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Sample records for co2-based heusler compounds

  1. Electronic and magnetic properties of the Co2-based Heusler compounds under pressure: first-principles and Monte Carlo studies

    NASA Astrophysics Data System (ADS)

    Zagrebin, M. A.; Sokolovskiy, V. V.; Buchelnikov, V. D.

    2016-09-01

    Structural, magnetic and electronic properties of stoichiometric Co2 YZ Heusler alloys (Y  =  Cr, Fe, Mn and Z  =  Al, Si, Ge) have been studied by means of ab initio calculations and Monte Carlo simulations. The investigations were performed in dependence on different levels of approximations in DFT (FP and ASA modes, as well as GGA and GGA  +  U schemes) and external pressure. It is shown that in the case of the GGA scheme the half-metallic behavior is clearly observed for compounds containing Cr and Mn transition metals, while Co2FeZ alloys demonstrate the pseudo half-metallic behavior. It is demonstrated that an applied pressure and an account of Coulomb repulsion (U) lead to the stabilization of the half-metallic nature for Co2 YZ alloys. The strongest ferromagnetic inter-sublattice (Co–Y) interactions together with intra-sublattice (Co–Co and Y–Y) interactions explain the high values of the Curie temperature obtained by Monte Carlo simulations using the Heisenberg model. It is observed that a decrease in valence electrons of Y atoms (i.e. Fe substitution by Mn and Cr) leads to the weakening of the exchange interactions and to the reduction of the Curie temperature. Besides, in the case of the FP mode Curie temperatures were found in a good agreement with available experimental and theoretical data, where the latter were obtained by applying the empirical relation between the Curie temperature and the total magnetic moment.

  2. Basics and prospective of magnetic Heusler compounds

    SciTech Connect

    Felser, Claudia Wollmann, Lukas; Chadov, Stanislav; Fecher, Gerhard H.; Parkin, Stuart S. P.

    2015-04-01

    Heusler compounds are a remarkable class of materials with more than 1000 members and a wide range of extraordinary multi-functionalities including halfmetallic high-temperature ferri- and ferromagnets, multi-ferroics, shape memory alloys, and tunable topological insulators with a high potential for spintronics, energy technologies, and magneto-caloric applications. The tunability of this class of materials is exceptional and nearly every functionality can be designed. Co{sub 2}-Heusler compounds show high spin polarization in tunnel junction devices and spin-resolved photoemission. Manganese-rich Heusler compounds attract much interest in the context of spin transfer torque, spin Hall effect, and rare earth free hard magnets. Most Mn{sub 2}-Heusler compounds crystallize in the inverse structure and are characterized by antiparallel coupling of magnetic moments on Mn atoms; the ferrimagnetic order and the lack of inversion symmetry lead to the emergence of new properties that are absent in ferromagnetic centrosymmetric Heusler structures, such as non-collinear magnetism, topological Hall effect, and skyrmions. Tetragonal Heusler compounds with large magneto crystalline anisotropy can be easily designed by positioning the Fermi energy at the van Hove singularity in one of the spin channels. Here, we give a comprehensive overview and a prospective on the magnetic properties of Heusler materials.

  3. Basics and prospective of magnetic Heusler compounds

    NASA Astrophysics Data System (ADS)

    Felser, Claudia; Wollmann, Lukas; Chadov, Stanislav; Fecher, Gerhard H.; Parkin, Stuart S. P.

    2015-04-01

    Heusler compounds are a remarkable class of materials with more than 1000 members and a wide range of extraordinary multi-functionalities including halfmetallic high-temperature ferri- and ferromagnets, multi-ferroics, shape memory alloys, and tunable topological insulators with a high potential for spintronics, energy technologies, and magneto-caloric applications. The tunability of this class of materials is exceptional and nearly every functionality can be designed. Co2-Heusler compounds show high spin polarization in tunnel junction devices and spin-resolved photoemission. Manganese-rich Heusler compounds attract much interest in the context of spin transfer torque, spin Hall effect, and rare earth free hard magnets. Most Mn2-Heusler compounds crystallize in the inverse structure and are characterized by antiparallel coupling of magnetic moments on Mn atoms; the ferrimagnetic order and the lack of inversion symmetry lead to the emergence of new properties that are absent in ferromagnetic centrosymmetric Heusler structures, such as non-collinear magnetism, topological Hall effect, and skyrmions. Tetragonal Heusler compounds with large magneto crystalline anisotropy can be easily designed by positioning the Fermi energy at the van Hove singularity in one of the spin channels. Here, we give a comprehensive overview and a prospective on the magnetic properties of Heusler materials.

  4. EDITORIAL: Cluster issue on Heusler compounds and devices Cluster issue on Heusler compounds and devices

    NASA Astrophysics Data System (ADS)

    Felser, Claudia; Hillebrands, Burkard

    2009-04-01

    This is the third cluster issue of Journal Physics D: Applied Physics devoted to half-metallic Heusler compounds and devices utilizing this class of materials. Heusler compounds are named after Fritz Heusler, the owner of a German copper mine, the Isabellenhütte, who discovered this class of materials in 1903 [1]. He synthesized mixtures of Cu2Mn alloys with various main group metals Z = Al, Si, Sn, Sb, which became ferromagnetic despite all constituents being non-magnetic. The recent success story of Heusler compounds began in 1983 with the discovery of the half-metallic electronic structure in NiMnSb [2] and Co2MnZ [3], making these and similar materials, in particular PtMnSb, also useful for magneto-optical data storage media applications due to their high Kerr rotation. The real breakthrough, however, came in 2000 with the observation of a large magnetoresistance effect in Co2Cr0.6Fe0.4Al [4]. The Co2YZ (Y = Ti, Cr, Mn, Fe) compounds are a special class of materials, which follow the Slater-Pauling rule [5], and most of them are half-metallic bulk materials. The electronic structure of Heusler compounds is well understood [6] and Curie temperatures up to 1100 K have been observed [7]. In their contribution to this cluster issue, Thoene et al predict that still higher Curie temperatures can be achieved. A breakthrough from the viewpoint of materials design is the synthesis of nanoparticles of Heusler compounds as reported in the contribution by Basit et al. Nano-sized half- metallic ferromagnets will open new directions for spintronic applications. The challenge, however, is still to produce spintronic devices with well defined interfaces to take advantage of the half-metallicity of the electrodes. Several groups have succeeded in producing excellent tunnel junctions with high magnetoresistance effects at low temperatures and decent values at room temperature [8-11]. Spin-dependent tunnelling characteristics of fully epitaxial magnetic tunnel junctions with a

  5. Thermodynamic properties and phase equilibria of selected Heusler compounds

    NASA Astrophysics Data System (ADS)

    Yin, Ming

    Heusler compounds are ternary intermetallics with many promising properties such as spin polarization and magnetic shape memory effect. A better understanding of their thermodynamic properties facilitates future design and development. Therefore, standard enthalpies of formation and heat capacities from room temperature to 1500 K of selected Heusler compounds X2YZ (X = Co, Fe, Ni, Pd, Rh, Ru; Y = Co, Cu, Fe, Hf, Mn, Ni, Ti, V, Zr; Z = Al, Ga, In, Si, Ge, Sn) and half-Heusler compounds XYSn (X = Au, Co, Fe, Ir, Ni, Pd, Pt, Rh; Y = Hf, Mn, Ti, Zr) were measured using high temperature direct reaction calorimetry. The measured standard enthalpies of formation were compared with those predicted from ab initio calculations and the extended semi-empirical Miedema's model. Trends in standard enthalpy of formation with respect to the periodic classification of elements were discussed. The effect of a fourth element (Co, Cu, Fe, Pd; Ti, V; Al, Ga, In, Si, Ge) on the standard enthalpy of formation of Ni2MnSn was also investigated. Lattice parameters of the compounds with an L21 structure were determined using X-ray powder diffraction analysis. Differential scanning calorimetry was used to determine melting points and phase transformation temperatures. Phase relationships were investigated using scanning electron microscopy with an energy dispersive spectrometer. The isothermal section of the Fe-Sn-Ti ternary system at 873 K was established using equilibrated alloys. Three ternary compounds including the Heusler compound Fe2SnTi were observed. A new ternary compound Fe5Sn9Ti 6 was reported and the crystal structure of FeSnTi2 was determined for the first time.

  6. Spin-filter and spin-gapless semiconductors: The case of Heusler compounds

    NASA Astrophysics Data System (ADS)

    Galanakis, I.; Özdoǧan, K.; Şaşıoǧlu, E.

    2016-05-01

    We review our recent first-principles results on the inverse Heusler compounds and the ordered quaternary (also known as LiMgPdSn-type) Heusler compounds. Among these two subfamilies of the full-Heusler compounds, several have been shown to be magnetic semiconductors. Such material can find versatile applications, e.g. as spin-filter materials in magnetic tunnel junctions. Finally, a special case are the spin-gapless semiconductors, where the energy gap at the Fermi level for the one spin-direction is almost vanishing, offering novel functionalities in spintronic/magnetoelectronic devices.

  7. Titanium nitride as a seed layer for Heusler compounds

    NASA Astrophysics Data System (ADS)

    Niesen, Alessia; Glas, Manuel; Ludwig, Jana; Schmalhorst, Jan-Michael; Sahoo, Roshnee; Ebke, Daniel; Arenholz, Elke; Reiss, Günter

    2015-12-01

    Titanium nitride (TiN) shows low resistivity at room temperature (27 μΩ cm), high thermal stability and thus has the potential to serve as seed layer in magnetic tunnel junctions. High quality TiN thin films with regard to the crystallographic and electrical properties were grown and characterized by x-ray diffraction and 4-terminal transport measurements. Element specific x-ray absorption spectroscopy revealed pure TiN inside the thin films. To investigate the influence of a TiN seed layer on a ferro(i)magnetic bottom electrode in magnetic tunnel junctions, an out-of-plane magnetized Mn2.45Ga as well as in- and out-of-plane magnetized Co2FeAl thin films were deposited on a TiN buffer, respectively. The magnetic properties were investigated using a superconducting quantum interference device and anomalous Hall effect for Mn2.45Ga. Magneto optical Kerr effect measurements were carried out to investigate the magnetic properties of Co2FeAl. TiN buffered Mn2.45Ga thin films showed higher coercivity and squareness ratio compared to unbuffered samples. The Heusler compound Co2FeAl showed already good crystallinity when grown at room temperature on a TiN seed-layer.

  8. Extrinsic doping of the half-Heusler compounds.

    PubMed

    Stern, Robin; Dongre, Bonny; Madsen, Georg K H

    2016-08-19

    Controlling the p- and n-type doping is a key tool to improve the power-factor of thermoelectric materials. In the present work we provide a detailed understanding of the defect thermochemistry in half-Heusler compounds. We calculate the formation energies of intrinsic and extrinsic defects in state of the art n-type TiNiSn and p-type TiCoSb thermoelectric materials. It is shown how the incorporation of online repositories can reduce the workload in these calculations. In TiNiSn we find that Ni- and Ti-interstitial defects play a crucial role in the carrier concentration of TiNiSn. Furthermore, we find that extrinsic doping with Sb can substantially enhance the carrier concentration, in agreement with experiment. In case of TiCoSb, we find ScTi, FeCo and SnSb being possible p-type dopants. While experimental work has mainly focussed on Sn-doping of the Sb site, the present result underlines the possibility to p-dope TiCoSb on all lattice sites. PMID:27389340

  9. Extrinsic doping of the half-Heusler compounds

    NASA Astrophysics Data System (ADS)

    Stern, Robin; Dongre, Bonny; Madsen, Georg K. H.

    2016-08-01

    Controlling the p- and n-type doping is a key tool to improve the power-factor of thermoelectric materials. In the present work we provide a detailed understanding of the defect thermochemistry in half-Heusler compounds. We calculate the formation energies of intrinsic and extrinsic defects in state of the art n-type TiNiSn and p-type TiCoSb thermoelectric materials. It is shown how the incorporation of online repositories can reduce the workload in these calculations. In TiNiSn we find that Ni- and Ti-interstitial defects play a crucial role in the carrier concentration of TiNiSn. Furthermore, we find that extrinsic doping with Sb can substantially enhance the carrier concentration, in agreement with experiment. In case of TiCoSb, we find ScTi, FeCo and SnSb being possible p-type dopants. While experimental work has mainly focussed on Sn-doping of the Sb site, the present result underlines the possibility to p-dope TiCoSb on all lattice sites.

  10. Titanium nitride as a seed layer for Heusler compounds

    SciTech Connect

    Niesen, Alessia Glas, Manuel; Ludwig, Jana; Schmalhorst, Jan-Michael; Reiss, Günter; Sahoo, Roshnee; Ebke, Daniel; Arenholz, Elke

    2015-12-28

    Titanium nitride (TiN) shows low resistivity at room temperature (27 μΩ cm), high thermal stability and thus has the potential to serve as seed layer in magnetic tunnel junctions. High quality TiN thin films with regard to the crystallographic and electrical properties were grown and characterized by x-ray diffraction and 4-terminal transport measurements. Element specific x-ray absorption spectroscopy revealed pure TiN inside the thin films. To investigate the influence of a TiN seed layer on a ferro(i)magnetic bottom electrode in magnetic tunnel junctions, an out-of-plane magnetized Mn{sub 2.45}Ga as well as in- and out-of-plane magnetized Co{sub 2}FeAl thin films were deposited on a TiN buffer, respectively. The magnetic properties were investigated using a superconducting quantum interference device and anomalous Hall effect for Mn{sub 2.45}Ga. Magneto optical Kerr effect measurements were carried out to investigate the magnetic properties of Co{sub 2}FeAl. TiN buffered Mn{sub 2.45}Ga thin films showed higher coercivity and squareness ratio compared to unbuffered samples. The Heusler compound Co{sub 2}FeAl showed already good crystallinity when grown at room temperature on a TiN seed-layer.

  11. Comparative ab initio study of half-Heusler compounds for optoelectronic applications

    NASA Astrophysics Data System (ADS)

    Gruhn, Thomas

    2010-09-01

    For the advancement of optoelectronic applications, such as thin-film solar cells or laser diodes, there is a strong demand for new semiconductor materials with tailored structural and electronic properties. The eight-electron half-Heusler compounds include many promising materials with a big variety of lattice constants and band gaps. So far only a small number of them have been investigated. With the help of ab initio calculations, we have studied all possible configurations of ternary 1:1:1 compounds in the half-Heusler structure. We have investigated 648 half-Heusler materials, including compounds of the types I-I-VI, I-II-V, I-III-IV, II-II-IV, and II-III-III. For all compounds, we have optimized the lattice constant and determined the most stable arrangement of elements on the half-Heusler lattice sites. Preferred configurations and semiconductivities are compared for the different half-Heusler types. A discussion of the lattice geometries provides a parameter-free function for estimating the lattice constants. The calculated band gaps and lattice constants are used to select potential substitute materials for CdS in the buffer layer of CuInSe2 and Cu(In,Ga)Se2 thin-film solar cells.

  12. Magnetic microstructure and magnetotransport in Co2FeAl Heusler compound thin films

    NASA Astrophysics Data System (ADS)

    Weiler, Mathias; Czeschka, Franz D.; Brandlmaier, Andreas; Imort, Inga-Mareen; Reiss, Günter; Thomas, Andy; Woltersdorf, Georg; Gross, Rudolf; Goennenwein, Sebastian T. B.

    2011-01-01

    We correlate simultaneously recorded magnetotransport and spatially resolved magneto-optical Kerr effect (MOKE) data in Co2FeAl Heusler compound thin films micropatterned into Hall bars. Room temperature MOKE images reveal the nucleation and propagation of domains in an externally applied magnetic field and are used to extract a macrospin corresponding to the mean magnetization direction in the Hall bar. The anisotropic magnetoresistance calculated using this macrospin is in excellent agreement with magnetoresistance measurements. This suggests that the magnetotransport in Heusler compounds can be adequately simulated using simple macrospin models, while the magnetoresistance contribution due to domain walls is of negligible importance.

  13. LaPtSb: a half-Heusler compound with high thermoelectric performance.

    PubMed

    Xue, Q Y; Liu, H J; Fan, D D; Cheng, L; Zhao, B Y; Shi, J

    2016-07-21

    The electronic and transport properties of the half-Heusler compound LaPtSb are investigated by performing first-principles calculations combined with semi-classical Boltzmann theory and deformation potential theory. Compared with many typical half-Heusler compounds, LaPtSb exhibits an obviously larger power factor at room temperature, especially for the n-type system. Together with the very low lattice thermal conductivity, the thermoelectric figure of merit (ZT) of LaPtSb can be optimized to a record high value of 2.2 by fine tuning the carrier concentration. PMID:27321233

  14. Evidence for localized moment picture in Mn-based Heusler compounds.

    PubMed

    Karel, J; Bernardi, F; Wang, C; Stinshoff, R; Born, N-O; Ouardi, S; Burkhardt, U; Fecher, G H; Felser, C

    2015-12-21

    X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) were used to probe the electronic structure and magnetic moment of Mn in Heusler compounds with different crystallographic structure. The results were compared with theoretical calculations of the magnetic and electronic properties, and it was found that in full and half Heusler alloys, Mn is metallic on both sublattices. The magnetic moment is large and localized when octahedrally coordinated by the main group element, consistent with previous theoretical work, and reduced when the main group coordination is tetrahedral. The magnetic and electronic properties of Mn in full and half Heusler compounds are strongly dependent on the structure and sublattice, a fact that can be exploited to design new materials. PMID:26559245

  15. Half-Heusler ternary compounds as new multifunctional experimental platforms for topological quantum phenomena

    NASA Astrophysics Data System (ADS)

    Lin, Hsin; Wray, L. Andrew; Xia, Yuqi; Xu, Suyang; Jia, Shuang; Cava, Robert J.; Bansil, Arun; Hasan, M. Zahid

    2010-07-01

    Recent discovery of spin-polarized single-Dirac-cone insulators, whose variants can host magnetism and superconductivity, has generated widespread research activity in condensed-matter and materials-physics communities. Some of the most interesting topological phenomena, however, require topological insulators to be placed in multiply connected, highly constrained geometries with magnets and superconductors, all of which thus require a large number of functional variants with materials design flexibility as well as electronic, magnetic and superconducting tunability. Given the optimum materials, topological properties open up new vistas in spintronics, quantum computing and fundamental physics. We have extended the search for topological insulators from the binary Bi-based series to the ternary thermoelectric Heusler compounds. Here we show that, although a large majority of the well-known Heuslers such as TiNiSn and LuNiBi are rather topologically trivial, the distorted LnPtSb-type (such as LnPtBi or LnPdBi, Ln=fn lanthanides) compounds belonging to the half-Heusler subclass harbour Z2=-1 topological insulator parent states, where Z2 is the band purity product index. Our results suggest that half-Heuslers provide a new platform for deriving a host of topologically exotic compounds and their nanoscale or thin-film device versions through the inherent flexibility of their lattice parameter, spin-orbit strength and magnetic moment tunability paving the way for the realization of multifunctional topological devices.

  16. EDITORIAL: New materials with high spin polarization: half-metallic Heusler compounds

    NASA Astrophysics Data System (ADS)

    Felser, Claudia; Hillebrands, Burkard

    2007-03-01

    The development of magnetic Heusler compounds, specifically designed as materials for spintronic applications, has made tremendous progress in the very recent past [1-21]. Heusler compounds can be made as half-metals, showing a high spin polarization of the conduction electrons of up to 100% [1]. These materials are exceptionally well suited for applications in magnetic tunnel junctions acting, for example, as sensors for magnetic fields. The tunnelling magneto-resistance (TMR) effect is the relative change in the electrical resistance upon application of a small magnetic field. Tunnel junctions with a TMR effect of 580% at 4 K were reported by the group of Miyazaki and Ando [1], consisting of two Co2MnSi Heusler electrodes. High Curie temperatures were found in Co2 Heusler compounds with values up to 1120 K in Co2FeSi [2]. The latest results are for a TMR device made from the Co2FeAl0.5Si0.5 Heusler compound and working at room temperature with a TMR effect of 174% [3]. The first significant magneto-resistance effect was discovered in Co2Cr0.6Fe0.4Al (CCFA) in Mainz [4]. With the classical Heusler compound CCFA as one electrode, the record TMR effect at 4 K is 240% [5]. Positive and negative TMR values at room temperature utilizing magnetic tunnel junctions with one Heusler compound electrode render magnetic logic possible [6]. Research efforts exist, in particular, in Japan and in Germany. The status of research as of winter 2005 was compiled in a recent special volume of Journal of Physics D: Applied Physics [7-20]. Since then specific progress has been made on the issues of (i) new advanced Heusler materials, (ii) advanced characterization, and (iii) advanced devices using the new materials. In Germany, the Mainz and Kaiserslautern based Research Unit 559 `New Materials with High Spin Polarization', funded since 2004 by the Deutsche Forschungsgemeinschaft, is a basic science approach to Heusler compounds, and it addresses the first two topics in particular

  17. Magnon excitation and temperature dependent transport properties in magnetic tunnel junctions with Heusler compound electrodes

    NASA Astrophysics Data System (ADS)

    Drewello, Volker; Ebke, Daniel; Schäfers, Markus; Kugler, Zoë; Reiss, Günter; Thomas, Andy

    2012-04-01

    Magnetic tunnel junctions were prepared with the Heusler compounds Co2FeAl, Co2FeSi, and Co2MnSi as the soft magnetic electrode. The Co2MnSi electrodes had a multilayer design that used either the Co2FeAl or the Co2FeSi compound as a buffer material. Pinned Co-Fe was used as the hard reference electrode. The electronic transport characteristics were analyzed by tunneling spectroscopy. The dependence of sample properties on the buffer material was of interest, especially the gap in the minority density of states of the Heusler electrode. The temperature dependence of the transport properties was also investigated.

  18. Half-Heusler Compounds as a New Class of Three-Dimensional Topological Insulators

    SciTech Connect

    Xiao, Di; Yao, yugui; Feng, wanxiang; Wen, Jun; Zhu, Wenguang; Chen, Xingqiu; Stocks, George Malcolm; Zhang, Zhenyu

    2010-01-01

    Using rst-principles calculations within density functional theory, we explore the feasibility of converting ternary half-Heusler compounds into a new class of three-dimensional topological insu- lators (3DTI). We demonstrate that the electronic structure of unstrained LaPtBi as a prototype system exhibits distinct band-inversion feature. The 3DTI phase is realized by applying a uni- axial strain along the [001] direction, which opens a bandgap while preserving the inverted band order. A denitive proof of the strained LaPtBi as a 3DTI is provided by directly calculating the topological Z2 invariants in systems without inversion symmetry. We discuss the implications of the present study to other half-Heusler compounds as 3DTI, which, together with the magnetic and superconducting properties of these materials, may provide a rich platform for novel quantum phenomena.

  19. Multilayer heterostructures of magnetic Heusler and binary compounds from first principles

    NASA Astrophysics Data System (ADS)

    Garoufalis, Christos; Galanakis, Iosif

    2016-03-01

    Employing first-principles state-of-the-art electronic structure calculations, we study a series of multilayer heterostructures composed of ferro/ferrimagnetic half-metallic Heusler compounds and binary compounds presenting perpendicular magnetic anisotropy. We relax these heterostructures and study both their electronic and magnetic properties. In most studied cases the Heusler spacer keeps a large value of spin-polarization at the Fermi level even for ultrathin films which attends the maximum value of 100% in the case of the Mn2VSi/MnSi multilayer. Our results pave the way both experimentally and theoretically towards the growth of such multilayer heterostructures and their incorporation in spintronic/magnetoelectronic devices.

  20. Tunable damping in the Heusler compound Co2 -xIrxMnSi

    NASA Astrophysics Data System (ADS)

    Köhler, Albrecht; Wollmann, Lukas; Ebke, Daniel; Chadov, Stanislav; Kaiser, Christian; Diao, Zhitao; Zheng, Yuankai; Leng, Qunwen; Felser, Claudia

    2016-03-01

    Here we report on the realization of tuning the intrinsic damping in the half-metallic Heusler compound Co2MnSi by substituting Co by Ir. The work includes theoretical calculations and experimental measurements on bulk and thin films samples. Control of damping is to remove unwanted magnetization motion and suppress signal echoes through uncontrolled precession of the magnetization for future implementation of this material into, e.g., current perpendicular plane-giant-magnetoresistance sensors. Density functional calculations revealed stable magnetization and increasing damping parameter with Iridium concentration, whereas the half metallicity could be retained. The calculations are consistent with experimental results from bulk and thin film samples of this report and elucidate the linear dependence of the Gilbert damping parameter on the substituent concentration. This report again demonstrates the inherent tunability of Heusler compounds, which constitutes a pivotal feature of this material class.

  1. Non-Gilbert-damping Mechanism in a Ferromagnetic Heusler Compound Probed by Nonlinear Spin Dynamics.

    PubMed

    Pirro, P; Sebastian, T; Brächer, T; Serga, A A; Kubota, T; Naganuma, H; Oogane, M; Ando, Y; Hillebrands, B

    2014-11-28

    The nonlinear decay of propagating spin waves in the low-Gilbert-damping Heusler film Co_{2}Mn_{0.6}Fe_{0.4}Si is reported. Here, two initial magnons with frequency f_{0} scatter into two secondary magnons with frequencies f_{1} and f_{2}. The most remarkable observation is that f_{1} stays fixed if f_{0} is changed. This indicates, that the f_{1} magnon mode has the lowest instability threshold, which, however, cannot be understood if only Gilbert damping is present. We show that the observed behavior is caused by interaction of the magnon modes f_{1} and f_{2} with the thermal magnon bath. This evidences a significant contribution of the intrinsic magnon-magnon scattering mechanisms to the magnetic damping in high-quality Heusler compounds. PMID:25494091

  2. EDITORIAL: New materials with high spin polarization: half-metallic Heusler compounds

    NASA Astrophysics Data System (ADS)

    Felser, Claudia; Hillebrands, Burkard

    2007-03-01

    The development of magnetic Heusler compounds, specifically designed as materials for spintronic applications, has made tremendous progress in the very recent past [1-21]. Heusler compounds can be made as half-metals, showing a high spin polarization of the conduction electrons of up to 100% [1]. These materials are exceptionally well suited for applications in magnetic tunnel junctions acting, for example, as sensors for magnetic fields. The tunnelling magneto-resistance (TMR) effect is the relative change in the electrical resistance upon application of a small magnetic field. Tunnel junctions with a TMR effect of 580% at 4 K were reported by the group of Miyazaki and Ando [1], consisting of two Co2MnSi Heusler electrodes. High Curie temperatures were found in Co2 Heusler compounds with values up to 1120 K in Co2FeSi [2]. The latest results are for a TMR device made from the Co2FeAl0.5Si0.5 Heusler compound and working at room temperature with a TMR effect of 174% [3]. The first significant magneto-resistance effect was discovered in Co2Cr0.6Fe0.4Al (CCFA) in Mainz [4]. With the classical Heusler compound CCFA as one electrode, the record TMR effect at 4 K is 240% [5]. Positive and negative TMR values at room temperature utilizing magnetic tunnel junctions with one Heusler compound electrode render magnetic logic possible [6]. Research efforts exist, in particular, in Japan and in Germany. The status of research as of winter 2005 was compiled in a recent special volume of Journal of Physics D: Applied Physics [7-20]. Since then specific progress has been made on the issues of (i) new advanced Heusler materials, (ii) advanced characterization, and (iii) advanced devices using the new materials. In Germany, the Mainz and Kaiserslautern based Research Unit 559 `New Materials with High Spin Polarization', funded since 2004 by the Deutsche Forschungsgemeinschaft, is a basic science approach to Heusler compounds, and it addresses the first two topics in particular

  3. NMR Evidence for the Topologically Nontrivial Nature in a Family of Half-Heusler Compounds

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaoming; Hou, Zhipeng; Wang, Yue; Xu, Guizhou; Shi, Chenglong; Liu, Enke; Xi, Xuekui; Wang, Wenhong; Wu, Guangheng; Zhang, Xi-Xiang

    2016-03-01

    Spin-orbit coupling (SOC) is expected to partly determine the topologically nontrivial electronic structure of heavy half-Heusler ternary compounds. However, to date, attempts to experimentally observe either the strength of SOC or how it modifies the bulk band structure have been unsuccessful. By using bulk-sensitive nuclear magnetic resonance (NMR) spectroscopy combined with first-principles calculations, we reveal that 209Bi NMR isotropic shifts scale with relativity in terms of the strength of SOC and average atomic numbers, indicating strong relativistic effects on NMR parameters. According to first-principles calculations, we further claim that nuclear magnetic shieldings from relativistic p1/2 states and paramagnetic contributions from low-lying unoccupied p3/2 states are both sensitive to the details of band structures tuned by relativity, which explains why the hidden relativistic effects on band structure can be revealed by 209Bi NMR isotropic shifts in topologically nontrivial half-Heusler compounds. Used in complement to surface-sensitive methods, such as angle resolved photon electron spectroscopy and scanning tunneling spectroscopy, NMR can provide valuable information on bulk electronic states.

  4. NMR Evidence for the Topologically Nontrivial Nature in a Family of Half-Heusler Compounds.

    PubMed

    Zhang, Xiaoming; Hou, Zhipeng; Wang, Yue; Xu, Guizhou; Shi, Chenglong; Liu, EnKe; Xi, Xuekui; Wang, Wenhong; Wu, Guangheng; Zhang, Xi-Xiang

    2016-01-01

    Spin-orbit coupling (SOC) is expected to partly determine the topologically nontrivial electronic structure of heavy half-Heusler ternary compounds. However, to date, attempts to experimentally observe either the strength of SOC or how it modifies the bulk band structure have been unsuccessful. By using bulk-sensitive nuclear magnetic resonance (NMR) spectroscopy combined with first-principles calculations, we reveal that (209)Bi NMR isotropic shifts scale with relativity in terms of the strength of SOC and average atomic numbers, indicating strong relativistic effects on NMR parameters. According to first-principles calculations, we further claim that nuclear magnetic shieldings from relativistic p1/2 states and paramagnetic contributions from low-lying unoccupied p3/2 states are both sensitive to the details of band structures tuned by relativity, which explains why the hidden relativistic effects on band structure can be revealed by (209)Bi NMR isotropic shifts in topologically nontrivial half-Heusler compounds. Used in complement to surface-sensitive methods, such as angle resolved photon electron spectroscopy and scanning tunneling spectroscopy, NMR can provide valuable information on bulk electronic states. PMID:26980406

  5. NMR Evidence for the Topologically Nontrivial Nature in a Family of Half-Heusler Compounds

    PubMed Central

    Zhang, Xiaoming; Hou, Zhipeng; Wang, Yue; Xu, Guizhou; Shi, Chenglong; Liu, EnKe; Xi, Xuekui; Wang, Wenhong; Wu, Guangheng; Zhang, Xi-xiang

    2016-01-01

    Spin-orbit coupling (SOC) is expected to partly determine the topologically nontrivial electronic structure of heavy half-Heusler ternary compounds. However, to date, attempts to experimentally observe either the strength of SOC or how it modifies the bulk band structure have been unsuccessful. By using bulk-sensitive nuclear magnetic resonance (NMR) spectroscopy combined with first-principles calculations, we reveal that 209Bi NMR isotropic shifts scale with relativity in terms of the strength of SOC and average atomic numbers, indicating strong relativistic effects on NMR parameters. According to first-principles calculations, we further claim that nuclear magnetic shieldings from relativistic p1/2 states and paramagnetic contributions from low-lying unoccupied p3/2 states are both sensitive to the details of band structures tuned by relativity, which explains why the hidden relativistic effects on band structure can be revealed by 209Bi NMR isotropic shifts in topologically nontrivial half-Heusler compounds. Used in complement to surface-sensitive methods, such as angle resolved photon electron spectroscopy and scanning tunneling spectroscopy, NMR can provide valuable information on bulk electronic states. PMID:26980406

  6. Long-term stability of phase-separated half-Heusler compounds.

    PubMed

    Krez, J; Balke, B; Ouardi, S; Selle, S; Höche, T; Felser, C; Hermes, W; Schwind, M

    2015-11-28

    Half-Heusler (HH) compounds have shown high figure of merit up to 1.5. Here, we address the long-term stability of n- and p-type HH materials. For this purpose, we investigated HH materials based on the Ti0.3Zr0.35Hf0.35NiSn-system after 500 cycles (1700 h) from 373 to 873 K. Both compounds exhibit a maximum Seebeck coefficient of |α|≈ 210 μV K(-1) and a phase separation into two HH phases. The dendritic microstructure is temperature resistant and upon cycling the changes in the microstructure are so marginal that the low thermal conductivity values (κ < 4 W m(-1) K(-1)) could be maintained. Our results emphasize that phase-separated HH compounds are suitable low cost materials and can lead to enhanced thermoelectric efficiencies beyond the set benchmark for industrial applications. PMID:26488053

  7. Direct observation of half-metallicity in the Heusler compound Co2MnSi

    PubMed Central

    Jourdan, M.; Minár, J.; Braun, J.; Kronenberg, A.; Chadov, S.; Balke, B.; Gloskovskii, A.; Kolbe, M.; Elmers, H.J.; Schönhense, G.; Ebert, H.; Felser, C.; Kläui, M.

    2014-01-01

    Ferromagnetic thin films of Heusler compounds are highly relevant for spintronic applications owing to their predicted half-metallicity, that is, 100% spin polarization at the Fermi energy. However, experimental evidence for this property is scarce. Here we investigate epitaxial thin films of the compound Co2MnSi in situ by ultraviolet-photoemission spectroscopy, taking advantage of a novel multi-channel spin filter. By this surface sensitive method, an exceptionally large spin polarization of () % at room temperature is observed directly. As a more bulk sensitive method, additional ex situ spin-integrated high energy X-ray photoemission spectroscopy experiments are performed. All experimental results are compared with advanced band structure and photoemission calculations which include surface effects. Excellent agreement is obtained with calculations, which show a highly spin polarized bulk-like surface resonance ingrained in a half metallic bulk band structure. PMID:24875774

  8. Validity of Wiedemann-Franz law in thermoelectric half Heusler compounds

    NASA Astrophysics Data System (ADS)

    Lee, Mal-Soon; Mahanti, S. D.

    2010-03-01

    There is renewed interest in the field of thermoelectrics for power generation. Several promising thermoelectrics are half-Heusler narrow band gap semiconductors. The efficiency of thermoelectric energy conversion depends on the transport coefficients through the figure of merit ZT=σS^2T/κ. For large ZT , it is necessary to decrease the total thermal conductivity (κ=κl+κel) as well as increase the Seebeck coefficient (S) and the electrical conductivity (σ)To determine κl experimentally, one usually subtracts the electronic thermal conductivity (κel) from measured κ, using the Wiedemann-Franz law (κel=L0σT, L0=2.45x10-8Wφ/K^2). To examine the validity of this law in half-Heusler compounds, we have chosen HfCoS as an example. We have calculated the electronic transport coefficients by employing ab-initio electronic structure method and the Boltzmann transport equation in HfCoSb. We calculate κelat constant current J (κel,J) and constant electric filed E (κel,E) where κel,J=κel,E-TσS^2 which shows a significant deviation from values obtained with Wiedemann-Franz law. κel,J is much smaller than κel,Eat low carrier concentrations (n) and/or at high temperatures (T) and the ratio κel,J/κel,E->1 at high n and/or low T.

  9. Progress Report 2011: Understanding compound phase transitions in Heusler alloy giant magnetocaloric materials

    SciTech Connect

    Stadler, Shane

    2011-12-13

    Our goal is to gain insight into the fundamental physics that is responsible for magnetocaloric effects (MCE) and related properties at the atomic level. We are currently conducting a systematic study on the effects of atomic substitutions in Ni2MnGa-based alloys, and also exploring related full- and half-Heusler alloys, for example Ni-Mn-X (X=In, Sn, Sb), that exhibit a wide variety of interesting and potentially useful physical phenomena. It is already known that the magnetocaloric effect in the Heusler alloys is fundamentally connected to other interesting phenomena such as shape-memory properties. And the large magnetic entropy change in Ni2Mn0.75Cu0.25Ga has been attributed to the coupling of the first-order, martensitic transition with the second-order ferromagnetic paramagnetic (FM-PM) transition. Our research to this point has focused on understanding the fundamental physics at the origin of these complex, compound phase transitions, and the novel properties that emerge. We synthesize the materials using a variety of techniques, and explore their material properties through structural, magnetic, transport, and thermo-magnetic measurements.

  10. Rapid Microwave Preparation of Thermoelectric TiNiSn and TiCoSb Half-Heusler Compounds

    SciTech Connect

    Birkel, Christina S.; Zeier, Wolfgang G.; Douglas, Jason E.; Lettiere, Bethany R.; Mills, Carolyn E.; Seward, Gareth; Birkel, Alexander; Snedaker, Matthew L.; Zhang, Yichi; Snyder, G. Jeffrey; Pollock, Tresa M.; Seshadri, Ram; Stucky, Galen D.

    2012-10-25

    The 18-electron ternary intermetallic systems TiNiSn and TiCoSb are promising for applications as high-temperature thermoelectrics and comprise earth-abundant, and relatively nontoxic elements. Heusler and half-Heusler compounds are usually prepared by conventional solid state methods involving arc-melting and annealing at high temperatures for an extended period of time. Here, we report an energy-saving preparation route using a domestic microwave oven, reducing the reaction time significantly from more than a week to one minute. A microwave susceptor material rapidly heats the elemental starting materials inside an evacuated quartz tube resulting in near single phase compounds. The initial preparation is followed by a densification step involving hot-pressing, which reduces the amount of secondary phases, as verified by synchrotron X-ray diffraction, leading to the desired half-Heusler compounds, demonstrating that hot-pressing should be treated as part of the preparative process. For TiNiSn, high thermoelectric power factors of 2 mW/mK{sup 2} at temperatures in the 700 to 800 K range, and zT values of around 0.4 are found, with the microwave-prepared sample displaying somewhat superior properties to conventionally prepared half-Heuslers due to lower thermal conductivity. The TiCoSb sample shows a lower thermoelectric figure of merit when prepared using microwave methods because of a metallic second phase.

  11. Influence of main-group element on half-metallic properties in half-Heusler compound

    NASA Astrophysics Data System (ADS)

    Liu, Hongyan; Li, Yushan; Tian, Fuyang; Li, Getian

    2016-04-01

    We investigate the band structure, magnetism and density of states of half-Heusler compounds CoCrZ (Z = Si,Ge,P,As) based on the first-principle calculations. Combined with molecular orbital hybridization theory, we discuss the influence of the main-group element on half-metallic properties of CoCrZ. It is found that the replacement of Ge for Si in CoCrSi can adjust the position of the Fermi level, and while it has no impact on the energy gap width and magnetic structure. However, the substitution of P for Si can effectively adjust the magnetism without disrupting its half-metallicity. Our results demonstrate that the electronic structure of CoCrZ is mainly dependent on the number of valence electrons of the main-group element.

  12. Conditions for spin-gapless semiconducting behavior in Mn{sub 2}CoAl inverse Heusler compound

    SciTech Connect

    Galanakis, I.; Özdoğan, K.; Şaşıoğlu, E.; Blügel, S.

    2014-03-07

    Employing ab initio electronic structure calculations, we investigate the conditions for spin-gapless semiconducting (SGS) behavior in the inverse Mn{sub 2}CoAl Heusler compound. We show that tetragonalization of the lattice, which can occur during films growth, keeps the SGS character of the perfect cubic compound. On the contrary, atomic swaps even between sites with different local symmetry destroy the SGS character giving rise to a half-metallic state. Furthermore, the occurrence of Co-surplus leads also to half-metallicity. Thus, we propose that in order to achieve SGS behavior during the growth of Mn{sub 2}CoAl (and similar SGS Heusler compounds) thin films, one should minimize the occurrence of defects, while small deformations of the lattice, due to the lattice mismatch with the substrate, do not play a crucial role.

  13. Band structure and transport studies of half Heusler compound DyPdBi: An efficient thermoelectric material

    NASA Astrophysics Data System (ADS)

    Krishnaveni, S.; Sundareswari, M.; Deshmukh, P. C.; Valluri, S. R.; Roberts, Ken

    2016-05-01

    The discovery of Heusler alloys has revolutionized the research field of intermetallics due to the ease with which one can derive potential candidates for multifunctional applications. During recent years, many half Heusler alloys have been investigated for their thermoelectric properties. The f electron based rare earth ternary half Heusler compound DyPdBi has its f energy levels located close to the Fermi energy level. Other research efforts have emphasized that such materials have good thermoelectric capabilities. We have explored using first principles the electronic band structure of DyPdBi by use of different exchange correlation potentials in the density functional theoretical framework. Transport coefficients that arise in the study of thermoelectric properties of DyPdBi have been calculated and illustrate its potential as an efficient thermoelectric material. Both the theoretically estimated Seebeck coefficient and the power factor agree well with the available experimental results. Our calculations illustrate that it is essential to include spin-orbit coupling in these models of f electron half Heusler materials.

  14. Impact of local order and stoichiometry on the ultrafast magnetization dynamics of Heusler compounds

    NASA Astrophysics Data System (ADS)

    Steil, Daniel; Schmitt, Oliver; Fetzer, Roman; Kubota, Takahide; Naganuma, Hiroshi; Oogane, Mikihiko; Ando, Yasuo; Rodan, Steven; Blum, Christian G. F.; Balke, Benjamin; Wurmehl, Sabine; Aeschlimann, Martin; Cinchetti, Mirko

    2015-04-01

    Nowadays, a wealth of information on ultrafast magnetization dynamics of thin ferromagnetic films exists in the literature. Information is, however, scarce on bulk single crystals, which may be especially important for the case of multi-sublattice systems. In Heusler compounds, representing prominent examples for such multi-sublattice systems, off-stoichiometry and degree of order can significantly change the magnetic properties of thin films, while bulk single crystals may be generally produced with a much more well-defined stoichiometry and a higher degree of ordering. A careful characterization of the local structure of thin films versus bulk single crystals combined with ultrafast demagnetization studies can, thus, help to understand the impact of stoichiometry and order on ultrafast spin dynamics. Here, we present a comparative study of the structural ordering and magnetization dynamics for thin films and bulk single crystals of the family of Heusler alloys with composition Co2Fe1 - xMnxSi. The local ordering is studied by 59Co nuclear magnetic resonance (NMR) spectroscopy, while the time-resolved magneto-optical Kerr effect gives access to the ultrafast magnetization dynamics. In the NMR studies we find significant differences between bulk single crystals and thin films, both regarding local ordering and stoichiometry. The ultrafast magnetization dynamics, on the other hand, turns out to be mostly unaffected by the observed structural differences, especially on the time scale of some hundreds of femtoseconds. These results confirm hole-mediated spin-flip processes as the main mechanism for ultrafast demagnetization and the robustness of this demagnetization channel against defect states in the minority band gap as well as against the energetic position of the band gap with respect to the Fermi energy. The very small differences observed in the magnetization dynamics on the picosecond time-scale, on the other hand, can be explained by considering the

  15. Ferrimagnetism and disorder of epitaxial Mn2-xCoxVAl Heusler compound thin films

    SciTech Connect

    Meinert, Markus; Schmalhorst, Jan-Michael; Reiss, Gunter; Arenholz, Elke

    2011-01-29

    The quaternary full Heusler compound Mn{sub 2-x}Co{sub x}VAl with x = 1 is predicted to be a half-metallic antiferromagnet. Thin films of the quaternary compounds with x = 0-2 were prepared by dc and RF magnetron co-sputtering on heated MgO (0 0 1) substrates. The magnetic structure was examined by x-ray magnetic circular dichroism and the chemical disorder was characterized by x-ray diffraction. Ferrimagnetic coupling of V to Mn was observed for Mn{sub 2}VAl (x = 0). For x = 0.5, we also found ferrimagnetic order with V and Co antiparallel to Mn. The observed reduced magnetic moments are interpreted with the help of band structure calculations in the coherent potential approximation. Mn{sub 2}VAl is very sensitive to disorder involving Mn, because nearest-neighbour Mn atoms couple antiferromagnetically. Co{sub 2}VAl has B2 order and has reduced magnetization. In the cases with x {ge} 0.9 conventional ferromagnetism was observed, closely related to the atomic disorder in these compounds.

  16. Magnetism of ordered and disordered Ni2MnAl full Heusler compounds

    NASA Astrophysics Data System (ADS)

    Simon, E.; Vida, J. Gy.; Khmelevskyi, S.; Szunyogh, L.

    2015-08-01

    Based on ab initio calculations and Monte Carlo simulations, we present a systematic study of the magnetic ground state and finite temperature magnetism of ordered and disordered Ni2MnAl full Heusler compounds. By increasing the degree of the long-range chemical disorder between the Mn and Al sublattices, the magnetic order progressively changes from the ferromagnetic state in the ordered L 21 phase toward a fully compensated antiferromagnetic state in the disordered B 2 phase and we also conclude that the Ni atoms exhibit induced moments. We determine the Mn-Mn interactions by using the magnetic force theorem and find dominating, but rather weak ferromagnetic couplings in the ordered L 21 phase. We used a recently proposed renormalization technique to include the weak Ni moments into the spin model, which indeed remarkably increased the nearest-neighbor Mn-Mn interaction. In accordance with the total energy calculations, in the disordered compounds, strong antiferromagnetic site-antisite Mn-Mn interactions appear. Determining the spin-spin correlation functions from Monte Carlo simulations, we conclude that above the transition temperature, short-range antiferromagnetic correlations prevail between the Mn atoms. In view of the potential application of disordered Ni2MnAl as a room temperature antiferromagnet, we calculate the magnetic anisotropy energies of tetragonally distorted samples in the B 2 phase and find that they are smaller by two orders in magnitude than in the frustrated antiferromagnet IrMn3.

  17. Full-scale computation for all the thermoelectric property parameters of half-Heusler compounds.

    PubMed

    Hong, A J; Li, L; He, R; Gong, J J; Yan, Z B; Wang, K F; Liu, J-M; Ren, Z F

    2016-01-01

    The thermoelectric performance of materials relies substantially on the band structures that determine the electronic and phononic transports, while the transport behaviors compete and counter-act for the power factor PF and figure-of-merit ZT. These issues make a full-scale computation of the whole set of thermoelectric parameters particularly attractive, while a calculation scheme of the electronic and phononic contributions to thermal conductivity remains yet challenging. In this work, we present a full-scale computation scheme based on the first-principles calculations by choosing a set of doped half-Heusler compounds as examples for illustration. The electronic structure is computed using the WIEN2k code and the carrier relaxation times for electrons and holes are calculated using the Bardeen and Shockley's deformation potential (DP) theory. The finite-temperature electronic transport is evaluated within the framework of Boltzmann transport theory. In sequence, the density functional perturbation combined with the quasi-harmonic approximation and the Klemens' equation is implemented for calculating the lattice thermal conductivity of carrier-doped thermoelectric materials such as Ti-doped NbFeSb compounds without losing a generality. The calculated results show good agreement with experimental data. The present methodology represents an effective and powerful approach to calculate the whole set of thermoelectric properties for thermoelectric materials. PMID:26947395

  18. Full-scale computation for all the thermoelectric property parameters of half-Heusler compounds

    NASA Astrophysics Data System (ADS)

    Hong, A. J.; Li, L.; He, R.; Gong, J. J.; Yan, Z. B.; Wang, K. F.; Liu, J.-M.; Ren, Z. F.

    2016-03-01

    The thermoelectric performance of materials relies substantially on the band structures that determine the electronic and phononic transports, while the transport behaviors compete and counter-act for the power factor PF and figure-of-merit ZT. These issues make a full-scale computation of the whole set of thermoelectric parameters particularly attractive, while a calculation scheme of the electronic and phononic contributions to thermal conductivity remains yet challenging. In this work, we present a full-scale computation scheme based on the first-principles calculations by choosing a set of doped half-Heusler compounds as examples for illustration. The electronic structure is computed using the WIEN2k code and the carrier relaxation times for electrons and holes are calculated using the Bardeen and Shockley’s deformation potential (DP) theory. The finite-temperature electronic transport is evaluated within the framework of Boltzmann transport theory. In sequence, the density functional perturbation combined with the quasi-harmonic approximation and the Klemens’ equation is implemented for calculating the lattice thermal conductivity of carrier-doped thermoelectric materials such as Ti-doped NbFeSb compounds without losing a generality. The calculated results show good agreement with experimental data. The present methodology represents an effective and powerful approach to calculate the whole set of thermoelectric properties for thermoelectric materials.

  19. Full-scale computation for all the thermoelectric property parameters of half-Heusler compounds

    DOE PAGESBeta

    Hong, A. J.; Li, L.; He, R.; Gong, J. J.; Yan, Z. B.; Wang, K. F.; Liu, J. -M.; Ren, Z. F.

    2016-03-07

    The thermoelectric performance of materials relies substantially on the band structures that determine the electronic and phononic transports, while the transport behaviors compete and counter-act for the power factor PF and figure-of-merit ZT. These issues make a full-scale computation of the whole set of thermoelectric parameters particularly attractive, while a calculation scheme of the electronic and phononic contributions to thermal conductivity remains yet challenging. In this work, we present a full-scale computation scheme based on the first-principles calculations by choosing a set of doped half- Heusler compounds as examples for illustration. The electronic structure is computed using the WIEN2k codemore » and the carrier relaxation times for electrons and holes are calculated using the Bardeen and Shockley’s deformation potential (DP) theory. The finite-temperature electronic transport is evaluated within the framework of Boltzmann transport theory. In sequence, the density functional perturbation combined with the quasi-harmonic approximation and the Klemens’ equation is implemented for calculating the lattice thermal conductivity of carrier-doped thermoelectric materials such as Tidoped NbFeSb compounds without losing a generality. The calculated results show good agreement with experimental data. Lastly, the present methodology represents an effective and powerful approach to calculate the whole set of thermoelectric properties for thermoelectric materials.« less

  20. Full-scale computation for all the thermoelectric property parameters of half-Heusler compounds

    PubMed Central

    Hong, A. J.; Li, L.; He, R.; Gong, J. J.; Yan, Z. B.; Wang, K. F.; Liu, J. -M.; Ren, Z. F.

    2016-01-01

    The thermoelectric performance of materials relies substantially on the band structures that determine the electronic and phononic transports, while the transport behaviors compete and counter-act for the power factor PF and figure-of-merit ZT. These issues make a full-scale computation of the whole set of thermoelectric parameters particularly attractive, while a calculation scheme of the electronic and phononic contributions to thermal conductivity remains yet challenging. In this work, we present a full-scale computation scheme based on the first-principles calculations by choosing a set of doped half-Heusler compounds as examples for illustration. The electronic structure is computed using the WIEN2k code and the carrier relaxation times for electrons and holes are calculated using the Bardeen and Shockley’s deformation potential (DP) theory. The finite-temperature electronic transport is evaluated within the framework of Boltzmann transport theory. In sequence, the density functional perturbation combined with the quasi-harmonic approximation and the Klemens’ equation is implemented for calculating the lattice thermal conductivity of carrier-doped thermoelectric materials such as Ti-doped NbFeSb compounds without losing a generality. The calculated results show good agreement with experimental data. The present methodology represents an effective and powerful approach to calculate the whole set of thermoelectric properties for thermoelectric materials. PMID:26947395

  1. Observation of strong ferromagnetism in the half-Heusler compound CoTiSb system

    NASA Astrophysics Data System (ADS)

    Sedeek, K.; Hantour, H.; Makram, N.; Said, Sh. A.

