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Sample records for al ba fe

  1. Co{sub 2}FeAl based magnetic tunnel junctions with BaO and MgO/BaO barriers

    SciTech Connect

    Rogge, J.; Schmalhorst, J.; Hütten, A.; Hetaba, W.

    2015-07-15

    We succeed to integrate BaO as a tunneling barrier into Co{sub 2}FeAl based magnetic tunnel junctions (MTJs). By means of Auger electron spectroscopy it could be proven that the applied annealing temperatures during BaO deposition and afterwards do not cause any diffusion of Ba neither into the lower Heusler compound lead nor into the upper Fe counter electrode. Nevertheless, a negative tunnel magnetoresistance (TMR) ratio of -10% is found for Co{sub 2}FeAl (24 nm) / BaO (5 nm) / Fe (7 nm) MTJs, which can be attributed to the preparation procedure and can be explained by the formation of Co- and Fe-oxides at the interfaces between the Heusler and the crystalline BaO barrier by comparing with theory. Although an amorphous structure of the BaO barrier seems to be confirmed by high-resolution transmission electron microscopy (TEM), it cannot entirely be ruled out that this is an artifact of TEM sample preparation due to the sensitivity of BaO to moisture. By replacing the BaO tunneling barrier with an MgO/BaO double layer barrier, the electric stability could effectively be increased by a factor of five. The resulting TMR effect is found to be about +20% at room temperature, although a fully antiparallel state has not been realized.

  2. Mössbauer spectroscopy study of Al distribution in BaAlxFe12-xO19 thin films

    NASA Astrophysics Data System (ADS)

    Przybylski, M.; Żukrowski, J.; Harward, I.; Celiński, Z.

    2015-05-01

    Barium hexagonal ferrite (BaM) films grown on Si are a good candidate material for new-generations of on-wafer microwave devices operating at frequencies above 40 GHz. Doping BaM with Al increases the value of anisotropy field even more, and in combination with a large value of remanence, would allow one to create a self-biasing material/structure that would eliminate the need for permanent bias magnets in millimeter wave devices. To examine the occupation of Fe sublattices by Al ions, we carried out Conversion Electron Mössbauer Spectroscopy (CEMS) measurements at room temperature and zero magnetic field (after magnetizing the samples in a strong magnetic field). The spectra can be reasonably fitted with three components (sub-spectra) corresponding to different Fe sublattices. There are significant changes in the spectra with the addition of Al: The magnetic hyperfine field decreases for all three components, and their relative contributions also change remarkably. These observations are in agreement with the fact that the Al substitutes Fe, thus lowering the component contributions and the value of the hyperfine field. In addition, our previous XRD analysis indicates increasing grain misalignment with Al content, further supporting the CEMS data.

  3. Mössbauer spectroscopy study of Al distribution in BaAl{sub x}Fe{sub 12−x}O{sub 19} thin films

    SciTech Connect

    Przybylski, M. Żukrowski, J.; Harward, I.; Celiński, Z.

    2015-05-07

    Barium hexagonal ferrite (BaM) films grown on Si are a good candidate material for new-generations of on-wafer microwave devices operating at frequencies above 40 GHz. Doping BaM with Al increases the value of anisotropy field even more, and in combination with a large value of remanence, would allow one to create a self-biasing material/structure that would eliminate the need for permanent bias magnets in millimeter wave devices. To examine the occupation of Fe sublattices by Al ions, we carried out Conversion Electron Mössbauer Spectroscopy (CEMS) measurements at room temperature and zero magnetic field (after magnetizing the samples in a strong magnetic field). The spectra can be reasonably fitted with three components (sub-spectra) corresponding to different Fe sublattices. There are significant changes in the spectra with the addition of Al: The magnetic hyperfine field decreases for all three components, and their relative contributions also change remarkably. These observations are in agreement with the fact that the Al substitutes Fe, thus lowering the component contributions and the value of the hyperfine field. In addition, our previous XRD analysis indicates increasing grain misalignment with Al content, further supporting the CEMS data.

  4. Vibrational spectroscopic characterization of the phosphate mineral kulanite Ba(Fe2+,Mn2+,Mg)2(Al,Fe3+)2(PO4)3(OH)3

    NASA Astrophysics Data System (ADS)

    Frost, Ray L.; López, Andrés; Xi, Yunfei; Granja, Amanda; Scholz, Ricardo

    2013-11-01

    The mineral kulanite BaFe2Al2(PO4)3(OH)3, a barium iron aluminum phosphate, has been studied by using a combination of electron microscopy and vibrational spectroscopy. Scanning electron microscopy with EDX shows the mineral is homogenous with no other phases present. The Raman spectrum is dominated by an intense band at 1022 cm-1 assigned to the PO43- ν1 symmetric stretching mode. Low intensity Raman bands at 1076, 1110, 1146, 1182 cm-1 are attributed to the PO43 - ν3 antisymmetric stretching vibrations. The infrared spectrum shows a complex spectral profile with overlapping bands. Multiple phosphate bending vibrations supports the concept of a reduction in symmetry of the phosphate anion. Raman spectrum at 3211, 3513 and 3533 cm-1 are assigned to the stretching vibrations of the OH units. Vibrational spectroscopy enables aspects on the molecular structure of kulanite to be assessed.

  5. 57Fe NMR study of the magnetoelectric hexaferrite Ba0.5Sr1.5Zn2Fe12O22 and Ba0.5Sr1.5Zn2(Fe0.92Al0.08)12O22

    NASA Astrophysics Data System (ADS)

    Kwon, Sangil; Yoon, Dong Young; Lee, Soonchil; Chai, Yi Sheng; Chun, Sae Hwan; Kim, Kee Hoon

    2013-08-01

    Magnetoelectric hexaferrite Ba0.5Sr1.5Zn2Fe12O22 (BSZFO) and Ba0.5Sr1.5Zn2(Fe0.92Al0.08)12O22 (BSZFAO) were investigated by 57Fe nuclear magnetic resonance (NMR). The spin-canting angles of all NMR peaks were measured to assign each peak to corresponding Fe3+ sites. It was revealed that the spin-canting angle of Fe3+ ions at off-centered octahedra is fixed and Al3+ ions substitute for Fe3+ ions at those sites. The temperature dependence of the NMR frequency indicates that the low-temperature excitation is spin wave in ferromagnetic phase.

  6. Al doping effect on magnetic phase transitions of magnetoelectric hexaferrite Ba0.7Sr1.3Zn2(Fe1-xAlx)12O22

    NASA Astrophysics Data System (ADS)

    Chang, Hun; Lee, Hak Bong; Song, Young-Sang; Chung, Jae-Ho; Kim, S. A.; Oh, I. H.; Reehuis, M.; Schefer, J.

    2012-02-01

    We investigated the effect of Al doping in magnetic properties of the Y-type hexaferrite Ba0.7Sr1.3Zn2(Fe1-xAlx)12O22 (0≤x≤0.12), which exhibit field-induced magnetoelectric polarization. We find that Al doping increases the pitch of a spin helix and enhances c-axis magnetization, stabilizing longitudinal conical phases. These conical phases eventually collapse at x≥ 0.10. These results suggest that competitions between easy-axis and easy-plane anisotropy fields play a key role in generating stable magnetoelectric polarization in Y-type hexaferrites.

  7. Evolution of structure and magnetic properties for BaFe11.9Al0.1O19 hexaferrite in a wide temperature range

    NASA Astrophysics Data System (ADS)

    Trukhanov, A. V.; Trukhanov, S. V.; Panina, L. V.; Kostishyn, V. G.; Kazakevich, I. S.; Trukhanov, An. V.; Trukhanova, E. L.; Natarov, V. O.; Turchenko, V. A.; Salem, M. M.; Balagurov, A. M.

    2017-03-01

    M-type BaFe11.9Al0.1O19 hexaferrite was successfully synthesized by solid state reactions. Precision investigations of crystal and magnetic structures of BaFe11.9Al0.1O19 powder by neutron diffraction in the temperature range 4.2-730 K have been performed. Magnetic and electrical properties investigations were carried out in the wide temperature range. Neutron powder diffraction data were successfully refined in approximation for both space groups (SG): centrosymmetric #194 (standard non-polar phase) and non-centrosymmetric #186 (polar phase). It has been shown that at low temperatures (below room temperature) better fitting results (value χ2) were for the polar phase (SG: #186) or for the two phases coexistence (SG: #186 and SG: #194). At high temperatures (400-730 K) better fitting results were for SG: #194. It was established coexistence of the dual ferroic properties (specific magnetization and spontaneous polarization) at room temperature. Strong correlation between magnetic and electrical subsystems was demonstrated (magnetoelectrical effect). Temperature dependences of the spontaneous polarization, specific magnetization and magnetoelectrical effect were investigated.

  8. Effects of Al substitution and thermal annealing on magnetoelectric Ba0.5Sr1.5Zn2Fe12O22 investigated by the enhancement factor of 57Fe nuclear magnetic resonance.

    PubMed

    Kwon, Sangil; Kang, Byeongki; Kim, Changsoo; Jo, Euna; Lee, Soonchil; Chai, Yi Sheng; Chun, Sae Hwan; Kim, Kee Hoon

    2014-04-09

    The magnetoelectric properties of hexaferrite Ba0.5Sr1.5Zn2Fe12O22 are significantly improved by Al substitution and thermal annealing. Measuring the enhancement factor of 57Fe NMR, we found direct microscopic evidence that the magnetic moments of the L and S blocks are rotated by a magnetic field in such a way as to increase the net magnetic moment of a magnetic unit, even after the field is removed. Al substitution makes magnetoelectric property arise easily by suppressing the easy-plane anisotropy. The effect of thermal annealing is to stabilize the multiferroic state by reducing the number of pinning sites and the electron spin fluctuation. The transverse conic structure gradually changes to the alternating longitudinal conic structure where spins fluctuate more severely.

  9. Magnetic origin of giant magnetoelectricity in doped Y-type hexaferrite Ba(0.5)Sr(1.5)Zn(2)(Fe(1-x)Al(x))(12)O(22).

    PubMed

    Noh, Woo-Suk; Ko, Kyung-Tae; Chun, Sae Hwan; Kim, Kee Hoon; Park, Byeong-Gyu; Kim, Jae-Young; Park, Jae-Hoon

    2015-03-20

    We investigated site-specific magnetic behaviors of multiferroic Ba(0.5)Sr(1.5)Zn(2)(Fe(1-x)Al(x))(12)O(22) using Fe L(2,3)-edge x-ray magnetic circular dichroism. The Al dopants mostly replace the Fe(3+) ions at octahedral (O(h)) sites, which contribute unquenched angular momenta through off-centering displacements. This replacement greatly reduces the magnetic anisotropy energy to change the magnetic order from a helical to a heliconical type with enhanced magnetoelectric susceptibility (α(ME)). The tetrahedral (T(d)) Fe sites exhibit magnetic hysteresis distinguishable from that of the O(h) sites, especially at low magnetic fields. These results provide essential clues for the heliconical order with a giant α(ME) and multibit memory effects in the Al-doped Y-type hexaferrite.

  10. Magnetic structures and excitations in a multiferroic Y-type hexaferrite BaSrCo2Fe11AlO22

    DOE PAGES

    Nakajima, Taro; Tokunaga, Yusuke; Matsuda, Masaaki; ...

    2016-11-30

    Here, we have investigated magnetic orders and excitations in a Y-type hexaferrite BaSrCo2Fe11AlO22 (BSCoFAO), which was reported to exhibit spin-driven ferroelectricity at room temperature. By means of magnetization, electric polarization, and neutron-diffraction measurements using single-crystal samples, we establish a H-T magnetic phase diagram for magnetic field perpendicular to the c axis (H⟂c). This system exhibits an alternating longitudinal conical (ALC) magnetic structure in the ground state, and it turns into a non-co-planar commensurate magnetic order with spin-driven ferroelectricity under H⟂c. The field-induced ferroelectric phase remains as a metastable state after removing magnetic field below 250 K. This metastability is themore » key to understanding of magnetic field reversal of the spin-driven electric polarization in this system. Inelastic polarized neutron-scattering measurements in the ALC phase reveal a magnetic excitation at around 7.5 meV, which is attributed to spin components oscillating in a plane perpendicular to the cone axis. This phasonlike excitation is expected to be an electric-field active magnon, i.e., electromagnon excitation, in terms of the magnetostriction mechanism.« less

  11. Magnetic structures and excitations in a multiferroic Y-type hexaferrite BaSrCo2Fe11AlO22

    NASA Astrophysics Data System (ADS)

    Nakajima, Taro; Tokunaga, Yusuke; Matsuda, Masaaki; Dissanayake, Sachith; Fernandez-Baca, Jaime; Kakurai, Kazuhisa; Taguchi, Yasujiro; Tokura, Yoshinori; Arima, Taka-hisa

    2016-11-01

    We have investigated magnetic orders and excitations in a Y-type hexaferrite BaSrCo2Fe11AlO22 (BSCoFAO), which was reported to exhibit spin-driven ferroelectricity at room temperature [S. Hirose, K. Haruki, A. Ando, and T. Kimura, Appl. Phys. Lett. 104, 022907 (2014), 10.1063/1.4862432]. By means of magnetization, electric polarization, and neutron-diffraction measurements using single-crystal samples, we establish a H -T magnetic phase diagram for magnetic field perpendicular to the c axis (H⊥c). This system exhibits an alternating longitudinal conical (ALC) magnetic structure in the ground state, and it turns into a non-co-planar commensurate magnetic order with spin-driven ferroelectricity under H⊥c. The field-induced ferroelectric phase remains as a metastable state after removing magnetic field below ˜250 K. This metastability is the key to understanding of magnetic field reversal of the spin-driven electric polarization in this system. Inelastic polarized neutron-scattering measurements in the ALC phase reveal a magnetic excitation at around 7.5 meV, which is attributed to spin components oscillating in a plane perpendicular to the cone axis. This phasonlike excitation is expected to be an electric-field active magnon, i.e., electromagnon excitation, in terms of the magnetostriction mechanism.

  12. Preparation and characterization of (Ba,Cs)(M,Ti) 8O 16 (M = Al 3+, Fe 3+, Ga 3+, Cr 3+, Sc 3+, Mg 2+) hollandite ceramics developed for radioactive cesium immobilization

    NASA Astrophysics Data System (ADS)

    Aubin-Chevaldonnet, V.; Caurant, D.; Dannoux, A.; Gourier, D.; Charpentier, T.; Mazerolles, L.; Advocat, T.

    2007-06-01

    Among the different matrices proposed for selective and durable immobilization of radioactive cesium, (Ba x,Cs y)(M,Ti) 8O 16 hollandite ceramics, with x + y < 2 and M = divalent or trivalent cation appeared as the best candidates. In this study, hollandite ceramics were prepared using oxide route from oxide, carbonate and nitrate powders with and without Cs for different cations M (Al 3+, Cr 3+, Ga 3+, Fe 3+, Mg 2+, Sc 3+) of increasing size, in order to evaluate the effect of composition on ceramics microstructure and structure and on cesium incorporation. To reduce the risks of Cs vaporization during synthesis, calcined powders were sintered in air at moderate temperature (1200 °C). This oxide route appeared as an alternative to the alkoxide route generally proposed to prepare hollandite waste form. For y = 0, single phase Ba x(M,Ti) 8O 16 was obtained only for M 3+ = Al 3+, Cr 3+ and Fe 3+. For y ≠ 0 and Fe 3+, all cesium was incorporated in hollandite and ceramic was well densified. For Cr 3+ and Ga 3+, only 46% and 63%, respectively, of Cs were retained in hollandite phase. For these samples, a high fraction of Cs was either evaporated and/or concentrated in a Cs-rich parasitic phase. Mixed hollandite samples with M 3+ = Ga 3+ + Al 3+ and M 3+ = Fe 3+ + Al 3+ were also synthesized and the best results regarding Cs immobilization and ceramic density were obtained with iron + aluminum but the sample porosity was higher than that of the sample containing only iron. All results were discussed by considering cations size and refractory character of oxides and hollandite ceramics.

  13. Investigation of the crystal and magnetic structures of BaFe{sub 12-x}Al{sub x}O{sub 19} solid solutions (x = 0.1‒1.2)

    SciTech Connect

    Turchenko, V. A.; Trukhanov, A. V.; Bobrikov, I. A.; Trukhanov, S. V.; Balagurov, A. M.

    2015-09-15

    The structure of barium ferrite BaFe{sub 12-x}Al{sub x}O{sub 19} solid solutions (x = 0.1‒1.2) with iron partially replaced with diamagnetic aluminum ions has been studied by neutron diffraction. Experimental data have been collected at room temperature on a high-resolution diffractometer, which yielded precise information about the changes in the crystal and magnetic structures and data on the behavior of the sample microstructure. Barium hexaferrite retains a magnetoplumbite structure in the entire range of aluminum concentrations under study, and its magnetic structure is described within the Gorter model, with moments orientated along the hexagonal axis. The total magnetic moment per formula unit decreases while diamagnetic aluminum ions substitute for iron ions. Microstrains in crystallites increase with an increase in the diamagnetic ion concentration, which is related to the difference in the ionic radii of iron and aluminum ions.

  14. Magnetic field reversal of electric polarization and magnetoelectric phase diagram of the hexaferrite Ba1.3Sr0.7Co0.9Zn1.1Fe10.8Al1.2O22

    NASA Astrophysics Data System (ADS)

    Shen, Shipeng; Yan, Liqin; Chai, Yisheng; Cong, Junzhuang; Sun, Young

    2014-01-01

    Low magnetic field reversal of electric polarization has been demonstrated in the multiferroic Y-type hexaferrite Ba1.3Sr0.7Co0.9Zn1.1Fe10.8Al1.2O22 single crystal. The maximum magnetoelectric coefficient at 200 K reaches 1065 ps/m near zero magnetic field. By a systematic investigation of magnetic field dependence of magnetic and dielectric responses at various temperatures, we obtained the magnetoelectric phase diagram describing the detailed evolution of the spin-induced ferroelectric phases with temperature and magnetic field. Below 225 K, the transverse spin cone can be stabilized at zero magnetic field, which is responsible for the reversal behavior of electric polarization. Our study reveals how to eventually achieve magnetic field reversal of electric polarization in hexaferrites at room temperature.

  15. Magnetocaloric effect in multiferroic Y-type hexaferrite Ba0.5Sr1.5Zn2(Fe0.92Al0.08)12O22

    NASA Astrophysics Data System (ADS)

    Xu, Wenfei; Yang, Jing; Shen, Yude; Bai, Wei; Zhang, Yuanyuan; Liu, Jia; Tang, Kai; Wang, Zhi; Duan, Chun-gang; Tang, Xiaodong; Chu, Junhao

    2014-06-01

    Magnetocaloric effect is investigated in multiferroic Ba0.5Sr1.5Zn2(Fe0.92Al0.08)12O22 ceramic with Y-type hexagonal system. Three magnetic transitions, from alternating longitudinal conical to mixed conical at ˜240 K, to ferrimagnetic at ˜297 K, further to paramagnetic at ˜702 K, are unambiguously determined. Furthermore, obvious MCE is shown, and the maximum values of the magnetic entropy change and relative cooling power are evaluated to be 1.53 JKg-1K-1 and 280 JKg-1 for a field change of 7 T, respectively. In addition, inverse MCE is also observed, which might be associated with the first-order magnetic phase transition between two incommensurate longitudinal conical phases.

  16. Doping of the quadruple perovskites of type Nd 2Ba 2Cu 2Ti 2- xO xO 11,  Mn, Fe, Co, Al and NdBa 3Cu 2Ti 1+ xNb 1- xNb 1- xO 11

    NASA Astrophysics Data System (ADS)

    Rentschler, Thomas

    1997-02-01

    The synthesis of new ceramic materials NdBa 3Cu 2Ti 1+ xNb 1- xO 11 and Nd 2Ba 2Cu 2Ti 2- xM xO 11, M  Mn, Fe, Co, Al with a quadruple perovskite structure was successfully performed. Rietveld refinements verified the oxygen deficient layered a p ∗ a p ∗ 4a p superstructure (space group P4/mmm). Heterovalent doping in these groups of materials was carried out in order to provide a hole carrier concentration in the CuO 2 layers structurally related to the high- Tc superconductors. However, superconductivity was not observed. The formation of oxygen defects is discussed.

  17. Magnetoelectric effect in Fe-embedded BaTiO{sub 3} single crystal

    SciTech Connect

    Gupta, Arti; Chatterjee, Ratnamala

    2011-06-15

    In this work, we experimentally demonstrate the magnetoelectric effect in a multilayered structure of Fe-BaTiO{sub 3}-Fe, with 70 A BaTiO{sub 3} (BT) sandwiched between 2 layers of implanted Fe, which was further treated by swift heavy ion (Ag{sup +15}) induced ion beam mixing/annealing. Due to this specific experimental procedure, condition of atomic orbital overlap between the Fe and Ti atoms could be favored in Fe-implanted BT crystal, showing a magnetoelectric effect arising from interfacial bonding at Fe/BT interface, as proposed by Duan et al.[Phys. Rev. Lett. 97, 047201 (2006)]. Results are successfully interpreted in terms of magnetostriction behavior of polycrystalline Fe.

  18. Al substituted Ba ferrite films with high coercivity and excellent squareness for low noise perpendicular recording layer

    NASA Astrophysics Data System (ADS)

    Feng, J.; Matsushita, N.; Watanabe, K.; Nakagawa, S.; Naoe, M.

    1999-04-01

    Al substituted BaM (Al-BaM) ferrite films with composition of BaAlxFe12-xO19 (x=0,1,2) were deposited using facing targets sputtering apparatus on SiOx/Si wafers with a Pt seed layer. A postannealing process is necessary to crystallize the films. It was confirmed that the substrate temperature Ts is also one of the important parameters for the magnetic properties of the postannealed films. Al-BaM ferrite films exhibit the Ts dependence of magnetic properties different from that of simple BaM ones. With increase of the Al content x in Al-BaM ferrite films, 4πMs decreased, while Hc and the anisotropy field HA increased. It was found that acicular shape grains formed more easily in Al-BaM ferrite films than in simple BaM ones. The squareness S⊥ increased largely by substitution of Al for Fe. The Al-BaM ferrite films with high Hc⊥ (˜3 kOe) and large S⊥(˜0.9) may be applicable as perpendicular magnetic recording layers with low noise level.

  19. Al-Co-Fe (030)

    NASA Astrophysics Data System (ADS)

    Carow-Watamura, U.; Louzguine, D. V.; Takeuchi, A.

    This document is part of Part 1 http://dx.doi.org/10.1007/9getType="URL"/> 'Systems from Ag-Al-Ca to Au-Pd-Si' of Subvolume B 'Physical Properties of Ternary Amorphous Alloys' of Volume 37 'Phase Diagrams and Physical Properties of Nonequilibrium Alloys' of Landolt-Börnstein - Group III 'Condensed Matter'. It contains the Chapter 'Al-Co-Fe (030)' with the content:

  20. Heavy ion irradiations on synthetic hollandite-type materials: Ba1.0Cs0.3A2.3Ti5.7O16 (A=Cr, Fe, Al)

    NASA Astrophysics Data System (ADS)

    Tang, Ming; Tumurugoti, Priyatham; Clark, Braeden; Sundaram, S. K.; Amoroso, Jake; Marra, James; Sun, Cheng; Lu, Ping; Wang, Yongqiang; Jiang, Ying.-Bing.

    2016-07-01

    The hollandite supergroup of minerals has received considerable attention as a nuclear waste form for immobilization of Cs. The radiation stability of synthetic hollandite-type compounds described generally as Ba1.0Cs0.3A2.3Ti5.7O16 (A=Cr, Fe, Al) were evaluated by heavy ion (Kr) irradiations on polycrystalline single phase materials and multiphase materials incorporating the hollandite phases. Ion irradiation damage effects on these samples were examined using grazing incidence X-ray diffraction (GIXRD) and transmission electron microscopy (TEM). Single phase compounds possess tetragonal structure with space group I4/m. GIXRD and TEM observations revealed that 600 keV Kr irradiation-induced amorphization on single phase hollandites compounds occurred at a fluence between 2.5×1014 Kr/cm2 and 5×1014 Kr/cm2. The critical amorphization fluence of single phase hollandite compounds obtained by in situ 1 MeV Kr ion irradiation was around 3.25×1014 Kr/cm2. The hollandite phase exhibited similar amorphization susceptibility under Kr ion irradiation when incorporated into a multiphase system.

  1. Magnetic structure and effect of magnetic field on its domain structure in magnetoelectric Ba1.3Sr0.7CoZnFe11AlO22

    NASA Astrophysics Data System (ADS)

    Ueda, H.; Tanaka, Y.; Nakajima, H.; Mori, S.; Ohta, K.; Haruki, K.; Hirose, S.; Wakabayashi, Y.; Kimura, T.

    2016-10-01

    The magnetic structure and the effect of a magnetic field on its domain structure were investigated in a magnetoelectric Y-type hexaferrite, Ba1.3Sr0.7CoZnFe11AlO22, by means of mapping with a micro-focused and circularly polarized X-ray beam in the resonant X-ray diffraction. It was revealed that this hexaferrite exhibits a magnetic order characterized by two distinct antiferromagnetic components: incommensurate helical and commensurate collinear ones, which can be explained as the development of the so-called alternating longitudinal conical structure. A multi-domain state due to the handedness of the helical component, i.e., spin-chirality, is transformed into nearly a mono-domain one by using only a magnetic field. Furthermore, the sign of the spin-chirality in the mono-domain state is reversed by reversing the sign of a magnetic field. These results demonstrate that the spin-chirality in this hexaferrite can be manipulated by a magnetic field alone at room temperature.

  2. Strain induced superconductivity in the parent compound BaFe2As2.

    PubMed

    Engelmann, J; Grinenko, V; Chekhonin, P; Skrotzki, W; Efremov, D V; Oswald, S; Iida, K; Hühne, R; Hänisch, J; Hoffmann, M; Kurth, F; Schultz, L; Holzapfel, B

    2013-01-01

    The discovery of superconductivity with a transition temperature, Tc, up to 65 K in single-layer FeSe (bulk Tc=8 K) films grown on SrTiO3 substrates has attracted special attention to Fe-based thin films. The high Tc is a consequence of the combined effect of electron transfer from the oxygen-vacant substrate to the FeSe thin film and lattice tensile strain. Here we demonstrate the realization of superconductivity in the parent compound BaFe2As2 (no bulk Tc) just by tensile lattice strain without charge doping. We investigate the interplay between strain and superconductivity in epitaxial BaFe2As2 thin films on Fe-buffered MgAl2O4 single crystalline substrates. The strong interfacial bonding between Fe and the FeAs sublattice increases the Fe-Fe distance due to the lattice misfit, which leads to a suppression of the antiferromagnetic spin density wave and induces superconductivity with bulk Tc≈10 K. These results highlight the role of structural changes in controlling the phase diagram of Fe-based superconductors.

  3. Antiferromagnetic Critical Fluctuations in BaFe$_2$As$_2$

    SciTech Connect

    Wilson, Stephen D; Yamani, Z.; Rotundu, C. R.; Freelon, B.; Valdivia, P. N.; Bourret-Courchesne, E. D.; Lynn, J W; Chi, Songxue; Hong, Tao; Birgeneau, R. J.

    2010-01-01

    Magnetic correlations near the magnetostructural phase transition in the bilayer iron-pnictide parent compound, BaFe{sub 2}As{sub 2}, are measured. In close proximity to the antiferromagnetic phase transition in BaFe{sub 2}As{sub 2}, a crossover to three-dimensional critical behavior is anticipated and has been preliminarily observed. Here we report complementary measurements of two-dimensional magnetic fluctuations over a broad temperature range about T{sub N}. The potential role of two-dimensional critical fluctuations in the magnetic phase behavior of BaFe{sub 2}As{sub 2} and their evolution near the anticipated crossover to three-dimensional critical behavior and long-range order are discussed.

  4. Frustration of Negative Capacitance in Al2O3/BaTiO3 Bilayer Structure

    NASA Astrophysics Data System (ADS)

    Kim, Yu Jin; Park, Min Hyuk; Lee, Young Hwan; Kim, Han Joon; Jeon, Woojin; Moon, Taehwan; Do Kim, Keum; Jeong, Doo Seok; Yamada, Hiroyuki; Hwang, Cheol Seong

    2016-01-01

    Enhancement of capacitance by negative capacitance (NC) effect in a dielectric/ferroelectric (DE/FE) stacked film is gaining a greater interest. While the previous theory on NC effect was based on the Landau-Ginzburg-Devonshire theory, this work adopted a modified formalism to incorporate the depolarization effect to describe the energy of the general DE/FE system. The model predicted that the SrTiO3/BaTiO3 system will show a capacitance boost effect. It was also predicted that the 5 nm-thick Al2O3/150 nm-thick BaTiO3 system shows the capacitance boost effect with no FE-like hysteresis behavior, which was inconsistent with the experimental results; the amorphous-Al2O3/epitaxial-BaTiO3 system showed a typical FE-like hysteresis loop in the polarization – voltage test. This was due to the involvement of the trapped charges at the DE/FE interface, originating from the very high field across the thin Al2O3 layer when the BaTiO3 layer played a role as the NC layer. Therefore, the NC effect in the Al2O3/BaTiO3 system was frustrated by the involvement of reversible interface charge; the highly stored charge by the NC effect of the BaTiO3 during the charging period could not be retrieved during the discharging process because integral part of the polarization charge was retained within the system as a remanent polarization.

  5. Frustration of Negative Capacitance in Al2O3/BaTiO3 Bilayer Structure.

    PubMed

    Kim, Yu Jin; Park, Min Hyuk; Lee, Young Hwan; Kim, Han Joon; Jeon, Woojin; Moon, Taehwan; Kim, Keum Do; Jeong, Doo Seok; Yamada, Hiroyuki; Hwang, Cheol Seong

    2016-01-08

    Enhancement of capacitance by negative capacitance (NC) effect in a dielectric/ferroelectric (DE/FE) stacked film is gaining a greater interest. While the previous theory on NC effect was based on the Landau-Ginzburg-Devonshire theory, this work adopted a modified formalism to incorporate the depolarization effect to describe the energy of the general DE/FE system. The model predicted that the SrTiO3/BaTiO3 system will show a capacitance boost effect. It was also predicted that the 5 nm-thick Al2O3/150 nm-thick BaTiO3 system shows the capacitance boost effect with no FE-like hysteresis behavior, which was inconsistent with the experimental results; the amorphous-Al2O3/epitaxial-BaTiO3 system showed a typical FE-like hysteresis loop in the polarization - voltage test. This was due to the involvement of the trapped charges at the DE/FE interface, originating from the very high field across the thin Al2O3 layer when the BaTiO3 layer played a role as the NC layer. Therefore, the NC effect in the Al2O3/BaTiO3 system was frustrated by the involvement of reversible interface charge; the highly stored charge by the NC effect of the BaTiO3 during the charging period could not be retrieved during the discharging process because integral part of the polarization charge was retained within the system as a remanent polarization.

  6. Rapidly solidified NiAl and FeAl

    NASA Technical Reports Server (NTRS)

    Gaydosh, D. J.; Crimp, M. A.

    1984-01-01

    Melt spinning was used to produce rapidly solidified ribbons of the B2 intermetallics NiAl and FeAl. Both Fe-40Al and Fe-45Al possessed some bend ductility in the as spun condition. The bend ductility of Fe-40Al, Fe-45Al, and equiatomic NiAl increased with subsequent heat treatment. Heat treatment at approximately 0.85 T (sub m) resulted in significant grain growth in equiatomic FeAl and in all the NiAl compositions. Low bend ductility in both FeAl and NiAl generally coincided with intergranular failure, while increased bend ductility was characterized by increasing amounts of transgranular cleavage fracture.

  7. Light Sensitive Lattice Defects In BaTiO3 Containing Fe

    NASA Astrophysics Data System (ADS)

    Possenriede, Ewald; Schirmer, Ortwin F.; Godefroy, Genevieve; Maillard, Alain

    1989-01-01

    Electron spin resonance spectra, which can consistently be explained by the models Fe4+ - Vo and Fe5+ - vBa, have been observed with BaTiO3 containing Fe. Also Fe3+ and - Fe3+ - Vo have been identified. All these centers as well as several unidentified ones are observed to change their charge states under illumination. They thus are possibly in involved in photorefractive processes in BaTiO3 containing Fe.

  8. Crystal chemical aspects of superconductivity in BaFe2As2 and related compounds

    NASA Astrophysics Data System (ADS)

    Johrendt, Dirk

    2010-03-01

    BaFe2As2 is the parent compound of the 122-type iron arsenides.^1 Superconductivity can be induced by several kinds of doping^2-4 or by pressure.^5 It is widely accepted that superconductivity in iron arsenides is unconventional and a number of experiments agree with the s±-scenario.^6 The latter relies on Fermi surface nesting which depends on both the electron count and the lattice. However, the coincidence of doping and pressure effects on the structure of BaFe2As2 supports the role of the structure.^7 Another open issue is the co-existence of superconductivity and AF magnetic ordering. Our ^57Fe-M"ossbauer experiments with underdoped Ba0.8K0.2Fe2As2 (Tc = 24 K) revealed full magnetic splitting, which indicates such a co-existence.^8 Compounds like Sr2VO3FeAs (Tc = 37-45 K) are promising candidates for higher Tc, but their crystal chemistry is not yet understood. In non-superconducting Sr2CrO3FeAs, we have detected a non-stoichiometry of the Fe-site (Fe0.93(1)Cr0.07(1)) and C-type AF ordering of the Cr^3+-layers.^9 The Cr-doping of the FeAs layer is probably detrimental to superconductivity in Sr2CrO3FeAs, but a similar non-stoichiometry may play a vital role in Sr2VO3FeAs.-^1 M. Rotter, M. Tegel, I. Schellenberg, et al., Phys. Rev. B 78, 020503 (2008).^2 M. Rotter, M. Tegel, and D. Johrendt, Phys. Rev. Lett. 101, 107006 (2008).^3 S. Jiang, C. Wang, Z. Ren, et al., J. Phys.: Condens. Matter 21, 382203 (2009).^4 A. S. Sefat, R. Jin, M. A. McGuire, et al., Phys. Rev. Lett. 101, 117004 (2008).^5 P. L. Alireza, Y. T. C. Ko, J. Gillett, et al., J. Phys.: Condens. Matter 21, 012208 (2009).^6 I. Mazin, D. J. Singh, M. D. Johannes, et al., Phys. Rev. Lett. 101, 057003 (2008).^7 M. Rotter, M. Pangerl, M. Tegel, et al., Angew. Chem. Int. Ed. 47, 7949 (2008).^8 M. Rotter, M. Tegel, I. Schellenberg, et al., New J. Phys. 11, 025014 (2009).^9 M. Tegel, Y. Su, F. Hummel, et al., arXiv0911.0450.

  9. Synthesis, structural and magnetic characterisation of the fluorinated compound 15R-BaFeO{sub 2}F

    SciTech Connect

    Clemens, Oliver; Berry, Frank J.; Bauer, Jessica; Wright, Adrian J.; Knight, Kevin S.; Slater, Peter R.

    2013-07-15

    The compounds 15R-BaFeO{sub 2}F and 15R-BaFeO{sub 2.27}F{sub 0.5} have been synthesised by the low temperature fluorination of 15R-BaFeO{sub 3−d}F{sub 0.2} using polyvinylidenedifluoride (PVDF) as a fluorination agent. The materials have been structurally characterised by Rietveld analysis of the X-ray- and HRPD-powder neutron diffraction data. A detailed analysis of bond valence sums suggests that the oxide and fluoride ions order on the different anion sites. A reinvestigation of our recently published structure (Clemens et al., 2013) [34] of 6H-BaFeO{sub 2}F is also reported and incorporation of fluoride in h-type layers is also confirmed in this compound. The magnetic moments for 15R-BaFeO{sub 2}F and 15R-BaFeO{sub 2.25}F{sub 0.5} align in the a/b-plane with antiferromagnetic alignment of the moments between adjacent layers, and are flipped by 90° as compared to the precursor compound. 15R-BaFeO{sub 2}F exhibits very robust antiferromagnetism with a Néel temperature between 300 and 400 °C. - Graphical abstract: The crystal and magnetic structure of the perovskite phase 15R-BaFeO{sub 2}F. - Highlights: • 15R-BaFeO{sub 2}F and 15R-BaFeO{sub 2.27}F{sub 0.5}were prepared via low temperature fluorination using PVDF. • A structural investigation of the compounds BaFeO{sub 2}F is presented in detail. • This analysis suggests ordering of O{sup 2−} and F{sup −} anions between different layers. • 15R-BaFeO{sub 2}F shows antiferromagnetic ordering at 300 K with T{sub N} ∼300–400 °C. • The magnetic moments align in the a/b-plane.

  10. Innovative methodology for the synthesis of Ba-M hexaferrite BaFe{sub 12}O{sub 19} nanoparticles

    SciTech Connect

    Ahmed, M.A.; Helmy, N.; El-Dek, S.I.

    2013-09-01

    Graphical abstract: Transmission electron microscope images for the BaFe12O19. - Highlights: • BaFe{sub 12}O{sub 19}nanoparticles were prepared in single-phase from organometallic precursors. • BaFe{sub 12}O{sub 19} possesses small size 65 nm, H{sub C} = 3695 Oe and M{sub s} = 58 emu/g. • This method of preparation could be extended in the synthesis of other metal oxide nanoparticles. - Abstract: In this piece of work, high quality and homogeneity, barium hexaferrite (BaM) BaFe{sub 12}O{sub 19} nanoparticles were prepared from organometallic precursors for the 1st time. This method is based on the formation of supramolecular crystal structure of Ba[Fe(H{sub 3}NCH{sub 2}CH{sub 2}NH{sub 3})]Cl{sub 7}·8H{sub 2}O. The crystal structure, morphology and magnetic properties of BaFe{sub 12}O{sub 19} at two different annealing temperatures namely 1000 °C and 1200 °C were investigated using X-ray diffraction, transmission electron microscope TEM and vibrating sample magnetometry (VSM). The results show that monophasic nanoparticles of hexaferrites were obtained. Nanoparticles of crystallite size 40–50 nm distinguished by narrow distribution and excellent homogeneity were obtained with superior magnetic properties which suggested single-domain particles of Ba-M hexaferrite.

  11. High field nuclear magnetic resonance in transition metal substituted BaFe2As2

    NASA Astrophysics Data System (ADS)

    Garitezi, T. M.; Lesseux, G. G.; Rosa, P. F. S.; Adriano, C.; Reyes, A. P.; Kuhns, P. L.; Pagliuso, P. G.; Urbano, R. R.

    2014-05-01

    We report high field 75As nuclear magnetic resonance (NMR) measurements on Co and Cu substituted BaFe2As2 single crystals displaying same structural/magnetic transition T0≃128 K. From our anisotropy studies in the paramagnetic state, we strikingly found virtually identical quadrupolar splitting and consequently the quadrupole frequency νQ≃2.57(1) MHz for both compounds, despite the claim that each Cu delivers 2 extra 3d electrons in BaFe2As2 compared to Co substitution. These results allow us to conclude that a subtle change in the crystallographic structure, particularly in the Fe-As tetrahedra, must be the most probable tuning parameter to determine T0 in this class of superconductors rather than electronic doping. Furthermore, our NMR data around T0 suggest coexistence of tetragonal/paramagnetic and orthorhombic/antiferromagnetic phases between the structural and the spin density wave magnetic phase transitions, similarly to what was reported for K-doped BaFe2As2 [Urbano et al., Phys. Rev. Lett. 105, 107001 (2010)].

  12. Orientation relationship of eutectoid FeAl and FeAl2

    PubMed Central

    Scherf, A.; Kauffmann, A.; Kauffmann-Weiss, S.; Scherer, T.; Li, X.; Stein, F.; Heilmaier, M.

    2016-01-01

    Fe–Al alloys in the aluminium range of 55–65 at.% exhibit a lamellar microstructure of B2-ordered FeAl and triclinic FeAl2, which is caused by a eutectoid decomposition of the high-temperature Fe5Al8 phase, the so-called ∊ phase. The orientation relationship of FeAl and FeAl2 has previously been studied by Bastin et al. [J. Cryst. Growth (1978 ▸), 43, 745] and Hirata et al. [Philos. Mag. Lett. (2008 ▸), 88, 491]. Since both results are based on different crystallographic data regarding FeAl2, the data are re-evaluated with respect to a recent re-determination of the FeAl2 phase provided by Chumak et al. [Acta Cryst. (2010 ▸), C66, i87]. It is found that both orientation relationships match subsequent to a rotation operation of 180° about a 〈112〉 crystallographic axis of FeAl or by applying the inversion symmetry of the FeAl2 crystal structure as suggested by the Chumak data set. Experimental evidence for the validity of the previously determined orientation relationships was found in as-cast fully lamellar material (random texture) as well as directionally solidified material (∼〈110〉FeAl || solidification direction) by means of orientation imaging microscopy and global texture measurements. In addition, a preferential interface between FeAl and FeAl2 was identified by means of trace analyses using cross sectioning with a focused ion beam. On the basis of these habit planes the orientation relationship between the two phases can be described by (01)FeAl || (114) and [111]FeAl || [10]. There is no evidence for twinning within FeAl lamellae or alternating orientations of FeAl lamellae. Based on the determined orientation and interface data, an atomistic model of the structure relationship of Fe5Al8, FeAl and FeAl2 in the vicinity of the eutectoid decomposition is derived. This model is analysed with respect to the strain which has to be accommodated at the interface of FeAl and FeAl2. PMID:27047304

  13. Superconductivity in Al-substituted Ba8Si46 clathrates

    NASA Astrophysics Data System (ADS)

    Li, Yang; Garcia, Jose; Chen, Ning; Liu, Lihua; Li, Feng; Wei, Yuping; Bi, Shanli; Cao, Guohui; Feng, Z. S.

    2013-05-01

    There is a great deal of interest vested in the superconductivity of Si clathrate compounds with sp3 network, in which the structure is dominated by strong covalent bonds among silicon atoms, rather than the metallic bonding that is more typical of traditional superconductors. A joint experimental and theoretical investigation of superconductivity in Al-substituted type-I silicon clathrates is reported. Samples of the general formula Ba8Si46-xAlx, with different values of x were prepared. With an increase in the Al composition, the superconducting transition temperature TC was observed to decrease systematically. The resistivity measurement revealed that Ba8Si42Al4 is superconductive with transition temperature at TC = 5.5 K. The magnetic measurements showed that the bulk superconducting Ba8Si42Al4 is a type II superconductor. For x = 6 sample Ba8Si40Al6, the superconducting transition was observed down to TC = 4.7 K which pointed to a strong suppression of superconductivity with increasing Al content as compared with TC = 8 K for Ba8Si46. Suppression of superconductivity can be attributed primarily to a decrease in the density of states at the Fermi level, caused by reduced integrity of the sp3 hybridized networks as well as the lowering of carrier concentration. These results corroborated by first-principles calculations showed that Al substitution results in a large decrease of the electronic density of states at the Fermi level, which also explains the decreased superconducting critical temperature within the BCS framework. The work provided a comprehensive understanding of the doping effect on superconductivity of clathrates.

  14. Preparation and microwave absorption property of graphene/BaFe12O19/CoFe2O4 nanocomposite

    NASA Astrophysics Data System (ADS)

    Yang, Haibo; Ye, Ting; Lin, Ying; Liu, Miao

    2015-12-01

    The graphene/BaFe12O19/CoFe2O4 nanocomposite powders were successfully synthesized by a deoxidation technique. The phase composition, morphology and electromagnetic properties of the nanocomposites were characterized by various instruments. The as-prepared graphene/BaFe12O19/CoFe2O4 nanocomposite exhibits a saturated magnetization of 50.42 emu/g. The electromagnetic parameters of graphene/BaFe12O19/CoFe2O4 nanocomposite were investigated in the 2-18 GHz range. The graphene/BaFe12O19/CoFe2O4 nanocomposite exhibits better microwave absorbing properties than BaFe12O19/CoFe2O4 nanocomposite. The excellent microwave absorbing property is achieved and the minimum reflection loss of the nanocomposite can reach -32.4 dB, which is obviously enhanced compared with that of the BaFe12O19/CoFe2O4 nanocomposite.

  15. Growth of single crystals of BaFe12O19 by solid state crystal growth

    NASA Astrophysics Data System (ADS)

    Fisher, John G.; Sun, Hengyang; Kook, Young-Geun; Kim, Joon-Seong; Le, Phan Gia

    2016-10-01

    Single crystals of BaFe12O19 are grown for the first time by solid state crystal growth. Seed crystals of BaFe12O19 are buried in BaFe12O19+1 wt% BaCO3 powder, which are then pressed into pellets containing the seed crystals. During sintering, single crystals of BaFe12O19 up to ∼130 μm thick in the c-axis direction grow on the seed crystals by consuming grains from the surrounding polycrystalline matrix. Scanning electron microscopy-energy dispersive spectroscopy analysis shows that the single crystal and the surrounding polycrystalline matrix have the same chemical composition. Micro-Raman scattering shows the single crystal to have the BaFe12O19 structure. The optimum growth temperature is found to be 1200 °C. The single crystal growth behavior is explained using the mixed control theory of grain growth.

  16. Preparation and microwave properties of lamellar Fe/BaFeO2.5 composite particles with hydrogen-thermal reduction method

    NASA Astrophysics Data System (ADS)

    Gong, Yuanxun; Zhou, Zhongxiang; Jiang, Jiantang; Zhao, Hongjie

    2016-06-01

    Fe/BaFeO2.5 laminated composite particles were successfully prepared by hydrogen-thermal reducing BaFe12O19 particles. The average diameter of Fe/BaFeO2.5 composite particles is about 1 μm and the lamellar thickness is about 100 nm. The effective permittivity and permeability of Fe/BaFeO2.5 laminated composite particles were measured and EMA performance was evaluated. Compared with Fe particles with a similar diameter, the permeability of Fe/BaFeO2.5 composite particles is remarkably improved by the induction of insulator BaFeO2.5 phase. Due to the unique 2-dimension shape characteristic, ε‧ and μ‧ of Fe/BaFeO2.5 laminated composite particles is obviously higher than that of Fe/BaFeO2.5 composite particles without lamellar structure. EMA performance of coating containing Fe/BaFeO2.5 laminated composite particles as fillers is excellent, and a maximum reflection loss (RLmax) up to -29.94 dB was achieved in a coating of 1.36 mm. Meanwhile, the operation frequency band of coating containing Fe/BaFeO2.5 laminated composite particles as fillers covers completely X-band and Ku-band, which considerably wider than most of reported EMA coatings.

  17. Mechanism of thermal decomposition of K2FeO4 and BaFeO4: A review

    NASA Astrophysics Data System (ADS)

    Sharma, Virender K.; Machala, Libor

    2016-12-01

    This paper presents thermal decomposition of potassium ferrate(VI) (K2FeO4) and barium ferrate(VI) (BaFeO4) in air and nitrogen atmosphere. Mössbauer spectroscopy and nuclear forward scattering (NFS) synchrotron radiation approaches are reviewed to advance understanding of electron-transfer processes involved in reduction of ferrate(VI) to Fe(III) phases. Direct evidences of Fe V and Fe IV as intermediate iron species using the applied techniques are given. Thermal decomposition of K2FeO4 involved Fe V, Fe IV, and K3FeO3 as intermediate species while BaFeO3 (i.e. Fe IV) was the only intermediate species during the decomposition of BaFeO4. Nature of ferrite species, formed as final Fe(III) species, of thermal decomposition of K2FeO4 and BaFeO4 under different conditions are evaluated. Steps of the mechanisms of thermal decomposition of ferrate(VI), which reasonably explained experimental observations of applied approaches in conjunction with thermal and surface techniques, are summarized.

  18. Ultrafast structural dynamics of the Fe-pnictide parent compound BaFe(2)As(2).

    PubMed

    Rettig, L; Mariager, S O; Ferrer, A; Grübel, S; Johnson, J A; Rittmann, J; Wolf, T; Johnson, S L; Ingold, G; Beaud, P; Staub, U

    2015-02-13

    Using femtosecond time-resolved x-ray diffraction we investigate the structural dynamics of the coherently excited A(1g) phonon mode in the Fe-pnictide parent compound BaFe(2)As(2). The fluence dependent intensity oscillations of two specific Bragg reflections with distinctly different sensitivity to the pnictogen height in the compound allow us to quantify the coherent modifications of the Fe-As tetrahedra, indicating a transient increase of the Fe magnetic moments. By a comparison with time-resolved photoemission data, we derive the electron-phonon deformation potential for this particular mode. The value of Δμ/Δz=-(1.0-1.5)  eV/Å is comparable with theoretical predictions and demonstrates the importance of this degree of freedom for the electron-phonon coupling in the Fe pnictides.

  19. Crystal Structures at Atomic Resolution of the Perovskite-Related GdBaMnFeO5 and Its Oxidized GdBaMnFeO6.

    PubMed

    García-Martín, Susana; Manabe, Keisuke; Urones-Garrote, Esteban; Ávila-Brande, David; Ichikawa, Noriya; Shimakawa, Yuichi

    2017-02-06

    Perovskite-related GdBaMnFeO5 and the corresponding oxidized phase GdBaMnFeO6, with long-range layered-type ordering of the Ba and Gd atoms have been synthesized. Oxidation retains the cation ordering but drives a modulation of the crystal structure associated with the incorporation of the oxygen atoms between the Gd layers. Oxidation of GdBaMnFeO5 increases the oxidation state of Mn from 2+ to 4+, while the oxidation state of Fe remains 3+. Determination of the crystal structure of both GdBaMnFeO5 and GdBaMnFeO6 is carried out at atomic resolution by means of a combination of advanced transmission electron microscopy techniques. Crystal structure refinements from synchrotron X-ray diffraction data support the structural models proposed from the TEM data. The oxidation states of the Mn and Fe atoms are evaluated by means of EELS and Mössbauer spectroscopy, which also reveals the different magnetic behavior of these oxides.

  20. Structure and physical properties of Fe6 O8/ba Fe6 O11 nanostructure

    NASA Astrophysics Data System (ADS)

    Naseri, Mahmoud; Ghasemi, Rahmat

    2016-05-01

    The thermal treatment method was employed to prepare barium hexaferrite (Fe6 O8/Ba Fe6 O11) nanostructure. This method was attempted to achieve higher homogeneity of the final product. Specimens of barium hexaferrite nanostructure were characterized by various experimental techniques including X-ray diffraction (XRD), high resolution Field emission scanning electron microscope (FESEM) and Fourier transform infrared spectroscopy (FT-IR). X-ray diffraction results showed that there was no crystallinity in the predecessor and it had still amorphous phase. The formations of crystalline phases of barium hexaferrite nanostructures started from 673 to 973 K and the final products had different crystallite sizes ranging from 29 to 48 nm. The chemical analysis of the barium hexaferrite nanostructures was performed by energy dispersion X-ray analysis (EDXA), demonstrated that the barium hexaferrite nanostructures contained the elements of Ba, Fe, and O. The effect of calcination temperature on band gap energy was studied by UV-vis absorption spectra disclosed when calcination temperature increased, the appraised band gap energy values of the BaFe12O19 nanostructures decreased. The formed nanostructures exhibited ferromagnetic behaviors which were confirmed by using a vibrating sample magnetometer (VSM). The technique of the Electron paramagnetic resonance (EPR) spectroscopy was carried out at 300 K on the calcined specimens that exhibited the variation of the line-shapes of the spectra of with calcination temperature.

  1. Tetragonal magnetostriction and magnetoelastic coupling in Fe-Al, Fe-Ga, Fe-Ge, Fe-Si, Fe-Ga-Al, and Fe-Ga-Ge alloys

    NASA Astrophysics Data System (ADS)

    Restorff, J. B.; Wun-Fogle, M.; Hathaway, K. B.; Clark, A. E.; Lograsso, T. A.; Petculescu, G.

    2012-01-01

    This paper presents a comparative study on the tetragonal magnetostriction constant, λγ,2, [ = (3/2)λ100] and magnetoelastic coupling, b1, of binary Fe100-xZx (0 < x < 35, Z = Al, Ga, Ge, and Si) and ternary Fe-Ga-Al and Fe-Ga-Ge alloys. The quantities are corrected for magnetostrains due to sample geometry (the magnetostrictive form effect). Recently published elastic constant data along with magnetization measurements at both room temperature and 77 K make these corrections possible. The form effect correction lowers the magnetostriction by ˜10 ppm for high-modulus alloys and by as much as 30 ppm for low-modulus alloys. The elastic constants are also used to determine the values of the magnetoelastic coupling constant, b1. With the new magnetostriction data on the Fe-Al-Ga alloy, it is possible to show how the double peak magnetostriction feature of the binary Fe-Ga alloy flows into the single peak binary Fe-Al alloy. The corrected magnetostriction and magnetoelastic coupling data for the various alloys are also compared using the electron-per-atom ratio, e/a, as the common variable. The Hume-Rothery rules link the e/a ratio to the regions of phase stability, which appear to be intimately related to the magnetostriction versus the solute concentration curve in these alloys. Using e/a as the abscissa tends to align the peaks in the magnetostriction and magnetoelastic coupling for the Fe-Ga, Fe-Ge, Fe-Al, Fe-Ga-Al, and Fe-Ga-Ge alloys, but not for the Fe-Si alloys for which the larger atomic size difference may play a greater role in phase stabilization. Corrections for the form effect are also presented for the rhombohedral magnetostriction, λɛ,2, and the magnetoelastic coupling, b2, of Fe100-xGax (0 < x < 35) alloys.

  2. Site-related near-infrared luminescence in MAl{sub 12}O{sub 19} (M = Ca, Sr, Ba):Fe{sup 3+} phosphors

    SciTech Connect

    Li, Y.J.; Ma, Y.Y.; Ye, S.; Hu, G.P.; Zhang, Q.Y.

    2014-03-01

    Graphical abstract: - Highlights: • Intense 700–850 nm NIR emissions in MAl{sub 12}O{sub 19} (M = Ca, Sr, Ba):1%Fe{sup 3+} has been obtained. • The NIR emissions can be ascribed to the octahedral Fe{sup 3+} sites. • The site symmetry of Fe{sup 3+} in CA{sub 6} and SA{sub 6} may be lower than that in BA{sub 6}. • The phosphors may be potentially applied in the high-resolution bioimaging. - Abstract: Intense and broad near-infrared (NIR) photoluminescence (PL) peaks locating at 777, 808 and 810 nm is observed for BaAl{sub 12}O{sub 19} (BA{sub 6}):1%Fe{sup 3+}, CaAl{sub 12}O{sub 19} (CA{sub 6}):1%Fe{sup 3+} and SrAl{sub 12}O{sub 19} (SA{sub 6}):1%Fe{sup 3+}, respectively. Electron paramagnetic resonance (EPR) spectra show that Fe{sup 3+} ions substitute for the different types of Al{sup 3+} sites simultaneously. Meanwhile, the luminescence of Fe{sup 3+} in MAl{sub 12}O{sub 19} (M = Ca, Sr and Ba) are ascribed to octahedral Fe{sup 3+}. In addition, the site symmetry of Fe{sup 3+} in CA{sub 6}/SA{sub 6} is lower compared with BA{sub 6}, deduced from the photoluminescence excitation (PLE), EPR and Fourier-transform infrared (FT-IR) spectra. These phosphors can be considered as good candidates for the applications in the field of high-resolution bioimaging.

  3. Superconductivity in noncentrosymmetric BaAl4 derived structures

    NASA Astrophysics Data System (ADS)

    Kneidinger, F.; Salamakha, L.; Bauer, E.; Zeiringer, I.; Rogl, P.; Blaas-Schenner, C.; Reith, D.; Podloucky, R.

    2014-07-01

    Ternary intermetallics Ep-T-X, crystallizing in ordered variants of the BaAl4 structure type, have been investigated systematically with respect to their formation and stability. For this, a comprehensive overview of the BaAl4 derivative structure types including group-subgroup relations was established. Special emphasis was laid on compounds where inversion symmetry is missing in the respective crystal structures and where superconductivity is observed at low temperatures. EpTX3 compounds crystallize in the noncentrosymmetric BaNiSn3 structure type (space-group I4mm; a ≈0.4 and c ≈1 nm), an ordered ternary derivative of BaAl4. Superconductivity below 3 K was found for seven members of this series, as evidenced from heat capacity and electrical resistivity measurements. Although the Rashba-like spin-orbit coupling in noncentrosymmetric systems can enable a mixture of spin-singlet and spin-triplet pairs in the superconducting condensate, the experimental data basically indicate a predominant s-wave superconducting state in all of these compounds. For this family of compounds, fully relativistic density functional theory (DFT) calculations of the electronic structure and phonon properties were done. Despite the different size of spin-orbit coupling depending on the actual choice of elements for Ep, T, and X that result in different spin-orbit splittings of the Fermi surfaces, the experimental observation of a prevalent spin-singlet pairing in the superconducting phases of the EpTX3 compounds is supported.

  4. The Structural Disorder and Lattice Stability of (Ba,Sr)(Co,Fe)O3 Complex Perovskites

    SciTech Connect

    S.N.Rashkeev

    2011-05-01

    The structural disorder and lattice stability of complex perovskite (Ba,Sr)(Co,Fe)O3, a promising cathode material for solid oxide fuel cells and oxygen permeation membranes, is explored by means of first principles DFT calculations. It is predicted that Ba and Sr ions easily exchange their lattice positions (A-cation disorder) similarly to Co and Fe ions (B-cation disorder). The cation antisite defects (exchange of A- and B-type cations) have a relatively high formation energy. The BSCF is predicted to exist in an equilibrium mixture of several phases and can decompose exothermically into the Ba- and Co-rich hexagonal (Ba,Sr)CoO3 and Sr- and Fe-rich cubic (Ba,Sr)FeO3 perovskites.

  5. Antiperovskite Chalco-Halides Ba3(FeS4)Cl, Ba3(FeS4)Br, and Ba3(FeSe4)Br with Spin Super-Super Exchange

    PubMed Central

    Zhang, Xian; Liu, Kai; He, Jian-Qiao; Wu, Hui; Huang, Qing-Zhen; Lin, Jian-Hua; Lu, Zhong-Yi; Huang, Fu-Qiang

    2015-01-01

    Perovskite-related materials have received increasing attention for their broad applications in photovoltaic solar cells and information technology due to their unique electrical and magnetic properties. Here we report three new antiperovskite chalco-halides: Ba3(FeS4)Cl, Ba3(FeS4)Br, and Ba3(FeSe4)Br. All of them were found to be good solar light absorbers. Remarkably, although the shortest Fe-Fe distance exceeds 6 Å, an unexpected anti-ferromagnetic phase transition near 100 K was observed in their magnetic susceptibility measurement. The corresponding complex magnetic structures were resolved by neutron diffraction experiments as well as investigated by first-principles electronic structure calculations. The spin-spin coupling between two neighboring Fe atoms along the b axis, which is realized by the Fe-S···S-Fe super-super exchange mechanism, was found to be responsible for this magnetic phase transition. PMID:26525136

  6. Mechanical properties and electronic structures of Fe-Al intermetallic

    NASA Astrophysics Data System (ADS)

    Liu, YaHui; Chong, XiaoYu; Jiang, YeHua; Zhou, Rong; Feng, Jing

    2017-02-01

    Using the first-principles calculations, the elastic properties, anisotropy properties, electronic structures, Debye temperature and stability of Fe-Al (Fe3Al, FeAl, FeAl2, Fe2Al5 and FeAl3) binary compounds were calculated. The formation enthalpy and cohesive energy of these Fe-Al compounds are negative, and show they are thermodynamically stable structures. Fe2Al5 has the lowest formation enthalpy, which shows the Fe2Al5 is the most stable of Fe-Al binary compounds. These Fe-Al compounds display disparate anisotropy due to the calculated different shape of the 3D curved surface of the Young's modulus and anisotropic index. Fe3Al has the biggest bulk modulus with the value 233.2 GPa. FeAl has the biggest Yong's modulus and shear modulus with the value 296.2 GPa and 119.8 GPa, respectively. The partial density of states, total density of states and electron density distribution maps of the binary Fe-Al binary compounds are analyzed. The bonding characteristics of these Fe-Al binary compounds are mainly combination by covalent bond and metallic bonds. Meanwhile, also exist anti-bond effect. Moreover, the Debye temperatures and sound velocity of these Fe-Al compounds are explored.

  7. Magnetic field reversal of electric polarization and magnetoelectric phase diagram of the hexaferrite Ba{sub 1.3}Sr{sub 0.7}Co{sub 0.9}Zn{sub 1.1}Fe{sub 10.8}Al{sub 1.2}O{sub 22}

    SciTech Connect

    Shen, Shipeng; Yan, Liqin; Chai, Yisheng; Cong, Junzhuang; Sun, Young

    2014-01-20

    Low magnetic field reversal of electric polarization has been demonstrated in the multiferroic Y-type hexaferrite Ba{sub 1.3}Sr{sub 0.7}Co{sub 0.9}Zn{sub 1.1}Fe{sub 10.8}Al{sub 1.2}O{sub 22} single crystal. The maximum magnetoelectric coefficient at 200 K reaches 1065 ps/m near zero magnetic field. By a systematic investigation of magnetic field dependence of magnetic and dielectric responses at various temperatures, we obtained the magnetoelectric phase diagram describing the detailed evolution of the spin-induced ferroelectric phases with temperature and magnetic field. Below 225 K, the transverse spin cone can be stabilized at zero magnetic field, which is responsible for the reversal behavior of electric polarization. Our study reveals how to eventually achieve magnetic field reversal of electric polarization in hexaferrites at room temperature.

  8. Structure and magnetic properties of the cubic oxide fluoride BaFeO{sub 2}F

    SciTech Connect

    Berry, Frank J.; Coomer, Fiona C.; Hancock, Cathryn; Helgason, Orn; Moore, Elaine A.; Slater, Peter R.; Wright, Adrian J.; Thomas, Michael F.

    2011-06-15

    Fluorination of the parent oxide, BaFeO{sub 3-{delta}}, with polyvinylidine fluoride gives rise to a cubic compound with a=4.0603(4) A at 298 K. {sup 57}Fe Moessbauer spectra confirmed that all the iron is present as Fe{sup 3+}. Neutron diffraction data showed complete occupancy of the anion sites, indicating a composition BaFeO{sub 2}F, with a large displacement of the iron off-site. The magnetic ordering temperature was determined as T{sub N}=645{+-}5 K. Neutron diffraction data at 4.2 K established G-type antiferromagnetism with a magnetic moment per Fe{sup 3+} ion of 3.95 {mu}{sub B}. However, magnetisation measurements indicated the presence of a weak ferromagnetic moment that is assigned to the canting of the antiferromagnetic structure. {sup 57}Fe Moessbauer spectra in the temperature range 10-300 K were fitted with a model of fluoride ion distribution that retains charge neutrality of the perovskite unit cell. - Graphical abstract: The cubic oxide fluoride of composition BaFeO{sub 2}F has been synthesised and characterised. Highlights: > Fluorination of BaFeO{sub 3-{delta}} with polyvinylidene fluoride gives a cubic oxide fluoride of composition BaFeO{sub 2}F. > BaFeO{sub 2}F adopts a canted antiferromagnetic structure and is different from the related phase of composition SrFeO{sub 2}F. > A model of fluoride ion distribution about iron in BaFeO{sub 2}F has been explored.

  9. Ferroelectric switching induced magnetic anisotropy in Fe/BaTiO3 bilayers

    NASA Astrophysics Data System (ADS)

    Duan, Chun-Gang; Jaswal, S. S.; Tsymbal, E. Y.

    2007-03-01

    Ferromagnetic/ferroelectric heterostructures have recently attracted significantly interest due to their potential applications in multifunctional electronic devices. We have recently predicted a magnetoelectric effect at the Fe/BaTiO3 interface induced by ferroelectric polarization reversal [1]. In this report, calculations are being carried out on the magnetic anisotropy of Fe/BaTiO3 films. Preliminary results show that the ferroelectric switching of the BaTiO3 has appreciable effect on the magnetic anisotropy of magnetic Fe films. This should be of interest in multiferroic device applications. [1] Chun-gang Duan, S. S. Jaswal, E. Y. Tsymbal, Phys. Rev. Lett. 97, 047201 (2006).

  10. Enhanced and broadband microwave absorption of flake-shaped Fe and FeNi composite with Ba ferrites

    NASA Astrophysics Data System (ADS)

    Li, Wangchang; Lv, Junjun; Zhou, Xiang; Zheng, Jingwu; Ying, Yao; Qiao, Liang; Yu, Jing; Che, Shenglei

    2017-03-01

    In order to achieve a broad bandwidth absorber at high frequency, the composites of M-type ferrite BaCo1.0Ti1.0Fe10O19 (BaM) with flaked carbonyl iron powders (CIP) and flaked Fe50Ni50 were prepared to optimize the surface impedance in broadband frequency, respectively. The diameter of the flaked carbonyl iron powders (CIP) and Fe50Ni50 is in the range of 5-10 μm and 10-20 μm and the thickness of the CIP and Fe50Ni50 is close to 200 nm and 400 nm, respectively. The complex permeability and permittivity show that the addition of BaM obviously reduces the values of real part of permittivity and imaginary part of the permeability which can enhance the matched-wave-impedance. The absorption bands less than -10 dB of CIP-BaM and FeNi-BaM absorber approach to 5.5 GHz (5.7-11.2 GHz) and 7 GHz (11-18 GHz) at 1.5 mm. However, the bands of CIP and FeNi are only 1.9 GHz (4.7-6.6 GHz) and 2.1 GHz (4.0-6.1 GHz). Hence, the electromagnetic match property is greatly improved by BaM ferrites, and this composite shows a broaden absorption band.

  11. Magnetic properties of Al/57Fe/Cr multilayers

    NASA Astrophysics Data System (ADS)

    Jani, Snehal; Lakshmi, N.; Jain, Vishal; Reddy, V. R.; Gupta, Ajay; Venugopalan, K.

    2013-06-01

    Conversion Electron Mössbauer Spectroscopy (CEMS) and DC magnetization are used to compare magnetic properties of as-deposited multilayer (MLS) and Fe2CrAl thin film made from Al/57Fe/Cr MLS deposited by ion beam sputtering and then annealed in UHV. Interdiffusion of elements on annealing sample-1 at 500°C leads to formation of a single, disordered film of Fe2CrAl as evidenced by hyperfine field values obtained by CEMS in the film which compares well with that in bulk Fe2CrAl. CEMS also shows contributions from Fe, Fe/Cr and Fe/Al interfaces in the MLS. Saturation magnetization of as-deposited sample-1 is much less than pure Fe due to reduced Fe thickness because of interface formation and also reduction in Fe-Fe interaction due to intervening Al and Cr layers.

  12. Local environment analysis of Fe ions in BaMgSiO4

    NASA Astrophysics Data System (ADS)

    Kase, Junya; Shingaki, Yoshihiro; Inaba, Yuta; Meguro, Kazune; Murata, Hidenobu; Okajima, Toshihiro; Yamamoto, Tomoyuki

    2016-08-01

    Polycrystalline Fe-doped BaMgSiO4 is synthesized by the conventional solid state reaction method, which shows strong photochromism. Photochromic property of the synthesized specimens is investigated by measuring the diffuse reflectance spectrum. Local environment of doped Fe ions in BaMgSiO4 has been studied by the analysis of the X-ray absorption near-edge structure (XANES) spectrum with the aid of the first-principles calculations.

  13. Preparation, characterization and magnetic properties of the BaFe12O19 @ chitosan composites

    NASA Astrophysics Data System (ADS)

    Li, Lei; Zhang, Zunju; Xie, Yu; Zhao, Jie

    2016-07-01

    The BaFe12O19 @ chitosan composites are synthesized by the crosslinking reaction through chitosan and glutaraldehyde onto the surface of BaFe12O19. The structures of the samples were characterized by Fourier transform infrared spectroscopy and X-ray diffraction. The shape and size were observed by scanning electron microscopy and transmission electron microscopy. These results showed that chitosan has been decorated onto the surface of BaFe12O19, and the chitosan-glutaraldehyde Schiff-base composites have also been formed within the chitosan layers. Then, the magnetic properties of the samples were tested with the vibrating sample magnetometer. The magnetic saturation (MS), residual magnetization (Mr) and coercive force (Hc) values of the BaFe12O19 @ chitosan Schiff-base composite have achieved 44.94 emu/g, 27.82 emu/g and 3580.7 Oe, respectively. Compared with single BaFe12O19, the MS, and Mr of the BaFe12O19 @ chitosan composites decreases 12.31 emu/g and 8.58 emu/g, respectively. Finally, based on the experimental results, the probable formation mechanism of this composite has been investigated.

  14. Fabrication of Fe-Al nanoparticles by selective oxidation of Fe-Al thin films

    NASA Astrophysics Data System (ADS)

    Jang, Pyungwoo; Shin, Seungchan; Jung, Chip-Sup; Kim, Kwang-Ho; Seomoon, Kyu

    2013-04-01

    The possibility of a new technique for fabricating nanoparticles from thin films using selective oxidation in an atmosphere mixture of water vapor and hydrogen was investigated. Fe-5wt.%Al films were RF-sputtered and annealed in the atmosphere mixture at 900°C for up to 200 min, in order to oxidize aluminum selectively. Thermodynamics simulation showed that temperatures exceeding 800°C are necessary to prevent iron from being oxidized, as confirmed by the depth profile of XPS. As the annealing time increased, the morphology of the 200-nm Fe-Al films changed from the continuous to the discontinuous type; thus, particulate Fe-Al films formed after 100 min. The particulate 10- to 100-nm Fe-Al films showed super-paramagnetic behavior after the oxidation. Thus, a new technique for fabricating nanoparticles was successfully introduced using selective oxidation.

  15. Quantum oscillations in iron-based superconductors: BaFe2As2 vs. KFe2As2

    NASA Astrophysics Data System (ADS)

    Terashima, Taichi; Kurita, Nobuyuki; Kimata, Motoi; Tomita, Megumi; Tsuchiya, Satoshi; Satsukawa, Hidetaka; Harada, Atsushi; Hazama, Kaori; Imai, Motoharu; Sato, Akira; Uji, Shinya; Kihou, Kunihiro; Lee, Chul-Ho; Kito, Hijiri; Tomioka, Yasuhide; Ito, Toshimitsu; Iyo, Akira; Eisaki, Hiroshi; Liang, Tian; Nakajima, Masamichi; Ishida, Shigeyuki; Uchida, Shin-ichi; Saito, Taku; Fukazawa, Hideto; Kohori, Yoh; Harima, Hisatomo

    2013-07-01

    We present results of Shubnikov-de Haas oscillation measurements on detwinned BaFe2As2 and de Haas-van Alphen oscillation measurements on KFe2As2. The Fermi surface of BaFe2As2 in the antiferromagnetic phase is found to consist of one hole and two electron pockets, all of which are three-dimensional and closed, and can reasonably be accounted for by LSD A band calculations. We find only moderate mass enhancements m*/mband of 2-3. In the case of KFe2As2, four quasi-two-dimensional Fermi surface cylinders epsilon, α, ζ, and β are observed in qualitative agreement with previous ARPES data. In sharp contrast to BaFe2As2, agreement between the observed and LDA-calculated Fermi surface is poor: LDA calculations seem to predict wrong crystal-field splitting of Fe 3d states. Large effective masses up to 20 me, me being the free electron mass, are found. The Sommerfeld coefficient estimated from the observed Fermi surface and effective masses is consistent with the measured value of 93 mJ/K2mol [H. Fukazawa et al., J. Phys. Soc. Jpn. 80, SA118 (2011)] and is 8-9 times larger than the band value, indicating strong electronic correlations in KFe2As2.

  16. In-plane structural and electronic anisotropy in de-twinned (Ba1-xKx)Fe2As2

    NASA Astrophysics Data System (ADS)

    Blomberg, Erick; Tanatar, M. A.; Straszheim, W. E.; Shen, B.; Wen, H. H.; Prozorov, R.

    2012-02-01

    The iron-pnictides undergo a tetragonal to orthorhombic structural transition below a doping - dependent temperature Ts. In the absence of external stress or strain, the orthorhombic phase is divided into four degenerate, equally populated, ``twin'' structural domains, obscuring direct measurement of in-plane anisotropy. This degeneracy may be broken through mild mechanical stress or strain leaving the sample de-twinned. The properties of detwinned (Ba1-xKx)Fe2As2 with x=0.1, 0.18 (hole under-doped) were discussed previously [1]. Here we report polarized-light microscopy and AC transport measurements of strain-detwinned (Ba1-xKx)Fe2As2 with a dopping range from x=0.15 to x=0.35. Our results provide new insight into a region of coexisting magnetic and superconducting order parameters. [4pt] [1] J. J. Ying, et al. Phys. Rev. Lett. 107 067001 (2011).

  17. Forging of FeAl intermetallic compounds

    SciTech Connect

    Flores, O.; Juarez, J.; Campillo, B.; Martinez, L.; Schneibel, J.H.

    1994-09-01

    Much activity has been concentrated on the development of intermetallic compounds with the aim of improving tensile ductility, fracture toughness and high notch sensitivity in order to develop an attractive combination of properties for high and low temperature applications. This paper reports experience in processing and forging of FeAl intermetallic of B2 type. During the experiments two different temperatures were employed, and the specimens were forged after annealing in air, 10{sup {minus}2} torr vacuum and argon. From the results it was learned that annealing FeAl in argon atmosphere prior to forging resulted in better deformation behavior than for the other two environments. For the higher forging temperature used in the experiments (700C), the as-cast microstructure becomes partially recrystallized.

  18. Study of the structural, electronic, and magnetic properties of the barium-rich iron(IV) oxides, Ba(2)FeO(4) and Ba(3)FeO(5).

    PubMed

    Delattre, James L; Stacy, Angelica M; Young, Victor G; Long, Gary J; Hermann, Raphaël; Grandjean, Fernande

    2002-06-03

    Crystals of Ba(2)FeO(4) and Ba(3)FeO(5), grown from a "self-sealing" KOH-Ba(OH)(2) flux, have been characterized by single-crystal X-ray diffraction, Mössbauer spectroscopy, and magnetic measurements. Ba(2)FeO(4) forms nonmerohedral twinned crystals with the monoclinic space group P2(1)/n, a = 6.034(2) A, b = 7.647(2) A, c = 10.162(3) A, beta = 92.931(6) degrees, and Z = 4. Ba(3)FeO(5) crystallizes in the orthorhombic space group Pnma, with a = 10.301(1) A, b = 8.151(1) A, c = 7.611(1) A, and Z = 4. While both compounds feature discrete FeO(4)(4-) tetrahedra, the anion found in Ba(2)FeO(4) has shorter Fe-O bonds and is significantly distorted relative to the Ba(3)FeO(5) anion. An iron valence of 4+ was confirmed by magnet susceptibility measurements and by the low-temperature isomer shifts of -0.152 and -0.142 mm/s relative to alpha-iron for Ba(2)FeO(4) and Ba(3)FeO(5), respectively.

  19. Comparative study of flux pinning characteristics of Ba(Fe 1-x Cox)2 As 2 and BaFe2(As1-x Px)2 single crystals

    NASA Astrophysics Data System (ADS)

    Chikumoto, Noriko; Hirata, Wataru; Miyasaka, Shigeki; Tajima, Setsuko; Tanabe, Keiichi

    2011-03-01

    We have studied the magnetization behavior of iron-pnictide superconductor, Ba(Fe 1-x Co x)2 As 2 (Co-doped Fe122) with various Co doping and BaFe 2 (As 0.65 P0.35)2 (P-doped Fe122) single crystals. All of the Co-doped Fe122 crystals showed a very pronounced ``peak effect'' in all the temperature range, irrespective of doping state. It is important to mention that a similar peak effect was previously reported for REBa 2 Cu 3 Oy . In order to get further insight into the pinning mechanism of the present system, we analyzed the pinning force density Fp =Jc B . A good scaling of the Fp versus the reduced field, b = B /Birr , was established for all the Co-doped Fe122 crystals and the scaling curves were well fitted with the function given by Fp /Fp , max =Abp (1 - b)q , where A is a numerical parameter, p and q are describing the actual pinning mechanism. It was found that p value monotonically increases with x, while q value decreases with x. On the other hand, P-doped Fe122 did not show ``peak effect''. We will discuss about the possible pinning mechanism causing the peak effect. This work was supported by JSPS through FIRST Program.

  20. Magnetism of BaFe2Se3 studied by Mössbauer spectroscopy

    NASA Astrophysics Data System (ADS)

    Komędera, K.; Jasek, A. K.; Błachowski, A.; Ruebenbauer, K.; Piskorz, M.; Żukrowski, J.; Krztoń-Maziopa, A.; Pomjakushina, E.; Conder, K.

    2015-04-01

    The compound BaFe2Se3 (Pnma) has been synthesized in the form of single crystals with the average composition Ba0.992Fe1.998Se3. The Mössbauer spectroscopy used for investigation of the valence states of Fe in this compound at temperature ranging from 4.2 K till room temperature revealed the occurrence of mixed-valence state for iron. The spectrum is characterized by sharply defined electric quadrupole doublet above magnetic ordering at about 250 K. For the magnetically ordered state one sees four iron sites at least and each of them is described by separate axially symmetric electric field gradient tensor with the principal component making some angle with the hyperfine magnetic field. They form two groups occurring in equal abundances. It is likely that each group belongs to separate spin ladder with various tilts of the FeSe4 tetrahedral units along the ladder. Two impurity phases are found, i.e., superconducting FeSe and some other unidentified iron-bearing phase being magnetically disordered above 80 K. Powder form of BaFe2Se3 is unstable in contact with the air and decomposes slowly to this unidentified phase exhibiting almost the same quadrupole doublet as BaFe2Se3 above magnetic transition temperature.

