclic voltammetry (CV), and Raman spectroscopy. The loading level, morphology, and crystallinity of the Pt/SWNT catalysts were determined using TGA, SEM, and XRD. The electrochemically active catalytic surface area of the Pt/FCNT catalysts was 72.9 m(2)/g-Pt.

The inverse sandwich complex [(K(18-crown-6))2Cp][CpFe(CO)2]--unpredictable redox reactions of [CpFe(CO)2]I with the silanides Na[SiRtBu2] (R = Me, tBu) and the isoelectronic phosphanyl borohydride K[PtBu2BH3].

PubMed

Sänger, Inge; Kückmann, Theresa I; Dornhaus, Franz; Bolte, Michael; Wagner, Matthias; Lerner, Hans-Wolfram

2012-06-14

The dimeric iron carbonyl [CpFe(CO)(2)](2) and the iodosilanes tBu(2)RSiI were obtained from the reaction of [CpFe(CO)(2)]I with the silanides Na[SiRtBu(2)] (R = Me, tBu) in THF. By the reactions of [CpFe(CO)(2)]I and Na[SiRtBu(2)] (R = Me, tBu) the disilanes tBu(2)RSiSiRtBu(2) (R = Me, tBu) were additionally formed using more than one equivalent of the silanide. In this context it should be noted that reduction of [CpFe(CO)(2)](2) with Na[SitBu(3)] gives the disilanes tBu(3)SiSitBu(3) along with the sodium ferrate [(Na(18-crown-6))(2)Cp][CpFe(CO)(2)]. The potassium analogue [(K(18-crown-6))(2)Cp][CpFe(CO)(2)] (orthorhombic, space group Pmc2(1)), however, could be isolated as a minor product from the reaction of [CpFe(CO)(2)]I with [K(18-crown-6)][PtBu(2)BH(3)]. The reaction of [CpFe(CO)(2)](2) with the potassium benzophenone ketyl radical and subsequent treatment with 18-crown-6 yielded the ferrate [K(18-crown-6)][CpFe(CO)(2)] in THF at room temperature. The crown ether complex [K(18-crown-6)][CpFe(CO)(2)] was analyzed using X-ray crystallography (orthorhombic, space group Pna2(1)) and its thermal behaviour was investigated.

Laser-Heated DAC Mössbauer Study of Lower Mantle Phases: Spin Transitions and Implications for Mantle Heterogeneity

NASA Astrophysics Data System (ADS)

McCammon, C. A.; Dubrovinsky, L. S.; Potapkin, V.; Glazyrin, K.; Prescher, C.; Kupenko, I.; Chumakov, A.; Rüffer, R.; Kantor, A.; Kantor, I.; Smirnov, G. V.; Popov, S.

2011-12-01

57Fe Mössbauer spectroscopy measured in the energy domain remains one of the best methods to determine iron valence and the nature of spin transitions in lower mantle phases, but up until now measurements at high P,T using a diamond anvil cell (DAC) could only be made using external heating and hence were limited to a maximum of around 800 K. Higher temperatures are possible through laser heating; however conventional radioactive sources have limited intensity and essentially no possibilities for focusing in a laboratory setting. To overcome these limitations we have developed an energy domain synchrotron Mössbauer source (SMS) on beamline ID18 at the European Synchrotron Radiation Facility, enabling rapid collection of high quality energy domain Mössbauer spectra. Combined with a portable double-sided laser heating system, SMS spectra can be collected on iron-containing phases at P,T conditions up to those close to the base of the lower mantle in less than one hour. In the current study we performed SMS measurements on several compositions of (Mg,Fe)(Si,Al)O3 perovskite (Pv) as well as Mg0.8Fe0.2O (Fp) up to 122 GPa and 2500 K. All Mössbauer spectra at high pressure and room temperature are consistent with previous observations: a high-spin (HS) to intermediate-spin (IS) transition of Fe2+(Pv) starting at around 30 GPa, a HS to low-spin (LS) transition of Fe2+(Fp) starting at around 50 GPa, and no spin transition in Fe3+(Pv) up to at least 100 GPa. At high temperature all Fe2+ components show the expected strong decrease in both centre shift and quadrupole splitting, which provides an independent measure of temperature based on the Debye model, and shows clearly the strong temperature gradient in one-sided versus double-sided laser heating experiments. Preliminary fitting of the high P,T Mössbauer spectra is consistent with predominantly IS Fe2+ (Pv), HS Fe3+ (Pv) and mixed HS-LS Fe2+ (Fp). The relative proportion of Fe3+ (Pv) does not appear to change significantly on heating, and all of the original Mössbauer spectra are recovered after cooling. Based on our results, Fe2+ in silicate perovskite is inferred to be predominantly in the IS state throughout the lower mantle while Fe3+ remains in the HS state, implying that seismic velocity anomalies in the main part of the lower mantle cannot be attributed to iron spin transitions in silicate perovskite.

Magneto-ionic effect in CoFeB thin films with in-plane and perpendicular-to-plane magnetic anisotropy

NASA Astrophysics Data System (ADS)

Baldrati, L.; Tan, A. J.; Mann, M.; Bertacco, R.; Beach, G. S. D.

2017-01-01

The magneto-ionic effect is a promising method to control the magnetic properties electrically. Charged mobile oxygen ions can easily be driven by an electric field to modify the magnetic anisotropy of a ferromagnetic layer in contact with an ionic conductor in a solid-state device. In this paper, we report on the room temperature magneto-ionic modulation of the magnetic anisotropy of ultrathin CoFeB films in contact with a GdOx layer, as probed by polar micro-Magneto Optical Kerr Effect during the application of a voltage across patterned capacitors. Both Pt/CoFeB/GdOx films with perpendicular magnetic anisotropy and Ta/CoFeB/GdOx films with uniaxial in-plane magnetic anisotropy in the as-grown state exhibit a sizable dependence of the magnetic anisotropy on the voltage (amplitude, polarity, and time) applied across the oxide. In Pt/CoFeB/GdOx multilayers, it is possible to reorient the magnetic anisotropy from perpendicular-to-plane to in-plane, with a variation of the magnetic anisotropy energy greater than 0.2 mJ m-2. As for Ta/CoFeB/GdOx multilayers, magneto-ionic effects still lead to a sizable variation of the in-plane magnetic anisotropy, but the anisotropy axis remains in-plane.

Gigantic perpendicular magnetic anisotropy of heavy transition metal cappings on Fe/MgO(0 0 1)

NASA Astrophysics Data System (ADS)

Taivansaikhan, P.; Odkhuu, D.; Rhim, S. H.; Hong, S. C.

2017-11-01

Effects of capping layer by 5d transition metals (TM = Hf, Ta, W, Re, Os, Ir, Pt, and Au) on Fe/MgO(0 0 1), a typical magnetic tunneling junction, are systematically investigated using first-principles calculation for magnetism and magnetocrystalline-anisotropy (MCA). The early TMs having less than half-filled d bands favor magnetization antiparallel to Fe, whereas the late TMs having more than half-filled d bands favor parallel, which is explained in the framework of kinetic exchange energy. The Os capping, isovalent to Fe, enhances MCA significantly to gigantic energy of +11.31 meV/cell, where positive contribution is mostly from the partially filled majority d bands of magnetic quantum number of |m| = 1 along with stronger spin-orbit coupling of Os than Fe. Different TM cappings give different MCA energies as the Fermi level shifts according to the valence of TM: Re and Ir, just one valence more or less than Os, have still large PMCA but smaller than the Os. In the W and Pt cappings, valence difference by two, PMCA are further reduced; MCAs are lowered compared to Fe/MgO(0 0 1) by the cappings of the very early TMs (Hf and Ta), while the very late TM (Au) switches sign to in-plane MCA.

A study of the dispersity of iron oxide and iron oxide-noble metal (Me = Pd, Pt) supported systems

NASA Astrophysics Data System (ADS)

Cherkezova-Zheleva, Z. P.; Shopska, M. G.; Krstić, J. B.; Jovanović, D. M.; Mitov, I. G.; Kadinov, G. B.

2007-09-01

Samples of one-(Fe) and two-component (Fe-Pd and Fe-Pt) catalysts were prepared by incipient wetness impregnation of four different supports: TiO2 (anatase), γ-Al2O3, activated carbon, and diatomite. The chosen synthesis conditions resulted in the formation of nanosized supported phases—iron oxide (in the one-component samples), or iron oxide-noble metal (in the two-component ones). Different agglomeration degrees of these phases were obtained as a result of thermal treatment. Ultradisperse size of the supported phase was maintained in some samples, while a process of partial agglomeration occurred in others, giving rise to nearly bidisperse (ultra-and highdisperse) supported particles. The different texture of the used supports and their chemical composition are the reasons for the different stability of the nanosized supported phases. The samples were tested as heterogeneous catalysts in total benzene oxidation reaction.

Ferroelectric photovoltaic properties in doubly substituted (Bi0.9La0.1)(Fe0.97Ta0.03)O3 thin films

NASA Astrophysics Data System (ADS)

Katiyar, R. K.; Sharma, Y.; Barrionuevo, D.; Kooriyattil, S.; Pavunny, S. P.; Young, J. S.; Morell, G.; Weiner, B. R.; Katiyar, R. S.; Scott, J. F.

2015-02-01

Doubly substituted [Bi0.9La0.1][Fe0.97Ta0.03]O3 (BLFTO) films were fabricated on Pt/TiO2/SiO2/Si substrates by pulsed laser deposition. The ferroelectric photovoltaic properties of ZnO:Al/BLFTO/Pt thin film capacitor structures were evaluated under white light illumination. The open circuit voltage and short circuit current density were observed to be ˜0.20 V and ˜1.35 mA/cm2, respectively. The band gap of the films was determined to be ˜2.66 eV, slightly less than that of pure BiFeO3 (2.67 eV). The PV properties of BLFTO thin films were also studied for various pairs of planar electrodes in different directions in polycrystalline thin films.

Stereochemical Alignment in Triphospha[3]ferrocenophanes

PubMed Central

Borucki, Stefan; Kelemen, Zsolt; Maurer, Martin; Bruhn, Clemens

2017-01-01

Abstract A series of triphospha[3]ferrocenophanes of the type Fe(C5H4‐PtBu)2PX with X=H, F, Cl, Br, I, NEt2, tBu has been prepared and characterized by heteronuclear NMR spectroscopy and X‐ray crystallography. Despite having three stereogenic centers, the selective formation of a reduced number of diastereomers (either one or two) has been observed for these ferrocenophanes. Theoretical calculations revealed that the inversion of the central stereogenic center inverts the frontier orbital sequence leading to either an iron or a phosphorus centered HOMO depending on the respective diastereomer. CV measurements supported these results. For the all‐tert‐butyl substituted [3]ferrocenophane Fe(C5H4)2(PtBu)3 a chiral staggered conformation has been found in the solid state which differs substantially from the only other all‐organo substituted [3]ferrocenophane, Fe(C5H4)2(PPh)3. PMID:28557205

Ancient Chemistry "Pharaoh's Snakes" for Efficient Fe-/N-Doped Carbon Electrocatalysts.

PubMed

Ren, Guangyuan; Gao, Liangliang; Teng, Chao; Li, Yunan; Yang, Hequn; Shui, Jianglan; Lu, Xianyong; Zhu, Ying; Dai, Liming

2018-04-04

The method of fabricating nonprecious metal electrocatalysts with high activity and durability through a facile and eco-friendly procedure is of great significance to the development of low-cost fuel cells and metal-air batteries. Herein, we present that an ancient chemical reaction of "Pharaoh's snakes" can be a fast and convenient technique to prepare Fe-/N-doped carbon (Fe/N-C) nanosheet/nanotube electrocatalysts with sugar, soda, melamine, and iron nitrate as precursors. The resultant Fe/N-C catalyst has a hierarchically porous structure, a large surface area, and uniformly distributed active sites. The catalyst shows high electrocatalytic activities toward both the oxygen reduction reaction with a half-wave potential of 0.90 V (vs reversible hydrogen electrode) better than that of Pt/C and the oxygen evolution reaction with an overpotential of 0.46 V at the current density of 10 mA cm -2 comparable to that of RuO 2 . The activity and stability of the catalyst are also evaluated in primary and rechargeable Zn-air batteries. In both conditions, three-dimensional Fe/N-C exhibited performances superior to Pt/C. Our work demonstrates a success of utilizing an ancient science to make a state-of-the-art electrocatalyst.