    2016-06-01

    Strong ferromagnetism has been detected in the semiconducting half-Heusler CoTiSb compound. The synthesis process was carried out by direct fusion of highly pure Co, Ti, and Sb in an evacuated quartz tube. The structural, micro structural and magnetic properties were investigated. The crystal structure was refined from X-ray powder diffraction data by the Rietveld method. Applying the search match program, three nano-crystalline phases of CoTiSb, Ti3Sb and CoTi2 (50%, 33.3% and 16.7% respectively) were identified for the prepared system. The term "phase" is used to address the co-existence of different stable chemical composition for the same half-Heusler alloy. The scanning electron microscope SEM and the high resolution transmission electron microscope HR-TEM were applied to characterize the morphology, size, shape, crystallinity and lattice spacing. A mixture of ordered and disordered arrangement was detected. Well defined nano-crystalline structure with an average interatomic distance equals 0.333 nm and sharp diffraction spots were measured. Contrary to this, the HR-TEM and electron diffraction image shows distorted structured planes and smeared halo surrounded by weak rings. Thermo-magnetic measurements (M-T) have been measured between 640 °K and 920 °K. Clear magnetic phase transition is detected above 900 °K (Tc), in addition to a second possible phase transition (TFF) around 740 °K. The latter is clarified by plotting ΔM/ΔT vs. T. To determine the type of the detected phase transitions, the field dependence of magnetization was measured at 300 °K and 740 °K. Arrot plots (M2-H/M) confirm the ferromagnetic character at both temperatures. It may be reasonable to assume the TFF transition as an additional ferromagnetic contribution stemming from some sort of exchange interactions. A tentative magnetic phase diagram is given. Overall, the present results suggest that the prepared multiphases CoTiSb system does not obey the 18 valence electron/unit cell

  2. Enhanced Thermoelectric Properties of La-Doped ZrNiSn Half-Heusler Compound

    NASA Astrophysics Data System (ADS)

    Akram, Rizwan; Zhang, Qiang; Yang, Dongwang; Zheng, Yun; Yan, Yonggao; Su, Xianli; Tang, Xinfeng

    2015-10-01

    The effect of La doping on ZrNiSn half-Heusler (HH) compound has been studied to explore the composition variation and structural modifications for improvement of its thermoelectric performance. A series of La x Zr1- x NiSn ( x = 0, 0.005, 0.01, 0.015, 0.02, 0.03) alloys were prepared by induction melting combined with plasma-activated sintering. Structural analysis using x-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) confirmed the resulting material to be a composite of HH, NiZr, and La3Sn4-type phases. The volume fraction for the phases other than HH ranged from 1.5% to 25% with increasing La content, as estimated by Rietveld analysis. The solubility of La in ZrNiSn is estimated to be 1.5%. Point defects may play a significant role in carrier and phonon transport. Interestingly, the thermoelectric transport properties exhibited a considerable increase in electrical conductivity σ with La doping and a significant drop in thermal conductivity κ, leading to a thermoelectric figure of merit ( ZT) of 0.53 at 923 K, representing an improvement of about 37% compared with the undoped sample.

  3. Magneto-optical spectroscopy of Co{sub 2}FeSi Heusler compound

    SciTech Connect

    Veis, M. Beran, L.; Antos, R.; Legut, D.; Hamrle, J.; Pistora, J.; Sterwerf, Ch.; Meinert, M.; Schmalhorst, J.-M.; Kuschel, T.; Reiss, G.

    2014-05-07

    Magneto-optical and electronic properties of the Co{sub 2}FeSi Heusler compound were studied by polar Kerr magneto-optical spectroscopy and ab-initio calculations. The thin-film samples were grown by dc/rf magnetron co-sputtering on MgO(100) substrates. A Cr seed layer was deposited prior to the Co{sub 2}FeSi layer to achieve its epitaxial growth. The magneto-optical spectroscopy was carried out using generalized magneto-optical ellipsometry with rotating analyzer in the photon energy range from 1.4 to 5.5 eV with an applied magnetic field of up to 1.2 T. The polar Kerr spectra showed a smooth spectral behavior up to 5.5 eV indicating nearly free charge carriers. Experimental data were compared with ab-initio calculations based on density functional theory employing the full-potential linearized augmented plane wave method.

  4. Theoretical investigations of electronic structure and magnetism in Zr2CoSn full-Heusler compound

    NASA Astrophysics Data System (ADS)

    Birsan, A.; Kuncser, V.

    2015-08-01

    The half-metallic properties of a new and promising full-Heusler compound, Zr2CoSn, are investigated by means of ab initio calculations within the Density Functional Theory framework. It was shown that the ferromagnetic ordered Hg2CuTi-type crystal structure is energetically the most favorable for this compound. The total magnetic moment is 3 μB/f.u. and follows a typical Slater-Pauling dependence. The half metallicity disappears if the unit cell volume is contracted by more than 5%.

  5. Low-moment ferrimagnetic phase of the Heusler compound Cr2CoAl

    NASA Astrophysics Data System (ADS)

    Jamer, Michelle E.; Marshall, Luke G.; Sterbinsky, George E.; Lewis, Laura H.; Heiman, Don

    2015-11-01

    Synthesizing half-metallic fully compensated ferrimagnets that form in the inverse Heusler phase could lead to superior spintronic devices. These materials would have high spin polarization at room temperature with very little fringing magnetic fields. Previous theoretical studies indicated that Cr2CoAl should form in a stable inverse Heusler lattice due to its low activation energy. Here, stoichiometric Cr2CoAl samples were arc-melted and annealed at varying temperatures, followed by studies of their structural and magnetic properties. High-resolution synchrotron X-ray diffraction revealed a chemically ordered Heusler phase in addition to CoAl and Cr phases. Soft X-ray magnetic circular dichroism revealed that the Cr and Co magnetic moments are antiferromagnetically oriented leading to the observed low magnetic moment in Cr2CoAl.

  6. Growth and Electronic Structure of Heusler Compounds for Use in Electron Spin Based Devices

    NASA Astrophysics Data System (ADS)

    Patel, Sahil Jaykumar

    Spintronic devices, where information is carried by the quantum spin state of the electron instead of purely its charge, have gained considerable interest for their use in future computing technologies. For optimal performance, a pure spin current, where all electrons have aligned spins, must be generated and transmitted across many interfaces and through many types of materials. While conventional spin sources have historically been elemental ferromagnets, like Fe or Co, these materials pro duce only partially spin polarized currents. To increase the spin polarization of the current, materials like half-metallic ferromagnets, where there is a gap in the minority spin density of states around the Fermi level, or topological insulators, where the current transport is dominated by spin-locked surface states, show promise. A class of materials called Heusler compounds, with electronic structures that range from normal metals, to half metallic ferromagnets, semiconductors, superconductors and even topological insulators, interfaces well with existing device technologies, and through the use of molecular beam epitaxy (MBE) high quality heterostructures and films can be grown. This dissertation examines the electronic structure of surfaces and interfaces of both topological insulator (PtLuSb-- and PtLuBi--) and half-metallic ferromagnet (Co2MnSi-- and Co2FeSi--) III-V semiconductor heterostructures. PtLuSb and PtLuBi growth by MBE was demonstrated on Alx In1--xSb (001) ternaries. PtLuSb (001) surfaces were observed to reconstruct with either (1x3) or c(2x2) unit cells depending on Sb overpressure and substrate temperature. viii The electronic structure of these films was studied by scanning tunneling microscopy/spectroscopy (STM/STS) and photoemission spectroscopy. STS measurements as well as angle resolved photoemission spectropscopy (ARPES) suggest that PtLuSb has a zero-gap or semimetallic band structure. Additionally, the observation of linearly dispersing surface

  7. Anomalous Hall effect in the Co-based Heusler compounds Co2FeSi and Co2FeAI

    NASA Astrophysics Data System (ADS)

    Imort, I.-M.; Thomas, P.; Reiss, G.; Thomas, A.

    2012-04-01

    The anomalous Hall effect (AHE) in the Heusler compounds Co2FeSi and Co2FeAl is studied in dependence of the annealing temperature to achieve a general comprehension of its origin. We have demonstrated that the crystal quality affected by annealing processes is a significant control parameter to tune the electrical resistivity ρxx as well as the anomalous Hall resistivity ρahe. Analyzing the scaling behavior of ρahe in terms of ρxx points to a temperature-dependent skew scattering as the dominant mechanism in both Heusler compounds.

  8. Robust tunability of magnetoresistance in half-Heusler R PtBi (R =Gd , Dy, Tm, and Lu) compounds

    NASA Astrophysics Data System (ADS)

    Mun, Eundeok; Bud'ko, Sergey L.; Canfield, Paul C.

    2016-03-01

    We present the magnetic field dependencies of transport properties for R PtBi (R =Gd , Dy, Tm, and Lu) half-Heusler compounds. Temperature- and field-dependent resistivity measurements of high-quality R PtBi single crystals reveal an unusually large, nonsaturating magnetoresistance (MR) up to 300 K under a moderate magnetic field of H =140 kOe. At 300 K, the large MR effect decreases as the rare earth is traversed from Gd to Lu and the magnetic field dependence of MR shows a deviation from the conventional H2 behavior. The Hall coefficient (RH) for R =Gd indicates a sign change around 120 K, whereas RH curves for R =Dy , Tm, and Lu remain positive for all measured temperatures. At 300 K, the Hall resistivity reveals a deviation from the linear field dependence for all compounds. Thermoelectric power measurements on this family show strong temperature and magnetic field dependencies which are consistent with resistivity measurements. A highly enhanced thermoelectric power under applied magnetic field is observed as high as ˜100 μ V /K at 140 kOe. Analysis of the transport data in this series reveals that the rare-earth-based half-Heusler compounds provide opportunities to tune MR effect through lanthanide contraction and to elucidate the mechanism of nontrivial MR.

  9. 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

  10. Effects of Ga substitution on the structural and magnetic properties of half metallic Fe2MnSi Heusler compound

    NASA Astrophysics Data System (ADS)

    Pedro, S. S.; Caraballo Vivas, R. J.; Andrade, V. M.; Cruz, C.; Paixão, L. S.; Contreras, C.; Costa-Soares, T.; Caldeira, L.; Coelho, A. A.; Carvalho, A. Magnus G.; Rocco, D. L.; Reis, M. S.

    2015-01-01

    The so-called half-metallic magnets have been proposed as good candidates for spintronic applications due to the feature of exhibiting a hundred percent spin polarization at the Fermi level. Such materials follow the Slater-Pauling rule, which relates the magnetic moment with the valence electrons in the system. In this paper, we study the bulk polycrystalline half-metallic Fe2MnSi Heusler compound replacing Si by Ga to determine how the Ga addition changes the magnetic, the structural, and the half-metal properties of this compound. The material does not follow the Slater-Pauling rule, probably due to a minor structural disorder degree in the system, but a linear dependence on the magnetic transition temperature with the valence electron number points to the half-metallic behavior of this compound.

  11. Spin transport and accumulation in n{sup +}-Si using Heusler compound Co{sub 2}FeSi/MgO tunnel contacts

    SciTech Connect

    Ishikawa, Mizue Sugiyama, Hideyuki; Inokuchi, Tomoaki; Saito, Yoshiaki; Hamaya, Kohei

    2015-08-31

    We investigate spin transport and accumulation in n{sup +}-Si using Heusler compound Co{sub 2}FeSi/MgO/Si on insulator (SOI) devices. The magnitudes of the non-local four- and three-terminal Hanle effect signals when using Heusler compound Co{sub 2}FeSi/MgO/SOI devices are larger than when using CoFe/MgO/SOI devices, whereas the preparation methods of MgO layers on SOI are exactly same in both devices. Different bias voltage dependencies on the magnitude of spin accumulation signals are also observed between these devices. Especially, Co{sub 2}FeSi/MgO/SOI devices show large spin accumulation signals compared with CoFe/MgO/SOI devices in the low bias voltage region less than ∼1000 mV in which the increase of the spin polarization is expected from the estimation of the density of states in Heusler compound Co{sub 2}FeSi and CoFe under spin extraction conditions. These results indicate that the species of ferromagnetic material definitely affects the magnitude and behavior of the spin signals. The use of highly polarized ferromagnets such as Heusler compounds would be important for improving the spin polarization and the magnitude of spin signals through Si channels.

  12. Magnetic properties and Curie temperatures of disordered Heusler compounds: Co1 +xFe2 -xSi

    NASA Astrophysics Data System (ADS)

    Fischer, Julia Erika; Karel, Julie; Fabbrici, Simone; Adler, Peter; Ouardi, Siham; Fecher, Gerhard H.; Albertini, Franca; Felser, Claudia

    2016-07-01

    The local atomic environments and magnetic properties were investigated for a series of Co1 +xFe2 -xSi (0 ≤x ≤1 ) Heusler compounds. While the total magnetic moment in these compounds increases with the number of valance electrons, the highest Curie temperature (TC) in this series was found for Co1.5Fe1.5Si , with a TC of 1069 K (24 K higher than the well-known Co2FeSi ). 57Fe Mössbauer spectroscopy was used to characterize the local atomic order and to estimate the Co and Fe magnetic moments. Consideration of the local magnetic moments and the exchange integrals is necessary to understand the trend in TC.

  13. Soft X-ray photoemission study of Co2(Cr1-xFex)Ga Heusler compounds

    NASA Astrophysics Data System (ADS)

    Tsunekawa, Masanori; Hattori, Yoshiro; Sekiyama, Akira; Fujiwara, Hidenori; Suga, Shigemasa; Muro, Takayuki; Kanomata, Takeshi; Imada, Shin

    2015-08-01

    We have performed soft X-ray photoemission spectroscopy (SXPES) and X-ray absorption spectroscopy (XAS) of the Co-based Heusler compounds Co2(Cr1-xFex)Ga (x = 0.0, 0.4, and 1.0) in order to study their electronic structures. Band-structure calculation was carried out and compared with the experimental results. SXPES spectra show hν-dependence, revealing the contributions of the Co, Cr, and Fe 3d electronic states in the valence band. The band width observed by the SXPES seems to be narrower than that predicted by the band-structure calculation. XAS spectra depend strongly on the the value of x in Co2(Cr1-xFex)Ga. The electron correlation effects are found to be stronger as x changes from 0.0 to 1.0.

  14. Structural, elastic, electronic, magnetic and optical properties of RbSrX(C, SI, Ge) half-Heusler compounds

    NASA Astrophysics Data System (ADS)

    Ahmad, Mukhtar; Naeemullah; Murtaza, G.; Khenata, R.; Bin Omran, S.; Bouhemadou, A.

    2015-03-01

    In this study we present investigations pertaining to structural, elastic, electronic, magnetic and optical properties of RbSrC, RbSrSi and RbSrGe half-Heusler compounds. To carry out this study, full potential (FP) linearized augmented plane wave (LAPW), a scheme of calculations developed within the framework of density functional theory (DFT), is employed. To incorporate the exchange correlation (XC) energy and corresponding potential into the total energy calculations, generalized gradient approximation (GGA) parameterized by Wu-Cohen is taken into account. Analysis of band structures and densities of states (DOS) profiles illustrate the conducting nature in spin down state and the semiconducting nature in spin-up state. The bonding nature discussed via electron charge density plot reveals strong ionic bonding character of these compounds. At ambient conditions, calculations for elastic constants (Cij) and their related elastic moduli are also performed which point to their brittle character. The compounds are found to be ferromagnetic with 1 μB. The magnetic moment decreases from its integer value at high pressures for these compounds.

  15. Phonon anomalies and superconductivity in the Heusler compound YPd₂Sn

    SciTech Connect

    Tütüncü, H. M.; Srivastava, G. P.

    2014-07-07

    We have studied the structural and electronic properties of YPd₂Sn in the Heusler structure using a generalized gradient approximation of the density functional theory and the ab initio pseudopotential method. The electronic results indicate that the density of states at the Fermi level is primarily derived from Pd d states, which hybridize with Y d and Sn p states. Using our structural and electronic results, phonons and electron-phonon interactions have been studied by employing a linear response approach based on the density functional theory. Phonon anomalies have been observed for transverse acoustic branches along the [110] direction. This anomalous dispersion is merely a consequence of the strong coupling. By integrating the Eliashberg spectral function, the average electron-phonon coupling parameter is found to be λ=0.99. Using this value, the superconducting critical temperature is calculated to be 4.12 K, in good accordance with the recent experimental value of 4.7 K.

  16. Ab initio prediction of ferrimagnetism, exchange interactions and Curie temperatures in Mn2TiZ Heusler compounds

    NASA Astrophysics Data System (ADS)

    Meinert, M.; Schmalhorst, J.-M.; Reiss, G.

    2011-01-01

    The Heusler compounds Mn2TiZ (Z = Al, Ga, In, Si, Ge, Sn, P, As, Sb) are of great interest due to their potential ferrimagnetic properties and high spin polarization. Here, we present calculations of the structural and magnetic properties of these materials. Their magnetic moment follows the Slater-Pauling rule m = NV - 24. None of them is actually a perfect half-metallic ferrimagnet, but some exhibit more than 90% spin polarization and Curie temperatures well above room temperature. The exchange interactions are complex; direct and indirect exchange contributions are identified. The Curie temperature scales with the total magnetic moment, and it has a positive pressure dependence. The role of the Z element is investigated: it influences the properties of the compounds mainly via its valence electron number and its atomic radius, which determines the lattice parameter. Based on these results, Mn2TiSi, Mn2TiGe, and Mn2TiSn are proposed as candidates for spintronic applications.

  17. Termination layer compensated tunnelling magnetoresistance in ferrimagnetic Heusler compounds with high perpendicular magnetic anisotropy

    PubMed Central

    Jeong, Jaewoo; Ferrante, Yari; Faleev, Sergey V.; Samant, Mahesh G.; Felser, Claudia; Parkin, Stuart S. P.

    2016-01-01

    Although high-tunnelling spin polarization has been observed in soft, ferromagnetic, and predicted for hard, ferrimagnetic Heusler materials, there has been no experimental observation to date of high-tunnelling magnetoresistance in the latter. Here we report the preparation of highly textured, polycrystalline Mn3Ge films on amorphous substrates, with very high magnetic anisotropy fields exceeding 7 T, making them technologically relevant. However, the small and negative tunnelling magnetoresistance that we find is attributed to predominant tunnelling from the lower moment Mn–Ge termination layers that are oppositely magnetized to the higher moment Mn–Mn layers. The net spin polarization of the current reflects the different proportions of the two distinct termination layers and their associated tunnelling matrix elements that result from inevitable atomic scale roughness. We show that by engineering the spin polarization of the two termination layers to be of the same sign, even though these layers are oppositely magnetized, high-tunnelling magnetoresistance is possible. PMID:26776829

  18. First principle study of structural, electronic and magnetic properties of half-Heusler IrCrZ (Z=Ge, As, sn and sb) compounds

    NASA Astrophysics Data System (ADS)

    Allaf Behbahani, Marzieh; Moradi, Mahmood; Rostami, Mohammad; Davatolhagh, Saeed

    2016-05-01

    First-principle calculations based on the density functional theory for new half-Heusler IrCrZ (Z=Ge, As, Sn and Sb) alloys are performed. It is found that the half-Heusler IrCrGe and IrCrSn compounds have an antiferromagnetic ground state while the ferromagnetic state is more stable than the antiferromagnetic and non-magnetic states for both IrCrAs and IrCrSb compounds. IrCrAs and IrCrSb exhibit half-metallic property with integer magnetic moments of 2.00 μB per formula unit and half-metallic gaps of 0.28 and 0.27 eV at their equilibrium volume, respectively. In addition, the density of states (DOSs) and band structures of IrCrAs and IrCrSb compounds are studied and the origin of their half-metallic gaps are discussed in detail. The estimation of Curie temperatures of IrCrAs and IrCrSb compounds is performed within the mean field approximation (MFA). The Curie temperatures of IrCrAs and IrCrSb are estimated to be 1083 and 1470 K, respectively. The stability of the half-metallicity in IrCrAs and IrCrSb compounds with the variation of lattice constant are also investigated.

  19. Ground state properties and thermoelectric behavior of Ru2VZ (Z=Si, ge, sn) half-metallic ferromagnetic full-Heusler compounds

    NASA Astrophysics Data System (ADS)

    Yalcin, Battal Gazi

    2016-06-01

    The ground state properties namely structural, mechanical, electronic and magnetic properties and thermoelectric behavior of Ru2VZ (Z=Si, Ge and Sn) half-metallic ferromagnetic full-Heusler compounds are systematically investigated. These compounds are ferromagnetic and crystallize in the Heusler type L21 structure (prototype: Cu2MnAl, Fm-3m 225). This result is confirmed for Ru2VSi and Ru2VSn by experimental work reported by Yin and Nash using high temperature direct reaction calorimetry. The studied materials are half-metallic ferromagnets with a narrow direct band gap in the minority spin channel that amounts to 31 meV, 66 meV and 14 meV for Ru2VSi, Ru2VGe, and Ru2VSn, respectively. The total spin magnetic moment (Mtot) of the considered compounds satisfies a Slater-Pauling type rule for localized magnetic moment systems (Mtot=(NV-24)μB), where NV=25 is the number of valence electrons in the primitive cell. The Curie temperature within the random phase approximation (RPA) is found to be 23 K, 126 K and 447 K for Ru2VSi, Ru2VGe and Ru2VSn, respectively. Semi-classical Boltzmann transport theories have been used to obtain thermoelectric constants, such as Seebeck coefficient (S), electrical (σ/τ) and thermal conductivity (κ/τ), power factor (PF) and the Pauli magnetic susceptibility (χ). ZTMAX values of 0.016 (350 K), 0.033 (380 K) and 0.063 (315 K) are achieved for Ru2VSi, Ru2VGe and Ru2VSn, respectively. It is expected that the obtained results might be a trigger in future experimentally interest in this type of full-Heusler compounds.

  20. Comment on "Structural, elastic, electronic, magnetic and optical properties of RbSrX (C, SI, Ge) half-Heusler compounds"

    NASA Astrophysics Data System (ADS)

    Jalilian, Jaafar; Motiepour, Pouria

    2015-12-01

    In a recent article by Ahmad et al. (2015) [1] structural, elastic, electronic, magnetic and optical properties of RbSrX (C, Si, Ge) half-Heusler compounds have been studied by the first principles calculations. After studying this article, we found that there are some physical and computational mistakes in electronic and optical properties sections. In investigating optical properties, they did not consider intraband transitions contribution in complex dielectric function term, while this term has significant effect on optical spectra for half-metallic materials.

  1. 59Co nuclear magnetic resonance study of the local distribution of atoms in the Heusler compound Co2FeAl0.5Si0.5

    NASA Astrophysics Data System (ADS)

    Wurmehl, Sabine; Kohlhepp, Jürgen T.; Swagten, Henk J. M.; Koopmans, Bert

    2012-02-01

    In this work, the spin-echo nuclear magnetic resonance (NMR) technique is used to probe the local structure of Co2FeAl0.5Si0.5 bulk samples. The 59Co NMR spectrum of the Heusler compound Co2FeAl0.5Si0.5 consists of four main resonance lines with an underlying sub-structure. The splitting into the main resonance lines is explained by contributions of the B2 type structure. The sub-lines are attributed to a random distribution of Al and Si. By comparing the experimental results with an appropriate multinomial distribution, the fraction of the Al/Si intermixing and the ratio between the contributing structure types is assigned. The main structural contribution of as-cast bulk samples is of B2 type with 38% of L21 contributions. The L21 contribution can be enhanced to 59% by an appropriate annealing process. However, B2 contributions are still present after annealing. Additional foreign phases such as fcc-Co and Co-Al, with relative contributions of less than one percent, are also found in both as-cast and annealed samples. Resonance lines related to slight amounts of the ternary, parental Heusler compounds Co2FeAl and Co2FeSi are also observed.

  2. Electronic and magnetic properties of X2YZ and XYZ Heusler compounds: a comparative study of density functional theory with different exchange-correlation potentials

    NASA Astrophysics Data System (ADS)

    Rai, D. P.; Sandeep; Shankar, A.; Pradhan Sakhya, Anup; Sinha, T. P.; Khenata, R.; Ghimire, M. P.; Thapa, R. K.

    2016-07-01

    The electronic and magnetic properties of Heusler compounds X2YZ and XYZ (X = Co, Ni, Pt, Fe; Y = Mn, Cr, Vi; Z = Al, Sb, Ga) are investigated by using the density functional theory with generalized gradient approximation (GGA), GGA plus U (LSDA+U), and modified Becke‑Johnson (mBJ) exchange potential. It is found that the half-metallic gaps are generally widened reasonably by LSDA+U and mBJ as compared to the conventional GGA. For the Co-based Heusler compounds the inclusion of U in GGA leads to a larger minority band gap while it is destroyed for Fe2VAl and NiMnSb. The magnetic properties of Co2VSi and Co2VSn are well defined within LSDA+U and mBJ with an exact integer value of magnetic moment. The band gaps of Fe2VAl and CoMnSb given by mBJ are in good agreement with the available experimental data of x-ray absorption spectroscopy. Except for the reasonably larger band gap, the mBJ band structure is almost same as that of GGA but is remarkably different from that of LSDA+U.

  3. Effects of Ga substitution on the structural and magnetic properties of half metallic Fe{sub 2}MnSi Heusler compound

    SciTech Connect

    Pedro, S. S. Caraballo Vivas, R. J.; Andrade, V. M.; Cruz, C.; Paixão, L. S.; Contreras, C.; Costa-Soares, T.; Rocco, D. L.; Reis, M. S.; Caldeira, L.; Coelho, A. A.; Carvalho, A. Magnus G.

    2015-01-07

    The so-called half-metallic magnets have been proposed as good candidates for spintronic applications due to the feature of exhibiting a hundred percent spin polarization at the Fermi level. Such materials follow the Slater-Pauling rule, which relates the magnetic moment with the valence electrons in the system. In this paper, we study the bulk polycrystalline half-metallic Fe{sub 2}MnSi Heusler compound replacing Si by Ga to determine how the Ga addition changes the magnetic, the structural, and the half-metal properties of this compound. The material does not follow the Slater-Pauling rule, probably due to a minor structural disorder degree in the system, but a linear dependence on the magnetic transition temperature with the valence electron number points to the half-metallic behavior of this compound.

  4. Half-metallic ferromagnetism in full-Heusler compounds ACaX{sub 2} (A = K and Rb; X = N and O)

    SciTech Connect

    Umamaheswari, R. Vijayalakshmi, D. Yogeswari, M. Kalpana, G.

    2014-04-24

    Electronic structure and magnetic properties of hypothetical ACaX{sub 2} (A = K and Rb; X= N and O) compounds in full-Heusler phase have been investigated based on density functional theory (DFT) within the local density approximation (LDA). The electronic band structures and density of states of these compounds show that the spin-down electrons have metallic, and the spin-up electrons have a semi conducting gap resulting in stable half-metallic ferromagnetic behaviour. The strong spin polarization of 2p states of N and O atoms is found to be the origin of ferromagnetism which results in a total magnetic moment of 3{sub μB} and 1{sub μB} respectively.

  5. Structural, electronic, magnetic and thermodynamic properties of full-Heusler compound Co2VSi: Ab initio study

    NASA Astrophysics Data System (ADS)

    Bentouaf, Ali; Hassan, Fouad El Haj

    2015-05-01

    Density functional theory based on full-potential linearized augmented plane wave (FP LAPW) method is used to investigate the structural, electronic and magnetic properties of Co2VSi Heusler alloys, with L21 structure. It is shown that calculated lattice constants and spin magnetic moments using the general gradient approximation method are in good agreement with experimental values. We also presented the thermal effects using the quasi-harmonic Debye model, in which the lattice vibrations are taken into account. Temperature and pressure effects on the structural parameters, heat capacities, thermal expansion coefficient, and Debye temperatures are determined from the non-equilibrium Gibbs functions.

  6. Thermoelectric Figures of Merit of Zn4Sb3 and Zrnisn-based Half-heusler Compounds Influenced by Mev Ion-beam Bombardments

    NASA Astrophysics Data System (ADS)

    Budak, S.; Guner, S.; Muntele, C. I.; Ila, D.

    Semiconducting β-Zn4Sb3 and ZrNiSn-based half-Heusler compound thin films with applications as thermoelectric (TE) materials were prepared using ion beam assisted deposition (IBAD). High-purity solid zinc (Zn) and antimony (Sb) were evaporated by electron beam to grow the β-Zn4Sb3 thin film while high-purity zirconium (Zr) powder and nickel (Ni) tin (Sn) powders were evaporated by electron beam to grow the ZrNiSn-based half-Heusler compound thin film. Rutherford backscattering spectrometry (RBS) was used to analyze the composition of the thin films. The grown thin films were subjected to 5 MeV Si ions bombardment for generation of nanostructures in the films. We measured the thermal conductivity, Seebeck coefficient, and electrical conductivity of these two systems before and after 5 MeV Si ions beam bombardment. The two material systems have been identified as promising TE materials for the application of thermal-to-electrical energy conversion, but the efficiency still limits their applications. The electronic energy deposited due to ionization in the track of MeV ion beam couldcause localized crystallization. The nanostructures produced by MeV ion beam can cause significant change in both the electrical and the thermal conductivity of thin films, thereby improving the efficiency. We used the 3ω-method (3rd harmonic) measurement system to measure the cross-plane thermal conductivity, the van der Pauw measurement system to measure the electrical conductivity, and the Seebeck-coefficient measurement system to measure the cross-plane Seebeck coefficient. The thermoelectric figures of merit of the two material systems were then derived by calculations using the measurement results. The MeV ion-beam bombardment was found to decrease the thermal conductivity of thin films and increase the efficiency of thermal-to-electrical energy conversion.

  7. Structural, electronic, elastic, thermoelectric and thermodynamic properties of the NbMSb half heusler (M=Fe, Ru, Os) compounds with first principle calculations

    NASA Astrophysics Data System (ADS)

    Abid, O. Miloud; Menouer, S.; Yakoubi, A.; Khachai, H.; Omran, S. Bin; Murtaza, G.; Prakash, Deo; Khenata, R.; Verma, K. D.

    2016-05-01

    The structural, electronic, elastic, thermoelectric and thermodynamic properties of NbMSb (M = Fe, Ru, Os) half heusler compounds are reported. The full-potential linearized augmented plane wave (FP-LAPW) plus local orbital (lo) method, based on the density functional theory (DFT) was employed for the present study. The equilibrium lattice parameter results are in good compliance with the available experimental measurements. The electronic band structure and Boltzmann transport calculations indicated a narrow indirect energy band gap for the compound having electronic structure favorable for thermoelectric performance as well as with substantial thermopowers at temperature ranges from 300 K to 800 K. Furthermore, good potential for thermoelectric performance (thermopower S ≥ 500 μeV) was found at higher temperature. In addition, the analysis of the charge density, partial and total densities of states (DOS) of three compounds demonstrate their semiconducting, ionic and covalent characters. Conversely, the calculated values of the Poisson's ratio and the B/G ratio indicate their ductile makeup. The thermal properties of the compounds were calculated by quasi-harmonic Debye model as implemented in the GIBBS code.

  8. First principles study on d0 half-metallic properties of full-Heusler compounds RbCaX2 (X = C, N, and O)

    NASA Astrophysics Data System (ADS)

    Gao, Yong-Chun; Wang, Xiao-Tian; Habib, Rozale

    2015-06-01

    A first-principles approach is employed to study the structural, electronic, and magnetic properties of RbCaX2 (X = C, N, and O) full-Heusler compounds. It is observed that RbCaN2 and RbCaO2 are new d0 half-metals with an integer magnetic moment of 3 μB and 1 μB in their ferrimagnetic ground states, respectively, while RbCaC2 is a common metallic compound. Analysis of the density of states of these compounds indicates that the magnetic moment and furthermore, the half-metallicity primarily originate from the spin-polarization of the p-like states of N and O atoms. The half-metallic (HM) gaps of RbCaN2 and RbCaO2 are notably large; thus, the half-metallicity is robust against lattice distortion. Such materials are suitable to be grown on various semiconductor substrates. In addition, for RbCaN2 and RbCaO2, four possible terminations of the surface are also calculated. Project supported by the Science Director Foundation Project of the National Natural Science Foundation of China (Grant No. 11347179).

  9. Electronic structure and thermoelectric properties of half-Heusler compounds with eight electron valence count—KScX (X = C and Ge)

    NASA Astrophysics Data System (ADS)

    Ciftci, Yasemin O.; Mahanti, Subhendra D.

    2016-04-01

    Electronic band structure and structural properties of two representative half-Heusler (HH) compounds with 8 electron valence count (VC), KScC and KScGe, have been studied using first principles methods within density functional theory and generalized gradient approximation. These systems differ from the well studied class of HH compounds like ZrNiSn and ZrCoSb which have VC = 18 because of the absence of d electrons of the transition metal atoms Ni and Co. Electronic transport properties such as Seebeck coefficient (S), electrical conductivity (σ), electronic thermal conductivity (κe) (the latter two scaled by electronic relaxation time), and the power factor (S2σ) have been calculated using semi-classical Boltzmann transport theory within constant relaxation time approximation. Both the compounds are direct band gap semiconductors with band extrema at the X point. Their electronic structures show a mixture of heavy and light bands near the valance band maximum and highly anisotropic conduction and valence bands near the band extrema, desirable features of good thermoelectric. Optimal p- or n-type doping concentrations have been estimated based on thermopower and maximum power factors. The optimum room temperature values of S are ˜1.5 times larger than that of the best room temperature thermoelectric Bi2Te3. We also discuss the impact of the band structure on deviations from Weidemann-Franz law as one tunes the chemical potential across the band gap.

  10. First Principles Investigation of the Elastic, Optoelectronic and Thermal Properties of XRuSb: (X = V, Nb, Ta) Semi-Heusler Compounds Using the mBJ Exchange Potential

    NASA Astrophysics Data System (ADS)

    Bencherif, K.; Yakoubi, A.; Della, N.; Miloud Abid, O.; Khachai, H.; Ahmed, R.; Khenata, R.; Bin Omran, S.; Gupta, S. K.; Murtaza, G.

    2016-07-01

    Semi-Heusler materials are intensively investigated due to their potential use in diverse applications, such as in spintronics and green energy applications. In this work, we employ the density functional theory to calculate the structural, electronic, elastic, thermal and optical properties of the VRuSb, NbRuSb and TaRuSb semi-Heusler compounds. The calculated results for the lattice constants, bulk moduli and their corresponding pressure derivative values are in fairly good agreement with previous works. In addition, besides the local density approximation, the modified Becke-Johnson exchange potential is also used to improve the value of the band gaps. The bonding nature reveals a mixture of covalent and ionic bonding character of the VRuSb, NbRuSb and TaRuSb compounds. Furthermore, the elastic constants ( C ij) and the related elastic moduli confirm their stability in the cubic phase and demonstrate their ductile nature. We also analyze the influence of the pressure and temperature on the primitive cell volume, heat capacity, volume expansion coefficient, and Debye temperature of the semi-Heusler compounds. Additionally, we investigate the optical properties, such as the complex dielectric function, refractive index, reflectivity, and the energy loss function.

  11. First Principles Investigation of the Elastic, Optoelectronic and Thermal Properties of XRuSb: (X = V, Nb, Ta) Semi-Heusler Compounds Using the mBJ Exchange Potential

    NASA Astrophysics Data System (ADS)

    Bencherif, K.; Yakoubi, A.; Della, N.; Miloud Abid, O.; Khachai, H.; Ahmed, R.; Khenata, R.; Bin Omran, S.; Gupta, S. K.; Murtaza, G.

    2016-04-01

    Semi-Heusler materials are intensively investigated due to their potential use in diverse applications, such as in spintronics and green energy applications. In this work, we employ the density functional theory to calculate the structural, electronic, elastic, thermal and optical properties of the VRuSb, NbRuSb and TaRuSb semi-Heusler compounds. The calculated results for the lattice constants, bulk moduli and their corresponding pressure derivative values are in fairly good agreement with previous works. In addition, besides the local density approximation, the modified Becke-Johnson exchange potential is also used to improve the value of the band gaps. The bonding nature reveals a mixture of covalent and ionic bonding character of the VRuSb, NbRuSb and TaRuSb compounds. Furthermore, the elastic constants (C ij) and the related elastic moduli confirm their stability in the cubic phase and demonstrate their ductile nature. We also analyze the influence of the pressure and temperature on the primitive cell volume, heat capacity, volume expansion coefficient, and Debye temperature of the semi-Heusler compounds. Additionally, we investigate the optical properties, such as the complex dielectric function, refractive index, reflectivity, and the energy loss function.

  12. Engineering half-Heusler thermoelectric materials using Zintl chemistry

    NASA Astrophysics Data System (ADS)

    Zeier, Wolfgang G.; Schmitt, Jennifer; Hautier, Geoffroy; Aydemir, Umut; Gibbs, Zachary M.; Felser, Claudia; Snyder, G. Jeffrey

    2016-06-01

    Half-Heusler compounds based on XNiSn and XCoSb (X = Ti, Zr or Hf) have rapidly become important thermoelectric materials for converting waste heat into electricity. In this Review, we provide an overview on the electronic properties of half-Heusler compounds in an attempt to understand their basic structural chemistry and physical properties, and to guide their further development. Half-Heusler compounds can exhibit semiconducting transport behaviour even though they are described as ‘intermetallic’ compounds. Therefore, it is most useful to consider these systems as rigid-band semiconductors within the framework of Zintl (or valence-precise) compounds. These considerations aid our understanding of their properties, such as the bandgap and low hole mobility because of interstitial Ni defects in XNiSn. Understanding the structural and bonding characteristics, including the presence of defects, will help to develop different strategies to improve and design better half-Heusler thermoelectric materials.

  13. Electronic structure, transport properties, and excited states in CoTiSb, CoZrSb, and CoHfSb half-Heusler compounds

    NASA Astrophysics Data System (ADS)

    Janotti, Anderson; Gui, Zhigang; Kawasaki, Jason; Palmstrom, Chris; Himmetoglu, Burak

    CoTiSb is a member of a large family of half-Heusler compounds with 18 valence electrons. CoTiSb is semiconductor material with a band gap a little over 1 eV, and it has been considered promising for thermoelectric applications. It can be grown on conventional III-V semiconductors, and could potentially be integrated in III-V devices. Here we present results of first-principles calculations of electronic structure, transport properties, and excited states in CoTiSb, as well as CoZrSb and CoHfSb. Electronic structures are studied using density functional theory within the local density approximation, hybrid functional and quasiparticle GW methods. Both room-temperature Seebeck coefficient and carrier mobility are calculated from first-principles. We also determine the band alignments to III-V semiconductors, and all the results are presented and discussed in the light of available experimental data. This work was supported by the DOE.

  14. Effect of Si substitution on electronic structure and magnetic properties of Heusler compounds Co2TiAl1-xSix

    NASA Astrophysics Data System (ADS)

    Zareii, Seyyed Mojtaba; Arabi, Hadi; Sarhaddi, Reza

    2012-09-01

    The electronic structures of Co-based Heusler compounds CoTiAl1-xSix (x=0, 0.25, 0.5, 0.75 and 1) are calculated by first-principles using the full potential linearized augmented plane wave (FP-LAPW) method within GGA and LSDA+U scheme. Particular emphasis was put on the role of the main group elements. In recent years, the GGA calculations of Co2TiAl (x=0) and Co2TiSi (x=1) indicated that they are half-metallic, but the electronic structure of this compound with x=0.25, 0.5 and 0.75 has not been reported yet, neither theoretically nor experimentally. The calculated results reveal that these are half-metallic and exhibit an energy gap in the minority spin state and also show 100% spin polarization. The substitution of Al by Si leads to an increase in the number of valence electrons, with increasing x. Our calculated results clearly show that with the Si doping, the lattice parameter linearly decreases; bulk modulus increases, and the total magnetic moment increases. The calculated energy gap in the minority spin state, using GGA scheme, was smaller than that obtained by using LSDA+U scheme. The outcomes of this research also show that the Co-3d DOS and therefore, the magnetic properties of compounds are dependent on electron concentration of the main group elements and it will affect the degree of p-d orbital occupation.

  15. First principle investigations of the structural, electronic and magnetic properties of predicted new zirconium based full-Heusler compounds, Zr2MnZ (Z=Al, Ga and In)

    NASA Astrophysics Data System (ADS)

    Birsan, A.; Kuncser, V.

    2016-05-01

    The crystal structure, electronic and magnetic properties of predicted new full-Heusler compounds Zr2MnZ (Z=Al, Ga, In) were studied within the density functional theory (DFT) framework. These materials exhibit unique properties that connect the spin gapless semiconducting character with the completely compensated ferrimagnetism. Magnetically ordered Zr2MnZ (Z=Al, Ga, In) compounds crystallize in inverse Heusler structure are stable against decomposition and have zero magnetic moment per formula unit, in agreement with Slater-Pauling rule. The Zr2MnAl compound presents semiconducting properties with an energy band gap of 0.41 eV in the majority spin channel and a zero band gap in the minority spin channel. By substituting completely the Al in Zr2MnAl via Ga and In elements, semiconducting pseudo band gaps are formed in the majority spin channels due to different neighborhoods around the manganese atoms, which decreases the energy of Mn triple degenerated anti-bonding states.

  16. Ultralow Thermal Conductivity in Full Heusler Semiconductors.

    PubMed

    He, Jiangang; Amsler, Maximilian; Xia, Yi; Naghavi, S Shahab; Hegde, Vinay I; Hao, Shiqiang; Goedecker, Stefan; Ozoliņš, Vidvuds; Wolverton, Chris

    2016-07-22

    Semiconducting half and, to a lesser extent, full Heusler compounds are promising thermoelectric materials due to their compelling electronic properties with large power factors. However, intrinsically high thermal conductivity resulting in a limited thermoelectric efficiency has so far impeded their widespread use in practical applications. Here, we report the computational discovery of a class of hitherto unknown stable semiconducting full Heusler compounds with ten valence electrons (X_{2}YZ, X=Ca, Sr, and Ba; Y=Au and Hg; Z=Sn, Pb, As, Sb, and Bi) through high-throughput ab initio screening. These new compounds exhibit ultralow lattice thermal conductivity κ_{L} close to the theoretical minimum due to strong anharmonic rattling of the heavy noble metals, while preserving high power factors, thus resulting in excellent phonon-glass electron-crystal materials. PMID:27494488

  17. Ultralow Thermal Conductivity in Full Heusler Semiconductors

    NASA Astrophysics Data System (ADS)

    He, Jiangang; Amsler, Maximilian; Xia, Yi; Naghavi, S. Shahab; Hegde, Vinay I.; Hao, Shiqiang; Goedecker, Stefan; OzoliĆš, Vidvuds; Wolverton, Chris

    2016-07-01

    Semiconducting half and, to a lesser extent, full Heusler compounds are promising thermoelectric materials due to their compelling electronic properties with large power factors. However, intrinsically high thermal conductivity resulting in a limited thermoelectric efficiency has so far impeded their widespread use in practical applications. Here, we report the computational discovery of a class of hitherto unknown stable semiconducting full Heusler compounds with ten valence electrons (X2Y Z , X =Ca , Sr, and Ba; Y =Au and Hg; Z =Sn , Pb, As, Sb, and Bi) through high-throughput ab initio screening. These new compounds exhibit ultralow lattice thermal conductivity κL close to the theoretical minimum due to strong anharmonic rattling of the heavy noble metals, while preserving high power factors, thus resulting in excellent phonon-glass electron-crystal materials.

  18. Superconductivity and Shubnikov-de Haas oscillations in the noncentrosymmetric half-Heusler compound YPtBi

    NASA Astrophysics Data System (ADS)

    Pavlosiuk, Orest; Kaczorowski, Dariusz; Wiśniewski, Piotr

    2016-07-01

    Recent findings of possible topological superconductivity in YPtBi motivated us to grow and investigate single crystals of this material. The compound was studied by means of ac magnetic susceptibility, electrical resistivity, Hall resistivity, and heat capacity measurements, performed in wide ranges of temperature and magnetic field. The superconductivity below the critical temperature Tc=0.97 K was clearly reflected in the magnetic and electronic transport data. The upper critical field Bc 2 was estimated at 1.84 T. However, no obvious anomaly near Tc was found in the temperature dependence of the heat capacity. In the normal state YPtBi appears semimetallic but its electrical conductance can be described by two components corresponding to parallel channels: metallic and semiconducting, with the latter becoming negligible at temperatures below 40 K. Shubnikov-de Haas oscillations were observed at temperatures below 10 K. Nontrivial Berry phase together with weak antilocalization effect strongly support the presence of Dirac fermions in YPtBi.

  19. CO2-based in-line phase contrast imaging of small intestine in mice

    PubMed Central

    Tang, Rongbiao; Li, Wei-Xia; Huang, Wei; Yan, Fuhua; Chai, Wei-Min; Yang, Guo-Yuan; Chen, Ke-Min

    2013-01-01

    The objective of this study was to explore the potential of CO2 single contrast in-line phase contrast imaging (PCI) for pre-clinical small intestine investigation. The absorption and phase contrast images of CO2 gas production were attained and compared. A further increase in image contrast was observed in PCI. Compared with CO2-based absorption contrast imaging (ACI), CO2-based PCI significantly enhanced the detection of mucosal microstructures, such as pits and folds. The CO2-based PCI could provide sufficient image contrast for clearly showing the intestinal mucosa in living mice without using barium. We concluded that CO2-based PCI might be a novel and promising imaging method for future studies of gastrointestinal disorders. PMID:23896957

  20. CO2-based in-line phase contrast imaging of small intestine in mice

    NASA Astrophysics Data System (ADS)

    Tang, Rongbiao; Li, Wei-Xia; Huang, Wei; Yan, Fuhua; Chai, Wei-Min; Yang, Guo-Yuan; Chen, Ke-Min

    2013-07-01

    The objective of this study was to explore the potential of CO2 single contrast in-line phase contrast imaging (PCI) for pre-clinical small intestine investigation. The absorption and phase contrast images of CO2 gas production were attained and compared. A further increase in image contrast was observed in PCI. Compared with CO2-based absorption contrast imaging (ACI), CO2-based PCI significantly enhanced the detection of mucosal microstructures, such as pits and folds. The CO2-based PCI could provide sufficient image contrast for clearly showing the intestinal mucosa in living mice without using barium. We concluded that CO2-based PCI might be a novel and promising imaging method for future studies of gastrointestinal disorders.

  1. Impact of excess iron on the calculated electronic and magnetic properties of Co{sub 3–x}Fe{sub x}Si Heusler-compound

    SciTech Connect

    Debbichi, M.; Hamad, B.

    2014-09-14

    Ab initio density functional calculations are performed on the Co{sub 3–x}Fe{sub x}Si alloys with variable iron composition (1≤x≤3). The evolution of the structural, electronic, and magnetic properties is investigated within different levels of approximations. These alloys crystallize in cubic Heusler structures, which evolve from the regular L2₁ structure for Co₂FeSi to the inverse X structure for x≥2. Using on-site Coulomb interactions of U{sub eff}(Co)=3.07 eV and U{sub eff}(Fe)=3.4 eV is found to describe consistently the experimental properties for x≤2. A good agreement between calculated and experimental magnetic moments is found for the cubic inverse Heusler phases without the addition of Hubbard-model. The spin polarization is found to range from 1 for Fe concentrations of x≤2, indicating the half-metallic character, to –0.29 at x=3.

  2. Surface half-metallicity of half-Heusler compound FeCrSe and interface half-metallicity of FeCrSe/GaP

    NASA Astrophysics Data System (ADS)

    Khalaf Al-zyadi, Jabbar M.; Jolan, Mudhahir H.; Yao, Kai-Lun

    2016-04-01

    Recent studies showed that half-Heusler FeCrSe exhibits half-metallic ferromagnetism (Huang et al. [20]). In this paper, we investigate extensively the electronic, magnetic, and half-metallic properties of the half-Heusler alloy FeCrSe (111) and (001) surfaces and the interface with GaP (111) substrate by using the first-principles calculations within the density functional theory. The atomic density of states demonstrates that the half-me tallicity verified in the bulk FeCrSe is maintained at the CrSe-terminated (001) and Se-terminated (111) surfaces, but lost at both Cr- and Fe-terminated (111) surfaces and the Fe-terminated (001) surface. Alternatively, for the interface of FeCrSe/GaP (111), the bulk half-metallicity is destroyed at Se-P configuration while Se-Ga interface and subinterface show nearly 100% spin polarization. Moreover, the calculated interfacial adhesion energies exhibit that Se-Ga shape is more stable than the Se-P one. The calculated magnetic moments of Se, Ga at the Se-Ga (111) interface and P at the Se-P (111) interface increase with respect to the corresponding bulk values while the atomic magnetic moment of Se atom at the Se-P (111) interface decreases. We also notice that the magnetic moments of subinterface Fe at both Se-Ga and Se-P (111) interfaces decrease compared to the bulk values.

  3. International Round-Robin Study of the Thermoelectric Transport Properties of an n-Type Half-Heusler Compound from 300 K to 773 K

    NASA Astrophysics Data System (ADS)

    Wang, Hsin; Bai, Shengqiang; Chen, Lidong; Cuenat, Alexander; Joshi, Giri; Kleinke, Holger; König, Jan; Lee, Hee Woong; Martin, Joshua; Oh, Min-Wook; Porter, Wallace D.; Ren, Zhifeng; Salvador, James; Sharp, Jeff; Taylor, Patrick; Thompson, Alan J.; Tseng, Y. C.

    2015-11-01

    International transport property-measurement round-robins have been conducted by the thermoelectric annex under the International Energy Agency (IEA) Implementing Agreement on Advanced Materials for Transportation (AMT). Two previous round-robins used commercially available bismuth telluride as the test material, with the objectives of understanding measurement issues and developing standard testing procedures. This round-robin extended the measurement temperature range to 773 K. It was designed to meet the increasing demands for reliable transport data for thermoelectric materials used for power-generation applications. Eleven laboratories from six IEA-AMT member countries participated in the study. A half-Heusler ( n-type) material prepared by GMZ Energy was selected for the round-robin. The measured transport properties had a narrower distribution of uncertainty than previous round-robin results. The study intentionally included multiple testing methods and instrument types. Over the full temperature range, the measurement discrepancies for the figure of merit, ZT, in this round-robin were ±11.5 to ±16.4% from the averages.

  4. Investigations of the half-metallic behavior and the magnetic and thermodynamic properties of half-Heusler CoMnTe and RuMnTe compounds: A first-principles study

    NASA Astrophysics Data System (ADS)

    Djaafri, T.; Djaafri, A.; Elias, A.; Murtaza, G.; Khenata, R.; R., Ahmed; Bin Omran, S.; Rached, D.

    2014-08-01

    First-principles spin-polarized density functional theory (DFT) investigations of the structural, electronic, magnetic, and thermodynamics characteristics of the half-Heusler, CoMnTe and RuMnTe compounds are carried out. Calculations are accomplished within a state of the art full-potential (FP) linearized (L) augmented plane wave plus a local orbital (APW + lo) computational approach framed within DFT. The generalized gradient approximation (GGA) parameterized by Perdew, Burke, and Ernzerhof (PBE) is implemented as an exchange correlation functional as a part of the total energy calculation. From the analysis of the calculated electronic band structure as well as the density of states for both compounds, a strong hybridization between d states of the higher valent transition metal (TM) atoms (Co, Ru) and lower valent TM atoms of (Mn) is observed. Furthermore, total and partial density of states (PDOS) of the ground state and the results of spin magnetic moments reveal that these compounds are both stable and ideal half-metallic ferromagnetic. The effects of the unit cell volume on the magnetic properties and half-metallicity are crucial. It is worth noting that our computed results of the total spin magnetic moments, for CoMnTe equal to 4 μB and 3 μB per unit cell for RuMnTe, nicely follow the rule μtot = Zt - 18. Using the quasi-harmonic Debye model, which considers the phononic effects, the effecs of pressure P and temperature T on the lattice parameter, bulk modulus, thermal expansion coefficient, Debye temperature, and heat capacity for these compounds are investigated for the first time.

  5. Spectroscopy of the electronic states of the Heusler compounds Co2FeAl and Co2Cr0.6Fe0.4Al and the influence of oxidation

    NASA Astrophysics Data System (ADS)

    Jourdan, Martin; Große-Schulte, Fabian; Hahn, Michaela; Schönhense, Gerd

    2011-04-01

    The band structures of the Heusler compounds Co2Cr0.6Fe0.4Al and Co2FeAl were investigated in situ by angle-resolved ultraviolet photoemission spectroscopy. The samples were prepared by a sputtering process optimized for tunnelling junction preparation, the photoemission process in the normal direction of the (0 0 1)-oriented thin films was excited by a helium gas discharge lamp (hν = 21.2 eV and hν = 40.8 eV). The spectra of clean samples are compared with calculations of the total and partial bulk density of states and are evaluated within the three-step model of photoemission. Basic agreement with theoretical predictions of the bulk band structure is concluded. At oxygen exposures of the thin films of only 1 Langmuir a chemisorption phase with significant changes in the valence-band spectrum near the Fermi energy is observed. At 10 L oxygen the spectra are indicative of an oxide within the UPS probing depth.

  6. Local formation of a Heusler structure in CoFe-Al alloys

    NASA Astrophysics Data System (ADS)

    Wurmehl, S.; Jacobs, P. J.; Kohlhepp, J. T.; Swagten, H. J. M.; Koopmans, B.; Maat, S.; Carey, M. J.; Childress, J. R.

    2011-01-01

    We systematically study the changes in the local atomic environments of Co in CoFe-Al alloys as a function of Al content by means of nuclear magnetic resonance. We find that a Co2FeAl Heusler type structure is formed on a local scale. The observed formation of a highly spin-polarized Heusler compound may explain the improved magnetotransport properties in CoFe-Al based current-perpendicular-to-the-plane spin-valves.