  1. Structure and physical properties of the layered iron oxychalcogenide BaFe2Se2O

    NASA Astrophysics Data System (ADS)

    Lei, Hechang; Ryu, Hyejin; Ivanovski, V.; Warren, J. B.; Frenkel, A. I.; Cekic, B.; Yin, Wei-Guo; Petrovic, C.

    2012-11-01

    We have successfully synthesized a layered iron oxychalcogenide BaFe2Se2O single crystal. This compound is built up of Ba and Fe-Se(O) layers alternatively stacked along the c axis. The Fe-Se(O) layers contain double chains of edge-shared Fe-Se(O) tetrahedra that propagate along the b axis and are bridged by oxygen along the a axis. Physical property measurements indicate that BaFe2Se2O is a semiconductor without the Curie-Weiss behavior up to 350 K. There is a possible long-range antiferromagnetic transition at 240 K, corresponding to the peak in specific-heat measurement, and two transitions at 115 K and 43 K where magnetic susceptibility drops abruptly. The magnetic entropy up to 300 K is much smaller than the expected value for Fe2+ in tetrahedral crystal fields and the Mössbauer spectrum indicates that long-range magnetic order is unlikely at 294 K. Our results suggest that BaFe2Se2O is a magnetic insulator at the borderline between a long-range antiferromagnetic spin ordering and possible spin dimerization.

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

    SciTech Connect

    Bodeux, Romain; Michau, Dominique; Maglione, Mario; Josse, Michaël

    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 similar 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.

  3. Dielectric relaxation and polaronic conduction in epitaxial BaFe12O19 hexaferrite thin film

    NASA Astrophysics Data System (ADS)

    Tang, Rujun; Zhou, Hao; Zhao, Run; Jian, Jie; Wang, Han; Huang, Jijie; Fan, Meng; Zhang, Wei; Wang, Haiyan; Yang, Hao

    2016-03-01

    The dielectric properties of epitaxial BaFe12O19 hexaferrite thin film have been investigated as a function of frequency (50 Hz  -  2 MHz) and temperature (100-375 K). The frequency dependent permittivity, impedance ({{Z}\\prime \\prime} ) and modulus ({{M}\\prime \\prime} ) spectra show that the dielectric responses of BaFe12O19 thin film are thermally activated. The activation energy of BaFe12O19 film (E a) is much smaller than that of the polycrystalline bulk BaFe12O19. In addition, E a increases with increasing temperature and there is a distribution of relaxation time in the sample. The scaling behavior of {{Z}\\prime \\prime} and {{M}\\prime \\prime} spectra of the sample further suggest that the distribution of relaxation time is temperature independent at low temperatures (<250 K) and temperature dependent at high temperatures. The temperature dependent dc conductivity shows that small polaron hopping is the most probable conduction mechanism for BaFe12O19 film.

  4. Influence of the concentration in Fe-doped BaTiO 3 on magnetoelectric couping of layered composites BaTi 1-xFe xO 3-Tb 1-yDy yFe 2-z

    NASA Astrophysics Data System (ADS)

    Zhang, Ning; Wei, Jianjin

    Perovskites BaTi 1-xFe xO 3 has been synthesized with the concentration x ranging from 0.01 to 0.02. Their transformation point of ferroelectric to paraelectric and the corresponding latent heat of the phase transformation were observed to decrease with increasing the doping level of Fe 3+. Bonded layered composites BaTi 1-xFe xO 3-Tb 1-yDy yFe 2-z have been fabricated and their magnetoelectric effect has been investigated. The sample containing a layer of perovskite BaTi 0.985Fe 0.015O 3 was found to show the maximum transverse ME voltage coefficient, which is about 1422 mV Oe -1 cm -1 under a magnetic field of 1580 Oe, in these bilayers. Analysis shows that the Fe-doped BaTiO 3 with doping level at about 1.5% should have largest piezoelectric coefficient in these ceramics BaTi 1-xFe xO 3.

  5. Structural, optical and electrical properties of GdAlO3:Eu3+Ba2+

    NASA Astrophysics Data System (ADS)

    Selvalakshmi, T.; Tamilarasi, S.; Bose, A. Chandra

    2015-06-01

    Effect of Ba2+ ions concentration on the photoluminescence of GdAlO3:Eu3+ Ba2+ phosphor is investigated. The phosphors are synthesized by citrate-based sol-gel method and the formation of orthorhombic phase GdAlO3 is confirmed by XRD analysis. Kubelka-Munk function is used to estimate the band gap and the value varies with concentration of Ba2+ is observed. Photoluminescence spectra show a strong red emission peak at 616 nm corresponding to5D0→7F2 transition and its intensity increase with the addition of Ba2+ ions. The presence of Eu3+ and Ba2+ ions in GdAlO3 strongly influences the dielectric property of GdAlO3.

  6. Diamagnetic vortex barrier stripes in underdoped BaFe2(As1-xPx) 2

    NASA Astrophysics Data System (ADS)

    Yagil, A.; Lamhot, Y.; Almoalem, A.; Kasahara, S.; Watashige, T.; Shibauchi, T.; Matsuda, Y.; Auslaender, O. M.

    2016-08-01

    We report magnetic force microscopy (MFM) measurements on underdoped BaFe2(As1 -xPx)2 (x =0.26 ) that show enhanced superconductivity along stripes parallel to twin boundaries. These stripes of enhanced diamagnetic response repel superconducting vortices and act as barriers for them to cross. The width of the stripes is hundreds of nanometers, on the scale of the penetration depth, well within the inherent spatial resolution of MFM and implying that the width is set by the interaction of the superconductor with the MFM's magnetic tip. Unlike similar stripes observed previously by scanning SQUID in the electron doped Ba (Fe1 -xCox)2As2 , the stripes in the isovalently doped BaFe2(As1 -xPx)2 disappear gradually when we warm the sample towards the superconducting transition temperature. Moreover, we find that the stripes move well below the reported structural transition temperature in BaFe2(As1 -xPx)2 and that they can be much denser than in the Ba (Fe1 -xCox)2As2 study. When we cool in finite magnetic field we find that some vortices appear in the middle of stripes, suggesting that the stripes may have an inner structure, which we cannot resolve. Finally, we use both vortex decoration at higher magnetic field and deliberate vortex dragging by the MFM magnetic tip to obtain bounds on the strength of the interaction between the stripes and vortices. We find that this interaction is strong enough to play a significant role in determining the critical current in underdoped BaFe2(As1 -xPx)2 .

  7. Electric control of magnetism at the Fe/BaTiO3 interface

    NASA Astrophysics Data System (ADS)

    Radaelli, G.; Petti, D.; Plekhanov, E.; Fina, I.; Torelli, P.; Salles, B. R.; Cantoni, M.; Rinaldi, C.; Gutiérrez, D.; Panaccione, G.; Varela, M.; Picozzi, S.; Fontcuberta, J.; Bertacco, R.

    2014-03-01

    Interfacial magnetoelectric coupling is a viable path to achieve electrical writing of magnetic information in spintronic devices. For the prototypical Fe/BaTiO3 system, only tiny changes of the interfacial Fe magnetic moment upon reversal of the BaTiO3 dielectric polarization have been predicted so far. Here, by using X-ray magnetic circular dichroism in combination with high-resolution electron microscopy and first principles calculations, we report on an undisclosed physical mechanism for interfacial magnetoelectric coupling in the Fe/BaTiO3 system. At this interface, an ultrathin oxidized iron layer exists, whose magnetization can be electrically and reversibly switched on and off at room temperature by reversing the BaTiO3 polarization. The suppression/recovery of interfacial ferromagnetism results from the asymmetric effect that ionic displacements in BaTiO3 produces on the exchange coupling constants in the interfacial-oxidized Fe layer. The observed giant magnetoelectric response holds potential for optimizing interfacial magnetoelectric coupling in view of efficient, low-power spintronic devices.

  8. Electric control of magnetism at the Fe/BaTiO₃ interface.

    PubMed

    Radaelli, G; Petti, D; Plekhanov, E; Fina, I; Torelli, P; Salles, B R; Cantoni, M; Rinaldi, C; Gutiérrez, D; Panaccione, G; Varela, M; Picozzi, S; Fontcuberta, J; Bertacco, R

    2014-03-03

    Interfacial magnetoelectric coupling is a viable path to achieve electrical writing of magnetic information in spintronic devices. For the prototypical Fe/BaTiO₃ system, only tiny changes of the interfacial Fe magnetic moment upon reversal of the BaTiO₃ dielectric polarization have been predicted so far. Here, by using X-ray magnetic circular dichroism in combination with high-resolution electron microscopy and first principles calculations, we report on an undisclosed physical mechanism for interfacial magnetoelectric coupling in the Fe/BaTiO₃ system. At this interface, an ultrathin oxidized iron layer exists, whose magnetization can be electrically and reversibly switched on and off at room temperature by reversing the BaTiO₃ polarization. The suppression/recovery of interfacial ferromagnetism results from the asymmetric effect that ionic displacements in BaTiO₃ produces on the exchange coupling constants in the interfacial-oxidized Fe layer. The observed giant magnetoelectric response holds potential for optimizing interfacial magnetoelectric coupling in view of efficient, low-power spintronic devices.

  9. A first principles study on newly proposed (Ca/Sr/Ba)Fe2Bi2 compounds with their parent compounds

    NASA Astrophysics Data System (ADS)

    Sundareswari, M.; Jayalakshmi, D. S.; Viswanathan, E.

    2016-02-01

    The structural, electronic, bonding and magnetic properties of newly proposed iron-based compounds viz., CaFe2Bi2, SrFe2Bi2, BaFe2Bi2 with their Fermi surface topology are reported here for the first time by means of first principles calculation. All these properties of newly proposed compounds are compared and analysed along with their respective parent compounds namely (Ca,Sr,Ba)Fe2As2.

  10. Magnetic structures and excitations in a multiferroic Y-type hexaferrite BaSrCo2Fe11AlO22

    SciTech Connect

    Nakajima, Taro; Tokunaga, Yusuke; Matsuda, Masaaki; Dissanayake, Sachith E.; Fernandez-Baca, Jaime A.; Kakurai, Kazuhisa; Taguchi, Yasujiro; Tokura, Yoshinori; Arima, Taka-hisa

    2016-11-30

    Here, we have investigated magnetic orders and excitations in a Y-type hexaferrite BaSrCo2Fe11AlO22 (BSCoFAO), which was reported to exhibit spin-driven ferroelectricity at room temperature. By means of magnetization, electric polarization, and neutron-diffraction measurements using single-crystal samples, we establish a H-T magnetic phase diagram for magnetic field perpendicular to the c axis (H⟂c). This system exhibits an alternating longitudinal conical (ALC) magnetic structure in the ground state, and it turns into a non-co-planar commensurate magnetic order with spin-driven ferroelectricity under H⟂c. The field-induced ferroelectric phase remains as a metastable state after removing magnetic field below 250 K. This metastability is the key to understanding of magnetic field reversal of the spin-driven electric polarization in this system. Inelastic polarized neutron-scattering measurements in the ALC phase reveal a magnetic excitation at around 7.5 meV, which is attributed to spin components oscillating in a plane perpendicular to the cone axis. This phasonlike excitation is expected to be an electric-field active magnon, i.e., electromagnon excitation, in terms of the magnetostriction mechanism.

  11. Magnetotransport of proton-irradiated BaFe2As2 and BaFe1.985Co0.015As2 single crystals

    DOE PAGES

    Moseley, D. A.; Yates, K. A.; Peng, N.; ...

    2015-02-17

    In this paper, we study the magnetotransport properties of the ferropnictide crystals BaFe2As2 and BaFe1.985Co0.015As2. These materials exhibit a high field linear magnetoresistance that has been attributed to the quantum linear magnetoresistance model. In this model, the linear magnetoresistance is dependent on the concentration of scattering centers in the material. By using proton-beam irradiation to change the defect scattering density, we find that the dependence of the magnitude of the linear magnetoresistance on scattering quite clearly contravenes this prediction. Finally, a number of other scaling trends in the magnetoresistance and high field Hall data are observed and discussed.

  12. Synthesis and characterization of hollow mesoporous BaFe12O19 spheres

    SciTech Connect

    Xu, X; Park, J; Hong, YK; Lane, AM

    2015-02-01

    A facile method is reported to synthesize hollow mesoporous BaFe12O19 spheres using a template-free chemical etching process. Hollow BaFe12O19 spheres were synthesized by conventional spray pyrolysis. The mesoporous structure is achieved by alkaline ethylene glycol etching at 185 degrees C, with the porosity controlled by the heating time. The hollow porous structure is confirmed by SEM, TEM, and FIB-FESEM characterization. The crystal structure and magnetic properties are not significantly affected after the chemical etching process. The formation mechanism of the porous structure is explained by grain boundary etching. (C) 2014 Elsevier Inc. All rights reserved.

  13. Overview of the development of FeAl intermetallic alloys

    SciTech Connect

    Maziasz, P.J.; Liu, C.T.; Goodwin, G.M.

    1995-09-01

    B2-phase FeAl ordered intermetallic alloys based on an Fe-36 at.% Al composition are being developed to optimize a combination of properties that includes high-temperature strength, room-temperature ductility, and weldability. Microalloying with boron and proper processing are very important for FeAl properties optimization. These alloys also have the good to outstanding resistance to oxidation, sulfidation, and corrosion in molten salts or chlorides at elevated temperatures, characteristic of FeAl with 30--40 at.% Al. Ingot- and powder-metallurgy (IM and PM, respectively) processing both produce good properties, including strength above 400 MPa up to about 750 C. Technology development to produce FeAl components for industry testing is in progress. In parallel, weld-overlay cladding and powder coating technologies are also being developed to take immediate advantage of the high-temperature corrosion/oxidation and erosion/wear resistance of FeAl.

  14. Atomic absorption background of Ba in EXAFS analysis of BaFe(12)O(19) nanoparticles.

    PubMed

    Padeznik Gomilšek, Jana; Kodre, Alojz; Arčon, Iztok; de Panfilis, Simone; Makovec, Darko

    2011-07-01

    The approximate barium X-ray atomic absorption in the energy region of L-edges is reconstructed from the absorption spectrum of an aqueous solution of BaCl(2). The result is corroborated by comparison with pure atomic absorption spectra of neighbour elements Xe and Cs. The application of the atomic absorption signal as a proper EXAFS background is demonstrated and discussed in the analysis of Ba hexaferrite nanoparticles with a very weak structural signal. The essential gain is found in the decrease of uncertainty intervals of structural parameters and their correlations. A simple analytical model of the absorption background for the practical EXAFS analysis is demonstrated.

  15. Strong ferromagnetic exchange interaction under ambient pressure in BaFe2S3

    NASA Astrophysics Data System (ADS)

    Wang, Meng; Jin, S. J.; Yi, Ming; Song, Yu; Jiang, H. C.; Zhang, W. L.; Sun, H. L.; Luo, H. Q.; Christianson, A. D.; Bourret-Courchesne, E.; Lee, D. H.; Yao, Dao-Xin; Birgeneau, R. J.

    2017-02-01

    Inelastic neutron scattering measurements have been performed to investigate the spin waves of the quasi-one-dimensional antiferromagnetic ladder compound BaFe2S3 , where a superconducting transition was observed under pressure [H. Takahashi et al., Nat. Mater. 14, 1008 (2015), 10.1038/nmat4351; T. Yamauchi et al., Phys. Rev. Lett. 115, 246402 (2015), 10.1103/PhysRevLett.115.246402]. By fitting the spherically averaged experimental data collected on a powder sample to a Heisenberg Hamiltonian, we find that the one-dimensional antiferromagnetic ladder exhibits a strong nearest-neighbor ferromagnetic exchange interaction (S JR=-71 ±4 meV) along the rung direction, an antiferromagnetic S JL=49 ±3 meV along the leg direction, and a ferromagnetic S J2=-15 ±2 meV along the diagonal direction. Our data demonstrate that the antiferromagnetic spin excitations are a common characteristic for the iron-based superconductors, while specific relative values for the exchange interactions do not appear to be unique for the parent states of the superconducting materials.

  16. Magnetoelectric effect in laminate composites of Tb1-xDyxFe2-y and Fe-doped BaTiO3

    NASA Astrophysics Data System (ADS)

    Zhang, Ning; Fan, Junfeng; Rong, Xiaofang; Cao, Hongxia; Wei, Jianjun

    2007-03-01

    Fe-doped BaTiO3 has been synthesized with sol-gel technique. Its transformation point of ferroelectric to paraelectric and the latent heat of the transformation were observed at 103.27 °C and 169.9 J/mol, respectively. They are a little less than those for pure BaTiO3. Bonded layered composites Tb1-xDyxFe2-y/BaTi0.99Fe0.01O3 have been fabricated. Their magnetoelectric (ME) effect has been investigated. The transverse ME voltage coefficient for the bilayer Tb1-xDyxFe2-y-BaTi0.99Fe0.01O3 and the trilayer Tb1-xDyxFe2-y-BaTi0.99Fe0.01O3-Tb1-xDyxFe2-y can reach 578 (mv Oe-1 cm-1) and 2100 (mv Oe-1 cm-1), respectively, under a bias magnetic field of 350 Oe at room temperature. Those are about 50% larger than those for the bilayer and trilayer composed by pure BaTiO3. It suggests that the doped BaTiO3 can be a new choice of piezoelectrics to compose ME composites.

  17. Large miscibility gap in the Ba(MnxFe1-x)2As2 system

    NASA Astrophysics Data System (ADS)

    Pandey, Abhishek; Anand, V. K.; Johnston, D. C.

    2011-07-01

    The compounds BaMn2As2 and BaFe2As2 both crystallize in the body-centered-tetragonal ThCr2Si2-type (122-type) structure at room temperature but exhibit quite different unit cell volumes and very different magnetic and electronic transport properties. Evidently reflecting these disparities, we have discovered a large miscibility gap in the system Ba(MnxFe1-x)2As2. Rietveld refinements of powder x-ray diffraction (XRD) measurements on samples slow-cooled from 1000 °C to room temperature (RT) reveal a two-phase mixture of BaMn2As2 and Ba(Mn0.12Fe0.88)2As2 phases together with impurity phases for x=0.2, 0.4, 0.5, 0.6, and 0.8. We infer that there exists a miscibility gap in this system at 300 K with composition limits 0.12≲x≲1. For samples quenched from 1000 °C to 77 K, the refinements of RT XRD data indicate that the miscibility gap at RT narrows at 1000 °C to 0.2≲x≲0.8. Samples with x=0.4, 0.5, and 0.6 quenched from 1100 to 1400 °C to 77 K contain a single 122-type phase together with significant amounts of Fe1-xMnxAs and FeAs2 impurity phases. These results indicate that the system is not a pseudobinary system over the whole composition range and that the 122-type phase has a significant homogeneity range at these temperatures. Magnetic susceptibility χ, electrical resistivity ρ, and heat capacity measurements versus temperature T of the single-phase quenched polycrystalline samples with x=0.2 and 0.8 are reported. We also report attempts to grow single crystals of the substituted compounds Ba(Mn1-xTx)2As2 (T = Cr, Fe, Co, Ni, Cu, Ru, Rh, Pd, Re, and Pt) and BaMn2(As1-xSbx)2 out of Sn flux. Energy-dispersive x-ray analyses show that most of these elements do not substitute into the lattice in amounts greater than 0.5%. However, concentrations of 4.4%, ~10% and 2.6% were achieved for Cr, Fe, and Sb substitutions, respectively, and χ(T) and ρ(T) data for these crystals are presented.

  18. Superconductivity and fluctuations in Ba1–pKpFe2As2 and Ba(Fe1–nCon)2As2

    DOE PAGES

    Böhm, T.; Hosseinian Ahangharnejhad, R.; Jost, D.; ...

    2016-08-11

    In this paper, we study the interplay of fluctuations and superconductivity in BaFe2As2 (Ba-122) compounds with Ba and Fe substituted by K (p doping) and Co (n doping), respectively. To this end, we measured electronic Raman spectra as a function of polarization and temperature. We observe gap excitations and fluctuations for all doping levels studied. The response from fluctuations is much stronger for Co substitution and, according to the selection rules and the temperature dependence, originates from the exchange of two critical spin fluctuations with characteristic wave vectors (±π,0) and (0,±π). At 22% K doping (p = 0.22), we findmore » the same selection rules and spectral shape for the fluctuations but the intensity is smaller by a factor of 5. Since there exists no nematic region above the orthorhombic spin-density-wave (SDW) phase, the identification of the fluctuations via the temperature dependence is not possible. The gap excitations in the superconducting state indicate strongly anisotropic near-nodal gaps for Co substitution which make the observation of collective modes difficult. The variation with doping of the spectral weights of the A1g and B1g gap features does not support the influence of fluctuations on Cooper pairing. Thus, the observation of Bardasis–Schrieffer modes inside the nearly clean gaps on the K-doped side remains the only experimental evidence for the relevance of fluctuations for pairing.« less

  19. Structural and antiferromagnetic properties of Ba(Fe1-x-y Cox Rhy)2 As2 compounds

    NASA Astrophysics Data System (ADS)

    Kim, Min Gyu; Heitmann, T. W.; Mulcahy, S. R.; Bourret-Courchesne, E. D.; Birgeneau, R. J.

    We present a systematic investigation of the electrical, structural, and antiferromagnetic properties for the series of Ba(Fe1-x-y CoxRhy)2 As2 compounds with fixed x = 0.027 and 0 < y <0.035. We compare our results for the Co-Rh doped Ba(Fe1-x-y CoxRhy)2 As2 compounds with Ba(Fe 1-xCox)2 As2 compounds. We demonstrate that the electrical, structural, antiferromagnetic, and superconducting properties of the Co-Rh doped compounds are similar to the properties of the Co doped compounds. We find that the overall behaviors of Ba(Fe1-x-y CoxRhy)2 As2 and Ba(Fe1-x Cox)2 As2 compounds are very similar when the total number of the extra electrons per Fe/TM (TM = transition metal) site is considered, which is consistent with the rigid band model. Despite the similarity, we find that the details of the transitions are different in between Ba(Fe1-x-y CoxRhy)2 As2 and Ba(Fe1-x Cox)2 As2 compounds. The work at the Lawrence Berkeley National Laboratory was supported by the U.S. Department of Energy (DOE), Office of Basic Energy Sciences, Materials Sciences and Engineering Division, under Contract No. DE-AC02-05CH11231.

  20. Ba2F2Fe(1.5)Se3: An Intergrowth Compound Containing Iron Selenide Layers.

    PubMed

    Driss, Dalel; Janod, Etienne; Corraze, Benoit; Guillot-Deudon, Catherine; Cario, Laurent

    2016-03-21

    The iron selenide compound Ba2F2Fe(1.5)Se3 was synthesized by a high-temperature ceramic method. The single-crystal X-ray structure determination revealed a layered-like structure built on [Ba2F2](2+) layers of the fluorite type and iron selenide layers [Fe(1.5)Se3](2-). These [Fe1.5Se3](2-) layers contain iron in two valence states, namely, Fe(II+) and Fe(III+) located in octahedral and tetrahedral sites, respectively. Magnetic measurements are consistent with a high-spin state for Fe(II+) and an intermediate-spin state for Fe(III+). Moreover, susceptibility and resistivity measurements demonstrate that Ba2F2Fe(1.5)Se3 is an antiferromagnetic insulator.

  1. Stabilization of itinerant (band) magnetism in FeAl by Ga substitution for Al

    NASA Astrophysics Data System (ADS)

    Papaconstantopoulos, D. A.; Mazin, I. I.; Hathaway, K. B.

    2001-06-01

    Band structure calculations of FeGa1-xAlx have been performed, to further investigate the stability of ferromagnetism in FeAl. The Stoner parameter increases by about 20% at the FeGa end. This is also confirmed by our spin-polarized calculations. We conclude that Ga substitution for Al is likely to stabilize the elusive (or illusive) ferromagnetic state in FeAl.

  2. Different response of the crystal structure to isoelectronic doping in BaFe2(As1-xPx)2 and (Ba1-xSrx)Fe2As2

    NASA Astrophysics Data System (ADS)

    Rotter, Marianne; Hieke, Christine; Johrendt, Dirk

    2010-07-01

    Superconductivity up to 30 K in charge neutrally doped BaFe2(As1-xPx)2 has been ascribed to chemical pressure caused by the shrinking unit cell. But the latter induces no superconductivity in (Ba1-xSrx)Fe2As2 in spite of the same volume range. We show that the spin-density-wave (SDW) state of BaFe2As2 becomes suppressed in BaFe2(As1-xPx)2 by a subtle reorganization of the crystal structure, where arsenic and phosphorus are located at different coordinates zAs and zP . High-resolution x-ray diffraction experiments with BaFe2(As1-xPx)2 single crystals reveal almost unchanged Fe-P bonds, but a contraction of the Fe-As bonds, which remain nearly unchanged in (Ba1-xSrx)Fe2As2 . Since the Fe-As bond length is a gauge for the magnetic moment, our results show why the SDW is suppressed by P doping, but not by Sr doping. Only the Fe-P interaction increases the width of the iron 3d bands, which destabilizes the magnetic SDW ground state. The simultaneous contraction of the Fe-As bonds is rather a consequence of the vanishing magnetism. Ordered structure models of BaFe2(As1-xPx)2 obtained by density-functional theory calculations agree perfectly with the single-crystal x-ray structure determinations. The contraction of the Fe-As bonds saturates at doping levels above x≈0.3 , which corrects the unreasonable linear decrease in the so-called pnictide height.

  3. Preparation and electromagnetic properties of Polyaniline(polypyrrole)-BaFe12O19/Ni0.8Zn0.2Fe2O4 ferrite nanocomposites

    NASA Astrophysics Data System (ADS)

    Wang, Yan; Huang, Ying; Wang, Qiufen; He, Qian; Chen, Lin

    2012-10-01

    The nanocomposite of hard (BaFe12O19)/soft ferrite (Ni0.8Zn0.2 Fe2O4) was prepared by the sol-gel process, and then the polyaniline(PANI)/polypyrrole(PPY)-BaFe12O19/Ni0.8Zn0.2Fe2O4 was produced by in situ polymerization method. The structures, morphology and electromagnetic properties of the samples were characterized by various instruments. XRD, TEM, and FTIR analysis indicated that BaFe12O19/Ni0.8Zn0.2Fe2O4 ferrite were homogenously enwrapped by PANI(PPY) coating. The VSM and SDY-4 measurement show that the magnetic properties of the composites decreased with the increase in PANI(PPY) amount, However, the electrical conductivity is on the contrary. The electromagnetic properties of the composites were much better than BaFe12O19/Ni0.8Zn0.2Fe2O4 in the frequency range of 2-15 GHz, which mainly depends on the dielectric loss of PANI(PPY). A minimum reflection loss of the PANI(PPY)-BaFe12O19/Ni0.8Zn0.2Fe2O4 ferrite nanocomposite is -19.7 dB(-21.5 dB) at the frequency of 7.3 GHz (10.7 GHz).

  4. Synthesis, structural and magnetic characterisation of the fully fluorinated compound 6H-BaFeO{sub 2}F

    SciTech Connect

    Clemens, Oliver; Wright, Adrian J.; Berry, Frank J.; Smith, Ronald I.; Slater, Peter R.

    2013-02-15

    The compound 6H-BaFeO{sub 2}F (P6{sub 3}/mmc) was synthesised by the low temperature fluorination of 6H-BaFeO{sub 3-d} using polyvinylidenedifluoride (PVDF) as a fluorination agent. Structural characterisation by XRD and NPD suggests that the local positions of the oxygen and fluorine atoms vary with no evidence for ordering on the anion sites. This compound shows antiferromagnetic ordering at room temperature with antiparallel alignment of the magnetic moments along the c-axis. The use of PVDF also allows the possibility of tuning the fluorine content in materials of composition 6H-BaFeO{sub 3-d}F{sub y} to any value of 0BaFeO{sub 2}F. Highlights: Black-Right-Pointing-Pointer The crystal structure of the hexagonal perovskite phase 6H-BaFeO{sub 2}F. Black-Right-Pointing-Pointer H-BaFeO{sub 2}F and 6H-BaFeO{sub 3-d}F{sub y} were prepared via low temperature fluorination using PVDF. Black-Right-Pointing-Pointer A structural investigation of the compounds BaFeO{sub 2}F is presented in detail. Black-Right-Pointing-Pointer This analysis suggests differences for the local coordination of O{sup 2-} and F{sup -} anions. Black-Right-Pointing-Pointer H-BaFeO{sub 2}F shows antiferromagnetic ordering at 300 K. Black-Right-Pointing-Pointer The magnetic moments align parallel to the a-axis.

  5. Structural evolution in mechanically alloyed Al-Fe powders

    SciTech Connect

    Mukhopadhyay, D.K.; Suryanarayana, C.; Froes, F.H.

    1995-08-01

    The structural evolution in mechanically alloyed binary aluminum-iron powder mixtures containing 1, 4, 7.3, 10.7, and 25 at pct Fe was investigated using X-ray diffraction (XRD) and electron microscopic techniques. The constitution (number and identity of phases present), microstructure (crystal size, particle size), and transformation behavior of the powders on annealing were studied. The solid solubility of Fe in Al has been extended up to at least 4.5 at. pct, which is close to that observed using rapid solidification (RS) (4.4 at. pct), compared with the equilibrium value of 0.025 at. pct Fe at room temperature. Nanometer-sized grains were observed in as-milled crystalline powders in all compositions. Increasing the ball-to-powder weight ratio (BPR) resulted in a faster rate of decrease of crystal size. A fully amorphous phase was obtained in the Al-25 at. pct Fe composition, and a mixed amorphous phase plus solid solution of Fe in Al was developed in the Al-10.7 at. pct Fe alloy, agreeing well with the predictions made using the semiempirical Miedema model. Heat treatment of the mechanically alloyed powders containing the supersaturated solid solution or the amorphous phase resulted in the formation of the Al{sub 3}Fe intermetallic in all but the Al-25 at. pct Fe powders. In the Al-25 at. pct Fe powder, formation of nanocrystalline Al{sub 5}Fe{sub 2} was observed directly by milling. Electron microscope studies of the shock-consolidated mechanically alloyed Al-10.7 and 25 at. pct Fe powders indicated that nanometer-sized grains were retained after compaction.

  6. New insights into the application of the valence rules in Zintl phases-Crystal and electronic structures of Ba7Ga4P9, Ba7Ga4As9, Ba7Al4Sb9, Ba6CaAl4Sb9, and Ba6CaGa4Sb9

    NASA Astrophysics Data System (ADS)

    He, Hua; Stoyko, Stanislav; Bobev, Svilen

    2016-04-01

    Crystals of three new ternary pnictides-Ba7Al4Sb9, Ba7Ga4P9, and Ba7Ga4As9 have been prepared by reactions of the respective elements in molten Al or Pb fluxes. Single-crystal X-ray diffraction studies reveal that the three phases are isotypic, crystallizing in the orthorhombic Ba7Ga4Sb9-type structure (space group Pmmn, Pearson symbol oP40, Z=2), for which only the prototype is known. The structure is based on TrPn4 tetrahedra (Tr=Al, Ga; Pn=P, As, Sb), connected in an intricate scheme into 1D-ribbons. Long interchain Pn-Pn bonds (dP-P>3.0 Å; dAs-As>3.1 Å; dSb-Sb>3.3 Å) account for the realization of 2D-layers, separated by Ba2+ cations. Applying the classic valance rules to rationalize the bonding apparently fails, and Ba7Ga4Sb9 has long been known as a metallic Zintl phase. Earlier theoretical calculations, both empirical and ab-initio, suggest that the possible metallic properties originate from filled anti-bonding Pn-Pn states, and the special roles of the "cations" in this crystal structure. To experimentally probe this hypothesis, we sought to synthesize the ordered quaternary phases Ba6CaTr4Sb9 (Tr=Al, Ga). Single-crystal X-ray diffraction work confirms Ba6.145(3)Ca0.855Al4Sb9 and Ba6.235(3)Ca0.765Ga4Sb9, with Ca atoms preferably substituting Ba on one of the three available sites. The nuances of the five crystal structures are discussed, and the chemical bonding in Ba7Ga4As9 is interrogated by tight-binding linear muffin-tin orbital calculations.

  7. Physicochemical properties of high-temperature solutions of the systems BaO-B/sub 2/O/sub 3/-Fe/sub 2/O/sub 3/ and BaO-B/sub 2/O/sub 3/-BaF/sub 2/-Fe/sub 2/O/sub 3/ suitable for the growth of BaFe/sub 12/O/sub 19/ single crystals

    SciTech Connect

    Peshev, P.; Varadinov, R.; Nikolov, V. )

    1989-08-01

    The systems BaO-B/sub 2/O/sub 3/-Fe/sub 2/O/sub 3/ and BaO-B/sub 2/O/sub 3/-BaF/sub 2/-Fe/sub 2/O/sub 3/ have been investigated and the concentration and temperature regions of stability of the Ba Fe/sub 12/O/sub 19/ phase in them are determined with a view to choosing suitable solvents and growth conditions of barium hexaferrite single crystals. The temperature dependencies of the dynamic viscosity of solutions of these systems are studied. It is shown that solutions containing BaF/sub 2/ have considerably lower viscosity values. The density and volatility of the solutions at their saturation temperatures are determined. On the basis of the data obtained, an appropriate solvent composition from the system BaO-B/sub 2/O/sub 3/-BaF/sub 2/ is proposed.

  8. On the quasi-1D magnetic behavior of Ba 2MnCoAl 2F 14, Ba 2MnCuAl 2F 14 and related compounds

    NASA Astrophysics Data System (ADS)

    le Lirzin, A.; Darriet, J.; Georges, R.; Soubeyroux, J. L.

    1992-02-01

    Two new fluorides Ba 2MnCoAl 2F 14 and Ba 2MnCoAl 2F 14, isostructural with the natural compound usovite Ba 2CaMgAl 2F 14, have been synthesized. The nuclear structures of both compounds, refined from neutron diffraction data, give evidence for strongly disordered bimetallic chains MnCu or MnCo along the b-axis: two new theoretical treatments are suggested in order to account for the magnetic behavior of each compound but, due to their intrinsic limitations, they are in fact applied here to solid solutions between the parent compound and BaMnAlF 7, namely Ba 2Mn 1+ yCu 1- yAl2F14 and Ba 2Mn1+ yCo1- yAl 2F 14, leading to a rather good agreement with the measured values of the susceptibilities.

  9. Thermoelectric properties of Fe and Al co-added Ge

    NASA Astrophysics Data System (ADS)

    Sasaki, Takayuki; Kurosaki, Ken; Yusufu, Aikebaier; Ohishi, Yuji; Muta, Hiroaki; Yamanaka, Shinsuke

    2017-04-01

    The polycrystalline bulk samples of Fe and Al co-added Ge were synthesized by melt-spinning followed by spark plasma sintering and the thermoelectric properties were examined. Here, Al acts as a p-type dopant, while Fe is expected to form FeGe2 as precipitates. Since the lattice mismatch between Ge and FeGe2 is small (<4%), they would coherently connect with each other, reducing the thermal conductivity without affecting the electrical transport. In this study, a reduction in thermal conductivity was achieved by dispersing the FeGe2 precipitates in the Al-doped Ge matrix, while they had little influences on both the carrier mobility and the Seebeck coefficient. As the results, the maximum ZT value of 0.13 was obtained at 773 K, which is three times higher than that of single-crystal Ge reported by the authors’ group [Y. Ohishi et al., Jpn. J. Appl. Phys. 55, 051301 (2016)].

  10. Hyperfine fields in the BaFe2As2 family and their relation to the magnetic moment

    NASA Astrophysics Data System (ADS)

    Derondeau, Gerald; Minár, Ján; Ebert, Hubert

    2016-12-01

    The hyperfine field Bhf and the magnetic properties of the BaFe2As2 family are studied using the fully relativistic Dirac formalism for different types of substitution. The study covers electron doped Ba (Fe1-xCox) 2As2 and Ba (Fe1-xNix) 2As2 , hole doped (Ba1 -xKx) Fe2As2 , and also isovalently doped Ba (Fe1-xRux) 2As2 and BaFe2(As1-xPx) 2 for a wide range of the concentration x . For the substituted compounds the hyperfine fields show a very strong dependence on the dopant type and its concentration x . Relativistic contributions were found to have a significantly stronger impact for the iron pnictides when compared to bulk Fe. As an important finding, we demonstrate that it is not sensible to relate the hyperfine field Bhf to the average magnetic moment μ of the compound, as it was done in earlier literature.

  11. On synthesis of BaFe12O19, SrFe12O19, and PbFe12O19 hexagonal ferrite ceramics with multiferroid properties

    NASA Astrophysics Data System (ADS)

    Kostishin, V. G.; Panina, L. V.; Kozhitov, L. V.; Timofeev, A. V.; Zyuzin, A. K.; Kovalev, A. N.

    2015-08-01

    We analyze the possibility of obtaining M-type hexagonal ferrites of barium, strontium, and lead with multiferroid properties with the help of ceramic technology. Using the modified ceramic technology (especially pure initial raw materials, admixture of B2O3, and sintering in the oxygen atmosphere), we obtained for the first time the BaFe12O19 and SrFe12O19 samples with intense multiferroid properties at room temperature. At the same time, the employed technology does not make it possible to obtain PbFe12O19 samples exhibiting ferroelectricity. The multiferroid characteristics of experimental samples are compared with the characteristics of classical high-temperature multiferroic BiFeO3 and with the characteristics of BaFe12O19, SrFe12O19, and PbFe12O19 ferrite ceramics obtained in accordance with polymer precursor technology. We propose a mechanism explaining multiferroid properties of the hexagonal ferrite ceramic samples and note the importance of our results for applications.

  12. Effect of 3d doping on the electronic structure of BaFe2As2

    SciTech Connect

    McLeod, John A.; Buling, A.; Green, R.J.; Boyko, T.D.; Skorikov, N.A.; Kurmaev, E.Z.; Neumann, M.; Finkelstein, L.D.; Ni, Ni; Thaler, Alexander; Budko, Serguei L.; Canfield, Paul; Moewes, A.

    2012-04-25

    The electronic structure of BaFe2As2 doped with Co, Ni and Cu has been studied by a variety of experimental and theoretical methods, but a clear picture of the dopant 3d states has not yet emerged. Herein we provide experimental evidence of the distribution of Co, Ni and Cu 3d states in the valence band. We conclude that the Co and Ni 3d states provide additional free carriers to the Fermi level, while the Cu 3d states are found at the bottom of the valence band in a localized 3d10 shell. These findings help shed light on why superconductivity can occur in BaFe2As2 doped with Co and Ni but not Cu.

  13. Nematic spin fluid in the tetragonal phase of BaFe{<_2}As{<_2}.

    SciTech Connect

    Harriger, L. W.; Luo, H. Q.; Liu, M. S.; Frost, C.; Hu, J. P.; Norman, M. R.; Dai, P.

    2011-08-24

    We use inelastic neutron scattering to study spin waves below and above T{sub N} in iron-arsenide BaFe{sub 2}As{sub 2}. In the low-temperature orthorhombic phase, we find highly anisotropic spin waves with a large damping along the antiferromagnetic a-axis direction. On warming the system to the paramagnetic tetragonal phase, the low-energy spin waves evolve into quasi-elastic excitations, while the anisotropic spin excitations near the zone boundary persist. These results strongly suggest the presence of a spin nematic fluid in the tetragonal phase of BaFe{sub 2}As{sub 2}, which may cause the electronic and orbital anisotropy observed in these materials.

  14. Fe modified BaTiO{sub 3}: Influence of doping on ferroelectric property

    SciTech Connect

    Mishra, Ashutosh; Bisen, Supriya Jarabana, Kanaka Mahalakshmi; Mishra, Niyati

    2015-06-24

    We have investigate the ferroelectric property of Fe modified Barium Titanate (BaTiO{sub 3}) with possible tetragonal structure via solid state route was prepared. Modified sample of BaTi{sub 1−x}Fe{sub x}O{sub 3} (x=0.01, 0.02) were structural characterized by X-ray Diffraction (XRD) using a Bruker D8 Advance XRD instruments, the value of 2θ is in between 20° to 80°. Fourier transform infrared spectroscopy (FTIR) using a Bruker, vertex instruments has been performs to obtain Ti-O bonding in the modified sample; the region of wavenumber is from 4000 cm{sup −1} to 400 cm{sup −1}. P-E hysteresis loop measurements have been traced for different applied voltage- 100V, 300V and 500V.

  15. Strength anomaly in B2 FeAl single crystals

    SciTech Connect

    Yoshimi, K.; Hanada, S.; Yoo, M.H.; Matsumoto, N.

    1994-12-31

    Strength and deformation microstructure of B2 Fe-39 and 48%Al single crystals (composition given in atomic percent), which were fully annealed to remove frozen-in vacancies, have been investigated at temperatures between room temperature and 1073K. The hardness of as-homogenized Fe-48Al is higher than that of as-homogenized Fe-39Al while after additional annealing at 698K the hardness of Fe-48Al becomes lower than that of Fe-39Al. Fe-39Al single crystals slowly cooled after homogenizing at a high temperature were deformed in compression as a function of temperature and crystal orientation. A peak of yield strength appears around 0.5T{sub m} (T{sub m} = melting temperature). The orientation dependence of the critical resolved shear stress does not obey Schmid`s law even at room temperature and is quite different from that of b.c.c. metals and B2 intermetallics at low temperatures. At the peak temperature slip transition from <111>-type to <001>-type is found to occur macroscopically and microscopically, while it is observed in TEM that some of the [111] dislocations decompose into [101] and [010] on the (1096I) plane below the peak temperature. The physical sources for the positive temperature dependence of yield stress of B2 FeAl are discussed based on the obtained results.

  16. Synthesis and characterization of hollow mesoporous BaFe{sub 12}O{sub 19} spheres

    SciTech Connect

    Xu, Xia; Park, Jihoon; Hong, Yang-Ki; Lane, Alan M.

    2015-02-15

    A facile method is reported to synthesize hollow mesoporous BaFe{sub 12}O{sub 19} spheres using a template-free chemical etching process. Hollow BaFe{sub 12}O{sub 19} spheres were synthesized by conventional spray pyrolysis. The mesoporous structure is achieved by alkaline ethylene glycol etching at 185 °C, with the porosity controlled by the heating time. The hollow porous structure is confirmed by SEM, TEM, and FIB-FESEM characterization. The crystal structure and magnetic properties are not significantly affected after the chemical etching process. The formation mechanism of the porous structure is explained by grain boundary etching. - Graphical abstract: Hollow spherical BaFe{sub 12}O{sub 19} particles are polycrystalline with both grains and grain boundaries. Grain boundaries have less ordered structure and lower stability. When the particles are exposed to high temperature alkaline ethylene glycol, the grain boundaries are etched, leaving small grooves between grains. These grooves allow ethylene glycol to diffuse inside to further etch the grains. As the grain size decreases, gaps appear on the particle surfaces, and a porous structure is finally formed. - Highlights: • Two-step synthesis method for hollow mesoporous BaFe{sub 12}O{sub 19} spheres is proposed. • Porosity of the product can be regulated by controlling the second step of chemical etching. • The crystal structure and magnetic properties are examined to be little affected during the chemical etching. • The mesoporous structure formation mechanism is explained by grain boundary etching.

  17. EffectsofTransitionMetalSubstitutionsontheIncommensurabilityandSpinFluctuationsinBaFe2As2byElasticandInelasticNeutronScattering

    SciTech Connect

    Kim, M. G.; Lamsal, J.; Heitmann, T. W.; Tucker, G. S.; Pratt, Daniel; Khan, S. N.; Lee, Y. B.; Alam, A.; Thaler, A.; Ni, N; Ran, S.; Budko, S L; Marty, Karol J; Lumsden, Mark D; Canfield, Paul; Harmon, B. N.; Johnson, D. D.; Kreyssig, A.; Mcqueeney, R J; Goldman, A. I.

    2012-01-01

    Thespin uctuationspectrafromnonsuperconductingCu-substituted,andsuperconductingCo-substituted,BaFe2As2arecomparedquantitativelybyinelasticneutronscatteringmeasurementsandarefoundtobeindistinguishable.Whereasdiffractionstudiesshowtheappearanceofincommensu-ratespin-densitywaveorderinCoandNisubstitutedsamples,themagneticphasediagramforCusubstitutiondoesnotdisplayincommensurateorder,demonstratingthatsimpleelectroncountingbasedonrigid-bandconceptsisinvalid.Theseresults,supportedbytheoreticalcalculations,suggestthatsubstitu-tionalimpurityeffectsintheFeplaneplayasigni cantroleincontrollingmagnetismandtheappearanceofsuperconductivity,withCudistinguishedbyenhancedimpurityscatteringandsplit-bandbehavior.

  18. Fe K-edge X-ray resonant magnetic scattering from Ba(Fe1−xCox)2As2 superconductors

    SciTech Connect

    Kim, Min Gyu; Kreyssig, Andreas; Lee, Yongbin; McQueeney, Robert J.; Harmon, Bruce N.; Goldman, Alan I.

    2012-06-15

    We present an X-ray resonant magnetic scattering study at the Fe-K absorption edge of the BaFe2As2 compound. The energy spectrum of the resonant scattering, together with our calculation using the full-potential linear-augmented plane wave method with a local density functional suggests that the observed resonant scattering arises from electric dipole (E1) transitions. We discuss the role of Fe K-edge X-ray resonant magnetic scattering in understanding the relationship between the structure and the antiferromagnetic transition in the doped Ba(Fe1−xCox)2As2 superconductors.

  19. Fabric cutting application of FeAl-based alloys

    SciTech Connect

    Sikka, V.K.; Blue, C.A.; Sklad, S.P.; Deevi, S.C.; Shih, H.R.

    1998-11-01

    Four intermetallic-based alloys were evaluated for cutting blade applications. These alloys included Fe{sub 3}Al-based (FAS-II and FA-129), FeAl-based (PM-60), and Ni{sub 3}Al-based (IC-50). These alloys were of interest because of their much higher work-hardening rates than the conventionally used carbon and stainless steels. The FeAl-based PM-60 alloy was of further interest because of its hardening possibility through retention of vacancies. The vacancy retention treatment is much simpler than the heat treatments used for hardening of steel blades. Blades of four intermetallic alloys and commercially used M2 tool steel blades were evaluated under identical conditions to cut two-ply heavy paper. Comparative results under identical conditions revealed that the FeAl-based alloy PM-60 outperformed the other intermetallic alloys and was equal to or somewhat better than the commercially used M2 tool steel.

  20. Structural and magnetic studies of Co and Fe implanted BaTiO 3 crystals

    NASA Astrophysics Data System (ADS)

    Khalitov, N. I.; Khaibullin, R. I.; Valeev, V. F.; Dulov, E. N.; Ivoilov, N. G.; Tagirov, L. R.; Kazan, S.; Şale, A. G.; Mikailzade, F. A.

    2012-02-01

    Singly-charged Co or Fe ions with energy 40 keV were implanted into single-domain ferroelectric plates of barium titanate (BaTiO 3) with high fluences in the range of (0.5-1.5) × 10 17 ion/cm 2 to create new magnetoelectric materials. Scanning electron microscopy (SEM) and conversion electron Mössbauer spectroscopy (CEMS) studies have shown that high-fluence implantation with 3d-ions results in formation of cobalt or iron nanoparticles in the near-surface irradiated region of perovskite-type crystal. With increasing the fluence, the both Co- and Fe-implanted BaTiO 3 samples reveal at first superparamagnetic, and then ferromagnetic properties at room temperature. Analysis of magnetic hysteresis loops measured in the in-plane and out-of-plane geometries have shown that ferromagnetic BaTiO 3:Co(Fe) nanocomposite layers display the "easy plane" magnetic anisotropy similar to that found for thin granular magnetic films. Together with our previous observation of the magnetoelectric effect in these samples, our structural and magnetic investigations show that the ion implantation is suitable to synthesize the desired magnetoelectric nanocomposite materials.

  1. Oxidation behavior of FeAl+Hf,Zr,B

    NASA Technical Reports Server (NTRS)

    Smialek, James L.; Doychak, Joseph

    1988-01-01

    The oxidation behavior of Fe-40Al-1Hf, Fe-40Al-1Hf-0.4B, and Fe-40Al-0.1Zr-0.4B (at. percent) alloys was characterized after 900, 1000, and 100 C exposures. Isothermal tests revealed parabolic kinetics after a period of transitional theta-alumina scale growth. The parabolic growth rates for the subsequent alpha-alumina scales were about five times higher than those for NiAl+0.1Zr alloys. The isothermally grown scales showed a propensity toward massive scale spallation due to both extensive rumpling from growth stresses and to an inner layer of HfO2. Cyclic oxidation for 200 1-hr cycles produced little degradation at 900 or 1000 C, but caused significant spallation at 1100 C in the form of small segments of the outer scale. The major difference in the cyclic oxidation of the three FeAl alloys was increased initial spallation for FeAl+Zr,B. Although these FeAl alloys showed many similarities to NiAl alloys, they were generally less oxidation resistant. It is believed that this resulted from nonoptimal levels of dopants and larger thermal expansion mismatch stresses.

  2. Spin density wave (SDW) transition in Ru doped BaFeAs2 investigated by AC steady state calorimetry

    NASA Astrophysics Data System (ADS)

    Vinod, K.; Sharma, Shilpam; Sundar, C. S.; Bharathi, A.

    2015-06-01

    Heat capacity measurements were done on sub-micron sized BaFe2-xRuxAs2 single crystals using thin film membrane based the AC steady state calorimetry technique. Noticeable thermal hysteresis is observed in the heat capacity of the BaFe2-xRuxAs2 during cooling and warming cycles, indicating first order nature of the SDW transition.

  3. Spin density wave (SDW) transition in Ru doped BaFeAs{sub 2} investigated by AC steady state calorimetry

    SciTech Connect

    Vinod, K. Sharma, Shilpam; Sundar, C. S.; Bharathi, A.

    2015-06-24

    Heat capacity measurements were done on sub-micron sized BaFe{sub 2−x}Ru{sub x}As{sub 2} single crystals using thin film membrane based the AC steady state calorimetry technique. Noticeable thermal hysteresis is observed in the heat capacity of the BaFe{sub 2−x}Ru{sub x}As{sub 2} during cooling and warming cycles, indicating first order nature of the SDW transition.

  4. Temperature-dependent anisotropic resistivity in electron, hole and isoelectron - doped BaFe2As2 superconductors

    NASA Astrophysics Data System (ADS)

    Tanatar, M. A.

    2012-02-01

    Anisotropic electrical resistivity, ρ(T), was studied in iron-arsenide superconductors, obtained by doping the parent BaFe2As2 compound on three different sites: (1) electron donor transition metal (Co,Ni,Rh,Pd) substitution of Fe [1,2]; (2) hole donor K substitution of Ba [3]; (3) isoelectron P substitution of As. For all three types of dopants a range of T-linear behavior is found at the optimal doping in both the in-plane and the inter-plane ρ(T) above Tc. At some higher temperature this range of T-linear resistivity is capped by a slope-changing anomaly, which, by comparison with NMR, magnetic susceptibility and Hall effect measurements, can be identified with the onset of carrier activation over the pseudogap [1]. The doping-evolution of anisotropic temperature dependent ρ(T) and of the pseudogap are quite different for three types of doping. A three-dimensional T-H phase diagram summarizing our results will be presented. Furthermore, potential correlation of the anisotropic normal state transport and anisotropic superconducting state heat transport will be discussed. [4pt] In collaboration with N. Ni, A. Thaler, S.L.Bud'ko, P.C. Canfield, R. Prozorov, Bing Shen, Hai-Hu Wen, K. Hashimoto, S. Kasahara, T. Terashima, T. Shibauchi and Y. Matsuda. [4pt] [1] M.A.Tanatar et al. PRB 82, 134528 (2010)[0pt] [2] M.A.Tanatar et al. PRB 84, 014519 (2011)[0pt] [3] M.A.Tanatar et al. arXiv:1106.0533

  5. Impact of Fe on structural modification and room temperature magnetic ordering in BaTiO3

    NASA Astrophysics Data System (ADS)

    Rajan, Soumya; Gazzali, P. M. Mohammed; Chandrasekaran, G.

    2017-01-01

    Ba1 - xFexTiO3 (x = 0, 0.005, 0.01) polycrystalline ceramics are prepared using solid state reaction method. Structural studies through XRD, Raman and XPS confirm single tetragonal phase for BaTiO3 whereas a structural disorder tends to intervene with the introduction of smaller Fe ions which reduces the tolerance factor and tetragonality ratio. Grain size of the samples is estimated using SEM micrographs with ImageJ software and chemical composition is confirmed using EDX spectra. Raman spectra measured in the temperature range of 303 K to 573 K showers light on the structural phase transition exploiting a significant disappearance of the 306 cm- 1 mode. Further, structural analyses suggest the entry of Fe into the B-site upon increasing its concentration in BaTiO3. The dopant sensitive modes lying at around 640 cm- 1 and 650 cm- 1 are assigned to lattice strain. A reduction in ferroelectric to paraelectric transition temperature is observed with a transformation from diffused type to normal ferroelectric upon the increased Fe content. The oxidation state of Fe in the BaTiO3 lattice has been decided using EPR Spectra precisely. Room temperature magnetic ordering is observed in Fe substituted BaTiO3 using PPMS. The coexistence of ferroelectric and magnetic ordering is established in the present study for optimized Fe substituted BaTiO3.

  6. Thermodynamic stability of radiogenic Ba in CsAlSi2O6 pollucite

    NASA Astrophysics Data System (ADS)

    Jaffe, John; van Ginhoven, Renée; Jiang, Weilin

    2013-03-01

    Pollucite, a zeolite-like nanoporous aluminosilicate structure with nominal composition CsAlSi2O6, has been suggested as a nuclear waste storage form for fission-product radioactive isotopes of cesium, especially 137Cs. One factor affecting the long-term stability of this waste form is the valence change associated with the beta decay that converts Cs into barium. We have used first-principles density functional total energy calculations to evaluate the thermodynamic stability of pollucite with Ba replacing Cs at regular lattice sites with respect to the precipitation of Ba, Cs or their oxides. We included small clusters of substitutional BaCs as well as localized complexes of BaCs with compensating electron donor defects, specifically Cs vacancies and interstitial oxygen. We conclude that Cs-Ba pollucite is thermodynamically stable against precipitation of Cs or its oxide, but that partial precipitation of Ba or BaO may be thermodynamically favored under some conditions. Even this change may be kinetically limited, however. Fuel Cycle Research and Development, U.S. Department of Energy Waste Form Campaign

  7. Structural, Magnetic and Dielectric Properties of Fe-DOPED BaTiO3 Solids

    NASA Astrophysics Data System (ADS)

    Guo, Zhengang; Yang, Lihong; Qiu, Hongmei; Zhan, Xuedan; Yin, Jinhua; Cao, Lipeng

    The structural, ferroelectric and magnetic properties of bulk perovskite Fe-doped BaTiO3 (BFTO) prepared by standard solid-state reaction have been investigated. X-ray diffraction (XRD) identifies the tetragonal structure of BFTO samples. Rietveld refinements of XRD data indicates that the doping ions led to ab-plane expansion and out-of-ab-plane shrinkage of the BFTO phases. X-ray photoelectron spectroscopy (XPS) measurements for the prepared samples reveals that Fe3+ and Fe4+ ions replaces Ti4+ ions in the crystal lattice to form single-phase BFTO solids. The results of the temperature-dependent dielectric properties and magnetic hysteresis loops for the BFTO solids show simultaneously the ferroelectric order and ferromagnetic order at room temperature. The doping of magnetic element Fe brings about ferromagnetic order for the samples, and the measured magnetic moment for each Fe atom increases from 0.70 μB to 1.55 μB in BFTO samples. The origin of ferromagnetism of the BFTO samples should be attributed to the double exchange interactions of Fe3+-O2-Fe4+ ions.

  8. Structural, Electrical and Dielectrical Property Investigations of Fe-Doped BaZrO3 Nanoceramics

    NASA Astrophysics Data System (ADS)

    Khirade, Pankaj P.; Birajdar, Shankar D.; Humbe, Ashok V.; Jadhav, K. M.

    2016-06-01

    Nanocrystalline samples of BaZr1- x Fe x O3 ( x = 0.0, 0.05, 0.10, 0.20, 0.30, 0.40 and 0.50) ceramics were synthesized by the wet chemical sol-gel auto combustion method. The perovskite structured cubic phase formation of BaZr1- x Fe x O3 samples was confirmed by x-ray diffraction (XRD) data analysis. Various structural parameters such as lattice constant ( a), unit cell volume ( V), x-ray density ( ρ x), and porosity ( P) were determined using XRD data. The lattice constant ( a), x-ray density ( ρ x) and porosity ( P) decrease with an increase in Fe content x. The average particle size was calculated by using the Debye-Scherer's formula using XRD data and was 9-18 nm. The microstructural studies were investigated through scanning electron microscopy technique. Compositional stoichiometry was confirmed by energy dispersive spectrum analysis. The direct current electrical resistivity studies of the prepared samples were carried out in the temperature range of 343-1133 K using a standard two-probe method. The electrical conductivity ( σ) increases with temperature and Fe concentration. The dielectric parameters such as dielectric constant ( ɛ') and loss tangent (tan δ) were measured with frequency at room temperature in the frequency range 50 Hz to 5 MHz. The dielectric parameters show strong compositional as well as frequency dependences. The dielectric parameters were found to be higher at lower frequency.

  9. Interdependence of spin structure, anion height and electronic structure of BaFe2As2

    NASA Astrophysics Data System (ADS)

    Sen, Smritijit; Ghosh, Haranath

    2016-05-01

    Superconducting as well as other electronic properties of Fe-based superconductors are quite sensitive to the structural parameters specially, on anion height which is intimately related to zAs, the fractional z co-ordinate of As atom. Due to presence of strong magnetic fluctuation in these Fe-based superconductors, optimized structural parameters (lattice parameters a, b, c) including zAs using density functional theory (DFT) under generalized gradient approximation (GGA) does not match experimental values accurately. In this work, we show that the optimized value of zAs is strongly influenced by the spin structures in the orthorhombic phase of BaFe2As2 system. We take all possible spin structures for the orthorhombic BaFe2As2 system and then optimize zAs. Using these optimized structures we calculate electronic structures like density of states, band structures etc., for each spin configurations. From these studies we show that the electronic structure, orbital order which is responsible for structural as well as related to nematic transition, are significantly influenced by the spin structures.

  10. Observations of Al, Fe and Ca(+) in Mercury's Exosphere

    NASA Technical Reports Server (NTRS)

    Bida, Thomas A.; Killen, Rosemary M.

    2011-01-01

    We report 5-(sigma) tangent column detections of Al and Fe, and strict 3-(sigma) tangent column upper limits for Ca(+) in Mercury's exosphere obtained using the HIRES spectrometer on the Keck I telescope. These are the first direct detections of Al and Fe in Mercury's exosphere. Our Ca(-) observation is consistent with that reported by The Mercury Atmospheric and Surface Composition Spectrometer (MASCS) on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft.

  11. Metastable Phases of Rapidly Solidified Al-Rich Al-Fe Alloys

    DTIC Science & Technology

    1984-01-01

    same contrast. 20 FIGURE 9. Convergent beam diffraction pattern taken from a single crystal globular "S" phase. 21 FIGURE 10. The flower -like phase. 21...FIGURE 11. Convergent beam diffraction pattern obtained from the flower -like phase. 21 iii "- "’., % i ’ % " PAGE FIGURE 12. At-i wt.% Fe. Cellular...any of the previously reported aluminum-rich phases (Al3Fe, AlxFe, AI6Fe, A19Fe2, or AlmFe) [2,3]. An additional flower - shaped phase was detected in

  12. Alloy development and processing of FeAl: An overview

    SciTech Connect

    Maziasz, P.J.; Goodwin, G.M.; Alexander, D.J.; Viswanathan, S.

    1997-03-01

    In the last few years, considerable progress has been made in developing B2-phase FeAl alloys with improved weldability, room-temperature ductility, and high-temperature strength. Controlling the processing-induced microstructure is also important, particularly for minimizing trade-offs in various properties. FeAl alloys have outstanding resistance to high-temperature oxidation, sulfidation, and corrosion in various kinds of molten salts due to formation of protective Al{sub 2}O{sub 3} scales. Recent work shows that FeAl alloys are carburization-resistant as well. Alloys with 36 to 40 at. % Al have the best combination of corrosion resistance and mechanical properties. Minor alloying additions of Mo, Zr, and C, together with microalloying additions of B, produce the best combination of weldability and mechanical behavior. Cast FeAl alloys, with 200 to 400 {mu}m grain size and finely dispersed ZrC, have 2 to 5% tensile ductility in air at room-temperature, and a yield strength > 400 MPa up to about 700 to 750{degrees}C. Extruded ingot metallurgy (I/M) and powder metallurgy (P/M) materials with refined grain sizes ranging from 2 to 50 {mu}m, can have 10 to 15% ductility in air and be much stronger, and can even be quite tough, with Charpy impact energies ranging from 25 to 105 J at room-temperature. This paper highlights progress made in refining the alloy composition and exploring processing effects on FeAl for monolithic applications. It also includes recent progress on developing FeAl weld-overlay technology, and new results on welding of FeAl alloys. It summarizes some of the current industrial testing and interest for applications.

  13. Ultrafast structural dynamics of the orthorhombic distortion in the Fe-pnictide parent compound BaFe2As2.

    PubMed

    Rettig, L; Mariager, S O; Ferrer, A; Grübel, S; Johnson, J A; Rittmann, J; Wolf, T; Johnson, S L; Ingold, G; Beaud, P; Staub, U

    2016-03-01

    Using femtosecond time-resolved hard x-ray diffraction, we investigate the structural dynamics of the orthorhombic distortion in the Fe-pnictide parent compound BaFe2As2. The orthorhombic distortion analyzed by the transient splitting of the (1 0 3) Bragg reflection is suppressed on an initial timescale of 35 ps, which is much slower than the suppression of magnetic and nematic order. This observation demonstrates a transient state with persistent structural distortion and suppressed magnetic/nematic order which are strongly linked in thermal equilibrium. We suggest a way of quantifying the coupling between structural and nematic degrees of freedom based on the dynamics of the respective order parameters.

  14. Ultrafast structural dynamics of the orthorhombic distortion in the Fe-pnictide parent compound BaFe2As2

    PubMed Central

    Rettig, L.; Mariager, S. O.; Ferrer, A.; Grübel, S.; Johnson, J. A.; Rittmann, J.; Wolf, T.; Johnson, S. L.; Ingold, G.; Beaud, P.; Staub, U.

    2016-01-01

    Using femtosecond time-resolved hard x-ray diffraction, we investigate the structural dynamics of the orthorhombic distortion in the Fe-pnictide parent compound BaFe2As2. The orthorhombic distortion analyzed by the transient splitting of the (1 0 3) Bragg reflection is suppressed on an initial timescale of 35 ps, which is much slower than the suppression of magnetic and nematic order. This observation demonstrates a transient state with persistent structural distortion and suppressed magnetic/nematic order which are strongly linked in thermal equilibrium. We suggest a way of quantifying the coupling between structural and nematic degrees of freedom based on the dynamics of the respective order parameters. PMID:27158636

  15. Specific Heat vs Field in the 30 K Superconductor BaFe2(As0.7P0.3)2

    NASA Astrophysics Data System (ADS)

    Stewart, G. R.; Kim, J. S.; Hirschfeld, P. J.; Kasahara, S.; Shibauchi, T.; Terashima, T.; Matsuda, Y.

    2010-03-01

    Recently, superconductivity at 30 K has been reported [1] in P-doped BaFe2As2, with 1/3 of the As replaced by P. Magnetic penetration and thermal conductivity measurements [2] indicate a nodally gapped superconductor. We report here on measurements of the specific heat divided by temperature, C/T, as a function of field up to 15 T and down to 0.4 K in order to further investigate the nodal structure with another probe. [4pt] [1] S. Kasahara, et al., arXiv0905.4427. [0pt] [2] K. Hashimoto, et al., arXiv0907.4399.

  16. Fe Segregation Effects on Grain Boundary Migration in Al

    NASA Astrophysics Data System (ADS)

    Mendelev, Mikhail; Srolovitz, David; Ackland, Graeme; Han, Seungwu

    2004-03-01

    We investigate the effect of Fe impurities on grain boundary migration in Al. We fit a new interatomic potential to experimental data and our first principles results. This potential is validated by comparing simulated and experimental liquid Al-Fe alloy structure factors. This potential was used to simulate boundary migration in pure Al. The boundary velocity vs. driving force data at several temperatures were used to extract the boundary mobility and the activation energy for boundary migration. The activation energy was found to be at least an order of magnitude smaller than that obtained from experiment. This discrepancy is presumably associated with impurities in the Al samples. Therefore, we examined the effect of Fe on boundary migration in Al by determining the heat of segregation and the Fe diffusivity in Al as input to the Cahn-Lücke-Stüwe analytical impurity drag model. This analysis showed that even extremely small quantities of Fe (less than 1 ppm) in Al can reduce the grain boundary mobility by two orders of magnitude at T=723 K and even more at lower T, consistent with the extant experimental data.

  17. Uniaxial-strain mechanical detwinning of CaFe2As2 and BaFe2As2 crystals: Optical and transport study

    NASA Astrophysics Data System (ADS)

    Tanatar, M. A.; Blomberg, E. C.; Kreyssig, A.; Kim, M. G.; Ni, N.; Thaler, A.; Bud'Ko, S. L.; Canfield, P. C.; Goldman, A. I.; Mazin, I. I.; Prozorov, R.

    2010-05-01

    The parent compounds of iron-arsenide superconductors, AFe2As2 (A=Ca,Sr,Ba) , undergo a tetragonal to orthorhombic structural transition at a temperature TTO in the range 135-205 K depending on the alkaline-earth element. Below TTO the free standing crystals split into equally populated structural domains, which mask intrinsic, in-plane, anisotropic properties of the materials. Here we demonstrate a way of mechanically detwinning CaFe2As2 and BaFe2As2 . The detwinning is nearly complete, as demonstrated by polarized light imaging and synchrotron x-ray measurements, and reversible, with twin pattern restored after strain release. Electrical resistivity measurements in the twinned and detwinned states show that resistivity, ρ , decreases along the orthorhombic ao axis but increases along the orthorhombic bo axis in both compounds. Immediately below TTO the ratio ρbo/ρao=1.2 and 1.5 for Ca and Ba compounds, respectively. Contrary to CaFe2As2 , BaFe2As2 reveals an anisotropy in the nominally tetragonal phase, suggesting that either fluctuations play a larger role above TTO in BaFe2As2 than in CaFe2As2 or that there is a higher temperature crossover or phase transition.

  18. Electric control of magnetism at the Fe/BaTiO3 interface

    SciTech Connect

    Radaelli, G.; Petti, D.; Plekhanov, E.; Fina, I.; Torelli, P.; Salles, B. R.; Cantoni, M.; Rinaldi, C.; Gutiérrez, D.; Panaccione, G.; Varela, M.; Picozzi, S.; Fontcuberta, J.; Bertacco, R.

    2014-03-03

    Interfacial magnetoelectric coupling (MEC) is a viable path to achieve electrical writing of magnetic information in spintronic devices. For the prototypical Fe/BaTiO3 (BTO) system, only tiny changes of the interfacial Fe magnetic moment upon reversal of the BTO dielectric polarization have been predicted so far. Here, by using X-ray magnetic circular dichroism in combination with high resolution electron microscopy and first principles calculations, we report on an undisclosed physical mechanism for interfacial MEC in the Fe/BTO system. At the Fe/BTO interface, an ultrathin FeOx layer exists, whose magnetization can be electrically and reversibly switched on-off at room-temperature by reversing the BTO polarization. The suppression / recovery of interfacial ferromagnetism results from the asymmetric effect that ionic displacements in BTO produces on the exchange coupling constants in the adjacent FeOx layer. The observed giant magnetoelectric response holds potential for optimizing interfacial MEC in view of efficient, low-power spintronic devices.

  19. Electric control of magnetism at the Fe/BaTiO3 interface

    DOE PAGES

    Radaelli, G.; Petti, D.; Plekhanov, E.; ...

    2014-03-03

    Interfacial magnetoelectric coupling (MEC) is a viable path to achieve electrical writing of magnetic information in spintronic devices. For the prototypical Fe/BaTiO3 (BTO) system, only tiny changes of the interfacial Fe magnetic moment upon reversal of the BTO dielectric polarization have been predicted so far. Here, by using X-ray magnetic circular dichroism in combination with high resolution electron microscopy and first principles calculations, we report on an undisclosed physical mechanism for interfacial MEC in the Fe/BTO system. At the Fe/BTO interface, an ultrathin FeOx layer exists, whose magnetization can be electrically and reversibly switched on-off at room-temperature by reversing themore » BTO polarization. The suppression / recovery of interfacial ferromagnetism results from the asymmetric effect that ionic displacements in BTO produces on the exchange coupling constants in the adjacent FeOx layer. The observed giant magnetoelectric response holds potential for optimizing interfacial MEC in view of efficient, low-power spintronic devices.« less

  20. An Assessment of the Al- Fe- N System

    NASA Astrophysics Data System (ADS)

    Hillert, Mats; Jonsson, Stefan

    1992-11-01

    The thermodynamic properties of the Al-Fe-N system are assessed, taking various types of information into account. For solid AIN, a description very similar to that given by JANAF is found to yield reasonable predictions for the solubility of A1N in face-centered cubic (fcc) Fe and in liquid Fe. An ionic two-sublattice model is applied to the liquid phase, containing two N species, N-3 and N0 The melting point of A1N is taken as 3068 K, and a required gas pressure of 9.75 bar is predicted. A sublimation point of 2690 K at 1 bar is also predicted. A plot of the liquidus surfaces in the Fe-rich end of the Al-Fe-N system is presented.

  1. Oxidation Resistant Ti-Al-Fe Diffusion Barrier for FeCrAlY Coatings on Titanium Aluminides

    NASA Technical Reports Server (NTRS)

    Brady, Michael P. (Inventor); Smialke, James L. (Inventor); Brindley, William J. (Inventor)

    1996-01-01

    A diffusion barrier to help protect titanium aluminide alloys, including the coated alloys of the TiAl gamma + Ti3Al (alpha2) class, from oxidative attack and interstitial embrittlement at temperatures up to at least 1000 C is disclosed. The coating may comprise FeCrAlX alloys. The diffusion barrier comprises titanium, aluminum, and iron in the following approximate atomic percent: Ti-(50-55)Al-(9-20)Fe. This alloy is also suitable as an oxidative or structural coating for such substrates.

  2. Crystal and electronic structures of two new iron selenides: Ba{sub 4}Fe{sub 3}Se{sub 10} and BaFe{sub 2}Se{sub 4}

    SciTech Connect

    Berthebaud, David; Perez, Olivier; Tobola, Janusz; Pelloquin, Denis; Maignan, Antoine

    2015-10-15

    The new ternary selenides, Ba{sub 4}Fe{sub 3}Se{sub 10} and BaFe{sub 2}Se{sub 4,} were synthesized from a reaction of appropriate amounts of elements at high temperature in a silica sealed tube, and their structures were resolved using X-ray single crystal diffraction. BaFe{sub 2}Se{sub 4} crystallizes in the tetragonal space group I4/m with a=8.008(9) Å and c=5.483(3) Å as cell parameters. It is a new compound with a structure isotypical to the sulfide BaFe{sub 2}S{sub 4} which belongs to the infinitely adaptive structures series Ba{sub 1+x}Fe{sub 2}S{sub 4}. The second compound, Ba{sub 4}Fe{sub 3}Se{sub 10}, crystallizes in the monoclinic space group P2{sub 1}/n with a=8.8593(1) Å, b=8.8073(1) Å, c=12.2724(1) Å and β=109.037(6)° as cell parameters. It exhibits an original structure with a new type of iron selenide polyhedra. These data were consistent with the powder X-ray diffraction and TEM analyses. Their electronic structures point towards metallicity and electronic correlations for both selenides. - Graphical abstract: Experimental [010] oriented ED pattern and corresponding HREM image of Ba{sub 4}Fe{sub 3}Se{sub 10}. Image calculated with a focus and thickness to 15nm and 8 nm respectively is inserted. Bright contrasts are correlated to Se rows belonging to FeSe{sub 3}(Se{sub 2}){sup 2−}–FeSe{sub 6}–FeSe{sub 3}(Se{sub 2}){sup 2−} trimers. The corresponding structure projection is also shown. - Highlights: • Two new barium iron selenide compounds. • An original structure type Ba4Fe3Se10. • Electronic structure calculations.

  3. Role of magnetism in superconductivity of BaFe2As2: Study of 5d Au-doped crystals

    DOE PAGES

    Li, Li; Cao, Huibo; McGuire, Michael A.; ...

    2015-09-09

    We investigate properties of BaFe2As2 (122) single crystals upon gold doping, which is the transition metal with the highest atomic weight. The Au substitution into the FeAs-planes of 122 crystal structure (Au-122) is only possible up to a small amount of ~3%. We find that 5d is more effective in reducing magnetism in 122 than its counter 3d Cu, and this relates to superconductivity. We provide evidence of short-range magnetic fluctuations and local lattice inhomogeneities that may prevent strong percolative superconductivity in Ba(Fe1-xAux)2As2.

  4. Giant thermal vibrations in the framework compounds Ba1 -xSrxAl2O4

    NASA Astrophysics Data System (ADS)

    Kawaguchi, S.; Ishii, Y.; Tanaka, E.; Tsukasaki, H.; Kubota, Y.; Mori, S.

    2016-08-01

    Synchrotron x-ray diffraction experiments were performed on the network compounds Ba1 -xSrxAl2O4 at temperatures between 15 and 800 K. The ferroelectric phase of the parent BaAl2O4 is largely suppressed by substituting a small amount of Sr for Ba and disappears for x ≥0.1 . Structural refinements reveal that the isotropic atomic displacement parameter Biso in the bridging oxygen atom is largely independent of temperature and retains an anomalously large value in the adjacent paraelectric phase even at the lowest temperature. The Biso systematically increases as x increases, exhibiting an especially large value for x =0.5 . According to previous electron diffraction experiments for Ba1 -xSrxAl2O4 with x ≥0.1 , strong thermal diffuse scattering occurs at two reciprocal points relating to two distinct soft modes at the M and K points over a wide range of temperatures below 800 K [Y. Ishii et al., Sci. Rep. 6, 19154 (2016), 10.1038/srep19154]. Although the latter mode disappears at approximately 200 K, the former does not condense, at least down to 100 K. The anomalously large Biso observed in this study is ascribed to these soft modes existing in a wide temperature range.

  5. Large magnetostriction in directionally solidified FeGa and FeGaAl alloys

    NASA Astrophysics Data System (ADS)

    Srisukhumbowornchai, N.; Guruswamy, S.

    2001-12-01

    The magnetostriction of Fe-x at. % Ga (x=15, 20, and 27.5) was measured, for alloys processed under different directional solidification conditions, and the effect of partial substitution of Ga with Al on the magnetostriction of the alloys was examined. Magnetostriction measurements were carried out at different prestress levels varying from 0 to 55 MPa. Ga additions in the range of 15-27.5 at. % Ga in Fe were found to improve the magnetostriction of the disordered bcc phase of Fe by as much as 1 order of magnitude. The applied fields for saturation magnetostriction and the hysteresis observed were small. Magnetostriction values as high as 271×10-6 were obtained in polycrystalline Fe-27.5 at. % Ga rods prepared using a directional growth (DG) process at a growth rate of 22.5 mm/h. This process, which is essentially a seedless vertical Bridgman technique, resulted in near [001] textured polycrystalline Fe-Ga alloys. The preferred [001] crystallographic orientation of the DG alloys was approximately 14° away from the rod direction. For Ga contents between 15 and 27.5 at. % in Fe, the Ga atoms increase the Fe-Fe spacing in the disordered bcc (A2) phase and reduce the magnetic moment of Fe. Substitution of Ga with Al has a significant effect on the magnetostriction of the Fe-Ga alloys. Small substitution of 5 at. % Al for Ga in the Fe-20 at. % Ga alloy increases the magnetostriction in Fe, and the value is slightly larger than that of the Fe-20 at. % Ga alloy. A higher substitution amount of Al tends to decrease the magnetostriction.

  6. Segregation-Induced Subsurface Restructuring of FeAl(100)

    NASA Astrophysics Data System (ADS)

    Kottche, M.; Graupner, H.; Hammer, L.; Heinz, K.; Zehner, D. M.

    1996-03-01

    For FeAl, the stacking sequence in the [100] direction of the bulk crystal (CsCl structure) consists of alternating, single element planes. After sputtering, the selvedge region is depleted in Al. Following annealing to 350 ^circC, Al segregates to the surface region and a c(2 x 2) structure develops.(H. Graupner, L. Hammer, K. Müller, and D. M. Zehner, Surf. Sci. 322 (1995) 103. Research is sponsored by the *University of Erlangen-Nürnberg, Germany and DAAD, and the **Division of Materials Sciences, U.S. Department of Energy, under contract DE-AC05-84OR21400 with Lockheed Martin Energy Systems, Inc.) We have used low-energy electron diffraction (LEED) and Auger electron spectroscopy to investigate the structure and composition of this surface. From a detailed LEED I-V analysis, it has been determined that the subsurface region of the (100) surface orders with annealing, to form a stable Fe_3Al slab which is capped by an Al top layer and acts as an interface to the bulk FeAl. Within the limits of error, the interfacial Fe_3Al is similar to the bulk phase with some slight geometric rippling of the layers containing both elements. Annealing to higher temperatures leads to additional Al diffusion and eliminates the restructuring, resulting in a (1 x 1) phase.