Cap-Induced Magnetic Anisotropy in Ultra-thin Fe/MgO(001) Films

NASA Astrophysics Data System (ADS)

Brown-Heft, Tobias; Pendharkar, Mihir; Lee, Elizabeth; Palmstrom, Chris

Magnetic anisotropy plays an important role in the design of spintronic devices. Perpendicular magnetic anisotropy (PMA) is preferred for magnetic tunnel junctions because the resulting energy barrier between magnetization states can be very high and this allows enhanced device scalability suitable for magnetic random access memory applications. Interface induced anisotropy is often used to control magnetic easy axes. For example, the Fe/MgO(001) system has been predicted to exhibit PMA in the ultrathin Fe limit. We have used in-situ magneto optic Kerr effect and ex-situ SQUID to study the changes in anisotropy constants between bare Fe/MgO(001) films and those capped with MgO, Pt, and Ta. In some cases in-plane anisotropy terms reverse sign after capping. We also observe transitions from superparamagnetic to ferromagnetic behavior induced by capping layers. Perpendicular anisotropy is observed for Pt/Fe/MgO(001) films after annealing to 300°C. These effects are characterized and incorporated into a magnetic simulation that accurately reproduces the behavior of the films. This work was supported in part by the Semiconductor Research Corporation programs (1) MSR-Intel, and (2) C-SPIN.

In situ growth of NiFe alloy nanoparticles embedded into N-doped bamboo-like carbon nanotube as a bifunctional electrocatalyst for Zn-air battery.

PubMed

Bin, Duan; Yang, Beibei; Li, Chao; Liu, Yao; Zhang, Xiao; Wang, Yong-Gang; Xia, Yongyao

2018-06-26

Developing low-cost catalysts for electrochemical oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) with superior performance in alkaline solution is of significance for large-scale application in aqueous zinc-air batteries (ZABs). Herein, we describe in situ design of embedded NiFe nanoparticles into the N-doped bamboo-like carbon nanotube (NBCNT) with high catalytic performance and stability. The obtained NiFe@NBCNT hybrid exhibits a high electrochemical activity and stability with an unexpectedly low overpotential of ~195 mV for OER at 10 mA cm-2, and an onset potential at 1.03 V for ORR, superior to the state-of-the-art Pt/C and RuO2 catalysts. Additionally, compared to the mixture Pt/C and RuO2 cathode, the ZAB based on the NiFe@NBCNT cathode displays lower overpotential (0.80 V), higher stable round-trip efficiency (58.3%) and improved power density for 200 cycles at 10 mA cm-2. Apparently, the obtained results indicate that NiFe@NBCNT hybird is proven to be one of the best non-noble metal catalysts for achieving commercial implementation of rechargeable ZABs.

Improved ferroelectric polarization of V-doped Bi{sub 6}Fe{sub 2}Ti{sub 3}O{sub 18} thin films prepared by a chemical solution deposition

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

Song, D. P.; University of Science and Technology of China, Hefei 230026; Yang, J., E-mail: jyang@issp.ac.cn

We prepared V-doped Bi{sub 6}Fe{sub 2}Ti{sub 3}O{sub 18} thin films on Pt/Ti/SiO{sub 2}/Si (100) substrates by using a chemical solution deposition route and investigated the doping effect on the microstructure, dielectric, leakage, and ferroelectric properties of Bi{sub 6}Fe{sub 2}Ti{sub 3}O{sub 18} thin films. The Bi{sub 5.97}Fe{sub 2}Ti{sub 2.91}V{sub 0.09}O{sub 18} thin film exhibits improved dielectric properties, leakage current, and ferroelectric properties. The incorporation of vanadium resulted in a substantially enhanced remnant polarization (2P{sub r}) over 30 μC/cm{sup 2} in Bi{sub 5.97}Fe{sub 2}Ti{sub 2.91}V{sub 0.09}O{sub 18} thin film compared with 10 μC/cm{sup 2} in Bi{sub 6}Fe{sub 2}Ti{sub 3}O{sub 18} thin film. It ismore » demonstrated that the improved properties may stem from the improvement of crystallinity of the films with the contribution of suppressed oxygen vacancies and decreased mobility of oxygen vacancies caused by the V-doping. The results will provide a guidance to optimize the ferroelectric properties in Bi{sub 6}Fe{sub 2}Ti{sub 3}O{sub 18} thin films by chemical solution deposition, which is important to further explore single-phase multiferroics in the n = 5 Aurivillius thin films.« less

Synthesis and Characterization of Water-Soluble Polythiophene Derivatives for Cell Imaging

NASA Astrophysics Data System (ADS)

Wang, Fengyan; Li, Meng; Wang, Bing; Zhang, Jiangyan; Cheng, Yongqiang; Liu, Libing; Lv, Fengting; Wang, Shu

2015-01-01

In this work, four water-soluble polythiophene derivatives (PT, PT-DDA, PT-ADA, and PT-ADA-PPR) with different pendant moieties were synthesized via oxidative copolymerization by FeCl3. By increasing the hydrophobic ability of side chain moieties, there is a gradually blue shift for the maximum absorption wavelength and red shift for the maximum emission wavelength, a reducing trend for fluorescence quantum yields, a growing trend for Stokes shift, and an increasing trend for the mean sizes in the order of PT, PT-ADA, and PT-DDA. All the synthesized polymers show low toxicity and good photostability and accumulate in the lysosomes of A549 cells. Furthermore, the introduction of porphyrin group to PT-ADA side chain (PT-ADA-PPR) broadens the absorption and emission ranges of PT-ADA. PT-ADA-PPR could be excited at two different excitation wavelengths (488 nm and 559 nm) and exhibits two emission pathways, and dual-color fluorescence images (orange and red) of PT-ADA-PPR accumulated in A549 cells are observed. Thus, PT-ADA-PPR could be used as an excellent dual-color fluorescent and lysosome-specific imaging material.

Remarkable NO oxidation on single supported platinum atoms

DOE PAGES

Narula, Chaitanya K.; Allard, Lawrence F.; Stocks, G. M.; ...

2014-11-28

Our first-principles density functional theoretical modeling suggests that NO oxidation is feasible on fully oxidized single θ-alumina-supported platinum atoms via a modified Langmuir-Hinshelwood pathway. This is in contrast to the known decrease in NO oxidation activity of supported platinum with decreasing Pt particle size believed to be due to increased platinum oxidation. In order to validate our theoretical study, we evaluated single θ-Al 2O 3-supported platinum atoms and found them to exhibit remarkable NO oxidation activity. A comparison of turnover frequencies (TOF) of single supported Pt atoms with those of platinum particles for NO oxidation shows that single supported Ptmore » atoms are as active as fully formed platinum particles. The overall picture of NO oxidation on supported Pt is that NO oxidation activity decreases with decreasing Pt particle size but accelerates when Pt is present only as single atoms.« less

Highly Sensitive Electrochemical Biosensor for Evaluation of Oxidative Stress Based on the Nanointerface of Graphene Nanocomposites Blended with Gold, Fe3O4, and Platinum Nanoparticles.

PubMed

Wang, Le; Zhang, Yuanyuan; Cheng, Chuansheng; Liu, Xiaoli; Jiang, Hui; Wang, Xuemei

2015-08-26

High levels of H2O2 pertain to high oxidative stress and are associated with cancer, autoimmune, and neurodegenerative disease, and other related diseases. In this study, a sensitive H2O2 biosensor for evaluation of oxidative stress was fabricated on the basis of the reduced graphene oxide (RGO) nanocomposites decorated with Au, Fe3O4, and Pt nanoparticles (RGO/AuFe3O4/Pt) modified glassy carbon electrode (GCE) and used to detect the released H2O2 from cancer cells and assess the oxidative stress elicited from H2O2 in living cells. Electrochemical behavior of RGO/AuFe3O4/Pt nanocomposites exhibits excellent catalytic activity toward the relevant reduction with high selection and sensitivity, low overpotential of 0 V, low detection limit of ∼0.1 μM, large linear range from 0.5 μM to 11.5 mM, and outstanding reproducibility. The as-prepared biosensor was applied in the measurement of efflux of H2O2 from living cells including healthy normal cells and tumor cells under the external stimulation. The results display that this new nanocomposites-based biosensor is a promising candidate of nonenzymatic H2O2 sensor which has the possibility of application in clinical diagnostics to assess oxidative stress of different kinds of living cells.

AFLOWLIB.ORG: a Distributed Materials Properties Repository from High-throughput Ab initio Calculations

DTIC Science & Technology

2011-11-15

uncle) fcc (uncle) hcp (uncle) phase-diagram Ag Al Al Au Au Bi Bi Ca Ca Cd Cd Ce Ce Co Co Cr Cr Cu Cu Fe Fe Ga Ga Gd Gd Ge Ge Hf...Hf Hg Hg In In Ir Ir La La Li Li Mg Mg Mn Mn Mo Mo Na Na Nb Nb Ni Ni Os Os Pb Pb Pd Pd Pt Pt Rb Rb Re Re Rh Rh Ru Ru Sb Sb Sc...2 S. Curtarolo, A. N. Kolmogorov, and F. H. Cocks, High-throughput ab initio analysis of the Bi-In, Bi- Mg , Bi-Sb, In- Mg , In-Sb, and Mg -Sb systems

Direction control of anisotropy in the soft-magnetic underlayer for L10 Fe-Pt perpendicular media

NASA Astrophysics Data System (ADS)

Suzuki, Toshio

2005-05-01

Induced anisotropy of soft-magnetic underlayers (SUL) were pinned to radial and circumferential directions in double-layered perpendicular media, and effects of the directions on recording properties were studied for Fe-Pt media. A medium with the SUL of radial anisotropy showed a sharper cross-track profile than that of a medium with the SUL of circumferential anisotropy. Furthermore, signal-to-noise ratio (SNR) of the former was found to be 4dB higher than that of the latter at 500kfrpi. A SUL of radial anisotropy with an anisotropy-dispersion narrower could result in suppressing the fluctuation of write-field gradient and lead to further high SNR.

Site preference of ternary alloying additions to NiTi: Fe, Pt, Pd, Au, Al, Cu, Zr and Hf

NASA Technical Reports Server (NTRS)

Bozzolo, Guillermo; Noebe, Ronald D.; Mosca, Hugo O.

2004-01-01

Atomistic modeling of the site substitution behavior of Pd in NiTi (J. Alloys and Comp. (2004), in press) has been extended to examine the behavior of several other alloying additions, namely, Fe, Pt, Au, Al, Cu, Zr and Hf in this important shape memory alloy. It was found that all elements, to a varying degree, displayed absolute preference for available sites in the deficient sublattice. How- ever, the energetics of the different substitutional schemes, coupled with large scale simulations indicate that the general trend in all cases is for the ternary addition to want to form stronger ordered structures with Ti.

Tunable magnetotransport in Fe/hBN/graphene/hBN/Pt(Fe) epitaxial multilayers

NASA Astrophysics Data System (ADS)

Magnus Ukpong, Aniekan

2018-03-01

Theoretical and computational analysis of the magnetotransport properties and spin-transfer torque field-induced switching of magnetization density in vertically-stacked multilayers is presented. Using epitaxially-capped free layers of Pt and Fe, atom-resolved magnetic moments and spin-transfer torques are computed at finite bias. The calculations are performed within linear response approximation to the spin-density reformulation of the van der Waals density functional theory. Dynamical spin excitations are computed as a function of a spin-transfer torque induced magnetic field along the magnetic easy axis, and the corresponding spin polarization perpendicular to the easy axis is obtained. Bias-dependent giant anisotropic magnetoresistance of up to 3200% is obtained in the nonmagnetic-metal-capped Fe/hBN/graphene/hBN/Pt multilayer architecture. Since this specific heterostructure is not yet fabricated and characterized, the predicted high performance has not been demonstrated experimentally. Nevertheless, similar calculations performed on the Fe/hBN/Co stack show that the tunneling magnetoresistance obtained at the Fermi-level is in excellent agreement with results of recent magnetotransport measurements on magnetic tunnel junctions that contain the monolayer hBN tunnel region. The magnitude of the spin-transfer torque is found to increase as the tunneling spin current increases, and this activates the magnetization switching process due to increased charge accumulation. This mechanism causes substantial spin backflow, which manifests as rapid undulations in the bias-dependent tunneling spin currents. The implication of these findings on the design of nanoscale spintronic devices with spin-transfer torque tunable magnetization density is discussed. Insights derived from this study are expected to enhance the prospects for developing and integrating artificially assembled van der Waals multilayer heterostructures as the preferred material platform for efficient engineering of spin switches for spintronic applications.