  7. Doping effects on thermoelectric properties of the off-stoichiometric Heusler compounds Fe{sub 2−x}V{sub 1+x}Al

    SciTech Connect

    Nishino, Y. Tamada, Y.

    2014-03-28

    The thermoelectric properties of Heusler-type Fe{sub 2−x}V{sub 1+x}Al{sub 1−y}Si{sub y} and Fe{sub 2−x}V{sub 1+x−y}Ti{sub y}Al alloys have been investigated to clarify which off-stoichiometric alloy, i.e., V-rich (x > 0) or V-poor (x < 0), is more effective in enhancing the Seebeck coefficient when doped by Si and Ti, while retaining a low electrical resistivity. Large Seebeck coefficients of −182 μV/K and 110 μV/K at 300 K are obtained for n-type Fe{sub 1.95}V{sub 1.05}Al{sub 0.97}Si{sub 0.03} and p-type Fe{sub 2.04}V{sub 0.93}Ti{sub 0.03}Al, respectively. When the Seebeck coefficient is plotted as a function of valence electron concentration (VEC), the VEC dependence for the doped off-stoichiometric alloys falls on characteristic curves depending on the off-stoichiometric composition x. It is concluded that a larger Seebeck coefficient with a negative sign can be obtained for the V-rich alloys rather than the V-poor alloys, whilst good p-type materials are always derived from the V-poor alloys. Substantial enhancements in the Seebeck coefficient for the off-stoichiometric alloys could be achieved by a favorable modification in the electronic structure around the Fermi level through the antisite V or Fe defect formation.

  8. Electronic structure of Zr-Ni-Sn systems: role of clustering and nanostructures in half-Heusler and Heusler limits.

    PubMed

    Do, Dat T; Mahanti, S D; Pulikkoti, Jiji J

    2014-07-01

    Half-Heusler and Heusler compounds have been of great interest for several decades for thermoelectric, magnetic, half-metallic and many other interesting properties. Among these systems, Zr-Ni-Sn compounds are interesting thermoelectrics which can go from semiconducting half-Heusler (HH) limit, ZrNiSn, to metallic Heusler (FH) limit, ZrNi2Sn. Recently Makongo et al (2011 J. Am. Chem. Soc. 133 18843) found that dramatic improvement in the thermoelectric power factor of HH can be achieved by putting excess Ni into the system. This was attributed to an energy filtering mechanism due to the presence of FH nanostructures in the HH matrix. Using density functional theory we have investigated clustering and nanostructure formation in ZrNi1+xSn (0 ⩽ x ⩽ 1) systems near the HH (x = 0) and FH (x = 1) ends and have found that excess Ni atoms in HH tend to stay close to each other and form nanoclusters. On the other hand, there is competing interaction between Ni-vacancies occupying different sites in FH which prevents them from forming vacancy nanoclusters. Effects of nano-inclusions on the electronic structure near HH and FH ends are discussed. PMID:24925669

  9. Prediction of phase transition, mechanical and electronic properties of inverse Heusler compound Y2RuPb, via FP-LMTO method

    NASA Astrophysics Data System (ADS)

    Labair, M.; Rached, H.; Rached, D.; Benalia, S.; Abidri, B.; Khenata, R.; Ahmed, R.; Omran, S. Bin; Bouhemadou, A.; Syrotyuk, S. V.

    2016-03-01

    Topological insulators (TI) are immensely investigated due to their promising characteristics for spintronics and quantum computing applications. In this regard, although bismuth, telluride, selenide and antimony containing compounds are typically considered as topological insulators, materials with Hg2CuTi-type structure have also shown their potential for TIs as well. Here, we present first principles study of the Y2RuPb compound, pertaining to its structural, mechanical, electrical and the optical properties. Calculations are executed at the level of the parameterized Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA), employing the full-potential (FP) linearized muffin-tin orbital (LMTO) approach, as designed within the density functional theory (DFT). The study is carried out on the Hg2CuTi-type and Cu2MnAl-type structures of the Y2RuPb compound. From our structural calculations, it is found that Y2RuPb is more stable in its Hg2CuTi-type structure; however, the analysis of the mechanical properties reveals its stability in both phases against any kind of elastic deformation. Similarly, Dirac cone shaped surface energy levels found in the predicted electronic band structure of the Y2RuPb compound, and good agreement of the obtained results with Zhang et al., demonstrates that it is a topological insulating material. Additionally, the real and imaginary parts of the dielectric function ɛ (ω) and refractive index n (ω), for an energy range up to 14eV, are analyzed as well.

  10. Performance analysis of STT-RAM with cross shaped free layer using Heusler alloys

    NASA Astrophysics Data System (ADS)

    Bharat Kumary, Tangudu; Ghosh, Bahniman; Awadhiya, Bhaskar; Verma, Ankit Kumar

    2016-01-01

    We have investigated the performance of a spin transfer torque random access memory (STT-RAM) cell with a cross shaped Heusler compound based free layer using micromagnetic simulations. We have designed a free layer using a Cobalt based Heusler compound. Simulation results clearly show that the switching time from one state to the other state has been reduced, also it has been found that the critical switching current density (to switch the magnetization of the free layer of the STT RAM cell) is reduced.

  11. Disorder-induced cubic phase in Fe2-based Heusler alloys

    NASA Astrophysics Data System (ADS)

    Kiss, Janos; Chadov, Stanislav; Fecher, Gerhard H.; Felser, Claudia

    2013-06-01

    Based on the first-principles electronic structure calculations, we analyze the chemical and magnetic mechanisms stabilizing the cubic phase in Fe2-based Heusler materials, which were predicted to be tetragonal when being chemically ordered. In agreement with recent experimental data, we found that these compounds crystallize within the so-called “inverted” cubic Heusler structure perturbed by a certain portion of the intrinsic chemical disorder. Understanding of these mechanisms is a necessary step to guide the successful future synthesis of the stable Fe2-based tetragonal phases, which are promising candidates for the rare-earth-free permanent magnets.

  12. Geochemical Interaction of Middle Bakken Reservoir Rock and CO2 during CO2-Based Fracturing

    NASA Astrophysics Data System (ADS)

    Nicot, J. P.; Lu, J.; Mickler, P. J.; Ribeiro, L. H.; Darvari, R.

    2015-12-01

    This study was conducted to investigate the effects of geochemical interactions when CO2 is used to create the fractures necessary to produce hydrocarbons from low-permeability Middle Bakken sandstone. The primary objectives are to: (1) identify and understand the geochemical reactions related to CO2-based fracturing, and (2) assess potential changes of reservoir property. Three autoclave experiments were conducted at reservoir conditions exposing middle Bakken core fragments to supercritical CO2 (sc-CO2) only and to CO2-saturated synthetic brine. Ion-milled core samples were examined before and after the reaction experiments using scanning electron microscope, which enabled us to image the reaction surface in extreme details and unambiguously identify mineral dissolution and precipitation. The most significant changes in the reacted rock samples exposed to the CO2-saturated brine is dissolution of the carbonate minerals, particularly calcite which displays severely corrosion. Dolomite grains were corroded to a lesser degree. Quartz and feldspars remained intact and some pyrite framboids underwent slight dissolution. Additionally, small amount of calcite precipitation took place as indicated by numerous small calcite crystals formed at the reaction surface and in the pores. The aqueous solution composition changes confirm these petrographic observations with increase in Ca and Mg and associated minor elements and very slight increase in Fe and sulfate. When exposed to sc-CO2 only, changes observed include etching of calcite grain surface and precipitation of salt crystals (halite and anhydrite) due to evaporation of residual pore water into the sc-CO2 phase. Dolomite and feldspars remained intact and pyrite grains were slightly altered. Mercury intrusion capillary pressure tests on reacted and unreacted samples shows an increase in porosity when an aqueous phase is present but no overall porosity change caused by sc-CO2. It also suggests an increase in permeability

  13. Growth of Cr2CoGa and inverse Heusler thin films using Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Jamer, Michelle; Decapua, Matthew; Player, Gabriel; Heiman, Don

    Theoretical calculations have predicted the existence of inverse Heusler compounds that exhibit zero-moment magnetization while retaining their half-metallicity. These unique compounds have been labeled spin gapless semiconductors (SGS), where the density of states (DOS) can behave as a half-metal or gapless semiconductor. There is a special interest for zero-moment SGS compounds since traditional antiferromagnets cannot be spin-polarized. Such compounds are experimentally attractive for future spintronic devices due to their large magnetic transition temperature (400-800 K). This work focuses on zero-moment inverse Heusler compounds including Cr2CoGa and Mn3Al. Thin films have been grown using MBE and their magnetic, structural, and electrical properties of these compounds have been characterized by various techniques, including XMCD and magnetometry. The atomic moments are found to be large, but significant cancellations lead to small average moments. Supported by NSF Grant ECCS-1402738.

  14. Doping designed half-Heusler insulators

    NASA Astrophysics Data System (ADS)

    Yu, Yonggang; Zhang, Xiuwen; Yu, Liping; Yan, Feng; Nagaraja, A.; Mason, T. O.; Zunger, Alex

    2015-03-01

    The 18-valence-electron 1:1:1 compounds of the type III-X-V, IV-X-IV, IV-IX-V and V-IX-IV include thermoelectric materials, topological insulators, and recently a high mobility p-type transparent conductor TaIrGe (arXiv:1406.0872), yet their intrinsic doping trends are poorly known or understood. Using the ``modern theory of doping'' that addresses via DFT and HSE the thermodynamic formation energies and the DFT-corrected transition levels in the gap, we find the following interesting trends: (1) High atomic number compounds such as TaIrGe made of metallic elements can surprisingly have a large band gap (direct) of ~ 2.5 eV. (2) Half-Heusler such as A(IV)B(X)C(IV) is naturally n-type if its DFT calculated chemical stability field resides within the A-rich or B-rich domain of the stability triangle, while it is p-type if it resides within the C-rich domain. Such calculations provide a good metric. (3) When the B atom [at (1/4,1/4,1/4)] is as large as Ir or Pt, the compound prefers p-type because the C-on-A antisite [such as Ge Ta (1 -) ] is a shallow acceptor producing holes yet the hole-killer donor of B-interstitial is unfavorable. (4) When B =Ni or Co, the compound favors n-type due to the dominance of B-interstitial defects (e.g. TiCoSb). We will show the calculated leading defect types and the dependence of carrier concentrations on chemical conditions for newly predicted half-Heulser insulators. This study is supported by DOE, Office of Science, Basic Energy Science, MSE division grant to CU Boulder.

  15. A new n-type half-Heusler thermoelectric material NbCoSb

    SciTech Connect

    Huang, Lihong; He, Ran; Chen, Shuo; Zhang, Hao; Dahal, Keshab; Zhou, Haiqing; Wang, Hui; Zhang, Qinyong; Ren, Zhifeng

    2015-10-15

    Highlights: • Half-Heusler alloy NbCoSb with 19 valence electron count was studied as TE material. • It is surprising that NbCoSb is n-type. • A maximum ZT of ∼0.4 is achieved at 700 °C without optimization. • It opens up a new route to develop new half-Heusler thermoelectric materials. • It is very interesting that a traditionally thought of VEC of 18 is not required. - Abstract: We surprisingly made a new n-type thermoelectric compound NbCoSb with half-Heusler (HH) structure having valence electron count of 19, different from the traditional 18, which opens up a new route to develop new half-Heusler thermoelectric materials not following the traditional valence electron count of 18. The samples are made by arc melting followed by ball milling and hot pressing. The effect of hot pressing temperature on the thermoelectric properties of NbCoSb samples has been studied. A maximum thermoelectric figure-of-merit (ZT) of ∼0.4 is achieved at 700 °C in NbCoSb sample that is hot pressed at 1000 °C. This work add a new member to HH compounds for thermoelectric applications, although the peak ZT of ∼0.4 is still lower than that of the traditional HHs. Moreover, it is very interesting to see that a traditionally thought of valence electron counts of 18 is not required.

  16. Large non-collinearity and spin-reorientation in the novel Mn2RhSn Heusler magnet

    NASA Astrophysics Data System (ADS)

    Meshcheriakova, O.; Chadov, S.; Nayak, A.; Roessler, U. K.; Kuebler, J.; Andre, G.; Tsirlin, A. A.; Felser, C.

    2015-03-01

    Heusler compounds is a large class of materials, which exhibits diverse fundamental phenomena, together with the possibility of their specific tailoring for various engineering tasks. Present work discusses the magnetic noncollinearity in the family of noncentrosymmetric Mn2-based Heusler compounds. According to the experimental and theoretical results, Mn2YZ Heusler family is suspected to provide promising candidates for the formation of the skyrmion lattice. The work is focused on Mn2RhSn bulk polycrystalline sample, which serves as a prototype. It crystallizes in the tetragonal noncentrosymmetric structure (No. 119,I-4m2), which enables the anisotropic DM coupling. Additional short-range modulation, induced by the competing nearest and next-nearest interplanes Heisenberg exchange, is suppressed above the 80 K. This allows to develop the long-range modulations in the ideal ferrimagnetic structure within the ab crystallographic planes.

  17. Observation of a topologically non-trivial surface state in half-Heusler PtLuSb (001) thin films

    PubMed Central

    Logan, J. A.; Patel, S. J.; Harrington, S. D.; Polley, C. M.; Schultz, B. D.; Balasubramanian, T.; Janotti, A.; Mikkelsen, A.; Palmstrøm, C. J.

    2016-01-01

    The discovery of topological insulators, materials with bulk band gaps and protected cross-gap surface states in compounds such as Bi2Se3, has generated much interest in identifying topological surface states (TSSs) in other classes of materials. In particular, recent theoretical calculations suggest that TSSs may be found in half-Heusler ternary compounds. If experimentally realizable, this would provide a materials platform for entirely new heterostructure spintronic devices that make use of the structurally identical but electronically varied nature of Heusler compounds. Here we show the presence of a TSS in epitaxially grown thin films of the half-Heusler compound PtLuSb. Spin- and angle-resolved photoemission spectroscopy, complemented by theoretical calculations, reveals a surface state with linear dispersion and a helical tangential spin texture consistent with previous predictions. This experimental verification of topological behaviour is a significant step forward in establishing half-Heusler compounds as a viable material system for future spintronic devices. PMID:27346655

  18. Observation of a topologically non-trivial surface state in half-Heusler PtLuSb (001) thin films

    DOE PAGESBeta

    Logan, J. A.; Patel, S. J.; Harrington, S. D.; Polley, C. M.; Schultz, B. D.; Balasubramanian, T.; Janotti, A.; Mikkelsen, A.; Palmstrøm, C. J.

    2016-06-27

    The discovery of topological insulators, materials with bulk band gaps and protected cross-gap surface states in compounds such as Bi2Se3, has generated much interest in identifying topological surface states (TSSs) in other classes of materials. In particular, recent theoretical calculations suggest that TSSs may be found in half-Heusler ternary compounds. If experimentally realizable, this would provide a materials platform for entirely new heterostructure spintronic devices that make use of the structurally identical but electronically varied nature of Heusler compounds. Here we show the presence of a TSS in epitaxially grown thin films of the half-Heusler compound PtLuSb. Spin- and angle-resolvedmore » photoemission spectroscopy, complemented by theoretical calculations, reveals a surface state with linear dispersion and a helical tangential spin texture consistent with previous predictions. As a result, this experimental verification of topological behavior is a significant step forward in establishing half-Heusler compounds as a viable material system for future spintronic devices.« less

  19. Observation of a topologically non-trivial surface state in half-Heusler PtLuSb (001) thin films.

    PubMed

    Logan, J A; Patel, S J; Harrington, S D; Polley, C M; Schultz, B D; Balasubramanian, T; Janotti, A; Mikkelsen, A; Palmstrøm, C J

    2016-01-01

    The discovery of topological insulators, materials with bulk band gaps and protected cross-gap surface states in compounds such as Bi2Se3, has generated much interest in identifying topological surface states (TSSs) in other classes of materials. In particular, recent theoretical calculations suggest that TSSs may be found in half-Heusler ternary compounds. If experimentally realizable, this would provide a materials platform for entirely new heterostructure spintronic devices that make use of the structurally identical but electronically varied nature of Heusler compounds. Here we show the presence of a TSS in epitaxially grown thin films of the half-Heusler compound PtLuSb. Spin- and angle-resolved photoemission spectroscopy, complemented by theoretical calculations, reveals a surface state with linear dispersion and a helical tangential spin texture consistent with previous predictions. This experimental verification of topological behaviour is a significant step forward in establishing half-Heusler compounds as a viable material system for future spintronic devices. PMID:27346655

  20. Nanoscale structural heterogeneity in Ni-rich half-Heusler TiNiSn

    SciTech Connect

    Douglas, Jason E. Pollock, Tresa M.; Chater, Philip A.; Brown, Craig M.; Seshadri, Ram

    2014-10-28

    The structural implications of excess Ni in the TiNiSn half-Heusler compound are examined through a combination of synchrotron x-ray and neutron scattering studies, in conjunction with first principles density functional theory calculations on supercells. Despite the phase diagram suggesting that TiNiSn is a line compound with no solid solution, for small x in TiNi{sub 1+x}Sn there is indeed an appearance—from careful analysis of the scattering—of some solubility, with the excess Ni occupying the interstitial tetrahedral site in the half-Heusler structure. The analysis performed here would point to the excess Ni not being statistically distributed, but rather occurring as coherent nanoclusters. First principles calculations of energetics, carried out using supercells, support a scenario of Ni interstitials clustering, rather than a statistical distribution.

  1. Computational Discovery of a Novel Semiconductor: A Vacancy-Ordered Fe1.5TiSb Heusler Phase

    NASA Astrophysics Data System (ADS)

    Ishwar Hegde, Vinay; Naghibolashrafi, Nariman; Keshavarz, Sahar; Munira, Kamaram; Butler, William; Leclair, Patrick; Wolverton, Chris

    Many full- and half-Heusler phase compounds are half-metallic ferromagnets, and are attractive for spintronic applications due to their relatively high Curie temperatures. However, while it is known that defects such as vacancies (on the X site of an X2YZ Heusler phase) can lead to a loss of half-metallic character, their effect on the stability and order of these compounds has not been adequately explored. To address this shortcoming, we perform a binary cluster expansion (CE) of Fe and vacancies on the Fe sublattice of the FexVac2-xTiSb Heusler compound. From our CE, we computationally predict the stability of a novel semiconductor phase with an interesting new structure type: R 3 m spacegroup with composition Fe1.5TiSb, i.e., between the full- and half-Heusler compositions. By comparing the electronic structure of all the competing structures at x = 1 . 5 , we find that the gap opened in the minority-spin channel due to vacancies strongly correlates with the stability of the structure. We study the effect of vacancies on the structural order in Fe1.5TiSb by generating special quasi-random structures (SQSs) as approximations to the true disordered state, and find that the material undergoes an order-disorder transition at elevated temperatures of ~1450 K.

  2. Sequential fractionation of grape seeds into oils, polyphenols, and procyanidins via a single system employing CO2-based fluids.

    PubMed

    Ashraf-Khorassani, Mehdi; Taylor, Larry Thomas

    2004-05-01

    Pure supercritical CO(2) was used to remove >95% of the oil from the grape seeds. Subcritical CO(2) modified with methanol was used for the extraction of monomeric polyphenols, whereas pure methanol was used for the extraction of polyphenolic dimers/trimers and procyanidins from grape seed. At optimum conditions, 40% methanol-modified CO(2) removed >79% of catechin and epicatechin from the grape seed. This extract was light yellow in color, and no higher molecular weight procyanidins were detected. Extraction of the same sample after removal of the oils and polyphenols, but now under enhanced solvent extraction conditions using methanol as a solvent, provided a dark red solution shown via electrospray ionization HPLC-MS to contain a relatively high concentration of procyanidins. The uniqueness of the study is attested to by the use of CO(2)-based fluids and the employment of a single instrumental extraction system. PMID:15113138

  3. The intrinsic disorder related alloy scattering in ZrNiSn half-Heusler thermoelectric materials

    PubMed Central

    Xie, Hanhui; Wang, Heng; Fu, Chenguang; Liu, Yintu; Snyder, G. Jeffrey; Zhao, Xinbing; Zhu, Tiejun

    2014-01-01

    The intrinsic structural disorder dramatically affects the thermal and electronic transport in semiconductors. Although normally considered an ordered compound, the half-Heusler ZrNiSn displays many transport characteristics of a disordered alloy. Similar to the (Zr,Hf)NiSn based solid solutions, the unsubstituted ZrNiSn compound also exhibits charge transport dominated by alloy scattering, as demonstrated in this work. The unexpected charge transport, even in ZrNiSn which is normally considered fully ordered, can be explained by the Ni partially filling interstitial sites in this half-Heusler system. The influence of the disordering and defects in crystal structure on the electron transport process has also been quantitatively analyzed in ZrNiSn1-xSbx with carrier concentration nH ranging from 5.0×1019 to 2.3×1021 cm−3 by changing Sb dopant content. The optimized carrier concentration nH ≈ 3–4×1020 cm−2 results in ZT ≈ 0.8 at 875K. This work suggests that MNiSn (M = Hf, Zr, Ti) and perhaps most other half-Heusler thermoelectric materials should be considered highly disordered especially when trying to understand the electronic and phonon structure and transport features. PMID:25363573

  4. Thermoelectric properties of half-Heusler topological insulators MPtBi (M = Sc, Y, La) induced by strain

    NASA Astrophysics Data System (ADS)

    Ding, Guangqian; Gao, G. Y.; Yu, Li; Ni, Yun; Yao, KaiLun

    2016-01-01

    Thermoelectric (TE) materials and topological insulators (TIs) were recently known to exhibit close connection, which offers new prospects in improving the TE performance. However, currently known TE materials from TIs mostly belong to the early Bi2Te3 family. In order to extend TE materials to other classes of TIs, we use the first-principles combined with Boltzmann transport theory to study the electronic and TE properties of experimental half-Heusler compounds MPtBi (M = Sc, Y, La). We find that all MPtBi are topological semimetals at equilibrium lattices while TIs under a stretched uniaxial strain, which is in agreement with previous works. We further predict that comparable TE performance with Bi2Te3 can be realized in half-Heusler TI LaPtBi by an 8% stretched uniaxial strain. We also reveal that the lattice thermal conductivity of LaPtBi is unprecedented low compared with those of traditional half-Heusler compounds (not TIs). These findings indicate the potential of half-Heusler TIs as TE materials.

  5. Dynamical Effects of the Martensitic Transition in Magnetocaloric Heusler Alloys from Direct Δ Tad Measurements under Different Magnetic-Field-Sweep Rates

    NASA Astrophysics Data System (ADS)

    Gottschall, T.; Skokov, K. P.; Scheibel, F.; Acet, M.; Zavareh, M. Ghorbani; Skourski, Y.; Wosnitza, J.; Farle, M.; Gutfleisch, O.

    2016-02-01

    Large magnetocaloric effects can be obtained in Ni-Mn-based Heusler alloys due to the magnetostructural transition between martensite and austenite. This phase transformation proceeds via nucleation and growth. By direct measurements of the adiabatic temperature change Δ Tad using different magnetic-field-sweeping rates from 0.01 up to 1500 T s-1 , we study the dynamic behavior of the two Heusler compounds Ni50 Mn35 In15 and Ni45 Mn37 In13 Co5 transforming near room temperature. From these experiments, we conclude that the nucleation process is rather slow in contrast to the relatively fast movement of the phase boundary between martensite and austenite. This is a limiting factor for cooling concepts operating at frequencies beyond 100 Hz. However, the dynamic effects of the transition are negligible in field rates typically used in magnetic refrigeration. These findings are essential considering the suitability of Heusler compounds for energy-efficient solid-state cooling.

  6. Estimates of late middle Eocene pCO2 based on stomatal density of modern and fossil Nageia leaves

    NASA Astrophysics Data System (ADS)

    Liu, X. Y.; Gao, Q.; Han, M.; Jin, J. H.

    2016-02-01

    Atmospheric pCO2 concentrations have been estimated for intervals of the Eocene using various models and proxy information. Here we reconstruct late middle Eocene (42.0-38.5 Ma) pCO2 based on the fossil leaves of Nageia maomingensis Jin et Liu collected from the Maoming Basin, Guangdong Province, China. We first determine relationships between atmospheric pCO2 concentrations, stomatal density (SD) and stomatal index (SI) using "modern" leaves of N. motleyi (Parl.) De Laub, the nearest living species to the Eocene fossils. This work indicates that the SD inversely responds to pCO2, while SI has almost no relationship with pCO2. Eocene pCO2 concentrations can be reconstructed based on a regression approach and the stomatal ratio method by using the SD. The first approach gives a pCO2 of 351.9 ± 6.6 ppmv, whereas the one based on stomatal ratio gives a pCO2 of 537.5 ± 56.5 ppmv. Here, we explored the potential of N. maomingensis in pCO2 reconstruction and obtained different results according to different methods, providing a new insight for the reconstruction of paleoclimate and paleoenvironment in conifers.

  7. Phase separation of full-Heusler nanostructures in half-Heusler thermoelectrics and vibrational properties from first-principles calculations

    NASA Astrophysics Data System (ADS)

    Page, Alexander; Uher, Ctirad; Poudeu, Pierre Ferdinand; Van der Ven, Anton

    2015-11-01

    Previous studies have indicated that the figure of merit (ZT ) of half-Heusler (HH) alloys with composition M NiSn (M =Ti , Zr, or Hf) is greatly enhanced when the alloys contain a nano-scale full-Heusler (FH) MN i2Sn second phase. However, the formation mechanism of the FHnanostructures in the HH matrix and their vibrational properties are still not well understood. We report on first-principles studies of thermodynamic phase equilibria in the MNiSn-MN i2Sn pseudobinary system as well as HH and FH vibrational properties. Thermodynamic phase diagrams as functions of temperature and Ni concentration were developed using density functional theory (DFT) combined with a cluster expansion and Monte Carlo simulations. The phase diagrams show very low excess Ni solubility in HH alloys even at high temperatures, which indicates that any Ni excess will decompose into a two-phase mixture of HH and FH compounds. Vibrational properties of HH and FH alloys are compared. Imaginary vibrational modes in the calculated phonon dispersion diagram of TiN i2Sn indicate a dynamical instability with respect to cubic [001] transverse acoustic modulations. Displacing atoms along unstable vibrational modes in cubic TiN i2Sn reveals lower-energy structures with monoclinic symmetry. The energy of the monoclinic structures is found to depend strongly on the lattice parameter. The origin of the instability in cubic TiN i2Sn and its absence in cubic ZrN i2Sn and HfN i2Sn is attributed to the small size of the Ti 3 d shells compared to those of Zr and Hf atoms. Lattice constants and heat capacities calculated by DFT agree well with experiment.

  8. Observation of a topologically non-trivial surface state in half-Heusler PtLuSb (001) thin films

    NASA Astrophysics Data System (ADS)

    Logan, John; Patel, Sahil; Harrington, Sean; Polley, Craig; Schultz, Brian; Balasubramanian, T.; Janotti, Anderson; Mikkelsen, Anders; Palmstrøm, Chris

    Topological insulators are a recently discovered new quantum state of matter that has a bulk band gap but also possesses cross-gap surface states which are protected by time-reversal symmetry. The experimental realization of topologically non-trivial surface states (TSSs) in materials such as Bi2Se3 has generated widespread interest in identifying other material systems that exhibit TSSs due to their many uses including spintronic devices. In particular, recent theory calculations suggest that TSSs may be found in certain half-Heusler ternary compounds. If experimentally realizable, this would provide an opportunity for the creation of entirely new heterostructure spintronic devices that make use of the structurally-identical but electronically-varied nature of Heusler compounds. Here, we show the presence of a TSS in the half-Heusler compound PtLuSb. Spin and angle-resolved photoemission spectroscopy reveals a surface state with linear dispersion and a helical tangential spin texture consistent with theoretical predictions and the expectation for a topological insulator.

  9. Static and dynamic magnetic properties of cubic Mn-Co-Ga Heusler films

    SciTech Connect

    Demiray, A. S. Iihama, S.; Naganuma, H.; Oogane, M.; Ando, Y.; Kubota, T.; Mizukami, S. Miyazaki, T.

    2014-05-07

    We investigated the static and dynamic magnetic properties of thin films of Mn-Co-Ga Heusler compound. Gilbert damping and exchange stiffness constants of the films were evaluated by using the ferromagnetic resonance technique in the X-band regime (f = 9.4 GHz). By analyzing the experimental spectra, magnetic parameters of the films such as the line width and the Gilbert damping were deduced, and the exchange stiffness constant was estimated from the perpendicular standing spin-wave resonance. The Gilbert damping constant was estimated to be 0.017 in a specific film composition. The exchange stiffness constant showed a linear dependence on the film composition.

  10. A Study of Topological Insulator States of Half-Heusler Materials and the Momentum Density of Overdoped Cuprates

    NASA Astrophysics Data System (ADS)

    Al-Sawai, Wael M.

    We have applied first-principles calculations to investigate the topological insulator state of half-Heusler materials and the momentum density for overdoped cuprates. The specific topics addressed in this thesis are as follows. 1. Topological insulators are materials exhibiting a novel quantum state of matter; these insulators are characterized by a bulk excitation generated by the spin orbit interaction, and protected conducting states on their edge or surface. In this work we investigate in detail the electronic structure of a series of ternary half-Heusler compounds MM'X of MgAgAS-type with M = (Lu, La, Sc, Y) and M'X=(PtBi,AuPb,PdBi,PtSb,AuSn,NiBi,PdSb). The characteristic features of all half-Heusler compounds considered here are topological nontrivial semimetal, or nontrivial metal, or trivial insulator. The analysis of the relation among the band inversion strength (distance from the critical line), atomic number of constituents, and lattice constant could provide a methodology (a rule of thumb) to predict the topological order of hypothetical nonmagnetic half-Heusler compound more generally. 2. The bulk Fermi surface (FS) is observed in an overdoped ( x=0.3) single crystal of La2-xSrxCuO4 by using Compton scattering. A 2-D momentum density reconstruction from measured Compton profiles yields a clear FS signature in the third Brillouin zone along [100]. The quantitative agreement between density functional theory calculations and momentum density experiment suggests that Fermi-liquid physics is restored in the overdoped regime. The FS shows signs of a change topological of the FS found at lower doping. We find similar quantitative agreement between the measured 2D angular correlation of positron annihilation radiation (2D-ACAR) spectra and DFT simulations. However, 2D-ACAR does not give such a clear signature of the FS in the extended momentum space in either theory or experiment.

  11. A preliminary evaluation of an O2/CO2 based eddy covariance theory at Missouri AmeriFlux site

    NASA Astrophysics Data System (ADS)

    Yan, B.; Gu, L.

    2013-12-01

    The eddy covariance (EC) technique has been widely used at flux sites on every continent, across most ecosystem types and climates to monitor exchanges of momentum, mass and energy between land surface and atmosphere. In an attempt to develop a self-consistent theory for the EC technique, Gu et al. (2012) reformulated the fundamental equations for EC by introducing the concept of constraining gas that has no net ecosystem sink/source. Gu (2013) expanded the theory of Gu et al. (2012) to include paired gases whose ecosystem exchange ratios are stable over an averaging period (e.g. 30 min) and therefore can be used to constrain EC flux measurements of any gases. He proposed that O2 and CO2 are an ideal pair of gases as their biological processes are coupled and their ecosystem exchange ratio (also known as oxidative ratio) is close to 1. Advantages of this new O2/CO2 based EC theory include: 1) avoidance of covariance loss in calculating dry air density induced by spatial separation of measuring instruments and use of multiple indirectly derived variables, 2) the minimum number of assumptions adopted for the derivation of the equation, and 3) avoidance of errors related to linearization of ideal gas law. In this study, we conducted a preliminary evaluation for the basic principle of Gu (2013) EC theory. We crosschecked net ecosystem exchange (NEE) estimations from different, independent methods by using CO2 and H2O as paired constraining gases. Using CO2 and H2O instead of CO2 and O2 as paired constraining gases is not ideal in the framework of Gu (2013); however, no fast response O2 analyzer is currently available. CO2 and H2O are both transported between the inside of plants and canopy air through stomata on leaves in the processes of photosynthesis and transpiration which are known to be closely coupled. However, this close coupling is contaminated by other ecosystem sinks/sources, e.g. respiration of plants and soil for CO2 and evaporation of intercepted and soil

  12. Optimization of the thermoelectric properties of FeNbSb-based half-Heusler materials

    NASA Astrophysics Data System (ADS)

    Li, Wenfeng; Yang, Gui; Zhang, Jianwei

    2016-05-01

    FeNbSb-based half-Heusler compounds have recently been reported as promising materials for good high-temperature thermoelectric materials with a ZT  >  1. Their electronic structure and thermoelectric properties are investigated based on a first-principles simulation and the semi-classical Boltzmann transport theory. The band structures show not only light and heavy bands but also high band degeneracy near the valence band maximum, which is beneficial for thermoelectric performance. The calculated Seebeck coefficients of p-type FeNbSb at high carrier concentrations exhibit the expected high values, which is consistent with experimental data. The evolution of the electrical conductivity and power factor with carrier concentration at different temperatures is investigated. Our results show that the thermoelectric performance of p-type FeNbSb can be improved by appropriate substitution; for example, by doping Hf on the Nb site, the maximum ZT of the p-type FeNb1‑x Hf x Sb can reach ~1.5 at 1200 K. This study can provide some theoretical guidance for experimental research to improve the thermoelectric performance of FeNbSb-based half-Heusler compounds.

  13. Unconventional superconductivity in half-Heusler semimetals

    NASA Astrophysics Data System (ADS)

    Brydon, Philip; Wang, Limin; Weinert, Michael; Agterberg, Daniel

    We consider the superconductivity of the topological half-Heusler semimetals YPtBi and LuPtBi, where pairing occurs between j = 3 / 2 quasiparticles. This permits Cooper pairs with quintet or septet total angular momentum, in addition to singlet and triplet states. Purely on-site interactions can generate unconventional (quintet) time-reversal symmetry-breaking states with topologically nontrivial point or line nodes. Furthermore, due to the broken inversion symmetry in these materials, the usual s-wave singlet state can mix with a p-wave septet state, also with topologically stable line-nodes. We acknowledge support from Microsoft Station Q, LPS-CMTC, and JQI-NSF-PFC (P.M.R.B), J. Paglione and the U.S. Department of Energy Early Career Award DE-SC-0010605 (L.W.), and the NSF via DMREF-1335215 (D.F.A. and M.W.).

  14. Investigation of attractive and repulsive interactions associated with ketones in supercritical CO2, based on Raman spectroscopy and theoretical calculations

    NASA Astrophysics Data System (ADS)

    Kajiya, Daisuke; Saitow, Ken-ichi

    2013-08-01

    Carbonyl compounds are solutes that are highly soluble in supercritical CO2 (scCO2). Their solubility governs the efficiency of chemical reactions, and is significantly increased by changing a chromophore. To effectively use scCO2 as solvent, it is crucial to understand the high solubility of carbonyl compounds, the solvation structure, and the solute-solvent intermolecular interactions. We report Raman spectroscopic data, for three prototypical ketones dissolved in scCO2, and four theoretical analyses. The vibrational Raman spectra of the C=O stretching modes of ketones (acetone, acetophenone, and benzophenone) were measured in scCO2 along the reduced temperature Tr = T/Tc = 1.02 isotherm as a function of the reduced density ρr = ρ/ρc in the range 0.05-1.5. The peak frequencies of the C=O stretching modes shifted toward lower energies as the fluid density increased. The density dependence was analyzed by using perturbed hard-sphere theory, and the shift was decomposed into attractive and repulsive energy components. The attractive energy between the ketones and CO2 was up to nine times higher than the repulsive energy, and its magnitude increased in the following order: acetone < acetophenone < benzophenone. The Mulliken charges of the three solutes and CO2 molecules obtained by using quantum chemistry calculations described the order of the magnitude of the attractive energy and optimized the relative configuration between each solute and CO2. According to theoretical calculations for the dispersion energy, the dipole-induced-dipole interaction energy, and the frequency shift due to their interactions, the experimentally determined attractive energy differences in the three solutes were attributed to the dispersion energies that depended on a chromophore attached to the carbonyl groups. It was found that the major intermolecular interaction with the attractive shift varied from dipole-induced dipole to dispersion depending on the chromophore in the ketones in

  15. Thermoelectric Modules Based on Half-Heusler Materials Produced in Large Quantities

    NASA Astrophysics Data System (ADS)

    Bartholomé, Kilian; Balke, Benjamin; Zuckermann, Daniel; Köhne, Martin; Müller, Michael; Tarantik, Karina; König, Jan

    2014-06-01

    Half-Heusler (HH) compounds are some of the most promising candidates among the medium-temperature thermoelectric materials being investigated for automotive and industrial waste heat recovery applications. For n- as well as p-type material, peak ZT values larger than one have been published recently, and first modules have been built. The next step to facilitate the industrialization of thermoelectric module production is upscaling of material synthesis. In this paper, the latest results of the thermoelectric properties of HH compounds produced in kg batches are presented and compared with values published in the literature. The performance of modules built from these materials is analyzed with respect to power output and long-term stability of the material and electrical contacts.

  16. Phase stability of chromium based compensated ferrimagnets with inverse Heusler structure

    NASA Astrophysics Data System (ADS)

    Meinert, Markus; Geisler, Manuel P.

    2013-09-01

    Chromium based inverse Heusler compounds of the type Cr2YZ (Y=Co, Fe; Z=Al, Ga, In, Si, Ge, Sn) have been proposed as fully compensated half-metallic ferrimagnets. Such materials are of large interest for spintronics because they combine small magnetic moment with high spin polarization over a wide temperature range. We assess their thermodynamic stability by their formation enthalpies obtained from density functional theory calculations. All compounds under investigation are unstable. Cr2FeSi and Cr2CoAl are stable with respect to the elemental constituents, but decompose into binary phases. Cr2FeGe, Cr2CoGa, Cr2FeSn and Cr2CoIn are found to be unstable with respect to their elemental constituents. We identify possible binary decompositions.

  17. Design of compensated ferrimagnetic Heusler alloys for giant tunable exchange bias

    NASA Astrophysics Data System (ADS)

    Nayak, Ajaya K.; Nicklas, Michael; Chadov, Stanislav; Khuntia, Panchanana; Shekhar, Chandra; Kalache, Adel; Baenitz, Michael; Skourski, Yurii; Guduru, Veerendra K.; Puri, Alessandro; Zeitler, Uli; Coey, J. M. D.; Felser, Claudia

    2015-07-01

    Rational material design can accelerate the discovery of materials with improved functionalities. This approach can be implemented in Heusler compounds with tunable magnetic sublattices to demonstrate unprecedented magnetic properties. Here, we have designed a family of Heusler alloys with a compensated ferrimagnetic state. In the vicinity of the compensation composition in Mn-Pt-Ga, a giant exchange bias (EB) of more than 3 T and a large coercivity are established. The large exchange anisotropy originates from the exchange interaction between the compensated host and ferrimagnetic clusters that arise from intrinsic anti-site disorder. Our design approach is also demonstrated on a second material with a magnetic transition above room temperature, Mn-Fe-Ga, exemplifying the universality of the concept and the feasibility of room-temperature applications. These findings may lead to the development of magneto-electronic devices and rare-earth-free exchange-biased hard magnets, where the second quadrant magnetization can be stabilized by the exchange bias.

  18. Study of angle dependent magnetoresistance in half-Heusler YPtBi

    NASA Astrophysics Data System (ADS)

    Kim, Hyunsoo; Wang, Kefeng; Hodovanets, Halyna; Paglione, Johnpierre

    Semimetallic half-Heusler compounds (RTBi, R = rare earth, T = Pd, Pt) have been attracting much attention because multiple theoretical calculations predicted the topologically non-trivial band structure. However, the detail band structure near the Γ point depends on the specific calculation methods, and also the band structure inferred from experimental results show discrepancy from the theoretical one. Particularly in RPtBi (R=Y, Lu, Dy, Gd), the surface metallic states, which is absent in most of the theoretical results, were evident by recent ARPES measurements, but there has not been any detailed study on the metallic surface states. Moreover, the observation of topological nodal superconductivity in YPtBi makes the knowledge of Fermiology crucial to understand the pairing mechanism in the half-Heusler superconductors. Here, we present experimental results on angular dependence of magnetoresistance at various temperatures in single crystals of YPtBi. Based on observation of the angular dependence of Shubnikov-de Haas quantum oscillations, we discuss possible topologies of the bulk as well as the surface Fermi surfaces.

  19. Efficient Spin Injector Scheme Based on Heusler Materials

    NASA Astrophysics Data System (ADS)

    Chadov, Stanislav; Graf, Tanja; Chadova, Kristina; Dai, Xuefang; Casper, Frederick; Fecher, Gerhard H.; Felser, Claudia

    2011-07-01

    We present a rational design scheme intended to provide stable high spin polarization at the interfaces of the magnetoresistive junctions by fulfilling the criteria of structural and chemical compatibilities at the interface. This can be realized by joining the semiconducting and half-metallic Heusler materials with similar structures. The present first-principles calculations verify that the interface remains half-metallic if the nearest interface layers effectively form a stable Heusler material with the properties intermediately between the surrounding bulk parts. This leads to a simple rule for selecting the proper combinations.

  20. NiSn Half-Heusler Alloy

    NASA Astrophysics Data System (ADS)

    Appel, O.; Gelbstein, Y.

    2014-06-01

    We deal here with Sb and Bi doping effects of the n-type half-Heusler (HH) Ti0.3Zr0.35Hf0.35NiSn alloy on the measured thermoelectric properties. To date, the thermoelectric effects upon Bi doping on the Sn site of HH alloys have rarely been reported, while Sb has been widely used as a donor dopant. A comparison between the measured transport properties following arc melting and spark plasma sintering of both Bi- and Sb-doped samples indicates a much stronger doping effect upon Sb doping, an effect which was explained thermodynamically. Due to similar lattice thermal conductivity values obtained for the various doped samples, synthesized in a similar experimental route, no practical variations in the thermoelectric figure of merit values were observed between the various investigated samples, an effect which was attributed to compensation between the power factor and electrical thermal conductivity values regardless of the various investigated dopants and doping levels.

  1. Achieving perpendicular anisotropy in half-metallic Heusler alloys for spin device applications

    SciTech Connect

    Munira, Kamaram; Romero, Jonathon; Butler, William H.

    2014-05-07

    Various full Heusler alloys are interfaced with MgO and the magnetic properties of the Heusler-MgO junctions are studied. Next to MgO, the cubic Heusler system distorts to a tetragonal one, thereby inducing an anisotropy. The half-metallicity and nature of anisotropy (in-plane or perpendicular) in the Heusler-MgO system is governed mostly by the interface Heusler layers. There is a trend that Mn-O bonding near the MgO-Heusler junction results in perpendicular anisotropy. The ability to remain half-metallic and have perpendicular anisotropy makes some of these alloys potential candidates as free-layers in Spin Transfer Torque Random Access Memory (STT-RAM) devices, particularly, Cr{sub 2}MnAs-MgO system with MnAs interface layers and Co{sub 2}MnSi-MgO system with Mn{sub 2} interface layers.

  2. Quasiparticle band structure of the almost-gapless transition-metal-based Heusler semiconductors

    NASA Astrophysics Data System (ADS)

    Tas, M.; Şaşıoǧlu, E.; Galanakis, I.; Friedrich, C.; Blügel, S.

    2016-05-01

    Transition-metal-based Heusler semiconductors are promising materials for a variety of applications ranging from spintronics to thermoelectricity. Employing the G W approximation within the framework of the FLAPW method, we study the quasiparticle band structure of a number of such compounds being almost gapless semiconductors. We find that in contrast to the s p -electron based semiconductors such as Si and GaAs, in these systems, the many-body corrections have a minimal effect on the electronic band structure and the energy band gap increases by less than 0.2 eV, which makes the starting point density functional theory (DFT) a good approximation for the description of electronic and optical properties of these materials. Furthermore, the band gap can be tuned either by the variation of the lattice parameter or by the substitution of the s p -chemical element.

  3. Modeling and Analyzing Magnetocaloric Effect in Heusler Alloys

    NASA Astrophysics Data System (ADS)

    Ovichi, Maryam

    Modeling and Analyzing Magneto-caloric Effect in Heusler Alloys Heusler alloys feature both conventional and inverse magnetocaloric effects (MCE) near room temperature as they undergo two different transitions. In order to properly characterize these alloys, the mechanism of the transformations that accompanies the MCE peaks must be understood. These alloys have interesting magnetic behavior that can be modeled and predicted. Modeling the cluster compositions in the mixed-state regions, where two stable magnetic states co-exist, provides a perspective for enhancing the MCE effect through chemical substitution or similar process. By using a reliable mechanism for evaluating the magnetic characteristics, the material's behavior can be characterized based on the results of testing in relatively few applied fields, significantly reducing testing effort required when characterizing materials. Also by applying a few critical points in testing, the most accurate testing results can be achieved. In order to better utilize these magnetic materials, material composition must be improved to provide desired behavior with respect to magnetocaloric effect. By understanding the elemental contribution, the sample can be better tuned in composition to gain the desired behavior. Tuning behavior will result in a more useful composition and serve to further the overall research. This dissertation will contribute to the study of Heusler alloys for usage in magnetic refrigeration in the following areas. First, it will improve the self-similarity method for analyzing and evaluating the test data. By improving the method for analysis, it will also lead to a simplified testing process. Second, it will use the new analysis to understand the elemental contribution of specific elements added to Heusler alloys. Finally, it will increase the overall understanding of the magnetocaloric behavior of Heusler alloys.

  4. Large low-field positive magnetoresistance in nonmagnetic half-Heusler ScPtBi single crystal

    NASA Astrophysics Data System (ADS)

    Hou, Zhipeng; Wang, Yue; Liu, Enke; Zhang, Hongwei; Wang, Wenhong; Wu, Guangheng

    2015-11-01

    High-quality nonmagnetic half-Heusler ScPtBi single crystals were synthesized by a Bi self-flux method. This compound was revealed to be a hole-dominated semimetal with a large low-field magnetoresistance up to 240% at 2 K in a magnetic field of 1 T. Magneto-transport measurements demonstrated that the large low-field magnetoresistance effect resulted from the coexistence of field-induced metal-semiconductor transition and weak-antilocalization effect. Moreover, Hall measurements indicated that ScPtBi single crystal showed a high mobility over a wide temperature region even up to room temperature (4050 cm2V-1s-1 at 2 K-2016 cm2V-1s-1 at 300 K). These findings not only suggest the nonmagnetic ScPtBi semimetal a potential material candidate for applications in high-sensitivity magnetic sensors but also are of great significance to comprehensively understand the rare-earth based half-Heusler compounds.

  5. Structural, electronic and magnetic properties of Fe2-based full Heusler alloys: A first principle study

    NASA Astrophysics Data System (ADS)

    Dahmane, F.; Mogulkoc, Y.; Doumi, B.; Tadjer, A.; Khenata, R.; Bin Omran, S.; Rai, D. P.; Murtaza, G.; Varshney, Dinesh

    2016-06-01

    Using the first-principles density functional calculations, the structural, electronic and magnetic properties of the Fe2XAl (X=Cr, Mn, Ni) compounds in both the Hg2CuTi and Cu2MnAl-type structures were studied by the full-potential linearized augmented plane waves (FP-LAPW) method. The exchange and correlation potential is treated by the generalized-gradient approximation (GGA) where the results show that the Cu2MnAl-type structure is energetically more stable than the Hg2CuTi-type structure for the Fe2CrAl and Fe2MnAl compounds at the equilibrium volume. The full Heusler compounds Fe2XAl (X=Cr, Mn) are half-metallic in the Cu2MnAl-type structure. Fe2NiAl has a metallic character in both CuHg2Ti and AlCu2Mn-type structures. The total magnetic moments of the Fe2CrAl and Fe2MnAl compounds are 1.0 and 2.0 μB, respectively, which are in agreement with the Slater-Pauling rule Mtot=Ztot- 24.

  6. Role of structural defects on the half-metallic character of Heusler alloys and their junctions with Ge and GaAs

    NASA Astrophysics Data System (ADS)

    Picozzi, Silvia; Continenza, Alessandra; Freeman, Arthur J.

    2003-03-01

    Heusler-alloys, such as Co_2MnGe and Co_2MnSi, have been predicted from first-principles calculations to be half-metallic and have recently attracted great attention for spin-injection purposes. However, spin polarizations of only 50%-60% were experimentally obtained for Heusler thin films(M.P.Raphael et al.), Phys. Rev. B 66, 104429 (2002); B.Ravel et al., Appl. Phys. Lett. 81, 2812 (2002) - a decrease attributed to defects in the Mn and Co sublattices. We performed ab-initio FLAPW(E.Wimmer, H.Krakauer, M.Weinert, A.J.Freeman, Phys. Rev. B 24, 864 (1981)) calculations in order to determine the effects of several types of defects (Co and Mn antisites, vacancies, etc.) on the electronic and magnetic properties of the bulk Heusler compounds and their interfaces with Ge and GaAs. We analyze the results in terms of spatial and energy behavior of the defect- and interface-induced states. Our findings show that Co-antisites have low formation energies and locally destroy half-metallicity; the defect states are spatially localized and are screened out in a couple of atomic shells.

  7. Substitution effect on magnetic and electrical properties of half-Heusler alloy Ni{sub 1−x}Co{sub x}Mn{sub 1−y}Fe{sub y}Sb

    SciTech Connect

    Kushwaha, Varun Sharma, Himanshu Dixit, Dinesh Tomy, C. V.; Tulapurkar, Ashwin

    2014-04-24

    We have studied the effects of Co and Fe doping on the magnetic and electrical properties of half-Heusler compound NiMnSb. The alloys were prepared by arc-melting method in the presence of Argon gas. The powder X-ray diffraction of the each alloy was performed in air at room temperature. The magnetic and electrical properties were performed in the temperature range 2–400 K and in magnetic field up to 1 T.

  8. First-principles calculations of exchange interactions, spin waves, and temperature dependence of magnetization in inverse-Heusler-based spin gapless semiconductors

    NASA Astrophysics Data System (ADS)

    Jakobsson, A.; Mavropoulos, P.; Şaşıoǧlu, E.; Blügel, S.; Ležaić, M.; Sanyal, B.; Galanakis, I.

    2015-05-01

    Employing first-principles electronic-structure calculations in conjunction with the frozen-magnon method, we calculate exchange interactions, spin-wave dispersion, and spin-wave stiffness constants in inverse-Heusler-based spin gapless semiconductor (SGS) compounds Mn2CoAl , Ti2MnAl , Cr2ZnSi , Ti2CoSi , and Ti2VAs . We find that their magnetic behavior is similar to the half-metallic ferromagnetic full-Heusler alloys, i.e., the intersublattice exchange interactions play an essential role in the formation of the magnetic ground state and in determining the Curie temperature Tc. All compounds, except Ti2CoSi , possess a ferrimagnetic ground state. Due to the finite energy gap in one spin channel, the exchange interactions decay sharply with the distance, and hence magnetism of these SGSs can be described considering only nearest- and next-nearest-neighbor exchange interactions. The calculated spin-wave dispersion curves are typical for ferrimagnets and ferromagnets. The spin-wave stiffness constants turn out to be larger than those of the elementary 3 d ferromagnets. Calculated exchange parameters are used as input to determine the temperature dependence of the magnetization and Tc of the SGSs. We find that the Tc of all compounds is much above the room temperature. The calculated magnetization curve for Mn2CoAl as well as the Curie temperature are in very good agreement with available experimental data. This study is expected to pave the way for a deeper understanding of the magnetic properties of the inverse-Heusler-based SGSs and enhance the interest in these materials for application in spintronic and magnetoelectronic devices.

  9. Equiatomic quaternary Heusler alloys: A material perspective for spintronic applications

    NASA Astrophysics Data System (ADS)

    Bainsla, Lakhan; Suresh, K. G.