  7. Characteristics of B2O3 and Fe added into BaFe12O19 permanent magnets prepared at different milling time and sintering temperature

    NASA Astrophysics Data System (ADS)

    Sebayang, Perdamean; Sari, Ayu Yuswita; Ginting, Delovita; Allan, Yola; Nasruddin M., N.; Sebayang, Kerista

    2016-02-01

    The objective of present work is to investigate the characteristic of BaFe12O19, B2O3-BaFe12O19 and Fe-BaFe12O19 magnets fabricated at different milling time and sintering temperature. The characteristic of perrmanen magnet BaFe12O19 with different content of B2O3 and Fe which was fabricated at different milling time and sintering temperature were investigated. The powder mixtures were prepared by dry and wet milling at various milling time. The powder were mixtured and prepared by dry and wet milling at various milling time. The mixture powder was then compacted by anisotropic with compressive pressure of 50 N/cm2. The green bodies were sinter at 1050, 1100, 1150 and 1200°C and hold for 1 h, separately. The density, magnetic flux density and B-H curve were measured by Archimedes principle, Gauss meter and Permagraph, respectively. The microstructure and phase composition characterization were performed by SEM and XRD. The results of this study are presented in this paper. It shows that addition of Fe (in wet milling) and B2O3 (in dry milling) respectively give a potential benefit to reduce the sintering temperature and improve the magnetic flux density of barium hexaferrite.

  8. Structural and magnetic study of the double-perovskites Ba2(Fe, B)2O6 (B = Mo, W and Re)

    NASA Astrophysics Data System (ADS)

    Rammeh, N.; Bramnik, K. G.; Ehrenberg, H.; Ritter, C.; Fuess, H.; Cheikh-Rouhou, A.

    2004-05-01

    Ceramics of Ba2(Fe,B)2O6 double-perovskites have been prepared and studied for B = Mo, W and Re. Rietveld analysis confirms that all samples crystallize in a cubic double-perovskite structure with Fmm space group. Magnetization measurements performed in the temperature range from 5 K to 350 K show a ferromagnetic behaviour for both materials Ba2(Fe,Mo)2O6 and Ba2(Fe,Re)2O6, with TC = 335 K, 318 K respectively, and antiferromagnetic behaviour for Ba2(Fe,W)2O6 with TN = 20 K.

  9. An efficient synthesis of nanocrystalline BaFe12O19 materials by modified co-precipitation method

    NASA Astrophysics Data System (ADS)

    Habeeba, M.; Balamurugan, S.; Resmi, S. P.

    2016-05-01

    In this report, the nanocrystalline BaFe12O19 materials obtained by modified co-precipitation method using Na2CO3 and NaOH as precipitating agent are presented. In the modified co-precipitation process, instead of washing the co-precipitated product in mother liquor with de-ionized water, it was dried in a heating mantle, which has major influence as self flux in the single phase formation of BaFe12O19 phase. The co-precipitated product was annealed at 1000°C for 2 h under ambient pressure to obtain the required BaFe12O19 phase. The results based on XRD, average crystalline size, FT-IR, HR-SEM and EDX are reported. The annealed BaFe12O19 materials showed nanocrystalline single hexagonal phase with average crystalline size of ~ 102 nm. The annealed BaFe12O19 materials show particle sizes in the range of 280 ~ 326 nm and the thickness of ~ 57 nm in the high resolution micro-images.

  10. Superconductivity at 23 K and low anisotropy in Rb-substituted BaFe2As2 single crystals

    NASA Astrophysics Data System (ADS)

    Bukowski, Z.; Weyeneth, S.; Puzniak, R.; Moll, P.; Katrych, S.; Zhigadlo, N. D.; Karpinski, J.; Keller, H.; Batlogg, B.

    2009-03-01

    Single crystals of Ba1-xRbxFe2As2 with x=0.05-0.1 have been grown from Sn flux and are bulk superconductors with Tc up to 23 K. The crystal structure was determined by x-ray diffraction analysis, and Sn is found to be incorporated for ˜9% Ba, shifted by ˜1.1Å away from the Ba site toward the (Fe2As2) layers. The upper critical field deduced from resistance measurements is anisotropic with slopes of 7.1(3) T/K ( H∥ab plane) and 4.2(2) T/K ( H∥c axis), sufficiently far below Tc . The extracted upper critical field anisotropy γH˜3 close to Tc is in good agreement with the estimate from magnetic torque measurements. This indicates that the electronic properties in the doped BaFe2As2 compound are significantly more isotropic than those in the LnFeAsO family. The in-plane critical current density at 5 K exceeds 1×106A/cm2 , making Ba1-xRbxFe2As2 a promising candidate for technical applications.

  11. Comparison of metals extractability from Al/Fe-based drinking water treatment residuals.

    PubMed

    Wang, Changhui; Bai, Leilei; Pei, Yuansheng; Wendling, Laura A

    2014-12-01

    Recycling of drinking water treatment residuals (WTRs) as environment amendments has attracted substantial interest due to their productive reuse concomitant with waste minimization. In the present study, the extractability of metals within six Al/Fe-hydroxide-comprised WTRs collected throughout China was investigated using fractionation, in vitro digestion and the toxicity characteristic leaching procedure (TCLP). The results suggested that the major components and structure of the WTRs investigated were similar. The WTRs were enriched in Al, Fe, Ca, and Mg, also contained varying quantities of As, Ba, Be, Cd, Co, Cr, Cu, K, Mn, Mo, Na, Ni, Pb, Sr, V, and Zn, but Ag, Hg, Sb, and Se were not detected. Most of the metals within the WTRs were largely non-extractable using the European Community Bureau of Reference (BCR) procedure, but many metals exhibited high bioaccessibility based on in vitro digestion. However, the WTRs could be classified as non-hazardous according to the TCLP assessment method used by the US Environmental Protection Agency (USEPA). Further analysis showed the communication factor, which is calculated as the ratio of total extractable metal by BCR procedure to the total metal, for most metals in the six WTRs, was similar, whereas the factor for Ba, Mn, Sr, and Zn varied substantially. Moreover, metals in the WTRs investigated had different risk assessment code. In summary, recycling of WTRs is subject to regulation based on assessment of risk due to metals prior to practical application.

  12. Lateral electric-field control of giant magnetoresistance in Co/Cu/Fe/BaTiO{sub 3} multiferroic heterostructure

    SciTech Connect

    Savitha Pillai, S.; Kojima, H.; Itoh, M.; Taniyama, T.

    2015-08-17

    We report lateral electric-field-driven sizable changes in the magnetoresistance of Co/Cu/Fe tri-layered wires on BaTiO{sub 3} single crystal. While the observed change is marginal in the tetragonal phase of BaTiO{sub 3}, it reaches over 40% in the orthorhombic and rhombohedral phases with an electric field of 66 kV/cm. We attribute it to possible electric-field-induced variations of the spin-dependent electronic structures, i.e., spin polarization, of the Fe via interfacial strain transfer from BaTiO{sub 3}. The contrasting results for the different phases of BaTiO{sub 3} are discussed, associated with the distinct aspects of the ferroelectric polarization switching processes in each phase.

  13. Ferroelectric control of magnetism in BaTiO3/Fe heterostructures

    NASA Astrophysics Data System (ADS)

    Sahoo, Sarbeswar; Polisetty, Srinivas; Duan, Chun Gang; Jaswal, Sitaram; Tsymbal, Evgeny; Binek, Christian

    2008-03-01

    Multiferroics can offer the possibility to manipulate the cross coupled order parameters by conjugate electric and magnetic fields. Switching off ferromagnetic order by an electric field for instance promises significant impact in the design of novel spintronic devices. Here we report on the reversible control of magnetism for a Fe thin film in proximity of a BaTiO3 single-crystal. Large magnetization changes emerge in response to ferroelectric switching and structural transitions of BaTiO3 controlled by applied electric fields and temperature, respectively.^ Interface strain coupling is the primary mechanism altering the induced magnetic anisotropy. As a result, coercivity changes up to 120% occur between the various structural states of BaTiO3. Up to 20% coercivity change is achieved via electrical control at room temperature. Our all solid state ferroelectric-ferromagnetic heterostructures open viable possibilities for new technological applications. ^S. Sahoo, S. Polisetty, C.-G. Duan, S. S. Jaswal, E. Y. Tsymbal, and Ch. Binek, Phys. Rev. B 76, 092108 (2007).

  14. Cs, Sr, and Ba Sorption on Clays and Fe-Oxides

    SciTech Connect

    Anderson, H.L.; Brady, P.V.; Cygan, R.T.; Gruenhagen, S.E.; Nagy, K.L.; Westrich, H.R.

    1999-06-16

    Technical guidance for performance assessment (PA) of low-level radioactive waste (LLRW) sites is currently dependent upon experimental retardation factors (K{sub D}'s) to predict radionuclide transport. Accurate predictions of waste transport or retardation will require mechanistic models of radionuclide sorption so as to be applicable to a wide range of soil/groundwater environments. To that end, we have investigated Cs{sup +}, Sr{sup +}, and Ba{sup 2+} sorption on several clay and Fe-oxide minerals. Relative metal binding strengths for montmorillonite clay decrease from Ba{sup 2+} to Sr{sup +}, which is similar to that sorption trend noticed for kaolinite. Molecular dynamics simulations for kaolinite suggest that Cs{sup +} is sorbed at aluminol (010) edge sites as an inner-sphere complex and weakly sorbed as an outer-sphere complex on (001) basal surfaces. Sorption is thought to occur on similar sites for smectite clays, however, the basal plane residual charge and its increased basal plane exposure should have a greater influence on metal sorption. On the other hand, phase transformation kinetics (e.g., ferrihydrite to goethite) is a very important control of metal sorption and resorption for Fe-oxides/hydroxides. These results provide a basis for understanding and predicting metal sorption on complex soil minerals.

  15. Effect of divalent (Sr, Ba) doping on the structural and magnetic properties of BiFeO{sub 3}

    SciTech Connect

    Rangi, Manisha Sanghi, Sujata; Agarwal, Ashish; Jangra, Sandhaya; Singh, Ompal

    2015-06-24

    The effect of divalent substitution on the crystal structure and magnetic properties of BiFeO{sub 3} has been investigated using X-ray diffraction and magnetic measurements technique. Single phase Bi{sub 0.8}A{sub 0.2}FeO{sub 3} (A= Sr, Ba) multiferroics have been synthesized by solid state reaction method. Rietveld analysis of the XRD patterns revealed that the prepared ceramics exhibit rhombohedral structure with space group R3c. M–H hysteresis loops were recorded at 5K revealed that Sr and Ba substitution transformed antiferromagnetic BiFeO3 into weak ferromagnetic. The enhanced magnetization with Sr and Ba addition is confirmed by the MT curve recorded at 1T. It is closely related to intrinsic structural distortion and modification of the antiparallel spin structure.

  16. Ultrafast dynamics of quasiparticles and coherent acoustic phonons in slightly underdoped (BaK)Fe2As2

    PubMed Central

    Lin, Kung-Hsuan; Wang, Kuan-Jen; Chang, Chung-Chieh; Wen, Yu-Chieh; Lv, Bing; Chu, Ching-Wu; Wu, Maw-Kuen

    2016-01-01

    We have utilized ultrafast optical spectroscopy to study carrier dynamics in slightly underdoped (BaK)Fe2As2 crystals without magnetic transition. The photoelastic signals due to coherent acoustic phonons have been quantitatively investigated. According to our temperature-dependent results, we found that the relaxation component of superconducting quasiparticles persisted from the superconducting state up to at least 70 K in the normal state. Our findings suggest that the pseudogaplike feature in the normal state is possibly the precursor of superconductivity. We also highlight that the pseudogap feature of K-doped BaFe2As2 is different from that of other iron-based superconductors, including Co-doped or P-doped BaFe2As2. PMID:27180873

  17. The mechanically induced structural disorder in barium hexaferrite, BaFe12O19, and its impact on magnetism.

    PubMed

    Sepelák, V; Myndyk, M; Witte, R; Röder, J; Menzel, D; Schuster, R H; Hahn, H; Heitjans, P; Becker, K-D

    2014-01-01

    The response of the structure of the M-type barium hexaferrite (BaFe12O19) to mechanical action through high-energy milling and its impact on the magnetic behaviour of the ferrite are investigated. Due to the ability of the (57)Fe Mössbauer spectroscopic technique to probe the environment of the Fe nuclei, a valuable insight on a local atomic scale into the mechanically induced changes in the hexagonal structure of the material is obtained. It is revealed that the milling of BaFe12O19 results in the deformation of its constituent polyhedra (FeO6 octahedra, FeO4 tetrahedra and FeO5 triangular bi-pyramids) as well as in the mechanically triggered transition of the Fe(3+) cations from the regular 12k octahedral sites into the interstitial positions provided by the magnetoplumbite structure. The response of the hexaferrite to the mechanical treatment is found to be accompanied by the formation of a non-uniform nanostructure consisting of an ordered crystallite surrounded/separated by a structurally disordered surface shell/interface region. The distorted polyhedra and the non-equilibrium cation distribution are found to be confined to the amorphous near-surface layers of the ferrite nanoparticles with the thickness extending up to about 2 nm. The information on the mechanically induced short-range structural disorder in BaFe12O19 is complemented by an investigation of its magnetic behaviour on a macroscopic scale. It is demonstrated that the milled ferrite nanoparticles exhibit a pure superparamagnetism at room temperature. As a consequence of the far-from-equilibrium structural disorder in the surface shell of the nanoparticles, the mechanically treated BaFe12O19 exhibits a reduced magnetization and an enhanced coercivity.

  18. Electric-voltage control of magnetism in Fe/BaTiO3 heterostructured multiferroics

    NASA Astrophysics Data System (ADS)

    Venkataiah, G.; Wada, E.; Taniguchi, H.; Itoh, M.; Taniyama, T.

    2013-05-01

    Electric field (E) control of the magnetic anisotropy and coercivity (HC) of a Fe film in Fe/BaTiO3 (BTO) is demonstrated at room temperature in the tetragonal phase of BTO. Polarizing microscopy and x-ray diffraction analysis of BTO (001) surface show distinctly two different regions; one with a1, a2 and c domains separated by 180° and 90° domain boundaries (DBs) (region 1) and the other with a1 domains separated by 180° DBs (region 2). The Fe film on region 1 shows complex magnetic anisotropy with the net magnetic easy axis in between [100] and [110] directions of BTO, while the magnetic anisotropy in region 2 exhibits two fold symmetry with an easy axis along [100]. In applied electric field (±10 kV/cm), the magnetic easy axis of the Fe film in region 1 is switched to the [110] direction of BTO, whereas in region 2 it stays unaffected. The HC versus E curves in region 1 show a butterfly-like behavior, while in region 2 no changes are observed. Also, the HC measured in E = ±10 kV/cm at different magnetic field orientations shows dramatic changes in region 1 compared to region 2. The observed electric field dependent magnetic response in both regions can be understood based on the DBs modifications and associated strain effects.

  19. Crystallization kinetics of BaO-Al2O3-SiO2 glasses

    NASA Technical Reports Server (NTRS)

    Bansal, Narottam P.; Hyatt, Mark J.

    1988-01-01

    Barium aluminosilicate glasses are being investigated as matrix materials in high-temperature ceramic composites for structural applications. Kinetics of crystallization of two refractory glass compositions in the barium aluminosilicate system were studied by differential thermal analysis (DTA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). From variable heating rate DTA, the crystallization activation energies for glass compositions (wt percent) 10BaO-38Al2O3-51SiO2-1MoO3 (glass A) and 39BaO-25Al2O3-35SiO2-1MoO3 (glass B) were determined to be 553 and 558 kJ/mol, respectively. On thermal treatment, the crystalline phases in glasses A and B were identified as mullite (3Al2O3-2SiO2) and hexacelsian (BaO-Al2O3-2SiO2), respectively. Hexacelsian is a high-temperature polymorph which is metastable below 1590 C. It undergoes structural transformation into the orthorhombic form at approximately 300 C accompanied by a large volume change which is undesirable for structural applications. A process needs to be developed where stable monoclinic celsian, rather than hexacelsian, precipitates out as the crystal phase in glass B.

  20. Synthesis, crystal structure, and magnetic properties of quaternary iron selenides: Ba2FePnSe5 (Pn=Sb, Bi)

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

    Two new barium iron pnictide-selenides, Ba2FeSbSe5 and Ba2FeBiSe5, were synthesized by a high-temperature solid-state route and their crystal structures were determined using single crystal X-ray diffraction. Both compounds are isomorphic to the high pressure phase Ba3FeS5 and crystallize in the orthorhombic space group Pnma (No. 62) with cell parameters of a=12.603(2)/12.619(2) Å, b=9.106(1)/9.183(1) Å, c=9.145(1)/9.123(1) Å and Z=4 for Ba2FeSbSe5 and Ba2FeBiSe5, respectively. According to differential scanning calorimetry, Ba2FePnSe5 compounds exhibit high thermal stability and melt congruently at 1055(5) K (Pn=Sb) and 1105(5) K (Pn=Bi). Magnetic characterizations reveal strong antiferromagnetic nearest-neighbor interactions in both compounds resulting in an antiferromagnetic ordering at 58(1) K for Ba2FeSbSe5 and 79(2) K for Ba2FeBiSe5. The magnetic interactions between Fe3+ centers, which are at least 6 Å apart from each other, are mediated by superexchange interactions.

  1. Structural, magnetic and microwave properties of barium hexaferrite thick films with different Fe/Ba mole ratio

    NASA Astrophysics Data System (ADS)

    Verma, Samiksha; Dhawan, S. K.; Paesano, Andrea; Pandey, O. P.; Sharma, Puneet

    2015-12-01

    Barium hexaferrite (BaFe12O19) thick films (∼60 μm) with different BaO·xFe2O3 mole ratio (x=5.0-6.0) were prepared by screen printing method. X-ray diffraction analysis confirmed the formation of single phase BaFe12O19 (BaM). Preferential site occupation of Fe3+ ion at five different crystallographic sites, with varied mole ratio was measured by Mössbauer spectroscopy. Vacancy fraction found to be higher at 4f1, 4f2 and 2b sites for mole ratio 5.5 and 5.0 respectively. Magnetic measurement shows that the magnetization (M) and magnetocrystalline anisotropy field (Ha) depends upon mole ratio. M and Ha are found to be maximum for mole ratio 5.5, while the coercivity (Hc) remains constant. Reflection losses (RL) in the frequency range of 12-18 GHz were also studied. Present investigation demonstrates the effect of mole ratio on structural, magnetic and microwave absorption properties of BaM thick films for microwave device applications.

  2. Comparison of Fe-AlPILC and Fe-ZSM-5 catalysts used for degradation of methomyl

    NASA Astrophysics Data System (ADS)

    Lázár, Károly; Tomašević, Andjelka; Bošković, Goran; Kiss, Ernő

    2009-07-01

    Catalytic performances of Fe-AlPILC (14 wt.% Fe) and Fe-ZSM-5 (5 wt.% Fe) catalysts are compared in the wet oxidative degradation of methomyl. Fe-ZSM-5 exhibits outstanding whereas Fe-AlPILC shows only mediocre activity. Positions of iron are analysed in the two catalysts by Mössbauer spectroscopy. Iron is in highly dispersed state in Fe-AlPILC whereas in the other case a hematite/ZSM-5 composite is formed. The catalytic activity is attributed to iron located and stabilized in ionic dispersion.

  3. Dual ferroic properties of hexagonal ferrite ceramics BaFe12O19 and SrFe12O19

    NASA Astrophysics Data System (ADS)

    Kostishyn, V. G.; Panina, L. V.; Timofeev, A. V.; Kozhitov, L. V.; Kovalev, A. N.; Zyuzin, A. K.

    2016-02-01

    Dual ferroic properties of a strong magnetism and large ferroelectricity have been observed in barium BaFe12O19 and strontium SrFe12O19 hexaferrite ceramics. The samples were fabricated by a modified ceramic technique from highly purified raw materials with addition of boron oxide allowing the control of grain size and enhancement of bulk resistivity. Whereas the samples of PbFe12O19 fabricated by the same technological method did not have sufficient electric resistivity to support an electric field and did not exhibit the ferroelectric properties. The structure of the samples examined by X-ray diffraction is consistent with a single hexagonal phase. The grains are randomly oriented with the average grain size of 300-400 nm coated with boron oxide. The magnetic properties are characterised by standard ferrimagnetic behavior with the Neel temperature of about 450 °C. Large spontaneous polarization was observed with the maximal values of 45-50 μC/cm2 under an applied electric field of 100-300 kV/m. A strong coupling between magnetic and electric ordering was confirmed by measuring the magnetoelectric (ME) parameter and magnetodielectric ratio. These ME characteristics are more advanced than those for well-known room temperature multiferroic BiFeO3. Furthermore, by applying an electric field, the manipulation of magnetization in the range of up to 9% was observed, which is even greater than in some substituted hexaferrites with a non-collinear magnetic structure. The obtained results on electrical polarization are similar to the values reported for the corresponding hexaferrites sintered by polymer precursor technique. This suggests a promising potential of M-type hexaferrite ceramics in devices utilizing magnetoelectric coupling.

  4. Bandgap narrowing in the layered oxysulfide semiconductor Ba3Fe2O5Cu2S2: Role of FeO2 layer

    NASA Astrophysics Data System (ADS)

    Han, Zhang; Shifeng, Jin; Liwei, Guo; Shijie, Shen; Zhiping, Lin; Xiaolong, Chen

    2016-02-01

    A new layered Cu-based oxychalcogenide Ba3Fe2O5Cu2S2 has been synthesized and its magnetic and electronic properties were revealed. Ba3Fe2O5Cu2S2 is built up by alternatively stacking [Cu2S2]2- layers and iron perovskite oxide [(FeO2)(BaO)(FeO2)]2- layers along the c axis that are separated by barium ions with Fe3+ fivefold coordinated by a square-pyramidal arrangement of oxygen. From the bond valence arguments, we inferred that in layered CuCh-based (Ch = S, Se, Te) compounds the +3 cation in perovskite oxide sheet prefers a square pyramidal site, while the lower valence cation prefers the square planar sites. The studies on susceptibility, transport, and optical reflectivity indicate that Ba3Fe2O5Cu2S2 is an antiferromagnetic semiconductor with a Néel temperature of 121 K and an optical bandgap of 1.03 eV. The measurement of heat capacity from 10 K to room temperature shows no anomaly at 121 K. The Debye temperature is determined to be 113 K. Theoretical calculations indicate that the conduction band minimum is predominantly contributed by O 2p and 3d states of Fe ions that antiferromagnetically arranged in FeO2 layers. The Fe 3d states are located at lower energy and result in a narrow bandgap in comparison with that of the isostructural Sr3Sc2O5Cu2S2. Project supported by the National Natural Science Foundation of China (Grant Nos. 51472266, 51202286, and 91422303), the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (Grant No. XDB07020100) and the ICDD.

  5. Local anisotropic structure in amorphous Ba-Fe-O films and its role in determining magnetic anisotropy in crystallized Ba-hexaferrite films

    SciTech Connect

    Snyder, J.E.; Harris, V.G.; Koon, N.C.; Sui, X.; Kryder, M.H.

    1995-11-01

    Ba hexaferrite films with the easy direction of magnetization perpendicular or in-plane can be prepared by crystallization of amorphous films deposited under different sputtering conditions. Using polarization-dependent EXAFS (extended x-ray absorption fine structure), the authors have observed anisotropic local structure around the Fe atoms in as-sputtered amorphous Ba-Fe-O films. Such structure has not been detectable by conventional structural characterization techniques (x-ray diffraction, electron diffraction and transmission electron microscopy [TEM]). The results suggest that this local structural anisotropy determines the orientation of the fast-growing basal plane directions during post-deposition annealing and thus the directions of the c-axes and the magnetic anisotropy

  6. FeAl-TiC and FeAl-WC composites - melt infiltration processing, microstructure and mechanical properties

    SciTech Connect

    Subramanian, R.; Schneibel, J.H.

    1997-04-01

    TiC-based and WC-based cermets were processed with iron aluminide, an intermetallic, as a binder by pressureless melt infiltration to near full density (> 97 % theoretical density). Phase equilibria calculations in the quaternary Fe-Al-Ti-C and Fe-Al-W-C systems at 145{degrees}C were performed to determine the solubility of the carbide phases in liquid iron aluminide. This was done by using Thermocalc{trademark} and the results show that molten Fe-40 at.% Al in equilibrium with Ti{sub 0.512}C{sub 0.488} and graphite, dissolves 4.9 at% carbon and 64 atomic ppm titanium. In the Fe-Al-W-C system, liquid Fe-40 at.% Al in equilibrium with graphite dissolves about 5 at.% carbon and 1 at.% tungsten. Due to the low values for the solubility of the carbide phases in liquid iron aluminide, liquid phase sintering of mixed powders does not yield a dense, homogeneous microstructure for carbide volume fractions greater than 0.70. Melt infiltration of molten FeAl into TiC and WC preforms serves as a successful approach to process cermets with carbide contents ranging from 70 to 90 vol. %, to greater than 97% of theoretical density. Also, the microstructures of cermets prepared by melt infiltration were very homogeneous. Typical properties such as hardness, bend strength and fracture toughness are reported. SEM observations of fracture surfaces suggest the improved fracture toughness to result from the ductility of the intermetallic phase. Preliminary experiments for the evaluation of the oxidation resistance of iron aluminide bonded cermets indicate that they are more resistant than WC-Co cermets.

  7. Optical probes of symmetry breaking in magnetic and superconducting BaFe2(As1-xPx)2

    NASA Astrophysics Data System (ADS)

    Orenstein, Joseph

    The discovery of iron pnictide superconductors has opened promising new directions in the effort to fully understand the phenomenon of high-Tc, with a focus on the connections between superconductivity, magnetism, and electronic nematicity. The BaFe2(As1-xPx)2 (P:Ba122) system in particular has received attention because isovalent substitution of As for P generates less disorder than doping on the Fe site. The phase diagram of P:Ba122 is characterized by a line of simultaneous antiferromagnetic (AF) and tetragonal-to-orthorhombic transitions, Ts (x) , that penetrates the superconducting dome at x =0.28, just below optimal doping (xopt = 0.30). In this work, we use spatially-resolved optical polarimetry and photomodulated reflectance to detect linear birefringence and therefore breaking of 4-fold rotational (C4) symmetry. In underdoped (x<0.28) samples, birefringence appears at T>Tsand grows continuously with decreasing T . The birefringence is unidirectional in a large (300 μm x300 μm) field of view, suggesting that C4 breaking in this range of T is caused by residual strain that couples to a diverging nematic susceptibility. Birefringence maps just below Ts (x) show the appearance of domains, indicating the onset of spontaneous symmetry breaking to an AF ground state. Surprisingly, in samples with x>0.28, in which the low T phase is superconducting/ tetragonal rather than AF/orthorhombic, C4 breaking is observed as well, with an abrupt onset and domain formation at 55 K. We tentatively associate these features with a transition to an AF phase induced by residual strain, as previously proposed [H.-H. Kuo et al. Phys. Rev. B86, 134507 (2012)] to account for structure in resistivity vs. T. Time-resolved photomodulation allow us to follow the amplitude of the AF order with time following pulsed photoexcitation. Below Tc the AF order at first weakens , but then strengthens in response to the photoinduced weakening of superconductivity. This complex time evolution is

  8. Chlorine Insertion Promoting Iron Reduction in Ba-Fe Hexagonal Perovskites: Effect on the Structural and Magnetic Properties.

    PubMed

    Serrador, Laura; Hernando, María; Martínez, José L; González-Calbet, José M; Varela, Aurea; García-García, F Javier; Parras, Marina

    2016-06-20

    BaFeCl0.13(2)O2.48(2) has been synthesized and studied. A proper tuning of the synthetic route has been designed to stabilize this compound as a single phase. The thermal stability and evolution, along with the magnetic and structural properties are reported here. The crystal structure has been refined from neutron powder diffraction data, and it is of the type (hhchc)2-10H. It is stable up to a temperature of 900 °C, where the composition reads BaFeCl0.13(2)O2.34(2). The study by electron microscopy shows that the crystal structure suffers no changes in the whole BaFeCl0.13(1)O3-y (2.34 ≤ 3 - y ≤ 2.48) compositional range. Refinement of the magnetic structure shows that the Fe is antiferromagneticaly ordered, with the magnetic moment parallel to the ab plane of the hexagonal structure. At higher temperature, a nonreversible phase transition into a (hchc)-4H structure type takes place with overall composition BaFeCl0.13(1)O2.26(1). Microstructural characterization shows that, in some crystals, this phase intergrows with a seemingly cubic related phase. Differences between these two crystalline phases reside in the chlorine content, which keeps constant through the phase transition for the former and disappears for the latter.

  9. Microscopic distribution of metal dopants and anion vacancies in Fe-doped BaTiO3-δ single crystals

    NASA Astrophysics Data System (ADS)

    Chakraborty, Tanushree; Meneghini, Carlo; Aquilanti, Giuliana; Ray, Sugata

    2013-06-01

    A detailed microscopic structural study on two single crystalline dilute magnetic oxides, BaTi0.95Fe0.05O3-δ with and without perceptible δ, has been carried out. Although it has been reported earlier that varying δ significantly affects high temperature ferromagnetism, the real distribution/redistribution of vacancies and dopant Fe ions inside the 6H hexagonal structure was never probed. This study reveals that oxygen vacancies reduce the dopant Fe3+ ions to Fe2+ and mostly accumulate around these Fe2+ ions. Another distinct trend is the tendency of the dopant Fe ions to get closer instead of being distributed randomly, thereby creating {{Fe}}_{2}^{2+}{{O}}_{9-{\\delta }^{\\prime}} like dimers within the 6H hexagonal unit cell. This experimental observation definitively confirms previous hypotheses based on theoretical models.

  10. Processing and properties of FeAl-bonded composites

    SciTech Connect

    Schneibel, J.H.; Subramanian, R.; Alexander, K.B.; Becher, P.F.

    1996-12-31

    Iron aluminides are thermodynamically compatible with a wide range of ceramics such as carbides, borides, oxides, and nitrides, which makes them suitable as the matrix in composites or cermets containing fine ceramic particulates. For ceramic contents varying from 30 to 60 vol.%, composites of Fe-40 at. % Al with WC, TiC, TiB{sub 2}, and ZrB{sub 2} were fabricated by conventional liquid phase sintering of powder mixtures. For ceramic contents from 70 to 85 vol.%, pressureless melt infiltration was found to be a more suitable processing technique. In FeAl-60 vol.% WC, flexure strengths of up to 1.8 GPa were obtained, even though processing defects consisting of small oxide clusters were present. Room temperature fracture toughnesses were determined by flexure testing of chevron-notched specimens. FeAl/WC and FeAl/TiC composites containing 60 vol.% carbide particles exhibited K{sub Q} values around 20 MPa m{sup 1/2}. Slow crack growth measurements carried out in water and in dry oxygen suggest a relatively small influence of water-vapor embrittlement. It appears therefore that the mechanical properties of iron aluminides in the form of fine ligaments are quite different from their bulk properties. Measurements of the oxidation resistance, dry wear resistance, and thermal expansion of iron aluminide composites suggest many potential applications for these new materials.

  11. Temperature and composition phase diagram in the iron-based ladder compounds Ba1-xCsxFe2Se3

    NASA Astrophysics Data System (ADS)

    Hawai, Takafumi; Nambu, Yusuke; Ohgushi, Kenya; Du, Fei; Hirata, Yasuyuki; Avdeev, Maxim; Uwatoko, Yoshiya; Sekine, Yurina; Fukazawa, Hiroshi; Ma, Jie; Chi, Songxue; Ueda, Yutaka; Yoshizawa, Hideki; Sato, Taku J.

    2015-05-01

    We investigated the iron-based ladder compounds (Ba,Cs ) Fe2Se3 . Their parent compounds BaFe2Se3 and CsFe2Se3 have different space groups, formal valences of Fe, and magnetic structures. Electrical resistivity, specific heat, magnetic susceptibility, x-ray diffraction, and powder neutron diffraction measurements were conducted to obtain a temperature and composition phase diagram of this system. Block magnetism observed in BaFe2Se3 is drastically suppressed with Cs doping. In contrast, stripe magnetism observed in CsFe2Se3 is not so fragile against Ba doping. A new type of magnetic structure appears in intermediate compositions, which is similar to stripe magnetism of CsFe2Se3 , but interladder spin configuration is different. Intermediate compounds show insulating behavior, nevertheless a finite T -linear contribution in specific heat was obtained at low temperatures.

  12. Uniaxial ferroelectric quantum criticality in multiferroic hexaferrites BaFe12O19 and SrFe12O19

    PubMed Central

    Rowley, S. E.; Chai, Yi-Sheng; Shen, Shi-Peng; Sun, Young; Jones, A. T.; Watts, B. E.; Scott, J. F.

    2016-01-01

    BaFe12O19 is a popular M-type hexaferrite with a Néel temperature of 720 K and is of enormous commercial value ($3 billion/year). It is an incipient ferroelectric with an expected ferroelectric phase transition extrapolated to lie at 6 K but suppressed due to quantum fluctuations. The theory of quantum criticality for such uniaxial ferroelectrics predicts that the temperature dependence of the electric susceptibility χ diverges as 1/T3, in contrast to the 1/T2 dependence found in pseudo-cubic materials such as SrTiO3 or KTaO3. In this paper we present evidence of the susceptibility varying as 1/T3, i.e. with a critical exponent γ = 3. In general γ = (d + z – 2)/z, where the dynamical exponent for a ferroelectric z = 1 and the dimension is increased by 1 from deff = 3 + z to deff = 4 + z due to the effect of long-range dipole interactions in uniaxial as opposed to multiaxial ferroelectrics. The electric susceptibility of the incipient ferroelectric SrFe12O19, which is slightly further from the quantum phase transition is also found to vary as 1/T3. PMID:27185343

  13. Uniaxial ferroelectric quantum criticality in multiferroic hexaferrites BaFe12O19 and SrFe12O19

    NASA Astrophysics Data System (ADS)

    Rowley, S. E.; Chai, Yi-Sheng; Shen, Shi-Peng; Sun, Young; Jones, A. T.; Watts, B. E.; Scott, J. F.

    2016-05-01

    BaFe12O19 is a popular M-type hexaferrite with a Néel temperature of 720 K and is of enormous commercial value ($3 billion/year). It is an incipient ferroelectric with an expected ferroelectric phase transition extrapolated to lie at 6 K but suppressed due to quantum fluctuations. The theory of quantum criticality for such uniaxial ferroelectrics predicts that the temperature dependence of the electric susceptibility χ diverges as 1/T3, in contrast to the 1/T2 dependence found in pseudo-cubic materials such as SrTiO3 or KTaO3. In this paper we present evidence of the susceptibility varying as 1/T3, i.e. with a critical exponent γ = 3. In general γ = (d + z – 2)/z, where the dynamical exponent for a ferroelectric z = 1 and the dimension is increased by 1 from deff = 3 + z to deff = 4 + z due to the effect of long-range dipole interactions in uniaxial as opposed to multiaxial ferroelectrics. The electric susceptibility of the incipient ferroelectric SrFe12O19, which is slightly further from the quantum phase transition is also found to vary as 1/T3.

  14. Uniaxial ferroelectric quantum criticality in multiferroic hexaferrites BaFe12O19 and SrFe12O19.

    PubMed

    Rowley, S E; Chai, Yi-Sheng; Shen, Shi-Peng; Sun, Young; Jones, A T; Watts, B E; Scott, J F

    2016-05-17

    BaFe12O19 is a popular M-type hexaferrite with a Néel temperature of 720 K and is of enormous commercial value ($3 billion/year). It is an incipient ferroelectric with an expected ferroelectric phase transition extrapolated to lie at 6 K but suppressed due to quantum fluctuations. The theory of quantum criticality for such uniaxial ferroelectrics predicts that the temperature dependence of the electric susceptibility χ diverges as 1/T(3), in contrast to the 1/T(2) dependence found in pseudo-cubic materials such as SrTiO3 or KTaO3. In this paper we present evidence of the susceptibility varying as 1/T(3), i.e. with a critical exponent γ = 3. In general γ = (d + z - 2)/z, where the dynamical exponent for a ferroelectric z = 1 and the dimension is increased by 1 from deff = 3 + z to deff = 4 + z due to the effect of long-range dipole interactions in uniaxial as opposed to multiaxial ferroelectrics. The electric susceptibility of the incipient ferroelectric SrFe12O19, which is slightly further from the quantum phase transition is also found to vary as 1/T(3).

  15. Energy transfer between Eu-Mn and photoluminescence properties of Ba0.75Al11O17.25-BaMgAl10O17:Eu2+,Mn2+ solid solution

    NASA Astrophysics Data System (ADS)

    Zhou, Jun; Wang, Yuhua; Liu, Bitao; Li, Feng

    2010-08-01

    In order to evaluate the energy transfer between Eu-Mn in Ba0.75Al11O17.25-BaMgAl10O17 solid solution, Ba0.75Al11O17.25-BaMgAl10O17:Eu2+,Mn2+ phosphors were prepared by flux method. The crystal structure and the morphology of the solid solution were demonstrated by x-ray dirrfactometer and scanning electron microscopy. The photoluminescence mechanisms were explained by the energy transfer of Eu2+ to Mn2+ and the Dexter theory. A redshift of green emission peak and a decrease in decay time with the increase in Mn2+ concentration were observed. These phenomena are attributed to the formation of Mn2+ paired centers after analysis by a method of Pade approximations.

  16. Development of ODS-Fe{sub 3}Al alloys

    SciTech Connect

    Wright, I.G.; Pint, B.A.; Tortorelli, P.F.; McKamey, C.G.

    1997-12-01

    The overall goal of this program is to develop an oxide dispersion-strengthened (ODS) version of Fe{sub 3}Al that has sufficient creep strength and resistance to oxidation at temperatures in the range 1000 to 1200 C to be suitable for application as heat exchanger tubing in advanced power generation cycles. The main areas being addressed are: (a) alloy processing to achieve the desired alloy grain size and shape, and (b) optimization of the oxidation behavior to provide increased service life compared to semi-commercial ODS-FeCrAl alloys intended for the same applications. The recent studies have focused on mechanically-alloyed powder from a commercial alloy vendor. These starting alloy powders were very clean in terms of oxygen content compared to ORNL-produced powders, but contained similar levels of carbon picked up during the milling process. The specific environment used in milling the powder appears to exert a considerable influence on the post-consolidation recrystallization behavior of the alloy. A milling environment which produced powder particles having a high surface carbon content resulted in a consolidated alloy which readily recrystallized, whereas powder with a low surface carbon level after milling resulted in no recrystallization even at 1380 C. A feature of these alloys was the appearance of voids or porosity after the recrystallization anneal, as had been found with ORNL-produced alloys. Adjustment of the recrystallization parameters did not reveal any range of conditions where recrystallization could be accomplished without the formation of voids. Initial creep tests of specimens of the recrystallized alloys indicated a significant increase in creep strength compared to cast or wrought Fe{sub 3}Al, but the specimens failed prematurely by a mechanism that involved brittle fracture of one of the two grains in the test cross section, followed by ductile fracture of the remaining grain. The reasons for this behavior are not yet understood. The

  17. Magnetism in the magnetoelectric hexaferrite system (Ba1-xSrx)2Zn2Fe12O22

    NASA Astrophysics Data System (ADS)

    Novák, P.; Knížek, K.; Rusz, J.

    2007-07-01

    The hexaferrite system (Ba1-xSrx)2Zn2Fe12O22 possesses a rich magnetic phase diagram and for strontium content x=0.75 exhibits a magnetoelectricity, the existence of which is intimately connected to the noncollinear arrangement of the iron spins. The system comprises seven cation sublattices, two of which have tetrahedral coordination. The tetrahedral sublattices are partly occupied by Fe and partly by Zn. Using ab initio-calculated exchange interactions we show that the magnetism in the (Ba1-xSrx)2Zn2Fe12O22 system is sensitive to the Fe and Zn distributions. The region of existence of the noncollinear spin structure and hence of ferroelectricity is determined and found to be rather narrow. The critical temperature of magnetic ordering is calculated using molecular field and random phase approximations. The results are in good agreement with the experiment.

  18. Direct characterization of photoinduced lattice dynamics in BaFe2As2.

    PubMed

    Gerber, S; Kim, K W; Zhang, Y; Zhu, D; Plonka, N; Yi, M; Dakovski, G L; Leuenberger, D; Kirchmann, P S; Moore, R G; Chollet, M; Glownia, J M; Feng, Y; Lee, J-S; Mehta, A; Kemper, A F; Wolf, T; Chuang, Y-D; Hussain, Z; Kao, C-C; Moritz, B; Shen, Z-X; Devereaux, T P; Lee, W-S

    2015-06-08

    Ultrafast light pulses can modify electronic properties of quantum materials by perturbing the underlying, intertwined degrees of freedom. In particular, iron-based superconductors exhibit a strong coupling among electronic nematic fluctuations, spins and the lattice, serving as a playground for ultrafast manipulation. Here we use time-resolved X-ray scattering to measure the lattice dynamics of photoexcited BaFe2As2. On optical excitation, no signature of an ultrafast change of the crystal symmetry is observed, but the lattice oscillates rapidly in time due to the coherent excitation of an A1g mode that modulates the Fe-As-Fe bond angle. We directly quantify the coherent lattice dynamics and show that even a small photoinduced lattice distortion can induce notable changes in the electronic and magnetic properties. Our analysis implies that transient structural modification can be an effective tool for manipulating the electronic properties of multi-orbital systems, where electronic instabilities are sensitive to the orbital character of bands.

  19. Morphological evolution and strengthening behavior of α-Al(Fe,Mn)Si in Al-6Si-2Fe-xMn alloys

    NASA Astrophysics Data System (ADS)

    Gao, Tong; Hu, Kaiqi; Wang, Longshuai; Zhang, Bangran; Liu, Xiangfa

    β-Al5FeSi is preferred to form in Al-Si-Fe alloys, normally exhibiting needlelike, which is harmful for the mechanical properties. In this paper, with the addition of 1%, 1.5% and 3% Mn into an Al-6Si-2Fe alloy, β-Al5FeSi phase was found to transform to skeleton, flower-like and coarse dendritic α-Al(Fe,Mn)Si, respectively. The novel flower-like α-Al(Fe,Mn)Si crystals contain developed branches with the average diameter of ∼200 nm, performing strengthening effect on the tensile property. Detailed morphologies of α-Al(Fe,Mn)Si phase and the formation mechanism were discussed.

  20. Preparation and magnetic properties of BaFe12O19/Ni0.8Zn0.2Fe2O4 nanocomposite ferrite

    NASA Astrophysics Data System (ADS)

    Wang, Yan; Huang, Ying; Wang, Qiufen

    2012-09-01

    Nanocomposite of hard (BaFe12O19)/soft ferrite (Ni0.8Zn0.2Fe2O4) have been prepared by the sol-gel process. The nanocomposite ferrite are formed when the calcining temperature is above 800 °C. It is found that the magnetic properties strongly depend on the presintering treatment and calcining temperature. The “bee waist” type hysteresis loops for samples disappear when the presintering temperature is 400 °C and the calcination temperature reaches 1100 °C owing to the exchange-coupling interaction. The remanence of BaFe12O19/Ni0.8Zn0.2Fe2O4 nanocomposite ferrite with the mass ratio of 5:1 is higher than a single phase ferrite. The specific saturation magnetization, remanence magnetization and coercivity are 63 emu/g, 36 emu/g and 2750 G, respectively. The exchange-coupling interaction in the BaFe12O19/Ni0.8Zn0.2Fe2O4 nanocomposite ferrite is discussed.

  1. Composition and solidification microstructure selection in the interdendritic matrix between primary Al{sub 3}Fe dendrites in hypereutectic Al-Fe alloys

    SciTech Connect

    Liang, D.; Korgul, P.; Jones, H.

    1996-07-01

    The composition and constitution of matrix microstructure between plate-like Al{sub 3}Fe dendrites in Bridgman-grown hypereutectic Al-Fe alloys has been determined as a function of alloy concentration C{sub 0} and growth velocity V in the ranges 2.5 < C{sub 0} < 28.1 wt%Fe and 0.01 < V < 5.0 mm/s. The transition at V = 0.1 mm/s from a fully eutectic matrix at C{sub 0} = 3.5 wt%Fe to one containing {alpha}Al dendrites at C{sub 0} {ge} 4.7 wt%Fe is attributed to growth temperatures of {alpha}Al dendrites that are higher than those of eutectic in a matrix of lower iron-content, which results from these conditions. The matrix eutectic changes from irregular {alpha}-Al-Al{sub 3}Fe to regular {alpha}Al-Al{sub x}Fe with increasing V, the transition velocity increasing from 0.1 to 0.2 mm/s for C{sub 0} values of 9.5 and 14 wt%Fe up to 0.35--1.0 mm/s for C{sub 0} values of 18.7--28.1 wt%Fe. This increased transition velocity, compared with that for {alpha}-Al-Al{sub 3}Fe to {alpha}Al-Al{sub 6}Fe at lower concentration, is indicative of a lower formation temperature for the {alpha}Al-Al{sub x}Fe than the {alpha}Al-Al{sub 6}Fe eutectic.

  2. The effect of Al-substitution on superconducting type-I clathrate Ba8Si46

    NASA Astrophysics Data System (ADS)

    Liu, Lihua; Bi, Shanli; Chen, Ning; Li, Feng; Liu, Yang; Cao, Guohui; Li, Yang

    2014-11-01

    A series of samples with the chemical formula Ba8Si46-xAlx (x = 2, 3, 5, 6, 7 and 8) were prepared by arc melting, ball milling and washing with diluted HCl. The lattice parameter of Ba8Si46-xAlx increases linearly with the increase of nominal Al content x. The composition analysis by energy-dispersive X-ray spectroscopy (EDS) shown that the actual Al contents in clathrates are lager than the nominal compositions because the dilute Al-contained impurity phases were washed out. The experimental results show that the minimum incorporation of Al into clathrate structure is expected to be about 3 at ambient pressure, which is in agreement with a first-principle simulation. The Al substitution for Si results in the decrease of superconducting transition temperature TC, which can be explained on the BCS theoretical frame. The electron density of state at Fermi level N(EF) decreases with the increment of x except for an abnormal increase for the sample x = 6. Such sample has a higher spatial symmetry of the structure in which all the six Si atoms at 6c sites were substituted by Al atoms. Its higher N(EF) causes to a higher TC. In addition, we calculated the phonon-dispersion relations and vibrational density of states for Al-doped silicon clathrates. The high frequency acoustic branch has a red shift from 430 cm-1 to 420 cm-1 with the doping of Al. The decreased frequency of bond-stretching vibration modes is another reason for the suppression of TC induced by Al substitution.

  3. Corrosion performance of Fe-Cr-Al and Fe aluminide alloys in complex gas environments

    SciTech Connect

    Natesan, K.; Johnson, R.N.

    1995-05-01

    Alumina-forming structural alloys can offer superior resistance to corrosion in the presence of sulfur-containing environments, which are prevalent in coal-fired fossil energy systems. Further, Fe aluminides are being developed for use as structural materials and/or cladding alloys in these systems. Extensive development has been in progress on Fe{sub 3}Al-based alloys to improve their engineering ductility. In addition, surface coatings of Fe aluminide are being developed to impart corrosion resistance to structural alloys. This paper describes results from an ongoing program that is evaluating the corrosion performance of alumina-forming structural alloys, Fe-Al and Fe aluminide bulk alloys, and Fe aluminide coatings in environments typical of coal-gasification and combustion atmospheres. Experiments were conducted at 650-1000{degrees}C in simulated oxygen/sulfur gas mixtures. Other aspects of the program are corrosion evaluation of the aluminides in the presence of HCl-containing gases. Results are used to establish threshold Al levels in the alloys for development of protective alumina scales and to determine the modes of corrosion degradation that occur in the materials when they are exposed to S/Cl-containing gaseous environments.

  4. Effect of Fe-Ru doping in the electronic and thermoelectric properties of new filled skutterudite Ba(Fe,Ru)4As12

    NASA Astrophysics Data System (ADS)

    Shankar, A.; Sandeep, Rai, D. P.; Thapa, R. K.; Mandal, P. K.

    2017-02-01

    We have performed the density functional theory based calculation to study the electronic and thermoelectric properties of BaFe4-xRuxAs12 (x = 0%, 25%, 50%, 75%, and 100%) within the framework of the full potential-linearized augmented plane wave method. The composite alloys are found to be stable in their optimized crystal structures and their lattice constants are in close agreement with the corresponding experimental reports. The structural stability and mechanical properties are also studied using their elastic constants. The hardness of these materials increases with increasing concentration of Ru, which also donates the covalent nature of inter-atomic bonding of BaRu4As12. The analysis of energy bands and density of states reflects the semi-metallic nature of BaFe4As12 and BaRu4As12, whereas other doped materials show metallic character. The electronic structure calculation suggests the high Seebeck coefficient with the efficient thermoelectric application of these materials. The thermal transport investigation also supports the result obtained from the electronic structure calculation. The thermoelectric efficiency defined by the figure of merit (ZT) of pure BaFe4As12 (ZT = 0.004) and BaRu4As12 (ZT = 0.005) has been enhanced to 0.357 with 75% Ru doping. The spin-polarized calculation shows a significant effect on their energy band structure, giving magnetic behavior of the sample materials. The analysis of their magnetic profile suggests the ferromagnetic nature of these materials, except BaRu4As12, which shows a paramagnetic ground state.

  5. Effect of disorder on the resistivity anisotropy near the electronic nematic phase transition in pure and electron-doped BaFe(2)As(2).

    PubMed

    Kuo, Hsueh-Hui; Fisher, Ian R

    2014-06-06

    We show that the strain-induced resistivity anisotropy in the tetragonal state of the representative underdoped Fe arsenides BaFe_{2}As_{2}, Ba(Fe_{1-x}Co_{x})_{2}As_{2} and Ba(Fe_{1-x}Ni_{x})_{2}As_{2} is independent of disorder over a wide range of defect and impurity concentrations. This result demonstrates that the anisotropy in the in-plane resistivity in the paramagnetic orthorhombic state of this material is not due to elastic scattering from anisotropic defects. Conversely, our result can be most easily understood if the resistivity anisotropy arises primarily from an intrinsic anisotropy in the electronic structure.

  6. Nonvolatile bipolar resistive switching in Ba-doped BiFeO3 thin films

    NASA Astrophysics Data System (ADS)

    Deng, Haoliang; Zhang, Ming; Wei, Jizhou; Chu, Shangjie; Du, Minyong; Yan, Hui

    2015-07-01

    The Bi0.8Ba0.2FeO3 (BBFO) thin film was deposited on the conducting Nb:SrTiO3 (NSTO) (1 0 0) single crystal substrate by pulsed laser deposition. Nonvolatile bipolar resistive switching effect was observed in an Au/BBFO/NSTO capacitor structure. By changing the polarity of the external pulsed voltage, the device could be switched reversibly between two stable resistance states. The resistive ratio is about 10 at a read voltage of -0.5 V after applying ±1.5 V pulse voltages. The mechanism of the resistive switching behavior could be attributed to the electric field induced migration of oxygen vacancies, which changes the height and width of the barrier at the BBFO/NSTO interface.

  7. Strain-activated structural anisotropy in BaFe2As2

    NASA Astrophysics Data System (ADS)

    Chen, Xiang; Harriger, Leland; Sefat, Athena; Birgeneau, R. J.; Wilson, Stephen D.

    2016-04-01

    High-resolution single crystal neutron diffraction measurements are presented probing the magnetostructural response to uniaxial pressure in the iron pnictide parent system BaFe2As2 . Scattering data reveal a strain-activated, anisotropic broadening of nuclear Bragg reflections, which increase upon cooling below the resolvable onset of global orthorhombicity. This anisotropy in lattice coherence continues to build until a lower temperature scale—the first-order onset of antiferromagnetism—is reached. Our data suggest that antiferromagnetism and strong magnetoelastic coupling drive the strain-activated lattice response in this material and that the development of anisotropic lattice correlation lengths under strain is a possible origin for the high temperature transport anisotropy in this compound.

  8. Negative Capacitance in BaTiO3/BiFeO3 Bilayer Capacitors.

    PubMed

    Hou, Ya-Fei; Li, Wei-Li; Zhang, Tian-Dong; Yu, Yang; Han, Ren-Lu; Fei, Wei-Dong

    2016-08-31

    Negative capacitances provide an approach to reduce heat generations in field-effect transistors during the switch processes, which contributes to further miniaturization of the conventional integrated circuits. Although there are many studies about negative capacitances using ferroelectric materials, the direct observation of stable ferroelectric negative capacitances has rarely been reported. Here, we put forward a dc bias assistant model in bilayer capacitors, where one ferroelectric layer with large dielectric constant and the other ferroelectric layer with small dielectric constant are needed. Negative capacitances can be obtained when external dc bias electric fields are larger than a critical value. Based on the model, BaTiO3/BiFeO3 bilayer capacitors are chosen as study objects, and negative capacitances are observed directly. Additionally, the upward self-polarization effect in the ferroelectric layer reduces the critical electric field, which may provide a method for realizing zero and/or small dc bias assistant negative capacitances.

  9. Investigation of Phase Equilibria and Some Properties of Alloys of Ti-Al-Fe and Ti-Al-V Systems,

    DTIC Science & Technology

    Some data on the structure and properties of Ti-Al-Fe alloys are presented. The phase equilibria in alloys in the system Ti-Al-V were studies...However, the data available in the literature on phase equilibria in the systems Ti-Al-Fe and Ti-Al-V require refinement, as they are insufficiently

  10. Soft x-ray photoemission spectroscopy of the Ba atomic layer deposition on the ceramic multiferroic BiFeO3

    NASA Astrophysics Data System (ADS)

    Benemanskaya, G. V.; Dementev, P. A.; Lapushkin, M. N.; Timoshnev, S. N.; Senkovskiy, B.

    2017-04-01

    Electronic structure of the ceramic multiferroic BiFeO3 and the Ba/BiFeO3 nanointerface is investigated in situ in an ultrahigh vacuum by synchrotron-based photoemission spectroscopy with the excited photon energy from 120 eV to 900 eV. The Bi 4f, O 1s, Fe 2p, and Ba 5p core-levels spectra are studied. The Ba atomic layer deposition is found to induce a significant change in spectra that is originated from the charge transfer between Ba adatoms and Bi, O surface atoms with increasing the Bi-valency and O-ionicity. The Fe 2p3/2 core level spectrum for the clean BiFeO3 is shown to contain both the Fe2+ and Fe3+ ion components with the atomic ratio of Fe2+/Fe3+ ∼1. The Ba adsorption is found to increase the ratio up to ∼1.5. This new effect is clearly caused by recharge between Fe3+ ↔ Fe2+ ions with increasing the amount of Fe2+ ions.

  11. Development of Fe-Mn-Al-X-C alloys

    NASA Technical Reports Server (NTRS)

    Schuon, S. R.

    1982-01-01

    Development of a low cost Cr-free, iron-base alloy for aerospace applications involves both element substitution and enhancement of microstructural strengthening. When Mn is substituted for Ni and Al or Si is substituted for Cr, large changes occur in the mechanical and thermal stability of austenite in FeMnAlC alloys. The in situ strength of MC or M2C (M = Ti, V, Hf, Ta, or Mo) in FeMnAlC alloys was determined. The high temperature tensile strength depends more on the distribution of carbides than the carbide composition. Precipitation of a high volume percent-ordered phase was achieved in Fe2OMnlONi6Al6Ti (lC) alloys. As case, these alloys have a homogeneous austenitic structure. After solutioning at 1100 C for 5 hr followed by aging at 600 C for 16 hr, gamma prime or a perovskite carbide is precipitated. Overaging occurs at 900 C where eta is precipitated.

  12. Comparison of structural and magnetic properties of La3+ substituted BaFe12O19 prepared by different substitution methods

    NASA Astrophysics Data System (ADS)

    Verma, Samiksha; Pandey, O. P.; Paesano, Andrea; Sharma, Puneet

    2014-09-01

    Effect of La3+ substitution on structural and magnetic properties of Ba1-xLaxFe12O19 (x=0.0-0.2) prepared by two different methods was studied. For the first method, La3+ substituted BaFe12O19 has been directly prepared by solid state synthesis of Fe2O3 and BaCO3 at Fe/Ba molar ratio of 6. For the second method, solid state synthesis of Fe2O3 and Ba1-xLaxFe2O4 at molar composition of 5:1 has been adopted. As-prepared powders were characterized by X-ray diffraction, Mössbauer spectroscopy and vibration sample magnetometry. XRD patterns were refined by the Rietveld analysis method. Single phase barium hexaferrite was obtained by both the methods with a minor amount of residual hematite. Ba1-xLaxFe12O19 prepared from Ba1-xLaxFe2O4 showed higher magnetization (M) which was the maximum for x=0.1, without any remarkable change in the coercivity. The increase in M is attributed to increase in hyperfine field for 12k, 4f1, 4f2, 2a and 2b sites.

  13. Effects of Codoping with Ga and P on Thermoelectric Properties of Ba8Al16Si30 Clathrate System

    NASA Astrophysics Data System (ADS)

    Anno, Hiroaki; Ueda, Takahiro; Okamoto, Kazuya

    2017-01-01

    We have investigated the effects of Codoping With Ga and P on the thermoelectric properties of the Ba8Al16Si30 clathrate system, attempting to optimize the carrier concentration. The elastic properties, which are important for design of thermoelectric devices, were investigated by ultrasonic testing. Ga/P-codoped specimens with nominal compositions Ba8Al16Ga x Si30-2x P x (x = 1.0, 1.5, 2.0) were prepared by arc melting and spark plasma sintering and their Seebeck coefficient, electrical conductivity, and thermal conductivity were measured. Analytical studies revealed that the total content of Al and Ga, expressed as atoms per formula unit, increased to 15.65 at nominal x = 2.0, exceeding the maximum content (y = 15.16) of Al for the Ba8Al y Si46-y clathrate system. Ultrasonic tests determined the Young's modulus, shear modulus, bulk modulus, and Poisson's ratio to be 102.55 GPa, 40.14 GPa, 76.85 GPa, and 0.2775, respectively, for Ba8Al16Ga x Si30-2x P x (x = 2.0). The Hall carrier concentration decreased from ˜1.0 × 1021 cm-3 for Ba8Al y Si46-y to ˜6.3 × 1020 cm-3 for Ba8Al16Ga x Si30-2x P x (x = 2.0), suggesting that Ga/P codoping may be useful for tuning the carrier concentration. The value of the Seebeck coefficient at ˜320 K increased from -46 μV K-1 for Ba8Al y Si46-y to -67 μV K-1 for Ba8Al16Ga x Si30-2x P x (x = 2.0). The dimensionless thermoelectric figure␣of merit ZT at 900 K improved from ˜0.4 for Ba8Al y Si46-y to ˜0.47 for Ba8Al16Ga x Si30-2x P x (x = 2.0).

  14. Effects of Codoping with Ga and P on Thermoelectric Properties of Ba8Al16Si30 Clathrate System

    NASA Astrophysics Data System (ADS)

    Anno, Hiroaki; Ueda, Takahiro; Okamoto, Kazuya

    2017-03-01

    We have investigated the effects of Codoping With Ga and P on the thermoelectric properties of the Ba8Al16Si30 clathrate system, attempting to optimize the carrier concentration. The elastic properties, which are important for design of thermoelectric devices, were investigated by ultrasonic testing. Ga/P-codoped specimens with nominal compositions Ba8Al16Ga x Si30-2 x P x ( x = 1.0, 1.5, 2.0) were prepared by arc melting and spark plasma sintering and their Seebeck coefficient, electrical conductivity, and thermal conductivity were measured. Analytical studies revealed that the total content of Al and Ga, expressed as atoms per formula unit, increased to 15.65 at nominal x = 2.0, exceeding the maximum content ( y = 15.16) of Al for the Ba8Al y Si46- y clathrate system. Ultrasonic tests determined the Young's modulus, shear modulus, bulk modulus, and Poisson's ratio to be 102.55 GPa, 40.14 GPa, 76.85 GPa, and 0.2775, respectively, for Ba8Al16Ga x Si30-2 x P x ( x = 2.0). The Hall carrier concentration decreased from ˜1.0 × 1021 cm-3 for Ba8Al y Si46- y to ˜6.3 × 1020 cm-3 for Ba8Al16Ga x Si30-2 x P x ( x = 2.0), suggesting that Ga/P codoping may be useful for tuning the carrier concentration. The value of the Seebeck coefficient at ˜320 K increased from -46 μV K-1 for Ba8Al y Si46- y to -67 μV K-1 for Ba8Al16Ga x Si30-2 x P x ( x = 2.0). The dimensionless thermoelectric figure of merit ZT at 900 K improved from ˜0.4 for Ba8Al y Si46- y to ˜0.47 for Ba8Al16Ga x Si30-2 x P x ( x = 2.0).

  15. Al- and Cu-doped BaSi2 films on Si(111) substrate by molecular beam epitaxy and evaluation of depth profiles of Al and Cu atoms

    NASA Astrophysics Data System (ADS)

    Ajmal Khan, M.; Takeishi, M.; Matsumoto, Y.; Saito, T.; Suemasu, T.

    The main objective of the present work is to evaluate and compare the depth profiles of Al and Cu atoms in in-situ doped BaSi2. Furthermore, it is also desired to investigate and compare the carrier concentration of Al-doped as well as Cu-doped BaSi2 films and qualify as a potential dopant-candidate for more efficient solar cells of BaSi2. During the experiment, reactive deposition epitaxy and molecular beam epitaxy were used to develop the samples. X-ray diffraction (XRD) measurements and secondary ion mass spectroscopy (SIMS), were used to determine the structure, depth profile and composition of the already grown films. The electrical properties were characterized by Hall measurement using the van der Pauw method. In case of Al-doped BaSi2 films, it was not encouraging result due to diffusion and segregation of Al in both the surface and BaSi2/ Si interface regions. On the other hand, those phenomena were not observed for Cu-doped BaS2 films. Heavily Cu-doped BaSi2 showed n+ conductivity, differently from our prediction.

  16. Impact of Mn3+ upon structure and magnetism of the perovskite derivative Pb(2-x)Ba(x)FeMnO5 (x ∼ 0.7).

    PubMed

    Barrier, N; Lebedev, O I; Seikh, Md Motin; Porcher, F; Raveau, B

    2013-05-20

    On the basis of the Mn(3+) for Fe(3+) substitution in Pb(2-x)Ba(x)Fe2O5, a novel oxide Pb1.3Ba0.7MnFeO5 has been synthesized at normal pressure. Though it belongs to the same structural family, the mixed "MnFe" oxide exhibits a very different structural distortion of its framework compared to the pure "Fe2" oxide, due to the Jahn-Teller effect of Mn(3+). Combined neutron diffraction, high resolution electron microscopy/high angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) investigations allow the origin of this difference to be determined. Here we show that the MO6 octahedra of the double perovskite layers in the "MnFe" structure exhibit a strong tetragonal pyramidal distortion "5 + 1", whereas the "Fe2" structure shows a tetrahedral distortion "4 + 2" of the FeO6 octahedra. Similarly, the MO5 polyhedra of the "MnFe" structure tend toward a tetragonal pyramid, whereas the FeO5 polyhedra of the "Fe2" structure are closer to a trigonal bipyramid. Differently from the oxide Pb(2-x)Ba(x)Fe2O5, which is antiferromagnetic, the oxide Pb1.3Ba0.7MnFeO5 exhibits a spin glass behavior with Tg ∼ 50 K in agreement with the disordered distribution of the Mn(3+) and Fe(3+) species.

  17. Room-Temperature Ba(Fe1-x Cox)2 As2 is not Tetragonal: Direct Observation of Magnetoelastic Interactions in Pnictide Superconductors.

    PubMed

    Cantoni, Claudia; McGuire, Michael A; Saparov, Bayrammurad; May, Andrew F; Keiber, Trevor; Bridges, Frank; Sefat, Athena S; Sales, Brian C

    2015-05-06

    Lattice distortions corresponding to Ba displacements with respect to the FeAs sublattice are revealed to break the room-temperature tetragonal symmetry in Ba(Fe1-x Cox)2 As2. The displacements yield twin domains of the size of ≈10 nm. The domain size correlates with the magnitude of the local Fe magnetic moment and its non-monotonic dependence on Co concentration.

  18. Local manifestations of a static magnetoelectric effect in nanostructured BaTiO3-BaFe12O9 composite multiferroics.

    PubMed

    Trivedi, Harsh; Shvartsman, Vladimir V; Lupascu, Doru C; Medeiros, Marco S A; Pullar, Robert C; Kholkin, Andrei L; Zelenovskiy, Pavel; Sosnovskikh, Andrey; Shur, Vladimir Ya

    2015-03-14

    A study on magnetoelectric phenomena in the barium titanate-barium hexaferrite (BaTiO3-BaFe12O19) composite system, using high resolution techniques including switching spectroscopy piezoresponse force microscopy (SSPFM) and spatially resolved confocal Raman microscopy (CRM), is presented. It is found that both the local piezoelectric coefficient and polarization switching parameters change on the application of an external magnetic field. The latter effect is rationalized by the influence of magnetostrictive stress on the domain dynamics. Processing of the Raman spectral data using principal component analysis (PCA) and self-modelling curve resolution (SMCR) allowed us to achieve high resolution phase distribution maps along with separation of average and localized spectral components. A significant effect of the magnetic field on the Raman spectra of the BaTiO3 phase has been revealed. The observed changes are comparable with the classical pressure dependent studies on BaTiO3, confirming the strain mediated character of the magnetoelectric coupling in the studied composites.

  19. Crystal Growth, Structure, Resistivity, Magnetic, and Photoelectric Properties of One-Dimensional Selenometallate Ba2 BiFeSe5.

    PubMed

    Li, Xiaoshuang; Zhang, Xian; Kalai Selvan, G; Arumugam, S; Huang, Fuqiang; Wu, Yicheng; Yao, Jiyong

    2016-12-06

    Low-dimensional materials have attracted extensive research interest in recent years owing to their interesting structural chemistry and physical properties, which will greatly deepen our knowledge of these materials and could lead to additional breakthroughs in the future. Herein we have synthesized and characterized Ba2 BiFeSe5 , which adopts a quasi-one-dimensional structure and possesses some fascinating physical properties. The sharp divergences between the field-cooled (FC) and the zero-field-cooled (ZFC) data and the rather small magnetic moment per Fe(3+) (0.07 μB ) strongly suggest that the title compound is weakly ferromagnetic with a high magnetic transition temperature above room temperature, which is controlled by competing super-exchange interactions within and between [FeBiSe5 ]∞ anionic ladders. Moreover, with its narrow bandgap of 0.95 eV, Ba2 BiFeSe5 shows photoelectric properties with a photocurrent density of approximately 30 mA cm(2) at 5 V. Our study demonstrates that Ba2 FeBiSe5 might be a new type of multifunctional material that deserves further investigation.

  20. Anomalous magneto-elastic and charge doping effects in thallium-doped BaFe2As2

    DOE PAGES

    Sefat, Athena S.; Li, Li; Cao, Huibo B.; ...

    2016-02-12

    Within the BaFe2As2 crystal lattice, we partially substitute thallium for barium and report the effects of interlayer coupling in Ba1-xTlxFe2As2 crystals. We demonstrate the unusual effects of magneto-elastic coupling and charge doping in this iron-arsenide material, whereby Néel temperature rises with small x, and then falls with additional x. Specifically, we find that Néel and structural transitions in BaFe2As2 (TN = Ts = 133 K) increase for x = 0.05 (TN = 138 K, Ts = 140 K) from magnetization, heat capacity, resistivity, and neutron diffraction measurements. Evidence from single crystal X-ray diffraction and first principles calculations attributes the stronger magnetism in x = 0.05 to magneto-elastic coupling related to the shorter intraplanar Fe-Fe bondmore » distance. With further thallium substitution, the transition temperatures decrease for x = 0.09 (TN = Ts = 131 K), and this is due to charge doping. Finally, we illustrate that small changes related to 3d transition-metal state can have profound effects on magnetism.« less

  1. Spin-phonon coupling in BaFe{sub 12}O{sub 19} M-type hexaferrite

    SciTech Connect

    Silva Júnior, Flávio M.; Paschoal, Carlos W. A.

    2014-12-28

    The spin-phonon coupling in magnetic materials is due to the modulation of the exchange integral by lattice vibrations. BaFe{sub 12}O{sub 19} M-type hexaferrite, which is the most used magnetic material as permanent magnet, transforms into ferrimagnet at high temperatures, but no spin-phonon coupling was previously observed at this transition. In this letter, we investigated the temperature-dependent Raman spectra of polycrystalline BaFe{sub 12}O{sub 19} M-type hexaferrite from room temperature up to 780 K to probe spin-phonon coupling at the ferrimagnetic transition. An anomaly was observed in the position of the phonon attributed to the Fe{sup (4)}O{sub 6}, Fe{sup (5)}O{sub 6}, and Fe{sup (1)}O{sub 6} octahedra, evidencing the presence of a spin-phonon coupling in BaM in the ferrimagnetic transition at 720 K. The results also confirmed the spin-phonon coupling is different for each phonon even when they couple with the same spin configuration.

  2. Anomalous magneto-elastic and charge doping effects in thallium-doped BaFe2As2

    PubMed Central

    Sefat, Athena S.; Li, Li; Cao, Huibo B.; McGuire, Michael A.; Sales, Brian; Custelcean, Radu; Parker, David S.

    2016-01-01

    Within the BaFe2As2 crystal lattice, we partially substitute thallium for barium and report the effects of interlayer coupling in Ba1-xTlxFe2As2 crystals. We demonstrate the unusual effects of magneto-elastic coupling and charge doping in this iron-arsenide material, whereby Néel temperature rises with small x, and then falls with additional x. Specifically, we find that Néel and structural transitions in BaFe2As2 (TN = Ts = 133 K) increase for x = 0.05 (TN = 138 K, Ts = 140 K) from magnetization, heat capacity, resistivity, and neutron diffraction measurements. Evidence from single crystal X-ray diffraction and first principles calculations attributes the stronger magnetism in x = 0.05 to magneto-elastic coupling related to the shorter intraplanar Fe-Fe bond distance. With further thallium substitution, the transition temperatures decrease for x = 0.09 (TN = Ts = 131 K), and this is due to charge doping. We illustrate that small changes related to 3d transition-metal state can have profound effects on magnetism. PMID:26867821

  3. Molecular Beam Epitaxy Growth of Superconducting Ba1-xKxFe2As2 and SmFeAs(O,F) Films

    NASA Astrophysics Data System (ADS)

    Ueda, Shinya; Takeda, Soichiro; Takano, Shiro; Mitsuda, Akihiro; Naito, Michio

    2012-01-01

    We report the molecular beam epitaxy (MBE) growth of the iron-based superconductors, Ba1-xKxFe2As2 and SmFeAs(O,F). In the growth of Ba1-xKxFe2As2 films, the key to incorporating volatile K in films is low-temperature (≤350 °C) growth in reduced As flux. The highest Tc thus far obtained is Tcon (Tcend) = 38.0 K (35.8 K). In the growth of superconducting SmFeAs(O,F), we adopted two methods. In the first method, we first grew pristine SmFeAsO films, and subsequently introduced F into the films by diffusion from an overlayer of SmF3. In the second method, we grew as-grown superconducting SmFeAs(O,F) films by coevaporating Sm, SmF3, Fe, and As. Thus far, better results have been obtained by the first F diffusion method. The films prepared by F diffusion showed Tcon (Tcend) = 56.5 K (55.3 K), whereas the as-grown films showed Tcon (Tcend) = 51.5 K (48.0 K).

  4. Distribution of Al{sub 12}Fe{sub 3}Si and (FeAl{sub 6})Si in a HIPed Al-10.71 wt. % Si casting

    SciTech Connect

    Chama, C.C.

    1996-10-01

    An investigation on microstructural development in a hot isostatically pressed (HIPed) Al-10.71 wt. % Si casting is described. The as-cast material contained 0.006 total volume fraction of Al{sub 12}Fe{sub 3}Si and (FeAl{sub 6})Si particles but HIPing at 550 C and 68.95 MPa produced a moderate increase in this fraction, to a maximum value of 0.061 when HIPed for 120 min. Dislocations appeared to be the dominant nucleation sites for the particles in both the as-cast and the HIPed materials.

  5. Longitudinal spin excitations and magnetic anisotropy in antiferromagnetically ordered BaFe2As2

    NASA Astrophysics Data System (ADS)

    Li, Yuan; Wang, Chong; Zhang, Rui; Luo, Huiqian; Wang, Fa; Dai, Pengcheng; Regnault, Louis-Pierre

    2014-03-01

    In the iron-based superconductors, there is an outstanding debate on the microscopic origin of the magnetism, whether it arises from local moments or itinerant electrons with Fermi-surface nesting. To answer this question, we performed a spin-polarized inelastic neutron scattering study of spin waves in the antiferromagnetically ordered state of BaFe2As2. Three distinct excitation components are identified, with spins fluctuating along the c-axis, perpendicular to the ordering direction in the ab -plane, and parallel to the ordering direction. While the first two ``transverse'' components can be described by a linear spin-wave theory with magnetic anisotropy and inter-layer coupling, the third ``longitudinal'' component is generically incompatible with the local moment picture. It points towards a contribution of itinerant electrons to the magnetism already in the parent compound of this family of Fe-based superconductors. (arXiv:1309.7553) Supported by the National Basic Research Program of China, the National Science Foundation of China, and the US National Science Foundation.

  6. Disappearance of superconductivity in the solid solution between (Ca4Al2O6)(Fe2As2) and (Ca4Al2O6)(Fe2P2) superconductors.

    PubMed

    Shirage, Parasharam M; Kihou, Kunihiro; Lee, Chul-Ho; Takeshita, Nao; Eisaki, Hiroshi; Iyo, Akira

    2012-09-19

    The effect of alloying the two perovskite-type iron-based superconductors (Ca(4)Al(2)O(6))(Fe(2)As(2)) and (Ca(4)Al(2)O(6))(Fe(2)P(2)) was examined. While the two stoichiometric compounds possess relatively high T(c)'s of 28 and 17 K, respectively, their solid solutions of the form (Ca(4)Al(2)O(6))(Fe(2)(As(1-x)P(x))(2)) do not show superconductivity over a wide range from x = 0.50 to 0.95. The resultant phase diagram is thus completely different from those of other typical iron-based superconductors such as BaFe(2)(As,P)(2) and LaFe(As,P)O, in which superconductivity shows up when P is substituted for As in the non-superconducting "parent" compounds. Notably, the solid solutions in the non-superconducting range exhibit resistivity anomalies at temperatures of 50-100 K. The behavior is reminiscent of the resistivity kink commonly observed in various non-superconducting parent compounds that signals the onset of antiferromagnetic/orthorhombic long-range order. The similarity suggests that the suppression of the superconductivity in the present case also has a magnetic and/or structural origin.

  7. Concentration dependent structural parameters of liquid Al-Fe alloys

    NASA Astrophysics Data System (ADS)

    Lalnuntluanga, C.; Mishra, Raj Kumar

    2016-10-01

    Square well potential is perturbed over Lebowtiz solution of hard sphere mixtures to determine direct correlation function,C(0) ij(r) in repulsive and attractive regions under Mean Spherical Model Approximation [1]. Obtained direct correlation functions were employed to derive partial structure factors and then total structure factor, S(k) in liquid Al-Fe alloy at different atomic percent of Al. Fourier transform of partial and total structure factors gives partial and total radial distribution functions, g(r) from which partial and total coordination numbers and the partial nearest-neighbor distances were computed.

  8. Role of Fe and sign reversal of the Hall coefficient in quasicrystalline Al-Cu-Fe

    NASA Astrophysics Data System (ADS)

    Lindqvist, P.; Berger, C.; Klein, T.; Lanco, P.; Cyrot-Lackmann, F.; Calvayrac, Y.

    1993-07-01

    Electronic transport properties were measured for the stable icosahedral phase of Al-Cu-Fe for a large number of high-structural-quality samples of different compositions. At low temperature, the Hall coefficient RH and the conductivity σ are found to best correlate with the Fe content rather than with the electron per atom parameter which is usually used; RH changes sign at a concentration of 12.5 at. % Fe, where σ is at minimum. RH has a strong temperature dependence and can change sign with temperature. These features put the focus on the Fe d states and can be interpreted by a Hume-Rothery type of behavior including the sp-d hybridization effects.