Small-Angle Neutron Scattering Studies of Magnetic Correlation Lengths in Nanoparticle Assemblies

NASA Astrophysics Data System (ADS)

Majetich, Sara

2009-03-01

Small-angle neutron scattering (SANS) measurements of ordered arrays of surfactant-coated magnetic nanoparticle reveal characteristic length scales associated with interparticle and intraparticle magnetic ordering. The high degree of uniformity in the monodisperse nanoparticle size and spacing leads to a pronounced diffraction peak and allows for a straightforward determination of these length scales [1]. There are notable differences in these length scales depending on the particle moment, which depends on the material (Fe, Co, Fe3O4) and diameter, and also on whether the metal particle core is surrounded by an oxide shell. For 8.5 nm particles containing an Fe core and thick Fe3O4 shell, evidence of a spin flop phase is seen in the magnetite shell when a field is applied , but not when the shell thickness is ˜0.5 nm [2]. 8.0 nm particles with an e-Co core and 0.75 nm CoO shell show no exchange bias effects while similar particles with a 2 nm thick shell so significant training effects below 90 K. Polarized SANS studied of 7 nm Fe3O4 nanoparticle assemblies show the ability to resolve the magnetization components in 3D. [4pt] [1] M. Sachan, C. Bonnoit, S. A. Majetich, Y. Ijiri, P. O. Mensah-Bonsu, J. A. Borchers, and J. J. Rhyne, Appl. Phys. Lett. 92, 152503 (2008). [0pt] [2] Yumi Ijiri, Christopher V. Kelly, Julie A. Borchers, James J. Rhyne, Dorothy F. Farrell, Sara A. Majetich, Appl. Phys. Lett. 86, 243102-243104 (2005). [0pt] [3] K. L. Krycka, R. Booth, J. A. Borchers, W. C. Chen, C. Conlon, T. Gentile, C. Hogg, Y. Ijiri, M. Laver, B. B. Maranville, S. A. Majetich, J. Rhyne, and S. M. Watson, Physica B (submitted).

Enhanced photochemical hydrogen evolution from Fe4S4-based biomimetic chalcogels containing M2+ (M = Pt, Zn, Co, Ni, Sn) centers.

PubMed

Shim, Yurina; Young, Ryan M; Douvalis, Alexios P; Dyar, Scott M; Yuhas, Benjamin D; Bakas, Thomas; Wasielewski, Michael R; Kanatzidis, Mercouri G

2014-09-24

Naturally abundant enzymes often feature active sites comprising transition metal cluster units that catalyze chemical processes and reduce small molecules as well as protons. We introduce a family of new chalcogenide aerogels (chalcogels), aiming to model the function of active sites and the structural features of a larger protective framework. New metal incorporated iron sulfur tin sulfide chalcogels referred to as ternary chalcogels and specifically the chalcogels M-ITS-cg3, fully integrate biological redox-active Fe4S4 clusters into a semiconducting porous framework by bridging them with Sn4S10 linking units. In the M-ITS-cg3 system we can tailor the electro- and photocatalytic properties of chalcogels through the control of spatial distance of redox-active Fe4S4 centers using additional linking metal ions, M(2+) (Pt, Zn, Co, Ni, Sn). The presence of a third metal does not change the structural properties of the biomimetic chalcogels but modifies and even enhances their functional performance. M-ITS-cg3s exhibit electrocatalytic activity in proton reduction that arises from the Fe4S4 clusters but is tuned inductively by M(2+). The metal ions alter the reduction potential of Fe4S4 in a favorable manner for photochemical hydrogen production. The Pt incorporated ITS-cg3 shows the greatest improvement in the overall hydrogen yield compared to the binary ITS-cg3. The ability to manipulate the properties of biomimetic chalcogels through synthetic control of the composition, while retaining both structural and functional properties, illustrates the chalcogels' flexibility and potential in carrying out useful electrochemical and photochemical reactions.

Efficient decomposition of formaldehyde at room temperature over Pt/honeycomb ceramics with ultra-low Pt content.

PubMed

Nie, Longhui; Zheng, Yingqiu; Yu, Jiaguo

2014-09-14

Pt/honeycomb ceramic (Pt/HC) catalysts with ultra-low Pt content (0.005-0.055 wt%) were for the first time prepared by an impregnation of honeycomb ceramics with Pt precursor and NaBH4-reduction combined method. The microstructures, morphologies and textural properties of the resulting samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). The obtained Pt/HC catalysts were used for catalytic oxidative decomposition of formaldehyde (HCHO) at room temperature. It was found that the as-prepared Pt/HC catalysts can efficiently decompose HCHO in air into CO2 and H2O at room temperature. The catalytic activity of the Pt/HC catalysts increases with increasing the Pt loading in the range of 0.005-0.013 wt%, and the further increase of the Pt loading does not obviously improve catalytic activity. From the viewpoint of cost and catalytic performance, 0.013 wt% Pt loading is the optimal Pt loading amount, and the Pt/HC catalyst with 0.013 wt% Pt loading also exhibited good catalytic stability. Considering practical applications, this work will provide new insights into the low-cost and large-scale fabrication of advanced catalytic materials for indoor air purification.

Thermal Equation of State of Iron: Constraint on the Density Deficit of Earth's Core

NASA Astrophysics Data System (ADS)

Fei, Y.; Murphy, C. A.; Shibazaki, Y.; Huang, H.

2013-12-01

The seismically inferred densities of Earth's solid inner core and the liquid outer core are smaller than the measured densities of solid hcp-iron and liquid iron, respectively. The inner core density deficit is significantly smaller than the outer core density deficit, implying different amounts and/or identities of light-elements incorporated in the inner and outer cores. Accurate measurements of the thermal equation-of-state of iron over a wide pressure and temperature range are required to precisely quantify the core density deficits, which are essential for developing a quantitative composition model for the core. The challenge has been evaluating the experimental uncertainties related to the choice of pressure scales and the sample environment, such as hydrostaticity at multi-megabar pressures and extreme temperatures. We have conducted high-pressure experiments on iron in MgO, NaCl, and Ne pressure media and obtained in-situ X-ray diffraction data up to 200 GPa at room temperature. Using inter-calibrated pressure scales including the MgO, NaCl, Ne, and Pt scales, we have produced a consistent compression curve of hcp-Fe at room temperature. We have also performed laser-heated diamond-anvil cell experiments on both Fe and Pt in a Ne pressure medium. The experiment was designed to quantitatively compare the thermal expansion of Fe and Pt in the same sample environment using Ne as the pressure medium. The thermal expansion data of hcp-Fe at high pressure were derived based on the thermal equation of state of Pt. Using the 300-K isothermal compression curve of iron derived from our static experiments as a constraint, we have developed a thermal equation of state of hcp-Fe that is consistent with the static P-V-T data of iron and also reproduces the shock wave Hugoniot data for pure iron. The thermodynamic model, based on both static and dynamic data, is further used to calculate the density and bulk sound velocity of liquid iron. Our results define the solid inner core and liquid outer core density deficits, which can serve as the basis for any core composition models.

Effect of IrMn inserted layer on anomalous-Hall resistance and spin-Hall magnetoresistance in Pt/IrMn/YIG heterostructures

NASA Astrophysics Data System (ADS)

Shang, T.; Yang, H. L.; Zhan, Q. F.; Zuo, Z. H.; Xie, Y. L.; Liu, L. P.; Zhang, S. L.; Zhang, Y.; Li, H. H.; Wang, B. M.; Wu, Y. H.; Zhang, S.; Li, Run-Wei

2016-10-01

We report an investigation of anomalous-Hall resistance (AHR) and spin-Hall magnetoresistance (SMR) in Pt/Ir20Mn80/Y3Fe5O12 (Pt/IrMn/YIG) heterostructures. The AHR of Pt/IrMn/YIG heterostructures with an antiferromagnetic inserted layer is dramatically enhanced as compared to that of the Pt/YIG bilayer. The temperature dependent AHR behavior is nontrivial, while the IrMn thickness dependent AHR displays a peak at an IrMn thickness of 3 nm. The observed SMR in the temperature range of 10-300 K indicates that the spin current generated in the Pt layer can penetrate the IrMn layer (≤3 nm) to interact with the ferromagnetic YIG layer. The lack of conventional anisotropic magnetoresistance (AMR) implies that the insertion of the IrMn layer between Pt and YIG could efficiently suppress the magnetic proximity effect (MPE) on induced Pt moments by YIG.

Monolayer PtSe₂, a New Semiconducting Transition-Metal-Dichalcogenide, Epitaxially Grown by Direct Selenization of Pt.

PubMed

Wang, Yeliang; Li, Linfei; Yao, Wei; Song, Shiru; Sun, J T; Pan, Jinbo; Ren, Xiao; Li, Chen; Okunishi, Eiji; Wang, Yu-Qi; Wang, Eryin; Shao, Yan; Zhang, Y Y; Yang, Hai-tao; Schwier, Eike F; Iwasawa, Hideaki; Shimada, Kenya; Taniguchi, Masaki; Cheng, Zhaohua; Zhou, Shuyun; Du, Shixuan; Pennycook, Stephen J; Pantelides, Sokrates T; Gao, Hong-Jun

2015-06-10

Single-layer transition-metal dichalcogenides (TMDs) receive significant attention due to their intriguing physical properties for both fundamental research and potential applications in electronics, optoelectronics, spintronics, catalysis, and so on. Here, we demonstrate the epitaxial growth of high-quality single-crystal, monolayer platinum diselenide (PtSe2), a new member of the layered TMDs family, by a single step of direct selenization of a Pt(111) substrate. A combination of atomic-resolution experimental characterizations and first-principle theoretic calculations reveals the atomic structure of the monolayer PtSe2/Pt(111). Angle-resolved photoemission spectroscopy measurements confirm for the first time the semiconducting electronic structure of monolayer PtSe2 (in contrast to its semimetallic bulk counterpart). The photocatalytic activity of monolayer PtSe2 film is evaluated by a methylene-blue photodegradation experiment, demonstrating its practical application as a promising photocatalyst. Moreover, circular polarization calculations predict that monolayer PtSe2 has also potential applications in valleytronics.

Spin–orbit torque-assisted switching in magnetic insulator thin films with perpendicular magnetic anisotropy

DOE PAGES

Li, Peng; Liu, Tao; Chang, Houchen; ...

2016-09-01

As an in-plane charge current flows in a heavy metal film with spin-orbit coupling, it produces a torque on and thereby switches the magnetization in a neighbouring ferromagnetic metal film. Such spin-orbit torque (SOT)-induced switching has been studied extensively in recent years and has shown higher efficiency than switching using conventional spin-transfer torque. Here we report the SOT-assisted switching in heavy metal/magnetic insulator systems. The experiments used a Pt/BaFe 12O 19 bilayer where the BaFe 12O 19 layer exhibits perpendicular magnetic anisotropy. As a charge current is passed through the Pt film, it produces a SOT that can control themore » up and down states of the remnant magnetization in the BaFe 12O 19 film when the film is magnetized by an in-plane magnetic field. Furthermore, it can reduce or increase the switching field of the BaFe 12O 19 film by as much as about 500 Oe when the film is switched with an out-of-plane field.« less

Spin-orbit torque-assisted switching in magnetic insulator thin films with perpendicular magnetic anisotropy

NASA Astrophysics Data System (ADS)

Li, Peng; Liu, Tao; Chang, Houchen; Kalitsov, Alan; Zhang, Wei; Csaba, Gyorgy; Li, Wei; Richardson, Daniel; Demann, August; Rimal, Gaurab; Dey, Himadri; Jiang, J. S.; Porod, Wolfgang; Field, Stuart B.; Tang, Jinke; Marconi, Mario C.; Hoffmann, Axel; Mryasov, Oleg; Wu, Mingzhong

2016-09-01

As an in-plane charge current flows in a heavy metal film with spin-orbit coupling, it produces a torque on and thereby switches the magnetization in a neighbouring ferromagnetic metal film. Such spin-orbit torque (SOT)-induced switching has been studied extensively in recent years and has shown higher efficiency than switching using conventional spin-transfer torque. Here we report the SOT-assisted switching in heavy metal/magnetic insulator systems. The experiments used a Pt/BaFe12O19 bilayer where the BaFe12O19 layer exhibits perpendicular magnetic anisotropy. As a charge current is passed through the Pt film, it produces a SOT that can control the up and down states of the remnant magnetization in the BaFe12O19 film when the film is magnetized by an in-plane magnetic field. It can reduce or increase the switching field of the BaFe12O19 film by as much as about 500 Oe when the film is switched with an out-of-plane field.