    2016-09-01

    Half-metallic ferromagnetic (HMF) materials show high spin polarization and are therefore interesting to researchers due to their possible applications in spintronic devices. In these materials, while one spin sub band has a finite density of states at the Fermi level, the other sub band has a gap. Because of their high Curie temperature (TC) and tunable electronic structure, HMF Heusler alloys have a special importance among the HMF materials. Full Heusler alloys with the stoichiometric composition X2YZ (where X and Y are the transition metals and Z is a sp element) have the cubic L21 structure with four interpenetrating fcc sublattices. When each of these four fcc sublattices is occupied by different atoms (XX'YZ), a quaternary Heusler structure with different structural symmetries (space group F-43m, #216) is obtained. Recently, these equiatomic quaternary Heusler alloys (EQHAs) with 1:1:1:1 stoichiometry have attracted a lot of attention due to their superior magnetic and transport properties. A special class of HMF materials identified recently is known as spin gapless semiconductors (SGS). The difference in this case, compared with HMFs, is that the density of states for one spin band is just zero at the Fermi level, while the other has a gap as in the case of HMFs. Some of the reported SGS materials belong to EQHAs family. This review is dedicated to almost all reported materials belonging to EQHAs family. The electronic structure and hence the physical properties of Heusler alloys strongly depend on the degree of structural order and distribution of the atoms in the crystal lattice. A variety of experimental techniques has been used to probe the structural parameters and degree of order in these alloys. Their magnetic properties have been investigated using the conventional methods, while the spin polarization has been probed by point contact Andreev reflection technique. The experimentally obtained values of saturation magnetization are found to be in

  10. Perpendicular Magnetic Anisotropy in Co-Based Full Heusler Alloy Thin Films

    NASA Astrophysics Data System (ADS)

    Wu, Y.; Xu, X. G.; Miao, J.; Jiang, Y.

    2015-12-01

    Half-metallic Co-based full Heusler alloys have been qualified as promising functional materials in spintronic devices due to their high spin polarization. The lack of perpendicular magnetic anisotropy (PMA) is one of the biggest obstacles restricting their application in next generation ultrahigh density storage such as magnetic random access memory (MARM). How to induce the PMA in Co-based full Heusler alloy thin films has attracted much research interest of scientists. This paper presents an overview of recent progress in this research area. We hope that this paper would provide some guidance and ideas to develop highly spin-polarized Co-based Heusler alloy thin films with PMA.

  11. Large Noncollinearity and Spin Reorientation in the Novel Mn2RhSn Heusler Magnet

    NASA Astrophysics Data System (ADS)

    Meshcheriakova, O.; Chadov, S.; Nayak, A. K.; Rößler, U. K.; Kübler, J.; André, G.; Tsirlin, A. A.; Kiss, J.; Hausdorf, S.; Kalache, A.; Schnelle, W.; Nicklas, M.; Felser, C.

    2014-08-01

    Noncollinear magnets provide essential ingredients for the next generation memory technology. It is a new prospect for the Heusler materials, already well known due to the diverse range of other fundamental characteristics. Here, we present a combined experimental and theoretical study of novel noncollinear tetragonal Mn2RhSn Heusler material exhibiting unusually strong canting of its magnetic sublattices. It undergoes a spin-reorientation transition, induced by a temperature change and suppressed by an external magnetic field. Because of the presence of Dzyaloshinskii-Moriya exchange and magnetic anisotropy, Mn2RhSn is suggested to be a promising candidate for realizing the Skyrmion state in the Heusler family.

  12. Stabilizing and increasing the magnetic moment of half-metals: The role of Li in half-Heusler LiMn Z (Z =N,P,Si)

    NASA Astrophysics Data System (ADS)

    Damewood, L.; Busemeyer, B.; Shaughnessy, M.; Fong, C. Y.; Yang, L. H.; Felser, C.

    2015-02-01

    Due to their similarities to metastable zinc-blende half-metals, we systematically examined the half-Heusler compounds β -LiMnZ (Z =N,P and Si) for their electronic, magnetic, and stability properties at optimized lattice constants and strained lattice constants that exhibit half-metallic properties. We also report the other phases of the half-Heusler structure (α and γ phases), but they are unlikely to be grown. The magnetic moments of these stable Li-based compounds are expected to reach as high as 4 μB per unit cell when Z =Si and 5 μB per unit cell when Z =N and P; however, the antiferromagnetic spin configuration is energetically favored when Z is a pnictogen. β -LiMnSi at a lattice constant 14% larger than its equilibrium lattice constant is a promising half-metal due to its large magnetic moment, large gap, and vibrational stability. The modified Slater-Pauling rule for these compounds is determined. Finally, we investigated a plausible method for developing half-metallic Li xMn Z at equilibrium by tuning x , but this type of alloying introduces local structural changes that preclude half-metallicity.

  13. Realization of multifunctional shape-memory ferromagnets in all-d-metal Heusler phases

    SciTech Connect

    Wei, Z. Y.; Liu, E. K. Chen, J. H.; Xi, X. K.; Zhang, H. W.; Wang, W. H.; Wu, G. H.; Li, Y.; Liu, G. D.; Luo, H. Z.

    2015-07-13

    Heusler ferromagnetic shape-memory alloys (FSMAs) normally consist of transition-group d-metals and main-group p-elements. Here, we report the realization of FSMAs in Heusler phases that completely consist of d metals. By introducing the d-metal Ti into NiMn alloys, cubic B2-type Heusler phase is obtained and the martensitic transformation temperature is decreased efficiently. Strong ferromagnetism is established by further doping Co atoms into the B2-type antiferromagnetic Ni-Mn-Ti austenite. Based on the magnetic-field-induced martensitic transformations, collective multifunctional properties are observed in Ni(Co)-Mn-Ti alloys. The d metals not only facilitate the formation of B2-type Heusler phases but also establish strong ferromagnetic coupling and offer the possibility to tune the martensitic transformation.

  14. Effect of disorder on electronic and magnetic properties of Co{sub 2}VGa Heusler alloy

    SciTech Connect

    Seema, K.; Kumar, Ranjan

    2015-08-28

    This paper presents the effect of disorder on electronic, magnetic and half-metallic properties of Co{sub 2}VGa Heusler alloy using density functional theory. Binary mixing is the most common form of atomic disorder in these compounds. We have considered three types of disorders: DO{sub 3}, A2 and B2 disorder which corresponds to X-Y, X-Z and Y-Z mixing respectively. After structural optimization, we found that A2 disorder has high formation energy and is most unlikely to occur. The half-metallic nature of the alloy is destroyed in presence of DO{sub 3} and A2 disorder. The destruction of half-metallicity is due to reconstruction of energy states. Also the loss of half-metallicity is accompanied by reversal of spin-polarization at the Fermi level. B2 disorder retains the half-metallic nature of the alloy but spin-polarization value is reduced as compared to the ordered alloy.

  15. Composition induced metal-insulator quantum phase transition in the Heusler type Fe2VAl.

    PubMed

    Naka, Takashi; Nikitin, Artem M; Pan, Yu; de Visser, Anne; Nakane, Takayuki; Ishikawa, Fumihiro; Yamada, Yuh; Imai, Motoharu; Matsushita, Akiyuki

    2016-07-20

    We report the magnetism and transport properties of the Heusler compound Fe2+x V1-x Al at  -0.10  ⩽  x  ⩽  0.20 under pressure and a magnetic field. A metal-insulator quantum phase transition occurred at x  ≈  -0.05. Application of pressure or a magnetic field facilitated the emergence of finite zero-temperature conductivity σ 0 around the critical point, which scaled approximately according to the power law (P  -  P c ) (γ) . At x  ⩽  -0.05, a localized paramagnetic spin appeared, whereas above the ferromagnetic quantum critical point at x  ≈  0.05, itinerant ferromagnetism was established. At the quantum critical points at x  =  -0.05 and 0.05, the resistivity and specific heat exhibited singularities characteristic of a Griffiths phase appearing as an inhomogeneous electronic state. PMID:27218143

  16. Composition induced metal–insulator quantum phase transition in the Heusler type Fe2VAl

    NASA Astrophysics Data System (ADS)

    Naka, Takashi; Nikitin, Artem M.; Pan, Yu; de Visser, Anne; Nakane, Takayuki; Ishikawa, Fumihiro; Yamada, Yuh; Imai, Motoharu; Matsushita, Akiyuki

    2016-07-01

    We report the magnetism and transport properties of the Heusler compound Fe2+x V1‑x Al at  ‑0.10  ⩽  x  ⩽  0.20 under pressure and a magnetic field. A metal–insulator quantum phase transition occurred at x  ≈  ‑0.05. Application of pressure or a magnetic field facilitated the emergence of finite zero-temperature conductivity σ 0 around the critical point, which scaled approximately according to the power law (P  ‑  P c ) γ . At x  ⩽  ‑0.05, a localized paramagnetic spin appeared, whereas above the ferromagnetic quantum critical point at x  ≈  0.05, itinerant ferromagnetism was established. At the quantum critical points at x  =  ‑0.05 and 0.05, the resistivity and specific heat exhibited singularities characteristic of a Griffiths phase appearing as an inhomogeneous electronic state.

  17. Topological RPdBi half-Heusler semimetals: A new family of noncentrosymmetric magnetic superconductors

    PubMed Central

    Nakajima, Yasuyuki; Hu, Rongwei; Kirshenbaum, Kevin; Hughes, Alex; Syers, Paul; Wang, Xiangfeng; Wang, Kefeng; Wang, Renxiong; Saha, Shanta R.; Pratt, Daniel; Lynn, Jeffrey W.; Paglione, Johnpierre

    2015-01-01

    We report superconductivity and magnetism in a new family of topological semimetals, the ternary half-Heusler compound RPdBi (R: rare earth). In this series, tuning of the rare earth f-electron component allows for simultaneous control of both lattice density via lanthanide contraction and the strength of magnetic interaction via de Gennes scaling, allowing for a unique tuning of the normal-state band inversion strength, superconducting pairing, and magnetically ordered ground states. Antiferromagnetism with ordering vector (½,½,½) occurs below a Néel temperature that scales with de Gennes factor dG, whereas a superconducting transition is simultaneously supressed with increasing dG. With superconductivity appearing in a system with noncentrosymmetric crystallographic symmetry, the possibility of spin-triplet Cooper pairing with nontrivial topology analogous to that predicted for the normal-state electronic structure provides a unique and rich opportunity to realize both predicted and new exotic excitations in topological materials. PMID:26601201

  18. Transport signature of spin gapless semiconducting properties in quaternary Heusler of CoFeCrAl

    NASA Astrophysics Data System (ADS)

    Xu, Guizhou; Zhang, Xiaoming; Liu, Enke; Wang, Wenhong; Wu, Guangheng; Institute of physics Team

    2015-03-01

    Spin gapless semiconductors (SGS), since proposed by Wang in 2008, have attracted intensive attention due to its potential application in spintronics. In our previous works, we have predicted some quaternary Heusler alloys are promising to be candidates of SGS. In this presentation, we will report the transport signature of SGS properties for CoFeCrAl, one of SGS candidate. The results show that samples treated in different ways can present distinguished transport properties. On the one hand, the arc-melted bulk samples exhibit a negative temperature dependence of resistivity accompanying with a negative magnetoresistance from 5-300K, revealing a normal transport behavior signifying for a metallic magnetic system. On the other hand, for the melt-spun ribbon samples, a positive temperature dependence of the resistivity as well as positive sign of magnetoresistance were observed, which implies that a semiconducting-like transport mechanism dominate in this sample. Based on our first principles analysis, this difference can be attributed to the occurrence of anti-site occupation between Co/Cr atoms in the compound. Our findings raised the possibility to tune the properties of SGS through proper sample treatments due to its atomic-occupation sensitivity.

  19. Half-metallic properties of the new Ti2YPb(Y = Co, Fe) Heusler alloys

    NASA Astrophysics Data System (ADS)

    Hussain, Moaid K.; Gao, G. Y.; Yao, Kai-Lun

    2015-09-01

    The half-metallic properties of Ti2YPb(Y = Co, Fe) Heusler alloys with a CuHg2Ti-type structure were examined within the frame of the density functional theory and the Perdew-Burke-Ernzerh of generalized gradient approximation (GGA). Analysis of the electronic band structures and density of states for Ti2YPb(Y = Co, Fe) revealed that the spin-up bands are metallic, whereas the spin-down bands exhibit gaps of 0.73 and 0.70 eV, respectively. The magnetic moments calculated for the Ti2YPb(Y = Co, Fe) alloys were found to be equal to 3 μB/f.u. and 2 μB/f.u., values which both follows the Slater-Pauling rule of Mt = Zt - 18. The compounds’ negative enthalpy values should encourage their experimental realization in the future. The bandgap was elucidated to be mainly determined by the bonding and antibonding states created from the hybridizations of the d states between the Ti(1)-Ti(2) coupling and the Y = Co, Fe atom. The half-metallic properties of the Ti2YPb(Y = Co, Fe) compounds were found to be insensitive to lattice distortion, with full spin polarization achievable within a large range of lattice parameter values, making the alloys suitable for use in practical applications.

  20. Magnetism and electronic structure of CoFeCrX (X = Si, Ge) Heusler alloys

    NASA Astrophysics Data System (ADS)

    Jin, Y.; Kharel, P.; Lukashev, P.; Valloppilly, S.; Staten, B.; Herran, J.; Tutic, I.; Mitrakumar, M.; Bhusal, B.; O'Connell, A.; Yang, K.; Huh, Y.; Skomski, R.; Sellmyer, D. J.

    2016-08-01

    The structural, electronic, and magnetic properties of CoFeCrX (X = Si, Ge) Heusler alloys have been investigated. Experimentally, the alloys were synthesized in the cubic L21 structure with small disorder. The cubic phase of CoFeCrSi was found to be highly stable against heat treatment, but CoFeCrGe disintegrated into other new compounds when the temperature reached 402 °C (675 K). Although the first-principle calculation predicted the possibility of tetragonal phase in CoFeCrGe, the tetragonal phase could not be stabilized experimentally. Both CoFeCrSi and CoFeCrGe compounds showed ferrimagnetic spin order at room temperature and have Curie temperatures (TC) significantly above room temperature. The measured TC for CoFeCrSi is 790 K but that of CoFeCrGe could not be measured due to its dissociation into new compounds at 675 K. The saturation magnetizations of CoFeCrSi and CoFeCrGe are 2.82 μB/f.u. and 2.78 μB/f.u., respectively, which are close to the theoretically predicted value of 3 μB/f.u. for their half-metallic phases. The calculated band gaps for CoFeCrSi and CoFeCrGe are, respectively, 1 eV and 0.5 eV. These materials have potential for spintronic device applications, as they exhibit half-metallic electronic structures with large band gaps, and Curie temperatures significantly above room temperature.

  1. Ru9Zn7Sb8: a structure with a 2 × 2 × 2 supercell of the half-Heusler phase.

    PubMed

    Xiong, Ding-Bang; Zhao, Yufeng; Okamoto, Norihiko L; Pietzonka, Clemens; Waki, Takeshi; Inui, Haruyuki

    2010-11-15

    The title compound Ru(9)Zn(7)Sb(8) was synthesized via a high-temperature reaction from the elements in a stoichiometric ratio, and its structure was solved by a single-crystal X-ray diffraction method. The structure [cubic, space group Fm3m, Pearson symbol cF96, a = 11.9062(14) Å (293 K), and Z = 4] adopts a unique 2a(hh) × 2a(hh) × 2a(hh) supercell of a normal half-Heusler phase and shows abnormal features of atomic coordination against the Pauling rule. The formation of this superstructure was discussed in light of the valence electron concentration per unit cell. It is a metallic conductor [ρ(300 K) = 16 μΩ·m], and differential scanning calorimetry revealed that Ru(9)Zn(7)Sb(8) undergoes a transformation at 1356(1) K and melts, by all indications, congruently at 1386 K. At room temperature, its thermal conductivity is about 3 W/m·K, which is only one-quarter of that of most normal half-Heusler phases. Ru(9)Zn(7)Sb(8) as well as its analogues of iron-, cobalt-, rhodium-, and iridium-containing compounds are expected to serve as a new structure type for exploring new thermoelectric materials. PMID:20957992

  2. Growth and transport properties of epitaxial lattice matched half Heusler CoTiSb/InAlAs/InP(001) heterostructures

    SciTech Connect

    Kawasaki, Jason K.; Johansson, Linda I. M.; Schultz, Brian D.; Palmstrøm, Chris J.

    2014-01-13

    We demonstrate the integration of the lattice matched single crystal epitaxial Half Heusler compound CoTiSb with In{sub 0.52}Al{sub 0.48}As/InP(001) heterostructures using molecular beam epitaxy. CoTiSb belongs to the subset of Half Heusler compounds that is expected to be semiconducting, despite being composed entirely of metallic constituents. The lattice matching and epitaxial alignment of the CoTiSb films were confirmed by reflection high energy electron diffraction and X-ray diffraction. Temperature dependent transport measurements indicate semiconducting-like behavior, with a room temperature Hall mobility of 530 cm{sup 2}/Vs and background Hall carrier density of 9.0 × 10{sup 17} cm{sup −3}, which is comparable to n-Si with similar carrier density. Below 100 K, the films show a large negative magnetoresistance, and possible origins of this negative magnetoresistance are discussed.

  3. Lattice thermal conductivity of nanograined half-Heusler solid solutions

    SciTech Connect

    Geng, Huiyuan Meng, Xianfu; Zhang, Hao; Zhang, Jian

    2014-05-19

    We report a phenomenological model of atomic weight, lattice constant, temperature, and grain size to calculate the high-temperature lattice thermal conductivity of nanograined solid solutions. The theoretical treatment developed here is reasonably consistent with the experimental results of n-type MNiSn and p-type MCoSb alloys, where M is the combination of Hf, Zr, and Ti. For disordered half-Heusler alloys with moderated grain sizes, we predict that the reduction in lattice thermal conductivity due to grain boundary scattering is independent of the scattering parameter, which characterizes the phonon scattering cross section of point defects. In addition, the lattice thermal conductivity falls off with temperature as T{sup –1∕2} around the Debye temperature.

  4. Fully epitaxial C1b-type NiMnSb half-Heusler alloy films for current-perpendicular-to-plane giant magnetoresistance devices with a Ag spacer

    PubMed Central

    Wen, Zhenchao; Kubota, Takahide; Yamamoto, Tatsuya; Takanashi, Koki

    2015-01-01

    Remarkable magnetic and spin-dependent transport properties arise from well-designed spintronic materials and heterostructures. Half-metallic Heusler alloys with high spin polarization exhibit properties that are particularly advantageous for the development of high-performance spintronic devices. Here, we report fully (001)-epitaxial growth of a high-quality half-metallic NiMnSb half-Heusler alloy films, and their application to current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) devices with Ag spacer layers. Fully (001)-oriented NiMnSb epitaxial films with very flat surface and high magnetization were prepared on Cr/Ag-buffered MgO(001) single crystalline substrates by changing the substrate temperature. Epitaxial CPP-GMR devices using the NiMnSb films and a Ag spacer were fabricated, and room-temperature (RT) CPP-GMR ratios for the C1b-type half-Heusler alloy were determined for the first time. A CPP-GMR ratio of 8% (21%) at RT (4.2 K) was achieved in the fully epitaxial NiMnSb/Ag/NiMnSb structures. Furthermore, negative anisotropic magnetoresistance (AMR) ratio and small discrepancy of the AMR amplitudes between RT and 10 K were observed in a single epitaxial NiMnSb film, indicating robust bulk half metallicity against thermal fluctuation in the half-Heusler compound. The modest CPP-GMR ratios could be attributed to interface effects between NiMnSb and Ag. This work provides a pathway for engineering a new class of ordered alloy materials with particular emphasis on spintronics. PMID:26672482

  5. Fully epitaxial C1b-type NiMnSb half-Heusler alloy films for current-perpendicular-to-plane giant magnetoresistance devices with a Ag spacer

    NASA Astrophysics Data System (ADS)

    Wen, Zhenchao; Kubota, Takahide; Yamamoto, Tatsuya; Takanashi, Koki

    2015-12-01

    Remarkable magnetic and spin-dependent transport properties arise from well-designed spintronic materials and heterostructures. Half-metallic Heusler alloys with high spin polarization exhibit properties that are particularly advantageous for the development of high-performance spintronic devices. Here, we report fully (001)-epitaxial growth of a high-quality half-metallic NiMnSb half-Heusler alloy films, and their application to current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) devices with Ag spacer layers. Fully (001)-oriented NiMnSb epitaxial films with very flat surface and high magnetization were prepared on Cr/Ag-buffered MgO(001) single crystalline substrates by changing the substrate temperature. Epitaxial CPP-GMR devices using the NiMnSb films and a Ag spacer were fabricated, and room-temperature (RT) CPP-GMR ratios for the C1b-type half-Heusler alloy were determined for the first time. A CPP-GMR ratio of 8% (21%) at RT (4.2 K) was achieved in the fully epitaxial NiMnSb/Ag/NiMnSb structures. Furthermore, negative anisotropic magnetoresistance (AMR) ratio and small discrepancy of the AMR amplitudes between RT and 10 K were observed in a single epitaxial NiMnSb film, indicating robust bulk half metallicity against thermal fluctuation in the half-Heusler compound. The modest CPP-GMR ratios could be attributed to interface effects between NiMnSb and Ag. This work provides a pathway for engineering a new class of ordered alloy materials with particular emphasis on spintronics.

  6. Fully epitaxial C1b-type NiMnSb half-Heusler alloy films for current-perpendicular-to-plane giant magnetoresistance devices with a Ag spacer.

    PubMed

    Wen, Zhenchao; Kubota, Takahide; Yamamoto, Tatsuya; Takanashi, Koki

    2015-01-01

    Remarkable magnetic and spin-dependent transport properties arise from well-designed spintronic materials and heterostructures. Half-metallic Heusler alloys with high spin polarization exhibit properties that are particularly advantageous for the development of high-performance spintronic devices. Here, we report fully (001)-epitaxial growth of a high-quality half-metallic NiMnSb half-Heusler alloy films, and their application to current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) devices with Ag spacer layers. Fully (001)-oriented NiMnSb epitaxial films with very flat surface and high magnetization were prepared on Cr/Ag-buffered MgO(001) single crystalline substrates by changing the substrate temperature. Epitaxial CPP-GMR devices using the NiMnSb films and a Ag spacer were fabricated, and room-temperature (RT) CPP-GMR ratios for the C1b-type half-Heusler alloy were determined for the first time. A CPP-GMR ratio of 8% (21%) at RT (4.2 K) was achieved in the fully epitaxial NiMnSb/Ag/NiMnSb structures. Furthermore, negative anisotropic magnetoresistance (AMR) ratio and small discrepancy of the AMR amplitudes between RT and 10 K were observed in a single epitaxial NiMnSb film, indicating robust bulk half metallicity against thermal fluctuation in the half-Heusler compound. The modest CPP-GMR ratios could be attributed to interface effects between NiMnSb and Ag. This work provides a pathway for engineering a new class of ordered alloy materials with particular emphasis on spintronics. PMID:26672482

  7. Nuclear magnetic resonance study of thin Co2FeAl0.5Si0.5 Heusler films with varying thickness

    NASA Astrophysics Data System (ADS)

    Alfonsov, A.; Peters, B.; Yang, F. Y.; Büchner, B.; Wurmehl, S.

    2015-02-01

    Type, degree, and evolution of structural order are important aspects for understanding and controlling the properties of highly spin-polarized Heusler compounds, in particular, with respect to the optimal film growth procedure. In this work, we compare the structural order and the local magnetic properties revealed by nuclear magnetic resonance (NMR) spectroscopy with the macroscopic properties of thin Co2FeAl 0.5Si 0.5 Heusler films with varying thickness. A detailed analysis of the measured NMR spectra presented in this paper enables us to find a very high degree of L 21 -type ordering up to 81% concomitantly with excess Fe of 8%-13% at the expense of Al and Si. We show that the formation of certain types of order depends not only on the thermodynamic phase diagrams as in bulk samples, but also that the kinetic control may contribute to the phase formation in thin films. It is an exciting finding that Co2FeAl 0.5Si 0.5 can form an almost ideal L 21 structure in films, though with a considerable amount of Fe-Al/Si off stoichiometry. Moreover, the very good quality of the films as demonstrated by our NMR study suggests that the technique of off-axis sputtering used to grow the films sets the stage for the optimized performance of Co2FeAl 0.5Si 0.5 in spintronic devices.

  8. Contradictory role of the magnetic contribution in inverse magnetocaloric Heusler materials

    NASA Astrophysics Data System (ADS)

    Gottschall, Tino; Skokov, Konstantin P.; Benke, Dimitri; Gruner, Markus E.; Gutfleisch, Oliver

    2016-05-01

    In this paper, we illustrate the dilemma of inverse magnetocaloric materials using the example of Heusler alloys. For such materials, the magnetic and lattice contribution to the total entropy change are competing with each other. For the two paradigmatic Heusler systems of Ni-Mn-In and Ni-Mn-In-Co, we provide a systematic comparison of experimental data under different magnetic fields and hydrostatic pressures with magnetic and the magnetocaloric properties obtained from the Heisenberg model. This allows us to separate the lattice and the magnetic contribution to the total entropy of the martensitic transition. Our analysis reveals that a large magnetization change is parasitic, but at the same time it is necessary to drive the magnetocaloric effect. This contradicting role of the magnetic contribution—the dilemma—is a general characteristic of inverse magnetocaloric Heusler materials.

  9. Peculiarities of thermoelectric half-Heusler phase formation in Gd-Ni-Sb and Lu-Ni-Sb ternary systems

    NASA Astrophysics Data System (ADS)

    Romaka, V. V.; Romaka, L.; Horyn, A.; Rogl, P.; Stadnyk, Yu; Melnychenko, N.; Orlovskyy, M.; Krayovskyy, V.

    2016-07-01

    The phase equilibria in the Gd-Ni-Sb and Lu-Ni-Sb ternary systems were studied at 873 K by X-ray and metallographic analyses in the whole concentration range. The interaction of the elements in the Gd-Ni-Sb system results the formation of five ternary compounds at investigated temperature: Gd5Ni2Sb (Mo5SiB2-type), Gd5NiSb2 (Yb5Sb3-type), GdNiSb (MgAgAs-type), Gd3Ni6Sb5 (Y3Ni6Sb5-type), and GdNi0.72Sb2 (HfCuSi2-type). At investigated temperature the Lu-Ni-Sb system is characterized by formation of the LuNiSb (MgAgAs-type), Lu5Ni2Sb (Mo5SiB2-type), and Lu5Ni0.56Sb2.44 (Yb5Sb3-type) compounds. The disordering in the crystal structure of half-Heusler GdNiSb and LuNiSb was revealed by EPMA and studied by means of Rietveld refinement and DFT modeling. The performed electronic structure calculations are in good agreement with electrical transport property studies.

  10. Hyperfine magnetic fields in cobalt-based Heusler alloys

    SciTech Connect

    Yehia, M.S.

    1987-01-01

    Measurement of hyperfine interactions at Cd-111 and Sn-119 impurity nuclei in Co-based Heusler alloys Co/sub 2/YZ (Y = Mn, Ti, V, Zr and Z was Al, Ga, Ge, Si, Sn) were made within a temperature range 77 to 746 K using the time differential Perturbed Angular Correlation (TDPAC) and Mossbauer techniques. The hyperfine-field results in these alloys are discussed in terms of two models, the localized moment model and the Volume Overlap model. In the localized moment model a pre-asymptotic phase factor n = ..pi.. at distance r = a/2 was used to fit the experimental results on Co/sub 2/YZ (Y = Ti, V, Zr and Z = Al, Ga, Sn, Ge). In the Volume Overlap model the hyperfine field results in the series Co/sub 2/MnZ (Z = Ge, Si, Sn) was plotted against the lattice parameter of these alloys; a linear relationship was found, suggesting a non overlap term between the magnetic atom and the nonmagnetic impurity. A prediction of hyperfine magnetic filed less than 40 (kOe) on Sn-119 and of about -250(kOe) on Cd-111 in Co/sub 2/TiSi and Co/sub 2/TiGe is made. Temperature variation of the hyperfine magnetic field in the alloy Co/sub 2/MnSn with magnetic moments residing on two sites, has been studied. Results didn't show a dramatic deviation form the Brillouin function.

  11. Artificially engineered Heusler ferrimagnetic superlattice exhibiting perpendicular magnetic anisotropy

    PubMed Central

    Ma, Q. L.; Zhang, X. M.; Miyazaki, T.; Mizukami, S.

    2015-01-01

    To extend density limits in magnetic recording industry, two separate strategies were developed to build the storage bit in last decade, introduction of perpendicular magnetic anisotropy (PMA) and adoption of ferrimagnetism/antiferromagnetism. Meanwhile, these properties significantly improve device performance, such as reducing spin-transfer torque energy consumption and decreasing signal-amplitude-loss. However, materials combining PMA and antiferromagnetism rather than transition-metal/rare-earth system were rarely developed. Here, we develop a new type of ferrimagnetic superlattice exhibiting PMA based on abundant Heusler alloy families. The superlattice is formed by [MnGa/Co2FeAl] unit with their magnetizations antiparallel aligned. The effective anisotropy (Kueff) over 6 Merg/cm3 is obtained, and the SL can be easily built on various substrates with flexible lattice constants. The coercive force, saturation magnetization and Kueff of SLs are highly controllable by varying the thickness of MnGa and Co2FeAl layers. The SLs will supply a new choice for magnetic recording and spintronics memory application such as magnetic random access memory. PMID:25597496

  12. Artificially engineered Heusler ferrimagnetic superlattice exhibiting perpendicular magnetic anisotropy.

    PubMed

    Ma, Q L; Zhang, X M; Miyazaki, T; Mizukami, S

    2015-01-01

    To extend density limits in magnetic recording industry, two separate strategies were developed to build the storage bit in last decade, introduction of perpendicular magnetic anisotropy (PMA) and adoption of ferrimagnetism/antiferromagnetism. Meanwhile, these properties significantly improve device performance, such as reducing spin-transfer torque energy consumption and decreasing signal-amplitude-loss. However, materials combining PMA and antiferromagnetism rather than transition-metal/rare-earth system were rarely developed. Here, we develop a new type of ferrimagnetic superlattice exhibiting PMA based on abundant Heusler alloy families. The superlattice is formed by [MnGa/Co2FeAl] unit with their magnetizations antiparallel aligned. The effective anisotropy (K(u)(eff)) over 6 Merg/cm(3) is obtained, and the SL can be easily built on various substrates with flexible lattice constants. The coercive force, saturation magnetization and K(u)(eff) of SLs are highly controllable by varying the thickness of MnGa and Co2FeAl layers. The SLs will supply a new choice for magnetic recording and spintronics memory application such as magnetic random access memory. PMID:25597496

  13. Artificially engineered Heusler ferrimagnetic superlattice exhibiting perpendicular magnetic anisotropy

    NASA Astrophysics Data System (ADS)

    Ma, Q. L.; Zhang, X. M.; Miyazaki, T.; Mizukami, S.

    2015-01-01

    To extend density limits in magnetic recording industry, two separate strategies were developed to build the storage bit in last decade, introduction of perpendicular magnetic anisotropy (PMA) and adoption of ferrimagnetism/antiferromagnetism. Meanwhile, these properties significantly improve device performance, such as reducing spin-transfer torque energy consumption and decreasing signal-amplitude-loss. However, materials combining PMA and antiferromagnetism rather than transition-metal/rare-earth system were rarely developed. Here, we develop a new type of ferrimagnetic superlattice exhibiting PMA based on abundant Heusler alloy families. The superlattice is formed by [MnGa/Co2FeAl] unit with their magnetizations antiparallel aligned. The effective anisotropy (Kueff) over 6 Merg/cm3 is obtained, and the SL can be easily built on various substrates with flexible lattice constants. The coercive force, saturation magnetization and Kueff of SLs are highly controllable by varying the thickness of MnGa and Co2FeAl layers. The SLs will supply a new choice for magnetic recording and spintronics memory application such as magnetic random access memory.

  14. Characterization of half-Heusler unicouple for thermoelectric conversion

    NASA Astrophysics Data System (ADS)

    Hu, Xiaokai; Yamamoto, Atsushi; Nagase, Kazuo

    2015-06-01

    A thermoelectric unicouple is constructed with half-Heusler materials for characterizing power generation. The electric power and heat flow are measured simultaneously under various temperature differences, and the efficiencies are calculated. Phase structures and thermoelectric properties are characterized for the p- and n-type legs; the latter are used for finite-element simulations to calculate numerically the ideal electric power, heat flow and efficiency under the same temperature conditions. Seebeck voltage, internal resistance, electric power, heat flow, and efficiency are compared between the measurement and simulation. Thereby, the contact electrical resistance is estimated, and the extra thermal resistance is analyzed in terms of the compared open-circuit voltage and heat flow. The maximum efficiency of 4.0% is attained from the measurement with the hot side at 470 °C, in contrast to 5.7% from the simulation. The simulation permits an investigation on the one-dimensional heat flow through the p- and n-type legs that is coupled with Peltier, Thomson, and Joule heat.

  15. Half-Heusler Alloys for Efficient Thermoelectric Power Conversion

    NASA Astrophysics Data System (ADS)

    Chen, Long; Zeng, Xiaoyu; Tritt, Terry M.; Poon, S. Joseph

    2016-07-01

    Half-Heusler (HH) phases (space group F43m, Clb) are increasingly gaining attention as promising thermoelectric materials in view of their thermal stability and environmental benignity as well as efficient power output. Until recently, the verifiable dimensionless figure of merit (ZT) of HH phases has remained moderate near 1, which limits the power conversion efficiency of these materials. We report herein ZT ˜ 1.3 in n-type (Hf,Zr)NiSn alloys near 850 K developed through elemental substitution and simultaneous embedment of nanoparticles in the HH matrix, obtained by annealing the samples close to their melting temperatures. Introduction of mass fluctuation and scattering centers play a key role in the high ZT measured, as shown by the reduction of thermal conductivity and increase of thermopower. Based on computation, the power conversion efficiency of a n-p couple module based on the new n-type (Hf,Zr,Ti)NiSn particles-in-matrix composite and recently reported high-ZT p-type HH phases is expected to reach 13%, comparable to that of state-of-the-art materials, but with the mentioned additional materials and environmental attributes. Since the high efficiency is obtained without tuning the microstructure of the HH phases, it leaves room for further optimization.

  16. Study of potentially half-metallic cobalt-chromium-iron-aluminum Heusler alloys

    NASA Astrophysics Data System (ADS)

    Kelekar, Rajesh

    2006-12-01

    In the new class of materials known as half-metallic ferromagnets, all of the conduction electrons have the same spin at low temperature. This high spin polarization makes half-metals promising candidates for magnetoelectronic applications. In this work we study the Heusler alloy family of compounds Co2 Cr1-xFe xAl, predicted to be half-metallic for low Fe concentrations. Using DC magnetron sputtering, we have grown for the first time epitaxial thin films of these compounds. Basic characterization shows that the films crystallize in the B2 crystal structure, and that their magnetic and transport properties vary significantly with Fe concentration. We incorporate these thin films into epitaxial superlattices with Cr and simple spin valve trilayers with Cu and Co90Fe10. Though we do not observe evidence for antiferromagnetic coupling in the superlattices, we find large giant magnetoresistances in the spin valves of up to 7% for intermediate Fe concentrations, the highest to date for any material predicted to be half-metallic. We then measure the spin polarization of CO2Cr 0.6Fe0.4Al with point contact Andreev reflection spectroscopy, finding a value of 50%, lower than the 100% expected for a half-metal. We use x-ray magnetic circular dichroism to investigate the deficit in the saturation magnetic moments as compared to theory for films with low Fe concentrations. We develop a modified sum rule analysis for the extraction of the spin and orbital moments of Cr, Fe, and Co from the dichroism spectra. The average Cr spin moment has a value approximately 10% of the theoretical value; features of the Cr dichroism spectra suggest that the films may be composed of ordered B2 regions and disordered regions. We use tight binding theory to calculate the minority spin energy bands, finding a dominance of Co d states near the energy gap. This result, supported by more accurate calculations, suggests that the half-metallicity of these compounds may be especially sensitive to

  17. The electronic structure and spin polarization of Co2Mn0.75(Gd, Eu)0.25Z (Z=Si, Ge, Ga, Al) quaternary Heusler alloys

    NASA Astrophysics Data System (ADS)

    Berri, Saadi

    2016-03-01

    A first-principles approach is used to study the electronic and magnetic properties of Co2Mn0.75(Gd, Eu)0.25Z(Z=Si, Ge, Ga, Al) quaternary Heusler alloys. The investigation was done using the (FP-LAPW) method where the exchange-correlation potential was calculated with the frame of GGA-WC. At ambient conditions our calculated results of band structures reveal that for Co2Mn0.75(Gd, Eu)0.25Z(Z=Si, Ge) has a half-metallic (HM) band structure profile showing 100% spin polarization at the Fermi level. In contrast, Co2Mn0.75(Gd, Eu)0.25Z(Z=Ga, Al) alloys are found to be metallic. Finally, the half metallic compounds found in some structures of this series might be useful in spintronic devices.

  18. Spin Transfer Torque Switching and Perpendicular Magnetic Anisotropy in Full Heusler Alloy Co2FeAl-BASED Tunnel Junctions

    NASA Astrophysics Data System (ADS)

    Sukegawa, H.; Wen, Z. C.; Kasai, S.; Inomata, K.; Mitani, S.

    2014-12-01

    Some of Co-based full Heusler alloys have remarkable properties in spintronics, that is, high spin polarization of conduction electrons and low magnetic damping. Owing to these properties, magnetic tunnel junctions (MTJs) using Co-based full Heusler alloys are potentially of particular importance for spintronic application such as magnetoresistive random access memories (MRAMs). Recently, we have first demonstrated spin transfer torque (STT) switching and perpendicular magnetic anisotropy (PMA), which are required for developing high-density MRAMs, in full-Heusler Co2FeAl alloy-based MTJs. In this review, the main results of the experimental demonstrations are shown with referring to related issues, and the prospect of MTJs using Heusler alloys is also discussed.

  19. 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.

  20. Pairing of j=3/2 Fermions in Half-Heusler Superconductors.

    PubMed

    Brydon, P M R; Wang, Limin; Weinert, M; Agterberg, D F

    2016-04-29

    We theoretically consider the superconductivity of the topological half-Heusler semimetals YPtBi and LuPtBi. We show that pairing occurs between j=3/2 fermion states, which leads to qualitative differences from the conventional theory of pairing between j=1/2 states. In particular, this permits Cooper pairs with quintet or septet total angular momentum, in addition to the usual singlet and triplet states. Purely on-site interactions can generate s-wave quintet time-reversal symmetry-breaking states with topologically nontrivial point or line nodes. These local s-wave quintet pairs reveal themselves as d-wave states in momentum space. Furthermore, due to the broken inversion symmetry in these materials, the s-wave singlet state can mix with a p-wave septet state, again with topologically stable line nodes. Our analysis lays the foundation for understanding the unconventional superconductivity of the half-Heuslers. PMID:27176533

  1. Lateral spin valves with two-different Heusler-alloy electrodes on the same platform

    SciTech Connect

    Oki, S.; Yamada, S.; Tanikawa, K.; Yamasaki, K.; Miyao, M.; Hamaya, K.

    2013-11-18

    Using room-temperature molecular beam epitaxy on Si(111), we demonstrate Heusler-alloy bilayers consisting of L2{sub 1}-Co{sub 2}FeSi (CFS) and D0{sub 3}-Fe{sub 3}Si (FS). By fabricating lateral spin valves with L2{sub 1}-CFS and D0{sub 3}-FS electrodes, we can see ideal spin signals even though we use one L2{sub 1}-CFS as a spin injector and another D0{sub 3}-FS as a spin detector. The difference in the spin absorption between L2{sub 1}-CFS and D0{sub 3}-FS can also be examined, and we find that the spin resistance of D0{sub 3}-FS is larger than that of L2{sub 1}-CFS. This work will be useful for understanding spin transport in lateral spin-valve devices with different Heusler-alloy electrodes.

  2. Shell-ferromagnetism of nano-Heuslers generated by segregation under magnetic field

    PubMed Central

    Çakır, A.; Acet, M.; Farle, M.

    2016-01-01

    We report on a new functional property in an AF martensitic Heusler Ni50Mn45In5, which when annealed at high temperatures under a magnetic field, segregates and forms Ni50Mn25In25 Heusler precipitates embedded in a Ni50Mn50 matrix. The precipitates are paramagnetic whereas the matrix is antiferromagnetic. However, the spins at the interface with the Ni50Mn50 matrix align with the field during their nucleation and growth and become strongly pinned in the direction of the applied field during annealing, whereas the core spins become paramagnetic. This shell-ferromagnetism persists up to 600 K and is so strongly pinned that the remanent magnetization remains unchanged, even when the field is reversed or when the temperature is cycled between low temperatures and close to the annealing temperature. PMID:27412644

  3. Shell-ferromagnetism of nano-Heuslers generated by segregation under magnetic field.

    PubMed

    Çakır, A; Acet, M; Farle, M

    2016-01-01

    We report on a new functional property in an AF martensitic Heusler Ni50Mn45In5, which when annealed at high temperatures under a magnetic field, segregates and forms Ni50Mn25In25 Heusler precipitates embedded in a Ni50Mn50 matrix. The precipitates are paramagnetic whereas the matrix is antiferromagnetic. However, the spins at the interface with the Ni50Mn50 matrix align with the field during their nucleation and growth and become strongly pinned in the direction of the applied field during annealing, whereas the core spins become paramagnetic. This shell-ferromagnetism persists up to 600 K and is so strongly pinned that the remanent magnetization remains unchanged, even when the field is reversed or when the temperature is cycled between low temperatures and close to the annealing temperature. PMID:27412644

  4. Pairing of j =3 /2 Fermions in Half-Heusler Superconductors

    NASA Astrophysics Data System (ADS)

    Brydon, P. M. R.; Wang, Limin; Weinert, M.; Agterberg, D. F.

    2016-04-01

    We theoretically consider the superconductivity of the topological half-Heusler semimetals YPtBi and LuPtBi. We show that pairing occurs between j =3 /2 fermion states, which leads to qualitative differences from the conventional theory of pairing between j =1 /2 states. In particular, this permits Cooper pairs with quintet or septet total angular momentum, in addition to the usual singlet and triplet states. Purely on-site interactions can generate s -wave quintet time-reversal symmetry-breaking states with topologically nontrivial point or line nodes. These local s -wave quintet pairs reveal themselves as d -wave states in momentum space. Furthermore, due to the broken inversion symmetry in these materials, the s -wave singlet state can mix with a p -wave septet state, again with topologically stable line nodes. Our analysis lays the foundation for understanding the unconventional superconductivity of the half-Heuslers.

  5. High spin polarization in CoFeMnGe equiatomic quaternary Heusler alloy

    SciTech Connect

    Bainsla, Lakhan; Suresh, K. G.; Nigam, A. K.; Manivel Raja, M.; Varaprasad, B. S. D. Ch. S.; Takahashi, Y. K.; Hono, K.

    2014-11-28

    We report the structure, magnetic property, and spin polarization of CoFeMnGe equiatomic quaternary Heusler alloy. The alloy was found to crystallize in the cubic Heusler structure (prototype LiMgPdSn) with considerable amount of DO{sub 3} disorder. Thermal analysis result indicated the Curie temperature is about 750 K without any other phase transformation up to melting temperature. The magnetization value was close to that predicted by the Slater-Pauling curve. Current spin polarization of P = 0.70 ± 0.01 was deduced using point contact andreev reflection measurements. The temperature dependence of electrical resistivity has been fitted in the temperature range of 5–300 K in order to check for the half metallic behavior. Considering the high spin polarization and Curie temperature, this material appears to be promising for spintronic applications.

  6. Improvement of thermoelectric properties for half-Heusler TiNiSn by interstitial Ni defects

    SciTech Connect

    Hazama, Hirofumi; Matsubara, Masato; Asahi, Ryoji; Takeuchi, Tsunehiro

    2011-09-15

    We have synthesized off-stoichiometric Ti-Ni-Sn half-Heusler thermoelectrics in order to investigate the relation between randomly distributed defects and thermoelectric properties. A small change in the composition of Ti-Ni-Sn causes a remarkable change in the thermal conductivity. An excess content of Ni realizes a low thermal conductivity of 2.93 W/mK at room temperature while keeping a high power factor. The low thermal conductivity originates in the defects generated by an excess content of Ni. To investigate the detailed defect structure, we have performed first-principles calculations and compared with x ray photoemission spectroscopy measurement. Based on these analyses, we conclude that the excess Ni atoms randomly occupy the vacant sites in the half-Heusler structure, which play as phonon scattering centers, resulting in significant improvement of the figure of merit without any substitutions of expensive heavy elements, such as Zr and Hf.

  7. Premartensite transition in Ni{sub 2}FeGa Heusler alloy

    SciTech Connect

    Nath, Hrusikesh; Phanikumar, G.

    2015-04-15

    Martensitic phase transformation of Ni{sub 2}FeGa Heusler alloy was studied by differential scanning calorimetry. Atomic ordering induced in the austenite structure by quenching from high temperature plays a significant role on martensitic phase transformation. Higher magnetization and larger magneto-crystalline anisotropy of martensite phase than that of austenite phase are noticed. Tweed contrast regions observed in the transmission electron microscopy were correlated to premartensite phenomena. A shift in premartensitic transition temperature prior to martensitic transformation as measured by differential scanning calorimetry is being reported for the first time in this system. - Highlights: • Atomic ordering influences martensitic transformation in Ni{sub 2}FeGa Heusler alloy. • Observation of tweed contrast in TEM was correlated to premartensite phenomena. • For the first time the shift in premartensite peak was observed in DSC.

  8. Mechanical, electronic and thermodynamic properties of full Heusler compounds Fe2VX(X = Al, Ga)

    NASA Astrophysics Data System (ADS)

    Khalfa, M.; Khachai, H.; Chiker, F.; Baki, N.; Bougherara, K.; Yakoubi, A.; Murtaza, G.; Harmel, M.; Abu-Jafar, M. S.; Omran, S. Bin; Khenata, R.

    2015-11-01

    The electronic structure, mechanical and thermodynamic properties of Fe2VX, (with X = Al and Ga), have been studied self consistently by employing state-of-the-art full-potential linearized approach of augmented plane wave plus local orbitals (FP-LAPW + lo) method. The exchange-correlation potential is treated with the local density and generalized gradient approximations (LDA and GGA). Our predicted ground state properties such as lattice constants, bulk modulus and elastic constants appear more accurate when we employed the GGA rather than the LDA, and these results are in very good agreement with the available experimental and theoretical data. Further, thermodynamic properties of Fe2VAl and Fe2VGa are predicted with pressure and temperature in the ranges of 0-40 GPa and 0-1500 K using the quasi-harmonic Debye model. We have obtained successfully the variations of the heat capacities, primitive cell volume and volume expansion coefficient.

  9. Strategies to Bulk Half-Heusler Nanocomposites with Simultaneously Enhanced Power Factor and Reduced Thermal Conductivity

    NASA Astrophysics Data System (ADS)

    Poudeu, Pierre Ferdinand

    2011-03-01

    Among promising thermoelectric materials for power generation, half-Heusler (HH) phases with general compositions TNiSn and TCoSb (T = Ti, Zr, Hf) have attracted tremendous attention not only because they involve abundant and environmentally friendly elements, but also due to their combination of large Seebeck coefficients with moderately low electrical resistivities. However, the ability to synthesize HH based materials with decent figures of merit (ZT> 1) hasbeenjeopardizedbytheirverylargethermalconductivities . StrategiestoreducethethermalconductivityofHHphasesfocusingonmassfluctuationphononscatteringviasolidsolutionalloyingorphononscatteringatgrainboundariesandinterfacesinHHphaseswithembeddedpre - synthesizednanoparticleshavefailedtogeneratematerialswithhighfiguresofmeritduetosimultaneousreductionsinthepowerfactor . Here , weintroduceinnovativeapproachestorevolutionaryincreasesinthefigureofmeritofHHbasedmaterialsthroughsimultaneouslargeenhancementofthepowerfactoranddrasticreductioninthethermalconductivity . Ourstrategyisfocusedonatomic - scalestructuralengineeringoftheHHmatrixthroughtheconfinementoffull - Heusler (FH) inclusionphasesonthelatticeconstantlength - scale . Emphasiswillbeplacedonthen - typeZr 0.25 Hf 0.75 Ni 1+x Sn 1-y Pn y andTi 0.5 Zr 0.5 Ni 1+x Sn 1-y Pn y aswellasthep - typeTi 0.5 Zr 0.5 Co 1+x Pn 1-y Sn y , (Pn = Sb, Bi) nanocomposites. We will discuss the underlying mechanism for the formation of half-Heusler/full-Heusler (HH/FH) nanocomposites with coherent matrix/inclusion interfaces. The role of synthetic and processing methods; and size, dispersion and mole fraction of the FH inclusions on the thermoelectric performance of bulk HH/FH nanocomposites will be assessed by combining transmission electron microscopy studies with thermal and electronic charge transport data. Financial support from DARPA contract # HR 0011-08-1-0084 is greatly acknowledged. This work made use of the laser flash diffusivity apparatus (Netzsch-LFA457) purchased with

  10. Martensite Transformation and Magnetic Properties of Ni-Fe-Ga Heusler Alloys

    NASA Astrophysics Data System (ADS)

    Nath, Hrusikesh; Phanikumar, Gandham

    2015-11-01

    Compositional instability and phase formation in Ni-Fe-Ga Heusler alloys are investigated. The alloys are synthesized into two-phase microstructure. Their structures are identified as fcc and L 21, respectively. The γ-phase formation could be suppressed with higher Ga-content in the alloy as Ga stabilizes austenite phase, but Ga lowers the martensite transformation temperature. The increase of Fe content improves the magnetization value and the increase of Ni from 52 to 55 at. pct raises the martensite transformation temperature from 216 K to 357 K (-57 °C to 84 °C). Magnetic properties and martensitic transformation behavior in Ni-Fe-Ga Heusler alloys follow opposite trends, while Ni replaces either Fe or Ga, whereas they follow similar trends, while Fe replaces Ga. Modulated martensite structure has low twinning stress and high magneto crystalline anisotropic properties. Thus, the observation of 10- and 14 M-modulated martensite structures in the studied Ni-Fe-Ga Heusler alloys is beneficial for shape memory applications. The interdependency of alloy composition, phase formation, magnetic properties, and martensite transformation are discussed.

  11. Investigation of the electronic and thermoelectric properties of Fe2ScX (X = P, As and Sb) full Heusler alloys by using first principles calculations

    NASA Astrophysics Data System (ADS)

    Sharma, Sonu; Pandey, Sudhir K.

    2014-11-01

    By using ab initio electronic structure calculations here we report the three new full Heusler alloys—Fe2ScP, Fe2ScAs and Fe2ScSb. These alloys possess a very good thermoelectric behavior and are also expected to be synthesized in laboratories. The first two compounds are indirect band gap semiconductors and the last one shows a semimetallic ground state. The value of the band gap of Fe2ScP and Fe2ScAs is 0.3 eV and 0.09 eV, respectively. The presence of flat conduction bands along the Γ—X-direction suggest the large electron like effective mass and also promises a very good thermoelectric behavior of these compounds. At 200 K, the Seebeck coefficients of Fe2ScP, Fe2ScAs and Fe2ScSb compounds are -770, -386 and -192 µV K-1, respectively. The maximum power factor (PF) is expected for the n-type doping in these materials. The heavily doped Fe2ScP and Fe2ScAs have PF > 60 for a wide temperature range, which is comparable to the PF of Bi2Te3—a well known and one of the most commercially used thermoelectric materials. The present work suggests the possible thermoelectric applicability of these materials in a wide temperature range.

  12. Perpendicular magnetization of Co2FeAl full-Heusler alloy films induced by MgO interface

    NASA Astrophysics Data System (ADS)

    Wen, Zhenchao; Sukegawa, Hiroaki; Mitani, Seiji; Inomata, Koichiro

    2011-06-01

    The perpendicular magnetization of Co2FeAl (CFA) full-Heusler alloy films was achieved in the structures of CFA/MgO and MgO/CFA with the perpendicular magnetic anisotropy energy density (KU) of 2-3×106 erg/cm3, which can be used as the perpendicular ferromagnetic electrodes of MgO-based magnetic tunnel junctions (MTJs) with high thermal stability at sub-50-nm dimension. The CFA thickness dependence of KU was investigated at different annealing temperatures, indicating that the perpendicular anisotropy of CFA is contributed by the interfacial anisotropy between CFA and MgO. This letter will open up a way for obtaining perpendicular magnetization of Co-based full-Heusler alloys, which is promising for further reduction in the critical current of current induced magnetization switching in MgO-based MTJ nanopillars with perpendicular full-Heusler alloy electrodes.