  9. Towards a Superplastic Forming of Fe-Mn-Al Alloys

    SciTech Connect

    Guanabara, Paulo Jr.; Bueno, Levi de O.; Ferreira Batalha, Gilmar

    2011-01-17

    The aim is to study the characteristics of superplasticity, mostly on non qualified materials, such as austenitic steel of the Fe-Mn-Al alloy, which has some of the specific material parameters closely related to microstructural mechanisms. These parameters are used as indicators of material superplastic potentiality. The material was submitted to hot tensile testing, within a temperature range from 600 deg. C to 1000 deg. C and strain-rates varying from 10{sup -6} to 1 s{sup -1}. The strain rate sensitivity parameter (m) and observed maximum elongation until rupture ({epsilon}{sub r}) could be determined and also obtained from the hot tensile test. The experiments stated a possibility of superplastic behaviour in a Fe-Mn-Al alloy within a temperature range from 700 deg. C to 900 deg. C with grain size around 3 {mu}m (ASTM grain size 12) and average strain rate sensitivity of m {approx} 0.54, as well as a maximum elongation at rupture around 600%. The results are based on a more enhanced research from the authors; however, this paper has focused just on the hot tensile test, as further creep tests results are not available herein. There are rare examples of superplasticity study of an austenitic steel Fe-Mn-Al alloy, thus this work showed some possibility of exploring the potential use of such materials in this regime at temperatures {>=}700 deg. C.

  10. Yield stress anomaly in B2 FeAl

    SciTech Connect

    Yoshimi, K.; Hanada, S.; Yoo, M.H.

    1996-12-31

    The studies on yield stress anomaly of B2 FeAl single crystals are reviewed in this paper. A positive temperature dependence of yield stress, so-called yield stress anomaly, is observed in B2 FeAl in which excess vacancies are fully annealed out. Associated with the anomaly, characteristic asymmetry is found between tension and compression. While the strain-rate sensitivity is almost zero in the temperature range of the yield stress anomaly, the stress relaxation becomes significant with increasing temperature, indicating that a recovery process is thermally activated. It is ascertained by the two-surface trace analysis that slip transition from <111> direction at intermediate temperature to <100> at high temperature occurs around the peak temperature. Even at the peak temperature, in addition, operative slip vector for yielding is confirmed to be predominantly <111> by TEM. Also, it is observed that <111>-type superdislocations are frequently climb-dissociated in the temperature range of the anomaly. APB formation on {l_brace}111{r_brace} plane is energetically favorable, which is in agreement with the Flinn`s calculation for the B2 superlattice that APB energy on {l_brace}111{r_brace} plane is lower than that on {l_brace}110{r_brace} plane. Such an anisotropy of APB energy would offer specific driving force for the climb dissociation on <111> superdislocations. On the basis of the observed results, the anomalous strengthening behavior of B2 FeAl single crystals is discussed.

  11. Melting and casting of FeAl-based cast alloy

    SciTech Connect

    Sikka, V.K.; Wilkening, D.; Liebetrau, J.; Mackey, B.

    1998-11-01

    The FeAl-based intermetallic alloys are of great interest because of their low density, low raw material cost, and excellent resistance to high-temperature oxidation, sulfidation, carburization, and molten salts. The applications based on these unique properties of FeAl require methods to melt and cast these alloys into complex-shaped castings and centrifugal cast tubes. This paper addresses the melting-related issues and the effect of chemistry on the microstructure and hardness of castings. It is concluded that the use of the Exo-Melt{trademark} process for melting and the proper selection of the aluminum melt stock can result in porosity-free castings. The FeAl alloys can be melted and cast from the virgin and revert stock. A large variation in carbon content of the alloys is possible before the precipitation of graphite flakes occurs. Titanium is a very potent addition to refine the grain size of castings. A range of complex sand castings and two different sizes of centrifugal cast tubes of the alloy have already been cast.

  12. A propos de la ferroeléctricité dans BaAl 2O 4

    NASA Astrophysics Data System (ADS)

    Huang, Sui-Yang; Von Der Mühll, Régnault; Ravez, Jean; Chaminade, Jean Pierre; Hagenmuller, Paul; Couzi, Michel

    1994-03-01

    Structural, ferroelectric, pyroelectric, and optical properties of ceramics and crystals of BaAl 2O 4 have been investigated. A refinement of the atomic positions has been carried out from the X-ray powder data. BaAl 2O 4 shows anomalous behavior of the dielectric and pyroelectric properties: the dielectric constant ɛ 'r is very weak; its maximal value at Curie temperature for a crystal oriented along the hexagonal c-axis is about 15 and that of a ceramic of compactness 0.89 is around 7.5. The Curie-Weiss constant is relatively weak ( C = 125). The behavior of the spontaneous polarization Ps is unexpected with respect to that of classical ferroelectric materials: Ps increases with decreasing temperature from Tc and decreases again after having reached a maximum at 200 K. A model based on ferrielectric behavior and supported by the Landau equation has been proposed. La structure et les propriétés ferroélectriques, pyroélectriques et optiques de céramiques et de cristaux du composé BaAl 2O 4 ont été étudiées. Un affinement des positions atomiques a été entrepris à partir du spectre de diffraction X sur poudre. BaAl 2O 4 présente un comportement anormal des propriétés diélectriques et pyroélectriques: la constante diélectrique ɛ' r est faible, sa valeur maximale à Tc est voisine de 15 pour les cristaux et de 7,5 pour des céramiques de compacité 0,89. La constante de Curie est aussi relativement faible ( C = 125). Le comportement de la polarisation spontaneé Ps diffère de celui des matériaux ferroélectriques "classiques": Ps augmente lorsque T décroı̂t en-dessous de Tc pour atteindre un maximum à T = 200 K suivi d'une décroissance. Un modèle de comportement ferriélectrique s'appuyant sur la relation de Landau pourrait justifier les propriétés observées.

  13. Preparation and Pore Structure Stability at High Temperature of Porous Fe-Al Intermetallics

    NASA Astrophysics Data System (ADS)

    Shen, P. Z.; Gao, H. Y.; Song, M.; He, Y. H.

    2013-12-01

    Porous Fe-Al intermetallics with different nominal compositions (from Fe-8 wt.% Al to Fe-50 wt.% Al) were fabricated by Fe and Al elemental powders through reaction synthesis. The effects of the Al content on the pore structure properties, and the comparison of pore structure stabilities at high-temperatures among the porous Fe-Al intermetallics and porous Ti, Ni, 316L stainless steel samples, were systematically studied. Results showed that the open porosity, maximum pore size, and permeability vary with the Al content. Porous Fe-(25-30 wt.%) Al intermetallics show good shape controllability and excellent pore structure stability at 1073 K in air, which suggests that these porous Fe-Al intermetallics could be used for filtration at high temperatures.

  14. Giant magnetoelectric coupling interaction in BaTiO{sub 3}/BiFeO{sub 3}/BaTiO{sub 3} trilayer multiferroic heterostructures

    SciTech Connect

    Kotnala, R. K. E-mail: rkkotnala@gmail.com; Gupta, Rekha; Chaudhary, Sujeet

    2015-08-24

    Multiferroic trilayer thin films of BaTiO{sub 3}/BiFeO{sub 3}/BaTiO{sub 3} were prepared by RF-magnetron sputtering technique at different thicknesses of BiFeO{sub 3} layer. A pure phase polycrystalline growth of thin films was confirmed from X-ray diffraction results. The film showed maximum remnant electric polarization (2P{sub r}) of 13.5 μC/cm{sup 2} and saturation magnetization (M{sub s}) of 61 emu/cc at room temperature. Thermally activated charge transport dominated via oxygen vacancies as calculated by their activation energy, which was consistent with current–voltage characteristics. Magnetic field induced large change in resistance and capacitance of grain, and grain boundary was modeled by combined impedance and modulus spectroscopy in the presence of varied magnetic fields. Presence of large intrinsic magnetoelectric coupling was established by a maximum 20% increase in grain capacitance (C{sub g}) with applied magnetic field (2 kG) on trilayer having 20 nm BiFeO{sub 3} layer. Substantially higher magnetoelectric coupling in thinner films has been observed due to bonding between Fe and Ti atoms at interface via oxygen atoms. Room temperature magnetoelectric coupling was confirmed by dynamic magnetoelectric coupling, and maximum longitudinal magnetoelectric coupling of 515 mV/cm-Oe was observed at 20 nm thickness of BiFeO{sub 3}. The observed magnetoelectric properties are potentially useful for novel room temperature magnetoelectric and spintronic device applications for obtaining higher voltage at lower applied magnetic field.

  15. New insights into the application of the valence rules in Zintl phases—Crystal and electronic structures of Ba{sub 7}Ga{sub 4}P{sub 9}, Ba{sub 7}Ga{sub 4}As{sub 9}, Ba{sub 7}Al{sub 4}Sb{sub 9}, Ba{sub 6}CaAl{sub 4}Sb{sub 9}, and Ba{sub 6}CaGa{sub 4}Sb{sub 9}

    SciTech Connect

    He, Hua; Stoyko, Stanislav; Bobev, Svilen

    2016-04-15

    Crystals of three new ternary pnictides—Ba{sub 7}Al{sub 4}Sb{sub 9}, Ba{sub 7}Ga{sub 4}P{sub 9}, and Ba{sub 7}Ga{sub 4}As{sub 9} have been prepared by reactions of the respective elements in molten Al or Pb fluxes. Single-crystal X-ray diffraction studies reveal that the three phases are isotypic, crystallizing in the orthorhombic Ba{sub 7}Ga{sub 4}Sb{sub 9}-type structure (space group Pmmn, Pearson symbol oP40, Z=2), for which only the prototype is known. The structure is based on TrPn{sub 4} tetrahedra (Tr=Al, Ga; Pn=P, As, Sb), connected in an intricate scheme into 1D-ribbons. Long interchain Pn–Pn bonds (d{sub P–P}>3.0 Å; d{sub As–As}>3.1 Å; d{sub Sb–Sb}>3.3 Å) account for the realization of 2D-layers, separated by Ba{sup 2+} cations. Applying the classic valance rules to rationalize the bonding apparently fails, and Ba{sub 7}Ga{sub 4}Sb{sub 9} has long been known as a metallic Zintl phase. Earlier theoretical calculations, both empirical and ab-initio, suggest that the possible metallic properties originate from filled anti-bonding Pn–Pn states, and the special roles of the “cations” in this crystal structure. To experimentally probe this hypothesis, we sought to synthesize the ordered quaternary phases Ba{sub 6}CaTr{sub 4}Sb{sub 9} (Tr=Al, Ga). Single-crystal X-ray diffraction work confirms Ba{sub 6.145(3)}Ca{sub 0.855}Al{sub 4}Sb{sub 9} and Ba{sub 6.235(3)}Ca{sub 0.765}Ga{sub 4}Sb{sub 9}, with Ca atoms preferably substituting Ba on one of the three available sites. The nuances of the five crystal structures are discussed, and the chemical bonding in Ba{sub 7}Ga{sub 4}As{sub 9} is interrogated by tight-binding linear muffin-tin orbital calculations. - Graphical abstract: The new Zintl phases—Ba{sub 7}Al{sub 4}Sb{sub 9}, Ba{sub 7}Ga{sub 4}P{sub 9}, and Ba{sub 7}Ga{sub 4}As{sub 9}, and their quaternary variants Ba{sub 6}CaTr{sub 4}Sb{sub 9} (Tr=Al, Ga)—crystallize in the Ba{sub 7}Ga{sub 4}Sb{sub 9} structure type. The structures are based

  16. Evolution of Fe Bearing Intermetallics During DC Casting and Homogenization of an Al-Mg-Si Al Alloy

    NASA Astrophysics Data System (ADS)

    Kumar, S.; Grant, P. S.; O'Reilly, K. A. Q.

    2016-06-01

    The evolution of iron (Fe) bearing intermetallics (Fe-IMCs) during direct chill casting and homogenization of a grain-refined 6063 aluminum-magnesium-silicon (Al-Mg-Si) alloy has been studied. The as-cast and homogenized microstructure contained Fe-IMCs at the grain boundaries and within Al grains. The primary α-Al grain size, α-Al dendritic arm spacing, IMC particle size, and IMC three-dimensional (3D) inter-connectivity increased from the edge to the center of the as-cast billet; both α c-AlFeSi and β-AlFeSi Fe-IMCs were identified, and overall α c-AlFeSi was predominant. For the first time in industrial billets, the different Fe-rich IMCs have been characterized into types based on their 3D chemistry and morphology. Additionally, the role of β-AlFeSi in nucleating Mg2Si particles has been identified. After homogenization, α c-AlFeSi predominated across the entire billet cross section, with marked changes in the 3D morphology and strong reductions in inter-connectivity, both supporting a recovery in alloy ductility.

  17. Magnetic Origin of Giant Magnetoelectricity in Doped Y-type Hexaferrite Ba0.5Sr1.5Zn2(Fe1 -xAlx)12O22

    NASA Astrophysics Data System (ADS)

    Noh, Woo-Suk; Ko, Kyung-Tae; Chun, Sae Hwan; Kim, Kee Hoon; Park, Byeong-Gyu; Kim, Jae-Young; Park, Jae-Hoon

    2015-03-01

    We investigated site-specific magnetic behaviors of multiferroic Ba0.5Sr1.5Zn2(Fe1 -xAlx)12O22 using Fe L2 ,3-edge x-ray magnetic circular dichroism. The Al dopants mostly replace the Fe3 + ions at octahedral (Oh) sites, which contribute unquenched angular momenta through off-centering displacements. This replacement greatly reduces the magnetic anisotropy energy to change the magnetic order from a helical to a heliconical type with enhanced magnetoelectric susceptibility (αME). The tetrahedral (Td) Fe sites exhibit magnetic hysteresis distinguishable from that of the Oh sites, especially at low magnetic fields. These results provide essential clues for the heliconical order with a giant αME and multibit memory effects in the Al-doped Y-type hexaferrite.

  18. Elevated Temperature Deformation of Fe-39.8Al and Fe-15.6Mn-39.4Al

    NASA Technical Reports Server (NTRS)

    Whittenberger, J. Daniel

    2004-01-01

    The elevated temperature compressive properties of binary Fe-39.8 at % Al and Fe-15.6Mn-39.4Al have been measured between 1000 and 1300 K at strain rates between 10(exp 7) and 10(exp 3)/ s. Although the Mn addition to iron aluminide did not change the basic deformation characteristics, the Mn-modified alloy was slightly weaker. In the regime where deformation of FeAl occurs by a high stress exponent mechanism (n = 6), strength increases as the grain size decreases at least for diameters between approx. 200 and approx. 10 microns. Due to the limitation in the grain size-flow stress-temperature-strain rate database, the influence of further reductions of the grain size on strength is uncertain. Based on the appearance of subgrains in deformed iron aluminide, the comparison of grain diameters to expected subgrain sizes, and the grain size exponent and stress exponent calculated from deformation experiments, it is believed that grain size strengthening is the result of an artificial limitation on subgrain size as proposed by Sherby, Klundt and Miller.

  19. Three Oxidation States of Manganese in the Barium Hexaferrite BaFe12-xMnxO19.

    PubMed

    Nemrava, Sandra; Vinnik, Denis A; Hu, Zhiwei; Valldor, Martin; Kuo, Chang-Yang; Zherebtsov, Dmitry A; Gudkova, Svetlana A; Chen, Chien-Te; Tjeng, Liu Hao; Niewa, Rainer

    2017-04-03

    The coexistence of three valence states of Mn ions, namely, +2, +3, and +4, in substituted magnetoplumbite-type BaFe12-xMnxO19 was observed by soft X-ray absorption spectroscopy at the Mn-L2,3 edge. We infer that the occurrence of multiple valence states of Mn situated in the pristine purely iron(III) compound BaFe12O19 is made possible by the fact that the charge disproportionation of Mn(3+) into Mn(2+) and Mn(4+) requires less energy than that of Fe(3+) into Fe(2+) and Fe(4+), related to the smaller effective Coulomb interaction of Mn(3+) (d(4)) compared to Fe(3+) (d(5)). The different chemical environments determine the location of the differently charged ions: with Mn(3+) occupying positions with (distorted) octahedral local symmetry, Mn(4+) ions prefer octahedrally coordinated sites in order to optimize their covalent bonding. Larger and more ionic bonded Mn(2+) ions with a spherical charge distribution accumulate at tetrahedrally coordinated sites. Simulations of the experimental Mn-L2,3 XAS spectra of two different samples with x = 1.5 and x = 1.7 led to Mn(2+):Mn(3+):Mn(4+) atomic ratios of 0.16:0.51:0.33 and 0.19:0.57:0.24.

  20. Similarities between structural distortions under pressure and chemical doping in superconducting BaFe2As2.

    PubMed

    Kimber, Simon A J; Kreyssig, Andreas; Zhang, Yu-Zhong; Jeschke, Harald O; Valentí, Roser; Yokaichiya, Fabiano; Colombier, Estelle; Yan, Jiaqiang; Hansen, Thomas C; Chatterji, Tapan; McQueeney, Robert J; Canfield, Paul C; Goldman, Alan I; Argyriou, Dimitri N

    2009-06-01

    The discovery of a new family of high-T(C) materials, the iron arsenides (FeAs), has led to a resurgence of interest in superconductivity. Several important traits of these materials are now apparent: for example, layers of iron tetrahedrally coordinated by arsenic are crucial structural ingredients. It is also now well established that the parent non-superconducting phases are itinerant magnets, and that superconductivity can be induced by either chemical substitution or application of pressure, in sharp contrast to the cuprate family of materials. The structure and properties of chemically substituted samples are known to be intimately linked; however, remarkably little is known about this relationship when high pressure is used to induce superconductivity in undoped compounds. Here we show that the key structural features in BaFe2As2, namely suppression of the tetragonal-to-orthorhombic phase transition and reduction in the As-Fe-As bond angle and Fe-Fe distance, show the same behaviour under pressure as found in chemically substituted samples. Using experimentally derived structural data, we show that the electronic structure evolves similarly in both cases. These results suggest that modification of the Fermi surface by structural distortions is more important than charge doping for inducing superconductivity in BaFe2As2.

  1. First principles investigation of Fe and Al bearing phase H

    NASA Astrophysics Data System (ADS)

    Tsuchiya, J.; Tsuchiya, T.

    2015-12-01

    The global circulation of water in the earth is important to investigate the evolution history and dynamics of the earth, since the physical properties (e.g. atomic diffusivity, melting temperature, electrical conductivity and seismic velocities) of the constituent minerals are considerably changed by the presence of water. It has been believed that water is carried into the deep Earth's interior by hydrous minerals such as the dense hydrous magnesium silicates (DHMSs) which are also known as alphabet phases (phase A, superhydrous phase B, and phase D etc.) in the descending cold plate. It has been thought that the relay of these hydrous phases was terminated at ~1200 km depth by the dehydration of phase D which was the highest pressure phase of DHMSs. Recently, we have theoretically predicted the high pressure phase of phase D and experimentally confirmed the existence of this new DHMS in lower mantle pressure conditions above ~45 GPa. This phase has MgSiO4H2chemical composition and named as phase H. At the lower mantle pressure conditions, Al and H-bearing SiO2, δ-AlOOH, ɛ-FeOOH and phase H may be the relevant hydrous phases in the subducting slabs. Interestingly, the crystal structure of these hydrous phases are almost same and have CaCl2type structure. This suggests that these hydrous phases may potentially be able to make the wide range of solid solution. Some experimental studies already reported that Al preferentially partitioned into phase H and the stability of phase H drastically increased by incorporation of Al (Nishi et al. 2014, Ohira et al. 2014). The density of subducted MORB is reported to be denser than that of pyrolite in the lower mantle (e.g. Kawai et al. 2009). Therefore, there is a possibility that phase H containing Al and Fe in subducted MORB survive down to the bottom of lower mantle and the melting of phase H at the core mantle boundary may contribute to the cause of ultra-low velocity zones. In this study, we further extends our

  2. Magnetotransport of proton-irradiated BaFe2As2 and BaFe1.985Co0.015As2 single crystals

    SciTech Connect

    Moseley, D. A.; Yates, K. A.; Peng, N.; Mandrus, D.; Sefat, Athena Safa; Branford, W. R.; Cohen, L. F.

    2015-02-17

    In this paper, we study the magnetotransport properties of the ferropnictide crystals BaFe2As2 and BaFe1.985Co0.015As2. These materials exhibit a high field linear magnetoresistance that has been attributed to the quantum linear magnetoresistance model. In this model, the linear magnetoresistance is dependent on the concentration of scattering centers in the material. By using proton-beam irradiation to change the defect scattering density, we find that the dependence of the magnitude of the linear magnetoresistance on scattering quite clearly contravenes this prediction. Finally, a number of other scaling trends in the magnetoresistance and high field Hall data are observed and discussed.

  3. Al-Ca and Al-Fe metal-metal composite strength, conductivity, and microstructure relationships

    SciTech Connect

    Kim, Hyong June

    2011-01-01

    Deformation processed metal-metal composites (DMMC’s) are composites formed by mechanical working (i.e., rolling, swaging, or wire drawing) of two-phase, ductile metal mixtures. Since both the matrix and reinforcing phase are ductile metals, the composites can be heavily deformed to reduce the thickness and spacing of the two phases. Recent studies have shown that heavily drawn DMMCs can achieve anomalously high strength and outstanding combinations of strength and conductivity. In this study, Al-Fe wire composite with 0.07, 0.1, and 0.2 volume fractions of Fe filaments and Al-Ca wire composite with 0.03, 0.06, and 0.09 volume fractions of Ca filaments were produced in situ, and their mechanical properties were measured as a function of deformation true strain. The Al-Fe composites displayed limited deformation of the Fe phase even at high true strains, resulting in little strengthening effect in those composites. Al-9vol%Ca wire was deformed to a deformation true strain of 13.76. The resulting Ca second-phase filaments were deformed to thicknesses on the order of one micrometer. The ultimate tensile strength increased exponentially with increasing deformation true strain, reaching a value of 197 MPa at a true strain of 13.76. This value is 2.5 times higher than the value predicted by the rule of mixtures. A quantitative relationship between UTS and deformation true strain was determined. X-ray diffraction data on transformation of Al + Ca microstructures to Al + various Al-Ca intermetallic compounds were obtained at the Advanced Photon Source at Argonne National Laboratory. Electrical conductivity was measured over a range of true strains and post-deformation heat treatment schedules.

  4. Strikingly dissimilar effect of Mn and Zn dopants imposed on local structural distortion of Ba0.5K0.5Fe2As2 superconductor.

    PubMed

    Cheng, Jie; Dong, Peng; Chu, Wangsheng; Xu, Wei; Wen, Haihu; Marcelli, Augusto; Wu, Ziyu

    2013-05-01

    To clarify the contrasting impurity effects of Mn and Zn dopants on the critical temperature of optimally doped Ba0.5K0.5Fe2As2 superconductors, extended X-ray absorption fine-structure spectroscopy was implemented at the Fe and As K-edge. In Mn-doped compounds a gradual deviation of the symmetric FeAs4 tetrahedron and weakening of the Fe-As bond was observed. Conversely, in Zn-doped compounds the perfect FeAs4 tetrahedron is maintained and the Fe-As bond is rigid. The local structural details are consistent with the development of superconductivity in these two systems, suggesting a significant role played by the topology of the FeAs4 tetrahedron and rigidness of the Fe-As bond in Mn/Zn-doped Ba0.5K0.5Fe2As2 superconductors.

  5. Identification of an incommensurate FeAl{sub 2} overlayer on FeAl(110) using x-ray diffraction and reflectivity

    SciTech Connect

    Baddorf, A.P.; Chandavarkar, S.S.

    1995-06-30

    FeAl, like NiAl, crystallizes in the CsCl structure. Consequently the (110) planes contain equal amounts of Fe and Al distributed as interlocking rectangles. Unlike the NiAI(110) surface, which retains the (1{times}l) in-plane symmetry of the bulk, FeAl(l10) reconstructs to form an ordered, incommensurate overlayer. The reconstructed layer introduces x-ray diffraction rods at half-order positions along the [1{bar 1}0] direction, and displaced {plus_minus}0.2905 from integer positions along the [001] direction. Peak widths reveal excellent long range order. Specular reflectivity measurements above and below the Fe K{alpha} edge can be reproduced using a model containing a single reconstructed overlayer with an Fe:Al ratio of 1:2, consistent with FeA{sub I}2.

  6. Sulfation and Desulfation Behavior of Pt-BaO/MgO-Al2O3 NOx Storage Reduction Catalyst.

    PubMed

    Jeong, Soyeon; Kim, Do Heui

    2016-05-01

    The comparative study between Pt-BaO/Al2O3 and Pt-BaO/MgO-Al2O3 gives the information about the effect of MgO addition to Al2O3 support on the sulfation and desulfation behavior of Pt-BaO/MgO-Al2O3 NOx storage reduction catalyst. The sulfated two samples were analyzed by using element analysis (EA), X-ray diffraction (XRD), H2 temperature programmed reaction (H2 TPRX) and NOx uptake measurement. The amount of sulfur uptake on 2 wt% Pt-20 wt% BaO/Al2O3 and 2 wt% Pt-20 wt% BaO/MgO-Al2O3 are almost identical as 0.45 and 0.40 of S/Ba, respectively, which yields the drastic decrease in NOx uptake for both sulfated samples. However, after desulfa- tion with H2 at 600 degrees C, the residual sulfur amount on MgO-Al2O3 supported catalyst is three times larger than that on Al2O3 supported one, indicating that sulfur species formed on the former are more stable than those on the latter. It is also well corresponding to the H2 TPRX results where the main H2S peak from MgO-Al2O3 supported sample is observed at higher temperature than Al2O3 supported one, resulting in the lower NOx uptake activity of former sample than the latter one. Meanwhile, after desulfation of MgO-Al2O3 supported sample at 700 degrees C and 800 degrees C, the activity is recovered more significantly due to the removal of the large amount of sulfur while Al2O3 supported one decreases monotonically due to the sintering of Pt crystallite and the formation of BaAl2O4 phase. It is summarized that MgO-Al2O3 supported catalyst enhances the thermal stability of the catalyst, however, forms the stable sulfate species, which needs to be improved to develop the more sulfur resistant NSR catalyst system.

  7. Decomposition of Al2.7Fe0.3Ti in heated Al-Al2.7Fe0.3Ti refiner fabricated by spark plasma sintering and its refining performance

    NASA Astrophysics Data System (ADS)

    Watanabe, Yoshimi; Hamada, Takayuki; Sato, Hisashi

    2017-01-01

    In our previous study, a novel Al-L12-type Al2.7Fe0.3Ti refiner was fabricated by spark plasma sintering (SPS) and its refining performance was studied. It was found that L12-type Al2.7Fe0.3Ti particles can be favorable heterogeneous nucleation sites for Al casts, since the lattice matching between Al2.7Fe0.3Ti and Al is good. It was also found that the thermal stability of heterogeneous nucleation sites affects the grain-refining performance. In this study, the decomposition phenomena of the Al2.7Fe0.3Ti phase in a refiner are studied by heating an Al-Al2.7Fe0.3Ti refiner fabricated by SPS. In addition, the refining performance of a heated Al-Al2.7Fe0.3Ti refiner is investigated.

  8. Study of non-stoichiometric BaSrTiFeO3 oxide dedicated to semiconductor gas sensors

    NASA Astrophysics Data System (ADS)

    Fasquelle, D.; Verbrugghe, N.; Deputier, S.

    2016-11-01

    Developing instrumentation systems compatible with the European RoHS directive (restriction of hazardous substances) to monitor our environment is of great interest for our society. Our research therefore aims at developing innovating integrated systems of detection dedicated to the characterization of various environmental exposures. These systems, which integrate new gas sensors containing lead-free oxides, are dedicated to the detection of flammable and toxic gases. We have firstly chosen to study semiconductor gas sensors implemented with lead-free oxides in view to develop RoHS devices. Therefore thick films deposited by spin-coating and screen-printing have been chosen for their robustness, ease to realize and ease to finally obtain cost-effective sensors. As crystalline defects and ionic vacancies are of great interest for gas detection, we have decided to study a non-stoichiometric composition of the BaSrTiFeO3 sensible oxide. Nonstoichiometric BaSrTiFeO3 lead-free oxide thick films were deposited by screen-printing on polycrystalline AFO3 substrates covered by a layer of Ag-Pd acting as bottom electrode. The physical characterizations have revealed a crystalline structure mainly composed of BaTiO3 pseudo-cubic phase and Ba4Ti12O27 monoclinic phase for the powder, and a porous microstructure for the thick films. When compared to a BSTF thick film with a stoichiometric composition, a notable increase in the BSTF dielectric constant value was observed when taking into account of a similar microstructure and grain size. The loss tangent mean value varies more softly for the non-stoichiometric BaSrTiFeO3 films than for the perovskite BSTF film as tanδ decreases from 0.45 to 0.04 when the frequency increases from 100 Hz to 1 MHz.

  9. The crystal structure and magnetic properties of Ba2-xSrxCo2Fe12O22

    NASA Astrophysics Data System (ADS)

    Cho, Kwang Lae; Rhee, Chan Hyuk; Kim, Chul Sung

    2014-05-01

    We have synthesized the Ba2-xSrxCo2Fe12O22 samples (x = 0.1, 0.2, 0.3, 0.4, 0.5) by the solid-state reaction method and investigated their crystalline and magnetic properties by X-ray diffractometer (XRD), Mössbauer spectrometer, vibrating sample magnetometer, and network analyzer. XRD patterns show that all samples are rhombohedral with space group R-3m. The lattice constants a0 and c0 decrease with Sr substitution due to smaller ion radius of Sr2+ (1.27 Å) than that of Ba2+ (1.43 Å). The Mössbauer spectroscopy measurements show that the relative area ratios of Fe ion were maintained constant regardless of the Sr concentration. However, average magnetic hyperfine field slightly increased with the Sr concentration. This observation agrees with the fact that the saturation magnetization (Ms) linearly increases due to the increasing super-exchange interaction, originated from the difference in the ionic radius between Ba2+ and Sr2+. To investigate its properties at high frequency range, all samples were sintered at 1100 °C, and complex permeability and permittivity were measured by network analyzer between 100 MHz and 4 GHz. For x below 0.3, the initial permeability at 100 MHz increases, at higher values of x, its value decreases. Our study shows that magnetic properties of Sr2+ substitution for Ba2+ in Y-type hexaferrite as well as low magnetic loss less than 0.1 in 1 GHz band, indicating the potential application of Ba2-xSrxCo2Fe12O22 samples for RF and antenna devices in ultra high frequency band.

  10. Crystallographic and magnetic properties of the hyperthermia material CoFe2O4@AlFe2O4

    NASA Astrophysics Data System (ADS)

    Choi, Hyunkyung; An, Mijeong; Eom, Wonyoung; Lim, Sae Wool; Shim, In-Bo; Kim, Chul Sung; Kim, Sam Jin

    2017-01-01

    Hard/soft CoFe2O4@AlFe2O4 core/shell nanoparticles were prepared by using a high temperature thermal decomposition method with seed-mediated growth. The structural, magnetic and thermal properties of the nanoparticles were investigated by using X-ray diffraction, vibrating sample magnetometer, MagneTherm, and Mössbauer spectroscopy. The crystal structure of nanoparticles was determined to be cubic spinel ferrite with space group Fd-3m. The CoFe2O4 nanoparticles were found to show high magnetization and coercivity while AlFe2O4 nanoparticles were found to show low magnetization and coercivity. The CoFe2O4@AlFe2O4 core/shell nanoparticles showed intermediate values of magnetization and the coercivity between those of CoFe2O4 and AlFe2O4. Also, the blocking temperature ( T B ) of the nanoparticles (NPs) was observed to be 280, 50, and 225 K for CoFe2O4, AlFe2O4 and CoFe2O4@AlFe2O4, respectively. The core/shell ferrite shows a T B near 225 K, associated with the harder CoFe2O4 NPs. Temperatures below 225 K, the zero-field-cooled curves show changes in their slopes at a temperature near 50 K, corresponding to the second blocking temperature associated with the softer AlFe2O4 NPs.

  11. Close correlation between magnetic properties and the soft phonon mode of the structural transition in BaFe2As2 and SrFe2As2

    DOE PAGES

    Parshall, D.; Pintschovius, L.; Niedziela, Jennifer L.; ...

    2015-04-27

    Pmore » arent compounds of Fe-based superconductors undergo a structural phase transition from a tetragonal to an orthorhombic structure. We investigated the temperature dependence of the frequencies of TA phonons that extrapolate to the shear vibrational mode at the zone center, which corresponds to the orthorhombic deformation of the crystal structure at low temperatures in BaFe2As2 and SrFe2As2. We found that acoustic phonons at small wave vectors soften gradually towards the transition from high temperatures, tracking the increase of the size of slowly fluctuating magnetic domains. On cooling below the transition to base temperature the phonons harden, following the square of the magnetic moment (which we find is proportional to the anisotropy gap). Finally, our results provide evidence for close correlation between magnetic and phonon properties in Fe-based superconductors.« less

  12. Pressure-induced superconductivity in Ba0.5Sr0.5Fe2As2.

    PubMed

    Tsoi, Georgiy M; Malone, Walter; Uhoya, Walter; Mitchell, Jonathan E; Vohra, Yogesh K; Wenger, Lowell E; Sefat, Athena S; Weir, S T

    2012-12-12

    High-pressure electrical resistance measurements have been performed on single crystal Ba(0.5)Sr(0.5)Fe(2)As(2) platelets to pressures of 16 GPa and temperatures down to 10 K using designer diamond anvils under quasi-hydrostatic conditions with an insulating steatite pressure medium. The resistance measurements show evidence of pressure-induced superconductivity with an onset transition temperature at ∼31 K and zero resistance at ∼22 K for a pressure of 3.3 GPa. The transition temperature decreases gradually with increasing pressure before completely disappearing for pressures above 12 GPa. The present results provide experimental evidence that a solid solution of two 122-type materials, i.e., Ba(1-x)Sr(x)Fe(2)As(2) (0 < x < 1), can also exhibit superconductivity under high pressure.

  13. Aging effect in magnetotransport property of oxygen adsorbed BaFe{sub 2}As{sub 2}

    SciTech Connect

    Ghosh, Nilotpal E-mail: nilotpal@vit.ac.in; Raj, Santhosh

    2015-06-24

    Presence of oxygen (O{sub 2}) has been found by Energy Dispersive X-ray Analysis (EDAX) on the surfaces of flux grown BaFe{sub 2}As{sub 2} single crystals which were kept in air ambience for several months. Transport studies show that the O{sub 2} adsorbed crystals are more resistive and do not display any sharp slope change near 140 K which is the well known Spin Density Wave (SDW) transition temperature (T{sub SDW}) accompanying structural transition for as grown BaFe{sub 2}As{sub 2}. An anomalous slope change in resistivity is observed around 18 K at 0 and 5T. Magnetoresistance (MR) is noticed to increase as a function of applied field (H) quite differently than that for as grown crystals below T{sub SDW} which may be attributed to aging effect.

  14. High critical current density in BaAs2(Fe,Co)2 thin films up to 35 T

    NASA Astrophysics Data System (ADS)

    Jiang, J.; Tarantini, C.; Weiss, J. D.; Jaroszynsky, J.; Hellstrom, E. E.; Larbalestier, D. C.; Lee, S.; Bark, C. W.; Jang, H. W.; Folkman, C. M.; Baek, S. H.; Park, J. W.; Eom, C. B.; Zhang, Y.; Nelson, C. T.; Pan, X. Q.

    2011-03-01

    In the Co-doped BaFe 2 As 2 thin films we intensively investigated field and angular dependences of Jc down 4.2 K in high field. We found a strong correlated c-axis pinning and Jc for field along the c-axis exceeds Jc for H//ab plane up to ~ 20 T, inverting the expectation of the Hc2 anisotropy. As a consequence the angular dependence is very weak and Jc is still over 105 A/cm2 at 20T. Moreover the maximum pinning force Fp (4.2K) reaches 35-40 GN/ m 3 at 15-20T depending on the field configuration, indicative of strong high-field vortex pinning. High resolution transmission electron microscopy reveals that the strong vortex pinning is due to a high density of non-superconducting Ba-Fe-O nanocolumnar defects whose diameter is ~ 2 ξ , perfect conditions for a strong pinning.

  15. Effect of Uniaxial Strain on the Structural and Magnetic Phase Transitions in BaFe2As2

    SciTech Connect

    Dhital, Chetan; Yamani, Z; Tian, W.; Zeretsky, J; Safa-Sefat, Athena; Wang, Ziqiang; Birgeneau, R. J.; Wilson, Stephen

    2012-01-01

    We report neutron scattering experiments probing the influence of uniaxial strain on both the magnetic and structural order parameters in the parent iron pnictide compound, BaFe{sub 2}As{sub 2}. Our data show that modest strain fields along the in-plane orthorhombic b axis can affect significant changes in phase behavior simultaneous to the removal of structural twinning effects. As a result, we demonstrate in BaFe{sub 2}As{sub 2} samples detwinned via uniaxial strain that the in-plane C{sub 4} symmetry is broken by both the structural lattice distortion and long-range spin ordering at temperatures far above the nominal (strain-free) phase transition temperatures. Surprising changes in the magnetic order parameter of this system under relatively small strain fields also suggest the inherent presence of magnetic domains fluctuating above the strain-free ordering temperature in this material.

  16. Raman spectra and vibrational analysis of BaFe{sub 12}O{sub 19} hexagonal ferrite

    SciTech Connect

    Kreisel, J.; Lucazeau, G.; Vincent, H.

    1998-04-01

    This paper reports on the first Raman spectra of barium hexaferrite, BaFe{sub 12}O{sub 19}, as a member of the magnetoplumbite-type structure. The spectra, recorded from 150 to 1,000 cm{sup {minus}1} at room and liquid nitrogen temperature, are analyzed on the basis of D{sub 6h} factor group selection rules. The iron atom on the bi-pyramidal site is discussed with regard to its particular dynamics. The distribution of normal modes in BaFe{sub 12}O{sub 19} is examined on the basis of the Raman spectra of {beta}-alumina and a series of ferrites. Emphasis has been put on the factors influencing the Raman frequencies, namely the value of the coordination number, the degree of connection of a coordinated group, and the mass effect.

  17. Magnetoelectric memory effect in the Y-type hexaferrite BaSrZnMgFe12O22

    NASA Astrophysics Data System (ADS)

    Wang, Fen; Shen, Shi-Peng; Sun, Young

    2016-08-01

    We report on the magnetic and magnetoelectric properties of the Y-type hexaferrite BaSrZnMgFe12O22, which undergoes transitions from a collinear ferrimagnetic phase to a proper screw phase at 310 K and to a longitudinal conical phase at 45 K. Magnetic and electric measurements revealed that the magnetic structure with spiral spin order can be modified by applying a magnetic field, resulting in magnetically controllable electric polarization.It was observed that BaSrZnMgFe12O22 exhibits an anomalous magnetoelectric memory effect: the ferroelectric state can be partially recovered from the paraelectric phase with collinear spin structure by reducing magnetic field at 20 K. We ascribe this memory effect to the pinning of multiferroic domain walls, where spin chirality and structure are preserved even in the nonpolar collinear spin state. Project supported by the National Natural Science Foundation of China (Grant Nos. 11534015 and 51371193).

  18. Structural, electro-magnetic, and optical properties of Ba(Fe,Ni)2As2 single-crystal thin film

    NASA Astrophysics Data System (ADS)

    Yoon, Sejun; Seo, Yu-Seong; Lee, Seokbae; Weiss, Jeremy D.; Jiang, Jianyi; Oh, MyeongJun; Lee, Jongmin; Seo, Sehun; Jo, Youn Jung; Hellstrom, Eric E.; Hwang, Jungseek; Lee, Sanghan

    2017-03-01

    We investigated the superconducting transition temperature (T c), critical current density (J c) and optical properties of optimally doped Ba(Fe0.95Ni0.05)2As2 (Ni-Ba122) single-crystalline epitaxial thin films grown by pulsed laser deposition for the first time. The T c at zero resistivity was about 20.5 K and the J c at self-field and 4.2 K was 2.8 MA cm-2 calculated by the Bean model. The superconducting properties such as T c and J c of thin films are comparable to those of bulk single-crystal samples. The superfluid plasma frequency (λ p,S) of Ni-Ba122 thin film is ˜7033 cm-1 obtained by optical spectroscopic technique. Based on this plasma frequency, we obtained the London penetration depth (λ L), ˜226 nm at 8 K, which is comparable to those of optimally Co- and K-doped BaFe2As2 single crystals.

  19. Strain mediated magnetoelectric coupling in a NiFe2O4-BaTiO3 multiferroic composite

    NASA Astrophysics Data System (ADS)

    Gorige, Venkataiah; Kati, Raju; Yoon, D. H.; Kumar, P. S. Anil

    2016-10-01

    In this paper we demonstrate significant magnetoelectric coupling in ferrimagnetic, NiFe2O4, and ferroelectric, BaTiO3, multiferroic composite bulk materials by measuring temperature dependent magnetization. X-ray diffraction, scanning electron microscopy and high resolution transmission electron microscopy data show that the two phases coexist with a highly crystalline and sharp interface without any detectable impurities, which enables significant magnetoelectric (ME) coupling. The temperature dependent magnetization data of the composite clearly show the jumps in magnetization curves at the structural phase transitions of BaTiO3, thereby indicating their origin in ME coupling. The change in coercivity of composite sample in different ferroelectric phases of BaTiO3 has been observed compared to the NiFe2O4 sample. The different lattice strains corresponding to different ferroelectric phases of BaTiO3 could be the driving force for modulating the magnetization and coercivity of the composite material. This is clear evidence of strain mediated ME coupling in ferrimagnetic and ferroelectric composite materials.

  20. Aliovalent Ba2+ doping: A way to reduce oxygen vacancy in multiferroic BiFeO3

    NASA Astrophysics Data System (ADS)

    Das, Rajasree; Sharma, Sucheta; Mandal, Kalyan

    2016-03-01

    This paper demonstrates the impact of Ba2+ substitution on the structural, dielectric relaxation and AC conductivity properties of Bi1-xBaxFeO3 (0 ≤ x ≤ 0.25) ceramics. Ba doping incorporates rhombohedral to tetragonal structural transformation in perovskite BFO. XPS data shows change in oxygen vacancy concentration with Ba doping and it also suggests that schoimetry of the doped compounds is not maintained by creating mix valance state of Fe. Reduction in oxygen vacancy (OVs) in the doped samples is explained by Kroger-Vink notation. Arrhenius plot shows activation energy for dielectric relaxation of the doped samples lies between ~1.16 and 1.44 eV. AC conductivity of material decreases as Ba ion substitution increases in the parent compound. Electrical conductivity is attributed to the correlated barrier hopping (CBH) motion of the oxygen vacancies in the samples. Coulombic potential barrier (WM) height, calculated from Elliott model for CBH motion of charge carriers shows correlation with the activation energy of AC conductivity at low temperature. Activation energy value obtained from the impedance measurements of the samples implies short range migration of oxygen vacancies dominates the frequency dependent conductivity while the frequency independent part of conductivity is the result of long range migration of oxygen vacancies.

  1. Chemical mixing at “Al on Fe” and “Fe on Al” interfaces

    SciTech Connect

    Süle, P.; Horváth, Z. E.; Kaptás, D.; Bujdosó, L.; Balogh, J.; Nakanishi, A.

    2015-10-07

    The chemical mixing at the “Al on Fe” and “Fe on Al” interfaces was studied by molecular dynamics simulations of the layer growth and by {sup 57}Fe Mössbauer spectroscopy. The concentration distribution along the layer growth direction was calculated for different crystallographic orientations, and atomically sharp “Al on Fe” interfaces were found when Al grows over (001) and (110) oriented Fe layers. The Al/Fe(111) interface is also narrow as compared to the intermixing found at the “Fe on Al” interfaces for any orientation. Conversion electron Mössbauer measurements of trilayers—Al/{sup 57}Fe/Al and Al/{sup 57}Fe/Ag grown simultaneously over Si(111) substrate by vacuum evaporation—support the results of the molecular dynamics calculations.

  2. Signatures of filamentary superconductivity in antiferromagnetic BaFe2As2 single crystals

    DOE PAGES

    Moseley, D. A.; Yates, K. A.; Branford, W. R.; ...

    2015-08-24

    In this paper, we present ac susceptibility and magnetotransport measurements on aged single crystals of the ferropnictide parent compound, BaFe2As2 with a paramagnetic-to-antiferromagnetic transition temperature of 134 K. The ac susceptibility shows the clear onset of a partial diamagnetic response with an onset temperature, commensurate with a subtle downturn in resistivity at approximately 20 K. Below 20 K the magnetotransport shows in-plane anisotropy, magnetic-field history dependence and a hysteretic signature. Above 20 K the crystals show the widely reported high-field linear magnetoresistance. An enhanced noise signature in ac susceptibility is observed above 20 K, which varies in character with amplitude and frequency of the ac signal. The hysteresis in magnetoresistance and the observed sensitivity of the superconducting phase to the amplitude of the ac signal are indicative characteristics of granular or weakly linked filamentary superconductivity. Furthermore, these features taken together with the observed noise signature abovemore » $$T_{\\mathrm{c}}$$ suggests a link between the formation of the superconducting filamentary phase and the freezing of antiphase domain walls, known to exist in these materials.« less

  3. Order parameter fluctuation and ordering competition in Ba1 -xKxFe2As2

    NASA Astrophysics Data System (ADS)

    Wang, Jing; Liu, Guo-Zhu; Efremov, Dmitry V.; van den Brink, Jeroen

    2017-01-01

    The competition among superconductivity, stripe-type magnetic order, and a new type of C4 symmetric magnetic order in Ba1-xKxFe2As2 is theoretically studied, focusing on its impact on the global phase diagram. By carrying out a renormalization group analysis of an effective field theory, we obtain the energy-scale dependent flows of all the model parameters, and then apply the results to understand the observed phase diagram. On the basis of the renormalization group analysis, we show that the critical line of nematic order has a negative slope in the superconducting dome and superconductivity is suppressed near the magnetic quantum critical point, which are both consistent with recent experiments. Moreover, we find that, although the observed C4 symmetric magnetic state could be a charge-spin density wave or a spin-vortex crystal at high temperatures, charge-spin density wave is the only stable C4 magnetic state in the low-temperature regime. Therefore, ordering competition provides a method to distinguish these two candidate C4 magnetic states.

  4. Quantum criticality in electron-doped BaFe2-xNixAs2.

    PubMed

    Zhou, R; Li, Z; Yang, J; Sun, D L; Lin, C T; Zheng, Guo-qing

    2013-01-01

    A quantum critical point is a point in a system's phase diagram at which an order is completely suppressed at absolute zero temperature (T). The presence of a quantum critical point manifests itself in the finite-T physical properties, and often gives rise to new states of matter. Superconductivity in the cuprates and in heavy fermion materials is believed by many to be mediated by fluctuations associated with a quantum critical point. In the recently discovered iron-pnictide superconductors, we report transport and NMR measurements on BaFe(2-x)Ni(x)As₂ (0≤x≤0.17). We find two critical points at x(c1)=0.10 and x(c2)=0.14. The electrical resistivity follows ρ=ρ₀+AT(n), with n=1 around x(c1) and another minimal n=1.1 at x(c2). By NMR measurements, we identity x(c1) to be a magnetic quantum critical point and suggest that x(c2) is a new type of quantum critical point associated with a nematic structural phase transition. Our results suggest that the superconductivity in carrier-doped pnictides is closely linked to the quantum criticality.

  5. Nearly isotropic superconductivity in (Ba,K)Fe(2)As(2).

    PubMed

    Yuan, H Q; Singleton, J; Balakirev, F F; Baily, S A; Chen, G F; Luo, J L; Wang, N L

    2009-01-29

    Superconductivity was recently observed in iron-arsenic-based compounds with a superconducting transition temperature (T(c)) as high as 56 K, naturally raising comparisons with the high-T(c) copper oxides. The copper oxides have layered crystal structures with quasi-two-dimensional electronic properties, which led to speculation that reduced dimensionality (that is, extreme anisotropy) is a necessary prerequisite for superconductivity at temperatures above 40 K (refs 8, 9). Early work on the iron-arsenic compounds seemed to support this view. Here we report measurements of the electrical resistivity in single crystals of (Ba,K)Fe(2)As(2) in a magnetic field up to 60 T. We find that the superconducting properties are in fact quite isotropic, being rather independent of the direction of the applied magnetic fields at low temperature. Such behaviour is strikingly different from all previously known layered superconductors, and indicates that reduced dimensionality in these compounds is not a prerequisite for 'high-temperature' superconductivity. We suggest that this situation arises because of the underlying electronic structure of the iron-arsenic compounds, which appears to be much more three dimensional than that of the copper oxides. Extrapolations of low-field single-crystal data incorrectly suggest a high anisotropy and a greatly exaggerated zero-temperature upper critical field.

  6. Dielectric properties of Ti4+ substituted BaFe12O19 nanoparticles

    NASA Astrophysics Data System (ADS)

    Ghoneim, A. I.; Amer, M. A.; Meaz, T. M.; Attalah, S. S.

    2017-02-01

    Series of nanocrystalline BaTixFe12-(4/3)xO19 hexagonal ferrites, 0≤x≤1, was prepared using the chemical co-precipitation method. As-prepared samples were heated at 1200 °C for 20 h and slowly cooled to room temperature (RT). XRD studies proved that the samples have single phase M-type hexagonal nanostructure, where their grain size lies in the range of 42.4 - 61.3 nm. Their dielectric properties were studied against temperature (T) and frequency (F). DC conductivity showed increase against T, whereas AC conductivity showed increase with increasing both T and F. This proved the semiconducting behavior of the samples. Activation energies were found to lie in the range of 0.054-0.169 eV for temperature range of RT 373 K and of 0.114-0.274 eV for higher temperatures up to 473 K. Variation of the dielectric constant and AC conductivity against F revealed dispersion in all these hexagonal nanostructures, which was assigned to Maxwell-Wagner type of interfacial polarization. Variation of the dielectric loss tangent against F showed a relaxation spectrum for all samples, whereas the dielectric constant and loss tangent showed an increasing trend against T. The relative magnetic permeability μr showed an increasing trend with temperature.

  7. Magnetic Ordering in BaFe_{11.9}In_{0.1}O_{19} Hexaferrite

    NASA Astrophysics Data System (ADS)

    Trukhanov, S. V.; Trukhanov, A. V.; Turchenko, V. O.; Kostishin, V. G.; Panina, L. V.; Kazakevich, I. S.; Balagurov, A. M.

    2017-01-01

    The crystal and magnetic structure by powder neutron diffractometry as well as the magnetic properties by vibration sample magnetometry for the BaFe_{11.9}In_{0.1}O_{19} polycrystalline sample have been performed in a wide temperature range from 10 up to 730 K and in magnetic field up to 14 T. The atomic coordinates and lattice parameters have been Rietveld refined. The Invar effect has been observed in the low-temperature range below 150 K. It was explained by the thermal oscillation anharmonicity of atoms. The increase of the microstress value with decreasing temperature has been defined from Rietveld refinement. It is established that the ferrimagnet-paramagnet phase transition is a standard second-order one. From the macroscopic magnetization measurement, the Curie temperature and ordered magnetic moment per nominal iron ion are obtained. From the microscopic diffraction measurement, the magnetic moments at different atomic position and total magnetic moment per iron ion have been defined at different temperatures. The most likely reasons and the mechanism of magnetic ordering are discussed.

  8. Structural feature controlling superconductivity in compressed BaFe{sub 2}As{sub 2}

    SciTech Connect

    Yang, Wenge; Jia, Feng-Jiang; Tang, Ling-Yun; Tao, Qian; Xu, Zhu-An; Chen, Xiao-Jia

    2014-02-28

    Superconductivity can be induced with the application of pressure but it disappears eventually upon heavy compression in the iron-based parent compound BaFe{sub 2}As{sub 2}. Structural evolution with pressure is used to understand this behavior. By performing synchrotron X-ray powder diffraction measurements with diamond anvil cells up to 26.1 GPa, we find an anomalous behavior of the lattice parameter with a S shape along the a axis but a monotonic decrease in the c-axis lattice parameter with increasing pressure. The close relationship between the axial ratio c/a and the superconducting transition temperature T{sub c} is established for this parent compound. The c/a ratio is suggested to be a measure of the spin fluctuation strength. The reduction of T{sub c} with the further increase of pressure is a result of the pressure-driven weakness of the spin-fluctuation strength in this material.

  9. ABO3 (A = La, Ba, Sr, K; B = Co, Mn, Fe) perovskites for thermochemical energy storage

    NASA Astrophysics Data System (ADS)

    Babiniec, Sean M.; Coker, Eric N.; Ambrosini, Andrea; Miller, James E.

    2016-05-01

    The use of perovskite oxides as a medium for thermochemical energy storage (TCES) in concentrating solar power systems is reported. The known reduction/oxidation (redox) active perovskites LaxSr1-xCoyMn1-yO3 (LSCM) and LaxSr1-xCoyFe1-yO3 (LSCF) were chosen as a starting point for such research. Materials of the LSCM and LSCF family were previously synthesized, their structure characterized, and thermodynamics reported for TCES operation. Building on this foundation, the reduction onset temperatures are examined for LSCM and LSCF compositions. The reduction extents and onset temperatures are tied to the crystallographic phase and reaction enthalpies. The effect of doping with Ba and K is discussed, and the potential shortcomings of this subset of materials families for TCES are described. The potential for long-term stability of the most promising material is examined through thermogravimetric cycling, scanning electron microscopy, and dilatometry. The stability over 100 cycles (450-1050 °C) of an LSCM composition is demonstrated.

  10. Preparation and radar absorptive properties of BaFe12O19 -coated glass fiber

    NASA Astrophysics Data System (ADS)

    Jia, F.; Xu, M.; Bao, H. Q.; Cui, K.; Zhang, F.

    2016-07-01

    Traditional passive jamming materials such as chaff and foil showed some limitations in use because they can only reflect the electromagnetic wave. Therefore, to develop a kind of absorptive passive jamming material to make up for deficiencies of traditional passive jamming materials and improve the jamming efficiency is of great significance. In this paper, the BaFe12O19-coated glass fiber, used as a kind of radar absorptive chaff, was prepared by sol-gel dip-coating method. The effects of heat treatment temperature, heat treatment time and coating times on film quality, tensile strength and attenuation efficiency of the samples were discussed. The study shows that an increase of the heat treatment temperature and an extension of the heat treatment time is conducive to the growth of barium ferrite grain, while they would introduce the loss of chaff strength at the same time. In addition, multi-coating process can improve the film quality and attenuation efficiency of the sample. Data show that the 10 times coated samples have a best reflectivity of (15GHz, -6.65dB) and the bandwidth of reflectivity lower than -5dB is11.8 GHz. According to the test results, the prepared material has certain attenuation efficiency in the range of 2GHz-18GHz, having a high practical value.

  11. Nematic Quantum Critical Fluctuations in BaFe_{2-x}Ni_{x}As_{2}.

    PubMed

    Liu, Zhaoyu; Gu, Yanhong; Zhang, Wei; Gong, Dongliang; Zhang, Wenliang; Xie, Tao; Lu, Xingye; Ma, Xiaoyan; Zhang, Xiaotian; Zhang, Rui; Zhu, Jun; Ren, Cong; Shan, Lei; Qiu, Xianggang; Dai, Pengcheng; Yang, Yi-Feng; Luo, Huiqian; Li, Shiliang

    2016-10-07

    We have systematically studied the nematic fluctuations in the electron-doped iron-based superconductor BaFe_{2-x}Ni_{x}As_{2} by measuring the in-plane resistance change under uniaxial pressure. While the nematic quantum critical point can be identified through the measurements along the (110) direction, as studied previously, quantum and thermal critical fluctuations cannot be distinguished due to similar Curie-Weiss-like behaviors. Here we find that a sizable pressure-dependent resistivity along the (100) direction is present in all doping levels, which is against the simple picture of an Ising-type nematic model. The signal along the (100) direction becomes maximum at optimal doping, suggesting that it is associated with nematic quantum critical fluctuations. Our results indicate that thermal fluctuations from striped antiferromagnetic order dominate the underdoped regime along the (110) direction. We argue that either there is a strong coupling between the quantum critical fluctuations and the fermions, or more exotically, a higher symmetry may be present around optimal doping.

  12. Electrochemical properties of mixed conducting (La,M)(CoFe) oxide perovskites (M=3DSr, Ca, and Ba)

    SciTech Connect

    Stevenson, J.W.; Armstrong, T.R.; Bates, J.L.

    1996-04-01

    Electrical properties and oxygen permeation properties of solid mixed-conducting electrolytes (La,M)(CoFe) oxide perovskites (M=3DSr, Ca, and Ba) have been characterized. These materials are potentially useful as passive membranes to separate high purity oxygen from air and as the cathode in a fuel cell. Dilatometric linear expansion measurements were performed as a function of temperature and oxygen partial pressure to evaluate the stability.

  13. Conductor-backed coplanar waveguide resonators of Y-Ba-Cu-O and Tl-Ba-Ca-Cu-O on LaAlO3

    NASA Technical Reports Server (NTRS)

    Miranda, F. A.; Bhasin, K. B.; Stan, M. A.; Kong, K. S.; Itoh, T.

    1992-01-01

    Conductor-backed coplanar waveguide (CBCPW) resonators operating at 10.8 GHz have been fabricated from Tl-Ba-Ca-O (TBCCO) and Y-Ba-Cu-O (YBCO) thin films on LaAlO3. The resonators consist of a coplanar waveguide (CPW) patterned on the superconducting film side of the LaAlO3 substrate with a gold ground plane coated on the opposite side. These resonators were tested in the temperature range from 14 to 106 K. At 77 K, the best of our TBCCO and YBCO resonators have an unloaded quality factor (Qo) 7 and 4 times, respectively, larger than that of a similar all-gold resonator. In this study, the Qo's of the TBCCO resonators were larger than those of their YBCO counterparts throughout the aforementioned temperature range.

  14. Water oxidation catalysis: an amorphous quaternary Ba-Sr-Co-Fe oxide as a promising electrocatalyst for the oxygen-evolution reaction.

    PubMed

    Zhang, Cuijuan; Berlinguette, Curtis P; Trudel, Simon

    2016-01-25

    We present an amorphous quaternary Ba-Sr-Co-Fe oxide (a-BSCF) with a specific stoichiometry, readily fabricated via a photochemical decomposition method. a-BSCF demonstrates high catalytic activity towards the oxygen-evolution reaction (OER).

  15. Structural and magnetic properties and superconductivity in Ba(Fe1-xTMx)2As2

    SciTech Connect

    Thaler, Alexander

    2012-01-01

    We studied the effects on structural and magnetic phase transitions and the emergence of superconductivity in transition metal substituted BaFe2As2. We grew four series of Ba(Fe1-xTM2)2As2 (TM=Ru, Mn, Co+Cr and Co+Mn) and characterized them by crystallographic, magnetic and transport measurements. We also subjected Ba(Fe1-xCrx)2As2 and Ba(Fe1-xCox)2As2 to heat treatment to explore what changes might be induced.

  16. Magnetic properties of ball milled Fe-40Al at.% alloys

    SciTech Connect

    Amils, X.; Nogues, J.; Surinach, S.; Baro, M.D.; Munoz, J.S.

    1998-07-01

    A direct correlation between the lattice parameter and the saturation magnetization, during the disordering (ball milling) and posterior reordering (annealing) processes, has been found in Fe-40Al At.% compounds. These results indicate that the paramagnetic-ferromagnetic-paramagnetic transitions induced by ball milling and subsequent annealing could be related to the changes in volume, and not only to nearest neighbors effects as is commonly assumed. Moreover, these alloys have been found to become spin glass at low temperatures, independently of their structural state (ordered or disordered).

  17. MOKE Study of Fe/Co/Al Multilayers

    SciTech Connect

    Jani, Snehal; Lakshmi, N.; Venugopalan, K.; Rajput, Parasmani; Zajaoc, M.; Rueffer, R.; Reddy, V. R.; Gupta, Ajay

    2011-07-15

    The multilayer system (MLS)-[{sup 57}Fe{sub 25}A/Co{sub 11}A/Al{sub 17}A]x20 has been deposited by Ion beam sputtering (IBS) technique. The MLS has been annealed at 700 deg. C for 1 h. Overall composition of as deposited and annealed MLS have been characterized by EDX and magnetic properties have been studied through angular dependent magneto optic Kerr effect (MOKE) hysteresis curves. The study shows that the as-deposited MLS has excellent soft magnetic properties coupled with perpendicular magnetic isotropy which is destroyed on annealing.

  18. High calcination of ferroelectric BaTiO₃ doped Fe nanoceramics prepared by a solid-state sintering method.

    PubMed

    Samuvel, K; Ramachandran, K

    2015-07-05

    This study examined the effects of the combination of starting materials on the properties of solid-state reacted BaTiO3 using two different types of BaCO3 and TiO2. In addition, the effect of mechanochemical activation by high energy milling and the Ba/Ti molar ratio on the reaction temperature, particle size and tetragonality were investigated. The TiO2 phase and size plays a major role in increasing the reaction temperature and particle size. With the optimum selection of starting materials and processing conditions, BaTiO3 with a particle size <200 nm (Scherrer's formula) and a tetragonality c/a of approximately 1.007 was obtained. Broadband dielectric spectroscopy is applied to investigate the electrical properties of disordered perovskite-like ceramics in a wide temperature range. From the X-ray diffraction analysis it was found that the newly obtained BaTi0.5Fe0.5O3 ceramics consist of two chemically different phases. The electric modulus M∗ formalism used in the analysis enabled us to distinguish and separate the relaxation processes, dominated by marked conductivity in the ε∗(ω) representation. Interfacial effects on the dielectric properties of the samples have been understood by Cole-Cole plots in complex impedance and modulus formalism. Modulus formalism has identified the effects of both grain and grain boundary microstructure on the dielectric properties, particularly in solid state routed samples.

  19. Pressure-Induced Metallization in Iron-Based Ladder Compounds Ba1-xCsxFe2Se3

    NASA Astrophysics Data System (ADS)

    Hawai, Takafumi; Kawashima, Chizuru; Ohgushi, Kenya; Matsubayashi, Kazuyuki; Nambu, Yusuke; Uwatoko, Yoshiya; Sato, Taku J.; Takahashi, Hiroki

    2017-02-01

    Electrical resistivity measurements have been performed on the iron-based ladder compounds Ba1-xCsxFe2Se3 (x = 0, 0.25, 0.65, and 1) under high pressure. A cubic anvil press was used up to 8.0 GPa, whereas further higher pressure was applied using a diamond anvil cell up to 30.0 GPa. Metallic behavior of the electrical conductivity was confirmed in the x = 0.25 and 0.65 samples for pressures greater than 11.3 and 14.4 GPa, respectively, with the low-temperature log T upturn being consistent with weak localization of 2D electrons due to random potential. At pressures higher than 23.8 GPa, three-dimensional Fermi-liquid-like behavior was observed in the latter sample. No metallic conductivity was observed in the parent compounds BaFe2Se3 (x = 0) up to 30.0 GPa and CsFe2Se3 (x = 1) up to 17.0 GPa. The present results indicate that the origins of the insulating ground states in the parent and intermediate compounds are intrinsically different; the former is a Mott insulator, whereas the latter is an Anderson insulator owing to the random substitution of Cs for Ba.

  20. Phase diagram and superconducting gap structure of the iron-pnictide superconductor (Ba,K) Fe 2 As 2

    NASA Astrophysics Data System (ADS)

    Luo, Xigang

    2011-03-01

    Measurements of the Nernst and Seebeck coefficients were used to delineate the T-x phase diagram of the iron-pnictide superconductor Ba 1-x Kx Fe 2 As 2 . The sensitivity of these two coefficients to the reconstruction of the Fermi surface caused by the onset of antiferromagnetic order below a temperature TN allowed us to track TN precisely as a function of concentration x, even when the electrical resistivity, for example, shows no anomaly at the magnetic transition. In the region of concentrations where superconductivity appears out of an antiferromagnetic normal state (T T N) , weinvestigatetheevolutionofthesuperconductinggapstructureofBa 1-x K x Fe 2 As 2 bymeasuringthethermalconductivityintheT = 0 limit . Thisisasensitiveanddirectionalprobeofnodalquasiparticles . Astheconcentrationxisreduced , wefindasuddenchangeinthegapstructurefromafullgapwithoutnodestoagapwithnodes . Weascribethischangetotheonsetofantiferromagnetismbelowacriticaldopingx N insidethesuperconductingphase , whoseeffectismostlikelytoalterboththeFermisurfaceandtheangulardependenceofthegap . WecomparetheseresultswithourearlierstudyonBa (Fe 1-x Co x)2 As 2 [1,2]. This work was performed in collaboration with H. Shakeripour, J. Chang, F. Laliberte, J.-Ph. Reid, N. Doiron-Leyraud, L. Taillefer, M.A. Tanatar, R. Prozorov, H. Q. Luo, Z. S. Wang, H.-H. Wen.

  1. Structural and magnetic phase transitions near optimal superconductivity in BaFe2(As1-xPx)2

    DOE PAGES

    Hu, Ding; Lu, Xingye; Zhang, Wenliang; ...

    2015-04-17

    In this study, we use nuclear magnetic resonance (NMR), high-resolution x-ray and neutron scattering to study structural and magnetic phase transitions in phosphorus-doped BaFe2(As1-xPx)2. Thus, previous transport, NMR, specific heat, and magnetic penetration depth measurements have provided compelling evidence for the presence of a quantum critical point (QCP) near optimal superconductivity at x = 0.3. However, we show that the tetragonal-to-orthorhombic structural (Ts) and paramagnetic to antiferromagnetic (AF, TN) transitions in BaFe2(As1-xPx)2 are always coupled and approach to TN ≈ Ts ≥ Tc (≈ 29 K) for x = 0.29 before vanishing abruptly for x ≥ 0.3. These results suggestmore » that AF order in BaFe2(As1-xPx)2 disappears in a weakly first order fashion near optimal superconductivity, much like the electron-doped iron pnictides with an avoided QCP.« less

  2. Enhancement of Magnetoelectric Coupling in CoGaxFe2-xO4/BaTiO3 Composite

    NASA Astrophysics Data System (ADS)

    Ni, Yan; Zhang, Zhen; Jiles, David; Nlebedim, Cajetan

    2015-03-01

    Multiferroic materials exhibit magnetoelectric coupling and promise new device applications including magnetic sensors, generators and filters. An effective method for developing magnetoelectric (ME) materials with enhanced ME effect is achieved by the coupling through the interfacial strain between piezoelectric and magnetostrictive materials. In this study, enhancement of magnetoelectric coupling was found by systematically studying the electrical and magnetic properties of CoGaxFe2-xO4/BaTiO3 composite. It is found that Ga doping not only stabilizes the magnetic phase of composites but also increases the sensitivity of magnetoelastic response by 30%. Moreover, Ga doping reduces the electrical conductivity and the dielectric loss of composite. An enhancement of the electrostrain with doping Ga is also observed in CoGaxFe2-xO4/BaTiO3 (x =0.3). As both the sensitivity of magnetostriction and the change in the electric field with strain increase, the ME voltage coefficient also increase. Thus, our work is beneficial for the application of CoFe2O4/BaTiO3-based multiferroic materials. This work was supported by the USDoE, Office of Science, Basic Energy Sciences, Materials Science and Engineering Division. The research was performed at Ames Laboratory, operated for the USDoE by Iowa State University (contract # DE-AC02-07CH11358)

  3. Structural and dielectric properties of La and Ni-doped M-type BaFe12O19 ceramics

    NASA Astrophysics Data System (ADS)

    Sharma, Poorva; Kumar, Ashwini; Dube, Avinash; Li, Qi; Varshney, Dinesh

    2016-05-01

    BaFe12O19 and Ba0.98La0.02Fe12-xNixO19 (x = 0.02, 0.05) samples synthesized using solid-state reaction route crystallizes in hexagonal structure with space group P63/mmc as revealed from X-ray diffraction. A Raman spectrum shows seven strong and sharp modes at 291.9 (A1g), 410.4 (E2g), 496.09 (A1g), 611.3 (E2g), 681(A1g), 1048.0 (A1g+A1g) and 1313.3 cm-1 (A1g+E2g), identifying the presence of barium hexaferrite phase. The higher values of the dielectric constant at lower frequency and lower values at higher frequency indicate the dispersion due to interfacial polarization. Dielectric constant decreases as the doping concentration of Ni increases due to increase in band gap. A resonance peak has been observed in all three sample and is attributed to the fact that hopping frequency of charge carrier matches well with the frequency of the applied field. Henceforth, Ba0.98La0.02Fe12-xNixO19 (x = 0.02, 0.05) is suitable novel materials for microwave application with low dielectric constant and dielectric loss values.

  4. Low-loss Z-type hexaferrite (Ba3Co2Fe24O41) for GHz antenna applications

    NASA Astrophysics Data System (ADS)

    Lee, Woncheol; Hong, Yang-Ki; Park, Jihoon; LaRochelle, Gatlin; Lee, Jaejin

    2016-09-01

    We report a low magnetic loss Ba3Co2Fe24O41 (Co2Z) hexaferrite for use in gigahertz (GHz) antennas. Acid-etching was very effective in removal of unwanted Y-type hexaferrite (Ba2Co2Fe12O22) from calcined Co2Z powder. It is found that the calcined and acid etched (AE) Co2Z hexaferrite shows a low magnetic loss tangent (tan δμ) of 0.012 and 0.037 at 1 and 2 GHz, respectively. These low tan δμ are attributed to removal of Y-type hexaferrite, which possesses a lower anisotropy field (Hk) than W-type hexaferrite (BaCo2Fe16O27). The figure of merit (FOM) of the AE Co2Z hexaferrite is 141.7 and 48.7 at 1 and 2 GHz, respectively. These FOM are much higher than the FOM of previously reported low-loss magnetic materials. Therefore, the AE Co2Z hexaferrite can be a good candidate for GHz antenna application in the ultra-high frequency (UHF) band.

  5. Cyclic Oxidation of FeCrAlY/Al2O3 Composites

    NASA Technical Reports Server (NTRS)

    Nesbitt, James A.; Draper, Susan L.; Barrett, Charles A.

    1999-01-01

    Three-ply FeCrAlY/Al2O3 composites and FeCrAlY matrix-only samples were cyclically oxidized at 1000 C and 1100 C for up to 1000 1-hr cycles. Fiber ends were exposed at the ends of the composite samples. Following cyclic oxidation, cracks running parallel to and perpendicular to the fibers were observed on the large surface of the composite. In addition, there was evidence of increased scale damage and spallation around the exposed fiber ends, particularly around the middle ply fibers. This damage was more pronounced at the higher temperature. The exposed fiber ends showed cracking between fibers in the outer plies, occasionally with Fe and Cr-rich oxides growing out of the cracks. Large gaps developed at the fiber/matrix interface around many of the fibers, especially those in the outer plies. Oxygen penetrated many of these gaps resulting in significant oxide formation at the fiber/matrix interface far within the composite sample. Around several fibers, the matrix was also internally oxidized showing Al2O3 precipitates in a radial band around the fibers. The results show that these composites have poor cyclic oxidation resistance due to the CTE mismatch and inadequate fiber/matrix bond strength at temperatures of 1000 C and above.

  6. Preparation of iron aluminate (FeAl2O4) nanoparticles from FeAl2O4 hollow particles fabricated by using a spray pyrolysis process

    NASA Astrophysics Data System (ADS)

    Yun, Jaecheol; Kim, Yangdo; Park, Dahee; Yun, Jung-Yeul

    2015-05-01

    Iron aluminate (FeAl2O4) hollow particles with a spinel structure were synthesized by using a spray pyrolysis process. FeAl2O4 hollow particles were formed at a reaction temperature of 900 °C at a flow rate of 40 L/min as a result of the rapid solvent evaporation and decomposition gases from the droplets in the spray solution prepared from metal salts and organic reagents. FeAl2O4 hollow particles were fabricated at a reaction temperature of 900 °C with a flow rate of 40 L/min. The FeAl2O4 hollow particles were heat treated for 3 hours at 600 °C in a 5% H2/Ar atmosphere to form the crystal particles. Subsequently, FeAl2O4 nanoparticles were fabricated from the FeAl2O4 hollow particles by using the wet milling process. After milling for 60 minutes, transmission electron microscopy revealed the FeAl2O4 particles to have a mean size of approximately 50 nm. The FeAl2O4 nanoparticles were fabricated successfully by using a two-step process, spray pyrolysis and wet milling.

  7. Crystallographic and magnetic structure of the perovskite-type compound BaFeO2.5: unrivaled complexity in oxygen vacancy ordering.

    PubMed

    Clemens, Oliver; Gröting, Melanie; Witte, Ralf; Perez-Mato, J Manuel; Loho, Christoph; Berry, Frank J; Kruk, Robert; Knight, Kevin S; Wright, Adrian J; Hahn, Horst; Slater, Peter R

    2014-06-16

    We report here on the characterization of the vacancy-ordered perovskite-type structure of BaFeO2.5 by means of combined Rietveld analysis of powder X-ray and neutron diffraction data. The compound crystallizes in the monoclinic space group P2(1)/c [a = 6.9753(1) Å, b = 11.7281(2) Å, c = 23.4507(4) Å, β = 98.813(1)°, and Z = 28] containing seven crystallographically different iron atoms. The coordination scheme is determined to be Ba7(FeO4/2)1(FeO3/2O1/1)3(FeO5/2)2(FeO6/2)1 = Ba7Fe([6])1Fe([5])2Fe([4])4O17.5 and is in agreement with the (57)Fe Mössbauer spectra and density functional theory based calculations. To our knowledge, the structure of BaFeO2.5 is the most complicated perovskite-type superstructure reported so far (largest primitive cell, number of ABX2.5 units per unit cell, and number of different crystallographic sites). The magnetic structure was determined from the powder neutron diffraction data and can be understood in terms of "G-type" antiferromagnetic ordering between connected iron-containing polyhedra, in agreement with field-sweep and zero-field-cooled/field-cooled measurements.

  8. Phase Separation kinetics in an Fe-Cr-Al alloy

    SciTech Connect

    Capdevila, C.; Miller, Michael K; Chao, J.

    2012-01-01

    The {alpha}-{alpha}{prime} phase separation kinetics in a commercial Fe-20 wt.% Cr-6 wt.% Al oxide dispersion-strengthened PM 2000{trademark} steel have been characterized with the complementary techniques atom probe tomography and thermoelectric power measurements during isothermal aging at 673, 708, and 748 K for times up to 3600 h. A progressive decrease in the Al content of the Cr-rich {alpha}{prime} phase was observed at 708 and 748 K with increasing time, but no partitioning was observed at 673 K. The variation in the volume fraction of the {alpha}{prime} phase well inside the coarsening regime, along with the Avrami exponent 1.2 and activation energy 264 kJ mol{sup -1}, obtained after fitting the experimental results to an Austin-Rickett type equation, indicates that phase separation in PM 2000{trademark} is a transient coarsening process with overlapping nucleation, growth, and coarsening stages.

  9. Formation of layered Fe(II)-Al(III)-hydroxides during reaction of Fe(II) with aluminum oxide.

    PubMed

    Elzinga, Evert J

    2012-05-01

    The reactivity of aqueous Fe(II) with aluminum oxide in anoxic solutions was investigated with batch kinetic experiments combined with Fe K edge X-ray absorption spectroscopy measurements to characterize Fe(II) sorption products. Formation of Fe(II)-Al(III)-layered double hydroxides with an octahedral sheet structure similar to nikischerite (NaFe(II)(6) Al(3)(SO(4))(2)(OH)(18) (H(2)O)(12)) was observed within a few hours during sorption at pH 7.5 and aqueous Fe(II) concentrations of 1-3 mM. These Fe(II) phases are composed of brucite-like Fe(II)(OH)(2) sheets with partial substitution of Al(III) for Fe(II), charge balanced by anions coordinated along the basal planes. Their fast rate of formation suggests that these previously unrecognized Fe(II) phases, which are structurally and compositionally similar to green rust, may be an important sink of Fe(II) in suboxic and anoxic geochemical environments, and impact the fate of structurally compatible trace metals, such as Co(II), Ni(II), and Zn(II), as well as redox-reactive species including Cr(VI) and U(VI). Further studies are required to assess the thermodynamics, formation kinetics, and stability of these Fe(II) minerals under field conditions.

  10. Strain induced enhancement of magnetization in Ba2FeMoO6 based heterostructure with (BaxSr1-x)TiO3

    NASA Astrophysics Data System (ADS)

    Kim, Kyeong-Won; Ghosh, Siddhartha; Buvaev, Sanal; Hebard, Arthur F.; Norton, David P.

    2016-05-01

    High quality epitaxial Ba2FeMoO6 thin films and Ba2FeMoO6-(BaxSr1-x)TiO3 bi-layer (BL) and superlattice (SL) structures were grown via pulsed laser deposition under low oxygen pressure, and their structural, magnetic, and magneto-transport properties were examined. Superlattice and bi-layer structures were confirmed by X-ray diffraction patterns. Low temperature magnetic measurement shows that the saturation magnetization (MS) is significantly higher for SLs and almost similar or lower for BLs, when compared to phase pure Ba2FeMoO6 thin films. The variation of the coercive field (HC) follows exact opposite trend, where BL samples have higher HC and SL samples have lower HC than pure Ba2FeMoO6 thin films. Also, a significant decrease of the Curie temperature is found in both BL and SL structures compared to pure Ba2FeMoO6 thin films. Negative magneto-resistance is seen in all the BL and SL structures as well as in pure Ba2FeMoO6 thin films. In contrast to the magnetic properties, the magneto-transport properties do not show much variation with induced strain.

  11. Importance of doping and frustration in itinerant Fe-doped Cr2Al

    DOE PAGES

    Susner, M. A.; Parker, D. S.; Sefat, A. S.