Modeling of hysteretic Schottky diode-like conduction in Pt/BiFeO3/SrRuO3 switches

NASA Astrophysics Data System (ADS)

Miranda, E.; Jiménez, D.; Tsurumaki-Fukuchi, A.; Blasco, J.; Yamada, H.; Suñé, J.; Sawa, A.

2014-08-01

The hysteresis current-voltage (I-V) loops in Pt/BiFeO3/SrRuO3 structures are simulated using a Schottky diode-like conduction model with sigmoidally varying parameters, including series resistance correction and barrier lowering. The evolution of the system is represented by a vector in a 3D parameter space describing a closed trajectory with stationary states. It is shown that the hysteretic behavior is not only the result of a Schottky barrier height (SBH) variation arising from the BiFeO3 polarization reversal but also a consequence of the potential drop distribution across the device. The SBH modulation is found to be remarkably lower (<0.07 eV) than previously reported (>0.5 eV). It is also shown that the p-type semiconducting nature of BiFeO3 can explain the large ideality factors (>6) required to simulate the I-V curves as well as the highly asymmetric set and reset voltages (4.7 V and -1.9 V) exhibited by our devices.

Magnetic nanoparticles: synthesis, functionalization, and applications in bioimaging and magnetic energy storage.

PubMed

Frey, Natalie A; Peng, Sheng; Cheng, Kai; Sun, Shouheng

2009-09-01

This tutorial review summarizes the recent advances in the chemical synthesis and potential applications of monodisperse magnetic nanoparticles. After a brief introduction to nanomagnetism, the review focuses on recent developments in solution phase syntheses of monodisperse MFe(2)O(4), Co, Fe, CoFe, FePt and SmCo(5) nanoparticles. The review further outlines the surface, structural, and magnetic properties of these nanoparticles for biomedicine and magnetic energy storage applications.

Ensemble averaged structure–function relationship for nanocrystals: effective superparamagnetic Fe clusters with catalytically active Pt skin

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

Petkov, Valeri; Prasai, Binay; Shastri, Sarvjit

2017-09-12

Practical applications require the production and usage of metallic nanocrystals (NCs) in large ensembles. Besides, due to their cluster-bulk solid duality, metallic NCs exhibit a large degree of structural diversity. This poses the question as to what atomic-scale basis is to be used when the structure–function relationship for metallic NCs is to be quantified precisely. In this paper, we address the question by studying bi-functional Fe core-Pt skin type NCs optimized for practical applications. In particular, the cluster-like Fe core and skin-like Pt surface of the NCs exhibit superparamagnetic properties and a superb catalytic activity for the oxygen reduction reaction,more » respectively. We determine the atomic-scale structure of the NCs by non-traditional resonant high-energy X-ray diffraction coupled to atomic pair distribution function analysis. Using the experimental structure data we explain the observed magnetic and catalytic behavior of the NCs in a quantitative manner. Lastly, we demonstrate that NC ensemble-averaged 3D positions of atoms obtained by advanced X-ray scattering techniques are a very proper basis for not only establishing but also quantifying the structure–function relationship for the increasingly complex metallic NCs explored for practical applications.« less

High-performance electrochemical mercury aptasensor based on synergistic amplification of Pt nanotube arrays and Fe3O4/rGO nanoprobes.

PubMed

Luo, Jingyi; Jiang, Danfeng; Liu, Tao; Peng, Jingmeng; Chu, Zhenyu; Jin, Wanqin

2018-05-01

In this work, a novel sandwich-type aptasensor was designed for the ultrasensitive recognition of trace mercury ions in water. Numerous oriented platinum nanotube arrays (PtNAs) were in-situ crystallized on a flexible electrode as a sensing interface, while thionine labelled Fe 3 O 4 /rGO nanocomposites as signal amplifiers. Both PtNAs/CF and nanocomposites were synthesized by easy hydrothermal processes. With their large surface area, it was favorable for electrochemical performance and immobilization of capture DNAs (cDNA) and report DNAs (rDNA). Upon the existence of Hg 2+ , partial linker DNAs were tightly bound with cDNAs through thymine-Hg 2+ -thymine pairing (T-Hg 2+ -T). Then rDNAs attached Fe 3 O 4 /rGO nanoprobes were fixed on the electrode through the match of remaining linker DNAs and rDNAs. Under the optimal conditions, the Hg 2+ aptasensor showed a synergistic amplification performance with a wide linear range from 0.1nM to 100nM, as well as a low detection limit of 30pM. Moreover, the as-prepared aptasensor also exhibited reliable performance for assay in real lake water samples. Copyright © 2017. Published by Elsevier B.V.

High Performance Relaxor-Based Ferroelectric Single Crystals for Ultrasonic Transducer Applications

PubMed Central

Chen, Yan; Lam, Kwok-Ho; Zhou, Dan; Yue, Qingwen; Yu, Yanxiong; Wu, Jinchuan; Qiu, Weibao; Sun, Lei; Zhang, Chao; Luo, Haosu; Chan, Helen L. W.; Dai, Jiyan

2014-01-01

Relaxor-based ferroelectric single crystals Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) have drawn much attention in the ferroelectric field because of their excellent piezoelectric properties and high electromechanical coupling coefficients (d33∼2000 pC/N, kt∼60%) near the morphotropic phase boundary (MPB). Ternary Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) single crystals also possess outstanding performance comparable with PMN-PT single crystals, but have higher phase transition temperatures (rhombohedral to tetragonal Trt, and tetragonal to cubic Tc) and larger coercive field Ec. Therefore, these relaxor-based single crystals have been extensively employed for ultrasonic transducer applications. In this paper, an overview of our work and perspectives on using PMN-PT and PIN-PMN-PT single crystals for ultrasonic transducer applications is presented. Various types of single-element ultrasonic transducers, including endoscopic transducers, intravascular transducers, high-frequency and high-temperature transducers fabricated using the PMN-PT and PIN-PMN-PT crystals and their 2-2 and 1-3 composites are reported. Besides, the fabrication and characterization of the array transducers, such as phased array, cylindrical shaped linear array, high-temperature linear array, radial endoscopic array, and annular array, are also addressed. PMID:25076222

High Performance Heteroatoms Quaternary-doped Carbon Catalysts Derived from Shewanella Bacteria for Oxygen Reduction.

PubMed

Guo, Zhaoyan; Ren, Guangyuan; Jiang, Congcong; Lu, Xianyong; Zhu, Ying; Jiang, Lei; Dai, Liming

2015-11-25

A novel heteroatoms (N, P, S and Fe) quaternary-doped carbon (HQDC-X, X refers to the pyrolysis temperature) can be fabricated by directly pyrolyzing a gram-negative bacteria, S. oneidensis MR-1 as precursors at 800 °C, 900 °C and 1000 °C under argon atmosphere. These HQDC-X catalysts maintain the cylindrical shape of bacteria after pyrolysis under high temperatures, while heteroatoms including N, P, S and Fe distribute homogeneously on the carbon frameworks. As a result, HQDC-X catalysts exhibit excellent electrocatalytic activity for ORR via a dominant four-electron oxygen reduction pathway in alkaline medium, which is comparable with that of commercial Pt/C. More importantly, HQDC-X catalysts show better tolerance for methanol crossover and CO poisoning effects, long-term durability than commercial Pt/C, which could be promising alternatives to costly Pt-based electrocatalysts for ORR. The method may provide a promising avenue to develop cheap ORR catalysts from inexpensive, scalable and biological recursors.

Phosphinosilylenes as a novel ligand system for heterobimetallic complexes.

PubMed

Breit, Nora C; Eisenhut, Carsten; Inoue, Shigeyoshi

2016-04-25

A dihydrophosphinosilylene iron complex [LSi{Fe(CO)4}PH2] has been prepared and utilized in the synthesis of novel heterobimetallic complexes. The phosphine moiety in this phosphinosilylene complex allows coordination towards tungsten leading to the iron-tungsten heterobimetallic complex [LSi{Fe(CO)4}PH2{W(CO)5}]. In contrast, the reaction of [LSi{Fe(CO)4}PH2] with ethylenebis(triphenylphosphine)platinum(0) results in the formation of the iron-platinum heterobimetallic complex [LSi{Fe(CO)4}PH{PtH(PPh3)2}] via oxidative addition.

Microbial Communities and Electrochemical Performance of Titanium-Based Anodic Electrodes in a Microbial Fuel Cell▿

PubMed Central

Michaelidou, Urania; ter Heijne, Annemiek; Euverink, Gerrit Jan W.; Hamelers, Hubertus V. M.; Stams, Alfons J. M.; Geelhoed, Jeanine S.

2011-01-01

Four types of titanium (Ti)-based electrodes were tested in the same microbial fuel cell (MFC) anodic compartment. Their electrochemical performances and the dominant microbial communities of the electrode biofilms were compared. The electrodes were identical in shape, macroscopic surface area, and core material but differed in either surface coating (Pt- or Ta-coated metal composites) or surface texture (smooth or rough). The MFC was inoculated with electrochemically active, neutrophilic microorganisms that had been enriched in the anodic compartments of acetate-fed MFCs over a period of 4 years. The original inoculum consisted of bioreactor sludge samples amended with Geobacter sulfurreducens strain PCA. Overall, the Pt- and Ta-coated Ti bioanodes (electrode-biofilm association) showed higher current production than the uncoated Ti bioanodes. Analyses of extracted DNA of the anodic liquid and the Pt- and Ta-coated Ti electrode biofilms indicated differences in the dominant bacterial communities. Biofilm formation on the uncoated electrodes was poor and insufficient for further analyses. Bioanode samples from the Pt- and Ta-coated Ti electrodes incubated with Fe(III) and acetate showed several Fe(III)-reducing bacteria, of which selected species were dominant, on the surface of the electrodes. In contrast, nitrate-enriched samples showed less diversity, and the enriched strains were not dominant on the electrode surface. Isolated Fe(III)-reducing strains were phylogenetically related, but not all identical, to Geobacter sulfurreducens strain PCA. Other bacterial species were also detected in the system, such as a Propionicimonas-related species that was dominant in the anodic liquid and Pseudomonas-, Clostridium-, Desulfovibrio-, Azospira-, and Aeromonas-related species. PMID:21131513

Doping - dependent anisotropy of the superconducting gap in underdoped pnictide superconductors

NASA Astrophysics Data System (ADS)

Prozorov, Ruslan

2012-02-01

The in-plane London penetration depth, δλ(T), was studied in single crystals of Ba1-xKxFe2As2 (``Ba122") and Ca10(Pt3As8)[(Fe1-xPtx)2As2]5 (``10-3-8"). Whereas in Ba122 magnetism and superconductivity coexist in the underdoped regime, the 10-3-8 compound exhibits a clear separation of two order parameters. By comparing the results obtained in these two systems, we could study general features of the superconducting gap structure as function of doping in the underdoped regime. Similar to all other pnictides, the low-temperature variation of London penetration depth exhibits a power-law behavior, δλ(T)= AT^n, in both systems. Moving towards the underdoped edge of the superconducting dome, the exponent n decreases well below scattering - limited value of n=2 and, at the same time, the pre-factor A increases. Both trends indicate an increasing anisotropy of the superconducting gap in more underdoped compounds. These and previous results suggest that the development of the superconducting gap anisotropy towards the underdoped edge of the superconducting dome is an intrinsic property of iron pnictides, similar to the known tendency on the overdoped side where magnetism and superconductivity do not interfere.[4pt] In collboration with M.A. Tanatar, H. Kim, The Ames Laboratory; Bing Shen, Hai-Hu Wen, Nanjing University; and N. Ni, R.J. Cava, Princeton University.

Structural, dielectric and impedance characteristics of lanthanum-modified BiFeO3-PbTiO3 electronic system

NASA Astrophysics Data System (ADS)

Pradhan, S. K.; Das, S. N.; Bhuyan, S.; Behera, C.; Padhee, R.; Choudhary, R. N. P.