  13. Ab initio phonon properties of half-Heusler NiTiSn, NiZrSn and NiHfSn

    NASA Astrophysics Data System (ADS)

    Andrea, Luc; Hug, Gilles; Chaput, Laurent

    2015-10-01

    A theoretical investigation of phonon properties from first-principles calculations is carried out for the half-Heusler compounds NiXSn, X=\\text{Ti} , Zr and Hf. The crystal structures are optimised via ab initio calculations within the framework of density functional theory. The phonon properties are retrieved from harmonic and anharmonic interatomic force constants calculations using the finite size displacements method and many-body perturbation theory. A solution to the linearized phonon Boltzmann transport equation is then used to compute the ab initio thermal conductivities. For X   =   Ti, Zr and Hf, we found 15.4, 13.3 and 15.8 W m-1 K-1 at 300 K, respectively. Thanks to a spectral analysis of the velocities and lifetimes we were able appreciate the differences in the thermal conductivities between the three compounds under study. Our results provide insights to understand the behaviour of the thermal conductivity and therefore to improve the thermoelectric figure of merit for such materials.

  14. Ab initio phonon properties of half-Heusler NiTiSn, NiZrSn and NiHfSn.

    PubMed

    Andrea, Luc; Hug, Gilles; Chaput, Laurent

    2015-10-28

    A theoretical investigation of phonon properties from first-principles calculations is carried out for the half-Heusler compounds NiXSn, [Formula: see text], Zr and Hf. The crystal structures are optimised via ab initio calculations within the framework of density functional theory. The phonon properties are retrieved from harmonic and anharmonic interatomic force constants calculations using the finite size displacements method and many-body perturbation theory. A solution to the linearized phonon Boltzmann transport equation is then used to compute the ab initio thermal conductivities. For X   =   Ti, Zr and Hf, we found 15.4, 13.3 and 15.8 W m(-1) K(-1) at 300 K, respectively. Thanks to a spectral analysis of the velocities and lifetimes we were able appreciate the differences in the thermal conductivities between the three compounds under study. Our results provide insights to understand the behaviour of the thermal conductivity and therefore to improve the thermoelectric figure of merit for such materials. PMID:26441218

  15. Ab initio ground state and L{sub 2,3} x-ray magnetic circular dichroism of Mn-based Heusler alloys

    SciTech Connect

    Galanakis, I.; Ostanin, S.; Alouani, M.; Dreysse, H.; Wills, J. M.

    2000-02-01

    Relativistic full-potential calculations within the generalized gradient approximation (GGA) for a series of Mn-based Heusler alloys are presented. Calculated equilibrium lattice parameters deviate less than 1.2% from the experimental values. The main features of a half metallic system are present in the density of states for the PtMnSb and NiMnSb. We predict that PdMnSb shows half metallic character under hydrostatic pressure. The substitution of Sb in PtMnSb by Sn or Te destroys the minority spin band gap. Spin and orbital magnetic moments for all the systems are in good agreement with previous calculations and experimental data. L{sub 2,3} x-ray absorption and x-ray magnetic circular dichroism (XMCD) spectra are calculated for all the five compounds. Pt spectra present big deviations from system to system in the PtMnY (Y=Sn,Sb,Te) compounds while Mn spectra show only small deviations. For all these spectra GGA underestimates the L{sub 3}/L{sub 2} integrated branching ratio and produces a much smaller L{sub 2} peak intensity for the Ni site in NiMnSb. The XMCD sum rules are used to compute the spin and orbital magnetic moments and the results are compared to the direct calculations. (c) 2000 The American Physical Society.

  16. Electron dominated thermoelectric response in MNiSn (M: Ti, Zr, Hf) half-Heusler alloys.

    PubMed

    Gandi, Appala Naidu; Schwingenschlögl, Udo

    2016-05-18

    We solve the transport equations of the electrons and phonons to understand the thermoelectric behaviour of the technologically important half-Heusler alloys MNiSn (M: Ti, Zr, Hf). Doping is simulated within the rigid band approximation. We clarify the origin of the electron dominated thermoelectric response and determine the carrier concentrations with maximal figures of merit. The phonon mean free path is studied to calculate the grain size below which grain refinement methods can enforce ballistic heat conduction to enhance the figure of merit. PMID:27156360

  17. Elastic constants determined by nanoindentation for p-type thermoelectric half-Heusler

    SciTech Connect

    Gahlawat, S.; Wheeler, L.; White, K. W. E-mail: kwwhite@uh.edu; He, R.; Chen, S.; Ren, Z. F. E-mail: kwwhite@uh.edu

    2014-08-28

    This paper presents a study of the elastic properties of the p-type thermoelectric half-Heusler material, Hf{sub 0.44}Zr{sub 0.44}Ti{sub 0.12}CoSb{sub 0.8}Sn{sub 0.2}, using nanoindentation. Large grain-sized polycrystalline specimens were fabricated for these measurements, providing sufficient indentation targets within single grains. Electron Backscatter Diffraction methods indexed the target grains for the correlation needed for our elastic analysis of individual single crystals for this cubic thermoelectric material. Elastic properties, including the Zener ratio and the Poisson ratio, obtained from the elasticity tensor are also reported.

  18. Chemical disorder as an engineering tool for spin polarization in Mn3Ga -based Heusler systems

    NASA Astrophysics Data System (ADS)

    Chadov, S.; D'Souza, S. W.; Wollmann, L.; Kiss, J.; Fecher, G. H.; Felser, C.

    2015-03-01

    Our study highlights spin-polarization mechanisms in metals by focusing on the mobilities of conducting electrons with different spins instead of their quantities. Here, we engineer electron mobility by applying chemical disorder induced by nonstoichiometric variations. As a practical example, we discuss the scheme that establishes such variations in tetragonal Mn3Ga Heusler material. We justify this approach using first-principles calculations of the spin-projected conductivity components based on the Kubo-Greenwood formalism. It follows that, in the majority of cases, even a small substitution of some other transition element instead of Mn may lead to a substantial increase in spin polarization along the tetragonal axis.

  19. Uniaxial pressure setup for piezoresistance and magnetoresistance measurements in Heusler materials.

    PubMed

    Bourgault, D; Porcar, L; Bruyère, C; Jacquet, P; Courtois, P

    2013-01-01

    We report on a new uniaxial pressure experimental setup for electrical resistivity measurements working in a 77 K-500 K temperature range and in a magnetic field up to 8 T. Such a continuous uniaxial pressure device enables the study of the piezoresistance and the pressure induced change in electrical properties of bulk samples. Strong influence of uniaxial pressure on transport properties is shown for Ni-Co-Mn-In Heusler single crystal material. A shift of the martensite-austenite first order transformation temperature is measured with an applied uniaxial pressure leading to an electrical resistance changed by up to 120%. PMID:23387666

  20. Disorder dependent half-metallicity in Mn{sub 2}CoSi inverse Heusler alloy

    SciTech Connect

    Singh, Mukhtiyar; Saini, Hardev S.; Thakur, Jyoti; Reshak, Ali H.; Kashyap, Manish K.

    2013-12-15

    Heusler alloys based thin-films often exhibit a degree of atomic disorder which leads to the lowering of spin polarization in spintronic devices. We present ab-initio calculations of atomic disorder effects on spin polarization and half-metallicity of Mn{sub 2}CoSi inverse Heusler alloy. The five types of disorder in Mn{sub 2}CoSi have been proposed and investigated in detail. The A2{sub a}-type and B2-type disorders destroy the half-metallicity whereas it sustains for all disorders concentrations in DO{sub 3a}- and A2{sub b}-type disorder and for smallest disorder concentration studied in DO{sub 3b}-type disorder. Lower formation energy/atom for A2{sub b}-type disorder than other four disorders in Mn{sub 2}CoSi advocates the stability of this disorder. The total magnetic moment shows a strong dependence on the disorder and the change in chemical environment. The 100% spin polarization even in the presence of disorders explicitly supports that these disorders shall not hinder the use of Mn{sub 2}CoSi inverse Heusler alloy in device applications. - Graphical abstract: Minority-spin gap (E{sub g↓}) and HM gap (E{sub sf}) as a function of concentrations of various possible disorder in Mn{sub 2}CoSi inverse Heusler alloy. The squares with solid line (black color)/dotted line (blue color)/dashed line (red color) reperesents E{sub g↓} for DO{sub 3a}-/DO{sub 3b}-/A2{sub b}-type disorder in Mn{sub 2}CoSi and the spheres with solid line (black color)/dottedline (blue color)/dashed line (red color) represents E{sub sf} for DO{sub 3a}-/DO{sub 3b}-/A2{sub b}-type disorder in Mn{sub 2}CoSi. - Highlights: • The DO{sub 3}- and A2-type disorders do not affect the half-metallicity in Mn{sub 2}CoSi. • The B2-type disorder solely destroys half-metallicity in Mn{sub 2}CoSi. • The A2-type disorder most probable to occur out of all three types. • The total spin magnetic moment strongly depends on the disorder concentrations.

  1. Hyperfine magnetic field on Cd-111 in Heusler alloys Co2MnZ (Z = Si, Ga, Ge, Sn)

    NASA Technical Reports Server (NTRS)

    Jha, S.; Mitros, C.; Lahamer, Amer; Yehia, Sherif; Julian, Glenn M.

    1989-01-01

    The time differential perturbed angular correlation method has been used to measure, as a function of temperature, the hyperfine magnetic field at Cd sites in the Heusler alloys Co2MnZ (Z = Si, Ga, Ge, Sn). The hyperfine fields, normalized to the total magnetic moment per formula unit, show an approximately linear trend toward more positive values with increasing lattice parameter.

  2. Efficient and Robust Thermoelectric Power Generation Device Using Hot-Pressed Metal Contacts on Nanostructured Half-Heusler Alloys

    NASA Astrophysics Data System (ADS)

    Joshi, Giri; Poudel, Bed

    2016-06-01

    We report an efficient thermoelectric device with power density of 8.9 W/cm2 and efficiency of 8.9% at 678°C temperature difference using hot-pressed titanium metal contact layers on nanostructured half-Heusler materials. The high power density and efficiency are due to the efficient nanostructured materials and very low contact resistance of ~1 μΩ cm2 between the titanium layer and half-Heusler material. Moreover, the bonding strength between the titanium and half-Heusler is more than 50 MPa, significantly higher compared with conventional contact metallization methods. The low contact resistance and high bonding strength are due to thin-layer diffusion of titanium (<100 μm) into the half-Heusler at high temperature (>600°C). The low contact resistance and high bonding strength result in a stable and efficient power generation device with great potential for use in recovery of waste heat, e.g., in automotive and industrial applications.

  3. Itinerant G -type antiferromagnetism in D 03 -type V3Z (Z =Al , Ga, In) compounds: A first-principles study

    NASA Astrophysics Data System (ADS)

    Galanakis, Iosif; Tırpancı, Şaban; Özdoǧan, Kemal; Şaşıoǧlu, Ersoy

    2016-08-01

    Heusler compounds are widely studied due to their variety of magnetic properties making them ideal candidates for spintronic and magnetoelectronic applications. V3Al in its metastable D0 3-type Heusler structure is a prototype for a rare antiferromagnetic gapless behavior. We provide an extensive study on the electronic and magnetic properties of V3Al , V3Ga , and V3In compounds based on electronic structure calculations. We show that the ground state for all three is a G -type itinerant antiferromagnetic gapless semiconductor. The large antiferromagnetic exchange interactions lead to very high Néel temperatures, which are predicted to be around 1000 K. The coexistence of the gapless and antiferromagnetic behaviors in these compounds can be explained considering the simultaneous presence of three V atoms at the unit cell using arguments which have been employed for usual inverse Heusler compounds. We expect our study on these compounds to enhance further the interest on them towards the optimization of their growth conditions and their eventual incorporation in devices.

  4. Large Enhancements in Thermopower and Electrical Conductivity in Nano-structured Half-Heusler Alloys

    NASA Astrophysics Data System (ADS)

    Page, Alexander; van der Ven, Anton; Poudeu, Pierre; Uher, Ctirad

    2014-03-01

    Recent improvements have often been made to thermoelectric materials by adding nano-structures in order to scatter heat carrying phonons, however, the reduction in thermal conductivity is accompanied by large drops in the electrical conductivity caused by mobility reductions. In this work we show that Half-Heusler (HH) alloys can be combined with nano-scale Full-Heusler (FH) inclusions to simultaneously improve the power factor and reduce thermal conductivity. HH structures are of the form MNiSn and MCoSb (M = Ti, Zr, or Hf) and the FH counterparts are created by filling the vacancies on the Ni or Co planes respectively, giving MNi2Sn and MCo2Sb. Experimental results show FH nano-inclusions were coherently integrated into the matrix HH material resulting in enhanced ZT which is attributed to energy filtering effects that occur at the HH-FH grain boundaries as well as moderate reductions in thermal conductivity by nano-inclusion phonon scattering. Ab Initio calculations, in combination with a cluster expansion, are used to test the stability of FH structures in HH matrix and create thermodynamic pseudo-binary phase diagram for MNiSn-MNi2Sn compositions, elucidating the possibilities for future approaches to enhance ZT.

  5. Half-metallic Ni2MnSn Heusler alloy prepared by rapid quenching

    NASA Astrophysics Data System (ADS)

    Nazmunnahar, M.; Ryba, T.; del Val, J. J.; Ipatov, M.; González, J.; Hašková, V.; Szabó, P.; Samuely, P.; Kravcak, J.; Vargova, Z.; Varga, R.

    2015-07-01

    We have employed melt-spinning method to produce Ni2MnSn-based half-metallic Heusler alloy. It allows fast and simple production of large amount of materials in a single production step avoiding high temperature post-production annealing. Microstructural, magnetic and spin polarization study of Ni2MnSn ribbon is used for characterization. SEM analysis reveals the polycrystalline structure with the columnar crystals grown perpendicularly to the ribbon plane. A single-phase austenite with L21 structure was confirmed by X-ray. Magnetic measurements shows the ordinary ferromagnetic behavior with Curie temperature 344 K and magnetic moment 4.08 μB/f.u. Particular crystal structure leads to the well defined anisotropy having an easy plane in the ribbon's plane. Finally, the spin polarization parameter P0 estimated by Point-Contact Andreev-reflection Spectroscopy is varying in the range 40-70% for Ni2MnSn which is comparable with other values reported earlier for other Heusler alloys.

  6. Electronic structure, magnetism, and antisite disorder in CoFeCrGe and CoMnCrAl quaternary Heusler alloys

    SciTech Connect

    Enamullah, .; Venkateswara, Y.; Gupta, Sachin; Varma, Manoj Raama; Singh, Prashant; Suresh, K. G.; Alam, Aftab

    2015-12-10

    In this study, we present a combined theoretical and experimental study of two quaternary Heusler alloys CoFeCrGe (CFCG) and CoMnCrAl (CMCA), promising candidates for spintronics applications. Magnetization measurement shows the saturation magnetization and transition temperature to be 3 μB, 866 K and 0.9 μB, 358 K for CFCG and CMCA respectively. The magnetization values agree fairly well with our theoretical results and also obey the Slater-Pauling rule, a prerequisite for half metallicity. A striking difference between the two systems is their structure; CFCG crystallizes in fully ordered Y-type structure while CMCA has L21 disordered structure. The antisite disorder adds a somewhat unique property to the second compound, which arises due to the probabilistic mutual exchange of Al positions with Cr/Mn and such an effect is possibly expected due to comparable electronegativities of Al and Cr/Mn. Ab initio simulation predicted a unique transition from half metallic ferromagnet to metallic antiferromagnet beyond a critical excess concentration of Al in the alloy.

  7. Antiferromagnetism in R u2Mn Z (Z =Sn ,Sb ,Ge ,Si ) full Heusler alloys: Effects of magnetic frustration and chemical disorder

    NASA Astrophysics Data System (ADS)

    Khmelevskyi, Sergii; Simon, Eszter; Szunyogh, László

    2015-03-01

    We present systematic theoretical investigations to explore the microscopic mechanisms leading to the formation of antiferromagnetism in R u2Mn Z (Z =Sn ,Sb ,Ge ,Si ) full Heusler alloys. Our study is based on first-principles calculations of interatomic Mn-Mn exchange interactions to set up a suitable Heisenberg spin model and on subsequent Monte Carlo simulations of the magnetic properties at finite temperature. The exchange interactions are derived from the paramagnetic state, while a realistic account of long-range chemical disorder is made in the framework of the coherent potential approximation. We find that in the case of the highly ordered alloys (Z =Sn and Sb), the exchange interactions derived from the perfectly ordered L 21 structure lead to Néel temperatures in excellent agreement with the experiments, whereas, in particular in the case of Si, the consideration of chemical disorder is essential to reproduce the experimental Néel temperatures. Our numerical results suggest that by improving a heat treatment of the samples to suppress the intermixing between the Mn and Si atoms, the Néel temperature of the Si-based alloys can potentially be increased by more than 30%. Based on calculated biquadratic exchange couplings, we evidence a lifting of degeneracy of the antiferromagnetic ground states on a frustrated face-centered-cubic lattice in the fully ordered compounds. Furthermore, we show that in strongly disordered R u2MnSi alloys, a distinct change in the antiferromagnetic ordering occurs.

  8. Electronic, magnetic and thermal properties of Co2CrxFe1-xX (X=Al, Si) Heusler alloys: First-principles calculations

    NASA Astrophysics Data System (ADS)

    Guezlane, M.; Baaziz, H.; El Haj Hassan, F.; Charifi, Z.; Djaballah, Y.

    2016-09-01

    Density functional theory (DFT) based on the full-potential linearized augmented plane wave (FP-LAPW) method is used to investigate the structural, electronic, magnetic and thermal properties of Co2CrxFe1-xX (X=Al, Si) full Heusler alloys, with L21 structure. The structural properties and spin magnetic moments are investigated by the generalized gradient approximations (GGA) minimizing the total energy. For band structure calculations, GGA, the Engel-Vosko generalized gradient approximation (EVGGA) and modified Becke-Johnson (mBJ) schemes are used. Results of density of states (DOS) and band structures show that these alloys are half-metallic ferromagnets (HMFS). A regular-solution model has been used to investigate the thermodynamic stability of the compounds Co2CrxFe1-xX that indicates a phase miscibility gap. The thermal effects using the quasi-harmonic Debye model are investigated within the lattice vibrations. The temperature and pressure effects on the heat capacities, Debye temperatures and entropy are determined from the non-equilibrium Gibbs functions.

  9. Electron and phonon transport in Co-doped FeV0.6Nb0.4Sb half-Heusler thermoelectric materials

    NASA Astrophysics Data System (ADS)

    Fu, Chenguang; Liu, Yintu; Xie, Hanhui; Liu, Xiaohua; Zhao, Xinbing; Jeffrey Snyder, G.; Xie, Jian; Zhu, Tiejun

    2013-10-01

    The electron and phonon transport characteristics of n-type Fe1-xCoxV0.6Nb0.4Sb half-Heusler thermoelectric compounds is analyzed. The acoustic phonon scattering is dominant in the carrier transport. The deformation potential of Edef = 14.1 eV and the density of state effective mass m* ≈ 2.0 me are derived under a single parabolic band assumption. The band gap is calculated to be ˜0.3 eV. Electron and phonon mean free paths are estimated based on the low and high temperature measurements. The electron mean free path is higher than the phonon one above room temperature, which is consistent with the experimental result that the electron mobility decreases more than the lattice thermal conductivity by grain refinement to enhance boundary scattering. A maximum ZT value of ˜0.33 is obtained at 650 K for x = 0.015, an increase by ˜60% compared with FeVSb. The optimal doping level is found to be ˜3.0 × 1020 cm-3 at 600 K.

  10. Electronic structure, magnetism, and antisite disorder in CoFeCrGe and CoMnCrAl quaternary Heusler alloys

    DOE PAGESBeta

    Enamullah, .; Venkateswara, Y.; Gupta, Sachin; Varma, Manoj Raama; Singh, Prashant; Suresh, K. G.; Alam, Aftab

    2015-12-10

    In this study, we present a combined theoretical and experimental study of two quaternary Heusler alloys CoFeCrGe (CFCG) and CoMnCrAl (CMCA), promising candidates for spintronics applications. Magnetization measurement shows the saturation magnetization and transition temperature to be 3 μB, 866 K and 0.9 μB, 358 K for CFCG and CMCA respectively. The magnetization values agree fairly well with our theoretical results and also obey the Slater-Pauling rule, a prerequisite for half metallicity. A striking difference between the two systems is their structure; CFCG crystallizes in fully ordered Y-type structure while CMCA has L21 disordered structure. The antisite disorder adds amore » somewhat unique property to the second compound, which arises due to the probabilistic mutual exchange of Al positions with Cr/Mn and such an effect is possibly expected due to comparable electronegativities of Al and Cr/Mn. Ab initio simulation predicted a unique transition from half metallic ferromagnet to metallic antiferromagnet beyond a critical excess concentration of Al in the alloy.« less

  11. Thermal and electronic charge transport in bulk nanostructured Zr{sub 0.25}Hf{sub 0.75}NiSn composites with full-Heusler inclusions

    SciTech Connect

    Makongo, Julien P.A.; Misra, Dinesh K.; Salvador, James R.; Takas, Nathan J.; Wang, Guoyu; Shabetai, Michael R.; Pant, Aditya; Paudel, Pravin; Uher, Ctirad; Stokes, Kevin L.; Poudeu, Pierre F.P.

    2011-11-15

    Bulk Zr{sub 0.25}Hf{sub 075}NiSn half-Heusler (HH) nanocomposites containing various mole fractions of full-Heusler (FH) inclusions were prepared by solid state reaction of pre-synthesized HH alloy with elemental Ni at 1073 K. The microstructures of spark plasma sintered specimens of the HH/FH nanocomposites were investigated using transmission electron microscopy and their thermoelectric properties were measured from 300 K to 775 K. The formation of coherent FH inclusions into the HH matrix arises from solid-state Ni diffusion into vacant sites of the HH structure. HH(1-y)/FH(y) composites with mole fraction of FH inclusions below the percolation threshold, y{approx}0.2, show increased electrical conductivity, reduced Seebeck coefficient and increased total thermal conductivity arising from gradual increase in the carrier concentration for composites. A drastic reduction ({approx}55%) in {kappa}{sub l} was observed for the composite with y=0.6 and is attributed to enhanced phonon scattering due to mass fluctuations between FH and HH, and high density of HH/FH interfaces. - Graphical abstract: Large reduction in the lattice thermal conductivity of bulk nanostructured half-Heusler/full-Heusler (Zr{sub 0.25}Hf{sub 075}NiSn/ Zr{sub 0.25}Hf{sub 075}Ni{sub 2}Sn) composites, obtained by solid-state diffusion at 1073 K of elemental Ni into vacant sites of the half-Heusler structure, arising from the formation of regions of spinodally decomposed HH and FH phases with a spatial composition modulation of {approx}2 nm. Highlights: > Bulk composites from solid state transformation of half-Heusler matrix through Ni diffusion. > Formation of coherent phase boundaries between half-Heusler matrix and full-Heusler inclusion. > Alteration of thermal and electronic transports with increasing full-Heusler inclusion. > Enhanced phonon scattering at half-Heusler/ full-Heusler phase boundaries.

  12. Comparing magnetostructural transitions in Ni50Mn18.75Cu6.25Ga25 and Ni49.80Mn34.66In15.54 Heusler alloys

    NASA Astrophysics Data System (ADS)

    Dubenko, Igor; Granovsky, Alexander; Lahderanta, Erkki; Kashirin, Maxim; Makagonov, Vladimir; Aryal, Anil; Quetz, Abdiel; Pandey, Sudip; Rodionov, Igor; Samanta, Tapas; Stadler, Shane; Mazumdar, Dipanjan; Ali, Naushad

    2016-03-01

    The crystal structure, magnetic and transport properties, including resistivity and thermopower, of Ni50Mn18.75Cu6.25Ga25 and Ni49.80Mn34.66In15.54 Heusler alloys were studied in the (10-400) K temperature interval. We show that their physical properties are remarkably different, thereby pointing to different origin of their magnetostructural transition (MST). A Seebeck coefficient (S) was found to pass minimum of about -20 μV/K in respect of temperature for both compounds. It was shown that MST observed for both compounds results in jump-like changes in S for Ga-based compound and jump in resistivity of about 20 and 200 μΩ cm for Ga and In -based compounds, respectively. The combined analyzes of the present results with that from literature show that the density of states at the Fermi level does not change strongly at the MST in the case of Ni-Mn-In alloys as compared to that of Ni-Mn-Ga.

  13. Magnetic properties and atomic ordering of BCC Heusler alloy Fe2MnGa ribbons

    NASA Astrophysics Data System (ADS)

    Xin, Yuepeng; Ma, Yuexing; Luo, Hongzhi; Meng, Fanbin; Liu, Heyan

    2016-05-01

    The electronic structure, atomic disorder and magnetic properties of the Heusler alloy Fe2MnGa have been investigated experimentally and theoretically. BCC Fe2MnGa ribbon samples were prepared. Experimentally, a saturation magnetic moment (3.68 μB at 5 K) much larger than the theoretical value (2.04 μB) has been reported. First-principles calculations indicate that the difference is related to the Fe-Mn disorder between A, B sites, as can also be deduced from the XRD pattern. L21 type Fe2MnGa is a ferrimagnet with antiparallel Fe and Mn spin moments. However, when Fe-Mn disorder occurs, part of Mn moments will be parallel to Fe moments, and the Fe moments also clearly increase simultaneously. All this results in a total moment of 3.74 μB, close to the experimental value.

  14. Ab initio studies of Co2FeAl1-xSix Heusler alloys

    NASA Astrophysics Data System (ADS)

    Szwacki, N. Gonzalez; Majewski, Jacek A.

    2016-07-01

    We present results of extensive theoretical studies of Co2FeAl1-xSix Heusler alloys, which have been performed in the framework of density functional theory employing the all-electron full-potential linearized augmented plane-wave scheme. It is shown that the Si-rich alloys are more resistive to structural disorder and as a consequence Si stabilizes the L21 structure. Si alloying changes position of the Fermi level, pushing it into the gap of the minority spin-band. It is also shown that the hyperfine field on Co nuclei increases with the Si concentration, and this increase originates mostly from the changes in the electronic density of the valence electrons.

  15. Magnetic and structural anisotropies of Co2FeAl Heusler alloy epitaxial thin films

    NASA Astrophysics Data System (ADS)

    Gabor, M. S.; Petrisor, T., Jr.; Tiusan, C.; Hehn, M.; Petrisor, T.

    2011-10-01

    This paper shows the correlation between chemical order, lattice strains, and magnetic properties of Heusler Co2FeAl films epitaxially grown on MgO(001). A detailed magnetic characterization is performed using vector-field magnetometery combined with a numerical Stoner-Wohlfarth analysis. We demonstrate the presence of three types of in-plane anisotropies: one biaxial, as expected for the cubic symmetry, and two uniaxial. The three anisotropies show different behavior with the annealing temperature. The biaxial anisotropy shows a monotonic increase. The uniaxial anisotropy that is parallel to the hard biaxial axes (related to chemical homogeneity) decreases, while the anisotropy that is supposed to have a magnetostatic origin remains constant.

  16. Structural, magnetic and transport properties of Co2FeAl Heusler films with varying thickness

    NASA Astrophysics Data System (ADS)

    Wang, Xiaotian; Li, Yueqing; Du, Yin; Dai, Xuefang; Liu, Guodong; Liu, Enke; Liu, Zhongyuan; Wang, Wenhong; Wu, Guangheng

    2014-08-01

    We report on a systematic study of the structural, magnetic properties and the anomalous Hall effect, in the Heusler alloy Co2FeAl (CFA) epitaxial films on MgO (001), as a function of film thickness. It was found that the epitaxial CFA films show a highly ordered B2 structure with an in-plane uniaxial magnetic anisotropy. The electrical transport properties reveal that the lattice and magnon scattering contributions to the longitudinal resistivity. Independent on the thickness of films, the anomalous Hall resistivity of CFA films is found to be dominated by skew scattering only. Moreover, the anomalous Hall resistivity shows weakly temperature dependent behavior, and its absolute value increases as the thickness decreases. We attribute this temperature insensitivity in the anomalous Hall resistivity to the weak temperature dependent of tunneling spin-polarization in the CFA films, while the thickness dependence behavior is likely due to the increasing significance of interface or free surface electronic states.

  17. Static and dynamic magnetic properties of epitaxial Co2FeAl Heusler alloy thin films

    NASA Astrophysics Data System (ADS)

    Ortiz, G.; Gabor, M. S.; Petrisor, T., Jr.; Boust, F.; Issac, F.; Tiusan, C.; Hehn, M.; Bobo, J. F.

    2011-04-01

    Structural and magnetic properties of epitaxial Co2FeAl Heusler alloy thin films were investigated. Films were deposited on single crystal MgO (001XS) substrates at room temperature, followed by an annealing process at 600 °C. MgO and Cr buffer layers were introduced in order to enhance crystalline quality, and improve magnetic properties. Structural analyses indicate that samples have grown in the B2 ordered epitaxial structure. VSM measures show that the MgO buffered sample displays a magnetization saturation of 1010 ± 30 emu/cm3, and Cr buffered sample displays a magnetization saturation of 1032 ± 40 emu/cm3. Damping factor was studied by strip-line ferromagnetic resonance measures. We observed a maximum value for the MgO buffered sample of about 8.5 × 10-3, and a minimum value of 3.8 × 10-3 for the Cr buffered one.

  18. High tunneling magnetoresistance ratio in perpendicular magnetic tunnel junctions using Fe-based Heusler alloys

    NASA Astrophysics Data System (ADS)

    Wang, Yu-Pu; Lim, Sze-Ter; Han, Gu-Chang; Teo, Kie-Leong

    2015-12-01

    Heulser alloys Fe2Cr1-xCoxSi (FCCS) with different Co compositions x have been predicted to have high spin polarization. High perpendicular magnetic anisotropy (PMA) has been observed in ultra-thin FCCS films with magnetic anisotropy energy density up to 2.3 × 106 erg/cm3. The perpendicular magnetic tunnel junctions (p-MTJs) using FCCS films with different Co compositions x as the bottom electrode have been fabricated and the post-annealing effects have been investigated in details. An attractive tunneling magnetoresistance ratio as high as 51.3% is achieved for p-MTJs using Fe2CrSi (FCS) as the bottom electrode. The thermal stability Δ can be as high as 70 for 40 nm dimension devices using FCS, which is high enough to endure a retention time of over 10 years. Therefore, Heusler alloy FCS is a promising PMA candidate for p-MTJ application.

  19. Implicit measurement of the latent heat in a magnetocaloric NiMnIn Heusler alloy

    NASA Astrophysics Data System (ADS)

    Ghahremani, Mohammadreza; ElBidweihy, Hatem; Bennett, Lawrence H.; Della Torre, Edward; Zou, Min; Johnson, Francis

    2013-05-01

    The latent heat linked with the first-order transformation of a NiMnIn Heusler alloy has been studied through direct measurements of the adiabatic temperature change, ΔTad, during magnetization process. The experimental procedure used guarantees independent data points and negates any contribution of hysteretic losses to the magnetocaloric effect. Thus, the differences between the magnitudes of ΔTad measurements during the magnetization with the initial temperature change directions from low-to-high and high-to-low are solely attributed to the latent heat exchange, which accompanies the irreversible structural first-order transformation. An estimate of the latent heat inducing such differences is about 0.292 J/g.

  20. Electron spin resonance probed competing states in NiMnInSi Heusler alloy

    NASA Astrophysics Data System (ADS)

    Chen, Y. S.; Lin, J. G.; Titov, I. S.; Granovsky, A. B.

    2016-06-01

    Shape memory Heusler alloy Ni50Mn35In12Si3 is investigated with electron spin resonance (ESR) technique in a temperature range of 200-300 K. ESR is a dynamic probe allowing us to separate the responses from various magnetic phases, thus to study the complex phase transitions. The sample shows three transition temperatures: TcA (271 K), TM (247 K) and TcM (212 K), where TcA is the Curie temperature of austenitic phase, TM and TcM are the temperatures of magnetostructural martensitic transition and the Curie temperature of martensitic phase, respectively. Furthermore, ESR data reveals the coexistence of two magnetic modes in whole temperature range of 200-300 K. Particularly in martensitic phase, two magnetic modes are attributed to two different kinds of lattice deformation, the slip and twinning deformations.

  1. The Potential of FeVSb Half-Heusler Phase for Practical Thermoelectric Material

    NASA Astrophysics Data System (ADS)

    Yamamoto, Akio; Takeuchi, Tsunehiro

    2016-07-01

    The electronic structure and electron transport properties of FeVSb half-Heusler phase were calculated using first-principles calculations and Boltzmann transport equation. We found, as a result of theoretical calculations, that the magnitude of the dimensionless of figure of merit (ZT) could be increased up to ˜0.84 due to the drastic increase of the power factor when the carrier concentration of p-type FeVSb is optimized through element substitution to vary the valence electron concentration. We revealed that this large increase in ZT is closely related to the significant variations both in electronic density of states and spectral conductivity with decreasing energy at the top of the valence band.

  2. Exchange bias effects in Heusler alloy Ni2MnAl/Fe bilayers

    NASA Astrophysics Data System (ADS)

    Tsuchiya, Tomoki; Kubota, Takahide; Sugiyama, Tomoko; Huminiuc, Teodor; Hirohata, Atsufumi; Takanashi, Koki

    2016-06-01

    Ni2MnAl Heusler alloy thin films were epitaxially grown on MgO(1 0 0) single crystal substrates by ultra-high-vacuum magnetron sputtering technique. X-ray diffraction and transmission electron microscopy observation revealed that the structures of all the Ni2MnAl thin films were B2-ordered regardless of the deposition temperature ranging from room temperature to 600 °C. The temperature dependence of electrical resistivity showed a kink about 280 K, which was consistent with a reported value of the Néel temperature for antiferromagnetic B2-Ni2MnAl. The magnetization curves of Ni2MnAl/Fe bilayer samples showed a shift caused by the interfacial exchange interaction at 10 K. The maximum value of the exchange bias field H ex was 55 Oe corresponding to the exchange coupling energy J k of 0.03 erg cm‑2.

  3. Magnetic states of Co-, Fe- and Mn-atoms in some Heusler alloys

    NASA Astrophysics Data System (ADS)

    Kido, M.; Ido, H.; Kido, G.

    1992-02-01

    Magnetic and thermal measurements have been made for the Heusler-type alloys Co 2TiSn and Co 2TiAl. The magnetic behaviour of Co 2TiSn was found to be of a typical localized character, and the Co moment has been estimated from the saturation magnetization to be 0.99μ B(=μ f), which agrees well with the Co moment of 1.0μ B(=μ p) estimated by applying the Curie-Weiss law to the observed susceptibility (χ) vs temperature ( T) curve above TC. The magnetic behaviour of Co 2TiAl is similar to that of Co 2TiSn, however, μ p = 0.44μ B is a little larger than μ f = 0.37μ B. The difference between the magnetic properties of the above two alloys is discussed.

  4. Structural and magnetic properties of He+ irradiated Co2MnSi Heusler alloys

    NASA Astrophysics Data System (ADS)

    Abdallah, I.; Ratel-Ramond, N.; Magen, C.; Pecassou, B.; Cours, R.; Arnoult, A.; Respaud, M.; Bobo, J. F.; BenAssayag, G.; Snoeck, E.; Biziere, N.

    2016-04-01

    We have investigated the atomic disorder induced by a 150 keV He+ ion irradiation in a 40 nm thick Co2MnSi Heusler alloy. Disorder parameters on each atomic site are deduced from normal and anomalous x-ray diffraction measurements with Co and Cu Kα sources. While the film grows mainly in the L21 phase with inclusion of B2 grains, we observe an increase of both the Mn–Si and Co–Mn exchanges with the ion fluence. HAADF-STEM analysis demonstrates that the increase in Mn–Si disorder corresponds to a growing size of the B2 grains while the Co–Mn exchange is accounted for a D03 disorder type in the L21 matrix. These structural modifications are shown to decrease the average magnetization of the alloy, which is due to D03 disorder and local defects induced by irradiation.

  5. Simultaneous Large Enhancements in Thermopower and Electrical Conductivity of Bulk Nanostructured Half-Heusler Alloys

    SciTech Connect

    Makongo, Julien P. A.; Misra, Dinesh K.; Zhou, Xiaoyuan; Pant, Aditya; Shabetai, Michael R.; Su, Xianli; Uher, Ctirad; Stokes, Kevin L.; Poudeu, Pierre F. P.

    2011-10-04

    Large reductions in the thermal conductivity of thermoelectrics using nanostructures have been widely demonstrated. Some enhancements in the thermopower through nanostructuring have also been reported. However, these improvements are generally offset by large drops in the electrical conductivity due to a drastic reduction in the mobility. Here, we show that large enhancements in the thermopower and electrical conductivity of half-Heusler (HH) phases can be achieved simultaneously at high temperatures through coherent insertion of nanometer scale full-Heusler (FH) inclusions within the matrix. The enhancements in the thermopower of the HH/FH nanocomposites arise from drastic reductions in the “effective” carrier concentration around 300 K. Surprisingly, the mobility increases drastically, which compensates for the decrease in the carrier concentration and minimizes the drop in the electrical conductivity. Interestingly, the carrier concentration in HH/FH nanocomposites increases rapidly with temperature, matching that of the HH matrix at high temperatures, whereas the temperature dependence of the mobility significantly deviates from the typical T–α law and slowly decreases (linearly) with rising temperature. This remarkable interplay between the temperature dependence of the carrier concentration and mobility in the nanocomposites results in large increases in the power factor at 775 K. In addition, the embedded FH nanostructures also induce moderate reductions in the thermal conductivity leading to drastic increases in the ZT of HH(1 – x)/FH(x) nanocomposites at 775 K. By combining transmission electron microscopy and charge transport data, we propose a possible charge carrier scattering mechanism at the HH/FH interfaces leading to the observed anomalous electronic transport in the synthesized HH(1 – x)/FH(x) nanocomposites.

  6. Ab initio study of 59Co NMR spectra in Co2FeAl1-xSix Heusler alloys

    NASA Astrophysics Data System (ADS)

    Nishihara, H.; Sato, K.; Akai, H.; Takiguchi, C.; Geshi, M.; Kanomata, T.; Sakon, T.; Wada, T.

    2015-05-01

    Ab initio electronic structure calculation of a series of Co2FeAl1-xSix Heusler alloys has been performed, using the Korringa-Kohn-Rostoker-coherent potential approximation method to explain experimental 59Co NMR spectra. Two prominent features are explained semi-quantitatively-a global shift of the 59Co resonance line due to alloying with Al and Si atoms in Co2FeAl1-xSix, and the effect of local disorder in creating distinct satellite lines of 59Co NMR in Co2FeAl. The importance is stressed of the positive contribution to the 59Co hyperfine field from valence electron polarization, which emerges from the half-metallic band structure inherent in Co-based Heusler alloys.

  7. Large Linear Magnetoresistance and Shubnikov-de Hass Oscillations in Single Crystals of YPdBi Heusler Topological Insulators

    NASA Astrophysics Data System (ADS)

    Wang, Wenhong; Du, Yin; Xu, Guizhou; Zhang, Xiaoming; Liu, Enke; Liu, Zhongyuan; Shi, Youguo; Chen, Jinglan; Wu, Guangheng; Zhang, Xi-Xiang

    2013-07-01

    We report the observation of a large linear magnetoresistance (MR) and Shubnikov-de Hass (SdH) quantum oscillations in single crystals of YPdBi Heusler topological insulators. Owning to the successfully obtained the high-quality YPdBi single crystals, large non-saturating linear MR of as high as 350% at 5K and over 120% at 300 K under a moderate magnetic field of 7 T is observed. In addition to the large, field-linear MR, the samples exhibit pronounced SdH quantum oscillations at low temperature. Analysis of the SdH data manifests that the high-mobility bulk electron carriers dominate the magnetotransport and are responsible for the observed large linear MR in YPdBi crystals. These findings imply that the Heusler-based topological insulators have superiorities for investigating the novel quantum transport properties and developing the potential applications.

  8. Nature of electron correlation and hybridization in NixCu1-xMnSb Heusler alloys

    NASA Astrophysics Data System (ADS)

    Sarkar, I.; Yusuf, S. M.; Halder, M.; Gloskovskii, A.; Drube, W.

    2016-08-01

    The electronic structure of Heusler alloys having mixed magnetic phases, comprising of vicinal anti-ferromagnetic and ferromagnetic orders, is of great significance. We present the results of an electronic structure study on NixCu1-xMnSb Heusler alloys, using Mn-2p core-level photoemission spectroscopy. Room temperature data in the paramagnetic phase reveal a non-monotonic variation of both electron correlation strength and conduction-band hybridization such that the former enhances while the latter weakens for compositions showing a mixed phase relative to compositions at the phase boundaries to the ordered phases. The results suggest a possible electronic driving force for settling mixed-magnetic phases.

  9. Anti-site disorder and improved functionality of Mn₂NiX (X = Al, Ga, In, Sn) inverse Heusler alloys

    SciTech Connect

    Paul, Souvik; Kundu, Ashis; Ghosh, Subhradip; Sanyal, Biplab

    2014-10-07

    Recent first-principles calculations have predicted Mn₂NiX (X = Al, Ga, In, Sn) alloys to be magnetic shape memory alloys. Moreover, experiments on Mn₂NiGa and Mn₂NiSn suggest that the alloys deviate from the perfect inverse Heusler arrangement and that there is chemical disorder at the sublattices with tetrahedral symmetry. In this work, we investigate the effects of such chemical disorder on phase stabilities and magnetic properties using first-principles electronic structure methods. We find that except Mn₂NiAl, all other alloys show signatures of martensitic transformations in presence of anti-site disorder at the sublattices with tetrahedral symmetry. This improves the possibilities of realizing martensitic transformations at relatively low fields and the possibilities of obtaining significantly large inverse magneto-caloric effects, in comparison to perfect inverse Heusler arrangement of atoms. We analyze the origin of such improvements in functional properties by investigating electronic structures and magnetic exchange interactions.

  10. First-principles study of spin-dependent thermoelectric properties of half-metallic Heusler thin films between platinum leads

    NASA Astrophysics Data System (ADS)

    Comtesse, Denis; Geisler, Benjamin; Entel, Peter; Kratzer, Peter; Szunyogh, László

    2014-03-01

    The electronic and magnetic bulk properties of half-metallic Heusler alloys such as Co2FeSi,Co2FeAl, Co2MnSi, and Co2MnAl are investigated by means of ab initio calculations in combination with Monte Carlo simulations. The electronic structure is analyzed using the plane-wave code quantum espresso and the magnetic exchange interactions are determined using the Korringa-Kohn-Rostoker (KKR) method. From the magnetic exchange interactions, the Curie temperature is obtained via Monte Carlo simulations. In addition, electronic transport properties of trilayer systems consisting of two semi-infinite platinum leads and a Heusler layer in-between are obtained from the fully relativistic screened KKR method by employing the Kubo-Greenwood formalism. The focus is on thermoelectric properties, namely, the Seebeck effect and its spin dependence. It turns out that already thin Heusler layers provide highly spin-polarized currents. This is attributed to the recovery of half-metallicity with increasing layer thickness. The absence of electronic states of spin-down electrons around the Fermi level suppresses the contribution of this spin channel to the total conductance, which strongly influences the thermoelectric properties and results in a spin polarization of thermoelectric currents.

  11. Electronic and Magneto-Transport Across the Heusler Alloy (Co2FeAl)/ p-Si Interfacial Structure

    NASA Astrophysics Data System (ADS)

    Kumar, Arvind; Srivastava, P. C.

    2014-02-01

    Electronic and magneto-transport across the Heusler alloy Co2FeAl (CFA)/ p-Si structure have been studied. The morphology of the Heusler alloy film surface has also been characterized by atomic force microscopy and magnetic force microscopy (MFM). X-ray diffraction data revealed formation of the CFA alloy phase with the L21 structure. MFM results revealed formation of a fine domain structure of average size ˜10 nm and magnetic signal strength 0.23°. The I- V characteristics are strongly temperature-dependent between ˜80 K and 300 K for forward bias, compared with weak temperature dependence on reversing the polarity. At low temperature the I- V characteristics have the features of a backward diode. The observed strong temperature dependence is because of thermionic emission of carriers across the interface. The weak temperature dependence is because of dominant field-emission tunnelling of carriers across the interface. Large magnetic field sensitivity of the reverse current has also been observed. The observed magnetic field sensitivity for the reverse current shows the involvement of electronic spin in transport across the interface, from the Heusler alloy to the silicon. An MR of ˜35% in the presence of a magnetic field was estimated from the I- V data. The study has shown that spin-dependent tunnel transport from the CFA alloy to silicon across the interface results in the observed value of MR, which seems to be because of spin scattering.

  12. Magnetic and anomalous electronic transport properties of the quaternary Heusler alloys Co2Ti1-xFexGe

    NASA Astrophysics Data System (ADS)

    Venkateswarlu, B.; Midhunlal, P. V.; Babu, P. D.; Kumar, N. Harish

    2016-06-01

    The half-metallic Heusler alloy Co2TiGe has a ferromagnetic ground state with a low magnetic moment (2 μB). It is free of atomic antisite disorder but has low Curie temperature (~390 K). In contrast the other cobalt based Heusler alloy Co2FeGe has high Curie temperature (~980 K) and high magnetic moment (5.6 μB) while exhibiting antisite disorder and lack of half-metallicity. Hence it is of interest to investigate the magnetic and transport properties of solid solutions of these two materials with contrasting characteristics. We report the structural, magnetic and electronic transport properties of quaternary Co2Ti1-x FexGe (x=0.2, 0.4, 0.6, 0.8) Heusler alloys. The alloys crystallize in L21 structure but with antisite disorder. The magnetization measurements revealed that the alloys were of soft ferromagnetic type with high Curie temperatures. Deviation from Slater-Pauling behavior and drastic change in electronic transport properties with some anomalous features were observed.The complex electronic transport properties have been explained using different scattering mechanisms.

  13. First-principles studies of the Gilbert damping and exchange interactions for half-metallic Heuslers alloys

    NASA Astrophysics Data System (ADS)

    Chico, Jonathan; Keshavarz, Samara; Kvashnin, Yaroslav; Pereiro, Manuel; Di Marco, Igor; Etz, Corina; Eriksson, Olle; Bergman, Anders; Bergqvist, Lars

    2016-06-01

    Heusler alloys have been intensively studied due to the wide variety of properties that they exhibit. One of these properties is of particular interest for technological applications, i.e., the fact that some Heusler alloys are half-metallic. In the following, a systematic study of the magnetic properties of three different Heusler families Co2Mn Z ,Co2FeZ , and Mn2V Z with Z=(Al,Si,Ga,Ge) is performed. A key aspect is the determination of the Gilbert damping from first-principles calculations, with special focus on the role played by different approximations, the effect that substitutional disorder and temperature effects. Heisenberg exchange interactions and critical temperature for the alloys are also calculated as well as magnon dispersion relations for representative systems, the ferromagnetic Co2Fe Si and the ferrimagnetic Mn2V Al . Correlation effects beyond standard density-functional theory are treated using both the local spin density approximation including the Hubbard U and the local spin density approximation plus dynamical mean field theory approximation, which allows one to determine if dynamical self-energy corrections can remedy some of the inconsistencies which were previously reported for these alloys.

  14. Current-perpendicular-to-plane giant magnetoresistive properties in Co2Mn(Ge0.75Ga0.25)/Cu2TiAl/Co2Mn(Ge0.75Ga0.25) all-Heusler alloy pseudo spin valve

    NASA Astrophysics Data System (ADS)

    Li, S.; Takahashi, Y. K.; Sakuraba, Y.; Chen, J.; Furubayashi, T.; Mryasov, O.; Faleev, S.; Hono, K.

    2016-03-01

    Nonmagnetic Cu2TiAl (CTA) Heusler compound is proposed as a new spacer material for all-Heusler alloy current-perpendicular-to-plane giant magnetoresistance devices based on first-principle calculations. The (001)-orientated Co2Mn(Ge0.75Ga0.25) (CMGG)/CTA/CMGG epitaxial pseudo spin valve (PSV) grown on MgO(100) single crystal substrate showed relatively large MR output, ΔR A ˜5.4 mΩ μm2, which is comparable to that of the CMGG/Ag/CMGG PSV prepared with the same condition. Considering the short spin diffusion length in CTA, this result indicates a better electronic band matching for the CTA/CMGG interface than the Ag/CMGG interface in agreement with the first-principle calculation results. (001)- and (011)-orientated CMGG/CTA/CMGG PSV show similar MR outputs, indicating that the CTA spacer suppresses the orientation dependence of MR output which is usually observed in Ag-spacer CPP-PSV.

  15. Stability analysis of the martensitic phase transformation in Co2NiGa Heusler alloy

    NASA Astrophysics Data System (ADS)

    Talapatra, Anjana; Arróyave, Raymundo; Entel, Peter; Valencia-Jaime, I.; Romero, Aldo H.

    2015-08-01

    Phase competition and the subsequent phase selection are important characteristics of alloy systems exhibiting numerous states of distinct symmetry but comparable energy. The stoichiometric Co2NiGa Heusler alloy exhibits a martensitic transformation with concomitant reduction in symmetry from an austenitic L 21 phase (cubic) to a martensitic L 10 phase (tetragonal). A structural search was carried out for this alloy and it showed the existence of a number of structures with monoclinic and orthorhombic symmetry with ground state energies comparable to and even less than that of the L 10 structure, usually reported as the ground state at low temperatures. We describe these structures and focus in particular on the structural transition path from the L 21 to tetragonal and orthorhombic structures for this material. Calculations were carried out to study the Bain (L 21-L 10 ) and Burgers (L 21-hcp ) transformations. The barrierless Burgers path yielded a stable martensitic phase with orthorhombic symmetry (O ) with energy much lower—beyond the expected uncertainty of the calculation methods—than the known tetragonal L 10 martensitic structure. This low-energy structure (O ) has yet to be observed experimentally and it is thus of scientific interest to discern the cause for the apparent discrepancy between experiments and calculations. It is postulated that the Co2NiGa Heusler system exhibits a classic case of the phase selection problem: although the unexpected O phase may be relatively more stable than the L 10 phase, the energy barrier for the (L 21-O ) transformation may be much higher than the barrier to the (L 21-L 10 ) transformation. To validate this hypothesis, the stability of this structure was investigated by considering the contributions of elastic and vibrational effects, configurational disorder, magnetic disorder, and atomic disorder. The calculations simulating the effect of magnetic disorder/high temperature as well as the atomic disorder

  16. Correlation between processing conditions, microstructure and charge transport in half-Heusler alloys

    SciTech Connect

    Makongo, Julien P.A.; Zhou, Xiaoyuan; Misra, Dinesh K.; Uher, Ctirad; Poudeu, Pierre F.P.

    2013-05-01

    Five bulk samples of n-type Zr₀.₂₅Hf₀.₇₅NiSn₀.₉₇₅Sb₀.₀₂₅ half-Heusler (HH) alloy were fabricated by reacting elemental powders via (1) high temperature solid state (SS) reaction and (2) mechanical alloying (MA), followed by densification using spark plasma sintering (SPS) and/or hot pressing (HP). A portion of the sample obtained by SS reaction was mechanically alloyed before consolidation by hot pressing (SS–MA–HP). X-ray powder diffraction and transmission electron microscopy studies revealed that all SS specimen (SS–SPS, SS–HP, SS–MA–HP) are single phase HH alloys, whereas the MA sample (MA–SPS) contains metallic nanoprecipitates. Electronic and thermal transport measurements showed that the embedded nanoprecipitates induce a drastic increase in the carrier concentration (n), a large decrease in the Seebeck coefficient (S) and a marginal decrease in the lattice thermal conductivity (κl) of the MA–SPS sample leading to lower ZT values when compared to the SS–HP samples. Constant values of S are observed for the SS series regardless of the processing method. However, a strong dependence of the carrier mobility (μ), electrical conductivity (σ) and κl on the processing and consolidation method is observed. For instance, mechanical alloying introduces additional structural defects which enhance electron and phonon scattering leading to moderately low values of μ and large reduction in κl. This results in a net 20% enhancement in the figure of merit (ZT=0.6 at 775 K). HH specimen of the same nominal composition with higher ZT is anticipated from a combination of SS reaction, MA and SPS (SS–MA–SPS). - Graphical abstract: In half-Heusler alloys, thermopower values are insensitive to processing method, whereas carrier mobility (μ), electrical conductivity (σ), and κl strongly dependent on the microstructure which in turn is altered by the synthesis, processing and

  17. Electronic structure, magnetic properties and electrical resistivity of the Fe2V1-xTixAl Heusler alloys: experiment and calculation

    NASA Astrophysics Data System (ADS)

    Slebarski, A.; Goraus, J.; Deniszczyk, J.; Skoczen, L.