    2015-05-12

    We performed an experimental and theoretical study comparing the effects of Fe-doping of Cr2Al, an antiferromagnet with a N el temperature of 670 K, with known results on Fe-doping of antiferromagnetic bcc Cr. (Cr1-xFex)2Al materials are found to exhibit a rapid suppression of antiferromagnetic order with the presence of Fe, decreasing TN to 170 K for x=0.10. Antiferromagnetic behavior disappears entirely at x≈0.125 after which point increasing paramagnetic behavior is exhibited. Moreover, this is unlike the effects of Fe doping of bcc antiferromagnetic Cr, in which TN gradually decreases followed by the appearance of a ferromagnetic state. Theoretical calculations explainmore » that the Cr2Al-Fe suppression of magnetic order originates from two effects: the first is band narrowing caused by doping of additional electrons from Fe substitution that weakens itinerant magnetism; the second is magnetic frustration of the Cr itinerant moments in Fe-substituted Cr2Al. In pure-phase Cr2Al, the Cr moments have an antiparallel alignment; however, these are destroyed through Fe substitution and the preference of Fe for parallel alignment with Cr. This is unlike bulk Fe-doped Cr alloys in which the Fe anti-aligns with the Cr atoms, and speaks to the importance of the Al atoms in the magnetic structure of Cr2Al and Fe-doped Cr2Al.« less

  12. Weldability of Fe[sub 3]Al-type Aluminide

    SciTech Connect

    David, S.A.; Zacharia, T. )

    1993-05-01

    An investigation was carried out to determine the weldability of a series of Fe[sub 3]Al-type alloys. Autogenous welds were made on thin sheets of iron aluminide alloys using gas tungsten arc (GTA) and electron beam (EB) welding processes at different travel speeds and power levels. The results indicate that although these alloys can be successfully welded using the EB welding process, some compositions may hot crack during GTA welding. Boron and zirconium additions have been found to promote hot cracking in these alloys. Among the alloys investigated, Fe[sub 3]Al modified with chromium, niobium and carbon (FA-129) showed the most promise for good weldability. Hot-cracking severity of this alloy was further investigated using the Sigmajig test. The minimum threshold stress of 25 ksi measured is within the material range of other aluminides and some commercial stainless steels. Also, some of these alloys exhibited a tendency for cold cracking. This is related to severe hydrogen embrittlement associated with this class of alloys.

  13. Structure, magnetic, and microwave properties of thick Ba-hexaferrite films epitaxially grown on GaN/Al2O3 substrates

    NASA Astrophysics Data System (ADS)

    Chen, Z.; Yang, A.; Mahalingam, K.; Averett, K. L.; Gao, J.; Brown, G. J.; Vittoria, C.; Harris, V. G.

    2010-06-01

    Thick barium hexaferrite [BaOṡ(Fe2O3)6] films, having the magnetoplumbite structure (i.e., Ba M), were epitaxially grown on c-axis oriented GaN/Al2O3 substrates by pulsed laser deposition followed by liquid phase epitaxy. X-ray diffraction showed (0,0,2n) crystallographic alignment with pole figure analyses confirming epitaxial growth. High resolution transmission electron microscopy images revealed magnetoplumbite unit cells stacked with limited interfacial mixing. Saturation magnetization, 4πMs, was measured for as-grown films to be 4.1±0.3 kG with a perpendicular magnetic anisotropy field of 16±0.3 kOe. Ferromagnetic resonance linewidth, the peak-to-peak power absorption derivative at 53 GHz, was 86 Oe. These properties will prove enabling for the integration of low loss Ba M ferrite microwave passive devices with active semiconductor circuit elements in systems-on-a-wafer architecture.

  14. Tetragonal To Collapsed Tetragonal Phase Transition In BaFe{sub 2}As{sub 2} and CaFe{sub 2}As{sub 2}

    SciTech Connect

    Mittal, R.; Mishra, S. K.; Chaplot, S. L.; Ovsyannikov, S. V.; Trots, D. M.; Dubrovinsky, L.; Greenberg, E.; Su, Y.; Brueckel, Th.; Matsuishi, S.; Hosono, H.; Garbarino, G.

    2010-12-01

    Superconductivity in MFe{sub 2}As{sub 2} (M = Ba, Ca) compounds appears either at a critical doping level at ambient pressure or in the parent compound itself by application of pressure above a critical value. We report high pressure powder x-ray diffractions studies for these compounds at 300 K up to about 56 GPa using membrane diamond anvil cells. The measurements for BaFe{sub 2}As{sub 2} show a new tetragonal to collapsed tetragonal phase transition at about 22 GPa that remains stable upto 56 GPa. CaFe{sub 2}As{sub 2} is already known to transform to collapsed phase at 1.7 GPa at 300 K. Our measurements on CaFe{sub 2}As{sub 2} do not show any post collapsed phase transition on increase of pressure 50 GPa at 300 K. It is important to note that the transition in both compounds occurs when they are compressed to almost the same value of the unit cell volume and attain similar c{sub t}/a{sub t} ratios. We present a detailed analysis of the pressure dependence and structure phase transitions as well as equation of state in these important FeAs compounds that should be useful in the context of possible superconductivity in the collapsed phase.

  15. Electronic structures of doped BaFe2As2 materials: virtual crystal approximation versus super-cell approach

    NASA Astrophysics Data System (ADS)

    Sen, Smritijit; Ghosh, Haranath

    2016-12-01

    Using virtual crystal approximation and super-cell methods for doping, a detailed comparative study of electronic structures of various doped BaFe2As2 materials by first principles simulations is presented. Electronic structures remain unaltered for both the methods in case of passive site doping but in case of active site doping, the electronic structure for virtual crystal approximation method differ from that of the super-cell method specially in the higher doping concentrations. For example, both of these methods give rise to a similar density of states and band structures in case of hole doping (replacing K in place of Ba) and isovalent P doping on As site. But in case of electron doped (Co in place of Fe) systems with higher doping concentration, electronic structures calculated using virtual crystal approximation approach deviates from that of the super-cell method. On the other hand, in case of low isovalent Ru doping at the Fe site implemented by virtual crystal approximation, one acquires an extra shift in the chemical potential in comparison to that for the super-cell method. This shift may be utilized to predict the correct electronic structure as well as the calculated Fermi surfaces within virtual crystal approximation. But for higher Ru (that has different electronic configuration than Fe) doping concentration, simple shifting of chemical potential fails, the calculated electronic structure via virtual crystal approximation approach is very different from that by the super-cell formalism.

  16. Emergence of a fluctuating state in the stuffed tridymite-type oxides Ba1 -xSrxAl2O4

    NASA Astrophysics Data System (ADS)

    Ishii, Y.; Tsukasaki, H.; Tanaka, E.; Kawaguchi, S.; Mori, S.

    2016-11-01

    We investigated the crystal structures and dielectric properties of an improper ferroelectric Ba1 -xSrxAl2O4 (x ≤0.1 ) and revealed that suppressing the condensation of the M -point soft mode involves the emergence of a "fluctuating" state. In the low-Sr-concentration region of x ≤0.06 , crystals exhibit a ferroelectric phase transition at TC from a paraelectric phase with a space group P 6322 (PE phase) to a low-temperature ferroelectric phase with a P 63 structure with doubled a and b axes (FE phase). Additionally, the temperature dependence of the dielectric constant ɛ' exhibits a peak at TC. As x increases, TC decreases substantially, and the peak at TC becomes small. For x ≥0.07 , the peak is barely noticeable and becomes an anomaly at T*≈200 K, indicating that the system possesses another state (FL state) below the T*. The PE phase has been reported to possess two energetically competing soft modes at the M and K points. Electron diffraction (ED) experiments revealed that the superlattice reflections of the FE phase become diffuse scatterings originating from the M -point soft mode as the FE-FL boundary is approached. The K -point soft mode disappears in the FL state, whereas the M -point soft mode survives and fluctuates without condensation. Dark-field (DF) images revealed that the M -point soft mode exhibits coherent motion in nanodomains with sizes of approximately 10 nm in the FL state. The emergence of the FL state is ascribed to enhanced vibration of the AlO4 tetrahedra resulting from the substitution of Sr, which has a smaller ionic radius than Ba.

  17. Optical properties of A Fe2As2 (A =Ca , Sr, and Ba) single crystals

    NASA Astrophysics Data System (ADS)

    Dai, Y. M.; Akrap, Ana; Bud'ko, S. L.; Canfield, P. C.; Homes, C. C.

    2016-11-01

    The detailed optical properties have been determined for the iron-based materials A Fe2As2 , where A =Ca , Sr, and Ba, for light polarized in the iron-arsenic (a-b) planes over a wide frequency range, above and below the magnetic and structural transitions at TN=138 , 195, and 172 K, respectively. The real and imaginary parts of the complex conductivity are fit simultaneously using two Drude terms in combination with a series of oscillators. Above TN, the free-carrier response consists of a weak, narrow Drude term, and a strong, broad Drude term, both of which show only a weak temperature dependence. Below TN there is a slight decrease of the plasma frequency but a dramatic drop in the scattering rate for the narrow Drude term, and for the broad Drude term there is a significant decrease in the plasma frequency, while the decrease in the scattering rate, albeit significant, is not as severe. The small values observed for the scattering rates for the narrow Drude term for T ≪TN may be related to the Dirac conelike dispersion of the electronic bands. Below TN new features emerge in the optical conductivity that are associated with the reconstruction Fermi surface and the gapping of bands at Δ1≃45 -80 meV, and Δ2≃110 -210 meV. The reduction in the spectral weight associated with the free carriers is captured by the gap structure; specifically, the spectral weight from the narrow Drude term appears to be transferred into the low-energy gap feature, while the missing weight from the broad term shifts to the high-energy gap.

  18. Critical factor for epitaxial growth of cobalt-doped BaFe{sub 2}As{sub 2} films by pulsed laser deposition

    SciTech Connect

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

    2014-04-28

    We heteroepitaxially grew cobalt-doped BaFe{sub 2}As{sub 2} films on (La,Sr)(Al,Ta)O{sub 3} single-crystal substrates by pulsed laser deposition using four different wavelengths and investigated how the excitation wavelength and pulse energy affected growth. Using the tilting and twisting angles of X-ray diffraction rocking curves, we quantitatively analyzed the crystallinity of each film. We found that the optimal deposition rate, which could be tuned by pulse energy, was independent of laser wavelength. The high-quality film grown at the optimal pulse energy (i.e., the optimum deposition rate) exhibited high critical current density over 1 MA/cm{sup 2} irrespective of the laser wavelength.

  19. Structure and magnetic properties of the double-perovskites Ba2(B,Re)2O6 (B = Fe, Mn, Co and Ni)

    NASA Astrophysics Data System (ADS)

    Rammeh, N.; Ehrenberg, H.; Fuess, H.; Cheikkh-Rouhou, A.

    2006-09-01

    Structural and magnetic properties of Ba2(B,Re)2O6 (B = Fe, Mn, Co and Ni) double-perovskite oxides have been investigated. Rietveld analysis shows that all our synthesized samples are single phase and crystallize at room temperature in the cubic double-perovskite structure with Fm3m space group. Magnetization measurements versus temperature and versus magnetic applied field up to 5 T show that Ba2(Fe,Re)2O6, Ba2(Mn,Re)2O6 and Ba2(Ni,Re)2O6 are ferromagnetic at low temperature with TC = 318 K, 113 K and 32 K respectively while Ba2(Co,Re)2O6 is antiferromagnetic below TN = 25 K.

  20. Coexistence of the spini-density-wave and superconductivity in the Ba1-xKxFe2As2

    SciTech Connect

    Bao, Wei; Chen, H; Ren, Y; Qiu, Y; Liu, R; Wu, G H; Wu, T; Xie, Y L; Wang, F; Huang, Q; Chen, X H

    2008-01-01

    The relation between the spin-density-wave (SDW) and superconducting order is a central topic in current research on the FeAs-based high T{sub c} superconductors. Conflicting results exist in the LaFeAs(O,F)-class of materials, for which whether the SDW and superconductivity are mutually exclusive or they can coexist has not been settled. Here we show that for the (Ba,K)Fe{sub 2}As{sub 2} system, the SDW and superconductivity can coexist in an extended range of compositions. The availability of single crystalline samples and high value of the energy gaps would make the materials a model system to investigate the high T{sub c} ferropnictide superconductivity.

  1. Preparation and characterization of self-assembled percolative BaTiO3-CoFe2O4 nanocomposites via magnetron co-sputtering.

    PubMed

    Yang, Qian; Zhang, Wei; Yuan, Meiling; Kang, Limin; Feng, Junxiao; Pan, Wei; Ouyang, Jun

    2014-04-01

    BaTiO3-CoFe2O4 composite films were prepared on (100) SrTiO3 substrates by using a radio-frequency magnetron co-sputtering method at 750 °C. These films contained highly (001)-oriented crystalline phases of perovskite BaTiO3 and spinel CoFe2O4, which can form a self-assembled nanostructure with BaTiO3 well-dispersed into CoFe2O4 under optimized sputtering conditions. A prominent dielectric percolation behavior was observed in the self-assembled nanocomposite. Compared with pure BaTiO3 films sputtered under similar conditions, the nanocomposite film showed higher dielectric constants and lower dielectric losses together with a dramatically suppressed frequency dispersion. This dielectric percolation phenomenon can be explained by the 'micro-capacitor' model, which was supported by measurement results of the electric polarization and leakage current.

  2. Research and analysis on the thin films sputtered by the Ba-Al-S:Eu target fabricated by powder sintering

    NASA Astrophysics Data System (ADS)

    Zhang, Dongpu; Xu, Fang; Yu, Zhinong; Xue, Wei

    2014-11-01

    Europium-doped barium thioaluminate (BaAl2S4:Eu) is currently the most efficient blue phosphor for inorganic thin film electroluminescent (iEL) device. To produce the full-color EL device, several kinds of blue-emitting layer were attempted and tested. As a key point of blue-emitting layer fabrication, single target sputtering deposition is an effective method. In this work, new structural target is introduced and the fabricated process is expatiated. The PL spectra of as fabricated targets show that both of two, 3mol% and 5mol% europium-doped, have blue emitting property. According to the PL spectra excited by 290nm, 300nm and 320nm ultraviolet, emission peaks located in the region near 470nm. So the as-fabricated targets can be used in single target sputtering deposition on thin film of BaAl2S4:Eu. XRD pattern indicates that there are 4 different phases, barium tetraaluminum sulfide (BaAl4S7), barium sulfide (BaS), europium sulfide (EuS) and barium aluminum oxide (BaAl2O4), in target 1. Besides these four compounds, other two phases, aluminum sulfide (Al2S3) and barium thioaluminate (BaAl2S4), are detected in target 2. Considering the analysis results, especially the hydrolyzation of Al2S3, target 1 is more suitable for sputtering deposition of BaAl2S4:Eu thin film. XPS and X-ray Fluorescence patterns describe the precise molar ratio of each element. In target 1 the relative atom concentration of barium, aluminum, sulfur and oxygen can be calculated from the pattern and molar ratio is about 9:33:41:17. Molar ratio of barium and europium is about 1:0.03. In short, the barium thioaluminate doped by europium sputtering target 1 is better to be applied in the fabrication of blue-emitting layer in inorganic electro-luminescent devices.

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

    SciTech Connect

    Clemens, Oliver

    2015-05-15

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

  4. Microstructural characterization of the dispersed phases in Al-Ce-Fe system

    NASA Astrophysics Data System (ADS)

    Ayer, Raghavan; Angers, L. M.; Mueller, R. R.; Scanlon, J. C.; Klein, C. F.

    1988-07-01

    Analytical electron microscopy studies were conducted on a rapidly solidified Al-8.8Fe-3.7Ce alloy and arc melted buttons of aluminum rich Al-Fe-Ce alloys to determine the characteristics of the metastable and equilibrium phases. The rapidly solidified alloy consisted of binary and ternary metastable phases in the as-extruded condition. The binary metastable phase was identified to be Al6Fe, while the ternary metastable phases were identified to be Al10Fe2Ce and Al20Fe5Ce. The Al20Fe5Ce was a decagonal quasicrystal while the Al10Fe2Ce phase was determined to have an orthorhombic crystal structure belonging to space group Cmmm, Cmm2, or C222. Microscopy studies of RS alloy and cast buttons annealed at 700 K established the equilibrium phases to be Al13Fe4, Al4Ce, and an Al13Fe3Ce ternary phase which was first identified in the present study. The crystal structure of the equilibrium ternary phase was determined to be orthorhombic with a Cmcm or Cmc2 space group. The details of X-ray microanalysis and convergent beam electron diffraction analysis are described.

  5. Structural investigation of the (010) surface of the Al13 Fe4 catalyst.

    PubMed

    Ledieu, J; Gaudry, É; Loli, L N Serkovic; Villaseca, S Alarcón; de Weerd, M-C; Hahne, M; Gille, P; Grin, Y; Dubois, J-M; Fournée, V

    2013-02-15

    We have investigated the structure of the Al(13)Fe(4)(010) surface using both experimental and ab initio computational methods. The results indicate that the topmost surface layers correspond to incomplete puckered (P) planes present in the bulk crystal structure. The main building block of the corrugated termination consists of two adjacent pentagons of Al atoms, each centered by a protruding Fe atom. These motifs are interconnected via additional Al atoms referred to as "glue" atoms which partially desorb above 873 K. The surface structure of lower atomic density compared to the bulk P plane is explained by a strong Fe-Al-Fe covalent polar interaction that preserves intact clusters at the surface. The proposed surface model with identified Fe-containing atomic ensembles could explain the Al(13)Fe(4) catalytic properties recently reported in line with the site-isolation concept [M. Armbrüster et al., Nat. Mater. 11, 690 (2012)].

  6. Effect of nitrogen upon structural and magnetic properties of FePt in FePt/AlN multilayer structures

    SciTech Connect

    Gao, Tenghua Zhang, Cong; Sannomiya, Takumi; Muraishi, Shinji; Nakamura, Yoshio; Shi, Ji

    2014-09-01

    This paper investigates the effect of the addition of nitrogen in FePt layers for ultrathin FePt/AlN multilayer structures. X-ray diffraction results reveal that a compressive stress relaxation occurs after annealing owing to the release of interstitial nitrogen atoms in the FePt layers. The introduction of nitrogen also induces a large in-plane compressive strain during grain growth not seen in FePt deposited without nitrogen. This strain is considered to decrease the driving force for (111) grain growth and FePt ordering.

  7. Anomalous Dilatometric Response in Fe-Mn-Al-Si Steel

    NASA Astrophysics Data System (ADS)

    Ghosh, S. K.

    2012-04-01

    The present study deals with the transformation of an aggregate consisting of ferrite and pearlite into austenite in a Fe-0.36C-1.98Mn-1.97Al-0.30Si (wt%) steel. The transformation phenomenon has been studied using dilatometry which confirms that austenite starts to nucleate due to dissolution of ferrite and pearlite and subsequently it commences to grow when the appropriate elevated temperature is reached. The austenite formation has been accompanied with the formation of a hump in the dilatation curve which is different with respect to the results reported earlier. The non-conventional behaviour associated with the austenite formation has been explained using the X-ray diffraction data, microstructural investigation and also with MT-DATA theoretical calculations.

  8. Synthesis of BaTiO[subscript 3]-20wt%CoFe[subscript 2]O[subscript 4] Nanocomposites via Spark Plasma Sintering

    SciTech Connect

    Ghosh, Dipankar; Han, Hyuksu; Nino, Juan C.; Subhash, Ghatu; Jones, Jacob L.

    2012-10-23

    Barium titanate-20wt% cobalt ferrite (BaTiO{sub 3}-20wt%CoFe{sub 2}O{sub 4}) nanocomposites were sintered from nanocrystalline BaTiO{sub 3} and CoFe{sub 2}O{sub 4} powders using spark plasma sintering (SPS) and pressureless sintering (PS) techniques. Using SPS, dense polycrystalline composites were obtained at a sintering temperature as low as 860 C and a time of 5 min whereas PS required a higher sintering temperature (1150 C) and time (120 min) to obtain similarly dense composites. Microstructural analysis of the composites showed that both the techniques retained nanocrystalline grain sizes after sintering. High resolution X-ray diffraction measurements revealed that the BaTiO{sub 3}-20wt%CoFe{sub 2}O{sub 4} composites sintered by the SPS technique did not exhibit formation of any new phase(s) due to reaction between the BaTiO{sub 3} and CoFe{sub 2}O{sub 4} phases during sintering. However, the PS technique resulted in the formation of additional phases (other than the BaTiO{sub 3} and CoFe{sub 2}O{sub 4} phases) in the composites. While the composites synthesized by SPS were of superior phase-purity, evidence of Fe diffusion from the spinel to the perovskite phase was found from X-ray diffraction and permittivity measurements.

  9. Strongly enhanced flux pinning in one-step deposition of BaFe2(As0.66P0.33)2 superconductor films with uniformly dispersed BaZrO3 nanoparticles

    PubMed Central

    Miura, Masashi; Maiorov, Boris; Kato, Takeharu; Shimode, Takashi; Wada, Keisuke; Adachi, Seiji; Tanabe, Keiichi

    2013-01-01

    The high upper critical field and low anisotropy of the iron-based superconductor BaFe2As2 make it promising for its use in the construction of superconducting magnets. However, its critical current density in high magnetic fields needs to be improved. Here we demonstrate a simple, one-step and industrially scalable means of achieving just this. We show that introducing controlled amounts of uniformly dispersed BaZrO3 nanoparticles into carrier-doped BaFe2As2 significantly improves its superconducting performance without degrading its structural or superconducting properties. Our BaFe2(As0.66P0.33)2 films also exhibit an increase in both the irreversibility line and critical current density at all magnetic-field orientations. These films exhibit nearly isotropic critical current densities in excess of 1.5 MA cm−2 at 15 K and 1 T—seven times higher than previously reported for BaFe2As2 films. The vortex-pinning force in these films reaches ~59 GN m−3 at 5 K and 3–9 T, substantially higher than that of the conventional Nb3Sn wire. PMID:24051678

  10. Nanostructure evolution in joining of Al and Fe nanoparticles with femtosecond laser irradiation

    SciTech Connect

    Jiao, Z.; Huang, H.; Zhou, Y. E-mail: nzhou@uwaterloo.ca; Liu, L.; Hu, A.; Duley, W.; He, P. E-mail: nzhou@uwaterloo.ca

    2014-04-07

    The joining of Al-Fe nanoparticles (NPs) by femtosecond (fs) laser irradiation is reported in this paper. Fe and Al NPs were deposited on a carbon film in vacuum via fs laser ablation. Particles were then exposed to multiple fs laser pulses at fluences between 0.5 and 1.3 mJ/cm{sup 2}. Transmission Electron Microscopy (TEM) and Electron Diffraction X-ray observations indicate that Al and Fe NPs bond to each other under these conditions. For comparison, bonding of Al to Al and Fe to Fe NPs was also investigated. The nanostructure, as observed using TEM, showed that individual Al NPs were monocrystalline while individual Fe NPs were polycrystalline prior to joining and that these structures are retained after the formation of Al-Al and Fe-Fe NPs. Al-Fe NPs produced by fs laser joining exhibited a mixed amorphous and crystalline phase at the interface. Bonding is suggested to originate from intermixing within a region of high field intensity between particles.

  11. Strong electronic correlations in iron pnictides: Comparison of the optical spectra for BaFe2As2-related compounds

    NASA Astrophysics Data System (ADS)

    Nakajima, Masamichi

    2014-03-01

    The role of electronic correlations in iron pnictides is one of the hottest issues in research of iron-based superconductors. Utilizing optical spectroscopy, we quantified the strength of electronic correlations in BaFe2As2-related compounds. For the parent compound BaFe2As2, the fraction of the coherent spectral weight in the low-energy optical conductivity spectrum is distinctly small. Such a spectral feature is also observed in KFe2As2, indicating that the charge dynamics is highly incoherent in iron arsenides. It is found that the strength of electronic correlations significantly changes by chemical substitution, either through changing the electron filling and/or the As-Fe-As bond angle. The present result indicates that superconductivity of the iron pnictides emerges when the materials possess adequate amount of electronic correlations, and that either too weak or too strong correlations are not favorable for high-Tc superconductivity. The degree of electronic correlations in iron arsenides turns out to be comparable to that in the hole-underdoped cuprate superconductors. In this sense, the iron arsenides are classified into strongly correlated systems, probably arising from the Hund's rule coupling. This work was done in collaboration with S. Ishida, K. Kihou, Y. Tomioka, C. H. Lee, A. Iyo, T. Ito, H. Eisaki (AIST), T. Tanaka, T. Kakeshita, S. Uchida (University of Tokyo), T. Saito, H. Fukazawa, and Y. Kohori (Chiba University).

  12. Hall-plot of the phase diagram for Ba(Fe1-xCox)2As2

    NASA Astrophysics Data System (ADS)

    Iida, Kazumasa; Grinenko, Vadim; Kurth, Fritz; Ichinose, Ataru; Tsukada, Ichiro; Ahrens, Eike; Pukenas, Aurimas; Chekhonin, Paul; Skrotzki, Werner; Teresiak, Angelika; Hühne, Ruben; Aswartham, Saicharan; Wurmehl, Sabine; Mönch, Ingolf; Erbe, Manuela; Hänisch, Jens; Holzapfel, Bernhard; Drechsler, Stefan-Ludwig; Efremov, Dmitri V.

    2016-06-01

    The Hall effect is a powerful tool for investigating carrier type and density. For single-band materials, the Hall coefficient is traditionally expressed simply by , where e is the charge of the carrier, and n is the concentration. However, it is well known that in the critical region near a quantum phase transition, as it was demonstrated for cuprates and heavy fermions, the Hall coefficient exhibits strong temperature and doping dependencies, which can not be described by such a simple expression, and the interpretation of the Hall coefficient for Fe-based superconductors is also problematic. Here, we investigate thin films of Ba(Fe1-xCox)2As2 with compressive and tensile in-plane strain in a wide range of Co doping. Such in-plane strain changes the band structure of the compounds, resulting in various shifts of the whole phase diagram as a function of Co doping. We show that the resultant phase diagrams for different strain states can be mapped onto a single phase diagram with the Hall number. This universal plot is attributed to the critical fluctuations in multiband systems near the antiferromagnetic transition, which may suggest a direct link between magnetic and superconducting properties in the BaFe2As2 system.

  13. Hall-plot of the phase diagram for Ba(Fe1−xCox)2As2

    PubMed Central

    Iida, Kazumasa; Grinenko, Vadim; Kurth, Fritz; Ichinose, Ataru; Tsukada, Ichiro; Ahrens, Eike; Pukenas, Aurimas; Chekhonin, Paul; Skrotzki, Werner; Teresiak, Angelika; Hühne, Ruben; Aswartham, Saicharan; Wurmehl, Sabine; Mönch, Ingolf; Erbe, Manuela; Hänisch, Jens; Holzapfel, Bernhard; Drechsler, Stefan-Ludwig; Efremov, Dmitri V.

    2016-01-01

    The Hall effect is a powerful tool for investigating carrier type and density. For single-band materials, the Hall coefficient is traditionally expressed simply by , where e is the charge of the carrier, and n is the concentration. However, it is well known that in the critical region near a quantum phase transition, as it was demonstrated for cuprates and heavy fermions, the Hall coefficient exhibits strong temperature and doping dependencies, which can not be described by such a simple expression, and the interpretation of the Hall coefficient for Fe-based superconductors is also problematic. Here, we investigate thin films of Ba(Fe1−xCox)2As2 with compressive and tensile in-plane strain in a wide range of Co doping. Such in-plane strain changes the band structure of the compounds, resulting in various shifts of the whole phase diagram as a function of Co doping. We show that the resultant phase diagrams for different strain states can be mapped onto a single phase diagram with the Hall number. This universal plot is attributed to the critical fluctuations in multiband systems near the antiferromagnetic transition, which may suggest a direct link between magnetic and superconducting properties in the BaFe2As2 system. PMID:27328948

  14. High-field transport properties of a P-doped BaFe2As2 film on technical substrate

    PubMed Central

    Iida, Kazumasa; Sato, Hikaru; Tarantini, Chiara; Hänisch, Jens; Jaroszynski, Jan; Hiramatsu, Hidenori; Holzapfel, Bernhard; Hosono, Hideo

    2017-01-01

    High temperature (high-Tc) superconductors like cuprates have superior critical current properties in magnetic fields over other superconductors. However, superconducting wires for high-field-magnet applications are still dominated by low-Tc Nb3Sn due probably to cost and processing issues. The recent discovery of a second class of high-Tc materials, Fe-based superconductors, may provide another option for high-field-magnet wires. In particular, AEFe2As2 (AE: Alkali earth elements, AE-122) is one of the best candidates for high-field-magnet applications because of its high upper critical field, Hc2, moderate Hc2 anisotropy, and intermediate Tc. Here we report on in-field transport properties of P-doped BaFe2As2 (Ba-122) thin films grown on technical substrates by pulsed laser deposition. The P-doped Ba-122 coated conductor exceeds a transport Jc of 105 A/cm2 at 15 T for main crystallographic directions of the applied field, which is favourable for practical applications. Our P-doped Ba-122 coated conductors show a superior in-field Jc over MgB2 and NbTi, and a comparable level to Nb3Sn above 20 T. By analysing the E − J curves for determining Jc, a non-Ohmic linear differential signature is observed at low field due to flux flow along the grain boundaries. However, grain boundaries work as flux pinning centres as demonstrated by the pinning force analysis. PMID:28079117

  15. High-field transport properties of a P-doped BaFe2As2 film on technical substrate.

    PubMed

    Iida, Kazumasa; Sato, Hikaru; Tarantini, Chiara; Hänisch, Jens; Jaroszynski, Jan; Hiramatsu, Hidenori; Holzapfel, Bernhard; Hosono, Hideo

    2017-01-12

    High temperature (high-Tc) superconductors like cuprates have superior critical current properties in magnetic fields over other superconductors. However, superconducting wires for high-field-magnet applications are still dominated by low-Tc Nb3Sn due probably to cost and processing issues. The recent discovery of a second class of high-Tc materials, Fe-based superconductors, may provide another option for high-field-magnet wires. In particular, AEFe2As2 (AE: Alkali earth elements, AE-122) is one of the best candidates for high-field-magnet applications because of its high upper critical field, Hc2, moderate Hc2 anisotropy, and intermediate Tc. Here we report on in-field transport properties of P-doped BaFe2As2 (Ba-122) thin films grown on technical substrates by pulsed laser deposition. The P-doped Ba-122 coated conductor exceeds a transport Jc of 10(5) A/cm(2) at 15 T for main crystallographic directions of the applied field, which is favourable for practical applications. Our P-doped Ba-122 coated conductors show a superior in-field Jc over MgB2 and NbTi, and a comparable level to Nb3Sn above 20 T. By analysing the E - J curves for determining Jc, a non-Ohmic linear differential signature is observed at low field due to flux flow along the grain boundaries. However, grain boundaries work as flux pinning centres as demonstrated by the pinning force analysis.

  16. High-field transport properties of a P-doped BaFe2As2 film on technical substrate

    NASA Astrophysics Data System (ADS)

    Iida, Kazumasa; Sato, Hikaru; Tarantini, Chiara; Hänisch, Jens; Jaroszynski, Jan; Hiramatsu, Hidenori; Holzapfel, Bernhard; Hosono, Hideo

    2017-01-01

    High temperature (high-Tc) superconductors like cuprates have superior critical current properties in magnetic fields over other superconductors. However, superconducting wires for high-field-magnet applications are still dominated by low-Tc Nb3Sn due probably to cost and processing issues. The recent discovery of a second class of high-Tc materials, Fe-based superconductors, may provide another option for high-field-magnet wires. In particular, AEFe2As2 (AE: Alkali earth elements, AE-122) is one of the best candidates for high-field-magnet applications because of its high upper critical field, Hc2, moderate Hc2 anisotropy, and intermediate Tc. Here we report on in-field transport properties of P-doped BaFe2As2 (Ba-122) thin films grown on technical substrates by pulsed laser deposition. The P-doped Ba-122 coated conductor exceeds a transport Jc of 105 A/cm2 at 15 T for main crystallographic directions of the applied field, which is favourable for practical applications. Our P-doped Ba-122 coated conductors show a superior in-field Jc over MgB2 and NbTi, and a comparable level to Nb3Sn above 20 T. By analysing the E ‑ J curves for determining Jc, a non-Ohmic linear differential signature is observed at low field due to flux flow along the grain boundaries. However, grain boundaries work as flux pinning centres as demonstrated by the pinning force analysis.

  17. Formation of a paramagnetic Al complex and extrusion of Fe during the reaction of (diiminepyridine)Fe with AlR3 (R = Me, Et).

    PubMed

    Scott, Jennifer; Gambarotta, Sandro; Korobkov, Ilia; Knijnenburg, Quinten; de Bruin, Bas; Budzelaar, Peter H M

    2005-12-14

    The reaction of the {2,6-[2,6-(iPr)2PhN=C(CH3)]2(C5H3N)}FeCl2 catalyst precursor with R3Al [R = Me, Et] afforded {2,6-[2,6-(iPr)2PhN=C(CH3)]2(C5H3N)}AlMe2 (1) and [eta4-LAl2Et3(mu-Cl)]Fe-(eta6-C7H8) (2), respectively. These paramagnetic species arises from both transmetalation, during which the strong terdentate ligand loses the Fe center, and reduction. The extent of reduction depends on the nature of the Al alkylating agent. The electrons necessary for the reduction are likely to be provided by cleavage of Fe-C bond of transient low-valent organo-Fe species.

  18. High stability of magnetic parameters in Fe-Al nanocomposite powders

    NASA Astrophysics Data System (ADS)

    Jani, S.; Sebastian, V.; Sudheesh, V.; Nehra, J.; Lakshmi, N.; Venugopalan, K.

    2016-09-01

    The structural and magnetic properties of Fe75Al25 nanosystem prepared by high energy ball milling for 15 h milling time have been studied. Structural analysis shows the formation of distinct Fe-Al portions with Al at grain boundaries, indicating that Fe-Al nanocomposite formation is favored over alloying due to the formation of diffusion hindering Fe-Al phase at grain boundaries. The saturation magnetization (Ms) of the nanocomposite at 8 nm grain size is 117 emu/g (i.e. 55 % that of pure Fe). The Curie temperature (TC) 1053 K matches the value of pure bcc α-Fe. M-H curves recorded after M-T studies are the same as before indicating the extreme stability of this system against high temperatures. Low temperature M-T measurements and room temperature remanence measurements show that interparticle interactions are demagnetizing kind and dipolar in nature.

  19. Synthesis, Crystal and Electronic Structures of the Pnictides AE3TrPn3 (AE = Sr, Ba; Tr = Al, Ga; Pn = P, As)

    DOE PAGES

    Stoyko, Stanislav; Voss, Leonard; He, Hua; ...

    2015-09-24

    New ternary arsenides AE3TrAs3 (AE = Sr, Ba; Tr = Al, Ga) and their phosphide analogs Sr3GaP3 and Ba3AlP3 have been prepared by reactions of the respective elements at high temperatures. Single-crystal X-ray diffraction studies reveal that Sr3AlAs3 and Ba3AlAs3 adopt the Ba3AlSb3-type structure (Pearson symbol oC56, space group Cmce, Z = 8). This structure is also realized for Sr3GaP3 and Ba3AlP3. Likewise, the compounds Sr3GaAs3 and Ba3GaAs3 crystallize with the Ba3GaSb3-type structure (Pearson symbol oP56, space group Pnma, Z = 8). Both structures are made up of isolated pairs of edge-shared AlPn4 and GaPn4 tetrahedra (Pn = pnictogen, i.e.,more » P or As), separated by the alkaline-earth Sr2+ and Ba2+ cations. In both cases, there are no homoatomic bonds, hence, regardless of the slightly different atomic arrangements, both structures can be rationalized as valence-precise [AE2+]3[Tr3+][Pn3-]3, or rather [AE2+]6[Tr2Pn6]12-, i.e., as Zintl phases.« less

  20. Influence of doping and doping level on magnetoelectric coupling in layered composites Tb1-xDyxFe2-y/Ba-Ti1-zMzO3+δ (M = Fe, Cr, Mn, Co)

    NASA Astrophysics Data System (ADS)

    Zhang, N.; Fan, J. F.; Cao, H. X.; Wei, J. J.

    2010-06-01

    Perovskites BaTi1-zMzO3+δ (M = Fe, Cr, Mn, Co) has been sol-gel synthesized. Their transformation point of ferroelectric to paraelectric and the latent heat of the transformation were found a little lower than those for pure BaTiO3 (BTO), respectively. Layered composites Tb1-xDyxFe2-y-BaTi1-zMzO3+δ have been fabricated. Their magnetoelectric (ME) effect has been investigated. All the bilayers containing the doped BTO displayed a stronger ME effects than that containing pure BTO does. The bilayer Tb1-xDyxFe2-y-BaTi0.99Cr0.01O3+δ was observed to show a larger ME coupling in the composites containing other doped BTO. While Tb1-xDyxFe2-y-BaTi0.985Fe0.015O3+δ showed the largest ME effects in the bilayers Tb1-xDyxFe2-y-BaTi1-zFezO3+δ (0 ≤ z ≤ 0.02). Additionally, the ME voltage coefficient for the trilayers Tb1-xDyxFe2-y-BaTi0.99M0.01O3+δ-Tb1-xDyxFe2-y was observed to be two or three times larger than that observed in the bilayers composed by the same substances. Theoretical analyses have been given for these observations. All the results suggest that the doped BTO can be a new choice of piezoelectrics in fabricating layered ME composites.

  1. Luminescent properties of BaAl2Si2O8:Eu2+, Mn2+ phosphor for white LED

    NASA Astrophysics Data System (ADS)

    Shen, Changyu; Li, Ke

    2010-10-01

    BaAl2Si2O8:xEu2+, yMn2+ was prepared by high-temperature solid state reaction and X-ray powder diffraction analysis confirmed the formation of it. It was found experimentally that, its emission peaks situated at 420 nm and 570 nm respectively under excitation of 380 nm irradiation. The emission peaks at 420 nm originate from the transition 5d to 4f of Eu2+ ions that occupy the Ba2+ sites in the crystal of BaAl2Si2O8, while the 580nm emission is attributed to the energy transfer from Eu2+ ions to Mn2+ ions. The white light can be obtained by combining the 380 nm chip with the phosphor. When the concentrations of the Eu2+ ions and Mn2+ ions were 0.05 mol and 0.35 mol respectively, the sample presented intense white emitting. The near-ultraviolet InGaN-based BaAl2Si2O8:0.05Eu2+, 0.35Mn2+ LED achieves good color rendering of 85 with the CIE coordinate of (0.3183, 0.3036).

  2. Enhanced Homogenization of Vanadium in Spark Plasma Sintering of Ti-10V-2Fe-3Al Alloy from Titanium and V-Fe-Al Master Alloy Powder Blends

    NASA Astrophysics Data System (ADS)

    Yang, Y. F.; Imai, H.; Kondoh, K.; Qian, M.

    2017-02-01

    Strong and ductile powder metallurgy (PM) Ti-10V-2Fe-3Al alloy has been fabricated by spark plasma sintering (SPS) of titanium and V-Fe-Al master alloy powder blends at 1100°C for 30 min under 30 MPa. The homogenization of vanadium, which dictates the realization of a uniform microstructure of the Ti-10V-2Fe-3Al alloy, was markedly accelerated by SPS. The mechanism is attributed to the intensive Joule heating effect produced by the direct current passing through the electric conducting powder blends, rather than through spark plasma discharge, because homogenization occurred mainly after near full identification had been achieved. The chemical and microstructural homogeneity ensured the achievement of excellent tensile properties of PM Ti-10V-2Fe-3Al in the as-sintered state, with tensile strength >1250 MPa and elongation >10%.

  3. Brillouin light scattering study of Co2Cr0.6Fe0.4Al and Co2FeAl Heusler compounds

    NASA Astrophysics Data System (ADS)

    Gaier, O.; Hamrle, J.; Trudel, S.; Conca Parra, A.; Hillebrands, B.; Arbelo, E.; Herbort, C.; Jourdan, M.

    2009-04-01

    The thermal magnonic spectra of Co2Cr0.6Fe0.4Al (CCFA) and Co2FeAl were investigated using Brillouin light scattering (BLS) spectroscopy. For CCFA, the exchange constant A (exchange stiffness D) is found to be 0.48 ± 0.04 µerg cm-1 (203 ± 16 meV Å2), while for Co2FeAl the corresponding values of 1.55 ± 0.05 µerg cm-1 (370 ± 10 meV Å2) were found. The observed asymmetry in the BLS spectra between the Stokes and anti-Stokes frequencies was assigned to an interplay between the asymmetrical profiles of hybridized Damon-Esbach and perpendicular standing spin-wave modes, combined with the optical sensitivity of the BLS signal to the upper side of the CCFA or Co2FeAl film.

  4. Effects of uniaxial pressure and annealing on the resistivity of Ba(Fe1-xCox)2As2

    NASA Astrophysics Data System (ADS)

    Liang, T.; Nakajima, M.; Kihou, K.; Tomioka, Y.; Ito, T.; Lee, C. H.; Kito, H.; Iyo, A.; Eisaki, H.; Kakeshita, T.; Uchida, S.

    2011-05-01

    Single crystals of underdoped Ba(Fe1-xCox)2As2 were detwinned by applying uniaxial pressure. The anisotropic in-plane resistivity was measured using the Montgomery method without releasing pressure. The resistivity along the a-axis shows metallic behavior down to 5 K, while the resistivity along the b-axis shows an insulator-like behavior in some temperature range. Annealing the sample radically reduces the residual resistivity for x=0, and at the same time the anisotropy becomes much smaller at low temperatures.

  5. Effect of Fermi surface nesting on resonant spin excitations in Ba(1-x)K(x)Fe2As2.

    PubMed

    Castellan, J-P; Rosenkranz, S; Goremychkin, E A; Chung, D Y; Todorov, I S; Kanatzidis, M G; Eremin, I; Knolle, J; Chubukov, A V; Maiti, S; Norman, M R; Weber, F; Claus, H; Guidi, T; Bewley, R I; Osborn, R

    2011-10-21

    We report inelastic neutron scattering measurements of the resonant spin excitations in Ba(1-x)K(x)Fe(2)As(2) over a broad range of electron band filling. The fall in the superconducting transition temperature with hole doping coincides with the magnetic excitations splitting into two incommensurate peaks because of the growing mismatch in the hole and electron Fermi surface volumes, as confirmed by a tight-binding model with s(±)-symmetry pairing. The reduction in Fermi surface nesting is accompanied by a collapse of the resonance binding energy and its spectral weight, caused by the weakening of electron-electron correlations.

  6. Quantum Oscillations in the Parent pnictide BaFe2As2 : Itinerant Electrons in the Reconstructed State

    SciTech Connect

    Analytis, J.G.

    2010-05-26

    We report quantum oscillation measurements that enable the direct observation of the Fermi surface of the low temperature ground state of BaFe{sub 2}As{sub 2}. From these measurements we characterize the low energy excitations, revealing that the Fermi surface is reconstructed in the antiferromagnetic state, but leaving itinerant electrons in its wake. The present measurements are consistent with a conventional band folding picture of the antiferromagnetic ground state, placing important limits on the topology and size of the Fermi surface.

  7. Quantum oscillations in the parent pnictide BaFe2As2 : Itinerant electrons in the reconstructed state

    NASA Astrophysics Data System (ADS)

    Analytis, James G.; McDonald, Ross D.; Chu, Jiun-Haw; Riggs, Scott C.; Bangura, Alimamy F.; Kucharczyk, Chris; Johannes, Michelle; Fisher, I. R.

    2009-08-01

    We report quantum-oscillation measurements that enable the direct observation of the Fermi surface of the low-temperature ground state of BaFe2As2 . From these measurements we characterize the low-energy excitations, revealing that the Fermi surface is reconstructed in the antiferromagnetic state, but leaving itinerant electrons in its wake. The present measurements are consistent with a conventional band folding picture of the antiferromagnetic ground state, placing important limits on the topology and size of the Fermi surface.

  8. NMR evidence for inhomogeneous nematic fluctuations in BaFe2(As1-xPx)2

    DOE PAGES

    Dioguardi, A. P.; Kissikov, T.; Lin, C. H.; ...

    2016-03-10

    We present evidence for nuclear spin-lattice relaxation driven by glassy nematic fluctuations in isovalent P-doped BaFe2As2 single crystals. Both the 75As and 31P sites exhibit a stretched-exponential relaxation similar to the electron-doped systems. By comparing the hyperfine fields and the relaxation rates at these sites we find that the As relaxation cannot be explained solely in terms of magnetic spin fluctuations. We demonstrate that nematic fluctuations couple to the As nuclear quadrupolar moment and can explain the excess relaxation. Lastly, these results suggest that glassy nematic dynamics are a common phenomenon in the iron-based superconductors.

  9. ^93Nb NMR investigation of the multiferroic system Ba3NbFe3Si2O14

    NASA Astrophysics Data System (ADS)

    Lumata, Lloyd; Hoch, M. J. R.; Zhou, H. D.; Brooks, J. S.; Kuhns, P. L.; Reyes, A. P.; Wiebe, C. R.

    2009-03-01

    We present ^93Nb nuclear magnetic resonance spectroscopy and relaxation data on the new multiferroic system Ba3NbFe3Si2O14. The spin-lattice relaxation rate ^931/T1 and spin-spin relaxation rate ^931/T2 show a peak at 26 K accompanied by broadening of the NMR lineshapes, characteristic of N'eel ordering. Salient features of ^93Nb NMR lineshapes in the ordered phase and temperature-dependent ^93Nb Knight shifts will be discussed in relation to the possible bulking or tilting of the NbO6 octahedra (caused by magneto-lattice coupling) around the transition.

  10. SANS study of vortex lattice structural transition in optimally doped (Ba1-x K x )Fe2As2

    NASA Astrophysics Data System (ADS)

    Demirdiş, S.; van der Beek, C. J.; Mühlbauer, S.; Su, Y.; Wolf, Th

    2016-10-01

    Small-angle neutron scattering on high quality single crystalline Ba1-x K x Fe2As2 reveals the transition from a low-field vortex solid phase with orientational order to a vortex polycrystal at high magnetic field. The vortex order-disorder transition is correlated with the second-peak feature in isothermal hysteresis loops, and is interpreted in terms of the generation of supplementary vortex solid dislocations. The sharp drop of the structure factor above the second peak field is explained by the dynamics of freezing of the vortex ensemble in the high field phase.

  11. SANS study of vortex lattice structural transition in optimally doped (Ba1-x K x )Fe2As2.

    PubMed

    Demirdiş, S; van der Beek, C J; Mühlbauer, S; Su, Y; Wolf, Th

    2016-10-26

    Small-angle neutron scattering on high quality single crystalline Ba1-x K x Fe2As2 reveals the transition from a low-field vortex solid phase with orientational order to a vortex polycrystal at high magnetic field. The vortex order-disorder transition is correlated with the second-peak feature in isothermal hysteresis loops, and is interpreted in terms of the generation of supplementary vortex solid dislocations. The sharp drop of the structure factor above the second peak field is explained by the dynamics of freezing of the vortex ensemble in the high field phase.

  12. Fabrication and magnetic property of BaSm(x)Fe(12-x)O19 (x < or = 0.4) nanofibers.

    PubMed

    Xian-Feng, Meng; Li-Ju, Guo

    2012-03-01

    BaSm(x)Fe(12-x)O19 (x < or = 0.4) ferrite nanofibers were prepared by sol-gel method from starting reagents of metal salts and citric acid. These nanofibers were characterized by TG-DTA, FTIR, SEM, XRD and VSM. These results show that the BaSm(x)Fe(12-x)O19 (x < or = 0.4) ferrite nanofibers were obtained subsequently from calcination at 750 degrees C for 1 h. The BaSm(x)Fe(12-x)O19 (x < or = 0.4) microstructure and magnetic property are mainly influenced by chemical composition and heat-treatment temperature. The grain sizes of BaSm0.3Fe11.7O19 ferrite nanofibers are in a nanoscale from 40 nm to 62 nm corresponding to the calcination temperature from 750 degrees C to 1050 derees C. The saturation magnetization of BaSm(x)Fe(12-x)O19 ferrite nanofiber calcined at 950 degrees C for 1 h initially decreases with the Sm content from 0 to 0.3 and then increases with a further Sm content, while the coercivity exhibits a continuous increase from 348 kA x m(-1) (x = 0) to 427 kA x m(-1) (x = 0.4). The differences of magnetic properties are attributed to lattice distortion and enhancement for the anisotropy energy.

  13. Preparation of thermal infrared and microwave absorber using SrTiO3/BaFe12O19/polyaniline nanocomposites

    NASA Astrophysics Data System (ADS)

    Hosseini, Seyed Hossein; Zamani, Parisa

    2016-01-01

    In this research, first, SrTiO3 was synthesized as thermal infrared (TIR) absorbent and core and then BaFe12O19 as microwave absorbent was prepared on SrTiO3 via co-precipitation method as first shell. Second, polyaniline (PANI) was coated on SrTiO3/BaFe12O19 NPs (NPs) via in situ polymerization by multi core-shell structures (SrTiO3/BaFe12O19/PANI). Nanometer size and structures of samples were measured by TEM, XRD and FTIR. Morphology of nanocomposite was showed by SEM images. The magnetic and electric properties were also performed by VSM and four probe methods. The TIR absorption and microwave reflection loss of nanocomposites were investigated at 10-40 μm and 8-12 GHz, TIR and microwave frequencies, respectively. The results showed that the SrTiO3/BaFe12O19/PANI nanocomposites have good compatible electric and magnetic properties and hence the microwave absorbency show wide bandwidth properties. The infrared thermal image testing showed that the ability of infrared thermal imaging was increased by increasing SrTiO3/BaFe12O19 as core and independent to increasing PANI as final shell.

  14. Infrared Brazing Fe3Al Using Ag-Based Filler Metals

    NASA Astrophysics Data System (ADS)

    Shiue, Ren-Kae; Li, Yao; Wu, Shyi-Kaan; Wu, Ling-Mei

    2010-11-01

    The microstructural evolution and bonding shear strength of infrared brazed Fe3Al using Ag and BAg-8 (72Ag-28Cu in wt pct) braze alloys have been studied. The Ag-rich phase alloyed with Al dominates the entire Ag brazed joints, and the shear strength is independent of the brazing time. The BAg-8 brazed joint contains Ag-Cu eutectic for all brazing conditions, and its shear strength increases slightly with increasing brazing time. The highest shear strength of 181 MPa is acquired from the joint infrared brazed at 1073 K (800 °C) for 600 seconds. A thin layer of Fe3Al is identified at the interface between the brazed zone and the substrate for both braze alloys. An Al depletion zone in the Fe3Al substrate next to the interfacial Fe3Al is identified as the α-Fe phase. The dissolution of Al from the Fe3Al substrate into the molten braze causes the formation of α-Fe in the Fe3Al substrate.

  15. Investigation on photoluminescence properties and defect chemistry of GdAlO3:Dy3+ Ba2+ phosphors

    NASA Astrophysics Data System (ADS)

    Selvalakshmi, Thangaraj; Sellaiyan, Selvakumar; Uedono, Akira; Semba, Takaaki; Bose, Arumugam Chandra

    2016-08-01

    GdAlO3:Dy3+ Ba2+ phosphors are synthesized by citrate-based sol-gel method. Photoluminescence and positron annihilation studies are used to investigate the emission and defect chemistry of the phosphors respectively. The strong yellow (Dy3+) emission properties of phosphors are discussed for various concentrations of Dy3+ ions. Upon the addition of Ba2+ ion, an enhancement in emission intensity is observed due to the lattice distortions around Dy3+ ion. The positron studies indicate the presence of defects at crystallite boundaries, vacancy clusters and large voids in the materials. The influence of Ba2+ ion on the photoluminescence and lattice distortion around Dy3+ is also explored.

  16. Investigation de l'anisotropie du gap supraconducteur dans les composes Ba(Fe(1-x)Co(x))2As2, Ba(1-x)K(x)Fe2As2, LiFeAs et Fe1-deltaTe(1-x)Se(x)

    NASA Astrophysics Data System (ADS)

    Reid, Jean-Philippe

    ommaire La structure du gap supraconducteur et sa modulation sont intimement liees au potentiel d'interaction responsable de l'appariement des electrons d'un supraconducteur. Ainsi, l'etude de la structure du gap-SC et de sa modulation permettent de faire la lumiere sur la nature du mecanisme d'appariement des electrons. A cet egard, les resultats experimentaux des supraconducteurs a base de fer ne cadrent pas dans un seul ensemble, ce qui est en opposition au gap-SC universel des cuprates. Dans ce qui suit, nous presenterons une etude systematique du gap-SC pour plusieurs pnictides. En effet, en utilisant la conductivite thermique, une sonde directionnelle du gap-SC, nous avons ete en mesure de reveler la structure du gap-SC pour les composes suivants : Ba1-xKxFe 2As2, Ba(Fe1-xCo x)2As2, LiFeAs et Fe1-deltaTe 1-xSex. L'etude de ces quatre composes, de trois differentes familles structurales, a pu etablir un tableau partiel mais tres exhaustif de la structure du gap-SC de pnictides. En effet, tel qu'illustre dans cette these, ces quatre composes ne possedent aucun noeud dans leur structure du gap-SC a dopage optimal. Toutefois, a une concentration differente de celle optimale pour les composes K-Ba122 et Co-Ba122, des noeuds apparaissent sur la surface de Fermi, aux extremites 'du dome supraconducteur. Ceci suggere fortement que, pour ces composes, la presence de noeuds sur la surface de Fermi est nuisible a la phase supraconductrice. Mots-cles: Supraconducteurs a base de fer, Pnictides, Structure du gap supraconducteur, Conductivite thermique

  17. What Controls the Phase Diagram and Superconductivity in Ru-Substituted BaFe2As2?

    SciTech Connect

    Dhaka, R. S.; Liu, Chang; Fernandes, R.M.; Jiang, Riu; Strehlow, C.P.; Kondo, Takeshi; Thaler, A.; Schmalian, Joerg; Bud-ko, S.J.; Canfield, P.C.; Kaminski, A.

    2011-12-23

    We use high resolution angle-resolved photoemission to study the electronic structure of the iron based high-temperature superconductors Ba(Fe{sub 1-x}Ru{sub x}){sub 2}As{sub 2} as a function of Ru concentration. We find that substitution of Ru for Fe is isoelectronic, i.e., it does not change the value of the chemical potential. More interestingly, there are no measured, significant changes in the shape of the Fermi surface or in the Fermi velocity over a wide range of substitution levels (0 < x < 0.55). Given that the suppression of the antiferromagnetic and structural phase is associated with the emergence of the superconducting state, Ru substitution must achieve this via a mechanism that does not involve changes of the Fermi surface. We speculate that this mechanism relies on magnetic dilution which leads to the reduction of the effective Stoner enhancement.

  18. Anomalies in Transport and Superconducting Properties of Ba1-xKxFe2As2 Single Crystals

    NASA Astrophysics Data System (ADS)

    Zverev, Vladimir N.; Korobenko, Alexey V.; Sun, Guoli L.; Sun, Dunlu L.; Lin, Chengtian T.; Boris, Alexander V.

    2011-05-01

    The transport and superconducting properties of Ba1-xKxFe2As2 single crystals were studied. Both in-plane and out-of-plane resistivity were measured by Montgomery method. The in-plain resistivity temperature dependence was found to be nonlinear with the tendency to saturate at high temperature. We have found that the resistivity anisotropy is almost independent of temperature and lies in the range 10-40 for the studied samples. We explain this result by the extrinsic nature of high out-of-plane resistivity, which may be due to the presence of flat defects along Fe-As layers. This statement is supported by comparatively small effective mass anisotropy, obtained from the upper critical field measurements.

  19. Ca and In co-doped BaFeO3-δ as a cobalt-free cathode material for intermediate-temperature solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Wang, Jian; Lam, Kwun Yu; Saccoccio, Mattia; Gao, Yang; Chen, Dengjie; Ciucci, Francesco

    2016-08-01

    We report Ba0·95Ca0·05Fe0·95In0·05O3-δ (BCFI), a novel cobalt-free perovskite, as a promising cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs). We synthesize this new material, and systematically characterize its lattice structure, thermal stability, chemical composition, electrical conductivity, and oxygen reduction reaction (ORR) activity. The cubic phase of BaFeO3-δ is stabilized by light isovalent and lower-valence substitution, i.e., 5% Ca2+ in the Ba2+ site and 5% In3+ in the Fe3+/Fe4+ site, in contrast with the typical approach of substituting elements of higher valence. Without resorting to co-doping strategy, the phase of BaFe0·95In0·05O3-δ (BFI) is rhombohedral, while Ba0·95Ca0·05FeO3-δ (BCF) is a mixture of the cubic phase together with BaFe2O4 impurities. The structure of BCFI is cubic from room temperature up to 900 °C with a moderate thermal expansion coefficient of 23.2 × 10-6 K-1. Thanks to the large oxygen vacancy concentration and fast oxygen mobility, BCFI exhibits a favorable ORR activity, i.e., we observe a polarization resistance as small as 0.038 Ω cm2 at 700 °C. The significantly enhanced performance, compared with BFI and BCF, is attributed to the presence of the cubic phase and the large oxygen vacancies brought by the isovalent substitution in the A-site and lower-valence doping in the B-site.

  20. Magnetic properties and pairing tendencies of the iron-based superconducting ladder BaFe2S3 : Combined ab initio and density matrix renormalization group study

    NASA Astrophysics Data System (ADS)

    Patel, Niravkumar D.; Nocera, Alberto; Alvarez, Gonzalo; Arita, Ryotaro; Moreo, Adriana; Dagotto, Elbio

    2016-08-01

    The recent discovery of superconductivity under high pressure in the two-leg ladder compound BaFe2S3 [H. Takahashi et al., Nat. Mater. 14, 1008 (2015), 10.1038/nmat4351] opens a broad avenue of research, because it represents the first report of pairing tendencies in a quasi-one-dimensional iron-based high-critical-temperature superconductor. Similarly, as in the case of the cuprates, ladders and chains can be far more accurately studied using many-body techniques and model Hamiltonians than their layered counterparts, particularly if several orbitals are active. In this publication, we derive a two-orbital Hubbard model from first principles that describes individual ladders of BaFe2S3 . The model is studied with the density matrix renormalization group. These first reported results are exciting for two reasons: (i) at half-filling, ferromagnetic order emerges as the dominant magnetic pattern along the rungs of the ladder, and antiferromagnetic order along the legs, in excellent agreement with neutron experiments; and (ii) with hole doping, pairs form in the strong coupling regime, as found by studying the binding energy of two holes doped on the half-filled system. In addition, orbital selective Mott phase characteristics develop with doping, with only one Wannier orbital receiving the hole carriers while the other remains half-filled. These results suggest that the analysis of models for iron-based two-leg ladders could clarify the origin of pairing tendencies and other exotic properties of iron-based high-critical-temperature superconductors in general.

  1. Magnetic properties and pairing tendencies of the iron-based superconducting ladder BaFe2S3: Combined ab initio and density matrix renormalization group study

    DOE PAGES

    Patel, Niravkumar D.; Nocera, Alberto; Alvarez, Gonzalo; ...

    2016-08-10

    The recent discovery of superconductivity under high pressure in the two-leg ladder compound BaFe2S3 [H. Takahashi et al., Nat. Mater. 14, 1008 (2015)] opens a broad avenue of research, because it represents the first report of pairing tendencies in a quasi-one-dimensional iron-based high-critical-temperature superconductor. Similarly, as in the case of the cuprates, ladders and chains can be far more accurately studied using many-body techniques and model Hamiltonians than their layered counterparts, particularly if several orbitals are active. In this publication, we derive a two-orbital Hubbard model from first principles that describes individual ladders of BaFe2S3. The model is studied withmore » the density matrix renormalization group. These first reported results are exciting for two reasons: (i) at half-filling, ferromagnetic order emerges as the dominant magnetic pattern along the rungs of the ladder, and antiferromagnetic order along the legs, in excellent agreement with neutron experiments; and (ii) with hole doping, pairs form in the strong coupling regime, as found by studying the binding energy of two holes doped on the half-filled system. In addition, orbital selective Mott phase characteristics develop with doping, with only oneWannier orbital receiving the hole carriers while the other remains half-filled. Lastly, these results suggest that the analysis of models for iron-based two-leg ladders could clarify the origin of pairing tendencies and other exotic properties of iron-based high-critical-temperature superconductors in general.« less

  2. Ba'id al Jimalah tungsten prospect, Najd region, Kingdom of Saudi Arabia

    NASA Astrophysics Data System (ADS)

    Lofts, P. G.

    The Ba'id al Jimalah tungsten prospect is located in the NE of the Arabian Shield, at 25°09'N, 42°41'E. Mineralization is associated with a late-Proterozoic, porphyritic microgranite emplaced in folded, fine-grained clastic rocks of the Murdama group, within an aureole of biotite-rich hornfels. The microgranite forms a 30 m-thick sill and numerous smaller sills and dikes cropping out along two low, sub-parallel ridges and several small hills in an area 700 m square. The form of the intrusion at depth is uncertain. It is slightly to intensely sericitized, in places greisenized, and is enriched in Li, F and Rb. Wolframite occurs with minor cassiterite, scheelite and sulfides in quartz veins cutting both microgranite and hornfelsed wall-rock. The veins have a dominant trend of 110-115°, and are thicker and more numerous in the microgranite. Gangue minerals include plagioclase and potassium feldspar, muscovite, sericite, fluorite and minor siderite. A major Najd fault trending 130-135° probably controlled magma emplacement and subsequent hydrothermal and pneumatolytic activity. A percussion drilling program, restricted to the outcrop of the sill on the north ridge, has outlined 800,000 tonnes grading 0.10% WO 3 and 0.01% Sn.

  3. CEMS study of defect annealing in Fe implanted AlN

    NASA Astrophysics Data System (ADS)

    Bharuth-Ram, K.; Geburt, S.; Ronning, C.; Masenda, H.; Naidoo, D.

    2016-12-01

    An AlN thin film grown on sapphire substrate was implanted with 45 keV 57Fe and 56Fe ions at several energies to achieve a homogeneous concentration profile of approximately 2.6 at.%. in the AlN film. Conversion electron Mössbauer Spectroscopy data were collected after annealing the sample up to 900 °C. The spectra were fitted with three components, a single line attributed to small Fe clusters, and two quadrupole split doublets attributed to Fe substituting Al in the wurtzite AlN lattice and to Fe located in implantation induced lattice damage. The damage component shows significant decrease on annealing up to 900 °C, accompanied by corresponding increases in the singlet component and the substitutional Fe.

  4. Reduced overpotentials for electrocatalytic water splitting over Fe- and Ni-modified BaTiO3.

    PubMed

    Artrith, Nongnuch; Sailuam, Wutthigrai; Limpijumnong, Sukit; Kolpak, Alexie M

    2016-10-26

    Water electrolysis is a key technology for the replacement of fossil fuels by environmentally friendly alternatives, but state-of-the-art water oxidation catalysts rely on rare elements such as Pt groups and other noble metals. In this article, we employ first-principles calculations to explore the potential of modified barium titanate (BaTiO3), an inexpensive perovskite oxide that can be synthesized from earth-abundant precursors, for the design of efficient water oxidation electrocatalysts. Our calculations identify Fe and Ni doping as a means to improve the electrical conductivity and to reduce the overpotential required for water oxidation over BaTiO3. Based on computed Pourbaix diagrams and pH/potential-dependent surface phase diagrams, we further show that BaTiO3 is stable under reaction conditions and is not sensitive with respect to poisoning by reaction intermediates and hydrogen adsorption. This proof of concept demonstrates that even minor compositional modifications of existing materials may greatly improve their catalytic activity, a fact that is often neglected when larger composition spaces are screened.

  5. Lattice dynamics of BaFe2X3(X=S,Se) compounds

    DOE PAGES

    Popović, Z. V.; Šćepanović, M.; Lazarević, N.; ...

    2015-02-27

    We present the Raman scattering spectra of the S=2 spin ladder compounds BaFe₂X₃ (X=S,Se) in a temperature range between 20 and 400 K. Although the crystal structures of these two compounds are both orthorhombic and very similar, they are not isostructural. The unit cell of BaFe₂S₃ (BaFe₂Se₃) is base-centered Cmcm (primitive Pnma), giving 18 (36) modes to be observed in the Raman scattering experiment. We have detected almost all Raman active modes, predicted by factor group analysis, which can be observed from the cleavage planes of these compounds. Assignment of the observed Raman modes of BaFe₂S(Se)₃ is supported by themore » lattice dynamics calculations. The antiferromagnetic long-range spin ordering in BaFe₂Se₃ below TN=255K leaves a fingerprint both in the A1g and B3g phonon mode linewidth and energy.« less

  6. Strong coercivity reduction and high initial permeability in NiCoP coated BaFe12O19-polystyrene bilayer composite

    NASA Astrophysics Data System (ADS)

    Hamad, Mahmoud A.; El-Sayed, Adly H.; Hemeda, O. M.; Tawfik, A.

    2016-03-01

    Soft-magnetic NiCoP coated hard-magnetic M-type ferrite BaFe12O19 (BaM)-polystyrene (PS) bilayer composite film was successfully synthesized. X-ray diffraction peaks exhibited no change in the structure of BaM after coating with PS. The NiCoP coated BaM-PS composite exhibited a wasp-waisted magnetic hysteretic loop with remarkable reduction in the coercivity, remanence and squareness with respect to BaM-PS, which is useful for the core of a magnetic switching device to control currents so large that they are unmanageable. Moreover, the initial permeability measurement exhibits initial permeability of around 100 000 and thermal stability up to 558 K, which is good for flux-amplifying components of smaller inductors.

  7. Fe electron transfer and atom exchange in goethite: influence of Al-substitution and anion sorption.

    PubMed

    Latta, Drew E; Bachman, Jonathan E; Scherer, Michelle M

    2012-10-02

    The reaction of Fe(II) with Fe(III) oxides and hydroxides is complex and includes sorption of Fe(II) to the oxide, electron transfer between sorbed Fe(II) and structural Fe(III), reductive dissolution coupled to Fe atom exchange, and, in some cases mineral phase transformation. Much of the work investigating electron transfer and atom exchange between aqueous Fe(II) and Fe(III) oxides has been done under relatively simple aqueous conditions in organic buffers to control pH and background electrolytes to control ionic strength. Here, we investigate whether electron transfer is influenced by cation substitution of Al(III) in goethite and the presence of anions such as phosphate, carbonate, silicate, and natural organic matter. Results from (57)Fe Mössbauer spectroscopy indicate that both Al-substitution (up to 9%) and the presence of common anions (PO(4)(3-), CO(3)(2-), SiO(4)(4-), and humic acid) does not inhibit electron transfer between aqueous Fe(II) and Fe(III) in goethite under the conditions we studied. In contrast, sorption of a long-chain phospholipid completely shuts down electron transfer. Using an enriched isotope tracer method, we found that Al-substitution in goethite (10%), does, however, significantly decrease the extent of atom exchange between Fe(II) and goethite (from 43 to 12%) over a month's time. Phosphate, somewhat surprisingly, appears to have little effect on the rate and extent of atom exchange between aqueous Fe(II) and goethite. Our results show that electron transfer between aqueous Fe(II) and solid Fe(III) in goethite can occur under wide range of geochemical conditions, but that the extent of redox-driven Fe atom exchange may be dependent on the presence of substituting cations such as Al.

  8. Transport characteristics of Co-doped BaFe2As2 epitaxial thin film 24deg grain-boundaries

    NASA Astrophysics Data System (ADS)

    Panyajirawut, P.; Smith, N.; Tarantini, C.; Lee, S.; Jiang, J.; Bark, C. W.; Weiss, J. D.; Folkman, C. M.; Baek, S. H.; Hellstrom, E. E.; Eom, C. B.; Larbalestier, D. C.; Rzchowski, M. S.

    2010-03-01

    We investigate [001] 24deg tilt GBs of epitaxial thin film of the pnictide superconductor Co-doped Ba(Fe0.92Co0.08)2As2 on (001) SrTiO3 bicrystal substrates. The films were grown by pulsed laser deposition (PLD) with KrF (248 nm) UW excimer laser in vacuum at a base pressure of 2x10-7 Torr. The chemical composition of the films determined by wavelength dispersive x-ray spectroscopy (WDS) is Ba : Fe : Co : As : O = 1 : 1.7 : 0.13 : 1.7 : 0.3. Four-circle x-ray diffraction exhibits excellent expitaxy with cube-on cube in-plane epitaxial relationship. The films have an onset Tc of 20.5 K, and a Tco of 19.8K. The intragrain Jc is over 1 MA/cm^2 (4.2K, self field) which is significantly higher than in previously reported thin films. The grain boundary couples at a slightly lower temperature of 19.7 K. We discuss magnetic field and temperature dependence of the IV characteristics, and microwave response.

  9. Localized GHz frequency electrodynamic behavior of an optimally-doped Ba(Fe1-xCox)2As2 epitaxial film

    NASA Astrophysics Data System (ADS)

    Tai, Tamin; Ghamsari, Behnood G.; Kang, J. H.; Lee, S.; Eom, C. B.; Anlage, Steven M.

    2017-01-01

    High frequency (several GHz) electrodynamic properties of a high-quality epitaxial, single-crystal Iron-Pnictide Ba(Fe1-xCox)2As2 thin film near optimal doping (x = 0.08) are measured under a localized and strong RF magnetic field created by a near-field microwave microscope. Linear response and third harmonic electrodynamic measurements are performed to understand the electromagnetic properties of Ba(Fe1-xCox)2As2 and contrasts are drawn with similar measurements on Nb. Our measurement results show that Ba(Fe1-xCox)2As2 has nonlinear response potentially arising from a number of mechanisms and may show evidence of a multi-gap nature.

  10. Synthesis and electromagnetic properties of BaFe{sub 11.92}(LaNd){sub 0.04}O{sub 19}/titanium dioxide composites

    SciTech Connect

    Xie, Yu; Hong, Xiaowei; Liu, Jinmei; Le, Zhanggao; Huang, Feihui; Qin, Yuancheng; Zhong, Rong; Gao, Yunhua; Pan, Jianfei; Ling, Yun

    2014-02-01

    Graphical abstract: Due to combining different functions and characteristics of individual materials, hybrid nanocomposite materials can strengthen their applications. Magnetic-conductive nanocomposites are the promising materials with electromagnetic loss, which have synergetic behavior between magnetic and conductive materials. It is the first time to report the synthesis of BaFe{sub 11.92}(LaNd){sub 0.04}O{sub 19}/titanium dioxide (BF/TD) composites by the gel-precursor self-propagating combustion process. The influence of mass ratio of BF and TD on the electromagnetic properties of BaFe{sub 11.92}(LaNd){sub 0.04}O{sub 19}/titanium dioxide composites was studied. The tgδ{sub μ} and tgδ{sub ε} of BF–TD composites. - Highlights: • It is the first time to report BaFe{sub 11.92}(LaNd){sub 0.04}O{sub 19}/titanium dioxide composites. • The composites are prepared by the gel-precursor self-propagating combustion. • The electromagnetic properties could be adjusted by the mass ratio of BF and TD. • The introduction of TD enhances the dielectric loss and widens the frequency bands. • BF/TD composites will be microwave absorption materials with wide frequency band. - Abstract: Doped BaFe{sub 11.92}(LaNd){sub 0.04}O{sub 19}/titanium dioxide composites have been prepared by the gel-precursor self-propagating combustion process. The characterization of the composites are performed by Fourier transform infrared (FT-IR), X-ray diffraction (XRD), Differential thermal analysis-thermo gravimetry (DTA–TG), scanning electron microscopy (SEM), vibrating sample magnetometer (VSM) and network analyzer. Both XRD and FT-IR indicate that the doped BaFe{sub 11.92}(LaNd){sub 0.04}O{sub 19}/titanium dioxide composites are successfully synthesized and there are some interactions between BaFe{sub 11.92}(LaNd){sub 0.04}O{sub 19} and titanium dioxide. DTA–TG analysis of BaFe{sub 11.92}(LaNd){sub 0.04}O{sub 19}/titanium dioxide composites shows that the composite gel

  11. Effect of the synthesis conditions on the magnetic and electrical properties of the BaFeO{sub 3-x} oxide: A metamagnetic behavior

    SciTech Connect

    Gil de Muro, Izaskun . E-mail: qiproapt@lg.ehu.es

    2005-05-15

    The BaFeO{sub 2.95} oxide has been obtained from thermal decomposition of the [BaFe(C{sub 3}H{sub 2}O{sub 4}){sub 2}(H{sub 2}O){sub 4}] metallo-organic precursor at 800 deg. C under atmospheric oxygen pressure as small and homogeneous particles. From electronic paramagnetic resonance data, a metallic behavior in the 230-130K temperature range has been observed. Magnetic measurements confirm the existence of a ferro-antiferromagnetic transition at 178K. The magnetic properties of the BaFeO{sub 2.95} oxide are strongly dependent on both temperature and magnetic field with a metamagnetic behavior. The synthesis conditions play an important role on the morphology and the electrical and magnetic properties. The syntherization of the sample produces a dramatic change in the transport properties and the existence of conductivity disappears.

  12. Multiple diffraction in an icosahedral Al-Cu-Fe quasicrystal

    NASA Astrophysics Data System (ADS)

    Fan, C. Z.; Weber, Th.; Deloudi, S.; Steurer, W.

    2011-07-01

    In order to reveal its influence on quasicrystal structure analysis, multiple diffraction (MD) effects in an icosahedral Al-Cu-Fe quasicrystal have been investigated in-house on an Oxford Diffraction four-circle diffractometer equipped with an Onyx™ CCD area detector and MoKα radiation. For that purpose, an automated approach for Renninger scans (ψ-scans) has been developed. Two weak reflections were chosen as the main reflections (called P) in the present measurements. As is well known for periodic crystals, it is also observed for this quasicrystal that the intensity of the main reflection may significantly increase if the simultaneous (H) and the coupling (P-H) reflections are both strong, while there is no obvious MD effect if one of them is weak. The occurrence of MD events during ψ-scans has been studied based on an ideal structure model and the kinematical MD theory. The reliability of the approach is revealed by the good agreement between simulation and experiment. It shows that the multiple diffraction effect is quite significant.

  13. On stoichiometry and intermixing at the spinel/perovskite interface in CoFe2O4/BaTiO3 thin films

    NASA Astrophysics Data System (ADS)

    Tileli, Vasiliki; Duchamp, Martial; Axelsson, Anna-Karin; Valant, Matjaz; Dunin-Borkowski, Rafal E.; Alford, Neil Mcn.

    2014-11-01

    The performance of complex oxide heterostructures depends primarily on the interfacial coupling of the two component structures. This interface character inherently varies with the synthesis method and conditions used since even small composition variations can alter the electronic, ferroelectric, or magnetic functional properties of the system. The focus of this article is placed on the interface character of a pulsed laser deposited CoFe2O4/BaTiO3 thin film. Using a range of state-of-the-art transmission electron microscopy methodologies, the roles of substrate morphology, interface stoichiometry, and cation intermixing are determined on the atomic level. The results reveal a surprisingly uneven BaTiO3 substrate surface formed after the film deposition and Fe atom incorporation in the top few monolayers inside the unit cell of the BaTiO3 crystal. Towards the CoFe2O4 side, a disordered region extending several nanometers from the interface was revealed and both Ba and Ti from the substrate were found to diffuse into the spinel layer. The analysis also shows that within this somehow incompatible composite interface, a different phase is formed corresponding to the compound Ba2Fe3Ti5O15, which belongs to the ilmenite crystal structure of FeTiO3 type. The results suggest a chemical activity between these two oxides, which could lead to the synthesis of complex engineered interfaces.The performance of complex oxide heterostructures depends primarily on the interfacial coupling of the two component structures. This interface character inherently varies with the synthesis method and conditions used since even small composition variations can alter the electronic, ferroelectric, or magnetic functional properties of the system. The focus of this article is placed on the interface character of a pulsed laser deposited CoFe2O4/BaTiO3 thin film. Using a range of state-of-the-art transmission electron microscopy methodologies, the roles of substrate morphology, interface

  14. Thermodynamic analysis of compatibility of several reinforcement materials with FeAl alloys

    NASA Technical Reports Server (NTRS)

    Misra, Ajay K.

    1988-01-01

    Chemical compatibility of several reinforcement materials with FeAl alloys within the concentration range 40 to 50 at pct Al have been analyzed from thermodynamic considerations at 1173 and 1273 K. The reinforcement materials considered in this study include carbides, borides, oxides, nitrides, and silicides. Although several chemically compatible reinforcement materials are identified, the coefficients of thermal expansion for none of these materials match closely with that of FeAl alloys and this might pose serious problems in the design of composite systems based on FeAl alloys.