2016-06-01

A lanthanum-modified BiFeO3-PbTiO3 binary electronic system has been fabricated by a high-temperature solid-state reaction technique. The structural, dielectric and electrical properties of a single phase of multicomponent system are investigated to understand its ferroelectrics as well as relaxation behavior. The X-ray diffraction structural analysis substantiates the formation of a new stable phase of tetragonal system (with a large c/a ratio 1.23) without any trace of impurity phase. The electrical behavior of the processed material is characterized through impedance spectroscopy in a wide frequency range (1 kHz-1 MHz) over a temperature range of 25-500 °C. It is observed that the substitution of lanthanum-modified PbTiO3 (PT) into BiFeO3 (BFO) reveals enviable multiferroic property which is evident from the ME coefficient measurement and ferroelectric loop. It also reduces the electrical leakage current or tangent loss. The ac conductivity of the solid solution increases with increase in frequency in the low-temperature region. The impedance spectroscopy of the synthesized material reflects the dielectric relaxation of non-Debye type.

Graphene-based copper oxide thin film nanostructures as high-efficiency photocathode for p-type dye-sensitized solar cells

NASA Astrophysics Data System (ADS)

Kilic, Bayram; Turkdogan, Sunay; Astam, Aykut; Baran, Sümeyra Seniha; Asgin, Mansur; Cebeci, Hulya; Urk, Deniz

2017-10-01

Graphene-based p-type dye-sensitized solar cells (p-DSSCs) have been proposed and fabricated using copper oxide urchin-like nanostructures (COUN) as photocathode with an FeS2 counter electrode (CE). COUN composed of Cu2O core sphere and CuO shell nanorods with overall diameters of 2 to 4 μm were grown by a simple hydrothermal method with self-assemble nucleation. It was figured out that the formation of copper oxide core/shell structures could be adjusted by an ammonia additive leading to pH change of the precursor solution. In addition to a photocathode, we also demonstrated FeS2 thin films as an efficient CE material alternative to the conventional Pt CEs in DSSCs. FeS2 nanostructures, with diameters of 50 to 80 nm, were synthesized by a similar hydrothermal approach. FeS2 nanostructures are demonstrated to be an outstanding CE material in p-DSSCs. We report graphene/COUN as photocathode and Pt/FeS2 as CE in p-DSSCs, and results show that the synergetic combination of electrodes in each side (increased interconnectivity between COUN and graphene layer, high surface area, and high catalytic activity of FeS2) increased the power conversion efficiency from 1.56% to 3.14%. The excellent performances of COUN and FeS2 thin film in working and CEs, respectively, make them unique choices among the various photocathode and CE materials studied.

46 CFR Appendix IV to Part 150 - Data Sheet

Code of Federal Regulations, 2014 CFR

2014-10-01

... 46 Shipping 5 2014-10-01 2014-10-01 false Data Sheet IV Appendix IV to Part 150 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) CERTAIN BULK DANGEROUS CARGOES COMPATIBILITY OF CARGOES Pt. 150, App. IV Appendix IV to Part 150—Data Sheet EC02FE91.080 EC02FE91.081 ...

46 CFR Appendix IV to Part 150 - Data Sheet

Code of Federal Regulations, 2013 CFR

2013-10-01

... 46 Shipping 5 2013-10-01 2013-10-01 false Data Sheet IV Appendix IV to Part 150 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) CERTAIN BULK DANGEROUS CARGOES COMPATIBILITY OF CARGOES Pt. 150, App. IV Appendix IV to Part 150—Data Sheet EC02FE91.080 EC02FE91.081 ...

46 CFR Appendix IV to Part 150 - Data Sheet

Code of Federal Regulations, 2012 CFR

2012-10-01

... 46 Shipping 5 2012-10-01 2012-10-01 false Data Sheet IV Appendix IV to Part 150 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) CERTAIN BULK DANGEROUS CARGOES COMPATIBILITY OF CARGOES Pt. 150, App. IV Appendix IV to Part 150—Data Sheet EC02FE91.080 EC02FE91.081 ...

46 CFR Appendix IV to Part 150 - Data Sheet

Code of Federal Regulations, 2011 CFR

2011-10-01

... 46 Shipping 5 2011-10-01 2011-10-01 false Data Sheet IV Appendix IV to Part 150 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) CERTAIN BULK DANGEROUS CARGOES COMPATIBILITY OF CARGOES Pt. 150, App. IV Appendix IV to Part 150—Data Sheet EC02FE91.080 EC02FE91.081 ...

46 CFR Appendix IV to Part 150 - Data Sheet

Code of Federal Regulations, 2010 CFR

2010-10-01

... 46 Shipping 5 2010-10-01 2010-10-01 false Data Sheet IV Appendix IV to Part 150 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) CERTAIN BULK DANGEROUS CARGOES COMPATIBILITY OF CARGOES Pt. 150, App. IV Appendix IV to Part 150—Data Sheet EC02FE91.080 EC02FE91.081 ...

Superconductivity and Magnetism in LaO1-xFxFeAs

NASA Astrophysics Data System (ADS)

Buechner, Bernd

2009-03-01

Measuring ^75As, ^139La, and ^57Fe Nuclear Magnetic Resonance (NMR) as well as μSR, transport and thermodynamic properties we have determined the phase diagram of LaO1-xFxAsFe superconductors [1-6]. In my talk, I will show experimental studies of the magnetic ordering [2, 5], properties of the superconducting state [1, 3, 5] and the normal state properties [1, 4, 6] in the superconducting regions of the phase diagram. While the temperature dependence of the London penetration as determined from μSR points to an isotropic s wave state [3], our early NMR data suggest singlet pairing and nodes of the order parameter [1]. Extending the NMR work to lower temperatures we find evidence for a deviation of the T^3 behaviour of the spin lattice relaxation, which would agree with the extended s-wave symmetry suggested in recent theoretical work. In the paramagnetic normal state, NMR on all three nuclei shows that the local electronic susceptibility rises with increasing temperature. This had led to suggest the presence of a pseudogap, which I will discuss in detail. The scaling of all NMR shifts with respect to the macroscopic susceptibility indicates that there is no apparent multiband effect through preferential hyperfine couplings. Relaxation measurements indicate a similar temperature-dependence for (T1T)-1, and suggest that the dynamical susceptibility changes uniformly in q space with varying temperature. The transport properties show some striking similarities to the findings in cuprates [6] and, finally, susceptibility [4] as well as NMR studies point to the antiferromagnetic fluctuations, whose relevance is also discussed in many theoretical models of the superconducting pairing mechanism. In collaboration with Hans-Joachim Grafe, Christian Hess, R"udiger Klingeler, G"unter Behr, Agnieszka Kondrat, Norman Leps, and Guillaume Lang, IFW Dresden; Hans-Henning Klauss, TU Dresden; and Hubertus Luetkens, PSI Villigen. [4pt] References: [0pt] [1] H.-J. Grafe et al., Phys. Rev. Lett. 101, 047003 (2008) [0pt] [2] H.-H. Klauss et al., Phys. Rev. Lett. 101, 077005 (2008) [0pt] [3] H. Luetkens et al., Phys- Rev. Lett. 101, 097009 (2008) [0pt] [4] R. Klingeler et al., arXiv: 0808.0708 (2008) [0pt] [5] H. Luetkens et al., arXiv: 0806.3533 (2008) [0pt] [6] C. Hess et al., arXiv: 0811.1601 (2008)

Monolayer PtSe 2 , a New Semiconducting Transition-Metal-Dichalcogenide, Epitaxially Grown by Direct Selenization of Pt

DOE PAGES

Wang, Yeliang; Li, Linfei; Yao, Wei; ...

2015-05-21

For single-layer transition-metal dichalcogenides (TMDs) receive significant attention due to their intriguing physical properties for both fundamental research and potential applications in electronics, optoelectronics, spintronics, catalysis, and so on. Here, we demonstrate the epitaxial growth of high-quality single-crystal, monolayer platinum diselenide (PtSe2), a new member of the layered TMDs family, by a single step of direct selenization of a Pt(111) substrate. We found that a combination of atomic-resolution experimental characterizations and first-principle theoretic calculations reveals the atomic structure of the monolayer PtSe2/Pt(111). Angle-resolved photoemission spectroscopy measurements confirm for the first time the semiconducting electronic structure of monolayer PtSe2 (in contrastmore » to its semimetallic bulk counterpart). The photocatalytic activity of monolayer PtSe2 film is evaluated by a methylene-blue photodegradation experiment, demonstrating its practical application as a promising photocatalyst. Moreover, circular polarization calculations predict that monolayer PtSe2 has also potential applications in valleytronics.« less

Precious metal enrichment at low-redox in terrestrial native Fe-bearing basalts investigated using laser-ablation ICP-MS

NASA Astrophysics Data System (ADS)

Howarth, Geoffrey H.; Day, James M. D.; Pernet-Fisher, John F.; Goodrich, Cyrena A.; Pearson, D. Graham; Luo, Yan; Ryabov, Viktor V.; Taylor, Lawrence A.

2017-04-01

Primary native Fe is a rare crystallizing phase from terrestrial basaltic magmas, requiring highly reducing conditions (fO2

High P-T Raman study of transitions in relaxor multiferroic Pb(Fe 0.5Nb 0.5)O 3

DOE PAGES

Wilfong, Brandon; Ahart, Muhtar; Gramsch, Stephen A.; ...

2015-09-02

The vibrational and structural properties of Pb(Fe 0.5Nb 0.5)O 3 have been investigated using Raman spectroscopy up to 40 GPa at 300 K and from 300 to 415 K at selected pressures. The measurements reveal three phase transitions at 5.5, 8.7 and 24 GPa at room temperature. The temperature dependences of the spectra indicated transitions at 1.5 GPa, at 335 and 365 K. The results support the appearance of an intermediate tetragonal P4mm phase between ferroelectric R3m and paraelectric Pm-3m phases. Furthermore, a P-T phase diagram is proposed that allows further insight into the magnetoelectric coupling present in this material.

FAST TRACK COMMUNICATION: Ferroelectric properties and dielectric responses of multiferroic BiFeO3 films grown by RF magnetron sputtering

NASA Astrophysics Data System (ADS)

Qi, Xiaoding; Tsai, Po-Chou; Chen, Yi-Chun; Ko, Cheng-Hung; Huang, Jung-Chun-Andrew; Chen, In-Gann

2008-12-01

Multiferroic BiFeO3 films have been grown on LaNiO3-x/SrTiO3 and Pt/Si substrates by RF magnetron sputtering. The films showed fully saturated ferroelectric hysteresis loops with large remanent polarization of 64 µC cm-2, suitable for most device applications. Piezoresponse force microscopy confirmed that the films were electrically writable. In addition to the high-frequency intrinsic dielectric loss of epitaxial films, the Argand diagram also revealed low-frequency contributions from both dc conductivity and interfacial polarization at electrodes. For polycrystalline films on Pt/Si, the dominant contribution to dielectric loss was space charge polarization at grain boundaries.

Dye-Sensitized Cu2 XSnS4 (X=Zn, Ni, Fe, Co, and Mn) Nanofibers for Efficient Photocatalytic Hydrogen Evolution.

PubMed

Gonce, Mehmet Kerem; Aslan, Emre; Ozel, Faruk; Hatay Patir, Imren

2016-03-21

The photocatalytic hydrogen evolution activities of low-cost and noble-metal-free Cu2 XSnS4 (X=Zn, Ni, Fe, Co, and Mn) nanofiber catalysts have been investigated using triethanolamine as an electron donor and eosin Y as a photosensitizer under visible-light irradiation. The rates of hydrogen evolution by Cu2 XSnS4 (X=Zn, Ni, Fe, Co, and Mn) nanofibers have been compared with each other and with that of the noble metal Pt. The hydrogen evolution rates for the nanofibers change in the order Cu2 NiSnS4 >Cu2 FeSnS4 >Cu2 CoSnS4 >Cu2 ZnSnS4 >Cu2 MnSnS4 (2028, 1870, 1926, 1420, and 389 μmol g(-1) h(-1) , respectively). The differences between the hydrogen evolution rates of the nanofibers could be attributed to their energy levels. Moreover, Cu2 NiSnS4, Cu2 FeSnS4 , and Cu2 CoSnS4 nanofibers show higher and more stable photocatalytic hydrogen production rates than that of the noble metal Pt under long-term irradiation with visible light. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The functional characterization and comparison of two single CRD containing C-type lectins with novel and typical key motifs from Portunus trituberculatus.