    2006-11-01

    The aim of this work is to investigate electronic structure, magnetic properties and electrical resistivity of Fe2V1-xTixAl Heusler alloys. Numerical calculations give a pseudogap at the Fermi level for the majority-spin band of Fe2TiAl and a magnetic moment larger than 0.9 μB, whereas the ground state of Fe2VAl is calculated as a nonmagnetic semimetal with a very low total density of states at the Fermi level. In our calculations the remaining alloys of the Fe2V1-xTixAl series are nonmagnetic for x<0.1 and weakly magnetic for 0.1compounds scales with the number of valence electrons and fits well to the Slater-Pauling curve. We also present a study of the electronic transport properties and magnetic susceptibility. The resistivities ρ(T) of Fe2VAl and Fe2V0.9Ti0.1Al are large and exhibit a negative temperature coefficient dρ/dT of the resistivity between 2 and 300 K. Below 20 K, ρ(T) also shows an activated character. The magnetic susceptibility of Fe2VAl and Fe2V0.9Ti0.1Al shows a maximum at ~2 K which could reflect either the disorder effect or the hybridization gap, characteristic of Kondo insulators.

  18. Electronic structure, magnetic properties and electrical resistivity of the Fe(2)V(1-x)Ti(x)Al Heusler alloys: experiment and calculation.

    PubMed

    Slebarski, A; Goraus, J; Deniszczyk, J; Skoczeń, L

    2006-11-22

    The aim of this work is to investigate electronic structure, magnetic properties and electrical resistivity of Fe(2)V(1-x)Ti(x)Al Heusler alloys. Numerical calculations give a pseudogap at the Fermi level for the majority-spin band of Fe(2)TiAl and a magnetic moment larger than 0.9 μ(B), whereas the ground state of Fe(2)VAl is calculated as a nonmagnetic semimetal with a very low total density of states at the Fermi level. In our calculations the remaining alloys of the Fe(2)V(1-x)Ti(x)Al series are nonmagnetic for x<0.1 and weakly magnetic for 0.1compounds scales with the number of valence electrons and fits well to the Slater-Pauling curve. We also present a study of the electronic transport properties and magnetic susceptibility. The resistivities ρ(T) of Fe(2)VAl and Fe(2)V(0.9)Ti(0.1)Al are large and exhibit a negative temperature coefficient dρ/dT of the resistivity between 2 and 300 K. Below 20 K, ρ(T) also shows an activated character. The magnetic susceptibility of Fe(2)VAl and Fe(2)V(0.9)Ti(0.1)Al shows a maximum at ∼2 K which could reflect either the disorder effect or the hybridization gap, characteristic of Kondo insulators. PMID:21690920

  19. Interfacial exchange coupling in cubic Heusler Co2FeZ (Z = Al and Si)/tetragonal Mn3Ga bilayers

    NASA Astrophysics Data System (ADS)

    Ranjbar, R.; Suzuki, K.; Sugihara, A.; Ma, Q. L.; Zhang, X. M.; Miyazaki, T.; Ando, Y.; Mizukami, S.

    2015-05-01

    We have fabricated bilayer films of tetragonal Heusler-like D022 Mn3Ga and cubic Heusler Co2FeZ (Z = Si and Al) on (100) single-crystalline MgO substrates and investigated their structural and interfacial exchange coupling. The coupling in the Mn3Ga/Co2FeAl bilayer was either ferromagnetic or antiferromagnetic, depending on annealing temperature, whereas only antiferromagnetic exchange coupling was observed in the Mn3Ga/Co2FeSi bilayers. The effects of annealing on the structure and coupling strength in the bilayers are discussed.

  20. Magnetic and half-metallic properties of the full-Heusler alloys Co2TiX(X=Al,Ga;Si,Ge,Sn;Sb)

    NASA Astrophysics Data System (ADS)

    Lee, S. C.; Lee, T. D.; Blaha, P.; Schwarz, K.

    2005-05-01

    The electronic structure and magnetic properties of the full-Heusler alloys Co2TiX (X element from groups III, IV and V) were studied by first principle calculations. Previous calculations found Co2TiAl and Co2TiSn not to be half metallic. In this paper, however, it will be shown that the alloys with X =Al,Si,Ge,Sn are half metallic and ferromagnetic. The effect of atomic disorder in the Ti-Al sublattices reduces the half metallicity of the Co2TiAl Heusler alloy.

  1. Magnetocrystalline anisotropy and its electric-field-assisted switching of Heusler-compound-based perpendicular magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Bai, Zhaoqiang; Shen, Lei; Cai, Yongqing; Wu, Qingyun; Zeng, Minggang; Han, Guchang; Feng, Yuan Ping

    2014-10-01

    Employing density functional theory combined with the non-equilibrium Green's function formalism, we systematically investigate the structural, magnetic and magnetoelectric properties of the Co2FeAl(CFA)/MgO interface, as well as the spin-dependent transport characteristics of the CFA/MgO/CFA perpendicular magnetic tunnel junctions (p-MTJs). We find that the structure of the CFA/MgO interface with the oxygen-top FeAl termination has high thermal stability, which is protected by the thermodynamic equilibrium limit. Furthermore, this structure is found to have perpendicular magnetocrystalline anisotropy (MCA). Giant electric-field-assisted modifications of this interfacial MCA through magnetoelectric coupling are demonstrated with an MCA coefficient of up to 10-7 erg V-1 cm. In addition, our non-collinear spin transport calculations of the CFA/MgO/CFA p-MTJ predict a good magnetoresistance performance of the device.

  2. Spin transport at high temperatures in epitaxial Heusler alloy/n-GaAs lateral spin valves

    NASA Astrophysics Data System (ADS)

    Peterson, Timothy A.; Christie, Kevin D.; Patel, Sahil J.; Crowell, Paul A.; Palmstrøm, Chris J.

    2015-03-01

    We report on electrical injection and detection of spin accumulation in ferromagnet/ n-GaAs lateral spin-valve devices, observed up to and above room temperature. The ferromagnet in these measurements is the Heusler alloy Co2FeSi, and the semiconductor channel is GaAs doped at 3 ×1016 cm-3. The spin signal is enhanced by operating the detection contact under forward bias. The enhancement originates from drift effects at low-temperatures and an increase of the detection efficiency at all temperatures. The detector bias dependence of the observed spin-valve signal is interpreted by taking into account the quantum well (QW) which forms in the degenerately doped region immediately behind the Schottky tunnel barrier. In particular, we believe the QW is responsible for the minority spin accumulation (majority spin current) under large forward bias. The spin diffusion length and lifetime are determined by measuring the separation dependence of the non-local spin valve signal in a family of devices patterned by electron beam lithography. A spin diffusion length of 700 nm and lifetime of 46 picoseconds are found at a temperature of 295 K. This work was supported by the NSF under DMR-1104951, the NSF MRSEC program and C-SPIN, a SRC STARNET center sponsored by MARCO and DARPA.

  3. Magnetic and superconducting phase diagram of the half-Heusler topological semimetal HoPdBi.

    PubMed

    Nikitin, A M; Pan, Y; Mao, X; Jehee, R; Araizi, G K; Huang, Y K; Paulsen, C; Wu, S C; Yan, B H; de Visser, A

    2015-07-15

    We report a study of the magnetic and electronic properties of the non-centrosymmetric half-Heusler antiferromagnet HoPdBi (TN = 2.0 K). Magnetotransport measurements show HoPdBi has a semimetallic behavior with a carrier concentration n = 3.7 × 10(18) cm(-3) extracted from the Shubnikov-de Haas effect. The magnetic phase diagram in the field-temperature plane has been determined by transport, magnetization, and thermal expansion measurements: magnetic order is suppressed at BM ~ 3.6 T for T --> 0. Superconductivity with Tc ~ 1.9 K is found in the antiferromagnetic phase. Ac-susceptibility measurements provide solid evidence for bulk superconductivity below Tc = 0.75 K with a screening signal close to a volume fraction of 100%. The upper critical field shows an unusual linear temperature variation with Bc2(T --> 0) = 1.1 T. We also report electronic structure calculations that classify HoPdBi as a new topological semimetal, with a non-trivial band inversion of 0.25 eV. PMID:26086396

  4. Electronic structures and the spin polarization of Heusler alloy Co2FeAl surface

    NASA Astrophysics Data System (ADS)

    Xu, Xiaoguang; Wang, Yankai; Zhang, Delin; Jiang, Yong

    2011-01-01

    The electronic structures of the Heusler alloy Co2FeAl surface are studied theoretically via first-principles calculations. The space localization of the surface states is the key effect on the electronic structures of the Co2FeAl surface. At the surface, the lattice parameter shrinks to minimize the total energy, and the minority spin gap disappears and shows a metallic band gap character. However, with the depth increasing, the lattice parameter equals to that of bulk phase, and there shows an energy gap opening at the Fermi level in the minority spin states. As a result, the spin polarization at the surface is lower than that of the bulk Co2FeAl, while it is close to that of bulk phase beneath the surface. According to the calculations, it is clear that the half-metallic property fading of the Co2FeAl films is caused by the surface states. Therefore, it is important to minimize the lattice mismatch at the interface of Co2FeAl in order to obtain a high tunneling magnetoresistance.

  5. First principles investigation of magnetocrystalline anisotropy at Full Heusler / MgO interfaces

    NASA Astrophysics Data System (ADS)

    Vadapoo, Rajasekarakumar; Hallal, Ali; Chshiev, Mairbek

    2014-03-01

    Magnetic tunnel junctions with perpendicular magnetic anisotropy (PMA) have the potential for realizing next generation high density nonvolatile memories and logic devices. The origin of high PMA in these interfaces has been explained by orbital hybridizations at interface along with spin-orbit interactions. Here we present a systematic study of PMA in Heusler alloy [X2YZ]/ MgO interfaces using first principle methods with X =Co, YZ =FeAl, MnGe and MnSi. Among the interfaces studied, we found that Co terminated interface of Co2FeAl/MgO gives rise to PMA value of 1.2erg/cm2 in agreement with recent experimental observations. On the contrary, FeAl terminated interfaces of the same structure shows in-plane magnetic anisotropy (IMA). We also found that the most of PMA contribution originates from dyz and dz2 orbitals of Co atoms at the interface. Finally, Co2MnGe and Co2MnSi structures tend to favor IMA for any termination.

  6. Synthesis and characterization of Co2FeAl Heusler alloy nanoparticles

    NASA Astrophysics Data System (ADS)

    Kumar, Arvind; Srivastava, P. C.

    2013-10-01

    Heusler alloy Co2FeAl (CFA) nanoparticles have been synthesized by reducing a mixture of the precursors: CoCl2·6H2O, Fe(NO3)3·9H2O and AlCl3·6H2O under H2 atmosphere. XRD, SEM and TEM techniques have been used for the characterization of the prepared material. XRD and SAED data from TEM show the formation of mixed phases of L21, B2 and A2 type crystal structure of the alloy. The estimated particle size from XRD data and TEM micrograph has been found in the range of 10 nm to 50 nm. The saturation magnetization has been found of 115 emu/g from M-H characteristics which is close to its bulk value of saturation magnetization. Chemical composition of the elements has also been estimated from EDAX, which shows a ratio of Co:Fe:Al as 2.12:1.06:0.81.

  7. High spin polarization and spin splitting in equiatomic quaternary CoFeCrAl Heusler alloy

    NASA Astrophysics Data System (ADS)

    Bainsla, Lakhan; Mallick, A. I.; Coelho, A. A.; Nigam, A. K.; Varaprasad, B. S. D. Ch. S.; Takahashi, Y. K.; Alam, Aftab; Suresh, K. G.; Hono, K.

    2015-11-01

    In this paper, we investigate CoFeCrAl alloy by means of ab-initio electronic structure calculations and various experimental techniques. The alloy is found to exist in the B2-type cubic Heusler structure, which is very similar to Y-type (or LiMgPdSn prototype) structure with space group F-43m (#216). Saturation magnetization (MS) of about 2 μB/f.u. is observed at 8 K under ambient pressure, which is in good agreement with the Slater-Pauling rule. MS values are found to be independent of pressure, which is a prerequisite for half-metals. The ab-initio electronic structure calculations predict half-metallicity for the alloy with a spin slitting energy of 0.31 eV. Importantly, this system shows a high current spin polarization value of 0.67±0.02, as deduced from the point contact Andreev reflection measurements. Linear dependence of electrical resistivity with temperature indicates the possibility of reasonably high spin polarization at elevated temperatures (~150 K) as well. All these suggest that CoFeCrAl is a promising material for the spintronic devices.

  8. Half-metallicity and tetragonal distortion in semi-Heusler alloy FeCrSe

    SciTech Connect

    Huang, H. M. Luo, S. J.; Yao, K. L.

    2014-01-28

    Full-potential linearized augmented plane wave methods are carried out to investigate the electronic structures and magnetic properties in semi-Heusler alloy FeCrSe. Results show that FeCrSe is half-metallic ferromagnet with the half-metallic gap 0.31 eV at equilibrium lattice constant. Calculated total magnetic moment of 2.00μ{sub B} per formula unit follows the Slater-Pauling rule quite well. Two kinds of structural changes are used to investigate the sensitivity of half-metallicity. It is found that the half-metallicity can be retained when lattice constant is changed by −4.56% to 3.52%, and the results of tetragonal distortion indicate the half-metallicity can be kept at the range of c/a ratio from 0.85 to 1.20. The Curie temperature, cohesive energy, and heat of formations of FeCrSe are also discussed.

  9. Domain wall dynamics of periodic magnetic domain patterns in Co2MnGe-Heusler microstripes

    NASA Astrophysics Data System (ADS)

    Gross, K.; Westerholt, K.; Zabel, H.

    2016-03-01

    Highly symmetric periodic domain patterns were obtained in Co2MnGe-Heusler microstripes as a result of the competition between growth-induced in-plane magnetic anisotropy and shape anisotropy. Zero field magnetic configurations and magnetic field-induced domain wall (DW) motion were studied by magnetic force microscopy-image technique for two different cases: dominant uniaxial- and dominant cubic in-plane anisotropy. We implemented a magneto-optical Kerr effect susceptometer to investigate the DW dynamics of periodic domain structures by measuring the in-phase and out-of-phase components of the Kerr signal as a function of magnetic field frequency and amplitude. The DW dynamics for fields applied transversally to the long stripe axis was found to be dominated by viscous slide motion. We used the inherent symmetry/periodicity properties of the magnetic domain structure to fit the experimental results with a theoretical model allowing to extract the DW mobility for the case of transverse DWs (μ TDW = 1.1 m s-1 Oe-1) as well as for vortex-like DWs (μ VDW = 8.7 m s-1 Oe-1). Internal spin structure transformations may cause a reduction of DW mobility in TDWs as observed by OMMFF simulations.

  10. On the Challenges of Reducing Contact Resistances in Thermoelectric Generators Based on Half-Heusler Alloys

    NASA Astrophysics Data System (ADS)

    Ngan, Pham Hoang; Van Nong, Ngo; Hung, Le Thanh; Balke, Benjamin; Han, Li; Hedegaard, Ellen Marie Jensen; Linderoth, Søren; Pryds, Nini

    2016-01-01

    A method using fast hot pressing to join half-Heusler (HH) thermoelectric materials directly to an electrical current collector (Ag electrode) without using a third filler material is introduced. The compositions of the HH alloys used are Hf0.5Zr0.5CoSn0.2Sb0.8 and Ti0.6Hf0.4NiSn for p- and n-type, respectively. Using this method, the quality of the HH-electrode contacts is improved due to their low electrical contact resistance and less reaction-diffusion layer. The microstructure and chemical composition of the joints were examined using a scanning electron microscope equipped with energy-dispersive x-ray analysis. The electrical characteristics of the interfaces at the contacts were studied based on electrical contact resistance and Seebeck scanning microprobe measurements. In this paper, we show that joining the HH to a Ag electrode directly using fast hot pressing resulted in lower contact resistance and better performance compared with the method of using active brazing filler alloy.

  11. Room-temperature tetragonal non-collinear Heusler antiferromagnet Pt2MnGa.

    PubMed

    Singh, Sanjay; D'Souza, S W; Nayak, J; Suard, E; Chapon, L; Senyshyn, A; Petricek, V; Skourski, Y; Nicklas, M; Felser, C; Chadov, S

    2016-01-01

    Antiferromagnetic spintronics is a rapidly growing field, which actively introduces new principles of magnetic storage. Despite that, most applications have been suggested for collinear antiferromagnets. In this study, we consider an alternative mechanism based on long-range helical order, which allows for direct manipulation of the helicity vector. As the helicity of long-range homogeneous spirals is typically fixed by the Dzyaloshinskii-Moriya interactions, bi-stable spirals (left- and right-handed) are rare. Here, we report a non-collinear room-temperature antiferromagnet in the tetragonal Heusler group. Neutron diffraction reveals a long-period helix propagating along its tetragonal axis. Ab-initio analysis suggests its pure exchange origin and explains its helical character resulting from a large basal plane magnetocrystalline anisotropy. The actual energy barrier between the left- and right-handed spirals is relatively small and might be easily overcome by magnetic pulse, suggesting Pt2MnGa as a potential candidate for non-volatile magnetic memory. PMID:27561795

  12. Room-temperature tetragonal non-collinear Heusler antiferromagnet Pt2MnGa

    PubMed Central

    Singh, Sanjay; D'Souza, S. W.; Nayak, J.; Suard, E.; Chapon, L.; Senyshyn, A.; Petricek, V.; Skourski, Y.; Nicklas, M.; Felser, C.; Chadov, S.

    2016-01-01

    Antiferromagnetic spintronics is a rapidly growing field, which actively introduces new principles of magnetic storage. Despite that, most applications have been suggested for collinear antiferromagnets. In this study, we consider an alternative mechanism based on long-range helical order, which allows for direct manipulation of the helicity vector. As the helicity of long-range homogeneous spirals is typically fixed by the Dzyaloshinskii–Moriya interactions, bi-stable spirals (left- and right-handed) are rare. Here, we report a non-collinear room-temperature antiferromagnet in the tetragonal Heusler group. Neutron diffraction reveals a long-period helix propagating along its tetragonal axis. Ab-initio analysis suggests its pure exchange origin and explains its helical character resulting from a large basal plane magnetocrystalline anisotropy. The actual energy barrier between the left- and right-handed spirals is relatively small and might be easily overcome by magnetic pulse, suggesting Pt2MnGa as a potential candidate for non-volatile magnetic memory. PMID:27561795

  13. Perpendicular magnetic anisotropy in Fe2Cr1 - xCoxSi Heusler alloy

    NASA Astrophysics Data System (ADS)

    Wang, Yu-Pu; Qiu, Jin-Jun; Lu, Hui; Ji, Rong; Han, Gu-Chang; Teo, Kie-Leong

    2014-12-01

    Perpendicular magnetic anisotropy (PMA) was achieved in annealed Fe2Cr1 - xCoxSi (FCCS) Heusler alloys with different Co compositions x. The Co composition is varied to tune the Fermi level in order to achieve both higher spin polarization and better thermal stability. The PMA is thermally stable up to 400 oC for FCCS with x = 0, 0.3, 0.5 and 350 oC for FCCS with x = 0.7, 0.9, 1. The thickness of FCCS films with PMA ranges from 0.6 to 1.2 nm. The annealing temperature and FCCS thickness are found to greatly affect the PMA. The magnetic anisotropy energy density KU is 2.8  ×  106 erg cm-3 for 0.8 nm Fe2CrSi, and decreases as the Co composition x increases, suggesting that the PMA induced at the FCCS/MgO interface is dominated by the contribution of Fe atoms. There is a trade-off between high spin polarization and strong PMA by adjusting the Co composition.

  14. Molecular beam epitaxy growth and magnetic properties of Cr-Co-Ga Heusler alloy films

    SciTech Connect

    Feng, Wuwei Wang, Weihua; Zhao, Chenglong; Van Quang, Nguyen; Cho, Sunglae; Dung, Dang Duc

    2015-11-15

    We have re-investigated growth and magnetic properties of Cr{sub 2}CoGa films using molecular beam epitaxy technique. Phase separation and precipitate formation were observed experimentally again in agreement with observation of multiple phases separation in sputtered Cr{sub 2}CoGa films by M. Meinert et al. However, significant phase separation could be suppressed by proper control of growth conditions. We showed that Cr{sub 2}CoGa Heusler phase, rather than Co{sub 2}CrGa phase, constitutes the majority of the sample grown on GaAs(001) at 450 {sup o}C. The measured small spin moment of Cr{sub 2}CoGa is in agreement with predicted HM-FCF nature; however, its Curie temperature is not as high as expected from the theoretical prediction probably due to the off-stoichiometry of Cr{sub 2}CoGa and the existence of the disorders and phase separation.

  15. Resonant impurity states in chemically disordered half-Heusler Dirac semimetals

    NASA Astrophysics Data System (ADS)

    Chadova, K.; Ködderitzsch, D.; Minár, J.; Ebert, H.; Kiss, J.; D'Souza, S. W.; Wollmann, L.; Felser, C.; Chadov, S.

    2016-05-01

    We address the electron transport characteristics in bulk half-Heusler alloys with their compositions tuned to the borderline between topologically nontrivial semimetallic and trivial semiconducting phases. Accurate first-principles calculations based on the coherent potential approximation (CPA) reveal that all the studied systems exhibit sets of dispersionless impurity-like resonant levels, with one of them being located at the Dirac point. By means of the Kubo-Bastin formalism we reveal that the residual conductivity of these alloys is strongly suppressed by impurity scattering, whereas the spin Hall conductivity exhibits a rather complex behavior induced by the resonant states. In particular for LaPt0.5Pd0.5Bi we find that the total spin Hall conductivity is strongly suppressed by two large and opposite contributions: the negative Fermi-surface contribution produced by the resonant impurity and the positive Fermi-sea term stemming from the occupied states. At the same time, we identify no conductivity contributions from the conical states.

  16. High tunneling magnetoresistance ratio in perpendicular magnetic tunnel junctions using Fe-based Heusler alloys

    SciTech Connect

    Wang, Yu-Pu; Lim, Sze-Ter; Han, Gu-Chang; Teo, Kie-Leong

    2015-12-21

    Heulser alloys Fe{sub 2}Cr{sub 1−x}Co{sub x}Si (FCCS) with different Co compositions x have been predicted to have high spin polarization. High perpendicular magnetic anisotropy (PMA) has been observed in ultra-thin FCCS films with magnetic anisotropy energy density up to 2.3 × 10{sup 6 }erg/cm{sup 3}. The perpendicular magnetic tunnel junctions (p-MTJs) using FCCS films with different Co compositions x as the bottom electrode have been fabricated and the post-annealing effects have been investigated in details. An attractive tunneling magnetoresistance ratio as high as 51.3% is achieved for p-MTJs using Fe{sub 2}CrSi (FCS) as the bottom electrode. The thermal stability Δ can be as high as 70 for 40 nm dimension devices using FCS, which is high enough to endure a retention time of over 10 years. Therefore, Heusler alloy FCS is a promising PMA candidate for p-MTJ application.

  17. Half-metallicity in Heusler-type Fe2Cr1-x Co x Si alloys

    NASA Astrophysics Data System (ADS)

    Ramudu, M.; Inamdar, Swaleha; Arout Chelvane, J.; Manivel Raja, M.; Kamat, S. V.

    2016-02-01

    The effects of the substitution of Cr with Co on microstructure, phase composition, structure, magnetic, and electrical properties in \\text{F}{{\\text{e}}2}\\text{C}{{\\text{r}}1-x}\\text{C}{{\\text{o}}x}\\text{Si} (0  ⩽  x  ⩽  1) alloys was investigated to identify the compositions with the potential to exhibit half-metallicity. The microstructural and structural studies revealed that only \\text{F}{{\\text{e}}2}\\text{C}{{\\text{r}}1-x}\\text{C}{{\\text{o}}x}\\text{Si} alloys with x  ⩾  0.5 exhibited the desired single phase L21 full Heusler alloy structure. Both the saturation magnetization (M s) and Curie temperature (T C) were found to increase with the increase in Co concentration. The experimentally measured M s values are in good agreement with the Slater-Pauling rule. The electrical resistivity measurements in the temperature range 10-300 K gives indirect evidence of half-metallic behaviour in these alloys at low temperatures. The temperature range in which the half-metallic behaviour was observed also increased with an increase in Co concentration.

  18. Electronic structure of Co-Ni-Ga Heusler alloys studied by resonant photoemission

    SciTech Connect

    Baral, Madhusmita Banik, Soma Ganguli, Tapas Chakrabarti, Aparna Deb, S. K.; Thamizhavel, A.; Wadikar, Avinash; Phase, D. M.

    2014-04-24

    The electronic structures of Co{sub 2.01}Ni{sub 1.05}Ga{sub 0.94} and Co{sub 1.76}Ni{sub 1.46}Ga{sub 0.78} Heusler alloys have been investigated by resonant photoemission spectroscopy across the 3p-3d transition of Co and Ni. For the Ni excess composition Co{sub 1.76}Ni{sub 1.46}Ga{sub 0.78}, the valence band peak shows a shift of 0.25 eV as compared to the near stoichiometric composition Co{sub 2.01}N1{sub 1.05}Ga{sub 0.94}. Also an enhancement is observed in the Ni related satellite features in the valence band for the Ni excess composition. Due to hybridization of Co and Ni 3d states in these systems, the Co and Ni 3p-3d resonance energies are found to be higher as compared to Co and Ni metals. Theoretical first principle calculation is performed to understand the features in the valence band and the shape of the resonance profile.

  19. Influence of the transition width on the magnetocaloric effect across the magnetostructural transition of Heusler alloys.

    PubMed

    Cugini, F; Porcari, G; Fabbrici, S; Albertini, F; Solzi, M

    2016-08-13

    We report a complete structural and magneto-thermodynamic characterization of four samples of the Heusler alloy Ni-Co-Mn-Ga-In, characterized by similar compositions, critical temperatures and high inverse magnetocaloric effect across their metamagnetic transformation, but different transition widths. The object of this study is precisely the sharpness of the martensitic transformation, which plays a key role in the effective use of materials and which has its origin in both intrinsic and extrinsic effects. The influence of the transition width on the magnetocaloric properties has been evaluated by exploiting a phenomenological model of the transformation built through geometrical considerations on the entropy versus temperature curves. A clear result is that a large temperature span of the transformation is unfavourable to the magnetocaloric performance of a material, reducing both isothermal entropy change and adiabatic temperature change obtainable in a given magnetic field and increasing the value of the maximum field needed to fully induce the transformation. The model, which is based on standard magnetometric and conventional calorimetric measurements, turns out to be a convenient tool for the determination of the optimum values of transformation temperature span in a trade-off between sheer performance and amplitude of the operating range of a material.This article is part of the themed issue 'Taking the temperature of phase transitions in cool materials'. PMID:27402934

  20. The structural, electronic and magnetic properties of quaternary Heusler alloy TiZrCoIn

    NASA Astrophysics Data System (ADS)

    Yan, Peng-Li; Zhang, Jian-Min; Xu, Ke-Wei

    2016-04-01

    Employing the first-principles calculations, we have investigated the structural, electronic and magnetic properties of quaternary Heusler alloy TiZrCoIn. The TiZrCoIn alloy with type (I) configuration is predicted to be half-metallic ferromagnet at its equilibrium lattice constant 6.525 Å with an indirect band gap of 0.930 eV in minority spin channel. The total magnetic moment is 2 μB/f.u., following the Slater-Pauling rule μt=Zt-18. Moreover, the negative formation energy indicates the thermodynamical stability of this alloy. The band gap of minority spin channel is determined by the bonding (t2g) and antibonding (t1u) states created from the hybridizations of the d states of transition metal atoms Ti, Zr and Co. In addition, the HM, character is kept as hydrostatic strain ranged from -10% to 7.6% and tetragonal strain ranged from -19% to 27%.

  1. Investigation of structural, electronic and magnetic properties of 1:1:1:1 stoichiometric quaternary Heusler alloys YCoCrZ (Z=Si, Ge, Ga, Al): An ab-initio study

    NASA Astrophysics Data System (ADS)

    Rasool, M. Nasir; Mehmood, Salman; Sattar, M. Atif; Khan, Muhammad Azhar; Hussain, Altaf

    2015-12-01

    Full potential linearized augmented plane wave method (FPLAPW) has been employed to probe the structural, electronic and magnetic properties of equiatomic yttrium based quaternary Heusler alloys YCoCrZ (Z=Si, Ge, Ga, Al). These calculations have been carried out via ab -initio simulations based on density functional theory (DFT) approach coded by Wien2K. The generalized gradient approximation of Perdew-Burke-Ernzerhof 96 scheme is engaged for calculations in all alloys under investigation. Equilibrium lattice constants are studied by structural optimization performed by computing total energies versus volumes. Structural optimization demonstrates that Y(3/4,3/4,3/4)Co(0,0,0)Cr(1/2,1/2,1/2)Z(1/4,1/4,1/4) (Type-1) configuration is the most stable one. The calculated electronic and magnetic properties based on type-1, indicate that YCoCrZ alloys are half-metallic ferromagnetic. The calculation of spin polarization is also made and further their total magnetic moments follow the Slater Pauling rule of Mtot=NVE-18 conceding the integer value i.e. 4.00μB and 3.00μB for YCoCrSi, Ge and YCoCrGa, Al respectively. The results of density of states (DOS) revealed that yttrium based quaternary Heusler alloys exhibit excellent band gaps i.e. 0.70, 0.65, 0.46 and 0.35 eV for YCoCrSi, Ge, Ga and Al respectively. The formation of band gaps owing to hybridization effect is also described. The half-metallic gaps of these compounds comprising the order YCoCrGa>YCoCrSi>YCoCrAl>YCoCrGe by size, is also manipulated. The incredible spin gapless semiconductor (SGS) type character of YCoCrGa and YCoCrAl having bantam DOS in spin up version is also discoursed. The optimised results of these compounds signpost that these are suitable candidates for spintronics applications.

  2. Growth temperature dependent structural and magnetic properties of epitaxial Co2FeAl Heusler alloy films

    NASA Astrophysics Data System (ADS)

    Qiao, Shuang; Nie, Shuaihua; Zhao, Jianhua; Zhang, Xinhui

    2013-06-01

    The structural and magnetic properties of a series of Co2FeAl Heusler alloy films grown on GaAs(001) substrate by molecular beam epitaxy have been studied. The epitaxial Co2FeAl films with an ordered L21 structure have been successfully obtained at growth temperature of 433 K, with an in-plane cubic magnetic anisotropy superimposed with an unusual uniaxial magnetic anisotropy. With increasing growth temperature, the ordered L21 structure degrades. Meanwhile, the uniaxial anisotropy decreases and eventually disappears above 673 K. The interfacial bonding between As and Co or Fe atom is suggested to be responsible for the additional uniaxial anisotropy.

  3. Modelling current-induced magnetization switching in Heusler alloy Co2FeAl-based spin-valve nanopillar

    NASA Astrophysics Data System (ADS)

    Huang, H. B.; Ma, X. Q.; Liu, Z. H.; Zhao, C. P.; Chen, L. Q.

    2014-04-01

    We investigated the current-induced magnetization switching in a Heusler alloy Co2FeAl-based spin-valve nanopillar by using micromagnetic simulations. We demonstrated that the elimination of the intermediate state is originally resulted from the decease of effective magnetic anisotropy constant. The magnetization switching can be achieved at a small current density of 1.0 × 104 A/cm2 by increasing the demagnetization factors of x and y axes. Based on our simulation, we found magnetic anisotropy and demagnetization energies have different contributions to the magnetization switching.

  4. Perpendicular Magnetic Anisotropy of Full-Heusler Films in Pt/Co2FeAl/MgO Trilayers

    NASA Astrophysics Data System (ADS)

    Li, Xiaoqi; Yin, Shaoqian; Liu, Yupeng; Zhang, Delin; Xu, Xiaoguang; Miao, Jun; Jiang, Yong

    2011-04-01

    We report on perpendicular magnetic anisotropy (PMA) in a Pt/Co2FeAl/MgO sandwiched structure with a thick Co2FeAl layer of 2-2.5 nm. The PMA is thermally stable and the anisotropy energy density Ku is 1.3×106 erg/cm3 for the structure with 2 nm Co2FeAl after annealing at 350 °C. The annealing temperature and Co2FeAl thickness greatly affect the PMA. Our results provide an effective way to realize relatively thick perpendicularly magnetized Heusler alloy films.

  5. Suppression of the ferromagnetic order in the Heusler alloy Ni50Mn35In15 by hydrostatic pressure

    NASA Astrophysics Data System (ADS)

    Salazar Mejía, C.; Mydeen, K.; Naumov, P.; Medvedev, S. A.; Wang, C.; Hanfland, M.; Nayak, A. K.; Schwarz, U.; Felser, C.; Nicklas, M.

    2016-06-01

    We report on the effect of hydrostatic pressure on the magnetic and structural properties of the shape-memory Heusler alloy Ni50Mn35In15. Magnetization and x-ray diffraction experiments were performed at hydrostatic pressures up to 5 GPa using diamond anvil cells. Pressure stabilizes the martensitic phase, shifting the martensitic transition to higher temperatures, and suppresses the ferromagnetic austenitic phase. Above 3 GPa, where the martensitic-transition temperature approaches the Curie temperature in the austenite, the magnetization shows no longer indications of ferromagnetic ordering. We further find an extended temperature region with a mixture of martensite and austenite phases, which directly relates to the magnetic properties.

  6. CO2-based mixtures as working fluids for geothermal turbines.

    SciTech Connect

    Wright, Steven Alan; Conboy, Thomas M.; Ames, David E.

    2012-01-01

    Sandia National Laboratories is investigating advanced Brayton cycles using supercritical working fluids for application to a variety of heat sources, including geothermal, solar, fossil, and nuclear power. This work is centered on the supercritical CO{sub 2} (S-CO{sub 2}) power conversion cycle, which has the potential for high efficiency in the temperature range of interest for these heat sources and is very compact-a feature likely to reduce capital costs. One promising approach is the use of CO{sub 2}-based supercritical fluid mixtures. The introduction of additives to CO{sub 2} alters the equation of state and the critical point of the resultant mixture. A series of tests was carried out using Sandia's supercritical fluid compression loop that confirmed the ability of different additives to increase or lower the critical point of CO{sub 2}. Testing also demonstrated that, above the modified critical point, these mixtures can be compressed in a turbocompressor as a single-phase homogenous mixture. Comparisons of experimental data to the National Institute of Standards and Technology (NIST) Reference Fluid Thermodynamic and Transport Properties (REFPROP) Standard Reference Database predictions varied depending on the fluid. Although the pressure, density, and temperature (p, {rho}, T) data for all tested fluids matched fairly well to REFPROP in most regions, the critical temperature was often inaccurate. In these cases, outside literature was found to provide further insight and to qualitatively confirm the validity of experimental findings for the present investigation.

  7. Synthesis and characterization of Fe-Ti-Sb intermetallic compounds: Discovery of a new Slater-Pauling phase

    NASA Astrophysics Data System (ADS)

    Naghibolashrafi, N.; Keshavarz, S.; Hegde, Vinay I.; Gupta, A.; Butler, W. H.; Romero, J.; Munira, K.; LeClair, P.; Mazumdar, D.; Ma, J.; Ghosh, A. W.; Wolverton, C.

    2016-03-01

    Compounds of Fe, Ti, and Sb were prepared using arc melting and vacuum annealing. Fe2TiSb , expected to be a full Heusler compound crystallizing in the L 21 structure, was shown by XRD and SEM analyses to be composed of weakly magnetic grains of nominal composition Fe1.5TiSb with iron-rich precipitates in the grain boundaries. FeTiSb, a composition consistent with the formation of a half-Heusler compound, also decomposed into Fe1.5TiSb grains with Ti-Sb rich precipitates and was weakly magnetic. The dominant Fe1.5TiSb phase appears to crystallize in a defective L 21 -like structure with iron vacancies. Based on this finding, a first-principles DFT-based binary cluster expansion of Fe and vacancies on the Fe sublattice of the L 21 structure was performed. Using the cluster expansion, we computationally scanned >103 configurations and predict a novel, stable, nonmagnetic semiconductor phase to be the zero-temperature ground state. This new structure is an ordered arrangement of Fe and vacancies, belonging to the space group R 3 m , with composition Fe1.5TiSb , i.e., between the full- and half-Heusler compositions. This phase can be visualized as alternate layers of L 21 phase Fe2TiSb and C 1b phase FeTiSb, with layering along the [111] direction of the original cubic phases. Our experimental results on annealed samples support this predicted ground-state composition, but further work is required to confirm that the R 3 m structure is the ground state.

  8. Electrical properties of ferromagnetic Ni{sub 2}MnGa and Co{sub 2}CrGa Heusler alloys

    SciTech Connect

    Kourov, N. I. Marchenkov, V. V.; Pushin, V. G.; Belozerova, K. A.

    2013-07-15

    The electrical properties of ferromagnetic Ni{sub 2}MnGa and Co{sub 2}CrGa Heusler alloys are measured in the temperature range 4-900 K. The effect of the energy gap near the Fermi level in the electronic spectrum on the behavior of electrical resistivity and absolute differential thermopower is discussed.

  9. Evolution of the electronic structure and physical properties of Fe2MeAl (Me = Ti, V, Cr) Heusler alloys

    NASA Astrophysics Data System (ADS)

    Shreder, E.; Streltsov, S. V.; Svyazhin, A.; Makhnev, A.; Marchenkov, V. V.; Lukoyanov, A.; Weber, H. W.

    2008-01-01

    We present the results of experiments on the optical, electrical and magnetic properties and electronic structure and optical spectrum calculations of the Heusler alloys Fe2TiAl, Fe2VAl and Fe2CrAl. We find that the drastic transformation of the band spectrum, especially near the Fermi level, when replacing the Me element (Me = Ti, V, Cr), is accompanied by a significant change in the electrical and optical properties. The electrical and optical properties of Fe2TiAl are typical for metals. The abnormal behavior of the electrical resistivity and the optical properties in the infrared range for Fe2VAl and Fe2CrAl are determined by electronic states at the Fermi level. Both the optical spectroscopic measurements and the theoretical calculations demonstrate the presence of low-energy gaps in the band spectrum of the Heusler alloys. In addition, we demonstrate that the formation of Fe clusters may be responsible for the large enhancement of the total magnetic moment in Fe2CrAl.

  10. Realizing high figure of merit in heavy-band p-type half-Heusler thermoelectric materials.

    PubMed

    Fu, Chenguang; Bai, Shengqiang; Liu, Yintu; Tang, Yunshan; Chen, Lidong; Zhao, Xinbing; Zhu, Tiejun

    2015-01-01

    Solid-state thermoelectric technology offers a promising solution for converting waste heat to useful electrical power. Both high operating temperature and high figure of merit zT are desirable for high-efficiency thermoelectric power generation. Here we report a high zT of ∼1.5 at 1,200 K for the p-type FeNbSb heavy-band half-Heusler alloys. High content of heavier Hf dopant simultaneously optimizes the electrical power factor and suppresses thermal conductivity. Both the enhanced point-defect and electron-phonon scatterings contribute to a significant reduction in the lattice thermal conductivity. An eight couple prototype thermoelectric module exhibits a high conversion efficiency of 6.2% and a high power density of 2.2 W cm(-2) at a temperature difference of 655 K. These findings highlight the optimization strategy for heavy-band thermoelectric materials and demonstrate a realistic prospect of high-temperature thermoelectric modules based on half-Heusler alloys with low cost, excellent mechanical robustness and stability. PMID:26330371

  11. Realizing high figure of merit in heavy-band p-type half-Heusler thermoelectric materials

    NASA Astrophysics Data System (ADS)

    Fu, Chenguang; Bai, Shengqiang; Liu, Yintu; Tang, Yunshan; Chen, Lidong; Zhao, Xinbing; Zhu, Tiejun

    2015-09-01

    Solid-state thermoelectric technology offers a promising solution for converting waste heat to useful electrical power. Both high operating temperature and high figure of merit zT are desirable for high-efficiency thermoelectric power generation. Here we report a high zT of ~1.5 at 1,200 K for the p-type FeNbSb heavy-band half-Heusler alloys. High content of heavier Hf dopant simultaneously optimizes the electrical power factor and suppresses thermal conductivity. Both the enhanced point-defect and electron-phonon scatterings contribute to a significant reduction in the lattice thermal conductivity. An eight couple prototype thermoelectric module exhibits a high conversion efficiency of 6.2% and a high power density of 2.2 W cm-2 at a temperature difference of 655 K. These findings highlight the optimization strategy for heavy-band thermoelectric materials and demonstrate a realistic prospect of high-temperature thermoelectric modules based on half-Heusler alloys with low cost, excellent mechanical robustness and stability.

  12. Realizing high figure of merit in heavy-band p-type half-Heusler thermoelectric materials

    PubMed Central

    Fu, Chenguang; Bai, Shengqiang; Liu, Yintu; Tang, Yunshan; Chen, Lidong; Zhao, Xinbing; Zhu, Tiejun

    2015-01-01

    Solid-state thermoelectric technology offers a promising solution for converting waste heat to useful electrical power. Both high operating temperature and high figure of merit zT are desirable for high-efficiency thermoelectric power generation. Here we report a high zT of ∼1.5 at 1,200 K for the p-type FeNbSb heavy-band half-Heusler alloys. High content of heavier Hf dopant simultaneously optimizes the electrical power factor and suppresses thermal conductivity. Both the enhanced point-defect and electron–phonon scatterings contribute to a significant reduction in the lattice thermal conductivity. An eight couple prototype thermoelectric module exhibits a high conversion efficiency of 6.2% and a high power density of 2.2 W cm−2 at a temperature difference of 655 K. These findings highlight the optimization strategy for heavy-band thermoelectric materials and demonstrate a realistic prospect of high-temperature thermoelectric modules based on half-Heusler alloys with low cost, excellent mechanical robustness and stability. PMID:26330371

  13. High-efficiency energy harvesting using TAGS-85/half-Heusler thermoelectric devices

    NASA Astrophysics Data System (ADS)

    Bulman, Gary; Cook, Bruce

    2014-06-01

    To improve the thermal-to-electrical conversion efficiency of waste exhaust heat at temperatures in the vicinity of 750°C, RTI has combined two different high-performance materials to form a high ZT, hybrid thermoelectric (TE) device. Recently-developed enhanced "TAGS-85", or e-TAGS, was employed as the p-leg, while the n leg was comprised of improved half-Heusler (HH) material. This hybrid material pair provides a high ZT, lead-free TE material solution for exhaust gas heat recovery for use in vehicle or industrial platforms. The improved HH material employs two novel techniques to reduce thermal conductivity: (1) high-energy milling, and (2) addition of coherent inclusions. Single n-/pcouples were produced that achieved a 9.2% efficiency with a power output of 205mW for Thot = 559°C and ΔT = 523K. This is a significant efficiency improvement at a lower hot side temperature with the hybrid e-TAGS/HH single couple over the performance of a conventional, all HH couple. By optimizing the cross sectional areas of the pellets for equal heat flow, the resulting asymmetric couple achieved 10.5% efficiency with a maximum power output of 317 mW at Thot = 537°C and ΔT = 497°C. A 49-couple hybrid module using other advanced HH materials paired with e-TAGS and operated with Thot up to 600°C reached a maximum efficiency of 10%. The improved module efficiency is believed to be due to both improved materials and optimized cross-sectional area ratios between the n- and p- elements.

  14. Compound matrices

    NASA Astrophysics Data System (ADS)

    Kravvaritis, Christos; Mitrouli, Marilena

    2009-02-01

    This paper studies the possibility to calculate efficiently compounds of real matrices which have a special form or structure. The usefulness of such an effort lies in the fact that the computation of compound matrices, which is generally noneffective due to its high complexity, is encountered in several applications. A new approach for computing the Singular Value Decompositions (SVD's) of the compounds of a matrix is proposed by establishing the equality (up to a permutation) between the compounds of the SVD of a matrix and the SVD's of the compounds of the matrix. The superiority of the new idea over the standard method is demonstrated. Similar approaches with some limitations can be adopted for other matrix factorizations, too. Furthermore, formulas for the n - 1 compounds of Hadamard matrices are derived, which dodge the strenuous computations of the respective numerous large determinants. Finally, a combinatorial counting technique for finding the compounds of diagonal matrices is illustrated.

  15. Large enhancement of bulk spin polarization by suppressing CoMn anti-sites in Co2Mn(Ge0.75Ga0.25) Heusler alloy thin film

    NASA Astrophysics Data System (ADS)

    Li, S.; Takahashi, Y. K.; Sakuraba, Y.; Tsuji, N.; Tajiri, H.; Miura, Y.; Chen, J.; Furubayashi, T.; Hono, K.

    2016-03-01

    We have investigated the structure and magneto-transport properties of Co2Mn(Ge0.75Ga0.25) (CMGG) Heusler alloy thin films with near-stoichiometric and Mn-rich compositions in order to understand the effect of Co-Mn anti-sites on bulk spin polarization. Anomalous x-ray diffraction measurements using synchrotron radiated x-rays confirmed that CoMn anti-sites easily form in the near-stoichiometric CMGG compound at annealing temperature higher than 400 °C, while it can be suppressed in Mn-rich CMGG films. Accordingly, large enhancement in negative anisotropic magnetoresistance of CMGG films and giant magnetoresistance (GMR) in current-perpendicular-to-plane (CPP) pseudo spin valves were observed in the Mn-rich composition. A large resistance-area product change (ΔRA) of 12.8 mΩ μm2 was demonstrated in the CPP-GMR pseudo spin valves using the Mn-rich CMGG layers after annealing at 600 °C. It is almost twice of the maximum output observed in the CPP-GMR pseudo spin valves using the near-stoichiometric CMGG. These indicate that the spin polarization of CMGG is enhanced in the Mn-rich composition through suppressing the formation of CoMn-antisites in CMGG films, being consistent with first-principle calculation results.

  16. The half-metallicity of LiMgPdSn-type quaternary Heusler alloys FeMnScZ (Z=Al, Ga, In): A first-principle study

    SciTech Connect

    Gao, Y. C.; Gao, X.

    2015-05-15

    Based on the first-principles calculations, quaternary Heusler alloys FeMnScZ (Z=Al, Ga, In) including its phase stability, band gap, the electronic structures and magnetic properties has been studied systematically. We have found that, in terms of the equilibrium lattice constants, FeMnScZ (Z=Al, Ga, In) are half-metallic ferrimagnets, which can sustain the high spin polarization under a very large amount of lattice distortions. The half-metallic band gap in FeMnScZ (Z=Al, Ga, In) alloys originates from the t{sub 1u}-t{sub 2g} splitting instead of the e{sub u}-t{sub 1u} splitting. The total magnetic moments are 3μB per unit cell for FeMnScZ (Z=Al, Ga, In) alloys following the Slater–Pauling rule with the total number of valence electrons minus 18 rather than 24. According to the study, the conclusion can be drawn that all of these compounds which have a negative formation energy are possible to be synthesized experimentally.

  17. Structural and magnetic properties of ion beam sputtered Co2FeAl full Heusler alloy thin films

    NASA Astrophysics Data System (ADS)

    Husain, Sajid; Kumar, Ankit; Chaudhary, Sujeet; Svedlindh, Peter

    2016-05-01

    Co2FeAl full Heusler alloy thin films grown at different temperatures on Si(100) substrates using ion beam sputtering system have been investigated. X-ray diffraction (XRD) patterns revealed the A2 disordered phase in these films. The deduced lattice parameter slightly increases with increase in the growth temperature. The saturation magnetization it is found to increase with increase in growth temperature. The magnetic anisotropy has been studied using angle dependent magneto-optical Kerr effect. In the room temperature deposited film, the combination of cubic and uniaxial anisotropy have been observed with weak in-plane uniaxial anisotropy which increases with growth temperature. The uniaxial anisotropy is attributed to the anisotropic interfacial bonding in these Co2FeAl /Si(100) heterostructures.

  18. Bending strain-tunable magnetic anisotropy in Co2FeAl Heusler thin film on KaptonxAE

    NASA Astrophysics Data System (ADS)

    Gueye, M.; Wague, B. M.; Zighem, F.; Belmeguenai, M.; Gabor, M. S.; Petrisor, T.; Tiusan, C.; Mercone, S.; Faurie, D.

    2014-08-01

    Bending effect on the magnetic anisotropy in 20 nm Co2FeAl Heusler thin film grown on Kapton® has been studied by ferromagnetic resonance and glued on curved sample carrier with various radii. The results reported in this Letter show that the magnetic anisotropy is drastically changed in this system by bending the thin films. This effect is attributed to the interfacial strain transmission from the substrate to the film and to the magnetoelastic behavior of the Co2FeAl film. Moreover, two approaches to determine the in-plane magnetostriction coefficient of the film, leading to a value that is close to λCFA= 14 × 10-6, have been proposed.

  19. Spin-transfer switching in full-Heusler Co2FeAl-based magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Sukegawa, Hiroaki; Wen, Zhenchao; Kondou, Kouta; Kasai, Shinya; Mitani, Seiji; Inomata, Koichiro

    2012-04-01

    We demonstrated spin-transfer magnetization switching using magnetic tunnel junctions (MTJs) with a full-Heusler alloy Co2FeAl (CFA). We prepared CFA (1.5 nm)/MgO/CoFe (4 nm) ("CFA-free") and CFA (30 nm)/MgO/CoFeB (2 nm) ("CFA-reference") MTJs on a Cr(001) layer. The intrinsic critical current density (Jc0) of the CFA-free (CFA-reference) MTJ was 29 MA/cm2 (7.1 MA/cm2). The larger Jc0 of the CFA-free MTJ is attributed to the significant enhancement of the Gilbert damping factor (˜0.04) of the CFA due to the Cr layer. The Jc0 of the CFA-reference is as small as that reported for typical CoFeB/MgO/CoFeB MTJs.

  20. Magnetic Tunnel Junctions with Perpendicular Anisotropy Using a Co2FeAl Full-Heusler Alloy

    NASA Astrophysics Data System (ADS)

    Wen, Zhenchao; Sukegawa, Hiroaki; Kasai, Shinya; Hayashi, Masamitsu; Mitani, Seiji; Inomata, Koichiro

    2012-06-01

    We fabricated perpendicularly magnetized magnetic tunnel junctions (p-MTJs) with an ultrathin Co2FeAl (CFA) full-Heusler alloy electrode having large interface magnetic anisotropy of CFA/MgO. An out-of-plane tunnel magnetoresistance (TMR) ratio of 53% at room temperature was observed in CFA/MgO/Co20Fe60B20 p-MTJs. By inserting a 0.1-nm-thick Fe (Co50Fe50) layer between the MgO and Co20Fe60B20 layers, The TMR ratio was significantly enhanced to 91% (82%) due to the improved interface. The bias voltage dependence of differential conductance did not clearly show coherent tunneling characteristics for ultrathin CFA-MTJs, suggesting that a higher TMR ratio may be achieved by improving the B2 ordering of CFA and/or interface structure.

  1. Pulsed high-magnetic-field experiments: New insights into the magnetocaloric effect in Ni-Mn-In Heusler alloys

    SciTech Connect

    Salazar Mejía, C. Nayak, A. K.; Felser, C.; Nicklas, M.; Ghorbani Zavareh, M.; Wosnitza, J.; Skourski, Y.

    2015-05-07

    The present pulsed high-magnetic-field study on Ni{sub 50}Mn{sub 35}In{sub 15} gives an extra insight into the thermodynamics of the martensitic transformation in Heusler shape-memory alloys. The transformation-entropy change, ΔS, was estimated from field-dependent magnetization experiments in pulsed high magnetic fields and by heat-capacity measurements in static fields. We found a decrease of ΔS with decreasing temperature. This behavior can be understood by considering the different signs of the lattice and magnetic contributions to the total entropy. Our results further imply that the magnetocaloric effect will decrease with decreasing temperature and, furthermore, the martensitic transition is not induced anymore by changing the temperature in high magnetic fields.

  2. Magnetic and Magnetocaloric Properties in Non-Stoichiometric Gallium Deficient Ni2MnGa1-x Heusler Alloys

    NASA Astrophysics Data System (ADS)

    Madden, Alexander; Corrigan, Mollie; Barton, Linda

    Magnetic data show that off-stoichiometric gallium deficient Heusler alloys of the form Ni2MnGa1-x have structural martensite transition temperatures that increase strongly with x, while their ferromagnetic Curie temperatures remain nearly unchanged. The martensite transition approaches room temperature for x = 0 . 13 . Samples were prepared by rf induction heating. The influence of quenching and post annealing on magnetic properties, as well as structural grain sizes and magnetic domain structure, were investigated. Since the first order structural phase transition can be adjusted to any convenient temperature, these materials offer intriguing possibilities as magnetic refrigerants. Magnetocaloric properties were investigated by direct measurement of ΔT with the application of field ΔH .