  15. Thermoelectric and Magnetic Properties of Pt-Substituted {BaFe_{4-{x}}Pt_{{x}}Sb_{12}} Compounds

    NASA Astrophysics Data System (ADS)

    Sertkol, Murat; Ballıkaya, Sedat; Aydoğdu, Fatih; Güler, Adil; Özdemir, Mustafa; Öner, Yıldırhan

    2017-01-01

    {BaFe_{4-{x}}Pt_{{x}}Sb_{12}} ( x = 0, 0.1, 0.2) compounds were prepared by melting and annealing, followed by a spark plasma sintering method. Low-temperature thermoelectric and magnetic properties were investigated based on Seebeck coefficient, electrical and thermal conductivity and magnetization measurements. The structural properties of {BaFe_{4-{x}}Pt_{{x}}Sb_{12}} ( x = 0, 0.1, 0.2) compounds were ascertained by powder x-ray diffraction analysis, confirming that all samples have a main phase of a skutterudite structure with the space group Im{bar{3}}. The lattice parameters obtained, 9.202(5), 9.199(5) and 9.202(1) Å for x = 0, 0.1 and 0.2, respectively, were found consistent with literature. The Seebeck coefficient sign shows that holes are dominant carriers in all compounds. The local maximum Seebeck coefficient was observed around 50 K which may be a trace of paramagnon-drag effect of charge carriers. Thermal conductivity and electrical resistivity measurements were carried out between 4.2 and 300 K. Temperature dependence of electrical resistivity reflects that all samples show semi-metallic behavior in our temperature range of 4.2-300 K. Samples for x = 0.1 and x = 0.2 show Kondo-like behavior. In magnetization measurement, we observe that there are two successive magnetic transitions in Pt-substituted compounds; however, there is only one (transition from a paramagnetic state to long-range magnetic ordering) in Pt-free compounds. In Pt-substituted compounds, the first transition appears at T _{ c} = 48 K. In addition, the second transition is observed at T _{ irr} = 30 K where an intermediate state is observed before the magnetic ordering transforms to an irreversible ferromagnetic state. We concluded that Pt substitution on the Fe side effectual on the thermoelectric and magnetic properties of {BaFe_{4-{x}}Pt_{{x}}Sb_{12}} ( x = 0, 0.1, 0.2) compounds.

  16. Application of FORC distributions to the study of magnetic interactions in ferrites of composition Ba1-xLaFe12-xCoxO19

    NASA Astrophysics Data System (ADS)

    Oliva, M. I.; Bercoff, P. G.; Bertorello, H. R.

    Magnetic interactions in hexaferrite samples of Ba1-xLaFe12-xCoxO19 composition were studied. The precursor powders—barium carbonate (BaCO3), lanthanum oxide (La 2O 3), hematite (Fe 2O 3) and cobalt acetate—were milled for 100 h in air atmosphere and heat-treated for 1 h at 1000C. The structural characterization was performed by X-ray diffraction. The FORC distributions show a single peak at high switching fields, indicating that the substituted systems are formed by weakly interacting particles. La excess induces the decoupling of the particles.

  17. Interface induced out-of-plane magnetic anisotropy in magnetoelectric BiFeO3-BaTiO3 superlattices

    NASA Astrophysics Data System (ADS)

    Lazenka, Vera; Jochum, Johanna K.; Lorenz, Michael; Modarresi, Hiwa; Gunnlaugsson, Haraldur P.; Grundmann, Marius; Van Bael, Margriet J.; Temst, Kristiaan; Vantomme, André

    2017-02-01

    Room temperature magnetoelectric BiFeO3-BaTiO3 superlattices with strong out-of-plane magnetic anisotropy have been prepared by pulsed laser deposition. We show that the out-of-plane magnetization component increases with the increasing number of double layers. Moreover, the magnetoelectric voltage coefficient can be tuned by varying the number of interfaces, reaching a maximum value of 29 V/cm Oe for the 20×BiFeO3-BaTiO3 superlattice. This enhancement is accompanied by a high degree of perpendicular magnetic anisotropy, making the latter an ideal candidate for the next generation of data storage devices.

  18. Preparation of Al-Cu-Fe-(Sn,Si) quasicrystalline bulks by laser multilayer cladding

    NASA Astrophysics Data System (ADS)

    Feng, Li-ping; Fleury, Eric; Zhang, Guo-sheng

    2012-05-01

    (Al65Cu20Fe15)100- x Sn x ( x=0, 12, 20, 30) and Al57Si10Cu18Fe15 powders were cladded on a medium carbon steel (45# steel) substrate by laser multilayer cladding, respectively. The phases and properties of the produced quasicrystalline bulks were investigated. It was found that the main phases in the Al65Cu20Fe15 sample were crystalline λ-Al13Fe4 and icosahedral quasicrystal together with a small volume fraction of θ-Al2Cu phase. The volume fraction of icosahedral phase decreased as the Sn content in the (Al65Cu20Fe15)100- x Sn x samples increased owing to the formation of β-CuSn phase. The increase of Sn content improved the brittleness of the quasicrystal samples. The morphology of the solidification microstructure in the Al57Si10Cu18Fe15 sample changed from elongated shape to spherical shape due to the addition of Si. The nanohardness of the laser multilayer cladded quasicrystal samples was equal to that of the as-cast sample prepared by vacuum quenching. In terms of hardness, the laser cladded Al57Si10Cu18Fe15 quasicrystalline alloy has the highest value among all the investigated samples.

  19. Specific heat discontinuity, ΔC, at Tc in BaFe2(As0.7P0.3)2-consistent with unconventional superconductivity.

    PubMed

    Kim, J S; Stewart, G R; Kasahara, S; Shibauchi, T; Terashima, T; Matsuda, Y

    2011-06-08

    We report the specific heat discontinuity, ΔC/T(c), at T(c) = 28.2 K of a collage of single crystals of BaFe(2)(As(0.7)P(0.3))(2) and compare the measured value of 38.5 mJ mol(-1) K(-2) with other iron pnictide and iron chalcogenide (FePn/Ch) superconductors. This value agrees well with the trend established by Bud'ko, Ni and Canfield, who found that ΔC/T(c) is proportional to aT(c)(2) for 14 examples of doped Ba(1 - x)K(x)Fe(2)As(2) and BaFe(2 - x)TM(x)As(2), where the transition metal TM = Co and Ni. We extend their analysis to include all the FePn/Ch superconductors for which ΔC/T(c) is currently known and find ΔC/T(c) is proportional to aT(c)(1.9) and a = 0.083 mJ mol(-1) K(-4). A comparison with the elemental superconductors with T(c) > 1 K and with A-15 superconductors shows that, contrary to the FePn/Ch superconductors, electron-phonon-coupled conventional superconductors exhibit a significantly different dependence of ΔC on T(c), namely ΔC/T(c) is proportional to aT(c)(1.9). However ΔC/γT(c) appears to be comparable in all three classes (FePn/Ch, elemental and A-15) of superconductors with, for example, ΔC/γT(c) = 2.4 for BaFe(2)(As(0.7)P(0.3))(2). A discussion of the possible implications of these phenomenological comparisons for the unconventional superconductivity believed to exist in the FePn/Ch is given.

  20. Coexisting charge and magnetic orders in the dimer-chain iridate Ba5AlIr2O11

    DOE PAGES

    Terzic, J.; Wang, J. C.; Ye, Feng; ...

    2015-06-29

    In this paper, we have synthesized and studied single-crystal Ba5AlIr2O11 that features dimer chains of two inequivalent octahedra occupied by tetravalent Ir4+(5d5) and pentavalent Ir5+(5d4) ions, respectively. Ba5AlIr2O11 is a Mott insulator that undergoes a subtle structural phase transition near TS=210K and a magnetic transition at TM=4.5K; the latter transition is surprisingly resistant to applied magnetic fields μoH≤12T but more sensitive to modest applied pressure (dTM/dp ≈ +0.61K/GPa). All results indicate that the phase transition at TS signals an enhanced charge order that induces electrical dipoles and strong dielectric response near TS. It is clear that the strong covalency andmore » spin-orbit interaction (SOI) suppress double exchange in Ir dimers and stabilize a novel magnetic state that is neither S=3/2 nor J=1/2, but rather lies in an “intermediate” regime between these two states. Finally, the novel behavior of Ba5AlIr2O11 therefore provides unique insights into the physics of SOI along with strong covalency in competition with double-exchange interactions of comparable strength.« less

  1. Activities of the components in a spinel solid solution of the Fe-Al-O system

    NASA Astrophysics Data System (ADS)

    Lykasov, A. A.; Kimyashev, A. A.

    2011-09-01

    The conditions of the equilibrium between the Fe3O4-FeAl2O4 solution and wustite are determined by measuring the EMF of galvanic cells containing a solid electrolyte, and the activities of the components in the Fe3O4-FeAl2O4 solution are calculated by treating the results of the experiment on the equilibrium between the spinel solution and wustite. Their properties are found to be different from those of ideal solutions at temperatures of 1000-1300 K. A significant positive deviation from the Raoult's law is believed to indicate the tendency of the solution to decompose. The experimental data are treated in terms of the theory of regular solutions, assuming the energy of mixing to be a function of temperature only. The critical temperature of decomposition for the Fe3O4-FeAl2O4 solution is found to be 1084 K.

  2. Experiments of eliminating the destructive effects of excessive Fe inclusions for Al secondary products

    NASA Astrophysics Data System (ADS)

    Sun, D. Q.; Dai, G. H.; Geng, F.; Yang, K.

    2017-02-01

    Excessive Fe content in Al alloys caused the serious decline of mechanical properties, such as the ductility and impact toughness. Carried out the experiments of eliminating the destructive effects of excessive Fe content by flux-adding technology, which including removing a part of Fe content from Al scrap melt and modifying the morphology of Fe rich precipitates. The experimental results showed that, the ratio of removing Fe element was above 20%, and the morphology of Fe rich precipitates changed from Lamellar to bulk or lath precipitations under the process parameters: the fluxing-agents composed of borax, and MnCl2 (mixed by mass ratio of 1:1), and the adding amount of fluxing-agents was about 1.5%; thrown the fluxing-agents into the Al scrap melt by powder injection process and kept for 30 min.

  3. Band-gap tuning and magnetic properties of heterovalent ions (Ba, Sr and Ca) substituted BiFeO3 nanoparticles

    NASA Astrophysics Data System (ADS)

    Chauhan, Sunil; Kumar, Manoj; Katyal, S. C.

    2016-05-01

    A Comparative study of heterovalent Ba, Sr and Ca ions substitution on the structural, vibrational, optical and magnetic properties of BiFeO3 nanoparticles was carried out. The distorted rhombohedral structure was confirmed from both X-ray diffraction and Raman spectroscopy techniques in pure BiFeO3 and Bi0.85A0.15FeO3 (A= Ba, Sr and Ca) samples. UV-Visible spectroscopy results show that the band-gap of BiFeO3 nanoparticles can be tuned by heterovalent ions substitution from 2.12 eV for BiFeO3 to 2.10, 2.06 and 2.03 eV for Ca, Sr and Ba substituted BiFeO3 nanoparticles respectively. The magnetic measurements indicate enhancement in magnetization for heterovalent A2+ substituted BiFeO3 samples and the magnetization increases with increase of ionic radius of the substituted ions.

  4. Influence of Co-substitution on the structural and magnetic properties of nanocrystalline Ba0.5Sr0.5Fe12O19

    NASA Astrophysics Data System (ADS)

    Ezhil Vizhi, R.; Harikrishnan, V.; Saravanan, P.; Rajan Babu, D.

    2016-10-01

    One-step citrate gel combustion method followed by annealing (800 °C/2 h) was employed to synthesize cobalt substituted barium strontium hexaferrite with a chemical composition of Ba0.5Sr0.5Fe12-xCoxO19 (x=0, 0.5, 0.7, and 0.9). A combination of thermo-gravimetric analysis and differential scanning calorimetry was employed to understand the thermo-chemical behavior of Ba0.5Sr0.5Fe12O19. X-ray diffraction (XRD) was used to evaluate the hexagonal phase evolution for the barium strontium ferrite nanopowders and a formation of secondary phase: α-Fe2O3 is evident for the Ba0.5Sr0.5Fe12O19. Raman spectroscopy confirmed the presence of different sublattices of Fe3+ present in the hexaferrite structure. Fourier transform infrared spectroscopy demonstrated the usual stretching vibrations of tetrahedral and octahedral M-O bands. The morphology and chemical composition of the samples were analyzed by transmission electron microscopy and field emission scanning electron microscopy attached with energy dispersive X-ray analysis, respectively. Selected area electron diffraction studies showed the nanocrystalline nature of the samples. The magnetic parameters such as saturation magnetization MS, coercivity, HC and remanent magnetization, MR were estimated from the hysteresis loops. Maximum value of MS (70.5 emu/g) was obtained for the Ba0.5Sr0.5Fe11.5Co0.5O19 nanoparticles. A possible growth mechanism on the crystallization of Ba0.5Sr0.5Fe12O19 hexagonal platelets during the citrate gel combustion synthesis is highlighted.

  5. One-step synthesis of homogeneous BaFe{sub 12}O{sub 19}/Y{sub 3}Fe{sub 5}O{sub 12} composite powders

    SciTech Connect

    Liu, Miao; Yang, Haibo Lin, Ying; Yang, Yanyan

    2014-12-15

    Highlights: • A simple one-step sol–gel method was used to synthesize composite magnets. • The composite powders show good homogeneity and exchange coupling. • The M{sub r}/M{sub s} value increases with the BaM concentration. - Abstract: BaFe{sub 12}O{sub 19}/Y{sub 3}Fe{sub 5}O{sub 12} (BaM/YIG) composite powders were synthesized via a simple one-step sol–gel method. The phase composition and morphology of the as-synthesized composite powders were characterized using an X-ray diffractometer and a scanning electron microscopy equipped with energy dispersive X-ray spectroscopy. The magnetic properties of the composite powders were investigated by a vibrating sample magnetometer. Compared with the composite powders prepared by the conventional physical mixing method, the BaM/YIG composite powders show better homogeneity and exchange coupling.

  6. Interplane resistivity of underdoped single crystals (Ba1-xKx)Fe2As2(0<= x < 0.34)

    SciTech Connect

    Tanatar, M A; Straszheim, W E; Kim, Hyunsoo; Murphy, J; Spyrison, N; Blomberg, E C; Cho, K; Reid, J -Ph; Shen, Bing; Taillefer, Louis; Wen, Hai-Hu; Prozorov, R

    2014-04-01

    The temperature-dependent interplane resistivity ρc(T) was measured in the hole-doped iron arsenide superconductor (Ba1-xKx)Fe2As2 over a doping range from parent compound to optimal doping at Tc≈38 K, 0≤x≤0.34. The measurements were undertaken on high-quality single crystals grown from FeAs flux. The coupled magnetic/structural transition at TSM leads to a clear accelerated decrease of ρc(T) on cooling in samples with Tc<26 K (x<0.25). This decrease in the hole-doped material is in notable contrast to the increase in ρc(T) in the electron-doped Ba(Fe1-xCox)Fe 2As2 and isoelectron-substituted BaFe2(As1-xPx)2. TSM decreases very sharply with doping, dropping from Ts=71 K to zero on increase of Tc from approximately 25 to 27 K. ρc(T) becomes linear in T close to optimal doping. The broad crossover maximum in ρc(T), found in the parent BaFe2As2 at around Tmax~200 K, shifts to higher temperature ~250 K with doping of x=0.34. The maximum shows clear correlation with the broad crossover feature found in the temperature-dependent in-plane resistivity ρa(T). The evolution with doping of Tmax in (Ba1-xKx)Fe2As2 is in notable contrast with both the rapid suppression of Tmax found in Ba(Fe1-xTx)2As2 (T=Co,Rh,Ni,Pd) and its rapid increase in BaFe2(As1-xPx)2. This observation suggests that pseudogap features are much stronger in hole-doped than in electron-doped iron-based superconductors, revealing significant electron-hole doping asymmetry similar to that in the cuprates.

  7. Influence of Be and Al on the magnetostrictive behavior of FeGa alloys

    SciTech Connect

    Mungsantisuk, Pinai; Corson, Robert P.; Guruswamy, Sivaraman

    2005-12-15

    The rare-earth-free body-centered-cubic FeGa-based alloys have an attractive combination of large low-field magnetostriction at room temperature, good mechanical properties, low hysteresis, and relatively low cost for use in sensor and actuator devices. This paper examines the influence of partially substituting Ga in FeGa alloys with Be and Al on their magnetostrictive behavior. Magnetic and magnetostrictive properties of the various ternary FeGaAl and FeGaBe alloys prepared by directional growth process are presented. It is shown that substitution of Ga with Al and Be can be made in FeGa alloys in certain composition ranges without a significant reduction in magnetostriction. Minimal reductions in magnetostriction when Ga is partially substituted by smaller Be or larger Al atoms in certain composition ranges indicate that local electronic environments are more important and that the effects of Ga and Be are additive.

  8. Point defect concentrations and solid solution hardening in NiAl with Fe additions

    SciTech Connect

    Pike, L.M.; Chang, Y.A.; Liu, C.T.

    1997-08-01

    The solid solution hardening behavior exhibited when Fe is added to NiAl is investigated. This is an interesting problem to consider since the ternary Fe additions may choose to occupy either the Ni or the Al sublattice, affecting the hardness at differing rates. Moreover, the addition of Fe may affect the concentrations of other point defects such as vacancies and Ni anti-sites. As a result, unusual effects ranging from rapid hardening to solid solution softening are observed. Alloys with varying amounts of Fe were prepared in Ni-rich (40 at. % Al) and stoichiometric (50 at. % Al) compositions. Vacancy concentrations were measured using lattice parameter and density measurements. The site occupancy of Fe was determined using ALCHEMI. Using these two techniques the site occupancies of all species could be uniquely determined. Significant differences in the defect concentrations as well as the hardening behavior were encountered between the Ni-rich and stoichiometric regimes.

  9. Influence of Be and Al on the magnetostrictive behavior of FeGa alloys

    NASA Astrophysics Data System (ADS)

    Mungsantisuk, Pinai; Corson, Robert P.; Guruswamy, Sivaraman

    2005-12-01

    The rare-earth-free body-centered-cubic FeGa-based alloys have an attractive combination of large low-field magnetostriction at room temperature, good mechanical properties, low hysteresis, and relatively low cost for use in sensor and actuator devices. This paper examines the influence of partially substituting Ga in FeGa alloys with Be and Al on their magnetostrictive behavior. Magnetic and magnetostrictive properties of the various ternary FeGaAl and FeGaBe alloys prepared by directional growth process are presented. It is shown that substitution of Ga with Al and Be can be made in FeGa alloys in certain composition ranges without a significant reduction in magnetostriction. Minimal reductions in magnetostriction when Ga is partially substituted by smaller Be or larger Al atoms in certain composition ranges indicate that local electronic environments are more important and that the effects of Ga and Be are additive.

  10. Slow-release formulations of the herbicide picloram by using Fe-Al pillared montmorillonite.

    PubMed

    Marco-Brown, Jose L; Undabeytia, Tomás; Torres Sánchez, Rosa M; Dos Santos Afonso, María

    2017-04-01

    Slow-release formulations of the herbicide picloram (PCM, 4-amino-3,5,6-trichloropyridine-2-carboxylic acid) were designed based on its adsorption on pillared clays (pillared clays (PILCs)) for reducing the water-polluting risk derived from its use in conventional formulations. Fe-Al PILCs were synthesized by the reaction of Na(+)-montmorillonite (SWy-2) with base-hydrolyzed solutions of Fe and Al. The Fe/(Fe + Al) ratios used were 0.15 and 0.50. The PCM adsorption isotherms on Fe-Al PILCs were well fitted to Langmuir and Freundlich models. The PCM adsorption capacity depended on the Fe content in the PILCs. Slow-release formulations were prepared by enhanced adsorption of the herbicide from PCM-cyclodextrin (CD) complexes in solution. CDs were able to enhance up to 2.5-fold the solubility of PCM by the formation of inclusion complexes where the ring moiety of the herbicide was partially trapped within the CD cavity. Competitive adsorption of anions such as sulfate, phosphate, and chloride as well as the FTIR analysis of PCM-PILC complexes provided evidence of formation of inner sphere complexes of PCM-CD on Fe-Al PILCs. Release of the herbicide in a sandy soil was lower from Fe-Al PILC formulations relative to a PCM commercial formulation.

  11. A Pyrolitic Lower Mantle with (Mg,Fe3+)(Si,Al3+)O3 Bridgmanite

    NASA Astrophysics Data System (ADS)

    Wang, X.; Tsuchiya, T.

    2014-12-01

    To better understand the Earth's lower mantle (LM), thermodynamic properties (TDPs) of LM minerals should be illustrated clearly. We have so far reported the TDPs of Fe (and Al)-bearing MgO, MgSiO3 bridgmanite (Br) and post bridgmanite [1-5] by using the internally consistent LSDA+U method and the lattice dynamics method. In this work, two spin states, the high (HS) and low spin (LS) state, and several possible distribution configurations are considered in the LM pressure range. For Fe incorporated in Br, only Fe3+ at the Si site undergoes a HS to LS transition. However, this is suppressed by Al incorporation, because Al3+ prefers the Si site and attracts HS Fe3+ at the adjacent Mg site forming Fe3+-Al3+ pair. Br with geophysically relevant 6.25 mol% Fe2+ or Fe3+-Al3+ pair is found vibrationally stable. Incorporation of these elements increases the Br volume a little but gives marginal effects on the TDPs. Simulated densities, adiabatic bulk moduli, and bulk sound velocities of possible LM mineral aggregations show that a composition close to pyrolite with (Mg,Fe3+)(Si,Al3+)O3 Br is accountable for the reference Earth model, while Fe2+-bearing Br instead gives unignorable disagreements in deeper part. Neither Si-richer nor Si-poorer composition improves the disagreements. This indicates that Fe in LM bridgmanite should predominantly be ferric acquiring the HS state, and pyrolitic composition with (Mg,Fe3+)(Si,Al3+)O3 Br is a reasonable LM model. References:[1] A. Metsue, and T. Tsuchiya, J. Geophys. Res. 116, B08207 (2011). [2] A. Metsue, and T. Tsuchiya, Geophys. J. Int. 190, 310 (2012). [3] H. Fukui, T. Tsuchiya, and A. Q. R. Baron, J. Geophys. Res. 117, B12202 (2012). [4] T. Tsuchiya, and X. Wang, J. Geophys. 118, 83 (2013). [5] X. Wang, and T. Tsuchiya, under reviewing.

  12. Development of ODS FeCrAl alloys for accident-tolerant fuel cladding

    SciTech Connect

    Dryepondt, Sebastien N.; Hoelzer, David T.; Pint, Bruce A.; Unocic, Kinga A.

    2015-09-18

    FeCrAl alloys are prime candidates for accident-tolerant fuel cladding due to their excellent oxidation resistance up to 1400 C and good mechanical properties at intermediate temperature. Former commercial oxide dispersion strengthened (ODS) FeCrAl alloys such as PM2000 exhibit significantly better tensile strength than wrought FeCrAl alloys, which would alloy for the fabrication of a very thin (~250 m) ODS FeCrAl cladding and limit the neutronic penalty from the replacement of Zr-based alloys by Fe-based alloys. Several Fe-12-Cr-5Al ODS alloys where therefore fabricated by ball milling FeCrAl powders with Y2O3 and additional oxides such as TiO2 or ZrO2. The new Fe-12Cr-5Al ODS alloys showed excellent tensile strength up to 800 C but limited ductility. Good oxidation resistance in steam at 1200 and 1400 C was observed except for one ODS FeCrAl alloy containing Ti. Rolling trials were conducted at 300, 600 C and 800 C to simulate the fabrication of thin tube cladding and a plate thickness of ~0.6mm was reached before the formation of multiple edge cracks. Hardness measurements at different stages of the rolling process, before and after annealing for 1h at 1000 C, showed that a thinner plate thickness could likely be achieved by using a multi-step approach combining warm rolling and high temperature annealing. Finally, new Fe-10-12Cr-5.5-6Al-Z gas atomized powders have been purchased to fabricate the second generation of low-Cr ODS FeCrAl alloys. The main goals are to assess the effect of O, C, N and Zr contents on the ODS FeCrAl microstructure and mechanical properties, and to optimize the fabrication process to improve the ductility of the 2nd gen ODS FeCrAl while maintaining good mechanical strength and oxidation resistance.

  13. Electronic structure and soft magnetic properties of Se/FeSiAl (110) films

    NASA Astrophysics Data System (ADS)

    Schwindt, V. Cardoso; Ardenghi, J. S.; Bechthold, P.; Juan, A.; Batic, B. Setina; Jenko, M.; González, E. A.; Jasen, P. V.

    2015-11-01

    The Se adsorption at different coverages on DO3 FeSiAl(110) surface is studied using density functional theory (DFT). Se adsorption is favorable in almost all surface high-symmetry sites, except for the bridge site formed by Fe-Si atoms. The most stable is a hollow site formed by four Fe atoms with adsorption energy of -5.30 eV. When the coverages increase, the energies decrease in the case of hollow sites. The surface present a reconstruction after Se adsorption, being the most important at 1/2 ML. The local magnetic moment for Fe atoms increase for the type A (all nearst neighbours (nn) are Fe atoms) and decrease for the type B (nn are Fe, Si and Al atoms). The most affected metal orbitals are Fe 4s and 4p. In the case of the hollow site the surface Fe-Fe bond is weakened after Se adsorption. A Fe-Se bond is developed at all coverages in both sites being the most important on top (dFe-Se = 2.23 Å, OP: 0.774 at 1/4 ML). The first and second layer Fe-Fe bond increase at 1/4 ML and decrease at 1/2 and 1 ML. Small Se-Se bonding interaction appear at 1/2 ML and increase noticeable for 1 ML. For the top site, the Se-Se bond appears at all coverage. The Fe-Fe surface bonds also decrease its strength with respect to the clean surface at all coverage. The first and second layer Fe-Fe bond increase at all coverage.

  14. Anomalous behaviour of critical fields near a superconducting quantum critical point in BaFe2(As1-xPx)2

    NASA Astrophysics Data System (ADS)

    Putzke, C.; Carrington, A.; Walmsley, P.; Malone, L.; Fletcher, J. D.; See, P.; Vignolles, D.; Proust, C.; Badoux, S.; Kasahara, S.; Mazukami, Y.; Shibauchi, T.; Matsuda, Y.

    2014-03-01

    BaFe2(As1-xPx)2 presents one of the cleanest and clearest systems in which to study the influence of quantum critical fluctuations on high temperature superconductivity. In this material a sharp maximum in the magnetic penetration depth has been found at the quantum critical point (QCP x = 0 . 3) where Tc is maximal1. Specific heat and de Haas-van Alphen effect measurements2 show that this peak is driven by a corresponding increase in the quasiparticle effective mass. Based on these previous results a simple one-band theory would suggest that at the QCP we should expect a large increase in Hc 2 and a corresponding dip in Hc 1 . Actual measurements of these critical fields, which we present here, shows quite different behavior which we suggest is caused by an anomalous enhancement in the vortex core energy close to the QCP. 1 K.Hashimoto et.al., Science 336, 1554 (2012) 2 P.Walmsley, C.Putzke et.al., Phys. Rev. Lett. 110, 257002 (2013) This work was supported by the Engineering and Physical Sciences Research Council, EuroMagNET II, and KAKENHI from JSPS.

  15. Composition dependence of the electronic properties of Al-Cu-Fe and Al-Cu-Ru-Si semimetallic quasicrystals

    NASA Astrophysics Data System (ADS)

    Pierce, F. S.; Bancel, P. A.; Biggs, B. D.; Guo, Q.; Poon, S. J.

    1993-03-01

    Electronic transport properties and specific heats of ordered icosahedral phase alloys in the Al-Cu-Ru-Si and Al-Cu-Fe systems are examined, and comparison with high-quality rhombohedral (3/2) approximant phase samples of Al-Cu-Fe is made. Strong temperature dependence and sensitivity to composition changes of these properties are observed. The similarity of transport properties between the icosahedral (i) and rhombohedral (r) phases of Al62.5Cu26.5Fe11 is noted. The results can be qualitatively interpreted in terms of band structure. There appears to be sufficient evidence for a rapidly varying conductivity spectrum σ(E) in the ordered i phases. However, important questions concerning the physics of these semimetallic quasicrystals remain to be answered.

  16. Quantum many-body intermetallics: Phase stability of Fe3Al and small-gap formation in Fe2VAl

    NASA Astrophysics Data System (ADS)

    Kristanovski, Oleg; Richter, Raphael; Krivenko, Igor; Lichtenstein, Alexander I.; Lechermann, Frank

    2017-01-01

    Various intermetallic compounds harbor subtle electronic correlation effects. To elucidate this fact for the Fe-Al system, we perform a realistic many-body investigation based on a combination of density functional theory with dynamical mean-field theory in a charge self-consistent manner. A better characterization and understanding of the phase stability of bcc-based D 03-Fe3Al through an improved description of the correlated charge density and the magnetic energy is achieved. Upon replacement of one Fe sublattice with V, the Heusler compound Fe2VAl is realized, known to display bad-metal behavior and increased specific heat. Here we document a charge-gap opening at low temperatures in line with previous experimental work. The gap structure does not match conventional band theory and is reminiscent of (pseudo)gap characteristics in correlated oxides.

  17. Phase equilibria and structural investigations in the system Al-Fe-Si.

    PubMed

    Marker, Martin C J; Skolyszewska-Kühberger, Barbara; Effenberger, Herta S; Schmetterer, Clemens; Richter, Klaus W

    2011-12-01

    The Al-Fe-Si system was studied for an isothermal section at 800 °C in the Al-rich part and at 900 °C in the Fe-rich part, and for half a dozen vertical sections at 27, 35, 40, 50 and 60 at.% Fe and 5 at.% Al. Optical microscopy and powder X-ray diffraction (XRD) was used for initial sample characterization, and Electron Probe Microanalysis (EPMA) and Scanning Electron Microscopy (SEM) of the annealed samples was used to determine the exact phase compositions. Thermal reactions were studied by Differential Thermal Analysis (DTA). Our experimental results are generally in good agreement with the most recent phase diagram versions of the system Al-Fe-Si. A new ternary high-temperature phase τ12 (cF96, NiTi2-type) with the composition Al48Fe36Si16 was discovered and was structurally characterized by means of single-crystal and powder XRD. The variation of the lattice parameters of the triclinic phase τ1 with the composition Al2+x Fe3Si3-x (-0.3 < x < 1.3) was studied in detail. For the binary phase FeSi2 only small solubility of Al was found in the low-temperature modification LT-FeSi2 (ζβ ) but significant solubility in the high-temperature modification HT-FeSi2 (ζα ) (8.5 at.% Al). It was found that the high-temperature modification of FeSi2 is stabilized down to much lower temperature in the ternary, confirming earlier literature suggestions on this issue. DTA results in four selected vertical sections were compared with calculated sections based on a recent CALPHAD assessment. The deviations of liquidus values are significant suggesting the need for improvement of the thermodynamic models.

  18. Phase separation in equiatomic AlCoCrFeNi high-entropy alloy.

    PubMed

    Manzoni, A; Daoud, H; Völkl, R; Glatzel, U; Wanderka, N

    2013-09-01

    The microstructure of the as-cast AlCoCrFeNi high entropy alloy has been investigated by transmission electron microscopy and atom probe tomography. The alloy shows a very pronounced microstructure with clearly distinguishable dendrites and interdendrites. In both regions a separation into an Al-Ni rich matrix and Cr-Fe-rich precipitates can be observed. Moreover, fluctuations of single elements within the Cr-Fe rich phase have been singled out by three dimensional atom probe measurements. The results of investigations are discussed in terms of spinodal decomposition of the alloying elements inside the Cr-Fe-rich precipitates.

  19. Structural, optical and magnetic properties of polycrystalline BaTi{sub 1-x}Fe{sub x}O{sub 3} ceramics

    SciTech Connect

    Dang, N. V.; Thanh, T. D.; Hong, L. V.; Lam, V. D.; Phan, The-Long

    2011-08-15

    Polycrystalline BaTi{sub 1-x}Fe{sub x}O{sub 3} ceramics have been prepared by conventional solid-state reaction. Their structural, optical and magnetic properties are then studied by means of x-ray diffraction (XRD), Raman scattering (RS) and absorption spectrometers, and a physical properties measurement system. Detailed analyses of XRD patterns and RS spectra reveal the phase separation of the tetragonal-hexagonal structure at a threshold concentration of x = 0.005. The increase in the Fe-doping content (x) leads to development of the hexagonal phase. Magnetic measurements prove that many BaTi{sub 1-x}Fe{sub x}O{sub 3} samples exhibit the room-temperature ferromagnetic order, excepting the samples with x = 0.02-0.06. The ferromagnetism depends strongly on concentration of Fe impurities. The nature of this ferromagnetism is discussed by means of the results of structural analyses and optical absorption spectra.

  20. A vibrational spectroscopic study of the phosphate mineral lulzacite Sr2Fe2+(Fe2+,Mg)2Al4(PO4)4(OH)10

    NASA Astrophysics Data System (ADS)

    Frost, Ray L.; López, Andrés; Belotti, Fernanda M.; Xi, Yunfei; Scholz, Ricardo

    2014-06-01

    The mineral lulzacite from Saint-Aubin des Chateaux mine, France, with theoretical formula Sr2Fe2+(Fe2+,Mg)2Al4(PO4)4(OH)10 has been studied using a combination of electron microscopy with EDX and vibrational spectroscopic techniques. Chemical analysis shows a Sr, Fe, Al phosphate with minor amounts of Ga, Ba and Mg. Raman spectroscopy identifies an intense band at 990 cm-1 with an additional band at 1011 cm-1. These bands are attributed to the PO43-ν1 symmetric stretching mode. The ν3 antisymmetric stretching modes are observed by a large number of Raman bands. The Raman bands at 1034, 1051, 1058, 1069 and 1084 together with the Raman bands at 1098, 1116, 1133, 1155 and 1174 cm-1 are assigned to the ν3 antisymmetric stretching vibrations of PO43- and the HOPO32- units. The observation of these multiple Raman bands in the symmetric and antisymmetric stretching region gives credence to the concept that both phosphate and hydrogen phosphate units exist in the structure of lulzacite. The series of Raman bands at 567, 582, 601, 644, 661, 673 and 687 cm-1 are assigned to the PO43-ν2 bending modes. The series of Raman bands at 437, 468, 478, 491, 503 cm-1 are attributed to the PO43- and HOPO32-ν4 bending modes. No Raman bands of lulzacite which could be attributed to the hydroxyl stretching unit were observed. Infrared bands at 3511 and 3359 cm-1 are ascribed to the OH stretching vibration of the OH units. Very broad bands at 3022 and 3299 cm-1 are attributed to the OH stretching vibrations of water. Vibrational spectroscopy offers insights into the molecular structure of the phosphate mineral lulzacite.

  1. Single crystals of LnFeAsO 1-xF x (Ln = La, Pr, Nd, Sm, Gd) and Ba 1-xRb xFe 2As 2: Growth, structure and superconducting properties

    NASA Astrophysics Data System (ADS)

    Karpinski, J.; Zhigadlo, N. D.; Katrych, S.; Bukowski, Z.; Moll, P.; Weyeneth, S.; Keller, H.; Puzniak, R.; Tortello, M.; Daghero, D.; Gonnelli, R.; Maggio-Aprile, I.; Fasano, Y.; Fischer, Ø.; Rogacki, K.; Batlogg, B.

    2009-05-01

    A review of our investigations on single crystals of LnFeAsO 1-xF x (Ln = La, Pr, Nd, Sm, Gd) and Ba 1-xRb xFe 2As 2 is presented. A high-pressure technique has been applied for the growth of LnFeAsO 1-xF x crystals, while Ba 1-xRb xFe 2As 2 crystals were grown using a quartz ampoule method. Single crystals were used for electrical transport, structure, magnetic torque and spectroscopic studies. Investigations of the crystal structure confirmed high structural perfection and show incomplete occupation of the (O, F) position in superconducting LnFeAsO 1-xF x crystals. Resistivity measurements on LnFeAsO 1-xF x crystals show a significant broadening of the transition in high magnetic fields, whereas the resistive transition in Ba 1-xRb xFe 2As 2 simply shifts to lower temperature. The critical current density for both compounds is relatively high and exceeds 2 × 10 9 A/m 2 at 15 K in 7 T. The anisotropy of magnetic penetration depth, measured on LnFeAsO 1-xF x crystals by torque magnetometry is temperature dependent and apparently larger than the anisotropy of the upper critical field. Ba 1-xRb xFe 2As 2 crystals are electronically significantly less anisotropic. Point-Contact Andreev-Reflection spectroscopy indicates the existence of two energy gaps in LnFeAsO 1-xF x. Scanning Tunneling Spectroscopy reveals in addition to a superconducting gap, also some feature at high energy (∼20 meV).

  2. Structural, Magnetic, and Microwave Properties of BaFe10.5Mn1.5O19 Thin Films

    SciTech Connect

    Geiler, A.; Yang, A; Zuo, X; Yoon, S; Chen, Y; Harris, V; Vittoria, C

    2008-01-01

    Epitaxial manganese substituted M-type barium ferrite thin films are deposited by alternating target laser ablation deposition (ATLAD) of BaFe{sub 2}O{sub 4}, Fe{sub 2}O{sub 3}, and MnFe{sub 2}O{sub 4} targets. The crystal structure and the epitaxy of the films are investigated by X-ray diffraction. Surface morphology is studied by atomic force microscopy. Magnetic properties of the films are characterized by vibrating sample magnetometry and magnetization as a function of temperature measurements. Ferromagnetic resonance (FMR) measurements are utilized to study the dynamic properties of the films. Possible mechanisms for main FMR linewidth broadening as a result of Mn substitution, such as increased conductivity and the presence of Jahn-Teller effect associated with octahedrally coordinated Mn{sup 3+} cations, are briefly discussed. Extended absorption X-ray fine structure measurements are performed to determine the cation distribution in the hexagonal unit cell. The observed 15-20% increase in saturation magnetization at 4 K and 50 K increase in the Neel temperature in comparison to bulk reference values are attributed to differences in cation distribution as a result of atomic scale deposition by the ATLAD technique.

  3. High frequency permeability and permittivity spectra of BiFeO{sub 3}/(CoTi)-BaM ferrite composites

    SciTech Connect

    Peng, Yun; Wu, Xiaohan; Li, Qifan; Yu, Ting; Feng, Zekun; Chen, Zhongyan; Su, Zhijuan; Chen, Yajie; Harris, Vincent G.

    2015-05-07

    Low magnetic loss ferrite composites consisting of Ba(CoTi){sub 1.2}Fe{sub 9.6}O{sub 19} and BiFeO{sub 3} (BFO) ferrite were investigated for permeability, permittivity, and high frequency losses at 10 MHz–1 GHz. The phase fraction of BiFeO{sub 3} was quantitatively analyzed by X-ray diffraction measurements. An effective medium approach was employed to predict the effective permeability and permittivity for the ferrite composites, which was found to be in good agreement with experimental data. The experiment demonstrated low magnetic losses (<0.128), modified by BFO phase fraction, while retaining high permeability (∼10.86) at 300 MHz. More importantly, the BFO phase resulted in a reduction of magnetic loss by 32%, as BFO phase increased from 2.7 vol. % to 12.6 vol. %. The effect of BFO phase on magnetic and dielectric properties revealed great potential for use in the miniaturization of high efficiency antennas.

  4. Orbital and Pauli limiting effects in heavily doped Ba0.05K0.95Fe2As2

    NASA Astrophysics Data System (ADS)

    Zhang, S.; Singh, Y. P.; Huang, X. Y.; Chen, X. J.; Dzero, M.; Almasan, C. C.

    We investigated the thermodynamic properties of the Fe-based lightly-disordered superconductor Ba0.05K0.95Fe2As2 in external magnetic field H applied along the FeAs layers (H||ab planes). The superconducting (SC) transition temperature for this doping level is Tc = 6.6 K. Our analysis of the specific heat C(T,H) measured for T

  5. Tuning ferromagnetic BaFe2(PO4)2 through a high Chern number topological phase

    NASA Astrophysics Data System (ADS)

    Song, Young-Joon; Ahn, Kyo-Hoon; Pickett, Warren E.; Lee, Kwan-Woo

    2016-09-01

    There is strong interest in discovering or designing wide-gap Chern insulators. Here we follow a Chern insulator to trivial Mott insulator transition versus interaction strength U in a honeycomb-lattice Fe-based transition-metal oxide, discovering that a spin-orbit coupling energy scale ξ =40 meV can produce and maintain a topologically entangled Chern insulating state against large band structure changes arising from an interaction strength U up to 60 times as large. Within the Chern phase the minimum gap switches from the zone corner K to the zone center Γ while maintaining the topological structure. At a critical strength Uc, the continuous evolution of the electronic structure encounters a gap closing then reopening, upon which the system reverts to a trivial Mott insulating phase. This Chern insulator phase of honeycomb lattice Fe2 +BaFe2 (PO4)2 corresponds to a large Chern number C =-3 that will provide enhanced anomalous Hall conductivity due to the associated three edge states threading through the bulk gap of 80 meV.

  6. Evidence for a Fe3+-rich pyrolitic lower mantle from (Al,Fe)-bearing bridgmanite elasticity data

    NASA Astrophysics Data System (ADS)

    Kurnosov, A.; Marquardt, H.; Frost, D. J.; Ballaran, T. Boffa; Ziberna, L.

    2017-03-01

    The chemical composition of Earth’s lower mantle can be constrained by combining seismological observations with mineral physics elasticity measurements. However, the lack of laboratory data for Earth’s most abundant mineral, (Mg,Fe,Al)(Al,Fe,Si)O3 bridgmanite (also known as silicate perovskite), has hampered any conclusive result. Here we report single-crystal elasticity data on (Al,Fe)-bearing bridgmanite (Mg0.9Fe0.1Si0.9Al0.1)O3 measured using high-pressure Brillouin spectroscopy and X-ray diffraction. Our measurements show that the elastic behaviour of (Al,Fe)-bearing bridgmanite is markedly different from the behaviour of the MgSiO3 endmember. We use our data to model seismic wave velocities in the top portion of the lower mantle, assuming a pyrolitic mantle composition and accounting for depth-dependent changes in iron partitioning between bridgmanite and ferropericlase. We find excellent agreement between our mineral physics predictions and the seismic Preliminary Reference Earth Model down to at least 1,200 kilometres depth, indicating chemical homogeneity of the upper and shallow lower mantle. A high Fe3+/Fe2+ ratio of about two in shallow-lower-mantle bridgmanite is required to match seismic data, implying the presence of metallic iron in an isochemical mantle. Our calculated velocities are in increasingly poor agreement with those of the lower mantle at depths greater than 1,200 kilometres, indicating either a change in bridgmanite cation ordering or a decrease in the ferric iron content of the lower mantle.

  7. Synthesis, crystal structure and electronic properties of the new iron selenide Ba{sub 9}Fe{sub 4}Se{sub 16}

    SciTech Connect

    Berthebaud, David Preethi Meher, K.R.S.; Pelloquin, Denis; Maignan, Antoine

    2014-03-15

    The new ternary selenide Ba{sub 9}Fe{sub 4}Se{sub 16} has been synthesized from the reaction of appropriate amounts of elements at high temperature in a silica sealed tube. The compound crystallizes in the tetragonal space group I4{sub 1}/a with a=10.0068(3) Å and c=35.6415(9) Å, Z=4. It is an isostructural compound to the sulfide α-Ba{sub 9}Fe{sub 4}S{sub 15}, which is a high temperature polymorph of β-Ba{sub 9}Fe{sub 4}Se{sub 15} that belongs to the indefinitely adaptive phases series Ba{sub 3}Fe{sub 1+x}S{sub 5}, 0≤x≤1. X-ray powder diffraction and TEM analyses of the synthesized compound were used to determine the phase composition and the structure. The crystal structure can be viewed as overlapping sections along the c axis. Those sections are formed by the coordination polyhedra around barium atoms which can be described as trigonal prisms and bidisphenoids. Within the sections formed by barium polyhedra, isolated pairs of edge sharing FeSe{sub 4} tetrahedra are found. Magnetic measurements performed on Ba{sub 9}Fe{sub 4}Se{sub 16} indicate an antiferromagnetic behavior with Néel temperature of ∼13 K. Possible influence of air exposure on the magnetic properties is also discussed here. The electric measurements show an insulating behavior below 160 K and the dielectric permittivity and loss tangent at the lowest frequency measured reveal a change of slope very close to T{sub N}. However no magneto dielectric effect was evidenced for magnetic fields of up to 3 T. Activation energy, E{sub A}=0.18 eV, was extracted from the AC conductivity plot in the temperature range of 160–300 K. -- Graphical abstract: Experimental electron diffraction (ED) patterns of Ba{sub 9}Fe{sub 4}Se{sub 16} recorded along a-[010]. Highlights: • A new iron selenide material. • A structure resolution by combination of XRD and TEM. • Magnetic properties of the new compound Ba{sub 9}Fe{sub 4}Se{sub 16} are discussed.

  8. Strain-induced magnetic domain wall control by voltage in hybrid piezoelectric BaTiO3 ferrimagnetic TbFe structures

    PubMed Central

    Rousseau, Olivier; Weil, Raphael; Rohart, Stanislas; Mougin, Alexandra

    2016-01-01

    This paper reports on the voltage dependence of the magnetization reversal of a thin amorphous ferromagnetic TbFe film grown on a ferroelectric and piezoelectric BaTiO3 single crystal. Magneto-optical measurements, at macroscopic scale or in a microscope, demonstrate how the ferroelectric BaTiO3 polarisation history influences the properties of the perpendicularly magnetized TbFe film. Unpolarised and twinned regions are obtained when the sample is zero voltage cooled whereas flat and saturated regions are obtained when the sample is voltage cooled through the ferroelectric ordering temperature of the BaTiO3 crystal, as supported by atomic force microscopy experiments. The two steps involved in the TbFe magnetization reversal, namely nucleation and propagation of magnetic domain walls, depend on the polarisation history. Nucleation is associated to coupling through strains with the piezoelectric BaTiO3 crystal and propagation to pinning with the ferroelastic surface patterns visible in the BaTiO3 topography. PMID:26987937

  9. Strain-induced magnetic domain wall control by voltage in hybrid piezoelectric BaTiO3 ferrimagnetic TbFe structures

    NASA Astrophysics Data System (ADS)

    Rousseau, Olivier; Weil, Raphael; Rohart, Stanislas; Mougin, Alexandra

    2016-03-01

    This paper reports on the voltage dependence of the magnetization reversal of a thin amorphous ferromagnetic TbFe film grown on a ferroelectric and piezoelectric BaTiO3 single crystal. Magneto-optical measurements, at macroscopic scale or in a microscope, demonstrate how the ferroelectric BaTiO3 polarisation history influences the properties of the perpendicularly magnetized TbFe film. Unpolarised and twinned regions are obtained when the sample is zero voltage cooled whereas flat and saturated regions are obtained when the sample is voltage cooled through the ferroelectric ordering temperature of the BaTiO3 crystal, as supported by atomic force microscopy experiments. The two steps involved in the TbFe magnetization reversal, namely nucleation and propagation of magnetic domain walls, depend on the polarisation history. Nucleation is associated to coupling through strains with the piezoelectric BaTiO3 crystal and propagation to pinning with the ferroelastic surface patterns visible in the BaTiO3 topography.

  10. Thermodynamic analysis of chemical compatibility of several compounds with Fe-Cr-Al alloys

    NASA Technical Reports Server (NTRS)

    Misra, Ajay K.

    1993-01-01

    Chemical compatibility between Fe-19.8Cr-4.8Al (weight percent), which is the base composition for the commercial superalloy MA956, and several carbides, borides, nitrides, oxides, and silicides was analyzed from thermodynamic considerations. The effect of addition of minor alloying elements, such as Ti, Y, and Y2O3, to the Fe-Cr-Al alloy on chemical compatibility between the alloy and various compounds was also analyzed. Several chemically compatible compounds that can be potential reinforcement materials and/or interface coating materials for Fe-Cr-Al based composites were identified.

  11. Structural Disorder and Magnetism in the Spin-Gapless Semiconductor CoFeCrAl

    DTIC Science & Technology

    2016-08-24

    semiconductor CoFeCrAl into a half- metallic ferrimagnet and increases the half- metallic band gap by 0.12 eV. Compared CoFeCrAl, the moment of...magnets. However, Si addition improves the degree of Heusler ordering and changes the electronic structure from a SGS to a half- metal with increased...total moment per relaxed unit cell are 1.71 µB (I), –0.60 µB (II), and 1.05 µB (III). None of the disordered CoFeCrAl structures is energetically

  12. Mechanochemical synthesis of pnictide compounds and superconducting Ba0.6K0.4Fe2As2 bulks with high critical current density

    NASA Astrophysics Data System (ADS)

    Weiss, J. D.; Jiang, J.; Polyanskii, A. A.; Hellstrom, E. E.

    2013-07-01

    BaFe2As2 (Ba-122) and Ba0.6K0.4Fe2As2 (K-doped Ba-122) powders were successfully synthesized from the elements using a reaction method that incorporates a mechanochemical reaction using high-impact ball milling. Mechanically activated, self-sustaining reactions (MSRs) were observed while milling the elements together to form these compounds. After the MSR, the Ba-122 phase had formed, the powder had an average grain size <1 μm, and the material was effectively mixed. X-ray diffraction confirmed Ba-122 was the primary phase present after milling. Heat treatment of the K-doped MSR powder at high temperature (1120 ° C) and pressure yielded dense samples with high phase purity, but only granular current flow could be visualized by magneto-optical imaging. In contrast, a short, low temperature (600 ° C) heat treatment at ambient pressure resulted in global current flow throughout the bulk sample even though the density was lower and impurity phases were more prevalent. An optimized heat treatment involving a two-step, low temperature (600 ° C) heat treatment of the MSR powder produced bulk material with very high critical current density above 0.1 MA cm-2 at 4.2 K and self-field (SF).

  13. Directional solidification of Al-8 wt. %Fe alloy under high magnetic field gradient

    NASA Astrophysics Data System (ADS)

    Wu, Mingxu; Liu, Tie; Dong, Meng; Sun, Jinmei; Dong, Shulin; Wang, Qiang

    2017-02-01

    We investigated applying a magnetic field (up to 6 T) during directional solidification of a hypereutectic Al-8 wt. %Fe alloy, finding that it dramatically affected the final microstructure. A eutectic area appeared at the top of the samples, and as the magnetic flux density increased, the eutectic area clearly enlarged. In addition, the Al3Fe phase was twisted and fractured, and some phases aggregated and distributed randomly in the samples. We also investigated the volume fraction distribution of the Al3Fe phase, revealing that applying the magnetic field during solidification caused dramatic disorder in the solute and phase distributions. The magnetic force induced by the interaction between the magnetic field gradient and the magnetic materials appeared to be the main reason not only for the occurrence and enlargement of the eutectic area but also for the movement of Fe-enriched zones during directional solidification. Otherwise, the deformation and fracture of the Al3Fe phase, the morphological instability in the interface between the eutectic area and the Al3Fe phase, and the random distribution of the aggregated Al3Fe phase appeared to come from the thermoelectric magnetic force/thermoelectric magnetic convection under the magnetic field.

  14. Tribological Properties of the Fe-Al-Cr Alloyed Layer by Double Glow Plasma Surface Metallurgy

    NASA Astrophysics Data System (ADS)

    Luo, Xixi; Yao, Zhengjun; Zhang, Pingze; Zhou, Keyin; Wang, Zhangzhong

    2016-09-01

    A Fe-Al-Cr alloyed layer was deposited onto the surface of Q235 low-carbon steel via double glow plasma surface metallurgy (DGPSM) to improve the steel's wear resistance. After the DGPSM treatment, the Fe-Al-Cr alloyed layer grown on the Q235 low-carbon steel was homogeneous and compact and had a thickness of 25 µm. The layer was found to be metallurgically adhered to the substrate. The frictional coefficient and specific wear rate of the sample with a Fe-Al-Cr alloyed layer (treated sample) were both lower than those of the bare substrate (untreated sample) at the measured temperatures (25, 250 and 450 °C). The results indicated that the substrate and the alloyed layer suffered oxidative wear and abrasive wear, respectively, and that the treated samples exhibited much better tribological properties than did the substrate. The formation of Fe2AlCr, Fe3Al(Cr), FeAl(Cr), Fe(Cr) sosoloid and Cr23C6 phases in the alloyed layer dramatically enhanced the wear resistance of the treated sample. In addition, the alloyed layer's oxidation film exhibited a self-healing capacity with lubrication action that also contributed to the improvement of the wear resistance at high temperature. In particular, at 450 °C, the specific wear rate of treated sample was 2.524 × 10-4 mm3/N m, which was only 45.2% of the untreated sample.

  15. Development of weldable, corrosion-resistant iron-aluminide (FeAl) alloys

    SciTech Connect

    Maziasz, P.J.; Goodwin, G.M.; Wang, X.L.; Alexander, D.J.

    1997-04-01

    A boron-microalloyed FeAl alloy (Fe-36Al-0.2Mo-0.05Zr-0.13C, at.%, with 100-400 appm B) with improved weldability and mechanical properties was developed in FY 1994. A new scale-up and industry technology development phase for this work began in FY 1995, pursuing two parallel paths. One path was developing monolithic FeAl component and application technology, and the other was developing coating/cladding technology for alloy steels, stainless steels and other Fe-Cr-Ni alloys. In FY 1995, it was found that cast FeAl alloys had good strength at 700-750{degrees}C, and some (2.5%) ductility in air at room-temperature. Hot-extruded FeAl with refined grain size was found to have ductility and to also have good impact-toughness at room-temperature. Further, it was discovered that powder-metallurgy (P/M) FeAl, consolidated by direct hot-extrusion at 950-1000{degrees}C to have an ultra fine-grained microstructure, had the highest ductility, strength and impact-toughness ever seen in such intermetallic alloys.

  16. Specific heat investigation for line nodes in heavily overdoped Ba1-xKxFe2As2

    DOE PAGES

    Kim, J. S.; Stewart, G. R.; Liu, Yong; ...

    2015-06-10

    Previous research has found that the pairing symmetry in the iron-based superconductor Ba1-xKxFe2As2 changes from nodeless s-wave near optimally doped, x≈0.4-0.55 and Tc>30 K, to nodal (either d-wave or s-wave) at the pure endpoint, x=1 and Tc<4 K. Intense theoretical interest has been focused on this possibility of changing pairing symmetry, where in the transition region both order parameters would be present and time reversal symmetry would be broken. Here we report specific heat measurements in zero and applied magnetic fields down to 0.4 K of three individual single crystals, free of low temperature magnetic anomalies, of heavily overdoped Ba1-xKxFe2As2,more » x= 0.91, 0.88, and 0.81. The values for Tcmid are 5.6, 7.2 and 13 K and for Hc2≈ 4.5, 6, and 20 T respectively. Furthermore, the data can be analyzed in a two gap scenario, Δ2/Δ1 ≈ 4, with the magnetic field dependence of γ (=C/T as T→0) showing an anisotropic ‘S-shaped’ behavior vs H, with the suppression of the lower gap by 1 T and γ ≈ H1/2 overall. Although such a non-linear γ vs H is consistent with deep minima or nodes in the gap structure, it is not clear evidence for one, or both, of the gaps being nodal in these overdoped samples. Thus, following the established theoretical analysis of the specific heat of d-wave cuprate superconductors containing line nodes, we present the specific heat normalized by H1/2 plotted vs T/H1/2 of these heavily overdoped Ba1-xKxFe2As2 samples which – thanks to the absence of magnetic impurities in our sample - convincingly shows the expected scaling for line node behavior for the larger gap for all three compositions. There is however no clear observation of the nodal behavior C ∝ αT2 in zero field at low temperatures, with α ≤ 2 mJ/molK3 being consistent with the data. Together with the scaling, this leaves open the possibility of extreme anisotropy in a nodeless larger gap, Δ2, such that the scaling works for fields above 0.25 – 0

  17. Superconductivity-induced re-entrance of the orthorhombic distortion in Ba1-xKxFe2As2.

    PubMed

    Böhmer, A E; Hardy, F; Wang, L; Wolf, T; Schweiss, P; Meingast, C

    2015-07-31

    Detailed knowledge of the phase diagram and the nature of the competing magnetic and superconducting phases is imperative for a deeper understanding of the physics of iron-based superconductivity. Magnetism in the iron-based superconductors is usually a stripe-type spin-density-wave, which breaks the tetragonal symmetry of the lattice, and is known to compete strongly with superconductivity. Recently, it was found that in some systems an additional spin-density-wave transition occurs, which restores this tetragonal symmetry, however, its interaction with superconductivity remains unclear. Here, using thermodynamic measurements on Ba1-xKxFe2As2 single crystals, we show that the spin-density-wave phase of tetragonal symmetry competes much stronger with superconductivity than the stripe-type spin-density-wave phase, which results in a novel re-entrance of the latter at or slightly below the superconducting transition.

  18. Voltage-current characteristics of epitaxial and misoriented Ba(Fe1-xCox) 2As2 thin films

    NASA Astrophysics Data System (ADS)

    Rodríguez, O.; Mariño, A.

    2015-06-01

    Ba(Fe1-xCox) 2As2 thin films were produced by Pulsed Laser Deposition (PLD). Epitaxial thin films were obtained when the deposition temperature was 700 °C while at 875 °C misoriented films were obtained. The presence of grain boundaries reduces the transport critical current Jc in almost two order of magnitude with respect to the textured thin films. The Voltage-Current (V-I) curves of misoriented films, exhibit a mixture of a non-ohmic linear differential (NOLD) and power law behaviors, due to the viscous flow of the flux lines along the grain boundaries lines, corresponding to the Jc limited by grain boundaries and Jc limited by intragrain, respectively. The misoriented thin films also present a kinked V-I curves attributed to a vortex channeling along the boundaries.

  19. The Ba 2LnFeNb 4O 15 "tetragonal tungsten bronze": Towards RT composite multiferroics

    NASA Astrophysics Data System (ADS)

    Josse, M.; Bidault, O.; Roulland, F.; Castel, E.; Simon, A.; Michau, D.; Von der Mühll, R.; Nguyen, O.; Maglione, M.

    2009-06-01

    Several Niobium oxides of formula Ba 2LnFeNb 4O 15 (Ln = La, Pr, Nd, Sm, Eu, Gd) with the "tetragonal tungsten bronze" (TTB) structure have been synthesised by conventional solid state methods. The neodymium, samarium and europium compounds are ferroelectric with Curie temperature ranging from 320 to 440 K. The praseodymium and gadolinium compounds behave as relaxors below 170 and 300 K respectively. The praseodymium, neodymium, samarium, europium and gadolinium compounds exhibit magnetic hysteresis loops at room temperature originating from traces of a barium ferrite secondary phase. The presence of both ferroelectric and magnetic hysteresis loops at room temperature allows considering these materials as composites multiferroic. Based on crystal-chemical analysis we propose some relationships between the introduction of Ln 3+ ions in the TTB framework and the chemical, structural and physical properties of these materials.

  20. Unconventional Electronic Reconstruction in Undoped (Ba,Sr)Fe2As2 Across the Spin Density Wave Transition

    SciTech Connect

    Yi, M.

    2010-06-02

    Through a systematic high-resolution angle-resolved photoemission study of the iron pnictide compounds (Ba,Sr)Fe{sub 2}As{sub 2}, we show that the electronic structures of these compounds are significantly reconstructed across the spin density wave transition, which cannot be described by a simple folding scenario of conventional density wave ordering. Moreover, we find that LDA calculations with an incorporated suppressed magnetic moment of 0.5{mu}{sub B} can match well the details in the reconstructed electronic structure, suggesting that the nature of magnetism in the pnictides is more itinerant than local, while the origin of suppressed magnetic moment remains an important issue for future investigations.

  1. Crossover from spin waves to diffusive spin excitations in underdoped Ba(Fe1-xCox)2 As2

    SciTech Connect

    Tucker, G S; Fernandes, R M; Pratt, D K; Thaler, A; Ni, N; Marty, K; Christianson, A D; Lumsden, M D; Sales, B C; Sefat, A S; Bud'ko, S L; Canfield, P C; Kreyssig, A; Goldman, A I; McQueeney, R J

    2014-05-01

    Using inelastic neutron scattering, we show that the onset of superconductivity in underdoped Ba(Fe1-xCox)2As2 coincides with a crossover from well-defined spin waves to overdamped and diffusive spin excitations. This crossover occurs despite the presence of long-range stripe antiferromagnetic order for samples in a compositional range from x=0.04 to 0.055, and is a consequence of the shrinking spin-density wave gap and a corresponding increase in the particle-hole (Landau) damping. The latter effect is captured by a simple itinerant model relating Co doping to changes in the hot spots of the Fermi surface. We argue that the overdamped spin fluctuations provide a pairing mechanism for superconductivity in these materials.

  2. Superconducting properties in heavily overdoped Ba(Fe0.86Co0.14)2As2 single crystals

    DOE PAGES

    Kim, Jeehoon; Haberkorn, N.; Gofryk, K.; ...

    2014-10-05

    Here, we report the intrinsic superconducting parameters in a heavily overdoped Ba(Fe1-xCox)2As2 (x=0.14) single crystal and their influence in the resulting vortex dynamics. We also find a bulk superconducting critical temperature of 9.8 K, magnetic penetration depth λab (0)=660 ± 50 nm, coherence length ζab (0)=6.4 ± 0.2 nm, and the upper critical field anisotropy γT→ Tc approximate to 3.7. The vortex phase diagram, in comparison with the optimally doped compound, presents a narrow collective creep regime. Furthermore, the intrinsic pinning energy plays an important role in the resulting vortex dynamics as compared with similar pinning landscape and comparable intrinsicmore » thermal fluctuations.« less

  3. Collapse of the spin resonance spectral weight in overdoped Ba1-x K x Fe 2 As 2

    NASA Astrophysics Data System (ADS)

    Osborn, Ray; Rosenkranz, Stephan; Castellan, John-Paul; Goremychkin, Eugene; Chung, Duck-Young; Claus, Helmut; Kanatzidis, Mercouri; Guidi, Tatiana

    2011-03-01

    We report inelastic neutron scattering measurements of magnetic excitations in Ba 1-x Kx Fe 2 As 2 over a broad range of electron band filling within the superconducting phase. In an itinerant model, these excitations are resonantly enhanced when the superconducting energy gap changes sign on different parts of the electron Fermi surface. They are therefore sensitive both to the superconducting gap symmetry and to the Fermi surface geometry. Our results show that, in addition to becoming incommensurate because of the growing mismatch in the hole and electron Fermi surface volumes, the resonant spectral weight decreases proportionally to the resonance binding energy, vanishing at x ~ 0.72 . A tight-binding model including s+/- -symmetry pairing is able to reproduce these observations confirming that the resonance arises from the pairing of band electrons. Supported by U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under contract No. DE-AC02-06CH11357.

  4. Enhancement of critical current densities in (Ba,K)Fe2As2 wires and tapes using HIP technique

    NASA Astrophysics Data System (ADS)

    Pyon, Sunseng; Suwa, Takahiro; Park, Akiyoshi; Kajitani, Hideki; Koizumi, Norikiyo; Tsuchiya, Yuji; Awaji, Satoshi; Watanabe, Kazuo; Tamegai, Tsuyoshi

    2016-11-01

    (Ba,K)Fe2As2 superconducting wires and tapes are fabricated by using hot isostatic pressing (HIP) technique, and their superconducting properties are studied. In the HIP round wire, transport critical current density (J c) at 4.2 K has achieved record-high value of 175 kA cm-2 at zero field, and exceeds 20 kA cm-2 even at 100 kOe. Improvement of polycrystalline powder synthesis may play a key role for the enhancement of J c. In the HIP tape, even larger transport J c of 380 kA cm-2 is realized at zero field. Based on magnetization and magneto-optical measurements, possible further enhancement of J c is discussed.

  5. Persistence of slow fluctuations in the overdoped regime of Ba (Fe1 -xRhx) 2As2 superconductors

    NASA Astrophysics Data System (ADS)

    Bossoni, L.; Moroni, M.; Julien, M. H.; Mayaffre, H.; Canfield, P. C.; Reyes, A.; Halperin, W. P.; Carretta, P.

    2016-06-01

    We present nuclear magnetic resonance evidence that very slow (≤1 MHz) spin fluctuations persist into the overdoped regime of Ba (Fe1 -xRhx) 2As2 superconductors. Measurements of the 75As spin echo decay rate, obtained both with Hahn Echo and Carr Purcell Meiboom Gill pulse sequences, show that the slowing down of spin fluctuations can be described by short-range diffusive dynamics, likely involving domain walls motions separating (π /a ,0 ) from (0 ,π /a ) correlated regions. This slowing down of the fluctuations is weakly sensitive to the external magnetic field and, although fading away with doping, it extends deeply into the overdoped regime.

  6. Ethylene glycol assisted spray pyrolysis for the synthesis of hollow BaFe12O19 spheres

    SciTech Connect

    Xu, X; Park, J; Hong, YK; Lane, AM

    2015-04-01

    Hollow spherical BaFe12O19 particles were synthesized by spray pyrolysis from a solution containing ethylene glycol (EG) and precursors at 1000 degrees C. The effects of EG concentration on particle morphology, crystallinity and magnetic properties were investigated. The hollow spherical particles were found to consist of primary particles, and higher EG concentration led to a bigger primary particle size. EG concentration did not show much effect on the hollow particle size. Better crystallinity and higher magnetic coercivity were obtained with higher EG concentration, which is attributed to further crystallization with the heat produced from EG combustion. Saturation magnetization (emu/g) decreased with increasing EG concentration due to residual carbon from EG incomplete combustion, contributing as a non-magnetic phase to the particles. Published by Elsevier B.V.

  7. Weak localization effect in topological insulator micro flakes grown on insulating ferrimagnet BaFe12O19

    PubMed Central

    Zheng, Guolin; Wang, Ning; Yang, Jiyong; Wang, Weike; Du, Haifeng; Ning, Wei; Yang, Zhaorong; Lu, Hai-Zhou; Zhang, Yuheng; Tian, Mingliang

    2016-01-01

    Many exotic physics anticipated in topological insulators require a gap to be opened for their topological surface states by breaking time reversal symmetry. The gap opening has been achieved by doping magnetic impurities, which however inevitably create extra carriers and disorder that undermine the electronic transport. In contrast, the proximity to a ferromagnetic/ferrimagnetic insulator may improve the device quality, thus promises a better way to open the gap while minimizing the side-effects. Here, we grow thin single-crystal Sb1.9Bi0.1Te3 micro flakes on insulating ferrimagnet BaFe12O19 by using the van der Waals epitaxy technique. The micro flakes show a negative magnetoresistance in weak perpendicular fields below 50 K, which can be quenched by increasing temperature. The signature implies the weak localization effect as its origin, which is absent in intrinsic topological insulators, unless a surface state gap is opened. The surface state gap is estimated to be 10 meV by using the theory of the gap-induced weak localization effect. These results indicate that the magnetic proximity effect may open the gap for the topological surface attached to BaM insulating ferrimagnet. This heterostructure may pave the way for the realization of new physical effects as well as the potential applications of spintronics devices. PMID:26891682

  8. Weak localization effect in topological insulator micro flakes grown on insulating ferrimagnet BaFe12O19

    NASA Astrophysics Data System (ADS)

    Zheng, Guolin; Wang, Ning; Yang, Jiyong; Wang, Weike; Du, Haifeng; Ning, Wei; Yang, Zhaorong; Lu, Hai-Zhou; Zhang, Yuheng; Tian, Mingliang

    2016-02-01

    Many exotic physics anticipated in topological insulators require a gap to be opened for their topological surface states by breaking time reversal symmetry. The gap opening has been achieved by doping magnetic impurities, which however inevitably create extra carriers and disorder that undermine the electronic transport. In contrast, the proximity to a ferromagnetic/ferrimagnetic insulator may improve the device quality, thus promises a better way to open the gap while minimizing the side-effects. Here, we grow thin single-crystal Sb1.9Bi0.1Te3 micro flakes on insulating ferrimagnet BaFe12O19 by using the van der Waals epitaxy technique. The micro flakes show a negative magnetoresistance in weak perpendicular fields below 50 K, which can be quenched by increasing temperature. The signature implies the weak localization effect as its origin, which is absent in intrinsic topological insulators, unless a surface state gap is opened. The surface state gap is estimated to be 10 meV by using the theory of the gap-induced weak localization effect. These results indicate that the magnetic proximity effect may open the gap for the topological surface attached to BaM insulating ferrimagnet. This heterostructure may pave the way for the realization of new physical effects as well as the potential applications of spintronics devices.

  9. Microstructure, Physical Properties, and Magnetic Flux Density Analysis of Permanent Magnet BaFe12O19 using Milling and Sintering Preparation Methods

    NASA Astrophysics Data System (ADS)

    Sardjono, Priyo; Suprapedi; Muljadi; Rusnaeni Djauhari, Nenen

    2016-08-01

    The purpose of this experiment is to analyze the influence of sintering temperature to the microstructure, physical, and magnetic properties of BaFe12O19 materials. The permanent magnet BaFe12O19 was made by using milling and sintering method, BaFe12O19 commercial powder was used as the raw material in this experiment. The raw material was pulverized by using ball mill for 15 hours and compacted at 400 MPa pressure to obtain a 16mm diameter and 4mm thick pellet. The pellet was sintered with 10oC/minute heating rate at various temperature ranges of 1050, 1100, 1150, and 1200oC for 1 hour. The microstructure and particle size of the pellet was investigated using XRD, SEM, and Particle Size Analyzer (PSA). The result shows that the milled powder has hexagonal BaFe12O19 crystal structure as the dominant phase, inhomogeneous size and shape of the grains, and average particle size is 19.60 pm. The bulk density measurement, shrinkage, and magnetic properties of the sintered samples were being observed and analyzed. It was found through this experiment that the optimum sintering temperature is 1150oC to obtain optimum bulk density (4.71 g/cm3), constant shrinkage (12.07%), 550 Gauss magnetic flux density, 1.79 kGauss remanence Br, and 1.75 kOe coercivity.

  10. Spin dynamics near a putative antiferromagnetic quantum critical point in Cu-substituted BaFe2As2 and its relation to high-temperature superconductivity

    DOE PAGES

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

    2015-12-02

    We present the results of elastic and inelastic neutron scattering measurements on nonsuperconducting Ba(Fe0.957Cu0.043)2As2, a composition close to a quantum critical point between antiferromagnetic (AFM) ordered and paramagnetic phases. By comparing these results with the spin fluctuations in the low-Cu composition as well as the parent compound BaFe2As2 and superconducting Ba(Fe1–xNix)2As2 compounds, we demonstrate that paramagnon-like spin fluctuations are evident in the antiferromagnetically ordered state of Ba(Fe0.957Cu0.043)2As2, which is distinct from the AFM-like spin fluctuations in the superconducting compounds. Our observations suggest that Cu substitution decouples the interaction between quasiparticles and the spin fluctuations. In addition, we show that themore » spin-spin correlation length ξ(T) increases rapidly as the temperature is lowered and find ω/T scaling behavior, the hallmark of quantum criticality, at an antiferromagnetic quantum critical point.« less

  11. Nodal structure and quantum critical point beneath the superconducting dome of BaFe2(As1-xPx)2

    NASA Astrophysics Data System (ADS)

    Matsuda, Yuji

    2012-02-01

    Among BaFe2As2 based materials , the isovalent pnictogen substituted system BaFe2(As1-xPx)2 appears to be the most suitable system to discuss many physical properties, because BaFe2(As1-xPx)2 can be grown with very clean and homogeneous, as evidenced by the quantum oscillations observed over a wide doping range even in the superconducting dome giving detailed knowledge on the electronic structure. We investigate the structure of the superconducting order parameter in BaFe2(As0.67P0.33)2 (Tc=31,) with line nodes by the angle-resolved thermal conductivity measurements in magnetic field. The experimental results are most consistent with the closed nodal loops located at the flat part of the electron Fermi surface with high Fermi velocity. The doping evolution of the penetration depth indicates that nodal loop is robust against P-doping. Moreover, the magnitude of the zero temperature penetration depth exhibits a sharp peak at x=0.3, indicating the presence of a quantum phase transition deep inside the superconducting dome.[4pt] This work has been done in collaboration with T. Shibauchi, K. Hashimoto, S. Kasahara, M. Yamashita, T. Terashima, H. Ikeda (Kyoto), A. Carrington (Bristol), K. Cho, R. Prozorov, M. Tanatar (Ames), A.B. Vorontsov (Montana) and I.Vekhter (Louisiana).

  12. Crystallite size characterization and magnetism properties of composite (BaFe12O19)1-X-(SrTiO3)X

    NASA Astrophysics Data System (ADS)

    Novizal, Manaf, Azwar; Doni, Rahmad

    2013-09-01

    A study conducted on the magnetic properties of composite material made of two materials i.e. BaFe12O19 (Barium Hexaferrite) and SrTiO3 (Strontium Titanate) using mechanical Alloy method. Composition proportion refers to the equation (BaFe12O19)1-X(SrTiO3)X X=20%, 50%,and 80% wt. Each BaFe12O19 material produced from base material of BaCO3 and Fe2O3 powder, SrTiO3 produced from mixture of SrCO3 and TiO2 powder. Each material are milled for 80 hours, of which on interval 20 hours, powder is extracted for particle measurement only for X=20 % wt composition, the X=50% wt and 80 % wt compositions are not measured. Next the material was made into bulk with 70 kN pressure die, and sintered at temperature of 1100°C for 4 hours, characterized with XRD, then magnetic character is measured with fermagraph.

  13. New high permittivity tetragonal tungsten bronze dielectrics Ba{sub 2}LaMNb{sub 4}O{sub 15}: M=Mn, Fe

    SciTech Connect

    McCabe, Emma E.; West, Anthony R.

    2010-03-15

    The new phases Ba{sub 2}LaMNb{sub 4}O{sub 15}: M=Mn, Fe were prepared by solid state reaction at 1100 deg. C. They have the tetragonal tungsten bronze structure, space group P4/mbm, at room temperature. The two octahedral sites show partial order of M and Nb with preferential occupancy of the smaller B(1) sites by M. Both phases have high permittivities 90+-15 over the range 10-320 K. Ba{sub 2}LaFeNb{sub 4}O{sub 15} is highly insulating with bulk conductivity <<10{sup -8} ohm{sup -1} cm{sup -1} at 25 deg. C and tan delta<<0.001 over the range 100-320 K and at 10{sup 5} Hz. Solid solutions between these new phases and the compositionally and structurally related relaxor ferroelectric Ba{sub 2}LaTi{sub 2}Nb{sub 3}O{sub 15} show gradual loss of ferroelectric behaviour attributed to replacement of polarisable Ti{sup 4+} by a mixture of (Mn, Fe){sup 3+} and Nb{sup 5+}. - Graphical Abstract: Tetragonal tungsten bronze structure of Ba{sub 2}La(Mn, Fe)Nb{sub 4}O{sub 15} from two different viewpoints.

  14. Spin anisotropy due to spin-orbit coupling in optimally hole-doped Ba0.67K0.33Fe2As2

    NASA Astrophysics Data System (ADS)

    Song, Yu; Man, Haoran; Zhang, Rui; Lu, Xingye; Zhang, Chenglin; Wang, Meng; Tan, Guotai; Regnault, L.-P.; Su, Yixi; Kang, Jian; Fernandes, Rafael M.; Dai, Pengcheng

    2016-12-01

    We use polarized inelastic neutron scattering to study the temperature and energy dependence of spin space anisotropies in the optimally-hole-doped iron pnictide Ba0.67K0.33Fe2As2 (Tc=38 K). In the superconducting state, while the high-energy part of the magnetic spectrum is nearly isotropic, the low-energy part displays a pronounced anisotropy, manifested by a c -axis polarized resonance. We also observe that the spin anisotropy in superconducting Ba0.67K0.33Fe2As2 extends to higher energies compared with electron-doped BaFe2 -xT MxAs2 (T M =Co , Ni) and isovalent-doped BaFe2As1.4P0.6 , suggesting a connection between Tc and the energy scale of the spin anisotropy. In the normal state, the low-energy spin anisotropy for hole- and electron-doped iron pnictides near optimal superconductivity onset at temperatures similar to the temperatures at which the elastoresistance deviates from Curie-Weiss behavior, pointing to a possible connection between the two phenomena. Our results highlight the relevance of the spin-orbit coupling to the superconductivity of the iron pnictides.

  15. Durability of PEM fuel cell cathode in the presence of Fe 3+ and Al 3+

    NASA Astrophysics Data System (ADS)

    Li, Hui; Tsay, Ken; Wang, Haijiang; Shen, Jun; Wu, Shaohong; Zhang, Jiujun; Jia, Nengyou; Wessel, Silvia; Abouatallah, Rami; Joos, Nathan; Schrooten, Jeremy

    The contamination effects of Fe 3+ and Al 3+ on the performance of polymer electrolyte membrane fuel cells were investigated by continuously injecting Fe 3+ or Al 3+ salt solution into the air stream of an operating fuel cell. Both metal ions individually caused significant cell performance degradation at a level of only 5 ppm mol in air. In addition, elevated temperature accelerated fuel cell performance degradation in the presence of Fe 3+. Moreover, the presence of Fe 3+ in an operating fuel cell resulted in the cell's sudden death, due to the formation of membrane pinholes that may have been promoted by the enhanced production of peroxy radicals catalyzed by Fe species. Half-cell tests in liquid electrolyte revealed that the presence of Al 3+ in the electrolyte changed the kinetics and mechanisms of the oxygen reduction reaction by reducing the kinetic current densities and the electron transfer number.

  16. Growth of epitaxial Ba 2YCu 3O 7- x films on LaAlO 3 (001)

    NASA Astrophysics Data System (ADS)

    Siegal, Michael P.; Phillips, Julia M.; Hsieh, Yong-Fen; Marshall, J. H.