PubMed

Huang, Mengmeng; Mu, Changkao; Wu, Yuehong; Ye, Fei; Wang, Dan; Sun, Cong; Lv, Zhengbing; Han, Bingnan; Wang, Chunlin; Xu, Xue-Wei

2017-11-01

C-type lectins are a superfamily of Ca 2+ -dependent carbohydrate-recognition proteins, which play crucial roles in innate immunity including nonself-recognition and pathogen elimination. In the present study, two single-CRD containing C-type lectins were identified from swimming crab Portunus trituberculatus (designated as PtCTL-2 and PtCTL-3). The open reading frame (ORF) of PtCTL-2 encoded polypeptides of 485 amino acids with a signal peptide and a single carbohydrate-recognition domain (CRD), while PtCTL-3's ORF encoded polypeptides of 241 amino acids with a coiled-coil region and a single-CRD. The key motifs determining carbohydrate binding specificity in PtCTL-2 and PtCTL-3 were EPR (Glu-Pro-Arg) and QPD (Gln-Pro-Asp). EPR is a motif being identified for the first time, whereas QPD is a typical motif in C-type lectins. Different PAMPs binding features of the two recombinant proteins - PtCTL-2 (rPtCTL-2) and PtCTL-3 (rPtCTL-3) have been observed in our experiments. rPtCTL-2 could bind three pathogen-associated molecular patterns (PAMPs) with relatively high affinity, including glucan, lipopolysaccharide (LPS) and peptidoglycan (PGN), while rPtCTL-3 could barely bind any of them. However, rPtCTL-2 could bind seven kinds of microbes and rPtCTL-3 could bind six kinds in microbe binding assay. Moreover, rPtCTL-2 and rPtCTL-3 exhibited similar agglutination activity against Gram-positive bacteria, Gram-negative bacteria and fungi in agglutination assay. All these results illustrated that PtCTL-2 and PtCTL-3 could function as important pattern-recognition receptors (PRR) with broad nonself-recognition spectrum involved in immune defense against invaders. In addition, the results of carbohydrate binding specificity showed that PtCTL-2 with novel key motif had broad carbohydrate binding specificity, while PtCTL-3 with typical key motif possessed different carbohydrate binding specificity from the classical binding rule. Furthermore, PtCTL-2 and PtCTL-3 could also function as opsonin to enhance encapsulation of hemocytes against Ni-NTA beads. Copyright © 2017 Elsevier Ltd. All rights reserved.

Nanoscale imaging of magnetization reversal driven by spin-orbit torque

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

Gilbert, Ian; Chen, P. J.; Gopman, Daniel B.

We use scanning electron microscopy with polarization analysis to image deterministic, spin-orbit torque-driven magnetization reversal of in-plane magnetized CoFeB rectangles in zero applied magnetic field. The spin-orbit torque is generated by running a current through heavy metal microstrips, either Pt or Ta, upon which the CoFeB rectangles are deposited. We image the CoFeB magnetization before and after a current pulse to see the effect of spin-orbit torque on the magnetic nanostructure. The observed changes in magnetic structure can be complex, deviating significantly from a simple macrospin approximation, especially in larger elements. Overall, however, the directions of the magnetization reversal inmore » the Pt and Ta devices are opposite, consistent with the opposite signs of the spin Hall angles of these materials. Lastly, our results elucidate the effects of current density, geometry, and magnetic domain structure on magnetization switching driven by spin-orbit torque.« less

Nanoscale imaging of magnetization reversal driven by spin-orbit torque

DOE PAGES

Gilbert, Ian; Chen, P. J.; Gopman, Daniel B.; ...

2016-09-23

We use scanning electron microscopy with polarization analysis to image deterministic, spin-orbit torque-driven magnetization reversal of in-plane magnetized CoFeB rectangles in zero applied magnetic field. The spin-orbit torque is generated by running a current through heavy metal microstrips, either Pt or Ta, upon which the CoFeB rectangles are deposited. We image the CoFeB magnetization before and after a current pulse to see the effect of spin-orbit torque on the magnetic nanostructure. The observed changes in magnetic structure can be complex, deviating significantly from a simple macrospin approximation, especially in larger elements. Overall, however, the directions of the magnetization reversal inmore » the Pt and Ta devices are opposite, consistent with the opposite signs of the spin Hall angles of these materials. Lastly, our results elucidate the effects of current density, geometry, and magnetic domain structure on magnetization switching driven by spin-orbit torque.« less

Effect of Silicon on Activity Coefficients of Platinum in Liquid Fe-Si, With Application to Core Formation

NASA Technical Reports Server (NTRS)

Righter, K.; Pando, K.; Danielson, L. R.; Humayun, M.

2017-01-01

Earth's core contains approximately 10% of a light element that is likely a combination of S, C, Si, and O, with Si possibly being the most abundant light element. Si dissolved into Fe liquids can have a large effect on the magnitude of the activity coefficient of siderophile elements (SE) in Fe liquids, and thus the partitioning behavior of those elements between core and mantle. The effect of Si can be small such as for Ni and Co, or large such as for Mo, Ge, Sb, As. The effect of Si on many siderophile elements is unknown yet could be an important, and as yet unquantified, influence on the core-mantle partitioning of SE. Here we report new experiments designed to quantify the effect of Si on the partitioning of Pt (with Re and Ru in progress or planned) between metal and silicate melt. The results will be applied to Earth, for which we have excellent constraints on the mantle Pt concentrations.

Enhanced room-temperature spin Seebeck effect in a YIG/C60/Pt layered heterostructure

NASA Astrophysics Data System (ADS)

Das, R.; Kalappattil, V.; Geng, R.; Luong, H.; Pham, M.; Nguyen, T.; Liu, Tao; Wu, Mingzhong; Phan, M. H.; Srikanth, H.

2018-05-01

We report on large enhancement of the longitudinal spin Seebeck effect (LSSE) in the Y3Fe5O12 (YIG)/Pt system at room temperature due to the addition of a thin layer of organic semiconductor (C60) in between the YIG and the Pt. LSSE measurements show that the LSSE voltage increases significantly, from the initial value of 150 nV for the YIG/Pt structure to 240 nV for the YIG/C60(5nm)/Pt structure. Radio-frequency transverse susceptibility experiments reveal a significant decrease in the surface perpendicular magnetic anisotropy (PMA) of the YIG film when C60 is deposited on it. These results suggest that the LSSE enhancement may be attributed to increased spin mixing conductance, the decreased PMA, and the large spin diffusion length of C60.

Formic acid decomposition on Pt1/Cu (111) single platinum atom catalyst: Insights from DFT calculations and energetic span model analysis

NASA Astrophysics Data System (ADS)

Wang, Ying-Fan; Li, Kun; Wang, Gui-Chang

2018-04-01

Inspired by the recent surface experimental results that the monatomic Pt catalysts has more excellent hydrogen production that Cu(111) surface, the mechanism of decomposition of formic acid on Cu(111) and single atom Pt1/Cu(111) surface was studied by periodic density functional theory calculations in the present work. The results show that the formic acid tends to undergo dehydrogenation on both surfaces to obtain the hydrogen product of the target product, and the selectivity and catalytic activity of Pt1/Cu (111) surface for formic acid dehydrogenation are better. The reason is that the single atom Pt1/Cu(111) catalyst reduces the reaction energy barrier (i.e., HCOO → CO2 + H) of the critical step of the dehydrogenation reaction due to the fact that the single atom Pt1/Cu(111) catalyst binds formate weakly compared to that of Cu (111) one. Moreover, it was found that the Pt1/Cu (111) binds CO more strongly than that of Cu (111) one and thus leading to the difficult for the formation of CO. These two factors would make the single Pt atom catalyst had the high selectivity for the H2 production. It is hoped that the present work may help people to design the efficient H2 production from HCOOH decomposition by reduce the surface binding strength of HCOO species, for example, using the low coordination number active site like single atom or other related catalytic system.

Single Platinum Atoms Electrocatalysts: Oxygen Reduction and Hydrogen Oxidation Reactions

DOE PAGES

Vukmirovic, Miomir B.; Teeluck, Krishani M.; Liu, Ping; ...

2017-08-08

We prepared atomically dispersed catalyst consisting of Pt atoms arranged in a c(2 × 2) array on RuO2(110) substrate. A large interatomic distance of Pt atoms in a c(2 × 2) phase precludes the reactants to interact with more than one Pt atoms. A strong bond of Pt atoms with RuO2 prevents agglomeration of Pt atoms to form 2D-islands or 3D-clusters. The activities of single Pt atom catalyst for the oxygen reduction and hydrogen oxidation reactions were determined and compared with those of bulk Pt. It has lower catalytic activity for the oxygen reduction reaction and similar activity for hydrogenmore » oxidation reaction compared to Pt(111). This was explained by a large calculated up-shift of the dband center of Pt atoms and larger Pt-Pt interatomic distance than that of Pt(111). Our information is of considerable interest for further development of electrocatalysis.« less

Reforming and oxidative dehydrogenation of ethane with CO 2 as a soft oxidant over bimetallic catalysts

DOE PAGES

Myint, MyatNoeZin; Yan, Binhang; Wan, Jie; ...

2016-02-26

An efficient mitigation of abundantly available CO 2 is critical for sustainable environmental impact as well as for novel industrial applications. Using ethane, CO 2 can be catalytically converted into a useful feedstock (synthesis gas) and a value-added monomer (ethylene) via the dry reforming pathway through the C–C bond scission and the oxidative dehydrogenation pathway through the C–H bond scission, respectively. Results from the current flow-reactor study show that the precious metal bimetallic CoPt/CeO 2 catalyst undergoes the reforming reaction to produce syngas with enhanced activity and stability compared to the parent monometallic catalysts. In this paper, in order tomore » replace Pt, the activities of non-precious CoMo/CeO 2 and NiMo/CeO 2 are investigated and the results indicate that NiMo/CeO 2 is nearly as active as CoPt/CeO 2 for the reforming pathway. Furthermore, FeNi/CeO 2 is identified as a promising catalyst for the oxidative dehydrogenation to produce ethylene. Finally, density functional theory (DFT) calculations are performed to further understand the different pathways of the CoPt/CeO 2 and FeNi/CeO 2 catalysts.« less

Reforming and oxidative dehydrogenation of ethane with CO 2 as a soft oxidant over bimetallic catalysts

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

Myint, MyatNoeZin; Yan, Binhang; Wan, Jie

An efficient mitigation of abundantly available CO 2 is critical for sustainable environmental impact as well as for novel industrial applications. Using ethane, CO 2 can be catalytically converted into a useful feedstock (synthesis gas) and a value-added monomer (ethylene) via the dry reforming pathway through the C–C bond scission and the oxidative dehydrogenation pathway through the C–H bond scission, respectively. Results from the current flow-reactor study show that the precious metal bimetallic CoPt/CeO 2 catalyst undergoes the reforming reaction to produce syngas with enhanced activity and stability compared to the parent monometallic catalysts. In this paper, in order tomore » replace Pt, the activities of non-precious CoMo/CeO 2 and NiMo/CeO 2 are investigated and the results indicate that NiMo/CeO 2 is nearly as active as CoPt/CeO 2 for the reforming pathway. Furthermore, FeNi/CeO 2 is identified as a promising catalyst for the oxidative dehydrogenation to produce ethylene. Finally, density functional theory (DFT) calculations are performed to further understand the different pathways of the CoPt/CeO 2 and FeNi/CeO 2 catalysts.« less

Making ultrafine and highly-dispersive multimetallic nanoparticles in three-dimensional graphene with supercritical fluid as excellent electrocatalyst for oxygen reduction reaction

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

Zhou, Yazhou; Yen, Clive H.; Hu, Yun Hang

2016-01-01

Three-dimensional (3D) graphene showed an advanced support for designing porous electrode materials due to its high specific surface area, large pore volume, and excellent electronic property. However, the electrochemical properties of reported porous electrode materials still need to be improved further. The current challenge is how to deposit desirable nanoparticles (NPs) with controllable structure, loading and composition in 3D graphene while maintaining the high dispersion. Herein, we demonstrate a modified supercritical fluid (SCF) technique to address this issue by controlling the SCF system. Using this superior method, a series of Pt-based/3D graphene materials with the ultrafine-sized, highly dispersive and controllablemore » composition multimetallic NPs were successfully synthesized. Specifically, the resultant Pt40Fe60/3D graphene showed a significant enhancement in electrocatalytic performance for the oxygen reduction reaction (ORR), including a factor of 14.2 enhancement in mass activity (1.70 A mgPt 1), a factor of 11.9 enhancement in specific activity (1.55 mA cm 2), and higher durability compared with that of Pt/C catalyst. After careful comparison, the Pt40Fe60/3D graphene catalyst shows the higher ORR activity than most of the reported similar 3D graphene-based catalysts. The successful synthesis of such attractive materials by this method also paves the way to develop 3D graphene in widespread applications.« less

Effects of electrodes on the properties of sol-gel PZT based capacitors in FeRAM

NASA Astrophysics Data System (ADS)

Zhang, Ming-Ming; Jia, Ze; Ren, Tian-Ling

2009-05-01

The effects of electrodes on the properties of capacitors applied in ferroelectric random access memories (FeRAM) are investigated in this work. Pt and Ir are used as bottom and top electrodes (BE and TE), respectively, in sol-gel Pb(Zr xTi 1-x)O 3 (PZT) based capacitors. Bottom electrodes are found to play a dominant role in the properties of PZT films and capacitors. Capacitors using Pt as bottom electrode have larger remnant polarization (2Pr) than those using Ir which may result from the different orientations of PZT films. The higher Schottky barrier, more dense film and smaller roughness are believed to be the reasons for the better leakage performance of capacitors using Pt as bottom electrodes. Different vacancies types and interface conditions are believed to be the main reasons for the better fatigue (less than 10% initial 2Pr loss after 10 11 fatigue cycles) and better imprint properties of TE/PZT/Ir capacitors. Top electrodes are found to have smaller impact on the properties of capacitors compared with bottom electrodes. A decrease in 2Pr is found when Ir is used as top electrode instead of Pt for PZT/Pt, which is believed to be caused by the stress resulting from lattice mismatch. The different thermal processes that top and bottom electrodes suffered are believed to be the reason for the different impacts they have on capacitors.