  3. The effects of substituting Ag for In on the magnetoresistance and magnetocaloric properties of Ni-Mn-In Heusler alloys

    NASA Astrophysics Data System (ADS)

    Pandey, Sudip; Quetz, Abdiel; Aryal, Anil; Dubenko, Igor; Samanta, Tapas; Mazumdar, Dipanjan; Stadler, Shane; Ali, Naushad

    2016-05-01

    The effect of substituting Ag for In on the structural, magnetocaloric, and thermomagnetic properties of Ni50Mn35In15-xAgx (x = 0.1, 0.2, 0.5, and 1) Heusler alloys was studied. The magnitude of the magnetization change at the martensitic transition temperature (TM) decreased with increasing Ag concentration. Smaller magnetic entropy changes (ΔSM) were observed for the alloys with larger Ag concentrations and the martensitic transition shifted to higher temperature. A shift of TM by about 25 K to higher temperature was observed for an applied hydrostatic pressure of P = 6.6 kbar with respect to ambient pressure. A large drop in resistivity was observed for large Ag concentration. The magnetoresistance was dramatically suppressed due to an increase in the disorder of the system with increasing Ag concentration. Possible mechanisms responsible for the observed behavior are discussed.

  4. The realization of ferro-ferrimagnetic transition and half-metallicity in half-Heusler CoMnGa alloy

    NASA Astrophysics Data System (ADS)

    Wang, L. Y.; Dai, X. F.; Wang, X. T.; Liu, X. F.; Li, P. P.; Cui, Y. T.; Liu, E. K.; Wang, W. H.; Wu, G. H.; Liu, G. D.

    2014-11-01

    We theoretically predicted that half-Heusler CoMnGa alloy to be half-metallic ferrimagnet at the equilibrium lattice parameter. With the lattice expansion, a local energy minimum occurs at a larger lattice parameter where CoMnGa alloy is in a metastable ferromagnetic state. However, a ferro-ferrimagnetic transition (Fo-Fi-T) is not observed in experiment. We found the Co-Mn antisites can induce the Fo-Fi-T by adjusting the driving force of magnetic transition and the energy barrier. The antisites are sensitive to the preparation methods and annealing temperatures. The highly ordered CoMnGa is achieved by annealing at 1073 K. The Fo-Fi-T occurs in a sample annealed at 1083 K.

  5. B2+L2{sub 1} ordering in Co{sub 2}MnAl Heusler alloy

    SciTech Connect

    Vinesh, A.; Sudheesh, V. D.; Lakshmi, N.; Venugopalan, K.

    2014-04-24

    Magnetic and structural properties of B2 ordered Co{sub 2}MnAl Heusler alloy have been studied by X-ray diffraction and DC magnetization techniques. X-ray diffractogram shows the structure is of B2 type with preferential site disorder between Mn and Al atoms and presence of a small L2{sub 1} phase. DC magnetization studies at low temperature establish that the antiferromagnetic nature arises mainly due to the antiparallel coupling of spin moments of 3d electrons of Co with Mn atoms. Curie temperature (T{sub c}) is 733 K which is close to T{sub c} of the L2{sub 1} phase.

  6. Large half-metallic gap in ferromagnetic semi-Heusler alloys CoCrP and CoCrAs

    SciTech Connect

    Yao Zhongyu; Zhang, Y. S.; Yao, K. L.

    2012-08-06

    We investigate the electronic structure and magnetism of semi-Heusler alloys CoCrP and CoCrAs using the full-potential linearized augmented plane wave method. The calculations reveal that CoCrP and CoCrAs are half-metallic (HM) ferromagnets with the same magnetic moment of 2.00 {mu}{sub B} per formula unit. Both alloys have large half-metallic gaps (up to 0.50 eV) and wide band gaps (above 1 eV). The half-metallicity of CoCrP and CoCrAs can be retained even when their lattice constants are changed by -4.8% to 6.6% and -7.7% to 4.5%, respectively. The two alloys show great promise in the applications of spin valve and magnetic tunnel junction.

  7. Growth temperature dependent structural and magnetic properties of epitaxial Co{sub 2}FeAl Heusler alloy films

    SciTech Connect

    Qiao, Shuang; Nie, Shuaihua; Zhao, Jianhua; Zhang, Xinhui

    2013-06-21

    The structural and magnetic properties of a series of Co{sub 2}FeAl Heusler alloy films grown on GaAs(001) substrate by molecular beam epitaxy have been studied. The epitaxial Co{sub 2}FeAl films with an ordered L{sub 21} structure have been successfully obtained at growth temperature of 433 K, with an in-plane cubic magnetic anisotropy superimposed with an unusual uniaxial magnetic anisotropy. With increasing growth temperature, the ordered L{sub 21} structure degrades. Meanwhile, the uniaxial anisotropy decreases and eventually disappears above 673 K. The interfacial bonding between As and Co or Fe atom is suggested to be responsible for the additional uniaxial anisotropy.

  8. Electronic structures, magnetic properties and half-metallicity in Heusler alloys Zr2CoZ (Z=Al, Ga, In, Sn)

    NASA Astrophysics Data System (ADS)

    Yan, Peng-Li; Zhang, Jian-Min; Xu, Ke-Wei

    2015-10-01

    The electronic structures, magnetic properties, and half-metallicity of full-Heusler alloys Zr2 CoZ (Z=Al, Ga, In, Sn) with the Hg2 CuTi -type structure have been studied by using the first-principles projector augmented wave (PAW) potential within the generalized gradient approximation (GGA). The Zr2 CoZ (Z=Al, Ga, In, Sn) are found to be half-metallic ferrimagnets within a certain range of the lattice constant. The total magnetic moments (μt) of the Zr2 CoZ alloys are calculated to be 2 for Z=Al, Ga, In and 3 for Z=Sn, linearly scaled with the total number of valence electrons (Zt) by μt =Zt - 18 . The origin of the band gap for these half-metallic alloys is well understood. These new Zr-based Heusler alloys are the ideal candidates for spintronic devices.

  9. Tunable ferromagnetic and antiferromagnetic interfacial exchange coupling in perpendicularly magnetized L10-MnGa/Co2FeAl Heusler bilayers

    NASA Astrophysics Data System (ADS)

    Ma, Q. L.; Mizukami, S.; Zhang, X. M.; Miyazaki, T.

    2014-12-01

    In this work, we report a tailorable exchange coupling (Jex) at the Mn62Ga38/Co2FeAl interface, where Mn62Ga38 and Co2FeAl alloys are tetragonal Heusler alloy with high perpendicular magnetic anisotropy and typical cubic Heusler alloy with soft magnetism, respectively. As the post annealing temperature (Ta) is lower than 375 °C, the Jex is ferromagnetic with strength controllable from 7.5 to 0.5 erg/cm2. Interestingly, as Ta increases higher than 400 °C, an antiferromagnetic Jex of -5.5 erg/cm2 is observed. The ferromagnetic/antiferromagnetic transition is further evidenced by the spin dependent transport property of the magnetic tunnel junctions with Mn62Ga38/Co2FeAl as electrode. Based on structure characterization, the variation of Jex during annealing is discussed.

  10. Fabrication of highly ordered Co2Fe0.4Mn0.6Si Heusler alloy films on Si substrates

    NASA Astrophysics Data System (ADS)

    Koike, Takeo; Oogane, Mikihiko; Ono, Atsuo; Ando, Yasuo

    2016-08-01

    The structural and magnetic properties of Si(100)/MgO/Co2Fe0.4Mn0.6Si (CFMS) Heusler alloy thin films were systematically investigated. Highly B2-ordered CFMS Heusler films with an ordering parameter of ca. 70–80% were obtained by both the insertion of a very thin Mg layer into the Si/MgO interfaces to prevent oxidation of the Si surface and the optimization of the annealing temperature for the CFMS films. The prepared CFMS films exhibited high magnetization close to that of the CFMS bulk. Such highly B2-ordered CFMS films are very useful for realizing high spin injection efficiency in Si because of the half-metallicity of the CFMS films.

  11. Effect of graphene tunnel barrier on Schottky barrier height of Heusler alloy Co2MnSi/graphene/n-Ge junction

    NASA Astrophysics Data System (ADS)

    Gui-fang, Li; Jing, Hu; Hui, Lv; Zhijun, Cui; Xiaowei, Hou; Shibin, Liu; Yongqian, Du

    2016-02-01

    We demonstrate that the insertion of a graphene tunnel barrier between Heusler alloy Co2MnSi and the germanium (Ge) channel modulates the Schottky barrier height and the resistance-area product of the spin diode. We confirm that the Fermi level is depinned and a reduction in the electron Schottky barrier height (SBH) occurs following the insertion of the graphene layer between Co2MnSi and Ge. The electron SBH is modulated in the 0.34 eV-0.61 eV range. Furthermore, the transport mechanism changes from rectifying to symmetric tunneling following the insertion. This behavior provides a pathway for highly efficient spin injection from a Heusler alloy into a Ge channel with high electron and hole mobility. Project supported by the National Natural Science Foundation of China (Grant No. 61504107) and the Fundamental Research Funds for the Central Universities, China (Grant Nos. 3102014JCQ01059 and 3102015ZY043).

  12. High-field magnetization of heusler alloys Fe2 XY ( X = Ti, V, Cr, Mn, Fe, Co, Ni; Y = Al, Si)

    NASA Astrophysics Data System (ADS)

    Kourov, N. I.; Marchenkov, V. V.; Korolev, A. V.; Belozerova, K. A.; Weber, H. W.

    2015-10-01

    The magnetization curves of ferromagnetic Heusler alloys Fe2 XY (where X = Ti, V, Cr, Mn, Fe, Co, Ni are transition 3 d elements and Y = Al, Si are the s and p elements of the third period of the Periodic Table) have been measured at T = 4.2 K in the field range H ≤ 70 kOe. It has been shown that the high-field ( H ≥ 20 kOe) magnetization is described within the Stoner model.

  13. Covalence and ionicity in MgAgAs-type compounds.

    PubMed

    Bende, David; Grin, Yuri; Wagner, Frank R

    2014-07-28

    MgAgAs-type "half-Heusler" compounds are known to realize two out of three possible atomic arrangements of this structure type. The number of transition metal components typically determines which of the alternatives is favored. On the basis of DFT calculations for all three variants of 20 eight- and eighteen-valence-electron compounds, the experimentally observed structural variant was found to be determined by basically two different bonding patterns. They are quantified by employing two complementary position-space bonding measures. The Madelung energy E((M)(QTAIM)) calculated with the QTAIM effective charges reflects contributions of the ionic interactions to the total energy. The sum of nearest-neighbor delocalization indices ςnn characterizes the covalent interactions through electron sharing. With the aid of these quantities, the energetic sequence of the three atomic arrangements for each compound is rationalized. The resulting systematic is used to predict a scenario in which an untypical atomic arrangement becomes most favorable. PMID:24990108

  14. Polybenzimidazole compounds

    DOEpatents

    Klaehn, John R.; Peterson, Eric S.; Wertsching, Alan K.; Orme, Christopher J.; Luther, Thomas A.; Jones, Michael G.

    2010-08-10

    A PBI compound that includes imidazole nitrogens, at least a portion of which are substituted with an organic-inorganic hybrid moiety. At least 85% of the imidazole nitrogens may be substituted. The organic-inorganic hybrid moiety may be an organosilane moiety, for example, (R)Me.sub.2SiCH.sub.2--, where R is selected from among methyl, phenyl, vinyl, and allyl. The PBI compound may exhibit similar thermal properties in comparison to the unsubstituted PBI. The PBI compound may exhibit a solubility in an organic solvent greater than the solubility of the unsubstituted PBI. The PBI compound may be included in separatory media. A substituted PBI synthesis method may include providing a parent PBI in a less than 5 wt % solvent solution. Substituting may occur at about room temperature and/or at about atmospheric pressure. Substituting may use at least five equivalents in relation to the imidazole nitrogens to be substituted or, preferably, about fifteen equivalents.

  15. Multipurpose Compound

    NASA Technical Reports Server (NTRS)

    1983-01-01

    Specially formulated derivatives of an unusual basic compound known as Alcide may be the answer to effective treatment and prevention of the disease bovine mastitis, a bacterial inflammation of a cow's mammary gland that results in loss of milk production and in extreme cases, death. Manufactured by Alcide Corporation the Alcide compound has killed all tested bacteria, virus and fungi, shortly after contact, with minimal toxic effects on humans or animals. Alcide Corporation credits the existence of the mastitis treatment/prevention products to assistance provided the company by NERAC, Inc.

  16. Panoscopically optimized thermoelectric performance of a half-Heusler/full-Heusler based in situ bulk composite Zr(0.7)Hf(0.3)Ni(1+x)Sn: an energy and time efficient way.

    PubMed

    Bhardwaj, A; Chauhan, N S; Sancheti, Bhagyashree; Pandey, G N; Senguttuvan, T D; Misra, D K

    2015-11-28

    All scale hierarchical architecturing, matrix/inclusion band alignment and intra-matrix electronic structure engineering, the so called panoscopic approach for thermoelectric materials has been demonstrated to be an effective paradigm for optimizing high ZT. To achieve such hierarchically organized microstructures, composition engineering has been considered to be an efficient strategy. In this work, such a panoscopic concept has been extended to demonstrate for the first time in the case of half-Heusler based thermoelectric materials via a composition engineering route. A series of new off-stoichiometric n-type Zr0.7Hf0.3Ni1+xSn (0 ≤x≤ 0.10) HH compositions have been modified to derive HH(1 -x)/full-Heusler (FH)(x) composite with an all scale hierarchically modified microstructure with FH inclusions within the matrix to study the temperature dependent thermoelectric properties. The structural analysis employing XRD, FE-SEM and HR-TEM of these materials reveal a composite of HH and FH, with hierarchically organized microstructures. In such a submicron/nano-composite, the electronic properties are observed to be well optimized yielding a large power factor; α(2)σ (∼30.7 × 10(-4) W m(-1) K(-2) for Zr0.7Hf0.3Ni1.03Sn) and reduced thermal conductivity (∼2.4 W m(-1) K(-1) for Zr0.7Hf0.3Ni1.03Sn) yielding a high ZT∼ 0.96 at 773 K for composition Zr0.7Hf0.3Ni1.03Sn which is ∼250% larger than the normal HH Zr0.7Hf0.3NiSn (ZT∼ 0.27 at 773 K). The enhancement in ZT of these composites has been discussed in terms of primary electron filtering, electron injection and several phonon scattering mechanisms such as alloy scattering, point defect scattering, and grain boundary scattering. The Bergman and Fel model is used to calculate effective thermoelectric parameters of these composites for comparing the experimental results. PMID:26499748

  17. Magnesium compounds

    USGS Publications Warehouse

    Kramer, D.A.

    2001-01-01

    Seawater and natural brines accounted for about 63% of US magnesium compounds production during 2000. Premier Services in Florida, Dow Chemical in Michigan, Martin Marietta Magnesia Specialties, and Rohm & Haas recovered dead-burned and caustic-calcined magnesias from seawater. And Premier Services' recoveries, in Nevada, were from magnasite.

  18. Fermi surface study of ScAu{sub 2}(Al, In) and ScPd{sub 2}(Sn, Pb) compounds

    SciTech Connect

    Reddy, P. V. Sreenivasa; Kanchana, V.; Vaitheeswaran, G.

    2015-06-24

    A detailed study on the electronic structure and Fermi surface (FS) of superconducting Heusler compounds ScAu{sub 2}(Al, In) and ScPd{sub 2}(Sn, Pb) has been carried out using first principles electronic structure calculations. The spin orbit coupling is found to play a major role in understanding the band structure and FS. Analysis of the data shows the importance of spin orbit coupling effect in the above compounds. The bands which cross Fermi level (EF) are found to be dominated by the Sc d{sub t2g}-states. The calculated total density of states are in good agreement with the experimentally reported value for ScPd{sub 2}Sn. Under compression we find a change in the Fermi surface topology of ScPd{sub 2}Sn at V/V{sub 0} = 0.95 (pressure of≈15 GPa), which is explained using the band structure calculations.

  19. Magnesium compounds

    USGS Publications Warehouse

    Kramer, D.A.

    2003-01-01

    Seawater and natural brines accounted for about 60 percent of U.S. magnesium compounds production during 2002. Dead-burned and caustic-calcined magnesias were recovered from seawater by Premier Chemicals in Florida. They were also recovered from well brines in Michigan by Dow Chemical, Martin Marietta Magnesia Specialties and Rohm & Haas. And they were recovered from magnesite in Nevada by Premier Chemicals.

  20. Magnesium compounds

    USGS Publications Warehouse

    Kramer, D.A.

    2006-01-01

    In 2005, seawater and natural brines accounted for 51% of US magnesium compounds production. World magnesia production was estimated to be 14.5 Mt. Most of the production came from China, North Korea, Russia and Turkey. Although no specific production figures are available, Japan and the United States are estimated to account for almost one-half of the world's capacity from seawater and brines.

  1. Over 50% reduction in the formation energy of Co-based Heusler alloy films by two-dimensional crystallisation

    SciTech Connect

    Sagar, James; Fleet, Luke R.; Walsh, Michael; Whear, Oliver; Huminiuc, Teodor; Lari, Leonardo; Boyes, Edward D.; Vick, Andrew; Hirohata, Atsufumi

    2014-07-21

    Crystalline formation of high magnetic-moment thin films through low-temperature annealing processes compatible with current semiconductor technologies is crucial for the development of next generation devices, which can utilise the spin degree of freedom. Utilising in-situ aberration corrected electron microscopy, we report a 235 °C crystallisation process for a Co-based ternary Heusler-alloy film whose initial nucleation is initiated by as few as 27 unit cells. The crystallisation occurs preferentially in the 〈111〉 crystalline directions via a two-dimensional (2D) layer-by-layer growth mode; resulting in grains with [110] surface normal and [111] plane facets. This growth process was found to reduce the crystallisation energy by more than 50% when compared to bulk samples whilst still leading to the growth of highly ordered grains expected to give a high degree of spin-polarisation. Our findings suggest that the 2D layer-by-layer growth minimises the crystallisation energy allowing for the possible implementation of highly spin-polarised alloy films into current chip and memory technologies.

  2. Over 50% reduction in the formation energy of Co-based Heusler alloy films by two-dimensional crystallisation

    NASA Astrophysics Data System (ADS)

    Sagar, James; Fleet, Luke R.; Walsh, Michael; Lari, Leonardo; Boyes, Edward D.; Whear, Oliver; Huminiuc, Teodor; Vick, Andrew; Hirohata, Atsufumi

    2014-07-01

    Crystalline formation of high magnetic-moment thin films through low-temperature annealing processes compatible with current semiconductor technologies is crucial for the development of next generation devices, which can utilise the spin degree of freedom. Utilising in-situ aberration corrected electron microscopy, we report a 235 °C crystallisation process for a Co-based ternary Heusler-alloy film whose initial nucleation is initiated by as few as 27 unit cells. The crystallisation occurs preferentially in the ⟨111⟩ crystalline directions via a two-dimensional (2D) layer-by-layer growth mode; resulting in grains with [110] surface normal and [111] plane facets. This growth process was found to reduce the crystallisation energy by more than 50% when compared to bulk samples whilst still leading to the growth of highly ordered grains expected to give a high degree of spin-polarisation. Our findings suggest that the 2D layer-by-layer growth minimises the crystallisation energy allowing for the possible implementation of highly spin-polarised alloy films into current chip and memory technologies.

  3. Galvanomagnetic properties of Fe2YZ (Y = Ti, V, Cr, Mn, Fe, Ni; Z = Al, Si) heusler alloys

    NASA Astrophysics Data System (ADS)

    Kourov, N. I.; Marchenkov, V. V.; Belozerova, K. A.; Weber, H. W.

    2015-11-01

    The Hall effect and the magnetoresistance of Fe2YZ Heusler alloys, where Y = Ti, V, Cr, Mn, Fe, and Ni, are the 3 d transition metals and Z = Al and Si are the s, p elements of the third period of the periodic table, are studied at T = 4.2 K in magnetic fields H ≤ 100 kOe. It is shown that, in the high-field limit ( H > 10 kOe), the value and the sign of the normal ( R 0) and anomalous ( R s ) Hall coefficients change anomalously during transition from paramagnetic (Y = Ti, V) to ferromagnetic (Y = Cr, Mn, Fe, Ni) alloys. These coefficients have different signs for all alloys. Constant R s in the ferromagnetic alloys is positive, proportional to the residual resistivity ratio ( R s ∝ ρ 0 3.1 ), and inversely proportional to spontaneous magnetization. The magnetoresistance of the alloys is a few percent and has a negative sign. A positive addition to transverse magnetoresistance is only detected in high magnetic fields, H > 10 kOe.

  4. Electric field tunability of microwave soft magnetic properties of Co2FeAl Heusler alloy film

    NASA Astrophysics Data System (ADS)

    Li, Shandong; Xu, Jie; Xue, Qian; Du, Honglei; Li, Qiang; Chen, Caiyun; Yang, Ru; Xie, Shiming; Liu, Ming; Nan, Tianxiang; Sun, Nian X.; Shao, Weiquan

    2015-05-01

    Co2FeAl Heusler alloy film with 100 nm in thickness was sputtered on (011)-cut lead zinc niobate-lead titanate (PZN-PT) single crystal slabs. It was revealed that this multiferroic laminate shows very large electric field (E-field) tunability of microwave soft magnetic properties. With the increase of electric field from 0 to 8 kV/cm on PZN-PT, the anisotropy field, HK, of the Co2FeAl film along [100] direction of PZN-PT is dramatically enhanced from 65 to 570 Oe due to the strong magnetoelectric (ME) coupling between ferromagnetic Co2FeAl film and ferroelectric substrate. At the same time, the damping constant α of Co2FeAl film dramatically decreases from 0.20 to 0.029. As a result, a significantly shift of self-biased ferromagnetic resonance frequency, fFMR, from 1.86 to 6.68 GHz with increment of 3.6 times was obtained. These features demonstrate that Co2FeAl/PZN-PT multiferroic laminate is promising in fabrication of E-field tunable microwave components.

  5. Temperature dependence of tunneling magnetoresistance in epitaxial magnetic tunnel junctions using a Co2FeAl Heusler alloy electrode

    NASA Astrophysics Data System (ADS)

    Wang, Wenhong; Sukegawa, Hiroaki; Inomata, Koichiro

    2010-09-01

    Spin-valve-type epitaxial magnetic tunnel junctions (MTJs) consisting of a full-Heusler alloy Co2FeAl (CFA) and a MgO tunnel barrier were fabricated on a single-crystal MgO(001) substrate using sputtering method for all the layers. Experimental temperature-dependent tunnel magnetoresistance in the MTJs was revealed to be fitted well using spin wave excitation model for tunneling spin polarization, P(T)=P0(1-αT3/2) up to room temperature, where P0 is the spin polarization at 0 K and α is a fitting parameter. The determined P and α are shown to be significantly different between bottom and top CFA electrodes facing a MgO barrier. It is demonstrated that the bottom CFA deposited on a Cr buffer has a low α and behaves as a half-metal with P˜1 in terms of the Δ1 symmetry due to the coherent tunneling through a MgO barrier.

  6. Epitaxial growth of Heusler alloy Co{sub 2}MnSi/MgO heterostructures on Ge(001) substrates

    SciTech Connect

    Li Guifang; Taira, Tomoyuki; Matsuda, Ken-ichi; Arita, Masashi; Uemura, Tetsuya; Yamamoto, Masafumi

    2011-06-27

    We prepared Heusler alloy Co{sub 2}MnSi/MgO heterostructures on single-crystal Ge(001) substrates through magnetron sputtering for Co{sub 2}MnSi and electron beam evaporation for MgO as a promising candidate for future generation spin-based functional devices. Structural investigations showed that the Co{sub 2}MnSi/MgO heterostructure was grown epitaxially on a Ge(001) substrate with extremely smooth and abrupt interfaces and showed the L2{sub 1} structure for the Co{sub 2}MnSi film. Furthermore, a sufficiently high saturation magnetization ({mu}{sub s}) value of 5.1 {mu}{sub B}/f.u. at 10 K, which is close to the theoretically predicted {mu}{sub s} of 5.0 {mu}{sub B}/f.u. for half-metallic Co{sub 2}MnSi, was obtained for prepared Co{sub 2}MnSi films.

  7. Galvanomagnetic properties of Fe{sub 2}YZ (Y = Ti, V, Cr, Mn, Fe, Ni; Z = Al, Si) heusler alloys

    SciTech Connect

    Kourov, N. I. Marchenkov, V. V.; Belozerova, K. A.; Weber, H. W.

    2015-11-15

    The Hall effect and the magnetoresistance of Fe{sub 2}YZ Heusler alloys, where Y = Ti, V, Cr, Mn, Fe, and Ni, are the 3d transition metals and Z = Al and Si are the s, p elements of the third period of the periodic table, are studied at T = 4.2 K in magnetic fields H ≤ 100 kOe. It is shown that, in the high-field limit (H > 10 kOe), the value and the sign of the normal (R{sub 0}) and anomalous (R{sub s}) Hall coefficients change anomalously during transition from paramagnetic (Y = Ti, V) to ferromagnetic (Y = Cr, Mn, Fe, Ni) alloys. These coefficients have different signs for all alloys. Constant R{sub s} in the ferromagnetic alloys is positive, proportional to the residual resistivity ratio (R{sub s} ∝ ρ{sub 0}{sup 3.1}), and inversely proportional to spontaneous magnetization. The magnetoresistance of the alloys is a few percent and has a negative sign. A positive addition to transverse magnetoresistance is only detected in high magnetic fields, H > 10 kOe.

  8. Effect of Off-Stoichiometry on the Thermoelectric Properties of Heusler-Type Fe2VAl Sintered Alloys

    NASA Astrophysics Data System (ADS)

    Mikami, M.; Inukai, M.; Miyazaki, H.; Nishino, Y.

    2016-03-01

    Heusler-type Fe2V1- x Al1+ x sintered alloys with micrometer-sized grains were fabricated by the powder metallurgical process using mechanical alloying and pulse-current sintering. Both positive (˜90 μV/K) and negative (˜-140 μV/K) Seebeck coefficients were obtained for the composition ranges of x > 0 and x < 0, respectively, resulting from a Fermi level shift caused by the change in the valence electron concentration. The electrical resistivity was reduced by the carrier doping effect, especially at lower temperatures, resulting in an increased thermoelectric power factor of 2.8 mW/m-K2 for the p-type alloy with x = 0.06 and 5.0 mW/m-K2 for the n-type alloy with x = -0.06. In addition, the lattice thermal conductivity decreased with | x| because of phonon scattering at crystal lattice defects induced by the off-stoichiometry. Consequently, the thermoelectric figure of merit, ZT, was enhanced and reached 0.07 for p-type alloys with 0.06 < x < 0.15 and 0.18 for n-type alloys with -0.15 < x < -0.10 around 500 K. The ZT value was especially enhanced at higher temperatures by the off-stoichiometric composition control, which could extend the range of heat source temperatures for thermoelectric power generation applications using this alloy.

  9. Correlation effect investigations on the Magneto-optical Kerr Spectra of Co-based Heusler alloys from first principles

    NASA Astrophysics Data System (ADS)

    Kim, Miyoung; Lim, Hanjo; Lee, Jae Il

    2011-03-01

    Here, we report our ab-initio calculational results on the electronic structures and magneto-optical (MO) properties of the ferromagnetic Co 2 Mn X full Heusler alloys. Employing the +U corrections for the transition metal 3 d bands in addition to the local density approximation (LDA), we investigate the correlation effect on the MO spectra in polar geometry as well as the detailed electronic structures using FLAPW method. Results show that the correlation effect results in a blue-shift of the peak positions and large enhancement of the low energy MO spectra, which are attributed to the increased t 2g - e g splitting of spin minority Co and Mn d - bands indicating the suppression of diagonal elements of optical conductivity at energy region of 1 ~ 2 eV where the interband transitions are forbidden. This work is supported by Korean Research Foundation Grant by MOEHRD (KRF 2007-412-J04001) and also by Basic Science Research Program through the National Research Foundation of Korea (NRF-2010-0005387).

  10. On the half-metallicity of Co2FeSi Heusler alloy: Point-contact Andreev reflection spectroscopy and ab initio study

    NASA Astrophysics Data System (ADS)

    Makinistian, L.; Faiz, Muhammad M.; Panguluri, Raghava P.; Balke, B.; Wurmehl, S.; Felser, C.; Albanesi, E. A.; Petukhov, A. G.; Nadgorny, B.

    2013-06-01

    Co2FeSi, a Heusler alloy with the highest magnetic moment per unit cell and the highest Curie temperature, has largely been described theoretically as a half-metal. This conclusion, however, disagrees with point contact Andreev reflection (PCAR) spectroscopy measurements, which give much lower values of spin polarization, P. Here, we present the spin polarization measurements of Co2FeSi by the PCAR technique, along with a thorough computational exploration, within the DFT and a GGA+U approach, of the Coulomb exchange U parameters for Co and Fe atoms, taking into account spin-orbit coupling. We find that the orbital contribution (mo) to the total magnetic moment (mT) is significant, since it is at least 3 times greater than the experimental uncertainty of mT. The account of mo radically affects the acceptable values of U. Specifically, we find no values of U that would simultaneously satisfy the experimental values of the magnetic moment and result in the half-metallicity of Co2FeSi. On the other hand, the ranges of U that we report as acceptable are compatible with spin polarization measurements (ours and the ones found in the literature), which all are within approximately the 40-60 % range. Thus, based on reconciling experimental and computational results, we conclude that (a) spin-orbit coupling cannot be neglected in calculating Co2FeSi magnetic properties, and (b) Co2FeSi Heusler alloy is not half-metallic. We believe that our approach can be applied to other Heusler alloys such as Co2FeAl.

  11. Structural and chemical ordering of Heusler CoxMnyGez epitaxial films on Ge (111). Quantitative study using traditional and anomalous x-ray diffraction techniques

    DOE PAGESBeta

    Collins, B. A.; Chu, Y.; He, L.; Haskel, D.; Tsui, F.

    2015-12-14

    We found that epitaxial films of CoxMnyGez grown on Ge (111) substrates by molecular-beam-epitaxy techniques have been investigated as a continuous function of composition using combinatorial synchrotron x-ray diffraction (XRD) and x-ray fluorescence (XRF) spectroscopy techniques. A high-resolution ternary epitaxial phase diagram is obtained, revealing a small number of structural phases stabilized over large compositional regions. Ordering of the constituent elements in the compositional region near the full Heusler alloy Co2MnGe has been examined in detail using both traditional XRD and a new multiple-edge anomalous diffraction (MEAD) technique. Multiple-edge anomalous diffraction involves analyzing the energy dependence of multiple reflections acrossmore » each constituent absorption edge in order to detect and quantify the elemental distribution of occupation in specific lattice sites. Results of this paper show that structural and chemical ordering are very sensitive to the Co : Mn atomic ratio, such that the ordering is the highest at an atomic ratio of 2 but significantly reduced even a few percent off this ratio. The in-plane lattice is nearly coherent with that of the Ge substrate, while the approximately 2% lattice mismatch is accommodated by the out-of-plane tetragonal strain. Furthermore, the quantitative MEAD analysis reveals no detectable amount (<0.5%) of Co-Mn site swapping, but instead high levels (26%) of Mn-Ge site swapping. Increasing Ge concentration above the Heusler stoichiometry (Co 0.5 Mn 0.25 Ge 0.25 ) is shown to correlate with increased lattice vacancies, antisites, and stacking faults, but reduced lattice relaxation. The highest degree of chemical ordering is observed off the Heusler stoichiometry with a Ge enrichment of 5 at.%.« less

  12. Magnesium compounds

    USGS Publications Warehouse

    Kramer, D.A.

    2010-01-01

    Seawater and natural brines accounted for about 40 percent of U.S. magnesium compounds production in 2009. Dead-burned magnesia was produced by Martin Marietta Magnesia Specialties from well brines in Michigan. Caustic-calcined magnesia was recovered from seawater by Premier Chemicals in Florida, from well brines in Michigan by Martin Marietta and from magnesite in Nevada by Premier Chemicals. Intrepid Potash-Wendover, and Great Salt Lake Minerals Corp. recovered magnesium chloride brines from the Great Salt Lake in Utah. Magnesium hydroxide was produced from seawater by SPI Pharma in Delaware and Premier Chemicals in Florida, and by Martin Marietta from its operation mentioned above.

  13. Magnesium compounds

    USGS Publications Warehouse

    Kramer, D.A.

    2002-01-01

    Seawater and natural brines accounted for about 60% of US magnesium compounds production in 2001. Dead-burned and caustic-calcined magnesias were recovered from seawater in Florida by Premier Chemicals. They were also recovered from Michigan well brines by Dow Chemical, Martin Marietta Magnesia Specialties and Rohm & Haas. And Premier Chemicals recovered dead-burned and caustic-calcined magnesias from magnesite in Nevada. Reilly Industries and Great Salt Lake Minerals recovered magnesium chloride brines from the Great Salt Lake in Utah.

  14. Magnesium compounds

    USGS Publications Warehouse

    Kramer, D.A.

    2011-01-01

    Seawater and natural brines accounted for about 54 percent of U.S. magnesium compounds production in 2010. Dead-burned magnesia was produced by Martin Marietta Magnesia Specialties from well brines in Michigan. Caustic-calcined magnesia was recovered from seawater by Premier Magnesia in Florida, from well brines in Michigan by Martin Marietta and from magnesite in Nevada by Premier Magnesia. Intrepid Potash-Wendover and Great Salt Lake Minerals Corp. recovered magnesium chloride brines from the Great Salt Lake in Utah. Magnesium hydroxide was produced from seawater by SPI Pharma in Delaware and Premier Magnesia in Florida, and by Martin Marietta from its operation mentioned above.

  15. Fe{sub 2-x}Co{sub x}MnSi (x = 0, 1 and 2) Heusler alloys: Structural, magnetic and atomic site disorder properties

    SciTech Connect

    Bhatt, Harsh; Mukadam, M. D.; Meena, S. S.; Yusuf, S. M.

    2015-06-24

    The Heusler alloy series Fe{sub 2-x}Co{sub x}MnSi (x = 0, 1 and 2) is theoretically predicted to be half metallic. We prepared the sample series and determined the structural and magnetic properties to check if these materials are suitable for spintronics applications. The Curie temperatures of two of the alloys have been found to be well above the room temperature. But the presence of elements with atoms of similar size leads to atomic site disorder in these alloys, which may destroy the half metallic nature. The atomic site disorder has been confirmed by Mössbauer spectroscopy.

  16. Modelling current-induced magnetization switching in Heusler alloy Co{sub 2}FeAl-based spin-valve nanopillar

    SciTech Connect

    Huang, H. B.; Ma, X. Q.; Liu, Z. H.; Zhao, C. P.; Chen, L. Q.

    2014-04-07

    We investigated the current-induced magnetization switching in a Heusler alloy Co{sub 2}FeAl-based spin-valve nanopillar by using micromagnetic simulations. We demonstrated that the elimination of the intermediate state is originally resulted from the decease of effective magnetic anisotropy constant. The magnetization switching can be achieved at a small current density of 1.0 × 10{sup 4} A/cm{sup 2} by increasing the demagnetization factors of x and y axes. Based on our simulation, we found magnetic anisotropy and demagnetization energies have different contributions to the magnetization switching.

  17. Magnesium compounds

    USGS Publications Warehouse

    Kramer, D.A.

    2007-01-01

    Seawater and natural brines accounted for about 52 percent of U.S. magnesium compounds production in 2006. Dead-burned magnesia was produced by Martin Marietta Magnesia Specialties from well brines in Michigan. Caustic-calcined magnesia was recovered from sea-water by Premier Chemicals in Florida; from well brines in Michigan by Martin Marietta and Rohm and Haas; and from magnesite in Nevada by Premier Chemicals. Intrepid Potash-Wendover and Great Salt Lake Minerals recovered magnesium chloride brines from the Great Salt Lake in Utah. Magnesium hydroxide was produced from brucite by Applied Chemical Magnesias in Texas, from seawater by SPI Pharma in Delaware and Premier Chemicals in Florida, and by Martin Marietta and Rohm and Haas from their operations mentioned above. About 59 percent of the magnesium compounds consumed in the United States was used for refractories that are used mainly to line steelmaking furnaces. The remaining 41 percent was consumed in agricultural, chemical, construction, environmental and industrial applications.

  18. Intermetallic Compounds

    NASA Astrophysics Data System (ADS)

    Takagiwa, Y.; Matsuura, Y.; Kimura, K.

    2014-06-01

    We have focused on the binary narrow-bandgap intermetallic compounds FeGa3 and RuGa3 as thermoelectric materials. Their crystal structure is FeGa3-type (tetragonal, P42/ mnm) with 16 atoms per unit cell. Despite their simple crystal structure, their room temperature thermal conductivity is in the range 4-5-W-m-1-K-1. Both compounds have narrow-bandgaps of approximately 0.3-eV near the Fermi level. Because their Seebeck coefficients are quite large negative values in the range 350-<-| S 373K|-<-550- μV-K-1 for undoped samples, it should be possible to obtain highly efficient thermoelectric materials both by adjusting the carrier concentration and by reducing the thermal conductivity. Here, we report the effects of doping on the thermoelectric properties of FeGa3 and RuGa3 as n and p-type materials. The dimensionless figure of merit, ZT, was significantly improved by substitution of Sn for Ga in FeGa3 (electron-doping) and by substitution of Zn for Ga in RuGa3 (hole-doping), mainly as a result of optimization of the electronic part, S 2 σ.

  19. Magnesium compounds

    USGS Publications Warehouse

    Kramer, D.A.

    2012-01-01

    Seawater and natural brines accounted for about 57 percent of magnesium compounds produced in the United States in 2011. Dead-burned magnesia was produced by Martin Marietta Magnesia Specialties LLC from well brines in Michigan. Caustic-calcined magnesia was recovered from seawater by Premier Magnesia LLC in Florida, from well brines in Michigan by Martin Marietta and from magnesite in Nevada by Premier Magnesia. Intrepid Potash Wendover LLC and Great Salt Lake Minerals Corp. recovered magnesium chloride brines from the Great Salt Lake in Utah. Magnesium hydroxide was produced from seawater by SPI Pharma Inc. in Delaware and Premier Magnesia in Florida, and by Martin Marietta from its brine operation in Michigan.

  20. Bismaleimide compounds

    DOEpatents

    Adams, Johnnie E.; Jamieson, Donald R.

    1986-01-14

    Bismaleimides of the formula ##STR1## wherein R.sub.1 and R.sub.2 each independently is H, C.sub.1-4 -alkyl, C.sub.1-4 -alkoxy, C1 or Br, or R.sub.1 and R.sub.2 together form a fused 6-membered hydrocarbon aromatic ring, with the proviso that R.sub.1 and R.sub.2 are not t-butyl or t-butoxy; X is O, S or Se; n is 1-3; and the alkylene bridging group, optionally, is substituted by 1-3 methyl groups or by fluorine, form polybismaleimide resins which have valuable physical properties. Uniquely, these compounds permit extended cure times, i.e., they remain fluid for a time sufficient to permit the formation of a homogeneous melt prior to curing.

  1. Bismaleimide compounds

    DOEpatents

    Adams, J.E.; Jamieson, D.R.

    1986-01-14

    Bismaleimides of the formula shown in the diagram wherein R[sub 1] and R[sub 2] each independently is H, C[sub 1-4]-alkyl, C[sub 1-4]-alkoxy, Cl or Br, or R[sub 1] and R[sub 2] together form a fused 6-membered hydrocarbon aromatic ring, with the proviso that R[sub 1] and R[sub 2] are not t-butyl or t-butoxy; X is O, S or Se; n is 1--3; and the alkylene bridging group, optionally, is substituted by 1--3 methyl groups or by fluorine, form polybismaleimide resins which have valuable physical properties. Uniquely, these compounds permit extended cure times, i.e., they remain fluid for a time sufficient to permit the formation of a homogeneous melt prior to curing.

  2. Design of Fatigue Resistant Heusler-strengthened PdTi-based Shape Memory Alloys for Biomedical Applications

    NASA Astrophysics Data System (ADS)

    Frankel, Dana J.

    The development of non-surgical transcatheter aortic valve implantation (TAVI) techniques, which utilize collapsible artificial heart valves with shape memory alloy (SMA)-based frames, pushes performance requirements for biomedical SMAs beyond those for well-established vascular stent applications. Fatigue life for these devices must extend into the ultra-high cycle fatigue (UHCF) regime (>600M cycles) with zero probability of failure predicted at applied strain levels. High rates of Ni-hypersensitivity raise biocompatibility concerns, driving the development of low-Ni and Ni-free SMAs. This work focuses on the development of biocompatible, precipitation-strengthened, fatigue-resistant PdTi-based SMAs for biomedical applications. Functional and structural fatigue are both manifestations of cyclic instability resulting in accumulation of slip and eventual structural damage. While functional fatigue is easily experimentally evaluated, structural fatigue is more difficult to measure without the proper equipment. Therefore, in this work a theoretical approach using a model well validated in steels is utilized to investigate structural fatigue behavior in NiTi in the UHCF regime, while low cycle functional fatigue is evaluated in order to monitor the core phenomena of the cyclic instability. Results from fatigue simulations modeling crack nucleation at non-metallic inclusions in commercial NiTi underscore the importance of increasing yield strength for UHCF performance. Controlled precipitation of nanoscale, low-misfit, L21 Heusler aluminides can provide effective strengthening. Phase relations, precipitation kinetics, transformation temperature, transformation strain, cyclic stability, and mechanical properties are characterized in both Ni-free (Pd,Fe)(Ti,Al) and low-Ni high-strength "hybrid" (Pd,Ni)(Ti,Zr,Al) systems. Atom probe tomography is employed to measure phase compositions and particle sizes used to calibrate LSW models for coarsening kinetics and Gibbs

  3. Two successive magneto-structural transformations and their relation to enhanced magnetocaloric effect for Ni55.8Mn18.1Ga26.1 Heusler alloy

    PubMed Central

    Li, Zhe; Xu, Kun; Zhang, Yuanlei; Tao, Chang; Zheng, Dong; Jing, Chao

    2015-01-01

    In the present work, two successive magneto-structural transformations (MSTs) consisting of martensitic and intermartensitic transitions have been observed in polycrystalline Ni55.8Mn18.1Ga26.1 Heusler alloy. Benefiting from the additional latent heat contributed from intermediate phase, this alloy exhibits a large transition entropy change ΔStr with the value of ~27 J/kg K. Moreover, the magnetocaloric effect (MCE) has been also evaluated in terms of Maxwell relation. For a magnetic field change of 30 kOe, it was found that the calculated value of refrigeration capacity in Ni55.8Mn18.1Ga26.1 attains to ~72 J/kg around room temperature, which significantly surpasses those obtained for many Ni-Mn based Heusler alloys in the same condition. Such an enhanced MCE can be ascribed to the fact that the isothermal entropy change ΔST is spread over a relatively wide temperature interval owing to existence of two successive MSTs for studied sample. PMID:26450663

  4. Effect of an interface Mg insertion layer on the reliability of a magnetic tunnel junction based on a Co2FeAl full-Heusler alloy

    NASA Astrophysics Data System (ADS)

    Lee, Jung-Min; Kil, Gyu Hyun; Lee, Gae Hun; Choi, Chul Min; Song, Yun-Heub; Sukegawa, Hiroaki; Mitani, Seiji

    2014-04-01

    The reliability of a magnetic tunnel junction (MTJ) based on a Co2FeAl (CFA) full-Heusler alloy with a MgO tunnel barrier was evaluated. In particular, the effect of a Mg insertion layer under the MgO was investigated in view of resistance drift by using various voltage stress tests. We compared the resistance change during constant voltage stress (CVS) and confirmed a trap/detrap phenomenon during the interval stress test for samples with and without a Mg insertion layer. The MTJ with a Mg insertion layer showed a relatively small resistance change for the CVS test and a reduced trap/detrap phenomenon for the interval stress test compared to the sample without a Mg insertion layer. This is understood to be caused by the improved crystallinity at the bottom of the CFA/MgO interface due to the Mg insertion layer, which provides a smaller number of trap site during the stress test. As a result, the interface condition of the MgO layer is very important for the reliability of a MTJ using a full-Heusler alloy, and the the insert of a Mg layer at the MgO interface is expected to be an effective method for enhancing the reliability of a MTJ.

  5. Structural and magnetic properties of epitaxial Heusler alloy Fe{sub 2}Cr{sub 0.5}Co{sub 0.5}Si

    SciTech Connect

    Wang, Yu-Pu; Han, Gu-Chang; Qiu, Jinjun; Yap, Qi-Jia; Lu, Hui; Teo, Kie-Leong

    2014-05-07

    This paper reports the study of structural and magnetic properties of Heusler alloy Fe{sub 2}Cr{sub 0.5}Co{sub 0.5}Si (FCCS) thin film and its tunnel magnetoresistance (TMR) effect. The smooth quaternary Heusler alloy FCCS film with surface roughness of rms value of 0.25 nm measured by atomic force microscopy and partial L2{sub 1} phase was obtained by magnetron sputtering at room temperature followed by in-situ annealing at 400 °C. The saturation magnetization and coercivity of FCCS are 410 emu/cm{sup 3} and 20 Oe, respectively. The magnetic tunnel junctions (MTJs) using FCCS as free layer were studied in detail as a function of post-annealing temperature. A TMR ratio of 15.6% has been achieved with 300 °C post-annealing. This is about twice the highest TMR ratio obtained in MTJs using Fe{sub 2}CrSi. The enhancement of TMR ratio can be attributed to the successful tuning of the Fermi level of Fe{sub 2}CrSi close to the center of the minority band gap by Co-doping.

  6. Tunable ferromagnetic and antiferromagnetic interfacial exchange coupling in perpendicularly magnetized L1{sub 0}-MnGa/Co{sub 2}FeAl Heusler bilayers

    SciTech Connect

    Ma, Q. L. Mizukami, S.; Zhang, X. M.; Miyazaki, T.

    2014-12-21

    In this work, we report a tailorable exchange coupling (J{sub ex}) at the Mn{sub 62}Ga{sub 38}/Co{sub 2}FeAl interface, where Mn{sub 62}Ga{sub 38} and Co{sub 2}FeAl alloys are tetragonal Heusler alloy with high perpendicular magnetic anisotropy and typical cubic Heusler alloy with soft magnetism, respectively. As the post annealing temperature (T{sub a}) is lower than 375 °C, the J{sub ex} is ferromagnetic with strength controllable from 7.5 to 0.5 erg/cm{sup 2}. Interestingly, as T{sub a} increases higher than 400 °C, an antiferromagnetic J{sub ex} of −5.5 erg/cm{sup 2} is observed. The ferromagnetic/antiferromagnetic transition is further evidenced by the spin dependent transport property of the magnetic tunnel junctions with Mn{sub 62}Ga{sub 38}/Co{sub 2}FeAl as electrode. Based on structure characterization, the variation of J{sub ex} during annealing is discussed.

  7. Magnetic and structural anisotropies in laser ablated epitaxial thin films of full-Heusler alloy Co2MnSi on SrTiO3

    NASA Astrophysics Data System (ADS)

    Pandey, Himanshu; Rout, P. K.; Budhani, R. C.

    2013-03-01

    We present the thickness dependent magnetic properties of laser ablated epitaxial Co2MnSi (CMS)Heusler alloy thin films grown on (001) oriented SrTiO3 substrate. In order to study the intrinsic magnetic anisotropy, a highly ordered single crystal thin film of Heusler alloys is necessary. This provides a unique opportunity to determine the behavior of magnetization reversal, and affect important properties such as the coercive field and remanence. The two important sources of the magnetic anisotropy are the magnetic dipolar interaction and the spin-orbit interaction. The strain in films due to the lattice mismatch with the substrate affects the shape anisotropy while spin-orbit coupling changes magneto-crystalline anisotropy. We have observed an in-plane biaxial compressive strain in the films which relaxes with increasing film thickness. Although the hysteresis loops show an in-plane easy axis for all films, the single-domain phase diagram reveals a gradual transition from in-plane to out-of-plane transition of magnetization as the film thickness is decreased. The magnetization starts to cant as film thickness start to decrease and we found a canting angle of ~ 31.8° with respect to the film plane for our thinnest 5 nm CMS films. We acknowledge support from DIT, DST, CSIR and IIT Kanpur.

  8. A low-temperature fabricated gate-stack structure for Ge-based MOSFET with ferromagnetic epitaxial Heusler-alloy/Ge electrodes

    NASA Astrophysics Data System (ADS)

    Fujita, Yuichi; Yamada, Michihiro; Nagatomi, Yuta; Yamamoto, Keisuke; Yamada, Shinya; Sawano, Kentarou; Kanashima, Takeshi; Nakashima, Hiroshi; Hamaya, Kohei

    2016-06-01

    A possible low-temperature fabrication process of a gate-stack for Ge-based spin metal–oxide–semiconductor field-effect transistor (MOSFET) is investigated. First, since we use epitaxial ferromagnetic Heusler alloys on top of the phosphorous doped Ge epilayer as spin injector and detector, we need a dry etching process to form Heusler-alloy/n+-Ge Schottky-tunnel contacts. Next, to remove the Ge epilayers damaged by the dry etching process, the fabricated structures are dipped in a 0.03% diluted H2O2 solution. Finally, Al/SiO2/GeO2/Ge gate-stack structures are fabricated at 300 °C as a top gate-stack structure. As a result, the currents in the Ge-MOSFET fabricated here can be modulated by applying gate voltages even by using the low-temperature formed gate-stack structures. This low-temperature fabrication process can be utilized for operating Ge spin MOSFETs with a top gate electrode.

  9. The ``Missing Compounds'' affair in functionality-driven material discovery

    NASA Astrophysics Data System (ADS)

    Zunger, Alex

    2014-03-01

    as (b) Use of ``first principles thermodynamics'' to discern which of the previously ``missing compounds'' should, in fact exist and in which structure. Synthesis efforts by Poeppelmeier group at NU realized 20 never-before-made half-Heusler compounds out of the 20 predicted ones, in our predicted space groups. This type of theory-led experimental search of designed materials with target functionalities may shorten the current process of discovery of interesting functional materials. Supported by DOE ,Office of Science, Energy Frontier Research Center for Inverse Design

  10. A p-type Heusler compound: Growth, structure, and properties of epitaxial thin NiYBi films on MgO(100)

    SciTech Connect

    Shan Rong; Ouardi, Siham; Fecher, Gerhard H.; ViolBarbosa, Carlos E.; Felser, Claudia; Gao Li; Kellock, Andrew; Parkin, Stuart S. P.; Gloskovskii, Andrei; Ikenaga, Eiji

    2012-11-19

    Epitaxial semiconducting NiYBi thin films were directly prepared on MgO(100) substrates by magnetron sputtering. The intensity ratio of the (200) and (400) diffraction peaks, I(200)/I(400) = 2.93, was close to the theoretical value (3.03). The electronic structure of NiYBi was calculated using wien2k, and a narrow indirect band gap of width of 210 meV was found. The valence band spectra of the films obtained by linear dichroism in hard x-ray photoelectron spectroscopy exhibit clear structures that are in good agreement with the calculated band structure of NiYBi.

  11. Low-temperature grown quaternary Heusler-compound Co{sub 2}Mn{sub 1-x}Fe{sub x}Si films on Ge(111)

    SciTech Connect

    Yamada, S.; Murakami, T.; Hamaya, K.; Varaprasad, B.; Rajanikanth, A.; Hono, K.; Takahashi, Y. K.; Miyao, M.

    2011-04-01

    Highly ordered quaternary Co{sub 2}Mn{sub 1-x}Fe{sub x}Si films on Ge(111) are explored for spintronic device applications on Si-large-scale integrated circuit (LSI) platform. By using low-temperature molecular beam epitaxy techniques, relatively large magnetic moments are demonstrated for x between 0.50 and 1.0 despite extremely low temperature growth of 130 deg. C. Also, L2{sub 1}-ordered crystal structures can be realized even on a group-IV semiconductor substrate, Ge, compatible with Si-LSI technologies. By the point contact Andreev reflection method, the spin polarization of Co{sub 2}Mn{sub 0.5}Fe{sub 0.5}Si films is estimated to be P= 0.58 {+-} 0.02. We believe that this study will be a first step for integration of high-performance spintronic applications with next ultra LSI.