    1990-12-01

    We report the ex situ growth of 1000 and 2000 Å epitaxial Ba 2YCu 3O 7- x ( BYCO) filmsonLaAlO3 (001 with surface morphologies and crystallinity generally associated with high quality in situ films. Films are grown by co-depositing BaF 2, Y and Cu in a stoichiometric ratio within 1% of 2:1:3, followed by annealing in a two-stage process in a tube furnace. By optimizing the annealing conditions, excellent crystallinity is obtained, with χ min∼ 2-4] from Rutherford backscattering/channeling. These films have sharp superconducting resistance transitions at 90-91 K. Critical current densities at 77 K are ∼ 10 6 A/cm 2 in zero magnetic field and ⪅ 10 5 A/cm 2 in H=0.9 T oriented perpendicular to the ab plane of the films.

  17. Temperature and composition phase diagram in the iron-based ladder compounds Ba 1 - x Cs x Fe 2 Se 3

    DOE PAGES

    Hawai, Takafumi; Nambu, Yusuke; Ohgushi, Kenya; ...

    2015-05-28

    We investigated the iron-based ladder compounds (Ba,Cs)Fe₂Se₃. Their parent compounds BaFe₂Se₃ and CsFe₂Se₃ have different space groups, formal valences of Fe, and magnetic structures. Electrical resistivity, specific heat, magnetic susceptibility, x-ray diffraction, and powder neutron diffraction measurements were conducted to obtain a temperature and composition phase diagram of this system. Block magnetism observed in BaFe₂Se₃ is drastically suppressed with Cs doping. In contrast, stripe magnetism observed in CsFe₂Se₃ is not so fragile against Ba doping. A new type of magnetic structure appears in intermediate compositions, which is similar to stripe magnetism of CsFe₂Se₃, but interladder spin configuration is different. Intermediatemore » compounds show insulating behavior, nevertheless a finite T-linear contribution in specific heat was obtained at low temperatures.« less

  18. Self-organized homo-epitaxial growth in nonlinear optical BaAlBO3F2 crystal crossing lines patterned by laser in glass

    NASA Astrophysics Data System (ADS)

    Shinozaki, K.; Abe, S.; Honma, T.; Komatsu, T.

    2015-11-01

    Crystallization processing of glasses is important as a novel technique for the development of new optical materials, and laser-induced crystallization provides a new challenge in science and technology of materials. Nonlinear optical BaAlBO3F2 crystal lines with crossing, bending, and spiral shapes were patterned at the surface of 2NiO-49BaF2-24.5Al2O3-24.5B2O3 (mol%) and 2.9NiO-48.5BaF2-24.3Al2O3-24.3B2O3 (mol%) glasses by laser irradiation (Yb:YVO4 laser with a wavelength of 1080 nm) and the orientation state of BaAlBO3F2 crystals was examined from birefringence image observations. The birefringence images indicate that the growth of highly c-axis oriented BaAlBO3F2 crystals follows along the laser scanning direction even if the laser scanning direction changes, and in particular the direction of the c-axis of BaAlBO3F2 crystals changes gradually at the crossing and bending points. The model of "self-organized homo-epitaxial growth" is proposed for the crystal orientation at the crossing and bending points, as a new crystal growth science and engineering beyond the wise providence of nature.

  19. Synthesis and Characterization of In Situ Dendritic/Particulate α-Al(Fe,TM)Si Phase Reinforced Al Matrix Composites

    NASA Astrophysics Data System (ADS)

    Hou, L. G.; Wang, Shuai; He, Z. B.; Zhang, D.; Wang, X. D.; Zhuang, L. Z.; Zhang, J. S.

    2016-12-01

    The strength and ductility of transition metallic element alloyed Al alloys could be inevitably and severely weakened if these elements appeared as coarse intermetallics. Present studies aimed to optimize the morphologies and sizes of these intermetallics via composition design and process selection so as to decrease their detrimental effects to the properties. It is shown that the dendritic α-Al(Fe,TM)Si phase solidified as primary phase can be refined into small dendrites or micro- and submicro-sized particles via controlling the cooling rate and alloy composition, and this phase exhibits better heat resistance. After spark plasma sintering (SPS) the atomized alloy powders, the bulk aluminum matrix composites (AMCs) were successfully prepared and well strengthened by the uniformly distributed particulate α-Al(Fe,TM)Si phase. These sintered bulk composites also possess good heat resistance that might facilitate their application for some heat-resistant parts. The transmission electron microscope (TEM) and high-resolution TEM (HRTEM) results indicate these α-Al(Fe,TM)Si phases possesses body-centered-cubic structure with a lattice constant of 1.25 to 1.27 nm. The solidification or phase formation of these alloys is discussed as well as the densification process for the SPS of powders. The present studies indicate a possibility to prepare in situ small dendritic/particulate α-Al(Fe,TM)Si phase reinforced AMCs by using the casting process and controlling the normal impurity elements in Al alloys.

  20. Theoretical analysis of compatibility of several reinforcement materials with NiAl and FeAl matrices

    NASA Technical Reports Server (NTRS)

    Misra, Ajay K.

    1989-01-01

    Several potential reinforcement materials were assessed for their chemical, coefficient of thermal expansion (CTE), and mechanical compatibility with the intermetallic matrices based on NiAl and FeAl. Among the ceramic reinforcement materials, Al2O3, TiC, and TiB2, appear to be the optimum choices for NiAl and FeAl matrices. However, the problem of CTE mismatch with the matrix needs to be solved for these three reinforcement materials. Beryllium-rich intermetallic compounds can be considered as potential reinforcement materials provided suitable reaction barrier coatings can be developed for these. Based on preliminary thermodynamic calculations, Sc2O3 and TiC appear to be suitable as reaction barrier coatings for the beryllides. Several reaction barrier coatings are also suggested for the currently available SiC fibers.

  1. Characterization of novel microstructures in Al-Fe-V-Si and Al-Fe-V-Si-Y alloys processed at intermediate cooling rates

    NASA Astrophysics Data System (ADS)

    Marshall, Ryan

    Samples of an Al-Fe-V-Si alloy with and without small Y additions were prepared by copper wedge-mold casting. Analysis of the microstructures developed at intermediate cooling rates revealed the formation of an atypical morphology of the cubic alpha-Al12(Fe/V)3Si phase (Im 3 space group with a = 1.26 nm) in the form of a microeutectic with alpha-Al that forms in relatively thick sections. This structure was determined to exhibit promising hardness and thermal stability when compared to the commercial rapidly solidified and processed Al-Fe-V-Si (RS8009) alloy. In addition, convergent beam electron diffraction (CBED) and selected area electron diffraction (SAD) were used to characterize a competing intermetallic phase, namely, a hexagonal phase identified as h-AlFeSi (P6/mmm space group with a = 2.45 nm c = 1.25 nm) with evidence of a structural relationship to the icosahedral quasicrystalline (QC) phase (it is a QC approximant) and a further relationship to the more desirable alpha-Al12(Fe/V) 3Si phase, which is also a QC approximant. The analysis confirmed the findings of earlier studies in this system, which suggested the same structural relationships using different methods. As will be shown, both phases form across a range of cooling rates and appear to have good thermal stabilities. Additions of Y to the alloy were also studied and found to cause the formation of primary YV2Al20 particles on the order of 1 microm in diameter distributed throughout the microstructure, which otherwise appeared essentially identical to that of the Y-free 8009 alloy. The implications of these results on the possible development of these structures will be discussed in some detail.

  2. The distribution alloying elements in alnico 8 and 9 magnets: Site preference of ternary Ti, Fe, Co, and Ni additions in DO3 Fe3Al, Co3Al, and Ni3Al based intermetallic phases

    NASA Astrophysics Data System (ADS)

    Samolyuk, G. D.; Újfalussy, B.; Stocks, G. M.

    2014-11-01

    Recently, interest in alnico magnetic alloys has been rekindled due to their potential to substitute for rare-earth based permanent magnets provided modest improvements in their coercivity can be achieved without loss of saturation magnetization. Recent experimental studies have indicated that atomic and magnetic structure of the two phases (one AlNi-based, the other FeCo-based) that comprise these spinodally decomposed alloy is not as simple as previously thought. A key issue that arises is the distribution of Fe, Co, and Ti within the AlNi-based matrix phase. In this paper, we report the results of first-principles calculations of the site preference of ternary alloying additions in DO3 Fe3Al, Co3Al, and Ni3Al alloys, as models for the aluminide phase. For compound compositions that are Al rich, which correspond to experimental situation, Ti and Fe are found to occupy the α sites, while Co and Ni prefer the γ sites of the DO3 lattice. An important finding is that the magnetic moments of transition metals in Fe3Al and Co3Al are ordered ferromagnetically, whereas the Ni3Al were found to be nonmagnetic unless the Fe or Co is added as a ternary element.

  3. The distribution alloying elements in alnico 8 and 9 magnets: Site preference of ternary Ti, Fe, Co, and Ni additions in DO3 Fe3Al, Co3Al, and Ni3Al based intermetallic phases

    DOE PAGES

    Samolyuk, G. D.; Újfalussy, B.; Stocks, G. M.

    2014-11-07

    Recently, interest in alnico magnetic alloys has been rekindled due to their potential to substitute for rare-earth based permanent magnets provided modest improvements in their coercivity can be achieved without loss of saturation magnetization. Recent experimental studies have indicated that atomic and magnetic structure of the two phases (one AlNi-based, the other FeCo-based) that comprise these spinodally decomposed alloy is not as simple as previously thought. A key issue that arises is the distribution of Fe, Co and Ti within the AlNi-based matrix phase. In our paper we report the results of first-principles calculations of the site preference of ternarymore » alloying additions in DO3 Fe3Al, Co3Al and Ni3Al alloys, as models for the aluminide phase. For compound compositions that are Al rich, which corresponds to experimental situation, Ti and Fe are found to occupy the sites, while Co and Ni prefer the sites of the DO3 lattice. Finally, an important finding is that the magnetic moments of transition metals in Fe3Al and Co3Al are ordered ferromagnetically, whereas the Ni3Al were found to be nonmagnetic unless the Fe or Co are added as a ternary element.« less

  4. Synthesis, Crystal and Electronic Structures of the Pnictides AE3TrPn3 (AE = Sr, Ba; Tr = Al, Ga; Pn = P, As)

    SciTech Connect

    Stoyko, Stanislav; Voss, Leonard; He, Hua; Bobev, Svilen

    2015-09-24

    New ternary arsenides AE3TrAs3 (AE = Sr, Ba; Tr = Al, Ga) and their phosphide analogs Sr3GaP3 and Ba3AlP3 have been prepared by reactions of the respective elements at high temperatures. Single-crystal X-ray diffraction studies reveal that Sr3AlAs3 and Ba3AlAs3 adopt the Ba3AlSb3-type structure (Pearson symbol oC56, space group Cmce, Z = 8). This structure is also realized for Sr3GaP3 and Ba3AlP3. Likewise, the compounds Sr3GaAs3 and Ba3GaAs3 crystallize with the Ba3GaSb3-type structure (Pearson symbol oP56, space group Pnma, Z = 8). Both structures are made up of isolated pairs of edge-shared AlPn4 and GaPn4 tetrahedra (Pn = pnictogen, i.e., P or As), separated by the alkaline-earth Sr2+ and Ba2+ cations. In both cases, there are no homoatomic bonds, hence, regardless of the slightly different atomic arrangements, both structures can be rationalized as valence-precise [AE2+]3[Tr3+][Pn3-]3, or rather [AE2+]6[Tr2Pn6]12-, i.e., as Zintl phases.

  5. Structure and electromagnetic properties of FeSiAl particles coated by MgO

    NASA Astrophysics Data System (ADS)

    Zhang, Yu; Zhou, Ting-dong

    2017-03-01

    FeSiAl particles with a layer of MgO surface coating have excellent soft magnetic and electromagnetic properties. In order to obtain the FeSiAl/MgO composites, Mg(OH)2 sol prepared by sol-gel process was well-mixed with FeSiAl flake particles, and then treated by calcination at 823 K in vacuum. The microstructural, morphological and electromagnetic parameters of FeSiAl/MgO particles were tested. Accordingly, the electromagnetic wave reflection loss in the frequency range of 0.5-18 GHz was calculated. The results show that the surface coating increases coercivity Hc and decreases complex permittivity, leading to a good impedance matching. When the coating amount was 7.5%, reflection loss of the composite particles can reach to -33 dB.

  6. Understanding phase stability of Al-Co-Cr-Fe-Ni high entropy alloys

    SciTech Connect

    Zhang, Chuan; Zhang, Fan; Diao, Haoyan; Gao, Michael C.; Tang, Zhi; Poplawsky, Jonathan D.; Liaw, Peter K.

    2016-07-19

    The concept of high entropy alloy (HEA) opens a vast unexplored composition range for alloy design. As a well-studied system, Al-Co-Cr-Fe-Ni has attracted tremendous amount of attention to develop new-generation low-density structural materials for automobile and aerospace applications. In spite of intensive investigations in the past few years, the phase stability within this HEA system is still poorly understood and needs to be clarified, which poses obstacles to the discovery of promising Al-Co-Cr-Fe-Ni HEAs. In the present work, the CALPHAD approach is employed to understand the phase stability and explore the phase transformation within the Al-Co-Cr-Fe-Ni system. As a result, the phase-stability mapping coupled with density contours is then constructed within the composition - temperature space, which provides useful guidelines for the design of low-density Al-Co-Cr-Fe-Ni HEAs with desirable properties.

  7. Expansion of the tetragonal magnetic phase with pressure in the iron arsenide superconductor Ba1-xKxFe2As2

    DOE PAGES

    Hassinger, Elena; Gredat, G.; Valade, F.; ...

    2016-04-01

    In the temperature-concentration phase diagram of most iron-based superconductors, antiferromagnetic order is gradually suppressed to zero at a critical point, and a dome of superconductivity forms around that point. The nature of the magnetic phase and its fluctuations is of fundamental importance for elucidating the pairing mechanism. In Ba1–xKxFe2As2 and Ba1–xNaxFe2As2, it has recently become clear that the usual stripelike magnetic phase, of orthorhombic symmetry, gives way to a second magnetic phase, of tetragonal symmetry, near the critical point, in the range from x = 0.24 to x = 0.28 for Ba1–xKxFe2As2. In a prior study, an unidentified phase wasmore » discovered for x < 0.24 but under applied pressure, whose onset was detected as a sharp anomaly in the resistivity. Here we report measurements of the electrical resistivity of Ba1–xKxFe2As2 under applied hydrostatic pressures up to 2.75 GPa, for x = 0.22, 0.24, and 0.28. The critical pressure above which the unidentified phase appears is seen to decrease with increasing x and vanish at x = 0.24, thereby linking the pressure-induced phase to the tetragonal magnetic phase observed at ambient pressure. In the temperature-concentration phase diagram of Ba1–xKxFe2As2, we find that pressure greatly expands the tetragonal magnetic phase, while the stripelike phase shrinks. As a result, this reveals that pressure may be a powerful tuning parameter with which to explore the interplay between magnetism and superconductivity in this material.« less

  8. Plasma Nitriding Behavior of Fe-C-M (M = Al, Cr, Mn, Si) Ternary Martensitic Steels

    NASA Astrophysics Data System (ADS)

    Tomio, Yusaku; Kitsuya, Shigeki; Oh-ishi, Keilchiro; Hono, Kazuhiro; Miyamoto, Goro; Furuhara, Tadashi

    2014-01-01

    Change in surface hardness and nitrides precipitated in Fe-0.6C binary and Fe-0.6 mass pct C-1 mass pct M (M = Al, Cr, Mn, Si) ternary martensitic alloys during plasma nitriding were investigated. Surface hardness was hardly increased in the Fe-0.6C binary alloy and slightly increased in Fe-0.6C-1Mn and Fe-0.6C-1Si alloys. On the other hand, it was largely increased in Fe-0.6C-1Al and Fe-0.6C-1Cr alloys. In all the Fe-0.6C-1M alloys except for the Si-added alloy, fine platelet alloy nitrides precipitated inside martensite laths. In the Fe-0.6C-1Si alloy, Si-enriched film was observed mainly at a grain boundary and an interface between cementite and matrix. Crystal structure of nitrides observed in the martensitic alloys was similar to those in Fe-M binary ferritic alloys reported previously. However, there was a difference in hardening behavior between ferrite and martensite due to a high density of dislocations acting as a nucleation site of the nitrides and partitioning of an alloying element between martensite and cementite changing the driving force of precipitation of the nitrides.

  9. Structure and magnetism of granular Fe-Al 2O 3

    NASA Astrophysics Data System (ADS)

    Santos, A.; Ardisson, J. D.; Viegas, A. D. C.; Schmidt, J. E.; Persiano, A. I. C.; Macedo, W. A. A.

    2001-05-01

    The structural and magnetic properties of granular Fe-Al 2O 3 nanocomposite obtained starting from sol-gel processing are presented. Samples with nominal Fe content ranging from 20% to 62% in volume were prepared. The conversion of Fe oxides into metallic Fe was obtained by calcination at 800°C followed by reduction at 600°C for 2 h in H 2 atmosphere. After reduction, our results indicated up to 78% α-Fe, preserving the mean diameter of the metallic nanoparticles between 50 and 80 nm, ˜16% Fe oxides and ˜7% interstitial Fe 2+ and substitutional Fe 3+ cations in the Al 2O 3 lattice. Vibrating sample magnetometry at 300 K resulted in coercivity between 400 and 630 Oe and saturation magnetization between 40 and 134 emu/g. From transport measurements, the highest magnetoresistance, close to 2% at room temperature, was observed for samples with 25% α-Fe and 51 vol% total Fe.

  10. Dielectric and Magnetic Properties of Ba(Fe1/2Ta1/2)O3-BiFeO3 Ceramics

    NASA Astrophysics Data System (ADS)

    Manotham, S.; Butnoi, P.; Jaita, P.; Pinitsoontorn, S.; Sweatman, D.; Eitssayeam, S.; Pengpat, K.; Rujijanagul, G.

    2016-11-01

    The properties of (1- x)Ba(Fe1/2Ta1/2)O3- xBiFeO3 [(1- x)BFT- xBFO] ( x = 0.0, 0.1, 0.3, 0.5) ceramics have been investigated. (1- x)BFT- xBFO powders were synthesized by a modified two-step calcination technique, and ceramics were fabricated by a conventional technique. X-ray diffraction (XRD) analysis revealed that the modified ceramics exhibited a mixture of BFT cubic phase and BFO rhombohedral phase. The peaks shift increased with increasing BFO content to a maximum value for the composition with x = 0.5. The overall shift of the XRD patterns indicated distortion of the unit cell, which may be due to ions from BFO entering the BFT lattice. BFO additive promoted grain growth, while the maximum density of the studied ceramics was observed for the x = 0.1 composition. The modified ceramics presented enhanced thermal and frequency stability of the dielectric constant. BFO additive also reduced the loss tangent for the system. Improvement of the magnetic behavior was observed after adding BFO. Furthermore, all the ceramics, including pure BFT (a nonmagnetic phase at room temperature), presented a magnetocapacitance effect, which can be related to magnetoresistance along with Maxwell-Wagner polarization effects.

  11. A large iron isotope effect in SmFeAsO(1 - x)F(x) and Ba(1 - x)K(x)Fe(2)As(2).

    PubMed

    Liu, R H; Wu, T; Wu, G; Chen, H; Wang, X F; Xie, Y L; Ying, J J; Yan, Y J; Li, Q J; Shi, B C; Chu, W S; Wu, Z Y; Chen, X H

    2009-05-07

    The recent discovery of superconductivity in oxypnictides with a critical transition temperature (T(C)) higher than the McMillan limit of 39 K (the theoretical maximum predicted by Bardeen-Cooper-Schrieffer theory) has generated great excitement. Theoretical calculations indicate that the electron-phonon interaction is not strong enough to give rise to such high transition temperatures, but strong ferromagnetic/antiferromagnetic fluctuations have been proposed to be responsible. Superconductivity and magnetism in pnictide superconductors, however, show a strong sensitivity to the crystal lattice, suggesting the possibility of unconventional electron-phonon coupling. Here we report the effect of oxygen and iron isotope substitution on T(C) and the spin-density wave (SDW) transition temperature (T(SDW)) in the SmFeAsO(1 - x)F(x) and Ba(1 - x)K(x)Fe(2)As(2) systems. The oxygen isotope effect on T(C) and T(SDW) is very small, while the iron isotope exponent alpha(C) = -dlnT(C)/dlnM is about 0.35 (0.5 corresponds to the full isotope effect). Surprisingly, the iron isotope exchange shows the same effect on T(SDW) as T(C). This indicates that electron-phonon interaction plays some role in the superconducting mechanism, but a simple electron-phonon coupling mechanism seems unlikely because a strong magnon-phonon coupling is included.

  12. Anomalous magneto-elastic and charge doping effects in thallium-doped BaFe2As2

    SciTech Connect

    Sefat, Athena S.; Li, Li; Cao, Huibo B.; McGuire, Michael A.; Sales, Brian; Custelcean, Radu; Parker, David S.

    2016-02-12

    Within the BaFe2As2 crystal lattice, we partially substitute thallium for barium and report the effects of interlayer coupling in Ba1-xTlxFe2As2 crystals. We demonstrate the unusual effects of magneto-elastic coupling and charge doping in this iron-arsenide material, whereby Néel temperature rises with small x, and then falls with additional x. Specifically, we find that Néel and structural transitions in BaFe2As2 (TN = Ts = 133 K) increase for x = 0.05 (TN = 138 K, Ts = 140 K) from magnetization, heat capacity, resistivity, and neutron diffraction measurements. Evidence from single crystal X-ray diffraction and first principles calculations attributes the stronger magnetism in x = 0.05 to magneto-elastic coupling related to the shorter intraplanar Fe-Fe bond distance. With further thallium substitution, the transition temperatures decrease for x = 0.09 (TN = Ts = 131 K), and this is due to charge doping. Finally, we illustrate that small changes related to 3d transition-metal state can have profound effects on magnetism.

  13. Growth and characterization of insulating ferromagnetic semiconductor (Al,Fe)Sb

    SciTech Connect

    Anh, Le Duc Kaneko, Daiki; Tanaka, Masaaki; Hai, Pham Nam

    2015-12-07

    We investigate the crystal structure, transport, and magnetic properties of Fe-doped ferromagnetic semiconductor (Al{sub 1−x},Fe{sub x})Sb thin films up to x = 14% grown by molecular beam epitaxy. All the samples show p-type conduction at room temperature and insulating behavior at low temperature. The (Al{sub 1−x},Fe{sub x})Sb thin films with x ≤ 10% maintain the zinc blende crystal structure of the host material AlSb. The (Al{sub 1−x},Fe{sub x})Sb thin film with x = 10% shows intrinsic ferromagnetism with a Curie temperature (T{sub C}) of 40 K. In the (Al{sub 1−x},Fe{sub x})Sb thin film with x = 14%, a sudden drop of the hole mobility and T{sub C} was observed, which may be due to the microscopic phase separation. The observation of ferromagnetism in (Al,Fe)Sb paves the way to realize a spin-filtering tunnel barrier that is compatible with well-established III-V semiconductor devices.

  14. Hydrogen permeation in FeCrAl alloys for LWR cladding application

    DOE PAGES

    Hu, Xunxiang; Terrani, Kurt A.; Wirth, Brian D.; ...

    2015-03-19

    FeCrAl is an advanced oxidation-resistant iron-based alloy class, is a highly prevalent candidate as an accident-tolerant fuel cladding material. Compared with traditional zirconium alloy fuel cladding, increased tritium permeation through FeCrAl fuel cladding to the primary coolant is expected, raising potential safety concerns. In our study, the hydrogen permeability of several FeCrAl alloys was obtained using a static permeation test station, which was calibrated and validated using 304 stainless steel. The high hydrogen permeability of FeCrAl alloys leads to concerns with respect to potentially significant tritium release when used for fuel cladding in LWRs. Also, the total tritium inventory insidemore » the primary coolant of a light water reactor was quantified by applying a 1-dimensional steady state tritium diffusion model to demonstrate the dependence of tritium inventory on fuel cladding type. Furthermore, potential mitigation strategies for tritium release from FeCrAl fuel cladding were discussed and indicate the potential for application of an alumina layer on the inner clad surface to serve as a tritium barrier. More effort is required to develop a robust, economical mitigation strategy for tritium permeation in reactors using FeCrAl clad fuel assemblies.« less

  15. Viability of thin wall tube forming of ATF FeCrAl

    SciTech Connect

    Maloy, Stuart Andrew; Aydogan, Eda; Anderoglu, Osman; Lavender, Curt; Yamamoto, Yukinori

    2016-09-16

    Fabrication of thin walled tubing of FeCrAl alloys is critical to its success as a candidate enhanced accident-tolerant fuel cladding material. Alloys that are being investigated are Generation I and Generation II FeCrAl alloys produced at ORNL and an ODS FeCrAl alloy, MA-956 produced by Special Metals. Gen I and Gen II FeCrAl alloys were provided by ORNL and MA-956 was provided by LANL (initially produced by Special Metals). Three tube development efforts were undertaken. ORNL led the FeCrAl Gen I and Gen II alloy development and tube processing studies through drawing tubes at Rhenium Corporation. LANL received alloys from ORNL and led tube processing studies through drawing tubes at Century Tubing. PNNL led the development of tube processing studies on MA-956 through pilger processing working with Sandvik Corporation. A summary of the recent progress on tube development is provided in the following report and a separate ORNL report: ORNL/TM-2015/478, “Development and Quality Assessments of Commercial Heat Production of ATF FeCrAl Tubes”.

  16. Hydrogen permeation in FeCrAl alloys for LWR cladding application

    SciTech Connect

    Hu, Xunxiang; Terrani, Kurt A.; Wirth, Brian D.; Snead, Lance L.

    2015-03-19

    FeCrAl is an advanced oxidation-resistant iron-based alloy class, is a highly prevalent candidate as an accident-tolerant fuel cladding material. Compared with traditional zirconium alloy fuel cladding, increased tritium permeation through FeCrAl fuel cladding to the primary coolant is expected, raising potential safety concerns. In our study, the hydrogen permeability of several FeCrAl alloys was obtained using a static permeation test station, which was calibrated and validated using 304 stainless steel. The high hydrogen permeability of FeCrAl alloys leads to concerns with respect to potentially significant tritium release when used for fuel cladding in LWRs. Also, the total tritium inventory inside the primary coolant of a light water reactor was quantified by applying a 1-dimensional steady state tritium diffusion model to demonstrate the dependence of tritium inventory on fuel cladding type. Furthermore, potential mitigation strategies for tritium release from FeCrAl fuel cladding were discussed and indicate the potential for application of an alumina layer on the inner clad surface to serve as a tritium barrier. More effort is required to develop a robust, economical mitigation strategy for tritium permeation in reactors using FeCrAl clad fuel assemblies.

  17. Effect of surface morphology and magnetic impurities on the electronic structure in cobalt-doped BaFe2As2 superconductors

    DOE PAGES

    Zou, Qiang; Wu, Zhiming; Fu, Mingming; ...

    2017-01-31

    Combined scanning tunneling microscopy, spectroscopy, and local barrier height (LBH) studies show that low-temperature-cleaved optimally doped Ba(Fe1–xCox)2As2 crystals with x = 0.06, with Tc = 22 K, have complicated morphologies. Although the cleavage surface and hence the morphologies are variable, the superconducting gap maps show the same gap widths and nanometer size inhomogeneities irrelevant to the morphology. Based on the spectroscopy and LBH maps, the bright patches and dark stripes in the morphologies are identified as Ba- and As-dominated surface terminations, respectively. Magnetic impurities, possibly due to Co or Fe atoms, are believed to create local in-gap state and, inmore » addition, suppress the superconducting coherence peaks. Lastly, this study will clarify the confusion on the cleavage surface terminations of the Fe-based superconductors and its relation with the electronic structures.« less

  18. Effect of Surface Morphology and Magnetic Impurities on the Electronic Structure in Cobalt-Doped BaFe 2 As 2 Superconductors

    DOE PAGES

    Zou, Qiang; Wu, Zhiming; Fu, Mingming; ...

    2017-02-03

    Combined scanning tunneling microscopy, spectroscopy, and local barrier height (LBH) studies show that low-temperature-cleaved optimally doped Ba(Fe1–xCox)2As2 crystals with x = 0.06, with Tc = 22 K, have complicated morphologies. Although the cleavage surface and hence the morphologies are variable, the superconducting gap maps show the same gap widths and nanometer size inhomogeneities irrelevant to the morphology. Based on the spectroscopy and LBH maps, the bright patches and dark stripes in the morphologies are identified as Ba- and As-dominated surface terminations, respectively. Magnetic impurities, possibly due to Co or Fe atoms, are believed to create local in-gap state and, inmore » addition, suppress the superconducting coherence peaks. Lastly, this study will clarify the confusion on the cleavage surface terminations of the Fe-based superconductors and its relation with the electronic structures.« less

  19. Role of magnetism in superconductivity of BaFe2As2: Study of 5d Au-doped crystals

    SciTech Connect

    Li, Li; Cao, Huibo; McGuire, Michael A.; Kim, J. S.; Stewart, G. R.; Sefat, Athena Safa

    2015-09-09

    We investigate properties of BaFe2As2 (122) single crystals upon gold doping, which is the transition metal with the highest atomic weight. The Au substitution into the FeAs-planes of 122 crystal structure (Au-122) is only possible up to a small amount of ~3%. We find that 5d is more effective in reducing magnetism in 122 than its counter 3d Cu, and this relates to superconductivity. We provide evidence of short-range magnetic fluctuations and local lattice inhomogeneities that may prevent strong percolative superconductivity in Ba(Fe1-xAux)2As2.

  20. Synthesis of Cd/(Al+Fe) layered double hydroxides and characterization of the calcination products

    SciTech Connect

    Perez, M.R.; Barriga, C.; Fernandez, J.M.; Rives, V.; Ulibarri, M.A.

    2007-12-15

    Layered double hydroxides (LDHs) containing Cd(II), Al(III), and Fe(III) in the brucite-like layers with different starting Fe/Al atomic ratios and with nitrate as counteranion have been prepared following the coprecipitation method at a constant pH value of 8. An additional Cd(II),Al(III)-LDH sample interlayered with hexacyanoferrate(III) ions has been prepared by ionic exchange at pH 9. The samples have been characterized by elemental chemical analysis, powder X-ray diffraction (PXRD), and FT-IR spectroscopy. Their thermal stability has been assessed by thermogravimetric and differential thermal analyses (TG-DTA) and mass spectrometric analysis of the evolved gases. The PXRD patterns of the solids calcined at 800 deg. C show diffraction lines corresponding to Cd(Al)O and spinel-type materials, which precise nature (CdAl{sub 2}O{sub 4}, Cd{sub 1-x}Fe{sub 2+x}O{sub 4}, or Cd{sub x}Fe{sub 2.66}O{sub 4}) depends on location and concentration of iron in the parent material or precursor. - Graphical abstract: Layered double hydroxides (LDHs) containing Cd(II), Al(III), and Fe(III) in the brucite-like layers with different starting Fe/Al atomic ratios and with nitrate as counteranion have been prepared following the coprecipitation method. An additional Cd(II),Al(III)-LDH sample interlayered with hexacyanoferrate(III) ions has been prepared by ionic exchange. Calcination at 800 deg. C shows diffraction lines corresponding to CdO and to spinel-type materials. SEM micrograph of sample CdAlFe-N-0.

  1. Uniaxial-strain mechanical detwinning of CaFe[subscript 2]As[subscript 2] and BaFe[subscript 2]As[subscript 2] crystals: Optical and transport study

    SciTech Connect

    Tanatar, M.A.; Blomberg, E.C.; Kreyssig, A.; Kim, M.G.; Ni, N.; Thaler, A.; Bud’ko, S.L.; Canfield, P.C.; Goldman, A.I.; Mazin, I.I.; Prozorov, R.

    2010-10-22

    The parent compounds of iron-arsenide superconductors, AFe{sub 2}As{sub 2} (A=Ca, Sr, Ba), undergo a tetragonal to orthorhombic structural transition at a temperature T{sub TO} in the range 135-205 K depending on the alkaline-earth element. Below T{sub TO} the free standing crystals split into equally populated structural domains, which mask intrinsic, in-plane, anisotropic properties of the materials. Here we demonstrate a way of mechanically detwinning CaFe{sub 2}As{sub 2} and BaFe{sub 2}As{sub 2}. The detwinning is nearly complete, as demonstrated by polarized light imaging and synchrotron x-ray measurements, and reversible, with twin pattern restored after strain release. Electrical resistivity measurements in the twinned and detwinned states show that resistivity, {rho}, decreases along the orthorhombic a{sub o} axis but increases along the orthorhombic b{sub o} axis in both compounds. Immediately below T{sub TO} the ratio {rho}{sub bo}/{rho}{sub ao} = 1.2 and 1.5 for Ca and Ba compounds, respectively. Contrary to CaFe{sub 2}As{sub 2}, BaFe{sub 2}As{sub 2} reveals an anisotropy in the nominally tetragonal phase, suggesting that either fluctuations play a larger role above T{sub TO} in BaFe{sub 2}As{sub 2} than in CaFe{sub 2}As{sub 2} or that there is a higher temperature crossover or phase transition.

  2. High field superconducting properties of Ba(Fe1-xCox)2As2 thin films

    NASA Astrophysics Data System (ADS)

    Hänisch, Jens; Iida, Kazumasa; Kurth, Fritz; Reich, Elke; Tarantini, Chiara; Jaroszynski, Jan; Förster, Tobias; Fuchs, Günther; Hühne, Ruben; Grinenko, Vadim; Schultz, Ludwig; Holzapfel, Bernhard

    2015-11-01

    In general, the critical current density, Jc, of type II superconductors and its anisotropy with respect to magnetic field orientation is determined by intrinsic and extrinsic properties. The Fe-based superconductors of the ‘122’ family with their moderate electronic anisotropies and high yet accessible critical fields (Hc2 and Hirr) are a good model system to study this interplay. In this paper, we explore the vortex matter of optimally Co-doped BaFe2As2 thin films with extended planar and c-axis correlated defects. The temperature and angular dependence of the upper critical field is well explained by a two-band model in the clean limit. The dirty band scenario, however, cannot be ruled out completely. Above the irreversibility field, the flux motion is thermally activated, where the activation energy U0 is going to zero at the extrapolated zero-kelvin Hirr value. The anisotropy of the critical current density Jc is both influenced by the Hc2 anisotropy (and therefore by multi-band effects) as well as the extended planar and columnar defects present in the sample.

  3. High field superconducting properties of Ba(Fe1−xCox)2As2 thin films

    PubMed Central

    Hänisch, Jens; Iida, Kazumasa; Kurth, Fritz; Reich, Elke; Tarantini, Chiara; Jaroszynski, Jan; Förster, Tobias; Fuchs, Günther; Hühne, Ruben; Grinenko, Vadim; Schultz, Ludwig; Holzapfel, Bernhard

    2015-01-01

    In general, the critical current density, Jc, of type II superconductors and its anisotropy with respect to magnetic field orientation is determined by intrinsic and extrinsic properties. The Fe-based superconductors of the ‘122’ family with their moderate electronic anisotropies and high yet accessible critical fields (Hc2 and Hirr) are a good model system to study this interplay. In this paper, we explore the vortex matter of optimally Co-doped BaFe2As2 thin films with extended planar and c-axis correlated defects. The temperature and angular dependence of the upper critical field is well explained by a two-band model in the clean limit. The dirty band scenario, however, cannot be ruled out completely. Above the irreversibility field, the flux motion is thermally activated, where the activation energy U0 is going to zero at the extrapolated zero-kelvin Hirr value. The anisotropy of the critical current density Jc is both influenced by the Hc2 anisotropy (and therefore by multi-band effects) as well as the extended planar and columnar defects present in the sample. PMID:26612567

  4. Pressure-induced superconductivity in the iron-based ladder material BaFe2S3.

    PubMed

    Takahashi, Hiroki; Sugimoto, Akira; Nambu, Yusuke; Yamauchi, Touru; Hirata, Yasuyuki; Kawakami, Takateru; Avdeev, Maxim; Matsubayashi, Kazuyuki; Du, Fei; Kawashima, Chizuru; Soeda, Hideto; Nakano, Satoshi; Uwatoko, Yoshiya; Ueda, Yutaka; Sato, Taku J; Ohgushi, Kenya

    2015-10-01

    All the iron-based superconductors identified so far share a square lattice composed of Fe atoms as a common feature, despite having different crystal structures. In copper-based materials, the superconducting phase emerges not only in square-lattice structures but also in ladder structures. Yet iron-based superconductors without a square-lattice motif have not been found, despite being actively sought out. Here, we report the discovery of pressure-induced superconductivity in the iron-based spin-ladder material BaFe2S3, a Mott insulator with striped-type magnetic ordering below ∼120 K. On the application of pressure this compound exhibits a metal-insulator transition at about 11 GPa, followed by the appearance of superconductivity below Tc = 14 K, right after the onset of the metallic phase. Our findings indicate that iron-based ladder compounds represent promising material platforms, in particular for studying the fundamentals of iron-based superconductivity.

  5. Absence of strain-mediated magnetoelectric coupling at fully epitaxial Fe/BaTiO{sub 3} interface (invited)

    SciTech Connect

    Radaelli, G. Petti, D.; Cantoni, M.; Rinaldi, C.; Bertacco, R.

    2014-05-07

    Interfacial MagnetoElectric coupling (MEC) at ferroelectric/ferromagnetic interfaces has recently emerged as a promising route to achieve electrical writing of magnetic information in spintronic devices. For the prototypical Fe/BaTiO{sub 3} (BTO) system, various MEC mechanisms have been theoretically predicted. Experimentally, it is well established that using BTO single crystal substrates MEC is dominated by strain-mediated mechanisms. In case of ferromagnetic layers epitaxially grown onto BTO films, instead, no direct evidence for MEC has been provided, apart from the results obtained on tunneling junction sandwiching a BTO tunneling barrier. In this paper, MEC at fully epitaxial Fe/BTO interface is investigated by Magneto-Optical Kerr Effect and magnetoresistance measurements on magnetic tunnel junctions fabricated on BTO. We find no evidence for strain-mediated MEC mechanisms in epitaxial systems, likely due to clamping of BTO to the substrate. Our results indicate that pure electronic MEC is the route of choice to be explored for achieving the electrical writing of information in epitaxial ferromagnet-ferroelectric heterostructures.

  6. Giant magnetoelastic effect in multiferroic Ba0.6Sr1.4Zn2Fe12O22

    NASA Astrophysics Data System (ADS)

    Talbayev, Diyar; Averitt, Richard D.; Taylor, Antoinette J.; Kimura, Tsuyoshi

    2007-03-01

    Dynamical studies of multiferroic materials help unravel the fundamental interactions between various degrees of freedom and answer technological questions such as achievable switching speeds in multiferroic-based memory elements. We report the results of the ultrafast optical study of multiferroic Ba0.6Sr1.4Zn2Fe12O22, which reveals a giant magnetoelastic effect in the material. The compound exhibits a hexagonal crystal structure and a helical magnetic ground state below ˜ 330 K. In applied magnetic field, the hexaferrite undergoes a series of magnetic phase transitions and develops ferroelectric polarization. The magnetoelastic effect is detected via the measurement of the speed of sound in the crystal as a function of magnetic field. The oscillation in the optically induced transient reflectivity resulting from the propagating coherent-phonon strain pulse allows us to measure the field-induced changes in the speed of sound and the corresponding dramatic changes in the elastic stiffness. The dependence of the exchange interaction on the distance between Fe ions gives rise to the observed magnetoelasticity. Our results indicate a route towards the magnetically modulated transducers and piezoelectric devices.

  7. Structural transitions in iron-based Ba3NbFe3Si2O14 langasite at high pressures

    NASA Astrophysics Data System (ADS)

    Nikiforova, Yu. A.; Gavriliuk, A. G.; Lyubutin, I. S.; Ivanova, A. G.; Troyan, I. A.; Starchikov, S. S.; Aksenov, S. N.; Struzhkin, V. V.; Sul'yanov, S. N.; Glazyrin, K. V.

    2016-12-01

    Synchrotron X-ray diffraction studies of the structural characteristics of Ba3NbFe3Si2O14 langasite were performed at high hydrostatic pressures (up to 60 GPa) created in a diamond anvil cell. The Mössbauer absorption spectra of 57Fe nuclei and optical absorption spectra were recorded at pressures up to 10 and 54 GPa, respectively. The cascade of structural phase transitions at pressures of about ∼ 3, ∼ 20, and ∼ 41 GPa was discovered. The first transition corresponds to the displacements of light oxygen atoms and associated with an increase in the local symmetry of oxygen 3f tetrahedra surrounding iron ions. The volume drop at the first transition is about 1.5%. The second transition at ∼ 20 GPa is accompanied by a pronounced change in the lattice parameters a and c, while the unit cell volume undergoes a stepwise drop by 7%. Significant decrease in the parameter c at the structural transition should result in a strong increase of the exchange coupling constants between iron ions in neighboring ab planes, which may lead to a giant increase in the Néel temperature in this crystal at pressures above ∼ 20 GPa. At the third transition at about 38–44 GPa, only a small anomaly in the V\\text-P relation is observed, but this anomaly is accompanied by substantial changes in the optical gap and in the quadruple splitting parameter.

  8. Magnetic and microstructural properties of nanocrystalline Fe-25 at% Al and Fe-25 at% Al +0.2 at%B alloys prepared by mechanical alloying process

    NASA Astrophysics Data System (ADS)

    Ibn Gharsallah, H.; Makhlouf, T.; Escoda, L.; Suñol, J. J.; Khitouni, M.

    2016-04-01

    In the present work, structural and magnetic properties of nanocrystalline Fe-25at%Al and Fe-25at%Al+0.02at%B alloys produced by mechanical alloying were studied. Their microstructural properties were investigated by X-ray diffraction, scanning electron microscopy and vibrating sample magnetometer. A BCC-nanostructured Fe(Al,B) solid solution with an average crystallite size of about 18nm has been produced by milling for 4h. Whereas in Fe-25at%Al the alloying process has been accomplished after 16h of milling. It is found that B speeds up the formation of a bcc phase with finer microstructure (around 5nm) after 40h of milling. When increasing the milling time, the crystallite size decreases for all powders. An increase in microstrain was observed with increasing the milling time and also with addition of boron. Coercivity and the saturation magnetization of alloyed powders were measured at room temperature by a vibration sample magnetization. The magnetic measurements show a contrasting saturation magnetization and coercivity ( Hc) in both alloys. These variations are explained by crystallite size and strain variations in the samples during milling.

  9. Morphology and photoluminescence of BaAl12O19:Mn2+ green phosphor prepared by flux method

    NASA Astrophysics Data System (ADS)

    Zhou, Jun; Wang, Yu-Hua; Liu, Bi-Tao; Liu, Ji-Di

    2010-12-01

    This paper reports that the green phosphor BaAl11.9O19:0.1Mn2+ is prepared by a flux assisted solid state reaction method. The effect of flux systems on the crystal structure, morphology and luminescent properties of the phosphor are studied in detail. The samples are characterized by the application of x-ray diffraction patterns, scanning electron microscopy patterns, luminescent spectra and decay curves. The results show that a pure phase BaAl12O19 can be achieved at the firing temperature above 1300 °C by adding the proper flux system, the firing temperature is reduced at least 200 °C in comparison with the conventional solid state reaction method. Maximum photoluminescence emission intensity is observed at 517 nm for (AlF3+Li2CO3) flux system under vacuum ultraviolet region (147 nm) excitation. The photoluminescence emission intensity and the decay time of these phosphor is found to be more superior to that of the corresponding sample prepared by the conventional solid state reaction method implying the suitability of this route for the preparation of display device worthy phosphor materials.

  10. Anisotropy and Vortex Pinning of Heavy Ion irradiated SmFeAsO0.8F0.15 and BaFe2(As1-xPx)2 Crystals

    NASA Astrophysics Data System (ADS)

    Kwok, Wai-Kwong; Fang, Lei; Chaparro, Carlos; Jia, Ying; Welp, Ulrich; Koshelev, Alexei; Xu, Shaofei; Crabtree, George; Karpinski, Janusz

    2012-02-01

    We report specific heat and magnetization measurements on SmFeAsO0.8F0.15 and BaFe2(As1-xPx)2 single crystals irradiated with high energy heavy ions of 1.4GeV Pb to dose matching fields up to 4 Tesla. We find a nearly one half reduction in the superconducting anisotropy and doubling of the irreversibility field in SmFeAsO0.8F0.15 after irradiation and virtually no change in the zero-field superconducting transition temperature. In both SmFeAsO0.8F0.15 and BaFe2(As1-xPx)2 crystals, we find a substantial increase in the critical current determined from SQUID and micro-Hall probe magnetization measurements. Pinning force analysis on proton and heavy ion irradiated pristine overdoped BaFe2(As1-xPx)2 crystals indicates presence of induced δTc-type pinning defects in these samples.

  11. Preparation of nanofiber polythiophene layered on Ba x Sr1- x Fe12O19/Fe3O4/polyacrylic acid core-shell structure and its microwave absorption investigation

    NASA Astrophysics Data System (ADS)

    Hosseini, Seyed Hossein; Moloudi, Maryam

    2015-09-01

    Ba x Sr1- x Fe12O19/Fe3O4/polyacrylic acid/polythiophene (Ba x Sr1- x Fe12O19/Fe3O4/PAA/PTh) nanocomposites with multi-core-shell structure were successfully synthesized by four steps. The samples were characterized by FTIR, X-ray diffraction (XRD), transmission electron microscope (TEM), vibrating sample magnetometer, and radar absorbing material reflectivity far-field radar cross-section method, respectively. XRD and TEM results indicated that the obtained nanoparticles have multi-core-shell morphology. The magnetic properties and microwave absorption analyses reveal that there are interphase interactions at the interface of Ba x Sr1- x Fe12O19, Fe3O4, PAA, and PTh, which can affect the magnetic properties and microwave absorption properties of the samples. The microwave-absorbing properties of nanocomposites were investigated at 8-14 GHz. A typical layer absorber exhibited an excellent microwave absorption with a -26 dB maximum absorption at 14 GHz. Compared with core material, the coercivity and saturation magnetization of multi-core-shell nanocomposites decrease obviously, but the microwave absorption properties of nanocomposites are improved greatly. The results show that these composite could be used as advancing absorption and shielding materials due to their favorable microwave-absorbing properties.

  12. Electronic anisotropy from magneto-transport near Tc in SmFeAs(O0.7F0.25) and (Ba,Rb)Fe2As2 single crystals

    NASA Astrophysics Data System (ADS)

    Moll, Philip; Kunze, Karsten; Bukowski, Zbigniew; Zhigadlo, Nikolai; Karpinski, Janusz; Batlogg, Bertram

    2009-03-01

    We derived thermally activated flux flow (TAFF) activation energies Ea(H) and the upper critical fields Hc2(T) parallel to the c-axis and in the Lorentz-force free configuration (H || ab || j) of SmFeAs(O0.7F0.25) and (Ba,Rb)Fe2As2 single crystals from resistance measurements and compare them to the ones reported for other REFeAs(OF). A perfectly rectangular rod (67x11x4 μm), aligned with the crystal axes, was cut from a larger SmFeAs(O0.7F0.25) single crystal (˜ 200 μm) by a Focused Ion Beam (FIB) which allowed us to precisely control its geometry factor L/A = 0.89 1/μm. The FIB was also used to deposit 4 Pt contacts. We found a slope of Hc2, 50% (T), parallel to the c-axis, of 1.9 T/K for SmFeAs(O0.7F0.25) and 3.7 T/K for (Ba,Rb)Fe2As2 near Tc. The electronic anisotropy, derived from magneto-transport, is significantly larger in the REFeAs(OF) crystals than in (Ba,Rb)Fe2As2.

  13. Induced lattice strain in epitaxial Fe-based superconducting films on CaF{sub 2} substrates: A comparative study of the microstructures of SmFeAs(O,F), Ba(Fe,Co){sub 2}As{sub 2}, and FeTe{sub 0.5}Se{sub 0.5}

    SciTech Connect

    Ichinose, Ataru Tsukada, Ichiro; Nabeshima, Fuyuki; Imai, Yoshinori; Maeda, Atsutaka; Kurth, Fritz; Holzapfel, Bernhard; Iida, Kazumasa; Ueda, Shinya; Naito, Michio

    2014-03-24

    The microstructures of SmFeAs(O,F), Ba(Fe,Co){sub 2}As{sub 2}, and FeTe{sub 0.5}Se{sub 0.5} prepared on CaF{sub 2} substrates were investigated using transmission electron microscopy. The SmFeAs(O,F)/CaF{sub 2} interface is steep, without a disordered layer. By contrast, a chemical reaction occurs at the interface in the cases of Ba(Fe,Co){sub 2}As{sub 2} and FeTe{sub 0.5}Se{sub 0.5}. The reaction layers are located on opposite sides of the interface for Ba(Fe,Co){sub 2}As{sub 2} and FeTe{sub 0.5}Se{sub 0.5}. We found that the lattice distortion of the three superconducting films on the CaF{sub 2} substrates enhances the T{sub C} values compared with films prepared on oxide substrates. The origin of this lattice deformation varies depending on the superconducting material.

  14. Microstructured Al/Fe2O3/Nitrocellulose Energetic Fibers Realized by Electrospinning

    NASA Astrophysics Data System (ADS)

    Li, Rui; Xu, Hongmei; Hu, Hailong; Yang, Guangcheng; Wang, Jun; Shen, Jinpeng

    2014-01-01

    At present, metastable intermolecular composites (MICs) have been widely studied for their potential in high-density energetic materials and nanotechnology, but the relatively low-pressure discharge in a short period of time and the oxidation of Al powders have seriously impeded their applications in rocket solid fuels and explosives. In this work, the authors successfully fabricated microstructured Al/Fe2O3/nitrocellulose (Al/Fe2O3/NC) fibers via simple electrospinning, introducing nitrocellulose (NC), a gas generator to MICs. In view of previous reports, wrapping nAl in NC fibers might reduce their further oxidation during storage. In addition, the thermal properties and elastic modulus of NC fibers were measured before and after adding Al/Fe2O3.

  15. Microstructure properties and microhardness of rapidly solidified Al64Cu20Fe12Si4 quasicrystal alloy

    NASA Astrophysics Data System (ADS)

    Karaköse, Ercan; Keskin, Mustafa

    2012-04-01

    This paper presents differences in the microstructure and microhardness properties of conventional casting (ingot) and rapidly solidified Al64Cu20Fe12Si4 quasicrystal (QC) alloys. The phases present in the Al64Cu20Fe12Si4 ingot alloy were determined to be icosahedral quasicrystalline (IQC) Ψ-Al65Cu20Fe15, cubic β-AlFe, tetragonal θ-Al2Cu, and monoclinic λ-A13Fe4 phases, whereas only IQC Ψ-Al65Cu20Fe15 and cubic β-AlFe phases were identified in the rapidly solidified alloy. The microhardness value of the melt spun alloy was measured to be approximately 790 kg/mm2. Microhardness increases with increasing solidification rates.

  16. HPHT synthesis, structure and electrical properties of type-I clathrates Ba{sub 8}Al{sub x}Si{sub 46−x}

    SciTech Connect

    Liu, Binwu; Jia, Xiaopeng; Sun, Hairui; Sun, Bing; Zhang, Yuewen; Liu, Haiqiang; Kong, Lingjiao; Huo, Dexuan; Ma, Hongan

    2016-01-15

    Clathrate compounds Ba{sub 8}Al{sub x}Si{sub 46−x} were successfully synthesized using the method of high-pressure and high-temperature (HPHT). In this process, we used BaSi{sub 2} as one of the starting materials in place of Ba metals, which reduces the complexity of the program caused by the extremely high chemical reactivity. By using this method, the processing time was reduced from few days to an hour. X-ray diffraction and structural refinement indicated this composition crystallized in type-I clathrate phase. Bond length analysis showed the Ba atoms in small dodecahedron had spherical thermal ellipsoids while those in large tetrakaidecahedron displayed anisotropic thermal ellipsoids. The negative Seebeck coefficient indicated transport processes were dominated by electrons as carriers, and increased with the increasing temperature. The electrical properties, including Seebeck coefficient and Power factor, were greatly enhanced by Al substitution. - Graphical abstract: Left: The cavity structure diagram of a China-type large volume cubic high-pressure apparatus, and the Type-I clathrate structure of sample synthesized using HPHT. Middle: X-ray Rietveld refinement profile for Ba{sub 8}Si{sub 46} and element mapping for Ba{sub 8}Al{sub 16}Si{sub 30}. Right: Temperature dependence of Seebeck coefficient for Ba{sub 8}Al{sub x}Si{sub 46−x} prepared by HPHT. - Highlights: • HPHT is a simple and rapid synthetic approach. • We use BaSi{sub 2} as one of the starting materials replacing Ba metals. • The processing time reduces from few days to an hour. • Structure determination is refined by Rietveld analysis of XRD data. • Variable temperature electrical properties are characterized.

  17. A systematic ALCHEMI study of Fe-doped NiAl alloys

    SciTech Connect

    Anderson, I.M.; Bentley, J.; Duncan, A.J.

    1995-06-01

    ALCHEMI site-occupation studies of alloying additions to ordered aluminide intermetallic alloys have been performed with varying degrees of success, depending on the ionization delocalization correction. This study examines the variation in the site-occupancy of Fe in B2-ordered NiAl vs solute concentration and alloy stoichiometry. The fraction of Fe on the `Ni` site is plotted vs Fe concentration. The good separation among the data from alloys of the three stoichiometries shows that the site occupancy of iron depends on the relative concentrations of the Ni and Al host elements; however a preference for the `Ni` site is clearly indicated.

  18. Comparative study using MS and XRD of Fe80Al20 alloy produced by mechanical alloying

    NASA Astrophysics Data System (ADS)

    Hadef, F.; Otmani, A.; Grenèche, J. M.

    2013-08-01

    An X-ray diffraction and 57Fe Mössbauer effect study of mechanically alloyed Fe80Al20 is presented. X-ray measurements indicate that the disordered bcc α-Fe(Al) solid solution was formed after 2 h of milling, while the analysis of Mössbauer spectra suggested that total dissolution of aluminium is achieved after 10 h of milling. These differences can be attributed to: (i) rapid nanocrystallization of aluminium and/or (ii) small particles with small amounts of aluminium cannot be detected by the X-ray diffraction technique.

  19. Enhanced critical-current in P-doped BaFe2As2 thin films on metal substrates arising from poorly aligned grain boundaries

    PubMed Central

    Sato, Hikaru; Hiramatsu, Hidenori; Kamiya, Toshio; Hosono, Hideo

    2016-01-01

    Thin films of the iron-based superconductor BaFe2(As1−xPx)2 (Ba122:P) were fabricated on polycrystalline metal-tape substrates with two kinds of in-plane grain boundary alignments (well aligned (4°) and poorly aligned (8°)) by pulsed laser deposition. The poorly aligned substrate is not applicable to cuprate-coated conductors because the in-plane alignment >4° results in exponential decay of the critical current density (Jc). The Ba122:P film exhibited higher Jc at 4 K when grown on the poorly aligned substrate than on the well-aligned substrate even though the crystallinity was poorer. It was revealed that the misorientation angles of the poorly aligned samples were less than 6°, which are less than the critical angle of an iron-based superconductor, cobalt-doped BaFe2As2 (~9°), and the observed strong pinning in the Ba122:P is attributed to the high-density grain boundaries with the misorientation angles smaller than the critical angle. This result reveals a distinct advantage over cuprate-coated conductors because well-aligned metal-tape substrates are not necessary for practical applications of the iron-based superconductors. PMID:27833118

  20. Monolithic translucent BaMgAl10O17:Eu2+ phosphors for laser-driven solid state lighting

    NASA Astrophysics Data System (ADS)

    Cozzan, Clayton; Brady, Michael J.; O'Dea, Nicholas; Levin, Emily E.; Nakamura, Shuji; DenBaars, Steven P.; Seshadri, Ram

    2016-10-01

    With high power light emitting diodes and laser diodes being explored for white light generation and visible light communication, thermally robust encapsulation schemes for color-converting inorganic phosphors are essential. In the current work, the canonical blue-emitting phosphor, high purity Eu-doped BaMgAl10O17, has been prepared using microwave-assisted heating (25 min) and densified into translucent ceramic phosphor monoliths using spark plasma sintering (30 min). The resulting translucent ceramic monoliths convert UV laser light to blue light with the same efficiency as the starting powder and provide superior thermal management in comparison with silicone encapsulation.

  1. Perpendicular magnetic anisotropy in Ta|Co40Fe40B20|MgAl2O4 structures and perpendicular CoFeB|MgAl2O4|CoFeB magnetic tunnel junction

    NASA Astrophysics Data System (ADS)

    Tao, B. S.; Li, D. L.; Yuan, Z. H.; Liu, H. F.; Ali, S. S.; Feng, J. F.; Wei, H. X.; Han, X. F.; Liu, Y.; Zhao, Y. G.; Zhang, Q.; Guo, Z. B.; Zhang, X. X.

    2014-09-01

    Magnetic properties of Co40Fe40B20 (CoFeB) thin films sandwiched between Ta and MgAl2O4 layers have been systematically studied. For as-grown state, Ta/CoFeB/MgAl2O4 structures exhibit good perpendicular magnetic anisotropy (PMA) with interface anisotropy Ki = 1.22 erg/cm2, which further increases to 1.30 erg/cm2 after annealing, while MgAl2O4/CoFeB/Ta multilayer shows in-plane magnetic anisotropy and must be annealed in order to achieve PMA. For bottom CoFeB layer, the thickness window for PMA is from 0.6 to 1.0 nm, while that for top CoFeB layer is between 0.8 and 1.4 nm. Perpendicular magnetic tunnel junctions (p-MTJs) with a core structure of CoFeB/MgAl2O4/CoFeB have also been fabricated and tunneling magnetoresistance ratio of about 36% at room temperature and 63% at low temperature have been obtained. The intrinsic excitations in the p-MTJs have been identified by inelastic electron-tunneling spectroscopy.

  2. Thermal Stability of the Dynamic Magnetic Properties of FeSiAl-Al2O3 and FeSiAl-SiO2 Films Grown by Gradient-Composition Sputtering Technique

    NASA Astrophysics Data System (ADS)

    Zhong, Xiaoxi; Phuoc, Nguyen N.; Soh, Wee Tee; Ong, C. K.; Peng, Long; Li, Lezhong

    2017-01-01

    We carry out a systematic investigation of the dynamic magnetic properties of FeSiAl-Al2O3 and FeSiAl-SiO2 thin films prepared by gradient-composition deposition technique with respect to temperature in the range of 300 K to 420 K. It was found that the magnetic anisotropy field ( H K) and ferromagnetic resonance frequency ( f FMR) are increased with increasing deposition angle ( β) due to the enhancement of stress ( σ) when concentrations of Al and O or Si and O are increased. The thermal stability of FeSiAl-Al2O3 films show a very interesting behavior with the magnetic anisotropy increasing with temperature when the deposition angle is increased. In contrast, when the deposition angle is lower, the usual trend of decreasing magnetic anisotropy with increasing temperature is observed. Moreover, the temperature-dependent behaviors of the dynamic permeability and effective Gilbert damping coefficient ( α eff) for FeSiAl-Al2O3 and FeSiAl-SiO2 films at different deposition angles are discussed in detail.

  3. Influence of addition of Si in FeAl alloys: Theory

    NASA Astrophysics Data System (ADS)

    Apiñaniz, E.; Legarra, E.; Plazaola, F.; Garitaonandia, J. S.

    The magnetic behaviour of Fe-based magnetic systems has been studied theoretically and experimentally for many years [E.P. Wohlfath, K.H.J. Buschow, Handbook of Ferromagnetic Materials, vol. 4, North-Holland Elsevier Science Publishers, Amsterdam, New York, Oxford, Tokyo, 1988 (Chapter 1)]. Starting with Al dissolved in Fe, the first stable structure is the D03 cubic structure and it exists over the range 23-37 at% Al. In this range these alloys present interesting magnetic properties. The other stable compound existing over a wide range of composition is FeAl which is also cubic, with the B2 structure (CsCl), and it exists over the range 37-50 at% Al. On the other hand, the FeAlSi alloys show the D03 structure, but do not show the B2 structure. The effect of Si in these alloys is double; on the one hand, it contributes to the decrease of the lattice parameter which, as reported by Nogues et al. [Phys. Rev. B 74 (2006) 024407], has a major influence on the magnetism and, on the other hand, having one more p electron than the Al atom, it promotes the charge transfer from Si to Fe atoms, as reported by Legarra et al. [Hyperfine Interact. 169 (2006) 1217-1222]. In this work, we perform ab-initio electronic calculations by means of tight binding linear muffin-tin orbital (TBLMTO) and Vienna Ab-initio Simulation Package (VASP) in order to study the magnetic contribution of Si/Al substitution in the FeAl alloys.

  4. Mössbauer and electrical conduction investigations of LiFe(BaTi)(PO4) NASICON nano composite

    NASA Astrophysics Data System (ADS)

    Hassaan, M. Y.; Kaixin, Zhu; Wang, Junhu; Moustafa, M. G.

    2016-12-01

    NASICON glass sample with a composition of Li 1.3Fe 0.3(BaTi) 1.7(PO 4) 3 was prepared using the conventional melt-quenching technique at 1300 ∘C for one hour after two stages of calcination process at 300 ∘C and 600 ∘C respectively. DTA was used to determine (T g) and (T c) of the as-quenched glass sample. XRD was used to confirm the glassy state of the prepared sample. The as-quenched glass sample was heat treated near its onset crystallization temperature for different times 1, 2, 3, 4, and 5 hours. The gradual precipitation of the crystalline nano-particles with NASICON type structure was also confirmed using XRD. The as-prepared sample and the five heat treated (HT) samples were investigated using Mössbauer spectroscopy, DC and AC conductivities and dielectric permittivity. FTIR, density, and TEM measurements were also performed. After HT, XRD and FTIR measurements conformed the formation of NASICON phase. The results of the dielectric permittivity showed no maximum peak in the studied temperature and frequency ranges, which indicates the absence of ferroelectric behavior of the HT glass sample. Mössbauer data showed that the iron in the glass and its HT samples include two ionic states, Fe 3+ (O h) and Fe 2+ (O h) ions. It is observed that the DC conductivity of the HT glass for 5 h was almost two orders of magnitude higher than that of the parent glass.

  5. An overview of the welding of Ni{sub 3}Al and Fe{sub 3}Al alloys

    SciTech Connect

    Santella, M.L.

    1996-12-31

    Weldability (degree to which defect formation is resisted when an alloy is welded) is an issue in fabrication of Ni{sub 3}Al and Fe{sub 3}Al. Work to define and improve welding of Ni{sub 3}Al and Fe{sub 3}Al alloys is reviewed and progress illustrated by examples of current activities. The cast Ni{sub 3}Al alloys currently under development, IC221M and IC396M, have low resistance to solidification cracking and hence difficult to weld. Modifications to the composition of both base alloys and weld deposits,however, increase their resistance to cracking. Crack-free, full-penetration welds were made in centrifugally cast tubes of IC221M. Tensile and stress- rupture properties of the weldments compare favorably with base metal properties. Weldability issues have limited the use of Fe{sub 3}Al alloys to weld overlay applications. Filler metal compositions suitable for weld overlay cladding were developed, and the preheat and postweld heat treatment needed to avoid cracking, were determined experimentally.

  6. Interfacial perpendicular magnetic anisotropy and damping parameter in ultra thin Co2FeAl films

    NASA Astrophysics Data System (ADS)

    Cui, Yishen; Khodadadi, Behrouz; Schäfer, Sebastian; Mewes, Tim; Lu, Jiwei; Wolf, Stuart A.

    2013-04-01

    B2-ordered Co2FeAl films were synthesized using an ion beam deposition tool. A high degree of chemical ordering ˜81.2% with a low damping parameter (α) less than 0.004 was obtained in a 50 nm thick film via rapid thermal annealing at 600 °C. The perpendicular magnetic anisotropy (PMA) was optimized in ultra thin Co2FeAl films annealed at 350 °C without an external magnetic field. The reduced thickness and annealing temperature to achieve PMA introduced extrinsic factors thus increasing α significantly. However, the observed damping of Co2FeAl films was still lower than that of Co60Fe20B20 films prepared at the same thickness and annealing temperature.

  7. Magnetic properties and microstructure of L10-FePt/AlN perpendicular nanocomposite films

    NASA Astrophysics Data System (ADS)

    Feng, C.; Zhang, E.; Xu, C. C.; Li, N.; Jiang, Y.; Yu, G. H.; Li, B. H.

    2011-09-01

    Based on interfacial manipulation of a MgO (100) substrate and non-magnetic AlN compound, L10-FePt/AlN perpendicular nanocomposite films were designed and prepared. Systematic studies on magnetic properties and microstructure of the films show that the MgO substrate controls crystal orientation of the FePt lattice and induces perpendicular magnetic anisotropy (PMA). The AlN compound helps to control the island growth mode and acts as isolators of FePt islands to pin the sites of FePt domains, resulting in manipulation of coercivity and magnetic exchange interaction of the films. Moreover, PMA of the film was optimized by appropriately decreasing film thickness or increasing substrate temperature.

  8. Status of FeCrAl ODS Irradiations in the High Flux Isotope Reactor

    SciTech Connect

    Field, Kevin G.; Howard, Richard H.

    2016-08-19

    FeCrAl oxide-dispersion strengthened (ODS) alloys are an attractive sub-set alloy class of the more global FeCrAl material class for nuclear applications due to their high-temperature steam oxidation resistance and hypothesized enhanced radiation tolerance. A need currently exists to determine the radiation tolerance of these newly developed alloys. To address this need, a preliminary study was conducted using the High Flux Isotope Reactor (HFIR) to irradiate an early generation FeCrAl ODS alloy, 125YF. Preliminary post-irradiation examination (PIE) on these irradiated specimens have shown good radiation tolerance at elevated temperatures (≥330°C) but possible radiation-induced hardening and embrittlement at irradiations of 200°C to a damage level of 1.9 displacement per atom (dpa). Building on this experience, a new series of irradiations are currently being conceptualized. This irradiation series called the FCAD irradiation program will irradiate the latest generation FeCrAl ODS and FeCr ODS alloys to significantly higher doses. These experiments will provide the necessary information to determine the mechanical performance of irradiated FeCrAl ODS alloys at light water reactor and fast reactor conditions.

  9. Observations of the Minor Species Al, Fe and Ca(+) in Mercury's Exosphere

    NASA Technical Reports Server (NTRS)

    Bida, Thomas A.; Killen, Rosemary M.

    2011-01-01

    We report the first detections of Al and Fe, and strict upper limits for Ca(+) in the exosphere of Mercury, using the HIRES spectrometer at the Keck I telescope. We report observed 4-sigma tangent columns of 1.5x10(exp 7) Al atoms per square centimeter at an altitude of 1220 km (1.5 Mercury radii (R(sub M)) from planet center), and that for Fe of 1.6 x 10 per square centimeter at an altitude of 950 km (1.4 R(sub M)). The observed 3-sigma Ca(+) column was 3.9x10(exp 6) ions per square centimeter at an altitude of 1630 km (1.67 R(sub M). A simple model for zenith column abundances of the neutral species were 9.5 x 10(exp 7) Al per square centimeter, and 3.0 x 10(exp 8) Fe per square centimeter. The observations appear to be consistent with production of these species by impact vaporization with a large fraction of the ejecta in molecular form. The scale height of the Al gas is consistent with a kinetic temperature of 3000 - 9000 K while that of Fe is 10500 K. The apparent high temperature of the Fe gas would suggest that it may be produced by dissociation of molecules. A large traction of both Al and Fe appear to condense in a vapor cloud at low altitudes.

  10. Metal-insulator transition in Ba3Fe1 -xRu2 +xO9 : Interplay between site disorder, chemical percolation, and electronic structure

    NASA Astrophysics Data System (ADS)

    Middey, S.; Aich, Payel; Meneghini, C.; Mukherjee, K.; Sampathkumaran, E. V.; Siruguri, V.; Mahadevan, P.; Ray, Sugata

    2016-11-01

    Perovskites containing barium metal at the A site often take up unusual hexagonal structures having more than one type of possible sites for the B cation to occupy. This opens up various different B -B - or B -O-B -type connectivities and consequent physical properties which are naturally missing in cubic perovskites. BaRuO3 is one such system where doping of Ru (4 d4 ) by other transition metals (Mn +) creates similar conditions, giving rise to various M -Ru interactions. Interestingly, the 6 H hexagonal structure of doped barium ruthenate triple perovskite (Ba3M Ru2O9 ) seems to possess some internal checks because within the structure M ion always occupies the 2 a site and Ru goes to the 4 f site, allowing only M -O-Ru 180∘ and Ru-O-Ru 90∘ interactions to occur. The only exception is observed in the case of the Fe dopant, which allows us to study almost the full Ba3Fe1 -xRu2 +xO9 series of compounds with wide ranges of x because here Fe ions have the ability to freely go to the 4 f sites and Ru readily takes up the 2 a positions. Therefore, here one has the opportunity to probe the evolution of electronic and magnetic properties as a function of doping by going from BaRuO3 (paramagnetic metal) to BaFeO3 (ferromagnetic insulator). Our detailed experimental and theoretical results show that the series does exhibit a percolative metal-insulator transition with an accompanying but not coincidental magnetic transition as a function of x .

  11. Large magnetization and high Curie temperature in highly disordered nanoscale Fe2CrAl thin films

    NASA Astrophysics Data System (ADS)

    Dulal, Rajendra P.; Dahal, Bishnu R.; Forbes, Andrew; Pegg, Ian L.; Philip, John

    2017-02-01

    We have successfully grown nanoscale Fe2CrAl thin films on polished Si/SiO2 substrates using an ultra-high vacuum deposition with a base pressure of 9×10-10 Torr. The thickness of thin films ranges from 30 to 100 nm. These films exhibit cubic crystal structure with lattice disorder and display ferromagnetic behavior. The Curie temperature is greater than 400 K, which is much higher than that reported for bulk Fe2CrAl. The magnetic moments of the films varies from 2.5 to 2.8 μB per formula unit, which is larger than the reported bulk values. Thus, the disordered nanoscale Fe2CrAl films exhibit strong Fe-Fe exchange interactions through Fe-Cr-Fe and Fe-Al-Fe layers, resulting in both a large magnetization and a high Curie temperature.

  12. Atomic origin of the spin-polarization of the Co2FeAl Heusler compound

    NASA Astrophysics Data System (ADS)

    Liang, Jaw-Yeu; Lam, Tu-Ngoc; Lin, Yan-Cheng; Chang, Shu-Jui; Lin, Hong-Ji; Tseng, Yuan-Chieh

    2016-02-01

    Using synchrotron x-ray techniques, we studied the Co2FeAl spin-polarization state that generates the half-metallicity of the compound during an A2 (low-spin)  →  B2 (high-spin) phase transition. Given the advantage of element specificity of x-ray techniques, we could fingerprint the structural and magnetic cross-reactions between Co and Fe within a complex Co2FeAl structure deposited on a MgO (0 0 1) substrate. X-ray diffraction and extended x-ray absorption fine structure investigations determined that the Co atoms preferably populate the (1/4,1/4,1/4) and (3/4,3/4,3/4) sites during the development of the B2 phase. X-ray magnetic spectroscopy showed that although the two magnetic elements were ferromagnetically coupled, they interacted in a competing manner via a charge-transfer effect, which enhanced Co spin polarization at the expense of Fe spin polarization during the phase transition. This means that the spin-polarization of Co2FeAl was electronically dominated by Fe in A2 whereas the charge transfer turned the dominance to Co upon B2 formation. Helicity-dependent x-ray absorption spectra also revealed that only the minority state of Co/Fe was involved in the charge-transfer effect whereas the majority state was independent of it. Despite an overall increase of Co2FeAl magnetization, the charge-transfer effect created an undesired trade-off during the Co-Fe exchange interactions, because of the presence of twice as many X sites (Co) as Y sites (Fe) in the Heusler X 2 YZ formula. This suggests that the spin-polarization of Co2FeAl is unfortunately regulated by compromising the enhanced X (Co) sites and the suppressed Y (Fe) sites, irrespective of the development of the previously known high-spin-polarization phase of B2. This finding provides a possible cause for the limited half-metallicity of Co2FeAl discovered recently. Electronic tuning between the X and Y sites is necessary to further increase the spin-polarization, and likely the half

  13. The influence of cooling rate and Fe/Cr content on the evolution of Fe-rich compounds in a secondary Al-Si-Cu diecasting alloy

    NASA Astrophysics Data System (ADS)

    Fabrizi, A.; Timelli, G.

    2016-03-01

    This study investigates the morphological evolution of primary α-Al(Fe,Mn,Cr)Si phase in a secondary Al-Si-Cu alloy with respect to the initial Fe and Cr contents as well as to the cooling rate. The solidification experiments have been designed in order to cover a wide range of cooling rates, and the Fe and Cr contents have been varied over two levels. Metallographic and image analysis techniques have been used to quantitatively examine the microstructural changes occurring at different experimental conditions. The morphological evolution of the α-Fe phase has been also analysed by observing deep etched samples. By changing the cooling rate, α-Al15(Fe,Mn,Cr)3Si2 dodecahedron crystals, as well as Chinese- script, branched structures and dendrites form, while primary coarse β-Al5(Fe,Mn)Si needles appear in the alloy with the highest Fe content at low cooling rates.

  14. Transformation of α-Al(Fe,Mn)Si in Al-7Si-0.4Mg cast alloys after solution heat treatment

    NASA Astrophysics Data System (ADS)

    Han, Sang Won

    2013-01-01

    The α-Al(Fe,Mn)Si compound in an Al-7Si-0.35Mg-0.2Fe-xMn cast alloy has two shapes, a needle-like shape and a Chinese script shape. These two kinds of compounds are tinged with either white or gray tones irrespective of their shape. Unlike compounds with a white tone, during solution heat treatment, all α-Al (Fe,Mn)Si compounds with a gray tone experience severe dissolution. Concerning white-tinged α-Al (Fe,Mn)Si compounds, unlike the needle-like α-Al(Fe,Mn)Si, α-Al(Fe,Mn)Si that resembles Chinese script is rarely transformed.

  15. Fabrication of (Ba,K)Fe2As2 tapes by ex situ PIT process using Ag-Sn alloy single sheath

    NASA Astrophysics Data System (ADS)

    Togano, K.; Gao, Z.; Matsumoto, A.; Kikuchi, A.; Kumakura, H.

    2017-01-01

    Instead of ordinal pure Ag, Ag-based Sn binary alloys (up to 7.5 at%Sn) with higher mechanical strength are used for the sheath material of ex situ powder-in-tube (PIT)-processed (Ba,K)Fe2As2(Ba-122) tapes. We found that the use of the Ag-Sn alloy enhances the densification and texturing of the Ba-122 core, resulting in higher transport, J c. Moreover, the optimum heat treatment temperature for a high J c can be lowered by around 100 °C due to the higher packing density of the Ba-122 core prior to the final heat treatment. We also found that the smoothness of the interface between the sheath and Ba-122 core is significantly improved by using the Ag-Sn binary alloy sheaths. These results show that the Ag-Sn alloy is promising as a sheath material in PIT-processed Ba-122 superconducting wires.

  16. Magnetic properties of Nd-Fe-Co(Cu)-Al-B amorphous alloys prepared by nonequilibrium techniques

    NASA Astrophysics Data System (ADS)

    Kumar, G.; Eckert, J.; Roth, S.; Löser, W.; Ram, S.; Schultz, L.

    2002-03-01

    The amorphous alloys Nd40Fe40Co5Al8B7, Nd57Fe20Co5Al10B8, and Nd57Fe20Cu5Al10B8 were prepared by copper mold casting, melt spinning, and mechanical alloying. Despite their similar x-ray diffraction patterns, samples display different magnetic and thermal behavior correlated with the method of preparation. The fully amorphous melt-spun ribbons exhibit relatively soft magnetic properties with coercivities ≈40 kA/m at room temperature and a Curie temperature (TC)≈474 K. Apparently only the mold-cast cylinders of 3 mm diameter show hard magnetic behavior with a coercivity in the range of 258-270 kA/m (depending on composition) and have approximately the same TC as that of the melt-spun ribbons. An additional magnetic transition at 585 K due to the presence of Nd2Fe14B phase in the case of Nd40Fe40Co5Al8B7 cast rod has been observed. Heat treatment above crystallization temperature in as-cast Nd57Fe20Co5Al10B8 and Nd57Fe20Cu5Al10B8 samples destroys the hard magnetic properties. In contrast, mechanically alloyed amorphous samples are soft magnetic with maximum coercivity up to 11 kA/m but show an entirely different TC≈680-740 K, which is rather characteristic of an Fe solid solution. The magnetic properties are discussed in terms of different local atomic environment and cluster sizes in amorphous samples prepared by different methods.

  17. Phase Structure and High-Temperature Mechanical Properties of Two-Phase Fe-25Al- xZr Alloys Compared to Three-Phase Fe-30Al- xZr Alloys

    NASA Astrophysics Data System (ADS)

    Kejzlar, Pavel; Kratochvíl, Petr; Král, Robert; Vodičková, Věra

    2014-01-01

    The structure and high-temperature mechanical properties of Fe-30 at. pct Al and Fe-25 at. pct Al alloys with various Zr contents are compared. The scanning electron microscope images in chemical contrast mode (R-BSE) as well as EDS, EBSD, and X-ray diffraction were used to determine the structure and phase composition. The as-cast alloys (both Fe-30Al and Fe-25Al) were observed to be two-phase DO3/B2 + Laves phase λ 1 (Fe,Al)2Zr alloys with typical fine lamellar eutectic areas. During the heat treatment of the Fe-25Al alloys, their structure transformed from a DO3/B2 matrix with fine lamellar eutectic into λ 1 globular particles situated in a DO3/B2 matrix. The same structure of Fe-30Al alloys decomposed into three phases: λ 1 and τ 1 Zr(Fe,Al)12 particles in a DO3/B2 matrix. The hardening in both groups of alloys (Fe-25Al and Fe-30Al) due to the presence of Zr-containing λ 1 and τ 1 phases is compared.