Using magnons to probe spintronic materials properties

NASA Astrophysics Data System (ADS)

McMichael, Robert

2012-02-01

For many spin-based electronic devices, from the read sensors in modern hard disk drives to future spintronic logic concepts, the device physics originates in spin polarized currents in ferromagnetic metals. In this talk, I will describe a novel ``Spin Wave Doppler'' method that uses the interaction of spin waves with spin-polarized currents to determine the spin drift velocity and the spin current polarization [1]. Owing to differences between the band structures of majority-spin and minority-spin electrons, the electrical current also carries an angular momentum current and magnetic moment current. Passing these coupled currents though a magnetic wire changes the linear excitations of the magnetization, i.e spin waves. Interestingly, the excitations can be described as drifting ``downstream'' with the electron flow. We measure this drift velocity by monitoring the spin-wave-mediated transmission between pairs of periodically patterned antennas on magnetic wires as a function of current density in the wire. The transmission frequency resonance shifts by 2πδf = vk where the drift velocity v is proportional to both the current density and the current polarization P. I will discuss measurements of the spin polarization of the current in Ni80Fe20 [2], and novel alloys (CoFe)1-xGax [3] and (Ni80Fe20)1-xGdx [4]. [4pt] [1] V. Vlaminck and M. Bailleul, Science, 322, 410 (2008) [0pt] [2] M. Zhu, C. L. Dennis, and R. D. McMichael, Phys. Rev. B, 81, 140407 (2010). [0pt] [3] M. Zhu, B. D. Soe, R. D. McMichael, M. J. Carey, S. Maat, and J. R. Childress, Appl. Phys. Lett., 98, 072510 (2011). [0pt] [4] R. L. Thomas, M. Zhu, C. L. Dennis, V. Misra and R. D. McMichael, J. Appl. Phys., 110, 033902 (2011).

17 CFR Appendix C to Part 4 - Form CTA-PR

Code of Federal Regulations, 2014 CFR

2014-04-01

... 17 Commodity and Securities Exchanges 1 2014-04-01 2014-04-01 false Form CTA-PR C Appendix C to Part 4 Commodity and Securities Exchanges COMMODITY FUTURES TRADING COMMISSION COMMODITY POOL OPERATORS AND COMMODITY TRADING ADVISORS Pt. 4, App. C Appendix C to Part 4—Form CTA-PR ER24FE12.052 ER24FE12...

30 CFR Appendix to Subpart B - Optional Form for Certifying Mine Rescue Teams

Code of Federal Regulations, 2012 CFR

2012-07-01

... 30 Mineral Resources 1 2012-07-01 2012-07-01 false Optional Form for Certifying Mine Rescue Teams... EDUCATION AND TRAINING MINE RESCUE TEAMS Mine Rescue Teams for Underground Coal Mines Pt. 49, Subpt. B, App. Appendix to Subpart B—Optional Form for Certifying Mine Rescue Teams ER08FE08.000 ER08FE08.001 ...

30 CFR Appendix to Subpart B - Optional Form for Certifying Mine Rescue Teams

Code of Federal Regulations, 2010 CFR

2010-07-01

... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Optional Form for Certifying Mine Rescue Teams... EDUCATION AND TRAINING MINE RESCUE TEAMS Mine Rescue Teams for Underground Coal Mines Pt. 49, Subpt. B, App. Appendix to Subpart B—Optional Form for Certifying Mine Rescue Teams ER08FE08.000 ER08FE08.001 ...

30 CFR Appendix to Subpart B - Optional Form for Certifying Mine Rescue Teams

Code of Federal Regulations, 2011 CFR

2011-07-01

... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Optional Form for Certifying Mine Rescue Teams... EDUCATION AND TRAINING MINE RESCUE TEAMS Mine Rescue Teams for Underground Coal Mines Pt. 49, Subpt. B, App. Appendix to Subpart B—Optional Form for Certifying Mine Rescue Teams ER08FE08.000 ER08FE08.001 ...

Magnetic N-Enriched Fe3C/Graphitic Carbon instead of Pt as an Electrocatalyst for the Oxygen Reduction Reaction.

PubMed

Wang, Xiaobai; Zhang, Peng; Wang, Wei; Lei, Xiang; Yang, Hua

2016-03-24

A series of Fe3C/C-Nx nanoparticles (NPs) with different nitrogen content are prepared by a simple one-pot route. In the synthetic procedure, aniline and acetonitrile are simultaneously used as the carbon and nitrogen source. The effect of calcination temperature on the structural and functional properties of the materials is investigated. Magnetic measurement shows that the sample prepared at 800 °C (Fe3 C/C-N800 NPs) possesses the highest Ms value of 77.2 emu g(-1). On testing as oxygen reduction reaction (ORR) catalysts, the sample prepared at 750 °C (Fe3C/C-N750 NPs) shows the best ORR performance among the series, with a more positive onset potential (+0.99 V vs. RHE), higher selectivity (number of electron transfer n≈3.93), longer durability, and stronger tolerance against methanol crossover than commercial Pt/C catalysts in a 0.1 m KOH solution. Moreover, in acidic solution, the excellent ORR activity and stability are also exhibited. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Local modifications of magnetism and structure in FePt (001) epitaxial thin films by focused ion beam: Two-dimensional perpendicular patterns

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

Albertini, F.; Nasi, L.; Casoli, F.

Focused ion beam was utilized to locally modify magnetism and structure of L1{sub 0} FePt perpendicular thin films. As a first step, we have performed a magnetic, morphological, and structural study of completely irradiated FePt films with different Ga{sup +} doses (1x10{sup 13} -4x10{sup 16} ions/cm{sup 2}) and ion beam energy of 30 keV. For doses of 1x10{sup 14} ions/cm{sup 2} and above a complete transition from the ordered L1{sub 0} to the disordered A1 phase was found to occur, resulting in a drop of magnetic anisotropy and in the consequent moment reorientation from out-of-plane to in-plane. The lowest effectivemore » dose in disordering the structure (1x10{sup 14} ions/cm{sup 2}) was found not to affect the film morphology. Taking advantage of these results, continuous two-dimensional (2D) patterns of perpendicular magnetic structures (250 nm dots, 1 {mu}m dots, 1 {mu}m-large stripes) were produced by focused ion beam without affecting the morphology. The 2D patterns were revealed by means of magnetic force microscopy, that evidenced peculiar domain structures in the case of 1 {mu}m dots.« less

Thickness-dependent multiferroic behavior of BiFe0.75Cr0.25O3 films over Pt(111)/Ti/SiO2/Si substrate

NASA Astrophysics Data System (ADS)

William, R. V.; Sivaprakash, P.; Marikani, A.; Reddy, V. Raghavendra; Arumugam, S.

2018-02-01

We present here the experimental results of BiFe0.75Cr0.25O3 (BFCO) thin film deposited by sol-gel spin coating technique directly on Pt(111)/Ti/SiO2/Si substrate at different thicknesses. The crystal structure of BFCO has been investigated using X-ray diffraction which acts as a double perovskite structure with high crystallinity obtained at 400 °C. Further microscopic studies such as scanning electron microscope (SEM) with EDAX, transmission electron microscope (TEM) were also used in identifying the grain size and particle distribution over Pt (111) substrate. Atomic force microscopy (AFM) on the films at a different thickness (- 80 to - 250 nm) reveals that the surface roughness and other amplitude parameters increases with the increase in thickness signifying an increase of grain size with thickness. Increase in grain size and substrate clamping effect between the BFCO film and the substrate induces change in ferroelectric polarization and dielectric properties in relation to thickness effect. Similarly, decrease in magnetization from 9.241 emu/cm3 (- 80 nm) to 5.7791 emu/cm3 (- 250 nm) is attributed to the formation of anti-sites and anti-phase boundaries in the films. In addition, temperature dependence of magnetization reveals ferromagnetic super-exchange interaction of BFCO which is unlike the spin structure of antiferromagnetic BiFeO3.

A low-cost approach to electronic excitation energies based on the driven similarity renormalization group

NASA Astrophysics Data System (ADS)

Li, Chenyang; Verma, Prakash; Hannon, Kevin P.; Evangelista, Francesco A.

2017-08-01

We propose an economical state-specific approach to evaluate electronic excitation energies based on the driven similarity renormalization group truncated to second order (DSRG-PT2). Starting from a closed-shell Hartree-Fock wave function, a model space is constructed that includes all single or single and double excitations within a given set of active orbitals. The resulting VCIS-DSRG-PT2 and VCISD-DSRG-PT2 methods are introduced and benchmarked on a set of 28 organic molecules [M. Schreiber et al., J. Chem. Phys. 128, 134110 (2008)]. Taking CC3 results as reference values, mean absolute deviations of 0.32 and 0.22 eV are observed for VCIS-DSRG-PT2 and VCISD-DSRG-PT2 excitation energies, respectively. Overall, VCIS-DSRG-PT2 yields results with accuracy comparable to those from time-dependent density functional theory using the B3LYP functional, while VCISD-DSRG-PT2 gives excitation energies comparable to those from equation-of-motion coupled cluster with singles and doubles.

High-nuclearity Pt-Tl-Fe complexes: structural, electrochemistry, and spectroelectrochemistry studies.

PubMed

Díez, Alvaro; Fernández, Julio; Lalinde, Elena; Moreno, M Teresa; Sánchez, Sergio

2010-12-20

A series of heteropolynuclear Pt-Tl-Fe complexes have been synthesized and structurally characterized. The final structures strongly depend on the geometry of the precursor and the Pt/Tl ratio used. Thus, the anionic heteroleptic cis-configured [cis-Pt(C(6)F(5))(2)(C≡CFc)(2)](2-) and [Pt(bzq)(C≡CFc)(2)](-) (Fc = ferrocenyl) complexes react with Tl(+) to form discrete octanuclear (PPh(3)Me)(2)[{trans,cis,cis-PtTl(C(6)F(5))(2)(C≡CFc)(2)}(2)] (1), [PtTl(bzq)(C≡CFc)(2)](2) (5; bzq = benzoquinolate), and decanuclear [trans,cis,cis-PtTl(2)(C(6)F(5))(2)(C≡CFc)(2)](2) (3) derivatives, stabilized by both Pt(II)···Tl(I) and Tl(I)···η(2)(alkynyl) bonds. By contrast, Q(2)[trans-Pt(C(6)F(5))(2)(C≡CFc)(2)] (Q = NBu(4)) reacts with Tl(+) to give the one-dimensional (1-D) anionic [(NBu(4)){trans,trans,trans-PtTl(C(6)F(5))(2)(C≡CFc)(2)}](n) (2) and neutral [trans,trans,trans-PtTl(2)(C(6)F(5))(2)(C≡CFc)(2)](n) (4) polymeric chains based on [PtFc(2)](2-) platinate fragments and Tl(+) (2) or [Tl···Tl](2+) (4) units, respectively, connected by Pt(II)···Tl(I) and secondary weak κ-η(1) (2) or η(2) (4) alkynyl···Tl(I) bonding. The formation of 1-4 is reversible, and thus treatment of neutral 3 and 4 with PPh(3)MeBr causes the precipitation of TlBr, returning toward the formation of the anionic 1 and 2' (Q = PPh(3)Me). Two slightly different pseudopolymorphs were found for 2', depending on the crystallization solvent. Finally, the reaction of the homoleptic [Pt(C≡CFc)(4)](2-) with 2 equiv of Tl(+) affords the tetradecanuclear sandwich type complex [Pt(2)Tl(4)(C≡CFc)(8)] (6). Electrochemical, spectroelectrochemical, and theoretical studies have been carried out to elucidate the effect produced by the interaction of the Tl(+) with the Pt-C≡CFc fragments. The cyclic voltammetry (CV) and differential pulse voltammetry (DPV) of 1-5 reveal that, in general, neutralization of the anionic fragments increases the stability of the fully oxidized species and gives higher E(1/2) (Fc) values than those observed in their precursors, increasing with the number of Pt-Tl bonding interactions. However, the electronic communication between Fc groups is reduced or even lost upon Tl(+) coordination, as confirmed by electrochemical (CVs and DPVs voltammograms, 1-5) and spectroelectrochemical (UV-vis-NIR, 2-4) studies. Complexes 2 and 4 still display some electronic interaction between the Fc groups, supported by the presence of an IVCT band in their UV-vis-NIR spectra of oxidized species and additional comparative DFT calculations with the precursor [trans-Pt(C(6)F(5))(2)(C≡CFc)(2)](2-) and complex 3.