  18. Electronic structure and x-ray magnetic circular dichroism in A2FeReO6 (A =Ca ,Sr ,andBa ) oxides

    NASA Astrophysics Data System (ADS)

    Antonov, V. N.; Bekenov, L. V.; Ernst, A.

    2016-07-01

    A systematic electronic structure study of A2FeReO6 (A =Ba ,Sr ,andCa ) has been performed by employing the local-spin-density approximation (LSDA) and LSDA +U methods using the fully relativistic spin-polarized Dirac linear muffin-tin orbital band-structure method. We investigated the effects of the subtle interplay between spin-orbit coupling, electron correlations, and lattice distortion on the electronic structure of double perovskites. Ca2FeReO6 has a large distortion in the Fe-O-Re bond, and the electronic structure is mainly determined by electron correlations and lattice distortion. In the Ba -Sr -Ca row, the correlation effects at the Fe site are increased. The correlations at the Re site are small in the Ba- and Sr-based compounds but significant in Ca2FeReO6 . Ca2FeReO6 behaves like an insulator only if considered with a relatively large value of Coulomb repulsion Ueff=2.3 eV at the Re site in addition to Ueff=3.1 eV at the Fe site. Ca2FeReO6 possesses a phase transition at 140 K where the metal-insulator transition (MIT) occurs between metallic high-temperature and insulating low-temperature phases. The spin and orbital magnetic moments are linear functions of temperature before and after the MIT but change abruptly at the point of the phase transition. From theoretically calculated magnetocrystalline anisotropy energy (MAE), we found that the easy axis of magnetization for the low-temperature phase is along the b direction, in agreement with experimental data. We found that the major contribution to the MAE is due to the orbital magnetic anisotropy at the Re site. X-ray-absorption spectra and x-ray magnetic circular dichroism at the Re, Fe, and Ba L2 ,3 and Fe, Ca, and O K edges were investigated theoretically in the frame of the LSDA +U method. A qualitative explanation of the x-ray magnetic circular dichroism spectra shape is provided by an analysis of the corresponding selection rules, orbital character, and occupation numbers of individual orbitals

  19. Optimized Gen-II FeCrAl cladding production in large quantity for campaign testing

    SciTech Connect

    Yamamoto, Yukinori; Sun, Zhiqian; Pint, Bruce A.; Terrani, Kurt A.

    2016-06-03

    There are two major objectives in this report; (1) to optimize microstructure control of ATF FeCrAl alloys during tube drawing processes, and (2) to provide an update on the progress of ATF FeCrAl tube production via commercial manufacturers. Experimental efforts have been made to optimize the process parameters balancing the tube fabricability, especially for tube drawing processes, and microstructure control of the final tube products. Lab-scale sheet materials of Gen II FeCrAl alloys (Mo-containing and Nb-containing FeCrAl alloys) were used in the study, combined with a stepwise warm-rolling process and intermediate annealing, aiming to simulate the tube drawing process in a commercial tube manufacturer. The intermediate annealing at 650ºC for 1h was suggested for the tube-drawing process of Mo-containing FeCrAl alloys because it successfully softened the material by recovering the work hardening introduced through the rolling step, without inducing grain coarsening due to recrystallization. The final tube product is expected to have stabilized deformed microstructure providing the improved tensile properties with sufficient ductility. Optimization efforts on Nb-containing FeCrAl alloys focused on the effect of alloying additions and annealing conditions on the stability of deformed microstructure. Relationships between the second-phase precipitates (Fe2Nb-Laves phase) and microstructure stability are discussed. FeCrAl tube production through commercial tube manufacturers is currently in progress. Three different manufacturers, Century Tubes, Inc. (CTI), Rhenium Alloys, Inc. (RAI), and Superior Tube Company, Inc. (STC), are providing capabilities for cold-drawing, warm-drawing, and HPTR cold-pilgering, respectively. The first two companies are currently working on large quantity tube production (expected 250 ft length) of Gen I model FeCrAl alloy (B136Y3, at CTI) and Gen II (C35M4, at RAI), with the process parameters obtained from the experimental

  20. Stability of Fe,Al-bearing bridgmanite in the lower mantle and synthesis of pure Fe-bridgmanite

    PubMed Central

    Ismailova, Leyla; Bykova, Elena; Bykov, Maxim; Cerantola, Valerio; McCammon, Catherine; Boffa Ballaran, Tiziana; Bobrov, Andrei; Sinmyo, Ryosuke; Dubrovinskaia, Natalia; Glazyrin, Konstantin; Liermann, Hanns-Peter; Kupenko, Ilya; Hanfland, Michael; Prescher, Clemens; Prakapenka, Vitali; Svitlyk, Volodymyr; Dubrovinsky, Leonid

    2016-01-01

    The physical and chemical properties of Earth’s mantle, as well as its dynamics and evolution, heavily depend on the phase composition of the region. On the basis of experiments in laser-heated diamond anvil cells, we demonstrate that Fe,Al-bearing bridgmanite (magnesium silicate perovskite) is stable to pressures over 120 GPa and temperatures above 3000 K. Ferric iron stabilizes Fe-rich bridgmanite such that we were able to synthesize pure iron bridgmanite at pressures between ~45 and 110 GPa. The compressibility of ferric iron–bearing bridgmanite is significantly different from any known bridgmanite, which has direct implications for the interpretation of seismic tomography data. PMID:27453945

  1. Magnetic properties of the ternary aluminide TbFe2Al10

    NASA Astrophysics Data System (ADS)

    Khandelwal, Ashish; Sharma, V. K.; Sharath Chandra, L. S.; Singh, M. N.; Sinha, A. K.; Chattopadhyay, M. K.

    2013-09-01

    The magnetic properties of the ternary aluminide TbFe2Al10 have been studied with the help of magnetization measurements. From the temperature and field dependence of magnetization, a detailed magnetic phase diagram of TbFe2Al10 has been constructed. While the high- and low-temperature phases (in low fields) of TbFe2Al10 are paramagnetic and antiferromagnetic respectively, the signature of a field-induced ferromagnetic phase is obtained in the magnetization results in the intermediate temperature regime. While it was already known that TbFe2Al10 has a ferrimagnetic phase in between the low-field antiferromagnetic and the high-field ferromagnetic phases, the present results indicate the presence of a second intermediate-field-induced ferrimagnetic phase in the compound, in between the first ferrimagnetic and the high-field ferromagnetic phases. The possible magnetic structure for this second ferrimagnetic phase is proposed on the basis of existing neutron diffraction results. The successive field-induced or metamagnetic transitions in TbFe2Al10 are found to be induced by temperature as well, when the applied magnetic field is appropriate. The present magnetization results also indicate the presence of short-range magnetic correlations in TbFe2Al10 well inside the paramagnetic regime. Owing to the presence of successive temperature and field-induced magnetic phase transitions, TbFe2Al10 is found to exhibit a moderate magneto-caloric effect with a maximum of 7.86 J kg-1K-1 at 18.5 K. The magneto-caloric effect is found to persist well inside the paramagnetic regime because of the presence of short-range magnetic correlations at these temperatures. This leads to a substantial refrigerant capacity in the material, which could be useful information for future technology.

  2. Hydrothermal synthesis and properties of NiFe2O4@BaTiO3 composites with well-matched interface

    PubMed Central

    Zhou, Jian-Ping; Lv, Li; Liu, Qian; Zhang, Yu-Xiang; Liu, Peng

    2012-01-01

    NiFe2O4@BaTiO3 multiferroic composite particles were produced by a simple hydrothermal method in two steps: preparing NiFe2O4 nanoparticles and then synthesizing core-shell nanocomposites. Multiferroic composite ceramics were sintered from these powders. X-ray diffraction, Raman scattering and energy dispersive x-ray analyses indicated that the core-shell composites with a NiFe2O4 core and BaTiO3 shell were formed in the hydrothermal environment. Different types of sharp interfaces were self-assembled owing to the minimization of direct elastic energy. The saturation magnetization of the composites linearly increased with the NiFe2O4 content while the dielectric constant decreased. A dielectric peak appeared at around 460 °C because of the oxygen vacancies in the BaTiO3 ceramics. It resulted in an enhancement of magnetic permeability in the composites, indicating magnetoelectric coupling that was also observed by direct magnetoelectric measurements. PMID:27877501

  3. Structural and magnetic investigation of Ba 2(Fe,Re 1- xw x) 2O 6 (0⩽ x⩽0.5)

    NASA Astrophysics Data System (ADS)

    Rammeh, N.; Bramnik, K. G.; Ehrenberg, H.; Fuess, H.; Cheikh-Rouhou, A.

    2004-07-01

    The double-perovskite series Ba 2(Fe,Re 1- xW x) 2O 6, where x=0, 0.2, 0.4 and 0.5, have been prepared as pure powders by a conventional solid-state reaction and studied by X-ray powder diffraction and magnetization measurements. X-ray powder diffraction has been carried out at different temperatures (between 90 and 300 K) to study structural and magnetic properties of Ba 2(Fe,Re) 2O 6. Rietveld analysis of X-ray diffraction patterns show a partial disorder of Re/W and Fe on the B sites of the double-perovskite, which plays a dominant role in the structural and magnetic properties of these compounds. The symmetry is cubic ( Fm3¯m) for all samples, and no phase transition was detected for Ba 2(Fe,Re) 2O 6 between 95 K and room temperature. The magnetic properties of these series are remarkable: TC goes to a maximum reaching 338 K for x=0.2, with a spontaneous moment lower than the theoretical value.

  4. Structure, magnetic and complex impedance analysis of (1-x)BaTiO{sub 3}- xMgFe{sub 2}O{sub 4} composite

    SciTech Connect

    Zolkepli, M. F. A. Zainuddin, Z.

    2015-09-25

    MgFe{sub 2}O{sub 4} was synthesized by using sol-gel auto-combustion technique and coupled with BaTiO{sub 3} using the conventional solid state reaction method with different weight fraction of x = 0.00, 0.02, 0.04, 0.06 and 0.08 to form (1-x)BaTiO{sub 3} - xMgFe{sub 2}O{sub 4} composite. The structure, magnetic properties and complex impedance analysis of the composite samples were studied using X-ray diffraction technique (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM) and High-frequency response analyzer (HFRA) respectively. XRD patterns showed a single phase tetragonal BaTiO{sub 3} for each composition due to the very small amount of MgFe{sub 2}O{sub 4}. The hysteresis loop confirmed that the composite has soft magnetic properties by addition of MgFe{sub 2}O{sub 4}. Small coercive field, HC has been recorded and it decreased with the increasing of MgFe{sub 2}O{sub 4} weight fraction. However, magnetization increased when the amount of MgFe{sub 2}O{sub 4} is increased. Impedance analysis conducted in range of 0.1 Hz to 10 MHz showed two depressed semicircle arcs for samples with MgFe{sub 2}O{sub 4} due to the resistive and capacitive behavior of the bulk and grain boundaries of the samples.

  5. Fabrication and Characterization of PrBa2[CuxM1-x]3O7 (M=Ga, Al ,x=0.2) Epitaxial Thin Films

    NASA Astrophysics Data System (ADS)

    Kandel, Hom; Chen, Tar-Pin; Seo, Hye-Won; Iliev, Milko; Wadekar, Paritosh; Cui, Jing-Biao; Chen, Quark; Watanabe, Fumiya

    2010-03-01

    We have fabricated epitaxial thin films of highly resistive material PrBa2(Cu1-xMx)3O7 (M=Al, Ga, x = 0.2) by substituting Cu with Ga and Al in PrBa2Cu3O7.The electrical resistivity in these materials are many orders higher than in PrBa2Cu3O7 at 77K, which will provide an effective potential barrier to YBa2Cu3O7 in high Tc S-I-S Josephson junction. X-ray diffraction, atomic force microscopy, Raman and temperature dependent resistivity measurements were performed to characterize the thin films. We will discuss the results of Raman spectroscopy with regard to the site detection of incorporated dopants in PrBa2(Cu1-xMx)3O7 and transport studies with regard to the mechanism of hopping conductivity.

  6. Synthesis, crystal structure and properties of SmBaCo{sub 2−x}Fe{sub x}O{sub 5+δ}

    SciTech Connect

    Volkova, N.E.; Gavrilova, L.Ya.; Cherepanov, V.A.; Aksenova, T.V.; Kolotygin, V.A.; Kharton, V.V.

    2013-08-15

    The solid solution formation range in the SmBaCo{sub 2−x}Fe{sub x}O{sub 5+δ} (0≤x≤2) system examined at 1100 °C in air corresponds to 0≤x≤1.1. The crystal structure of SmBaCo{sub 2−x}Fe{sub x}O{sub 5+δ} with x≤0.5 was described as orthorhombic (space group Pmmm), and with 0.6≤x≤1.1—as tetragonal (P4/mmm). The introduction of iron into the cobalt sublattice leads to a gradual increase of the unit cell parameters and volume, accompanied with increasing oxygen content determined by thermogravimetry. The dilatometric curves collected at 25–1100 °C in air exhibit moderate nonlinearities associated with the orthorhombic→tetragonal phase transition, as confirmed by the high-temperature X-ray diffraction analysis. Temperature dependencies of the electrical conductivity measured by 4-probe dc method in the temperature range 25–1000 °C in air display maxima at 300–350 °C, whilst the conductivity decreases with iron additions. These trends were discussed in terms of the defect structure and nature of the main charge carriers in SmBaCo{sub 2−x}Fe{sub x}O{sub 5+δ}. It was also shown that SmBaCo{sub 2−x}Fe{sub x}O{sub 5+δ} is chemically stable with respect to the Ce{sub 0.8}Sm{sub 0.2}O{sub 1.9} solid electrolyte up to 1100 °S, but reacts with Zr{sub 0.85}Y{sub 0.15}O{sub 1.93} even at 900 °S. Highlights: • The solid solution formation range in the SmBaCo{sub 2−x}Fe{sub x}O{sub 5+δ} system at 1100 °C in air corresponds to 0≤x≤1.1. • The unit cell volume and oxygen content in the solid solutions increase with x. • Oxygen nonstoichiometry of SmBaCo{sub 2−x}Fe{sub x}O{sub 5+δ} solid solutions. • Temperature dependencies of the electrical conductivity exhibit maxima at the temperatures when oxygen exchange with the gaseous phase becomes significant.

  7. CaFeAl mixed oxide derived heterogeneous catalysts for transesterification of soybean oil to biodiesel.

    PubMed

    Lu, Yongsheng; Zhang, Zaiwu; Xu, Yunfeng; Liu, Qiang; Qian, Guangren

    2015-08-01

    CaAl layered double oxides (LDO) were prepared by co-precipitation and calcined at 750°C, and then applied to biodiesel production by transesterification reaction between methanol and soybean oil. Compared with characteristics of CaFe/LDO and CaAl/LDO, CaFeAl/LDO had the best performance based on prominent catalytic activity and stability, and achieved over 90% biodiesel yield, which stayed stable (over 85%) even after 8 cycles of reaction. The optimal catalytic reaction condition was 12:1M-ratio of methanol/oil, reaction temperatures of 60°C, 270rpm stirring rate, 60min reaction time, and 6% weight-ratio of catalyst/oil. In addition, the CaFeAl/LDO catalyst is insoluble in both methanol and methyl esters and can be easily separated for further reaction, turning it into an excellent alternative for biodiesel synthesis.

  8. Predictions of the Hunt-Lu array model compared with measurements for the growth undercooling of Al{sub 3}Fe dendrites in Al-Fe alloys

    SciTech Connect

    Liang, D.; Jones, H.

    1997-10-01

    Earlier contributions by the authors reported the first measurements of growth temperature as a function of growth velocity V and alloy concentration C{sub 0} for a dendritic intermetallic phase (Al{sub 3}Fe, in Al-rich Al-Fe alloys). Comparison with predictions of the model of Kurz, Giovanola and Trivedi (KGT model) of dendrite growth of a needle gave predicted {Delta}T a factor between 1.1 and 2.5 above the measured values. A subsequent paper presented evidence that the Al{sub 3}Fe dendrite tips were indeed needle-like under the conditions studied, as distinct from the plate-like morphology that develops behind the dendrite tips. The KGT model predicts T{sub G} and {Delta}T on the basis that marginal stability determines the operating condition at the dendrite tip. The present purpose is to compare the measurements with predictions of the more recently developed array model of Hunt and Lu.

  9. Kinetics and mechanism of the oxidation process of two-component Fe-Al alloys

    NASA Technical Reports Server (NTRS)

    Przewlocka, H.; Siedlecka, J.

    1982-01-01

    The oxidation process of two-component Fe-Al alloys containing up to 7.2% Al and from 18 to 30% Al was studied. Kinetic measurements were conducted using the isothermal gravimetric method in the range of 1073-1223 K and 1073-1373 K for 50 hours. The methods used in studies of the mechanism of oxidation included: X-ray microanalysis, X-ray structural analysis, metallographic analysis and marker tests.

  10. Persistent magnetism in silver-doped BaFe2As2 crystals

    DOE PAGES

    Li, Li; Cao, Huibo; Parker, David S.; ...

    2016-10-12

    Here, we investigate the thermodynamic and transport properties of silver-substituted BaF e 2 A s 2 (122) crystals up to ~ 4.5 % . Similar to other transition-metal substitutions in 122, Ag diminishes the antiferromagnetic ( T N ) and structural ( T S ) transition temperatures, but unlike other electron-doped 122s, T N and TS coincide without splitting. Though magnetism drops precipitously to T N = 84 K at doping x = 0.029 , it only weakly changes above this x , settling at T N = 80 K at x = 0.045 . Compared to this persistent magnetismmore » in Ag-122, doping other group 11 elements of either Cu or Au in 122 diminished T N and induced superconductivity near T c = 2 K at x = 0.044 or 0.031, respectively. Ag-122 crystals show reflective surfaces with surprising thicker cross sections for x ≥ 0.019 , the appearance that is in contrast to the typical thin stacked layered feature seen in all other flux-grown x-122 and lower Ag-122. We found that this physical trait may be a manifest of intrinsic weak changes in c lattice and T N . Our theoretical calculations suggest that Ag doping produces strong electronic scattering and yet a relatively small disruption of the magnetic state, both of which preclude superconductivity in this system.« less

  11. Enhanced piezoelectric and mechanical properties of AlN-modified BaTiO3 composite ceramics.

    PubMed

    Xu, Dan; Wang, Lidong; Li, Weili; Wang, Wei; Hou, Yafei; Cao, Wenping; Feng, Yu; Fei, Weidong

    2014-07-14

    BaTiO3-xAlN (BT-xAlN) composite ceramics were prepared by conventional solid state reaction sintering. The effects of the AlN content on the crystalline structures, densities, and electrical and mechanical properties of the BT ceramics were investigated. The BT-1.5%AlN ceramic exhibits a good piezoelectric constant of 305 pC N(-1) and an improved Vickers hardness of 5.9 GPa. The enhanced piezoelectricity originates from interactions between defect dipoles and spontaneous polarization inside the domains due to the occurrence of local symmetry, caused by the preferential distribution of the Al(3+)-N(3-) pairs vertical to the c axis. The hardening of the material is attributed to the improved density, and particle and grain boundary strengthening. Our work indicates that if a suitable doping ion pair is designed, lead-free ceramic systems prepared from ordinary raw materials by a conventional sintering method have a high probability of exhibiting good piezoelectric and mechanical properties simultaneously.

  12. Iron isotope effect on T c in optimally-doped (Ba,K)Fe 2As 2 ( T c = 38 K) and SmFeAsO 1-y ( T c = 54 K) superconductors

    NASA Astrophysics Data System (ADS)

    Shirage, P. M.; Kihou, K.; Miyazawa, K.; Lee, C. H.; Kito, H.; Yoshida, Y.; Eisaki, H.; Tanaka, Y.; Iyo, A.

    2010-11-01

    We report the iron isotope effect on a transition temperature (Tc) in an optimally-doped (Ba,K)Fe2As2 (Tc = 38 K) and SmFeAsO1-y (Tc = 54 K) superconductors. In order to obtain the reliable isotope shift in Tc, twin samples with different iron isotope mass are synthesized in the same conditions (simultaneously) under high-pressure. We have found that (Ba,K)Fe2As2 shows an inverse iron isotope effect αFe = -0.18 ± 0.03 while SmFeAsO1-y shows a small iron isotope effect αFe = -0.02 ± 0.01, where the isotope exponent α is defined by Tc ∼ M-α (M is the isotopic mass). The results show that αFe changes in the iron-based superconductors depending on the system. The distinct iron isotope effects imply the exotic coupling mechanism in the iron-based superconductors.

  13. Probing the pairing symmetry in the over-doped Fe-based superconductor Ba0.35Rb0.65Fe2As2 as a function of hydrostatic pressure

    NASA Astrophysics Data System (ADS)

    Guguchia, Z.; Khasanov, R.; Bukowski, Z.; von Rohr, F.; Medarde, M.; Biswas, P. K.; Luetkens, H.; Amato, A.; Morenzoni, E.

    2016-03-01

    We report muon spin rotation experiments on the magnetic penetration depth λ and the temperature dependence of λ-2 in the over-doped Fe-based high-temperature superconductor (Fe-HTS) Ba1 -xRbxFe2As2 (x = 0.65) studied at ambient and under hydrostatic pressures up to p =2.3 GPa. We find that in this system λ-2(T ) is best described by d -wave scenario. This is in contrast to the case of the optimally doped x =0.35 system which is known to be a nodeless s+--wave superconductor. This suggests that the doping induces the change of the pairing symmetry from s+- to d wave in Ba1 -xRbxFe2As2 . In addition, we find that the d -wave order parameter is robust against pressure, suggesting that d is the common and dominant pairing symmetry in over-doped Ba1 -xRbxFe2As2 . Application of pressure of p =2.3 GPa causes a decrease of λ (0) by less than 5 % , while at optimal doping x =0.35 a significant decrease of λ (0) was reported. The superconducting transition temperature Tc as well as the gap to Tc ratio 2 Δ /kBTc show only a modest decrease with pressure. By combining the present data with those previously obtained for optimally doped system x =0.35 and for the end member x = 1, we conclude that the SC gap symmetry as well as the pressure effects on the SC quantities strongly depend on the Rb doping level. These results are discussed in the light of the putative Lifshitz transition, i.e., a disappearance of the electron pockets in the Fermi surface of Ba1 -xRbxFe2As2 upon hole doping.

  14. Antiferromagnetic long-range spin ordering in Fe- and NiF e2 -doped BaTi O3 multiferroic layers

    NASA Astrophysics Data System (ADS)

    Barbier, A.; Aghavnian, T.; Badjeck, V.; Mocuta, C.; Stanescu, D.; Magnan, H.; Rountree, C. L.; Belkhou, R.; Ohresser, P.; Jedrecy, N.

    2015-01-01

    We report on the Fe doping and on the comparative Ni-Fe codoping with composition close to NiF e2 of fully oxidized BaTi O3 layers (˜20 nm) elaborated by atomic oxygen plasma assisted molecular beam epitaxy; specifically any role of oxygen vacancies can be excluded in our films. Additionally to the classical in situ laboratory tools, the films were thoroughly characterized by synchrotron radiation x-ray diffraction and x-ray absorption spectroscopy. For purely Fe-doped layers, the native tetragonal perovskite structure evolves rapidly toward cubiclike up to 5% doping level above which the crystalline order disappears. On the contrary, low codoping levels (˜5 %NiF e2 ) fairly improve the thin film crystalline structure and surface smoothness; high levels (˜27%) lead to more crystallographically disordered films, although the tetragonal structure is preserved. Synchrotron radiation magnetic dichroic measurements reveal that metal clustering does not occur, that the Fe valence evolves from Fe2 + for low Fe doping levels to Fe3 + for high doping levels, and that the introduction of Ni favors the occurrence of the Fe2 + valence in the films. For the lower codoping levels it seems that Fe2 + substitutes Ba2 +, whereas Ni2 + always substitutes Ti4 +. Ferromagnetic long-range ordering can be excluded with great sensitivity in all samples as deduced from our x-ray magnetic absorption circular dichroic measurements. On the contrary, our linear dichroic x-ray absorption results support antiferromagnetic long-range ordering while piezoforce microscopy gives evidence of a robust ferroelectric long-range ordering showing that our films are excellent candidates for magnetic exchange coupled multiferroic applications.

  15. Structural, electron transportation and magnetic behavior transition of metastable FeAlO granular films

    PubMed Central

    Bai, Guohua; Wu, Chen; Jin, Jiaying; Yan, Mi

    2016-01-01

    Metal-insulator granular film is technologically important for microwave applications. It has been challenging to obtain simultaneous high electrical resistivity and large saturation magnetization due to the balance of insulating non-magnetic and metallic magnetic components. FeAlO granular films satisfying both requirements have been prepared by pulsed laser deposition. The as-deposited film exhibits a high resistivity of 3700 μΩ∙cm with a negative temperature coefficient despite that Fe content (0.77) exceeds the percolation threshold. This originates from its unique microstructure containing amorphous Fe nanoparticles embedded in Al2O3 network. By optimizing the annealing conditions, superior electromagnetic properties with enhanced saturation magnetization (>1.05 T), high resistivity (>1200 μΩ∙cm) and broadened Δf (>3.0 GHz) are obtained. Phase separation with Al2O3 aggregating as inclusions in crystallized Fe(Al) matrix is observed after annealing at 673 K, resulting in a metallic-like resistivity. We provide a feasible way to achieve both high resistivity and large saturation magnetization for the FeAlO films with dominating metallic component and show that the microstructure can be tuned for desirable performance. PMID:27075955

  16. Mechanical Properties of In-Situ FeAl-TiB2 Intermetallic Matrix Composites

    NASA Astrophysics Data System (ADS)

    Kim, Jonghoon; Park, Bonggyu; Park, Yongho; Park, Ikmin; Lee, Heesoo

    Intermetallic matrix composites reinforced with ceramic particles have received a great deal of attention. Iron aluminide is known to be a good material for the matrix in such composites. Two processes were used to fabricate FeAl-TiB2 intermetallic matrix composites. One was liquid melt in-situ mixing, and the other was arc melting and suction casting processes. FeAl-TiB2 IMCs obtained by two different methods were investigated to elucidate the influence of TiB2 content. In both methods, the grain size in the FeAl alloy decreased with the presence of titanium diboride. The grain size of in-situ FeAl-TiB2 IMCs became smaller than that of arc FeAl-TiB2 IMCs. Significant increase in fracture stress and hardness was achieved in the composites. The in-situ process gives clean, contamination-free matrix/reinforcement interface which maintained good bonding causing high load bearing capability. This contributed to the increase in the mechanical properties of composites.

  17. Machinability of Intermetallic Compound Fe3Al from the Viewpoint of Tool Wear

    NASA Astrophysics Data System (ADS)

    Sasaki, Tomohiro; Yakou, Takao

    The intermetallic compound Fe3Al was processed by a reactive sintering process, and its machinability from the viewpoint of tool wear was investigated using dry turning. In cutting Fe3Al with a cemented carbide tool, the tool life was approximately one tenth that of cutting carbon tool steel SK3 because of intense flank wear. The tool life for cutting Fe3Al using the cemented carbide P20(WC-TiC-TaC-Co) tool was longer than for cemented carbide K10(WC-Co). In addition, a cermet tool reached its tool life limit by chipping for the whole cutting speed range measured. The roughness of the machined surface of Fe3Al cut using a cemented carbide tool was much smaller than for SK3. However, for cutting using the cermet tool, the roughness showed a sharp rise due to chipping. It was found that the wear rate of the WC particles in the tool material is larger than TiC particles. The results of the study suggest that the cemented carbide P20 is suitable for cutting Fe3Al.

  18. Microstructural Investigation and Phase Relationships of Fe-Al-Hf Alloys

    NASA Astrophysics Data System (ADS)

    Yildirim, Mehmet; Akdeniz, M. Vedat; Mekhrabov, Amdulla O.

    2014-07-01

    The effect of Hf addition on microstructures, phase relationships, microhardness, and magnetic properties of Fe50Al50- n Hf n alloys for n = 1, 3, 5, 7, and 9 at. pct has been investigated. At all investigated compositions, the ternary intermetallic HfFe6Al6 τ 1 phase forms due to the limited solid solubility of Hf in FeAl phase and tends to develop a eutectic phase mixture with the Fe-Al-based phase. The Hf concentration of the eutectic composition is found to be 7 at. pct from the microstructural examinations and the eutectic phase transition temperature is determined as 1521 K (1248 °C) independent of Hf amount by differential scanning calorimetry measurements. Furthermore, the enthalpies and activation energies (based on Kissinger and Ozawa methods) of eutectic phase transitions are reported. The minimum activation energy is calculated for the fully eutectic composition. Moreover, variation of the microhardness of Fe-Al-based alloys as a function of the Hf content is investigated, and its dependence on the thermal history of the alloys is explained.

  19. Structure evolution of Fe-50%Al coating prepared by mechanical alloying

    NASA Astrophysics Data System (ADS)

    Aryanto, D.; Wismogroho, A. S.; Sudiro, T.

    2016-08-01

    The deposition of Fe-50%Al coating (in at%) on low carbon steel was successfully prepared by using mechanical alloying (MA). The coating process was performed in a shaker mill with variation of milling times from 30 minute to 180 minutes. The deposited coating was then heat treated at 600°C for 2 hour in a vacuum furnace of 5.6 Pa. The structure evolution of mechanical alloyed samples before and after heat treatment was investigated by scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectrometer (EDX) and X-ray diffractometer (XRD). The results revealed that before heat treatment, the deposited coating on low carbon steel is composed of Fe and Al. The Fe(Al) solid solution was mostly formed after 180 minutes of milling time. Metallographic observation indicated that the surface of Fe-Al coating was rough and the coating thickness was increased with increasing milling time. Meanwhile, the heat treatment process led to structural evolution by forming FeAl intermetallic phase on the surface of low carbon steel.

  20. Development of a new graded-porosity FeAl alloy by elemental reactive synthesis

    SciTech Connect

    Shen, P Z; He, Y H; Gao, H Y; Zou, J; Xu, N P; Jiang, Y; Huang, B; Lui, C T

    2009-01-01

    A new graded-porosity FeAl alloy can be fabricated through Fe and Al elemental reactive synthesis. FeAl alloy with large connecting open pores and permeability were used as porous supports. The coating was obtained by spraying slurries consisting of mixtures of Fe powder and Al powder with 3 5 m diameter onto porous FeAl support and then sintered at 1100 C. The performances of the coating were compared in terms of thickness, pore diameter and permeability. With an increase in the coating thickness up to 200 m, the changes of maximum pore size decreased from 23.6 m to 5.9 m and the permeability decreased from 184.2 m3m 2kPa 1h 1 to 76.2 m3m 2kPa 1h 1, respectively, for a sintering temperature equal to 1100 C. The composite membranes have potential application for excellent filters in severe environments.

  1. [Release of Si, Al and Fe in red soil under simulated acid rain].

    PubMed

    Liu, Li; Song, Cun-yi; Li, Fa-sheng

    2007-10-01

    bstract:A laboratory leaching experiment on simulated acid rain was carried out using soil columns. The release of Si, Al and Fe from soils and pH values of eluates were investigated. The results showed that under the given leaching volume, the release amounts of cations were influenced by the pH value of simulated acid rain, while their response to acid rain was different. Acid rain led to Si release, nearly none of Fe. Within the range from pH 3.0 to 5.6, a little Al release but mass Al only release at the pH below 3.0, both Si and Al had a declining release ability with the undergoing eluviation. At pH 2.5, the release amounts of Si and Al, especially Al, increased significantly with the strengthened weathering process of soil mineral. With an increase of the leaching amount of acid rain, the release of Si and Al increased, but acceleration of Si was slower than Al which was slower and slower. When the soil pH falling down to a certain grade, there are negative correlation between pH and both Al and DOC concentration of eluate. released, but most of Al derived from the aluminosilicates dissolved. Acid deposition can result in solid-phase alumino-organics broken and Al released, but most of Al derived from the aluminosilicates dissolved.

  2. Large anisotropic Fe orbital moments in perpendicularly magnetized Co2FeAl Heusler alloy thin films revealed by angular-dependent x-ray magnetic circular dichroism

    NASA Astrophysics Data System (ADS)

    Okabayashi, Jun; Sukegawa, Hiroaki; Wen, Zhenchao; Inomata, Koichiro; Mitani, Seiji

    2013-09-01

    Perpendicular magnetic anisotropy (PMA) in Heusler alloy Co2FeAl thin films sharing an interface with a MgO layer is investigated by angular-dependent x-ray magnetic circular dichroism. Orbital and spin magnetic moments are deduced separately for Fe and Co 3d electrons. In addition, the PMA energies are estimated using the orbital magnetic moments parallel and perpendicular to the film surfaces. We found that PMA in Co2FeAl is determined mainly by the contribution of Fe atoms with large orbital magnetic moments, which are enhanced at the interface between Co2FeAl and MgO. Furthermore, element specific magnetization curves of Fe and Co are found to be similar, suggesting the existence of ferromagnetic coupling between Fe and Co PMA directions.

  3. Effect of Al substitution for Ga on the mechanical properties of directional solidified Fe-Ga alloys

    NASA Astrophysics Data System (ADS)

    Liu, Yangyang; Li, Jiheng; Gao, Xuexu

    2017-02-01

    Alloys of Fe82Ga18-xAlx (x=0, 4.5, 6, 9, 12, 13.5) were prepared by directional solidification technique and exhibited a <001> preferred orientation along the axis of alloy rods. The saturation magnetostriction value of the Fe82Ga13.5Al4.5 alloy was 247 ppm under no pre-stress. The tensile properties of alloys of Fe82Ga18-xAlx at room temperature were investigated. The results showed that tensile ductility of binary Fe-Ga alloy was significantly improved with Al addition. The fracture elongation of the Fe82Ga18 alloy was only 1.3%, while that of the Fe82Ga9Al9 alloy increased up to 16.5%. Addition of Al increased the strength of grain boundary and cleavage, resulting in the enhancement of tensile ductility of the Fe-Ga-Al alloys. Analysis of deformation microstructure showed that a great number of deformation twins formed in the Fe-Ga-Al alloys, which were thought to be the source of serrated yielding in the stress-strain curves. The effect of Al content in the Fe-Ga-Al alloys on tensile ductility was also studied by the analysis of deformation twins. It indicated that the joint effect of slip and twinning was beneficial to obtain the best ductility in the Fe82Ga9Al9 alloy.

  4. Polarized light microscopy study on the reentrant phase transition in a (Ba1–xKx)Fe2As2 single crystal with x = 0.24

    DOE PAGES

    Liu, Yong; Tanatar, Makariy A.; Timmons, Erik; ...

    2016-11-09

    In this study, a sequence of structural/magnetic transitions on cooling is reported in the literature for hole-doped iron-based superconductor (Ba1–xKx)Fe2As2 with x = 0.24. By using polarized light microscopy, we directly observe the formation of orthorhombic domains in (Ba1–xKx)Fe2As2 (x = 0.24) single crystal below a temperature of simultaneous structural/magnetic transition TN ~ 80 K. The structural domains vanish below ~30 K, but reappear below T = 15 K. Our results are consistent with reentrance transformation sequence from high-temperature tetragonal (HTT) to low temperature orthorhombic (LTO1) structure at TN ~ 80 K, LTO1 to low temperature tetragonal (LTT) structure atmore » Tc ~ 25 K, and LTT to low temperature orthorhombic (LTO2) structure at T ~ 15 K.« less

  5. Self-Propagating Combustion Triggered Synthesis of 3D Lamellar Graphene/BaFe12O19 Composite and Its Electromagnetic Wave Absorption Properties

    PubMed Central

    Zhao, Tingkai; Ji, Xianglin; Jin, Wenbo; Yang, Wenbo; Peng, Xiarong; Duan, Shichang; Dang, Alei; Li, Hao; Li, Tiehu

    2017-01-01

    The synthesis of 3D lamellar graphene/BaFe12O19 composites was performed by oxidizing graphite and sequentially self-propagating combustion triggered process. The 3D lamellar graphene structures were formed due to the synergistic effect of the tremendous heat induced gasification as well as huge volume expansion. The 3D lamellar graphene/BaFe12O19 composites bearing 30 wt % graphene present the reflection loss peak at −27.23 dB as well as the frequency bandwidth at 2.28 GHz (< −10 dB). The 3D lamellar graphene structures could consume the incident waves through multiple reflection and scattering within the layered structures, prolonging the propagation path of electromagnetic waves in the absorbers. PMID:28336889

  6. Improved microwave absorption and electromagnetic properties of BaFe12O19-poly(vinylidene fluoride) composites by incorporating reduced graphene oxides

    NASA Astrophysics Data System (ADS)

    He, Hongcai; Luo, Feifei; Qian, Neng; Wang, Ning

    2015-02-01

    Three-phase composites of poly(vinylidene fluoride)-BaFe12O19-reduced graphene oxide (PVDF-BFO-RGO) were synthesized by a facile wet chemical method and hot-pressing approach. The phase structure, topography of the hybrid materials were characterized by X-ray diffraction, scanning electron microscopy, and Raman spectra. Influence of RGO on their electromagnetic properties was investigated. Especially, improved microwave absorption and electromagnetic properties of BaFe12O19-PVDF composites by incorporating RGO were obtained and studied. The PVDF/BFO/RGO sample with m(RGO):m(BFO) = 5:100 shows the best microwave absorption properties with a minimum RL = -32 dB at 11 GHz and with the bandwidth less than -20 dB from 9.6 to 12.8 GHz. The composites were believed to have potential applications as the microwave absorber.

  7. A comparative study on the magnetic and electrical properties of MFe12O19 (M=Ba and Sr)/BiFeO3 nanocomposites

    NASA Astrophysics Data System (ADS)

    Ahmed, M. A.; Mansour, S. F.; Ismael, H.

    2015-03-01

    M-type hexaferrite (MFe12O19), M=Ba or Sr nanoparticles with hexagonal crystal structure have been successfully synthesized by a citrate auto-combustion method. BiFeO3 (BFO) was prepared by the flash auto-combustion technique. Different nanocomposites were prepared according to the formula [(1-X) MFe12O19+XBiFeO3; M=Ba or Sr, X=0.3, 0.4, 0.5 and 0.6]. The structure and morphology of the obtained nanocomposites have been determined by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). From the results, it is observed that the value of saturation magnetization decreases with increasing BFO content, which was mainly due to the contribution of the volume of the weak-magnetic BFO to the total sample volume.

  8. Lattice modulation induced by magnetic order in the magnetoelectric helimagnet Ba0.5Sr1.5Zn2Fe12O22

    NASA Astrophysics Data System (ADS)

    Asaka, T.; Yu, X. Z.; Hiraoka, Y.; Kimoto, K.; Hirayama, T.; Kimura, T.; Matsui, Y.

    2011-04-01

    By means of an electron diffraction technique, crystal-lattice modulations were investigated for a hexaferrite, Ba0.5Sr1.5Zn2Fe12O22, showing a helimagnetic order below TN=320 K. We observed a lattice modulation with a wave vector Q=(0,0,3δ) below TN. The value of δ varies between ~0.23 and 0.5 as a function of temperature and corresponds well to that of the magnetic modulation vector. By applying magnetic fields, Ba0.5Sr1.5Zn2Fe12O22 was found to exhibit successive changes in the lattice modulation, accompanied by the modifications of the helical magnetic order. We concluded that the observed lattice modulation is induced by the helical magnetic order via exchange magnetostriction.

  9. Multiple caloric effects in (Ba0.865Ca0.135Zr0.1089Ti0.8811Fe0.01)O3 ferroelectric ceramic

    NASA Astrophysics Data System (ADS)

    Patel, Satyanarayan; Chauhan, Aditya; Vaish, Rahul

    2015-07-01

    Multiple caloric effects have been investigated for Fe-doped bulk (Ba0.865Ca0.135Zr0.1089Ti0.8811Fe0.01)O3 (BCZTO-Fe) ferroelectric ceramic. Indirect predictions were made using Maxwell's relations in conjunction with data from experimental observations. It was revealed that bulk BCZTO-Fe has huge untapped potential for solid-state refrigeration. A peak electrocaloric effect of 0.45 K (347 K) was predicted for 0-3 kV.mm-1 electric field, significantly higher than other BCZTO based materials. A maximum elastocaloric cooling of 1.4 K (298 K) was achieved for applied stress of 0-200 MPa. Finally, an unforeseen component of electric field driven caloric effect has been reported as inverse piezocaloric effect, with a maximum temperature change of 0.28 K (298 K).

  10. Low loss Co2Z (Ba3Co2Fe24O41)-glass composite for gigahertz antenna application

    NASA Astrophysics Data System (ADS)

    Lee, Jaejin; Hong, Yang-Ki; Bae, Seok; Jalli, Jeevan; Abo, Gavin S.; Park, Jihoon; Seong, Won-Mo; Park, Sang-Hoon; Ahn, Won-Ki

    2011-04-01

    Low magnetic and dielectric loss Co2Z (Ba3Co2Fe24O41)-glass composite in the frequency range of 1-3 GHz is reported. Co2Z-glass composite was prepared by firing a mixture of 40 h shake-milled Co2Z hexaferrite powder and borosilicate glass at 950 °C for 1 h. The real part of permeability decreased slightly from 2.29 to 1.96 at 2.4 GHz as the glass content increased from 0 to 4 wt. %, but magnetic loss decreased less than 0.02. On the other hand, the real part of permittivity was 7.29 at 0 wt. % and 7.28 at 4 wt. % glass and dielectric loss was less than 0.01 at 2.4 GHz. The 3D peak gain of Co2Z-glass composite chip antenna was measured to be 3.32 dBi at 2.35 GHz. These results imply that the Co2Z-glass composite is an underpinning magnetodielectric material for gigahertz antenna applications.

  11. Signatures of filamentary superconductivity in antiferromagnetic BaFe2As2 single crystals

    SciTech Connect

    Moseley, D. A.; Yates, K. A.; Branford, W. R.; Sefat, Athena Safa; Mandrus, David; Stuard, S. J.; Salem-Sugui, S.; Cohen, L. F.

    2015-08-24

    In this paper, we present ac susceptibility and magnetotransport measurements on aged single crystals of the ferropnictide parent compound, BaFe2As2 with a paramagnetic-to-antiferromagnetic transition temperature of 134 K. The ac susceptibility shows the clear onset of a partial diamagnetic response with an onset temperature, commensurate with a subtle downturn in resistivity at approximately 20 K. Below 20 K the magnetotransport shows in-plane anisotropy, magnetic-field history dependence and a hysteretic signature. Above 20 K the crystals show the widely reported high-field linear magnetoresistance. An enhanced noise signature in ac susceptibility is observed above 20 K, which varies in character with amplitude and frequency of the ac signal. The hysteresis in magnetoresistance and the observed sensitivity of the superconducting phase to the amplitude of the ac signal are indicative characteristics of granular or weakly linked filamentary superconductivity. Furthermore, these features taken together with the observed noise signature above $T_{\\mathrm{c}}$ suggests a link between the formation of the superconducting filamentary phase and the freezing of antiphase domain walls, known to exist in these materials.

  12. the Characteristic Phase Transitions of Co-doped BaFe2 As2 Synthesized via Flux Growth

    NASA Astrophysics Data System (ADS)

    Shea, C. H.; Roncaioli, C.; Eckberg, C.; Drye, T.; Sulliavan, M. C.; Paglione, J.

    2015-03-01

    Since the discovery of a new family of type II superconductors in 2008, the iron pnictides, researches have had suspicions that they might bear similar electronic properties to the well-known (but not easily understood) oxide superconductors. For this reason studies on this family of compounds has been of great interest to the materials science community. Our efforts have been aimed at single crystal growth and measurement of a particular member of this family, BaFe2As2. While this material is not superconducting at standard pressure, the partial substitution of cobalt on the iron site has been shown to suppresses an anti-ferromagnetic phase transition occurring at lower temperatures allowing for the appearance of a superconducting phase. Transport and low field magnetization measurements taken on our samples show clean transitions, indicating Tc's of up to 24 K in optimally doped samples. We will discuss the growth methods and temperature dependent phase transitions of this material at different cobalt concentrations. This work was supported by NSF Grant DMR-1305637.

  13. Unconventional superconductivity in Ba(0.6)K(0.4)Fe2As2 from inelastic neutron scattering.

    PubMed

    Christianson, A D; Goremychkin, E A; Osborn, R; Rosenkranz, S; Lumsden, M D; Malliakas, C D; Todorov, I S; Claus, H; Chung, D Y; Kanatzidis, M G; Bewley, R I; Guidi, T

    2008-12-18

    A new family of superconductors containing layers of iron arsenide has attracted considerable interest because of their high transition temperatures (T(c)), some of which are >50 K, and because of similarities with the high-T(c) copper oxide superconductors. In both the iron arsenides and the copper oxides, superconductivity arises when an antiferromagnetically ordered phase has been suppressed by chemical doping. A universal feature of the copper oxide superconductors is the existence of a resonant magnetic excitation, localized in both energy and wavevector, within the superconducting phase. This resonance, which has also been observed in several heavy-fermion superconductors, is predicted to occur when the sign of the superconducting energy gap takes opposite values on different parts of the Fermi surface, an unusual gap symmetry which implies that the electron pairing interaction is repulsive at short range. Angle-resolved photoelectron spectroscopy shows no evidence of gap anisotropy in the iron arsenides, but such measurements are insensitive to the phase of the gap on separate parts of the Fermi surface. Here we report inelastic neutron scattering observations of a magnetic resonance below T(c) in Ba(0.6)K(0.4)Fe(2)As(2), a phase-sensitive measurement demonstrating that the superconducting energy gap has unconventional symmetry in the iron arsenide superconductors.

  14. Study of flux pinning mechanism under hydrostatic pressure in optimally doped (Ba,K)Fe2As2 single crystals

    PubMed Central

    Shabbir, Babar; Wang, Xiaolin; Ma, Y.; Dou, S. X.; Yan, S. S.; Mei, L. M.

    2016-01-01

    Strong pinning depends on the pinning force strength and number density of effective defects. Using the hydrostatic pressure method, we demonstrate here that hydrostatic pressure of 1.2 GPa can significantly enhance flux pinning or the critical current density (Jc) of optimally doped Ba0.6K0.4Fe2As2 crystals by a factor of up to 5 in both low and high fields, which is generally rare with other Jc enhancement techniques. At 4.1 K, high pressure can significantly enhance Jc from 5 × 105 A/cm2 to nearly 106 A/cm2 at 2 T, and from 2 × 105 A/cm2 to nearly 5.5 × 105 A/cm2 at 12 T. Our systematic analysis of the flux pinning mechanism indicates that both the pinning centre number density and the pinning force are greatly increased by the pressure and enhance the pinning. This study also shows that superconducting performance in terms of flux pinning or Jc for optimally doped superconducting materials can be further improved by using pressure. PMID:26983500

  15. Resonant Spin Excitation in the High Temperature Superconductor Ba0.6K0.4Fe2As2

    SciTech Connect

    Christianson, Andrew D; Goremychkin, E. A.; Osborn, R.; Rosenkranz, Stephen; Lumsden, Mark D; Malliakas, C.; Todorov, L.; Claus, H.; Chung, D.Y.; Kanatzidis, M.; Bewley, Robert I.; Guidi, T.

    2008-12-18

    A new family of superconductors containing layers of iron arsenide has attracted considerable interest because of their high transition temperatures (T{sub c}), some of which are >50 K, and because of similarities with the high-{sub c} copper oxide superconductors. In both the iron arsenides and the copper oxides, superconductivity arises when an antiferromagnetically ordered phase has been suppressed by chemical doping. A universal feature of the copper oxide superconductors is the existence of a resonant magnetic excitation, localized in both energy and wavevector, within the superconducting phase. This resonance, which has also been observed in several heavy-fermion superconductors is predicted to occur when the sign of the superconducting energy gap takes opposite values on different parts of the Fermi surface, an unusual gap symmetry which implies that the electron pairing interaction is repulsive at short range. Angle-resolved photoelectron spectroscopy shows no evidence of gap anisotropy in the iron arsenides, but such measurements are insensitive to the phase of the gap on separate parts of the Fermi surface. Here we report inelastic neutron scattering observations of a magnetic resonance below T{sub c} in Ba{sub 0.6}K{sub 0.4}Fe{sub 2}As{sub 2}, a phase-sensitive measurement demonstrating that the superconducting energy gap has unconventional symmetry in the iron arsenide superconductors.

  16. The Electronic Specific Heat of Ba1-xKxFe2As2 from 2K to 380K

    NASA Astrophysics Data System (ADS)

    Storey, James; Loram, John; Cooper, John; Bukowski, Zbigniew; Karpinski, Janusz

    2010-03-01

    Using a differential technique, we have measured the specific heats of polycrystalline Ba1-xKxFe2As2 samples with x = 0, 0.1 and 0.3, between 2K and 380K and in magnetic fields 0 - 13T. From this data we have determined the electronic specific coefficient γ(≡C^el/T) over the entire range for the three samples. The sample with x = 0.3 exhibits a large SC anomaly δγ(Tc) ˜ 48 mJ/mol K^2 at Tc = 36K, and we determine the energy gap, condensation energy, superfluid density and coherence length. In the normal state for the x = 0.3 sample, γ ˜ 45 mJ/mol K^2 is constant from Tc to 380K. In the parent compound (x = 0) there is a large almost first order anomaly at the SDW transition at To = 136K. The corresponding anomaly for the 0.1 sample at To ˜ 135K is smaller and broader than for x = 0. At low T, γ is strongly reduced by the SDW gap for both x = 0 and 0.1, but above To, γ for all three samples are similar.

  17. Structural and magnetic properties of transition metal substituted BaFe2As2 compounds studied by x-ray and neutron scattering

    SciTech Connect

    Kim, Min Gyu

    2012-01-01

    The purpose of my dissertation is to understand the structural and magnetic properties of the newly discovered FeAs-based superconductors and the interconnection between superconductivity, antiferromagnetism, and structure. X-ray and neutron scattering techniques are powerful tools to directly observe the structure and magnetism in this system. I used both x-ray and neutron scattering techniques on different transition substituted BaFe2As2 compounds in order to investigate the substitution dependence of structural and magnetic transitions and try to understand the connections between them.

  18. High spatial resolution PEELS characterization of FeAl nanograins prepared by mechanical alloying

    SciTech Connect

    Valdre, G. |; Botton, G.A.; Brown, L.M.

    1999-05-28

    The authors investigate the nanograin ``chemical`` structure in a nanostructured material of possible industrial application (Fe-Al system) prepared by conventional mechanical alloying via ball milling in argon atmosphere. They restrict themselves to the structural and nanochemical behavior of ball-milled nanocrystalline Fe-Al powders with atomic composition Fe{sub 3}Al, corresponding to a well-known intermetallic compound of the Fe-Al system. Scanning transmission electron microscopy (STEM) equipped with a parallel detection electron energy loss spectrometer (PEELS) has provided an insight on the ``chemical`` structure of both nanograins and their surface at a spatial resolution of better than 1 nm. The energy loss near edge structure of the Al L loss reveals that the Al coordination is similar to a B2 compound and the oxidation of the powder during processing may play a significant role in the stabilization of the intermetallic phases. Conventional transmission electron microscopy (TEM) was used for the structural characterization of the material after the ball milling; powder X-ray diffraction (XRD) aided the investigation.

  19. Magneto-optical properties BaBixLaxFe12-2xO19 (0.0≤x≤0.5) hexaferrites

    NASA Astrophysics Data System (ADS)

    Auwal, I. A.; Baykal, A.; Güner, S.; Sertkol, M.; Sözeri, H.

    2016-07-01

    BaBixLaxFe(12-2x)O19 (0.0≤x≤0.5) hexaferrites were synthesized by solid state synthesis route and the effects of Bi, La substitutions on structural, magnetic and optical properties were investigated. X-ray powder diffraction, Scanning electron microscopy, Vibrating sample magnetometer, and Percent diffuse reflectance spectroscopy were used to study the physical properties. Room temperature specific magnetization (M-H) curves revealed the ferromagnetic nature of all products. The increasing Bi, La compositions increased the magnetic properties at different magnitudes with respect to undoped BaFe12O19 sample. The maximum values of remnant specific magnetization (Mr=30.3 emu/g), extrapolated specific saturation magnetization (Ms=62.12 emu/g), and magneton number (nB=16.27) were recorded from BaBi0.2La0.2Fe11.4O19 hexaferrite. The average crystallite size varies in a range of (37.35-51.36) nm. The coercive field (Hc) of undoped hexaferrites is 1180 Oe and increased to maximum 2320 Oe belonging to BaBi0.4La0.4Fe11.2O19. Magnetic anisotropy was confirmed as uniaxial and calculated effective anisotropy constants (Keff) are between 4.27×105 Ergs/g and 5.05×105 Ergs/g. The high magnitudes of magnetocrystalline anisotropy (Ha) above than 16,200 Oe revealed that all samples are magnetically hard materials. The Tauc plots were drawn to extrapolate the direct optical energy band gap (Eg) of hexaferrites. The Eg values decreased from 1.76 eV to 1.47 eV with increasing Bi, La compositions.

  20. The Morphology and Chemistry Evolution of Inclusions in Fe-Si-Al-O Melts

    NASA Astrophysics Data System (ADS)

    Kwon, Youjong; Choi, Juhan; Sridhar, Seetharaman

    2011-08-01

    This study aims to elucidate the process of inclusion precipitation in Fe-Si and Fe-Si-Al melts. Deoxidation experiments were carried out in a vacuum induction furnace (VIF) at 1873 K (1600 °C). In the Si-deoxidation experiments, spherical SiO2 of 1~2 μm diameter was dominant. When 3 wt pct Si and 300 ppm Al were added, such that Al2O3 and mullite were thermodynamically stable, the resulting inclusions depended on the addition sequence. When aluminum was added before silicon, spherical aluminum oxides were dominant after the Al addition, but after the Si addition, the number and size of alumina decreased and Al-Si oxides and mullite appeared with increasing time. When silicon was added before aluminum, spherical SiO2 was dominant after the Si addition, but after the Al addition, spherical and polygonal alumina inclusions were dominant. When Al/Si was added simultaneously, polygonal alumina inclusions were dominant initially, but with time, Al-Si oxide and mullite inclusions increased in numbers. If the Al amount in the Al/Si addition was increased to 600 ppm, only alumina was found. This study shows how, under similar thermodynamic conditions, the transient evolution of inclusions in iron melts in the Si-Al-O system differ depending on the alloy addition sequence.

  1. Effect of the Chalcogenide Element Doping on the Electronic Properties of Co2FeAl Heusler Alloys

    NASA Astrophysics Data System (ADS)

    Huang, Ting; Cheng, Xiao-min; Guan, Xia-wei; Miao, Xiang-shui

    2016-02-01

    The electronic properties of the typical Heusler compound Co2FeAl with chalcogenide element doping were investigated by means of first principles calculations within the local spin-density approximation (LSDA) + Hubbard U parameter (U). The calculations indicate that, only when 25% of the number of Al atoms is substituted by the chalcogenide element, the chalcogenide element-doped Co2FeAl shows the half metallic properties. The Fermi energy ( E F) of the 25% chalcogenide element-doped Co2FeAl is located in the middle of the gap of the minority states instead of around the top of the valence band as in Co2FeAl. Moreover, the band gap of 25% Te-doped Co2FeAl (0.80 eV) is wider than that of Co2FeAl (0.74 eV). These improved electronic structures will make 25% chalcogenide element-doped Co2FeAl more stable against temperature variation. Therefore, the expected excellent stability of the 25% chalcogenide element-doped Co2FeAl make it more suitable for spintronic applications than Co2FeAl.

  2. Flaky FeSiAl alloy-carbon nanotube composite with tunable electromagnetic properties for microwave absorption

    PubMed Central

    Huang, Lina; Liu, Xiaofang; Chuai, Dan; Chen, Yaxin; Yu, Ronghai

    2016-01-01

    Flaky FeSiAl alloy/multi-wall carbon nanotube (FeSiAl/MWCNT) composite was fabricated by facile and scalable ball milling method. The morphology and electromagnetic properties of the FeSiAl alloy can be well tuned by controlling the milling time. It is found that the magnetic loss of the FeSiAl alloy is improved by optimizing the milling time due to the increased anisotropy field. Meanwhile the addition of MWCNTs enhances the dielectric loss of the composite by increasing the interfacial polarizations, dipolar polarizations and conductive paths. Relative to conventional FeSiAl absorbers, the FeSiAl/MWCNT composite exhibits greatly improved microwave absorption performance with advantages of strong absorption and small thickness. The minimum reflection loss of the composite reaches −42.8 dB at 12.3 GHz at a very thin thickness of 1.9 mm. PMID:27762327

  3. Flaky FeSiAl alloy-carbon nanotube composite with tunable electromagnetic properties for microwave absorption.

    PubMed

    Huang, Lina; Liu, Xiaofang; Chuai, Dan; Chen, Yaxin; Yu, Ronghai

    2016-10-20

    Flaky FeSiAl alloy/multi-wall carbon nanotube (FeSiAl/MWCNT) composite was fabricated by facile and scalable ball milling method. The morphology and electromagnetic properties of the FeSiAl alloy can be well tuned by controlling the milling time. It is found that the magnetic loss of the FeSiAl alloy is improved by optimizing the milling time due to the increased anisotropy field. Meanwhile the addition of MWCNTs enhances the dielectric loss of the composite by increasing the interfacial polarizations, dipolar polarizations and conductive paths. Relative to conventional FeSiAl absorbers, the FeSiAl/MWCNT composite exhibits greatly improved microwave absorption performance with advantages of strong absorption and small thickness. The minimum reflection loss of the composite reaches -42.8 dB at 12.3 GHz at a very thin thickness of 1.9 mm.

  4. Flaky FeSiAl alloy-carbon nanotube composite with tunable electromagnetic properties for microwave absorption

    NASA Astrophysics Data System (ADS)

    Huang, Lina; Liu, Xiaofang; Chuai, Dan; Chen, Yaxin; Yu, Ronghai

    2016-10-01

    Flaky FeSiAl alloy/multi-wall carbon nanotube (FeSiAl/MWCNT) composite was fabricated by facile and scalable ball milling method. The morphology and electromagnetic properties of the FeSiAl alloy can be well tuned by controlling the milling time. It is found that the magnetic loss of the FeSiAl alloy is improved by optimizing the milling time due to the increased anisotropy field. Meanwhile the addition of MWCNTs enhances the dielectric loss of the composite by increasing the interfacial polarizations, dipolar polarizations and conductive paths. Relative to conventional FeSiAl absorbers, the FeSiAl/MWCNT composite exhibits greatly improved microwave absorption performance with advantages of strong absorption and small thickness. The minimum reflection loss of the composite reaches ‑42.8 dB at 12.3 GHz at a very thin thickness of 1.9 mm.

  5. Magnetic properties of fibrous Fe-Al-O prepared by electrospinning

    NASA Astrophysics Data System (ADS)

    Lovchinov, V.; Simeonova, P.; Vanderbemden, Ph; Krezhov, K.

    2014-12-01

    Recently, we obtained a new Fe-Al-O fibrous material by applying the novel route of electrospinning. Here we report on the properties of the as prepared material established by PPMS magnetometry and X-ray diffraction. X-ray diffractograms revealed the coexistence of the orthorhombic multiferroic phase FeAlO3 along with traces of unreacted impurities. The structure of the FeAlO3 phase is described in the orthorhombic Pna21 space group and is of great current interest since the compound features piezoelectricity, ferrimagnetism and magnetoelectric effects at low temperatures. In contrast to known bulk material obtained by classical routes the new fibrous material shows a lower value of saturation magnetization and the magnetic transition occurs at a much lower temperature. In the discussion an attempt is made to disclose the reasons for the observed differences.

  6. Surface magneto-optical and Mössbauer observations of Fe-Al

    NASA Astrophysics Data System (ADS)

    Jirásková, Y.; Hendrych, A.; Životský, O.; Buršík, J.; Žák, T.; Procházka, I.; Janičkovič, D.

    2013-07-01

    The paper is devoted to detailed surface studies of the Fe82Al18 alloy prepared from high purity Fe and Al by arc melting. The results summarize observations of the surface sensitive methods - high resolution scanning electron microscopy (HRSEM), slow energy electron microscopy (SLEEM), magneto-optical Kerr effect (MOKE), and conversion electron Mössbauer spectrometry (CEMS). Morphology of grains and grain boundaries obtained by HRSEM is observed in more detail by SLEEM. The CEMS results analyzed using free components with characteristic hyperfine parameters and by theoretical model, give evidence for A2 order of the as-prepared and as-quenched Fe82Al18 sample surfaces. A small contribution of the oxide layer influences the shape of hysteresis loops and domain structure of the sample surface above all in the as-quenched state.

  7. Microstructural characterization of Ni-22Fe-22Cr-6Al metallic foam by transmission electron microscopy.

    PubMed

    Kim, Hyung Giun; Lee, Taeg Woo; Lee, Jae Young; Lee, Eui Sung; Oh, Kwon Oh; Lee, Chang Woo; Lim, Sung Hwan

    2012-01-01

    Ni-22Fe-22Cr-6Al metallic foam, prepared using a thermomechanical treatment and alloying elements, was studied via transmission electron microscopy (TEM) in order to clarify the relationship between the mechanical properties and the nanoscale microstructural characteristics. Due to the unique porous structure of the metallic foam, TEM specimens were prepared using an embedding-process-assisted-ion-milling technique and a focused-ion-beam method. The Cr-, Fe- and Al-clustered regions around the surface of the metallic foam were investigated using elemental maps. The Ni(3)Al (γ') precipitates, which can affect the mechanical properties of the Ni-Fe-Cr (γ) matrix, were characterized in the metallic foam.

  8. Irradiation-enhanced α' precipitation in model FeCrAl alloys

    SciTech Connect

    Edmondson, Philip D.; Briggs, Samuel A.; Yamamoto, Yukinori; Howard, Richard H.; Sridharan, Kumar; Terrani, Kurt A.; Field, Kevin G.

    2016-02-17

    We have irradiated the model FeCrAl alloys with varying compositions (Fe(10–18)Cr(10–6)Al at.%) with a neutron at ~ 320 to damage levels of ~ 7 displacements per atom (dpa) to investigate the compositional influence on the formation of irradiation-induced Cr-rich α' precipitates using atom probe tomography. In all alloys, significant number densities of these precipitates were observed. Cluster compositions were investigated and it was found that the average cluster Cr content ranged between 51.1 and 62.5 at.% dependent on initial compositions. Furthermore, this is significantly lower than the Cr-content of α' in binary FeCr alloys. As a result, significant partitioning of the Al from the α' precipitates was also observed.

  9. Irradiation-enhanced α' precipitation in model FeCrAl alloys

    DOE PAGES

    Edmondson, Philip D.; Briggs, Samuel A.; Yamamoto, Yukinori; ...

    2016-02-17

    We have irradiated the model FeCrAl alloys with varying compositions (Fe(10–18)Cr(10–6)Al at.%) with a neutron at ~ 320 to damage levels of ~ 7 displacements per atom (dpa) to investigate the compositional influence on the formation of irradiation-induced Cr-rich α' precipitates using atom probe tomography. In all alloys, significant number densities of these precipitates were observed. Cluster compositions were investigated and it was found that the average cluster Cr content ranged between 51.1 and 62.5 at.% dependent on initial compositions. Furthermore, this is significantly lower than the Cr-content of α' in binary FeCr alloys. As a result, significant partitioning ofmore » the Al from the α' precipitates was also observed.« less

  10. Electrochemical deposition and microstructural characterization of AlCrFeMnNi and AlCrCuFeMnNi high entropy alloy thin films

    NASA Astrophysics Data System (ADS)

    Soare, V.; Burada, M.; Constantin, I.; Mitrică, D.; Bădiliţă, V.; Caragea, A.; Târcolea, M.

    2015-12-01

    Al-Cr-Fe-Mn-Ni and Al-Cr-Cu-Fe-Mn-Ni high entropy alloy thin films were prepared by potentiostatic electrodeposition and the microstructure of the deposits was investigated. The thin films were co-deposited in an electrolyte based on a DMF (N,N-dimethylformamide)-CH3CN (acetonitrile) organic compound. The energy dispersive spectrometry investigation (EDS) indicated that all the five respectively six elements were successfully co-deposited. The scanning electron microscopy (SEM) analysis revealed that the film consists of compact and uniform particles with particle sizes of 500 nm to 4 μm. The X-ray diffractometry (XRD) patterns indicated that the as-deposited thin films were amorphous. Body-centered-cubic (BCC) structures were identified by XRD after the films were annealed at various temperatures under inert Ar atmosphere. The alloys adhesion on the substrate was determined by the scratch-testing method, with higher values obtained for the Al-Cr-Cu-Fe-Mn-Ni alloy.

  11. Influence of recrystallization on phase separation kinetics of oxide dispersion strengthened Fe Cr Al alloy

    SciTech Connect

    Capdevila, C.; Miller, Michael K; Pimentel, G.; Chao, J.

    2012-01-01

    The effect of different starting microstructures on the kinetics of Fe-rich ({alpha}) and Cr-rich ({alpha}') phase separation during aging of Fe-Cr-Al oxide dispersion strengthened (ODS) alloys has been analyzed with a combination of atom probe tomography and thermoelectric power measurements. The results revealed that the high recrystallization temperature necessary to produce a coarse grained microstructure in Fe-base ODS alloys affects the randomness of Cr-atom distributions and defect density, which consequently affect the phase separation kinetics at low annealing temperatures.

  12. Nanoparticle-Based Magnetoelectric BaTiO3-CoFe2O4 Thin Film Heterostructures for Voltage Control of Magnetism.

    PubMed

    Erdem, Derya; Bingham, Nicholas S; Heiligtag, Florian J; Pilet, Nicolas; Warnicke, Peter; Vaz, Carlos A F; Shi, Yanuo; Buzzi, Michele; Rupp, Jennifer L M; Heyderman, Laura J; Niederberger, Markus

    2016-11-22

    Multiferroic composite materials combining ferroelectric and ferromagnetic order at room temperature have great potential for emerging applications such as four-state memories, magnetoelectric sensors, and microwave devices. In this paper, we report an effective and facile liquid phase deposition route to create multiferroic composite thin films involving the spin-coating of nanoparticle dispersions of BaTiO3, a well-known ferroelectric, and CoFe2O4, a highly magnetostrictive material. This approach offers great flexibility in terms of accessible film configurations (co-dispersed as well as layered films), thicknesses (from 100 nm to several μm) and composition (5-50 wt % CoFe2O4 with respect to BaTiO3) to address various potential applications. A detailed structural characterization proves that BaTiO3 and CoFe2O4 remain phase-separated with clear interfaces on the nanoscale after heat treatment, while electrical and magnetic studies indicate the simultaneous presence of both ferroelectric and ferromagnetic order. Furthermore, coupling between these orders within the films is demonstrated with voltage control of the magnetism at ambient temperatures.

  13. Energy dependence of the spin excitation anisotropy in uniaxial-strained BaFe1.9Ni0.1As2

    DOE PAGES

    Song, Yu; Lu, Xingye; Abernathy, Douglas L.; ...

    2015-11-06

    In this study, we use inelastic neutron scattering to study the temperature and energy dependence of the spin excitation anisotropy in uniaxial-strained electron-doped iron pnictide BaFe1.9Ni0.1As2 near optimal superconductivity (Tc = 20K). Our work has been motivated by the observation of in-plane resistivity anisotropy in the paramagnetic tetragonal phase of electron-underdoped iron pnictides under uniaxial pressure, which has been attributed to a spin-driven Ising-nematic state or orbital ordering. Here we show that the spin excitation anisotropy, a signature of the spin-driven Ising-nematic phase, exists for energies below 60 meV in uniaxial-strained BaFe1.9Ni0.1As2. Since this energy scale is considerably larger thanmore » the energy splitting of the dxz and dyz bands of uniaxial-strained Ba(Fe1–xCox)2As2 near optimal superconductivity, spin Ising-nematic correlations are likely the driving force for the resistivity anisotropy and associated electronic nematic correlations.« less

  14. Influences of material processing on the microstructure and inter-granular current properties of polycrystalline bulk Ba(Fe,Co)2As2

    NASA Astrophysics Data System (ADS)

    Hayashi, Y.; Yamamoto, A.; Ogino, H.; Shimoyama, J.; Kishio, K.

    2014-09-01

    The phase formation, microstructure, magnetic, and transport properties of Ba(Fe,Co)2As2 polycrystalline bulks prepared by systematically varied synthesis conditions were studied to clarify the key issues for intergranular critical current properties. After optimization of heat treatment process, Ba(Fe0.92Co0.08)2As2 samples with high phase purity and Tc > 25 K were reproducibly obtained. Electron microscopy analyses showed that the use of refined starting powder by high-energy ball-milling yield microstructure with improved uniformity and Ba(Fe,Co)2As2 phase can be synthesized at lower temperature down to 500 °C owing to an increased reactivity. The samples synthesized at low temperature showed well-connected microstructure with fine grain size and intergranular critical current density progressively improved with lowering the heating temperature. Our results suggest that fine grain size and grain boundary structure formed at low temperature are favorable for increasing the area of effective transport current path, while they are electromagnetically weakly coupled and suppressed under external magnetic field.

  15. Grain boundary defect compensation in Ti-doped BaFe0.5Nb0.5O3 ceramics

    NASA Astrophysics Data System (ADS)

    Sun, Xiaojun; Deng, Jianming; Liu, Saisai; Yan, Tianxiang; Peng, Biaolin; Jia, Wenhao; Mei, Zaoming; Su, Hongbo; Fang, Liang; Liu, Laijun

    2016-09-01

    Giant dielectric ceramics Ba(Nb0.5Fe0.5- x Ti x )O3 (BNFT) have been fabricated by a conventional solid-state reaction. According to X-ray diffraction analysis, the crystal structure of these ceramics can be described by the cubic centrosymmetric with Pm- 3m space group. The real part ( ɛ') of dielectric permittivity and dielectric loss (tan δ) of the BNFT ceramics was measured in a frequency range from 40 Hz to 100 MHz at room temperature. The ( ɛ') of all these samples displays a high value (~6500) and a small frequency-dependence from 1 kHz to 1 MHz. We have established a link between conductivity activation energy and defect compensation at grain boundaries. The Ti4+-doped Ba(Nb0.5Fe0.5)O3 as a donor makes a great influence on the grain boundary behavior, which restricts the migration of oxygen vacancy and depresses dielectric loss factor for Ba(Nb0.5Fe0.5)O3 ceramics.

  16. Strain correlated effect on structural, magnetic, and dielectric properties in Ti4+ substituted Bi0.8Ba0.2Fe1-xTixO3

    NASA Astrophysics Data System (ADS)

    Paul Blessington Selvadurai, A.; Pazhanivelu, V.; Murugaraj, R.

    2015-08-01

    Ti4+ substituted Bi0.8Ba0.2Fe1-xTixO3 for x = 0.0, 0.1 and 0.2 are prepared by modified solid state reaction method. The prepared samples sintered at 850 °C for 1 h show a single phase nature. A structural change was observed on Ti4+ substitutions are confirmed through X-ray Diffraction, Fourier Transform Infrared spectroscopy and Raman spectra. An anomalous phase transition is observed in Bi0.8Ba0.2FeO3 at 1173 K. The absence of ferroelectric transition and enhancement of decomposition temperature is observed in the substituted samples from the thermal analysis. A dielectric spectroscopic measurement shows that on Ti4+ substitutions, the magnitude of dielectric constant and loss tangent (tan δ) value is decreased. Vibrating Sample Magnetometer (VSM) study shows both antiferromagnetic and ferromagnetic phases coexist in the M-H curve. On Ti4+ substitutions in Bi0.8Ba0.2FeO3, the antiferromagnetism dominates over the ferromagnetic phase. In corroboration to magnetisation process, ZFC-FC measurement confirms it that on Ti4+ substitution, the antiferromagnetic behaviour gets dominated. The report suggests that the interplay of strain upon Ti4+ substitution causes the structural and magnetic phase transition.

  17. Uniaxial pressure effect on the magnetic ordered moment and transition temperatures in BaFe2 -xTxAs2 (T =Co,Ni )

    NASA Astrophysics Data System (ADS)

    Tam, David W.; Song, Yu; Man, Haoran; Cheung, Sky C.; Yin, Zhiping; Lu, Xingye; Wang, Weiyi; Frandsen, Benjamin A.; Liu, Lian; Gong, Zizhou; Ito, Takashi U.; Cai, Yipeng; Wilson, Murray N.; Guo, Shengli; Koshiishi, Keisuke; Tian, Wei; Hitti, Bassam; Ivanov, Alexandre; Zhao, Yang; Lynn, Jeffrey W.; Luke, Graeme M.; Berlijn, Tom; Maier, Thomas A.; Uemura, Yasutomo J.; Dai, Pengcheng

    2017-02-01

    We use neutron diffraction and muon spin relaxation to study the effect of in-plane uniaxial pressure on the antiferromagnetic (AF) orthorhombic phase in BaFe2As2 and its Co- and Ni-substituted members near optimal superconductivity. In the low-temperature AF ordered state, uniaxial pressure necessary to detwin the orthorhombic crystals also increases the magnetic ordered moment, reaching an 11% increase under 40 MPa for BaFe1.9Co0.1As2 , and a 15% increase for BaFe1.915Ni0.085As2 . We also observe an increase of the AF ordering temperature (TN) of about 0.25 K/MPa in all compounds, consistent with density functional theory calculations that reveal better Fermi surface nesting for itinerant electrons under uniaxial pressure. The doping dependence of the magnetic ordered moment is captured by combining dynamical mean field theory with density functional theory, suggesting that the pressure-induced moment increase near optimal superconductivity is closely related to quantum fluctuations and the nearby electronic nematic phase.

  18. Flexible relaxor materials: Ba(2)Pr(x)Nd(1-x)FeNb(4)O(15) tetragonal tungsten bronze solid solution.

    PubMed

    Castel, Elias; Josse, Michaël; Michau, Dominique; Maglione, Mario

    2009-11-11

    Relaxors are very interesting materials but most of the time they are restricted to perovskite materials and thus their flexibility is limited. We have previously shown that tetragonal tungsten bronze (TTB) niobate Ba(2)PrFeNb(4)O(15) was a relaxor below 170 K and that Ba(2)NdFeNb(4)O(15) displays a ferroelectric behavior with a T(C) = 323 K. On scanning the whole solid solution Ba(2)Pr(x)Nd(1-x)FeNb(4)O(15) (x = 0, 0.2, 0.4, 0.5, 0.6, 0.8 and 1), we demonstrate here a continuous crossover between these end member behaviors with a coexistence of ferroelectricity and relaxor in the intermediate range. This tunability is ascribed to the peculiar structure of the TTB networks which is more open than the classical perovskites. This allows for the coexistence of long range and short range orders and thus opens up the range of relaxor materials.

  19. Room-temperature multiferroic and magnetocapacitance effects in M-type hexaferrite BaFe10.2Sc1.8O19

    NASA Astrophysics Data System (ADS)

    Tang, Rujun; Zhou, Hao; You, Wenlong; Yang, Hao

    2016-08-01

    The room-temperature multiferroic and magnetocapacitance (MC) effects of polycrystalline M-type hexaferrite BaFe10.2Sc1.8O19 have been investigated. The results show that the magnetic moments of insulating BaFe10.2Sc1.8O19 can be manipulated by the electric field at room temperature, indicating the existence of magnetoelectric coupling. Moreover, large MC effects are also observed around the room temperature. A frequency dependence analysis shows that the Maxwell-Wagner type magnetoresistance effect is the dominant mechanism for MC effects at low frequencies. Both the magnetoelectric-type and non-magnetoelectric-type spin-phonon couplings contribute to the MC effects at high frequencies with the former being the dominant mechanism. The above results show that the hexaferrite BaFe10.2Sc1.8O19 is a room-temperature multiferroic material that can be potentially used in magnetoelectric devices.

  20. First-principles study of multiferroic properties of Fe3O4/SrTiO3 and Fe3O4/BaTiO3 [001] superlattices

    NASA Astrophysics Data System (ADS)

    Park, Min Sik; Freeman, A. J.

    2007-03-01

    Multiferroic superlattices are good candidates for the study of the interplay between magnetism and ferroelectricity, and important for multifunctional device applications operating at room temperature. Recently, it was found that the magnetoresistance arising at the Fe3O4/BaTiO3 barrier is strongly bias dependent. We calculated the physical properties for multiferroic superlattices of spinel Fe3O4 (as a ferrimagnet) and perovskite SrTiO3, and BaTiO3 (as ferroelectric materials) by using first-principles density functional calculations with the highly precise full-potential linearized augmented plane wave (FLAPW) method. At the interface, the half-metallicity of bulk Fe3O4 is destroyed, and magnetic moments that are different from bulk Fe are obtained. The ferroelectric instability of BaTiO3 near the interface is also discussed. M. Ziese, A. Bollero, I. Panagiotopoulos, and N. Moutis, Appl. Phys. Lett., 88, 212502 (2006). Wimmer, Krakauer, Weinert, Freeman, Phys.Rev.B, 24, 864 (1981).