Novel Sn-Based Contact Structure for GeTe Phase Change Materials.

PubMed

Simchi, Hamed; Cooley, Kayla A; Ding, Zelong; Molina, Alex; Mohney, Suzanne E

2018-05-16

Germanium telluride (GeTe) is a phase change material (PCM) that has gained recent attention because of its incorporation as an active material for radio frequency (RF) switches, as well as memory and novel optoelectronic devices. Considering PCM-based RF switches, parasitic resistances from Ohmic contacts can be a limiting factor in device performance. Reduction of the contact resistance ( R c ) is therefore critical for reducing the on-state resistance to meet the requirements of high-frequency RF applications. To engineer the Schottky barrier between the metal contact and GeTe, Sn was tested as an interesting candidate to alter the composition of the semiconductor near its surface, potentially forming a narrow band gap (0.2 eV) SnTe or a graded alloy with SnTe in GeTe. For this purpose, a novel contact stack of Sn/Fe/Au was employed and compared to a conventional Ti/Pt/Au stack. Two different premetallization surface treatments of HCl and deionized (DI) H 2 O were employed to make a Te-rich and Ge-rich interface, respectively. Contact resistance values were extracted using the refined transfer length method. The best results were obtained with DI H 2 O for the Sn-based contacts but HCl treatment for the Ti/Pt/Au contacts. The as-deposited contacts had the R c (ρ c ) of 0.006 Ω·mm (8 × 10 -9 Ω·cm 2 ) for Sn/Fe/Au and 0.010 Ω·mm (3 × 10 -8 Ω·cm 2 ) for Ti/Pt/Au. However, the Sn/Fe/Au contacts were thermally stable, and their resistance decreased further to 0.004 Ω·mm (4 × 10 -9 Ω·cm 2 ) after annealing at 200 °C. In contrast, the contact resistance of the Ti/Pt/Au stack increased to 0.012 Ω·mm (4 × 10 -8 Ω·cm 2 ). Transmission electron microscopy was used to characterize the interfacial reactions between the metals and GeTe. It was found that formation of SnTe at the interface, in addition to Fe diffusion (doping) into GeTe, is likely responsible for the superior performance of Sn/Fe/Au contacts, resulting in one of the lowest reported contact resistances on GeTe.

Single-atom Catalysis Using Pt/Graphene Achieved through Atomic Layer Deposition

NASA Astrophysics Data System (ADS)

Sun, Shuhui; Zhang, Gaixia; Gauquelin, Nicolas; Chen, Ning; Zhou, Jigang; Yang, Songlan; Chen, Weifeng; Meng, Xiangbo; Geng, Dongsheng; Banis, Mohammad N.; Li, Ruying; Ye, Siyu; Knights, Shanna; Botton, Gianluigi A.; Sham, Tsun-Kong; Sun, Xueliang

2013-05-01

Platinum-nanoparticle-based catalysts are widely used in many important chemical processes and automobile industries. Downsizing catalyst nanoparticles to single atoms is highly desirable to maximize their use efficiency, however, very challenging. Here we report a practical synthesis for isolated single Pt atoms anchored to graphene nanosheet using the atomic layer deposition (ALD) technique. ALD offers the capability of precise control of catalyst size span from single atom, subnanometer cluster to nanoparticle. The single-atom catalysts exhibit significantly improved catalytic activity (up to 10 times) over that of the state-of-the-art commercial Pt/C catalyst. X-ray absorption fine structure (XAFS) analyses reveal that the low-coordination and partially unoccupied densities of states of 5d orbital of Pt atoms are responsible for the excellent performance. This work is anticipated to form the basis for the exploration of a next generation of highly efficient single-atom catalysts for various applications.

Single-atom Catalysis Using Pt/Graphene Achieved through Atomic Layer Deposition

PubMed Central

Sun, Shuhui; Zhang, Gaixia; Gauquelin, Nicolas; Chen, Ning; Zhou, Jigang; Yang, Songlan; Chen, Weifeng; Meng, Xiangbo; Geng, Dongsheng; Banis, Mohammad N.; Li, Ruying; Ye, Siyu; Knights, Shanna; Botton, Gianluigi A.; Sham, Tsun-Kong; Sun, Xueliang

2013-01-01

Platinum-nanoparticle-based catalysts are widely used in many important chemical processes and automobile industries. Downsizing catalyst nanoparticles to single atoms is highly desirable to maximize their use efficiency, however, very challenging. Here we report a practical synthesis for isolated single Pt atoms anchored to graphene nanosheet using the atomic layer deposition (ALD) technique. ALD offers the capability of precise control of catalyst size span from single atom, subnanometer cluster to nanoparticle. The single-atom catalysts exhibit significantly improved catalytic activity (up to 10 times) over that of the state-of-the-art commercial Pt/C catalyst. X-ray absorption fine structure (XAFS) analyses reveal that the low-coordination and partially unoccupied densities of states of 5d orbital of Pt atoms are responsible for the excellent performance. This work is anticipated to form the basis for the exploration of a next generation of highly efficient single-atom catalysts for various applications.

Ab initio construction of magnetic phase diagrams in alloys: The case of Fe 1-xMn xPt

DOE PAGES

Pujari, B. S.; Larson, P.; Antropov, V. P.; ...

2015-07-28

A first-principles approach to the construction of concentration-temperature magnetic phase diagrams of metallic alloys is presented. The method employs self-consistent total energy calculations based on the coherent potential approximation for partially ordered and noncollinear magnetic states and is able to account for competing interactions and multiple magnetic phases. The application to the Fe 1–xMn xPt “magnetic chameleon” system yields the sequence of magnetic phases at T = 0 and the c-T magnetic phase diagram in good agreement with experiment, and a new low-temperature phase is predicted at the Mn-rich end. The importance of non-Heisenberg interactions for the description of themore » magnetic phase diagram is demonstrated.« less

The memory effect of magnetoelectric coupling in FeGaB/NiTi/PMN-PT multiferroic heterostructure

PubMed Central

Zhou, Ziyao; Zhao, Shishun; Gao, Yuan; Wang, Xinjun; Nan, Tianxiang; Sun, Nian X.; Yang, Xi; Liu, Ming

2016-01-01

Magnetoelectric coupling effect has provided a power efficient approach in controlling the magnetic properties of ferromagnetic materials. However, one remaining issue of ferromagnetic/ferroelectric magnetoelectric bilayer composite is that the induced effective anisotropy disappears with the removal of the electric field. The introducing of the shape memory alloys may prevent such problem by taking the advantage of its shape memory effect. Additionally, the shape memory alloy can also “store” the magnetoelectric coupling before heat release, which introduces more functionality to the system. In this paper, we study a FeGaB/NiTi/PMN-PT multiferroic heterostructure, which can be operating in different states with electric field and temperature manipulation. Such phenomenon is promising for tunable multiferroic devices with multi-functionalities. PMID:26847469

Effect of silicon on activity coefficients of siderophile elements (Au, Pd, Pt, P, Ga, Cu, Zn, and Pb) in liquid Fe: Roles of core formation, late sulfide matte, and late veneer in shaping terrestrial mantle geochemistry

NASA Astrophysics Data System (ADS)

Righter, K.; Pando, K.; Humayun, M.; Waeselmann, N.; Yang, S.; Boujibar, A.; Danielson, L. R.

2018-07-01

Earth's core contains ∼10% of a light element that may be a combination of Si, S, C, O or H, with Si potentially being the major light element. Metal-silicate partitioning of siderophile elements can place important constraints on the P-T-fO2 and composition of the early Earth, but the effect of Si alloyed in Fe liquids is unknown for many of these elements. In particular, the effect of Si on the partitioning of highly siderophile elements (Au, Re and PGE) is virtually unknown. To address this gap in understanding, we have undertaken a systematic study of the highly siderophile elements Au, Pd, and Pt, and the volatile siderophile elements P, Ga, Cu, Zn, and Pb at variable Si content of metal, and 1600 °C and 1 GPa. From our experiments we derive epsilon interaction parameters between these elements and Si in Fe metallic liquids. The new parameters are used to update an activity model for trace siderophile elements in Fe alloys; Si causes large variation in the magnitude of activity coefficients of these elements in FeSi liquids. Because the interaction parameters are all positive, Si causes a decrease in their metal/silicate partition coefficients. We combine these new activity results with experimental studies of Au, Pd, Pt, P, Ga, Cu, Zn and Pb, to derive predictive expressions for metal/silicate partition coefficients which can then be applied to Earth. The expressions are applied to two scenarios for continuous accretion of Earth; specifically for constant and increasing fO2 during accretion. The results indicate that mantle concentrations of P, Ga, Cu, Zn, and Pb can be explained by metal-silicate equilibrium during accretion of the Earth where Earth's early magma ocean deepens to pressures of 40-60 GPa. Au, Pd, and Pt, on the other hand become too high in the mantle in such a scenario, and require a later removal mechanism, rather than an addition as traditionally argued. A late reduction event that removes 0.5% metal from a shallow magma ocean can lower the Au, Pd, and Pt contents to values near the current day BSE. On the other hand, removal of 0.2-1.0% of a late sulfide-rich matte to the core would lower the Au, Pd, and Pt concentrations in the mantle, but not to chondritic relative concentrations observed in the BSE. If sulfide matte is called upon to remove HSEs, they must be later added via a late veneer to re-establish the high and chondritic relative PUM concentrations. These results suggest that although accretion and core formation (involving a Si, S, and C-bearing metallic liquid) were the primary processes establishing many of Earth's mantle volatile elements and HSE, a secondary removal process is required to establish HSEs at their current and near-chondritic relative BSE levels. Mn and P - two siderophile elements that are central to biochemical processes (photosynthesis and triphosphates, respectively) - have significant and opposite interactions with FeSi liquids, and their mantle concentrations would be notably different if Earth had a Si-free core.

Spin-orbit assisted transmission at 3d/5d metallic interfaces

NASA Astrophysics Data System (ADS)

Jaffres, Henri; Barbedienne, Quentin; Jouy, Augustin; Reyren, Nicolas; George, Jean-Marie; Laboratoire de Physique Et Des Plasmas, Ecole Polytechnique, Palaiseau, France Team; Unite Mixte de Physique Cnrs-Thales, Palaiseau, France Team

We will describe the anatomy of spin-transport and spin-orbit torques (SOT) at spin-orbit active interfaces involving 5d transition metals (TM) as heavy metals spin-Hall effect (SHE) materials and 3d TM in [Co,Ni]/Pt, NiFe. NiFe/Au:W and Co/Pt/Au;W systems. In the case of Pt, recent studies have put forward the major role played by the spin-memory loss (SML), the electronic transparency at 3d/5d interfaces and the inhomogeneity of the conductivity in the CIP-geometry. Ingredients to consider for spin-transport and spin-Hall Magnetoresistance (SMR) are the conductivity, the spin-current profiles across the multilayers and the spin-transmission. We will present SMR measurements observed on these systems possibly involving interfacial Anisotropy of Magnetoresistance (AIMR) contributions. We analyze in large details our SMR signals in the series of samples owing: i) the exact conductivity profile across the multilayers via the Camley-Barnas approach and the spin current profile generated by SHE. We will discuss the role of the generalized spin-mixing conductance on the spin-transport properties and spin-orbit torques.