  12. Antiferromagnetism and superconductivity in the half-Heusler semimetal HoPdBi

    PubMed Central

    Pavlosiuk, Orest; Kaczorowski, Dariusz; Fabreges, Xavier; Gukasov, Arsen; Wiśniewski, Piotr

    2016-01-01

    We observed the coexistence of superconductivity and antiferromagnetic order in the single-crystalline ternary pnictide HoPdBi, a plausible topological semimetal. The compound orders antiferromagnetically at TN = 1.9 K and exhibits superconductivity below Tc = 0.7 K, which was confirmed by magnetic, electrical transport and specific heat measurements. The specific heat shows anomalies corresponding to antiferromagnetic ordering transition and crystalline field effect, but not to superconducting transition. Single-crystal neutron diffraction indicates that the antiferromagnetic structure is characterized by the propagation vector. Temperature variation of the electrical resistivity reveals two parallel conducting channels of semiconducting and metallic character. In weak magnetic fields, the magnetoresistance exhibits weak antilocalization effect, while in strong fields and temperatures below 50 K it is large and negative. At temperatures below 7 K Shubnikov-de Haas oscillations with two frequencies appear in the resistivity. These oscillations have non-trivial Berry phase, which is a distinguished feature of Dirac fermions. PMID:26728755

  13. Antiferromagnetism and superconductivity in the half-Heusler semimetal HoPdBi.

    PubMed

    Pavlosiuk, Orest; Kaczorowski, Dariusz; Fabreges, Xavier; Gukasov, Arsen; Wiśniewski, Piotr

    2016-01-01

    We observed the coexistence of superconductivity and antiferromagnetic order in the single-crystalline ternary pnictide HoPdBi, a plausible topological semimetal. The compound orders antiferromagnetically at TN = 1.9 K and exhibits superconductivity below Tc = 0.7 K, which was confirmed by magnetic, electrical transport and specific heat measurements. The specific heat shows anomalies corresponding to antiferromagnetic ordering transition and crystalline field effect, but not to superconducting transition. Single-crystal neutron diffraction indicates that the antiferromagnetic structure is characterized by the propagation vector. Temperature variation of the electrical resistivity reveals two parallel conducting channels of semiconducting and metallic character. In weak magnetic fields, the magnetoresistance exhibits weak antilocalization effect, while in strong fields and temperatures below 50 K it is large and negative. At temperatures below 7 K Shubnikov-de Haas oscillations with two frequencies appear in the resistivity. These oscillations have non-trivial Berry phase, which is a distinguished feature of Dirac fermions. PMID:26728755

  14. Electronic structure and half-metallicity of the Heusler alloy Co2ZrGe

    NASA Astrophysics Data System (ADS)

    Li, Songtao; Liu, Yang; Ren, Zhi; Zhang, Xiaohong; Liu, Guodong

    2014-10-01

    The site preference, the electronic structure and the magnetic properties of Co2ZrGe have been studied by using first-principles calculations, and the stabilities of the Cu2MnAl-type and the Hg2CuTi-type structures have been tested in this respect. The Cu2MnAltype structure is more favorable than the Hg2CuTitype structure for the Co2ZrGe compound, and the equilibrium lattice parameter of the Cu2MnAltype Co2ZrGe alloy is 6.06 Å. The Co2ZrGe alloy is found to have an energy gap in the minority spin direction at the Fermi level ( E F ) and the majority spin band shows strongly metallic characteristic. As a result, the Co2ZrGe alloy is predicted to be a half-metal with 100% spin polarization of the conduction electrons at the E F . The calculated total magnetic moment is 2.00µ B per unit cell, which is in line with the Slater-Pauling curve of M t = Z t - 24. The Co atom-projected spin moment is 1.02µ B , which mainly determines the total moment. Simultaneously, the Zr and the Ge atom moments are -0.08µ B and 0.04µ B , respectively. The Co2ZrGe alloy may be a promising material for application in future spintronics devices.

  15. Optical properties of heusler alloys Co2FeSi, Co2FeAl, Co2CrAl, and Co2CrGa

    NASA Astrophysics Data System (ADS)

    Shreder, E. I.; Svyazhin, A. D.; Belozerova, K. A.

    2013-11-01

    The results of an investigation of optical properties and the calculations of the electronic structure of Co2FeSi, Co2FeAl, Co2CrAl, and Co2CrGa Heusler alloys are presented. The main focus of our attention is the study of the spectral dependence of the real part (ɛ1) and imaginary part (ɛ2) of the dielectric constant in the range of wavelengths λ = 0.3-13 μm using the ellipsometric method. An anomalous behavior of the optical conductivity σ(ω) has been found in the infrared range in the Co2CrAl and Co2CrGa alloys, which differs substantially from that in the Co2FeSi and Co2FeAl alloys. The results obtained are discussed based on the calculations of the electronic structure.

  16. Lattice-matched magnetic tunnel junctions using a Heusler alloy Co2FeAl and a cation-disorder spinel Mg-Al-O barrier

    NASA Astrophysics Data System (ADS)

    Scheike, Thomas; Sukegawa, Hiroaki; Furubayashi, Takao; Wen, Zhenchao; Inomata, Koichiro; Ohkubo, Tadakatsu; Hono, Kazuhiro; Mitani, Seiji

    2014-12-01

    Perfectly lattice-matched magnetic tunnel junctions (MTJs) consisting of a Heusler alloy B2-Co2FeAl (CFA) electrode and a cation-disorder spinel (Mg-Al-O) barrier were fabricated by sputtering and plasma oxidation. We achieved a large tunnel magnetoresistance (TMR) ratio of 228% at room temperature (RT) (398% at 5 K) for the epitaxial CFA/MgAl-O/CoFe(001) MTJ, in which the effect of lattice defects on TMR ratios is excluded. With inserting a ultrathin (≤1.5 nm) CoFe layer between the CFA and Mg-Al-O, the TMR ratio further increased up to 280% at RT (453% at 5 K), which reflected the importance of controlling barrier-electrode interface states other than the lattice matching.

  17. Magnetization Dynamics Through Magnetoimpedance Effect in Isotropic Co2FeAl/Au/Co2FeAl Full-Heusler Alloy Trilayer Films

    NASA Astrophysics Data System (ADS)

    Assolin Corrêa, Marcio; Montardo Escobar, Vivian; Trigueiro-Neto, Osvaldo; Bohn, Felipe; Daiane Sossmeier, Kelly; Gomes Bezerra, Claudionor; Chesman, Carlos; Pearson, John; Hoffmann, Axel

    2013-09-01

    We investigate the magnetization dynamics in low damping parameter α systems by measuring the magnetoimpedance effect over a wide range of frequencies, from 0.1 to 3.0 GHz, in Co2FeAl/Au/Co2FeAl full-Heusler alloy trilayer films grown by magnetron sputtering on glass and MgO substrates. We show that the film produced on the glass substrate presents high magnetoimpedance performance, while that grown on the MgO substrate has low magnetoimpedance performance. Since both films are polycrystalline and have isotropic in-plane magnetic properties, we interpret the magnetoimpedance results in terms of the low damping parameter α and strain effects in the films. Thus, we verified that our films present good magnetoimpedance performance and showed that high performance can be achieved even in films with isotropic in-plane magnetic properties, since they present low damping parameter α.

  18. 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.

  19. Manipulating magnetic anisotropy of the ultrathin Co2FeAl full-Heusler alloy film via growth orientation of the Pt buffer layer

    NASA Astrophysics Data System (ADS)

    Wen, F. S.; Xiang, J. Y.; Hao, C. X.; Zhang, F.; Lv, Y. F.; Wang, W. H.; Hu, W. T.; Liu, Z. Y.

    2013-12-01

    The ultrathin films of Co2FeAl (CFA) full-Heusler alloy were prepared between two Pt layers on MgO single crystals by magnetron sputtering. By controlling the substrate temperature, different growth orientations of the Pt underlayers were realized, and their effects were investigated on the magnetic anisotropy of the ultrathin CFA film. It was revealed that different Pt orientations lead to distinctly different magnetic anisotropy for the sandwiched ultrathin CFA films. The Pt (111) orientation favors the perpendicular anisotropy, while the appearance of partial Pt (001) orientation leads to the quick decrease of perpendicular anisotropy and the complete Pt (001) orientation gives rise to the in-plane anisotropy. With the Pt (111) orientation, the temperature and thickness-induced spin reorientation transitions were investigated in the sandwiched ultrathin CFA films.

  20. Unveiling the Mechanism for the Split Hysteresis Loop in Epitaxial Co2Fe1-xMnxAl Full-Heusler Alloy Films

    PubMed Central

    Tao, X. D.; Wang, H. L.; Miao, B. F.; Sun, L.; You, B.; Wu, D.; Zhang, W.; Oepen, H. P.; Zhao, J. H.; Ding, H. F.

    2016-01-01

    Utilizing epitaxial Co2Fe1-xMnxAl full-Heusler alloy films on GaAs (001), we address the controversy over the analysis for the split hysteresis loop which is commonly found in systems consisting of both uniaxial and fourfold anisotropies. Quantitative comparisons are carried out on the values of the twofold and fourfold anisotropy fields obtained with ferromagnetic resonance and vibrating sample magnetometer measurements. The most suitable model for describing the split hysteresis loop is identified. In combination with the component resolved magnetization measurements, these results provide compelling evidences that the switching is caused by the domain wall nucleation and movements with the switching fields centered at the point where the energy landscape shows equal minima for magnetization orienting near the easy axis and the field supported hard axis. PMID:26733075

  1. Observation of giant exchange bias in bulk Mn{sub 50}Ni{sub 42}Sn{sub 8} Heusler alloy

    SciTech Connect

    Sharma, Jyoti; Suresh, K. G.

    2015-02-16

    We report a giant exchange bias (EB) field of 3520 Oe in bulk Mn{sub 50}Ni{sub 42}Sn{sub 8} Heusler alloy. The low temperature magnetic state of the martensite phase has been studied by DC magnetization and AC susceptibility measurements. Frequency dependence of spin freezing temperature (T{sub f}) on critical slowing down relation and observation of memory effect in zero field cooling mode confirms the super spin glass (SSG) phase at low temperatures. Large EB is attributed to the strong exchange coupling between the SSG clusters formed by small regions of ferromagnetic order embedded in an antiferromagnetic (AFM) matrix. The temperature and cooling field dependence of EB have been studied and related to the change in unidirectional anisotropy at SSG/AFM interface. The training effect also corroborates with the presence of frozen (SSG) moments at the interface and their role in EB.

  2. Giant spontaneous exchange bias triggered by crossover of superspin glass in Sb-doped Ni50Mn38Ga12 Heusler alloys

    NASA Astrophysics Data System (ADS)

    Tian, Fanghua; Cao, Kaiyan; Zhang, Yin; Zeng, Yuyang; Zhang, Rui; Chang, Tieyan; Zhou, Chao; Xu, Minwei; Song, Xiaoping; Yang, Sen

    2016-08-01

    A spontaneous exchange bias (SEB) discovered by Wang et al. [Phys. Rev. Lett. 106 (2011) 077203.] after zero-field cooling (ZFC) has attracted recent attention due to its interesting physics. In this letter, we report a giant SEB tuned by Sb-doping in Ni50Mn38Ga12-xSbx Heusler alloys. Such an SEB was switched on below the blocking temperature of approximately 50 K. The maximum exchange bias HE can arrive at 2930 Oe in a Ni50Mn38Ga10Sb2 sample after ZFC to 2 K. Further studies showed that this SEB was attributable to interaction of superspin glass (SSG) and antiferromagnetic matix, which was triggered by the crossover of SSG from canonical spin glass to a cluster spin glass. Our results not only explain the underlying physics of SEB, but also provide a way to tune and control the SEB performance.

  3. High strain in polycrystalline Ni48.8Mn31.4Ga19.8 Heusler alloys under overlapped static and oscillating magnetic fields

    NASA Astrophysics Data System (ADS)

    Montanher, D. Z.; Pereira, J. R. D.; Cótica, L. F.; Gotardo, R. A. M.; Viana, D. S. F.; Garcia, D.; Eiras, J. A.; Santos, I. A.

    2014-09-01

    Martensitic polycrystalline Ni48.8Mn31.4Ga19.8 Heusler alloys, with a stacking period of 14 atomic planes at room temperature, were innovatively processed by combining high-energy ball milling and powder metallurgy. Bulk samples were mechanically coupled to a piezoelectric material in a parallel configuration, and the mechanical deformation of the studied system due to the twin's variant motion was investigated under overlapped static and oscillating magnetic fields. A reversible and high mechanical deformation is observed when the frequency of the oscillating magnetic field is tuned with the natural vibration frequency of this system. In this condition, a linear deformation as a function of the static magnetic field amplitude occurs in the ±4 kOe range, and a mechanical deformation of 2% at 10 kOe is observed.

  4. Magnetic properties of Ni40+xMn39-xSn21 (x=0, 2, 4, 6 and 8 at.%) Heusler alloys

    SciTech Connect

    Lazpita, P.; Lograsso, T.; Schlagel, D. L.

    2014-01-27

    The low electron concentration region (e/a < 7.75) of the magnetic phase diagram of the off-stoichiometric Ni–Mn–Sn Heusler alloys was investigated in detail by DSC and magnetization measurements of the Ni40+xMn39−xSn21(x = 0, 2, 4, 6 and 8 at.%) alloys. The alloys show a stable austenitic phase without any martensitic transformation down to 5 K even after heat treatment. The Curie temperature exhibits a broad maximum over a large composition range. The evolution of the magnetic moment with the electron concentration fits the data of previous studies and confirms the peak-like dependence in the extended range of e/a values predicted by ab initio calculations. The explored part of the moment versus e/a curve can be explained in terms of a localized magnetic moment model and full atomic order in the alloys.

  5. Giant spontaneous exchange bias triggered by crossover of superspin glass in Sb-doped Ni50Mn38Ga12 Heusler alloys

    PubMed Central

    Tian, Fanghua; Cao, Kaiyan; Zhang, Yin; Zeng, Yuyang; Zhang, Rui; Chang, Tieyan; Zhou, Chao; Xu, Minwei; Song, Xiaoping; Yang, Sen

    2016-01-01

    A spontaneous exchange bias (SEB) discovered by Wang et al. [Phys. Rev. Lett. 106 (2011) 077203.] after zero-field cooling (ZFC) has attracted recent attention due to its interesting physics. In this letter, we report a giant SEB tuned by Sb-doping in Ni50Mn38Ga12-xSbx Heusler alloys. Such an SEB was switched on below the blocking temperature of approximately 50 K. The maximum exchange bias HE can arrive at 2930 Oe in a Ni50Mn38Ga10Sb2 sample after ZFC to 2 K. Further studies showed that this SEB was attributable to interaction of superspin glass (SSG) and antiferromagnetic matix, which was triggered by the crossover of SSG from canonical spin glass to a cluster spin glass. Our results not only explain the underlying physics of SEB, but also provide a way to tune and control the SEB performance. PMID:27478090

  6. Unveiling the Mechanism for the Split Hysteresis Loop in Epitaxial Co2Fe1-xMnxAl Full-Heusler Alloy Films

    NASA Astrophysics Data System (ADS)

    Tao, X. D.; Wang, H. L.; Miao, B. F.; Sun, L.; You, B.; Wu, D.; Zhang, W.; Oepen, H. P.; Zhao, J. H.; Ding, H. F.

    2016-01-01

    Utilizing epitaxial Co2Fe1-xMnxAl full-Heusler alloy films on GaAs (001), we address the controversy over the analysis for the split hysteresis loop which is commonly found in systems consisting of both uniaxial and fourfold anisotropies. Quantitative comparisons are carried out on the values of the twofold and fourfold anisotropy fields obtained with ferromagnetic resonance and vibrating sample magnetometer measurements. The most suitable model for describing the split hysteresis loop is identified. In combination with the component resolved magnetization measurements, these results provide compelling evidences that the switching is caused by the domain wall nucleation and movements with the switching fields centered at the point where the energy landscape shows equal minima for magnetization orienting near the easy axis and the field supported hard axis.

  7. Hysteresis and magnetocaloric effect at the magnetostructural phase transition of Ni-Mn-Ga and Ni-Mn-Co-Sn Heusler alloys

    NASA Astrophysics Data System (ADS)

    Basso, Vittorio; Sasso, Carlo P.; Skokov, Konstantin P.; Gutfleisch, Oliver; Khovaylo, Vladimir V.

    2012-01-01

    Hysteresis features of the direct and inverse magnetocaloric effect associated with first-order magnetostructural phase transitions in Ni-Mn-X (X = Ga, Sn) Heusler alloys have been disclosed by differential calorimetry measurements performed either under a constant magnetic field, H, or by varying H in isothermal conditions. We have shown that the magnetocaloric effect in these alloys crucially depends on the employed measuring protocol. Experimentally observed peculiarities of the magnetocaloric effect have been explained in the framework of a model that accounts for different contributions to the Gibbs energy of austenitic gA and martensitic gM phases. Obtained experimental results have been summarized by plotting a phase fraction of the austenite xA versus the driving force gM-gA. The developed approach allows one to predict reversible and irreversible features of the direct as well as inverse magnetocaloric effect in a variety of materials with first-order magnetic phase transitions.

  8. Miscibility Gap in the Phase Diagrams of Thermoelectric Half-Heusler Materials CoTi_{1-x}Y_xSb ( Y = Sc, V, Mn, Fe)

    NASA Astrophysics Data System (ADS)

    Mena, Joaquin Miranda; Rausch, Elisabeth; Ouardi, Siham; Gruhn, Thomas; Fecher, Gerhard H.; Schoberth, Heiko G.; Emmerich, Heike; Felser, Claudia

    2016-03-01

    The half-Heusler system CoTi{_{1-x}Y_x}Sb ( Y = Sc, V, Mn, Fe) has been investigated by means of an ab initio-based mean-field model which provides phase diagrams of alloys. Co(Ti, Y)Sb materials show a miscibility gap, which leads to spontaneous demixing within a spinodal region. The results are compared with experimental investigations of microstructure and transport properties of the alloys. The thermoelectric properties of the solid solution were investigated comprehensively by measuring the temperature dependence of the Seebeck coefficient as well as electrical and thermal conductivity. Compared with pure CoTiSb, the thermal conductivity of substituted CoTi{_{0.9}Y_{0.1}}Sb was significantly reduced by approximately 53% for Y = V. Here, we report on the effect of phase separation in the Co(Ti, Y)Sb system and its consequences for the thermoelectric figure or merit.

  9. A first principle study of phase stability, electronic structure and magnetic properties for Co2-xCrxMnAl Heusler alloys

    NASA Astrophysics Data System (ADS)

    Rached, H.; Rached, D.; Khenata, R.; Abidri, B.; Rabah, M.; Benkhettou, N.; Omran, S. Bin

    2015-04-01

    The structural stabilities, electronic and magnetic properties of Co2-xCrxMnAl alloys with (x=0,1 and 2) were investigated using the full-potential linear muffin-tin orbital (FP-LMTO) method, in the framework of the density functional theory (DFT) within the generalized gradient approximation (GGA) for the exchange correlation functional. The ground state properties including lattice parameter, bulk modulus for the two considered crystal structures Hg2CuTi-Type (X-Type) and Cu2MnAl-Type (L21-Type) are calculated. The half-metallicity within ferromagnetic ground state starts to appear in CoCrMnAl and Cr2MnAl. In the objective for the proposition of the new HM-FM in the Full-Heusler alloys, our results classified CoCrMnAl as new HM-FM material with high spin polarization.

  10. Unveiling the Mechanism for the Split Hysteresis Loop in Epitaxial Co2Fe1-xMnxAl Full-Heusler Alloy Films.

    PubMed

    Tao, X D; Wang, H L; Miao, B F; Sun, L; You, B; Wu, D; Zhang, W; Oepen, H P; Zhao, J H; Ding, H F

    2016-01-01

    Utilizing epitaxial Co2Fe1-xMnxAl full-Heusler alloy films on GaAs (001), we address the controversy over the analysis for the split hysteresis loop which is commonly found in systems consisting of both uniaxial and fourfold anisotropies. Quantitative comparisons are carried out on the values of the twofold and fourfold anisotropy fields obtained with ferromagnetic resonance and vibrating sample magnetometer measurements. The most suitable model for describing the split hysteresis loop is identified. In combination with the component resolved magnetization measurements, these results provide compelling evidences that the switching is caused by the domain wall nucleation and movements with the switching fields centered at the point where the energy landscape shows equal minima for magnetization orienting near the easy axis and the field supported hard axis. PMID:26733075

  11. Large magnetoresistance in Heusler-alloy-based epitaxial magnetic junctions with semiconducting Cu(In0.8Ga0.2)Se2 spacer

    NASA Astrophysics Data System (ADS)

    Kasai, S.; Takahashi, Y. K.; Cheng, P.-H.; Ikhtiar, Ohkubo, T.; Kondou, K.; Otani, Y.; Mitani, S.; Hono, K.

    2016-07-01

    We investigated the structure and magneto-transport properties of magnetic junctions using a Co2Fe(Ga0.5Ge0.5) Heusler alloy as ferromagnetic electrodes and a Cu(In0.8Ga0.2)Se2 (CIGS) semiconductor as spacers. Owing to the semiconducting nature of the CIGS spacer, large magnetoresistance (MR) ratios of 40% at room temperature and 100% at 8 K were obtained for low resistance-area product (RA) values between 0.3 and 3 Ω μm2. Transmission electron microscopy observations confirmed the fully epitaxial growth of the chalcopyrite CIGS layer, and the temperature dependence of RA indicated that the large MR was due to spin dependent tunneling.

  12. Optimization of exchange bias in Co{sub 2}FeAl{sub 0.5}Si{sub 0.5} Heusler alloy layers

    SciTech Connect

    Hirohata, Atsufumi; Izumida, Keisuke; Ishizawa, Satoshi; Nakayama, Tadachika; Sagar, James

    2014-05-07

    We have fabricated and investigated IrMn{sub 3}/Co{sub 2}FeAl{sub 0.5}Si{sub 0.5} stacks to meet the criteria for future spintronic device applications which requires low-temperature crystallisation (<250 °C) and a large exchange bias H{sub ex} (>500 Oe). Such a system would form the pinned layer in spin-valve or tunnel junction applications. We have demonstrated that annealing at 300 °C which can achieve crystalline ordering in the Co{sub 2}FeAl{sub 0.5}Si{sub 0.5} layer giving ∼80% of the predicted saturation magnetisation. We have also induced an exchange bias of ∼240 Oe at the interface. These values are close to the above criteria and confirm the potential of using antiferromagnet/Heusler-alloy stacks in current Si-based processes.

  13. Giant spontaneous exchange bias triggered by crossover of superspin glass in Sb-doped Ni50Mn38Ga12 Heusler alloys.

    PubMed

    Tian, Fanghua; Cao, Kaiyan; Zhang, Yin; Zeng, Yuyang; Zhang, Rui; Chang, Tieyan; Zhou, Chao; Xu, Minwei; Song, Xiaoping; Yang, Sen

    2016-01-01

    A spontaneous exchange bias (SEB) discovered by Wang et al. [Phys. Rev. Lett. 106 (2011) 077203.] after zero-field cooling (ZFC) has attracted recent attention due to its interesting physics. In this letter, we report a giant SEB tuned by Sb-doping in Ni50Mn38Ga12-xSbx Heusler alloys. Such an SEB was switched on below the blocking temperature of approximately 50 K. The maximum exchange bias HE can arrive at 2930 Oe in a Ni50Mn38Ga10Sb2 sample after ZFC to 2 K. Further studies showed that this SEB was attributable to interaction of superspin glass (SSG) and antiferromagnetic matix, which was triggered by the crossover of SSG from canonical spin glass to a cluster spin glass. Our results not only explain the underlying physics of SEB, but also provide a way to tune and control the SEB performance. PMID:27478090

  14. Probing the possibility of coexistence of martensite transition and half-metallicity in Ni and Co-based full-Heusler alloys: An ab initio calculation

    NASA Astrophysics Data System (ADS)

    Roy, Tufan; Pandey, Dhanshree; Chakrabarti, Aparna

    2016-05-01

    Using first-principles calculations based on density functional theory, we have studied the mechanical, electronic, and magnetic properties of Heusler alloys, namely, Ni2B C and Co2B C (B = Sc, Ti, V, Cr, and Mn as well as Y, Zr, Nb, Mo, and Tc; C = Ga and Sn). On the basis of electronic structure (density of states) and mechanical properties (tetragonal shear constant), as well as magnetic interactions (Heisenberg exchange coupling parameters), we probe the properties of these materials in detail. We calculate the formation energy of these alloys in the (face-centered) cubic austenite structure to probe the stability of all these materials. From the energetic point of view, we have studied the possibility of the electronically stable alloys having a tetragonal phase lower in energy compared to the respective cubic phase. A large number of the magnetic alloys is found to have the cubic phase as their ground state. On the other hand, for another class of alloys, the tetragonal phase has been found to have lower energy compared to the cubic phase. Further, we find that the values of tetragonal shear constant show a consistent trend: a high positive value for materials not prone to tetragonal transition and low or negative for others. In the literature, materials which have been seen to undergo the martensite transition are found to be metallic in nature. We probe here if there is any Heusler alloy which has a tendency to undergo a tetragonal transition and at the same time possesses a high spin polarization at the Fermi level. From our study, it is found that out of the four materials which exhibit a martensite phase as their ground state, three of these, namely, Ni2MnGa , Ni2MoGa , and Co2NbSn have a metallic nature; on the contrary, Co2MoGa exhibits a high spin polarization.

  15. Prediction of metallic and half-metallic structure and elastic properties of Fe2 Ti1-x Mnx Al Heusler alloys

    NASA Astrophysics Data System (ADS)

    Adebambo, P. O.; Adetunji, B. I.; Olowofela, J. A.; Oguntuase, J. A.; Adebayo, G. A.

    2016-03-01

    Detailed studies of structural and elastic properties of Fe2 Ti1-x Mnx Al Heusler alloys were carried out using density functional theory within the generalized gradient approximations. In each Heusler alloy, calculations of lattice constants were repeatedly done for successive increases in the lattice constants and the corresponding total energies were recorded. The graphs of the total energy as a function of lattice constant yielded parabolic curves. The present calculations revealed that among the doped alloys, Fe2 TiAl and Fe2 Ti0.75 Mn0.25 Al exhibit transitions of electrons from valence to conduction bands thereby making these alloys metallic. On the other hand, the ternary and quaternary alloys (Fe2 MnAl and Fe2 Ti0.25 Mn0.75 Al respectively) possess half-metallic behavior with direct band gaps of 0.56 eV and 0.41 eV respectively at the Γ-point in the minorities states. To determine the stability of these alloys, the three independent elastic constants in cubic structures (that included C11, C12, and C44 respectively) were obtained for all the compositions that confirmed their stabilities. The structural and elastic properties calculations confirmed the stabilities of Fe2 Ti0.25 Mn0.75 Al and Fe2 MnAl as some new half-metallic materials that can be applicable in spintronic devices. This work revealed the brittleness nature of Fe2 TiAl and Fe2 MnAl alloys.

  16. First-principles study on magnetism and half-metallicity in bulk and various (001) surfaces of Heusler alloy Zr2VSn with Hg2CuTi-type structure

    NASA Astrophysics Data System (ADS)

    Deng, Zun-Yi; Zhang, Jian-Min

    2016-07-01

    Structural, electronic and magnetic properties in the bulk and five different (001) surfaces (ZrV-, ZrSn-, VV-, ZrZr- and SnSn-terminations) of Zr2 VSn Heusler alloy with Hg2 CuTi -type structure are studied by using first-principles calculations based on density-functional theory. The bulk Zr2 VSn Heusler alloy is ferrimagnetic half-metallicity with equilibrium lattice constant 6.815 Å and total magnetic moment -1.000 μB / f.u . , following the Slater-Pauling rule μt =Zt - 18 . The atoms on different surface layers exhibit different displacements, electronic and magnetic properties. All five (001) surfaces lose the half-metallicity and are not usable in spintronics devices.

  17. Enhanced power factor and reduced thermal conductivity of a half-Heusler derivative Ti{sub 9}Ni{sub 7}Sn{sub 8}: A bulk nanocomposite thermoelectric material

    SciTech Connect

    Misra, D. K. E-mail: dakkmisra@gmail.com; Rajput, A.; Bhardwaj, A.; Chauhan, N. S.; Singh, Sanjay

    2015-03-09

    We report a half-Heusler (HH) derivative Ti{sub 9}Ni{sub 7}Sn{sub 8} with VEC = 17.25 to investigate the structural changes for the optimization of high thermoelectric performance. The structural analysis reveals that the resulting material is a nanocomposite of HH and full-Heusler with traces of Ti{sub 6}Sn{sub 5} type-phase. Interestingly, present nanocomposite exhibits a significant decrease in thermal conductivity due to phonon scattering and improvement in the power factor due to combined effect of nanoinclusion-induced electron injection and electron scattering at interfaces, leading to a boost in the ZT value to 0.32 at 773 K, which is 60% higher than its bulk counterpart HH TiNiSn.

  18. Interface magnetism of Co{sub 2}FeGe Heusler alloy layers and magnetoresistance of Co{sub 2}FeGe/MgO/Fe magnetic tunnel junctions

    SciTech Connect

    Tanaka, M. A. Maezaki, D.; Ishii, T.; Okubo, A.; Mibu, K.; Hiramatsu, R.; Ono, T.

    2014-10-28

    The interface magnetism between Co{sub 2}FeGe Heusler alloy layers and MgO layers was investigated using {sup 57}Fe Mössbauer spectroscopy. Interface-sensitive samples, where the {sup 57}Fe isotope was used only for the interfacial atomic layer of the Co{sub 2}FeGe layer on the MgO layer, were prepared using atomically controlled alternate deposition. The {sup 57}Fe Mössbauer spectra of the interface-sensitive samples at room temperature were found similar to those of the bulk-sensitive Co{sub 2}FeGe films in which the {sup 57}Fe isotope was distributed throughout the films. On the other hand, the tunnel magnetoresistance effect of magnetic tunnel junctions with Co{sub 2}FeGe layers as the ferromagnetic electrodes showed strong reduction at room temperature. These results indicate that the strong temperature dependence of the tunneling magnetoresistance of magnetic tunnel junctions using Heusler alloy electrodes cannot be attributed simply to the reduction of the magnetization at the interfaces between the Heusler alloy and insulator layers.

  19. Compounding in Ukraine.

    PubMed

    Zdoryk, Oleksandr A; Georgiyants, Victoriya A; Gryzodub, Oleksandr I; Schnatz, Rick

    2013-01-01

    Pharmaceutical compounding in modern Ukraine has a rich history and goes back to ancient times. Today in the Ukraine, there is a revival of compounding practice, the opening of private compounding pharmacies, updating of legislative framework and requirements of the State Pharmacopeia of Ukraine for compounding preparations, and the introduction of Good Pharmaceutical Practice. PMID:23696172

  20. Self-propagating high temperature synthesis for compound thermoelectrics and new criterion for applicability of combustion processing

    NASA Astrophysics Data System (ADS)

    Tang, Xinfeng; Su, Xianli; Uher, Ctirad; Tang's Group Team; Uher's Group Team

    2015-03-01

    Here we report compound thermoelectric materials (Bi2Te3, Bi2Se3, Cu2Se,Cu2SnSe3, half-Heusler alloys, lead chalcogenides, skutterudites, and magnesium silicides) with thermoelectric properties comparable with materials prepared by the traditional routes of synthesis can be synthesized at a minimal cost and on the time scale of seconds using the self-propagating high temperature synthesis method. Moreover, we found that the criterion often quoted in the literature as the necessary precondition for combustion synthesis, Tad >= 1800 K, is not universal and certainly not applicable to thermoelectric compound semiconductors. Instead, we offer new empirically-based criterion, Tad /Tm , L >1, i.e., the adiabatic temperature must be high enough to melt the lower melting point component, which covers all materials synthesized by self-propagating high temperature synthesis, including the high temperature refractory compounds for which the Tad >= 1800 K criterion was originally developed. Our work opens a new avenue for ultra-fast, low cost, mass production fabrication of efficient thermoelectric materials and the new criterion greatly broadens the scope of materials that can be successfully synthesized by self-propagating high temperature synthesis. We wish to acknowledge support from the National Basic Research Program of China (973 program) under Project 2013CB632502.

  1. Compounds affecting cholesterol absorption

    NASA Technical Reports Server (NTRS)

    Hua, Duy H. (Inventor); Koo, Sung I. (Inventor); Noh, Sang K. (Inventor)

    2004-01-01

    A class of novel compounds is described for use in affecting lymphatic absorption of cholesterol. Compounds of particular interest are defined by Formula I: ##STR1## or a pharmaceutically acceptable salt thereof.

  2. Dinitroso and polynitroso compounds

    PubMed Central

    Gowenlock, Brian G.; Richter-Addo, George B.

    2005-01-01

    The growing interest in the chemistry of C-nitroso compounds (RN=O; R = alkyl or aryl group) is due in part to the recognition of their participation in various metabolic processes of nitrogen-containing compounds. C-Nitroso compounds have a rich organic chemistry in their own right, displaying interesting intra- and intermolecular dimerization processes and addition reactions with unsaturated compounds. In addition, they have a fascinating coordination chemistry. While most of the attention has been directed towards C-nitroso compounds containing a single –NO moiety, there is an emerging area of research dealing with dinitroso and polynitroso compounds. In this critical review, we present and discuss the synthetic routes and properties of these relatively unexplored dinitroso and polynitroso compounds, and suggest areas of further development involving these compounds. (126 references.) PMID:16100619

  3. Caulking compound poisoning

    MedlinePlus

    Caulking compounds are substances used to seal cracks and holes around windows and other openings. Caulking compound poisoning occurs when someone swallows these substances. This is for information only and not for use in the ...

  4. The defect-induced changes of the electronic and magnetic properties in the inverse Heusler alloy Ti{sub 2}CoAl

    SciTech Connect

    Chen, Ying; Wu, Bo; Yuan, Hongkuan; Feng, Yu; Chen, Hong

    2015-01-15

    The first-principles calculations are performed to investigate the effect of swap, antisite and vacancy defects of three classes on the electronic and magnetic properties in the inverse Heusler alloy Ti{sub 2}CoAl of half-metallicity. Our calculations reveal that Ti(A/B)–Co and Co–Al swaps, Ti(A/B) and Al vacancy defects as well as Co{sub Ti(A)/Al} and Al{sub Ti(A)/Ti(B)} antisite defects are likely to form in a concentration as high as 12.5%. Among them, Co{sub Ti(A)} antisite is detected to be the most probable defect. It is shown that the spin polarizations of Ti{sub 2}CoAl are considerably reduced by the Ti(A/B)–Co swap and Ti(B)/Al vacancy defects, while a quite high spin polarization around 95% is observed in Co–Al swap as well as Ti(A) vacancy. Remarkably, all the likely antisite defects almost retain the half-metallic character in a concentration of 12.5% even if they have the possibility to form. However, induced by antisites, the Fermi levels shift to the edge of band gap with small peaks arising just above the Fermi level, which may destroy the half-metallicity by spin-flip excitation. - Graphical abstract: The spin polarization and formation energy of various possible defects in inverse Heusler alloy Ti{sub 2}CoAl. The triangle, star and square represent the swap, antisite and vacancy defects, respectively. - Highlights: • The swap, antisite, and vacancy defects are studied in half-metallic Ti{sub 2}CoAl. • The Co{sub Ti(A)} antisite is the most probable among the studied defects. • The antisite defects almost retain the half-metallicity. • Most of swap and vacancy defects have degraded the half-metallicity. • High spin polarizations are detected in Co–Al swap and Ti(A) vacancy defects.

  5. Preparation of Co{sub 2}FeSn Heusler alloy films and magnetoresistance of Fe/MgO/Co{sub 2}FeSn magnetic tunnel junctions

    SciTech Connect

    Tanaka, M. A.; Ishikawa, Y.; Wada, Y.; Hori, S.; Murata, A.; Horii, S.; Yamanishi, Y.; Mibu, K.; Kondou, K.; Ono, T.; Kasai, S.

    2012-03-01

    To obtain magnetic tunnel junctions (MTJs) composed of non-equilibrium alloy, Co{sub 2}FeSn films were prepared by atomically controlled alternate deposition at various substrate temperatures. X-ray diffraction patterns and Moessbauer spectra clarify that Co{sub 2}FeSn films in the Heusler alloy phase can be realized by growing at a substrate temperature of 250 deg. C or below. Phase separation into cubic CoSn, hexagonal CoSn and cubic CoFe phases occurs in films grown at substrate temperatures 300 deg. C or greater. Fe/MgO/Co{sub 2}FeSn MTJs were prepared with the Co{sub 2}FeSn layer grown at various substrate temperatures. The MTJs with the ferromagnetic Co{sub 2}FeSn layer grown at a substrate temperature of 250 deg. C showed tunnel magnetoresistance ratios of 72.2% and 43.5% at 2 K and 300 K, respectively.

  6. Large spontaneous exchange bias and giant magnetoresistance in Ni50Mn37-xFexIn13(x=2-4) Heusler alloys

    NASA Astrophysics Data System (ADS)

    Jing, Chao; Liu, Yang; Zheng, Dong; Wang, Xiaolong; Sun, Junkun; Zhang, Yuanlei; Liu, Changqin; Deng, Dongmei; Feng, Zhenjie; Xu, Kun; Li, Zhe

    2016-09-01

    In the present work, we have obtained a large zero-field cooled exchange-bias (spontaneous exchange bias, SEB) in Ni50Mn35Fe2In13 Heusler alloy. The experimental results indicate that the sample with x=2 exhibits super-spin glass (SSG), super-paramagnetic (SPM), super-ferromagnetic (SFM) and antiferromagnetic (AFM) behaviors in the martensite state at low temperature. Contributing to the complex magnetic interactions, a large SEB effect with the value of 1567 Oe was obtained at 5 K. At the same time, a non-monotonic behavior of spontaneous exchange bias field (spontaneous HEB) was observed with the variation of temperature, which is resulted from the competition between the volume fraction of SFM clusters and the exchange coupling of the SFM-AFM interface. In addition, during martensitic transformation (MT), extraordinary electrical transport properties of Ni50Mn37-xFexIn13 (x=2-4) alloys have been observed under various external magnetic field. The maximal value of the giant magnetoresistance (GMR) reaches about 57% at 135 K under the external magnetic field change of 50 kOe. The effect of field induced reverse martensitic transformation (FIRMT) on the GMR has been also discussed.

  7. The effect of Pd on martensitic transformation and magnetic properties for Ni50Mn38-xPdxSn12Heusler alloys

    NASA Astrophysics Data System (ADS)

    Jing, C.; Zheng, D.; Li, Z.; Yu, L. J.; Zhang, Y. L.; Liu, Y.; Sun, J. K.; Liu, C. Q.; Deng, D. M.; Yang, W. T.

    2016-05-01

    In the past decade, Mn rich Ni-Mn based alloys have attained considerable attention due to their abundant physics and potential application as multifunctional materials. In this paper, polycrystalline Ni50Mn38-xPdxSn12 (x = 0, 2, 4, 6) Heusler alloys have been prepared, and the martensitic phase transformation (MPT) together with the shape memory effect and the magnetocaloric effect has been investigated. The experimental result indicates that the MPT evidently shifts to a lower temperature with increase of Pd substitution for Mn atoms, which can be attributed to the weakness of the hybridization between the Ni atom and excess Mn on the Sn site rather than the electron concentration. The physics properties study focused on the sample of Ni50Mn34Pd4Sn12 shows a good two-way shape memory behavior, and the maximum value of strain Δ L/L reaches about 0.13% during the MPT. The small of both entropy change Δ ST and magnetostrain can be ascribed to the inconspicuous influence of magnetic field induced MPT.

  8. International Round-Robin Study on Thermoelectric Transport Properties of n-type Half-Heusler from 300 K to 773 K

    DOE PAGESBeta

    Wang, Hsin; Bai, Shengqiang; Chen, Lidong; Cuenat, Alexander; Joshi, Giri; Kleinke, Holger; Konig, Jan; Lee, Hee Woong; Martin, Joshua; Oh, Min-Wook; et al

    2015-01-01

    International transport property measurement round-robins have been conducted by the Thermoelectric Annex under the International Energy Agency (IEA) Implementing Agreement on Advanced Materials for Transportation (AMT). The previous round-robins used commercially available bismuth telluride as the testing material, with the goals of understanding measurement issues and developing standard testing procedures. The current round-robin extended the measurement temperature range to 773 K. It was designed to meet the increasing demands for reliable transport data of thermoelectric materials for power generation applications. Eleven laboratories from six IEA-AMT member countries participated in this study. Half-Heusler (n-type) material prepared by GMZ Energy was selectedmore » for the round-robin. The measured transport properties showed narrower distribution on uncertainties compared to previous round-robin efforts. The study intentionally included multiple testing methods and instrument types. Over the full temperature range, the measurement discrepancies on the figure of merit, ZT, in this round-robin were ±1.5 to ±16.4% from the averages.« less

  9. Magnesium and cadmium containing Heusler phases REPd2Mg, REPd2Cd, REAg2Mg, REAu2Mg and REAu2Cd

    NASA Astrophysics Data System (ADS)

    Johnscher, Michael; Stein, Sebastian; Niehaus, Oliver; Benndorf, Christopher; Heletta, Lukas; Kersting, Marcel; Höting, Christoph; Eckert, Hellmut; Pöttgen, Rainer

    2016-02-01

    Twenty-eight new Heusler phases REPd2Mg, REPd2Cd, REAg2Mg, REAu2Mg and REAu2Cd with different rare earth elements were synthesized from the elements in sealed niobium ampoules in a water-cooled sample chamber of an induction furnace. The samples were characterized by powder X-ray diffraction. The cell volumes show the expected lanthanide contraction. The structures of YPd2Cd, GdPd2Cd, GdAu2Cd, Y1.12Ag2Mg0.88 and GdAg2Mg were refined based on single crystal diffractometer data. The magnetic properties were determined for fifteen phase pure samples. LuAu2Mg is a weak Pauli paramagnet with a susceptibility of 1.0(2) × 10-5 emu mol-1 at room temperature. The remaining samples show stable trivalent rare earth ions and most of them order magnetically at low temperatures. The ferromagnet GdAg2Mg shows the highest ordering temperature of TC = 98.3 K. 113Cd and 89Y MAS NMR spectra of YAu2Cd and YPd2Cd confirm the presence of unique crystallographic sites. The resonances are characterized by large Knight shifts, whose magnitude can be correlated with electronegativity trends.

  10. Thermodynamic stability, magnetism and half-metallicity of Heusler alloy Co2MnX(X = Si, Ge, Sn)(1 0 0) surface

    NASA Astrophysics Data System (ADS)

    Wu, Bo; Yuan, Hongkuan; Kuang, Anlong; Chen, Hong; Feng, Yu

    2012-03-01

    The thermodynamic stability, magnetism and half-metallicity of Heusler alloy Co2MnX(X = Si, Ge, Sn)(1 0 0) surface are comprehensively investigated from the first-principles calculations. The calculated phase diagram indicates that with increasing core electrons of X atoms in Co2MnX(1 0 0) the CoCo termination will be faded out of the thermodynamic equilibrium region gradually. Due to the difference of Cosbnd X bonding the surface Co and Mn atoms prefer to move towards the slab and vacuum, respectively. By comparing with the bulk, the surface Co and Mn atomic magnetic moments (AMMs) are enhanced obviously because of the significant surface d-electronic localization. Further investigations of the partial density of states (PDOS) show that the half-metallicity observed in bulk has been destroyed by the surface states in deficient-Mn atomic terminated surface, only the terminations capped pure Mn atoms in Co2MnSi(1 0 0) and Co2MnGe(1 0 0) surfaces preserve spin-polarization of 100% instead of the Co2MnSn(1 0 0) surface, which is a possible explanation for low experimental tunnel magnetoresistance (TMR) value in Co2MnSn(1 0 0)-based magnetic tunnel junctions (TMJs).

  11. International Round-Robin Study on Thermoelectric Transport Properties of n-type Half-Heusler from 300 K to 773 K

    SciTech Connect

    Wang, Hsin; Bai, Shengqiang; Chen, Lidong; Cuenat, Alexander; Joshi, Giri; Kleinke, Holger; Konig, Jan; Lee, Hee Woong; Martin, Joshua; Oh, Min-Wook; Porter, Wallace D.; Ren, Zhifeng; Salvador, James R.; Sharp, Jeff W.; Taylor, Patrick; Thompson, Alan J.; Tseng, Yu -Chih

    2015-01-01

    International transport property measurement round-robins have been conducted by the Thermoelectric Annex under the International Energy Agency (IEA) Implementing Agreement on Advanced Materials for Transportation (AMT). The previous round-robins used commercially available bismuth telluride as the testing material, with the goals of understanding measurement issues and developing standard testing procedures. The current round-robin extended the measurement temperature range to 773 K. It was designed to meet the increasing demands for reliable transport data of thermoelectric materials for power generation applications. Eleven laboratories from six IEA-AMT member countries participated in this study. Half-Heusler (n-type) material prepared by GMZ Energy was selected for the round-robin. The measured transport properties showed narrower distribution on uncertainties compared to previous round-robin efforts. The study intentionally included multiple testing methods and instrument types. Over the full temperature range, the measurement discrepancies on the figure of merit, ZT, in this round-robin were ±1.5 to ±16.4% from the averages.

  12. Band-gap and Slater-Pauling rule in half-metallic Ti2-based Heusler alloys: A first-principles study

    NASA Astrophysics Data System (ADS)

    Zheng, Nan; Jin, Yingjiu

    2012-09-01

    Half-metals, which show 100% spin polarization at the Fermi level, have potential applications in spintronics. We investigated the half-metallicity of full-Heusler Ti2YAl (Y=V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) alloys with an Hg2CuTi-type structure by means of the all-electron full-potential linearized augmented plane-wave method within the generalized gradient approximation. The Ti2MnAl alloy is found to be a half-metallic antiferromagnet, and the Ti2YAl (Y=Fe, Co, and Ni) alloys are half-metallic ferrimagnets, whereas the Ti2YAl (Y=V, Cr, Cu, and Zn) alloys are conventional ferromagnets. Total magnetic moments (Mt) of the Ti2YAl (Y=Mn, Fe, Co, and Ni) alloys are calculated to be integers and linearly scaled with the total number of valence electrons (Zt) by Mt=Zt-18. Band-gaps are demonstrated to be mainly determined by the bonding t2 and antibonding t2* states created from the hybridizations of the d states between the Ti(A)-Ti(B) coupling and Y (Y=Mn, Fe, Co, and Ni) atom.

  13. Temperature-dependence of current-perpendicular-to-the-plane giant magnetoresistance spin-valves using Co2(Mn1-xFex)Ge Heusler alloys

    NASA Astrophysics Data System (ADS)

    Page, M. R.; Nakatani, T. M.; Stewart, D. A.; York, B. R.; Read, J. C.; Choi, Y.-S.; Childress, J. R.

    2016-04-01

    The properties of Co2(Mn1-xFex)Ge (CMFG) (x = 0-0.4) Heusler alloy magnetic layers within polycrystalline current-perpendicular-to-the plane giant magnetoresistance (CPP-GMR) spin-valves are investigated. CMFG films annealed at 220-320 °C exhibit partly ordered B2 structure with an order parameter SB2 = 0.3-0.4, and a lower SB2 was found for a higher Fe content. Nevertheless, CPP-GMR spin-valve devices exhibit a relatively high magnetoresistance ratio of ˜13% and a magnetoresistance-area product (ΔRA) of ˜6 mΩ μm2 at room temperature, which is almost independent of the Fe content in the CMFG films. By contrast, at low temperatures, ΔRA clearly increases with higher Fe content, despite the lower B2 ordering for increasing the Fe content. Indeed, first-principles calculations reveal that the CMFG alloy with a partially disordered B2 structure has a greater density of d-state at the Fermi level in the minority band compared to the Fe-free (Co2MnGe) alloy. This could explain the larger ΔRA measured on CMFG at low temperatures by assuming that s-d scattering mainly determines the spin asymmetry of resistivity as described in Mott's theory.

  14. Enhancement of current-perpendicular-to-plane giant magnetoresistance in Heusler-alloy based pseudo spin valves by using a CuZn spacer layer

    SciTech Connect

    Furubayashi, T. Takahashi, Y. K.; Sasaki, T. T.; Hono, K.

    2015-10-28

    Enhancement of magnetoresistance output was attained in current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) devices by using a bcc CuZn alloy for the spacer. Pseudo spin valves that consisted of the Co{sub 2}Fe(Ga{sub 0.5}Ge{sub 0.5}) Heusler alloy for ferromagnetic layers and CuZn alloy with the composition of Cu{sub 52.4}Zn{sub 47.6} for a spacer showed the large change of the resistance-area products, ΔRA, up to 8 mΩ·μm{sup 2} for a low annealing temperature of 350 °C. The ΔRA value is one of the highest reported so far for the CPP-GMR devices for the low annealing temperature, which is essential for processing read heads for hard disk drives. We consider that the enhancement of ΔRA is produced from the spin-dependent resistance at the Co{sub 2}Fe(Ga{sub 0.5}Ge{sub 0.5})/CuZn interfaces.

  15. The defect-induced changes of the electronic and magnetic properties in the inverse Heusler alloy Ti2CoAl

    NASA Astrophysics Data System (ADS)

    Chen, Ying; Wu, Bo; Yuan, Hongkuan; Feng, Yu; Chen, Hong

    2015-01-01

    The first-principles calculations are performed to investigate the effect of swap, antisite and vacancy defects of three classes on the electronic and magnetic properties in the inverse Heusler alloy Ti2CoAl of half-metallicity. Our calculations reveal that Ti(A/B)-Co and Co-Al swaps, Ti(A/B) and Al vacancy defects as well as CoTi(A)/Al and AlTi(A)/Ti(B) antisite defects are likely to form in a concentration as high as 12.5%. Among them, CoTi(A) antisite is detected to be the most probable defect. It is shown that the spin polarizations of Ti2CoAl are considerably reduced by the Ti(A/B)-Co swap and Ti(B)/Al vacancy defects, while a quite high spin polarization around 95% is observed in Co-Al swap as well as Ti(A) vacancy. Remarkably, all the likely antisite defects almost retain the half-metallic character in a concentration of 12.5% even if they have the possibility to form. However, induced by antisites, the Fermi levels shift to the edge of band gap with small peaks arising just above the Fermi level, which may destroy the half-metallicity by spin-flip excitation.

  16. Neutron diffraction study of the martensitic transformation and chemical order in Heusler alloy Ni1.91Mn1.29Ga0.8

    DOE PAGESBeta

    Ari-Gur, Pnina; Garlea, Vasile O.; Cao, Huibo; Ge, Y.; Aaltio, I.; Hannula, S. P.; Koledov, V.

    2015-11-05

    In this study, Heusler alloys of Ni-Mn-Ga compositions demonstrate ferromagnetic shape memory effect in the martensitic state. The transformation temperature and the chemical order depend strongly on the composition. In the current work, the structure and chemical order of the martensitic phase of Ni1.91Mn1.29Ga0.8 were studied using neutron diffraction; the diffraction pattern was refined using the FullProf software. It was determined that the structural transition occurs around 330 K. At room temperature, 300 K, which is below the martensite transformation temperature, all the Bragg reflections can be described by a monoclinic lattice with a symmetry of space group P 1more » 2/m 1 and lattice constants of a = 4.23047(7) [Å], b = 5.58333(6) [Å], c = 21.0179(2) [Å], beta = 90.328(1). The chemical order is of critical importance in these alloys, and it was previously studied at 363 K. Analysis of the neutron diffraction in the monoclinic phase shows that the chemical order is maintained during the martensitic transformation.« less

  17. Pressure-magnetic field induced phase transformation in Ni{sub 46}Mn{sub 41}In{sub 13} Heusler alloy

    SciTech Connect

    Rama Rao, N. V. Manivel Raja, M.; Pandian, S.; Esakki Muthu, S.; Arumugam, S.

    2014-12-14

    The effect of hydrostatic pressure and magnetic field on the magnetic properties and phase transformation in Ni{sub 46}Mn{sub 41}In{sub 13} Heusler alloy was investigated. Pressure (P)-magnetic field (H)-temperature (T) phase diagram has been constructed from experimental results. In the P–T contour of the phase diagram, the slope of the austenite-martensite phase boundary line appears positive (dT/dP > 0), while it appears negative (dT/dH < 0) in the H–T contour. The results revealed that pressure and magnetic field have opposite effect on phase stabilization. The combined effect of pressure and magnetic field on martensitic transition has led to two important findings: (i) pressure dependent shift of austenite start temperature (A{sub s}) is higher when larger field is applied, and (ii) field dependent shift of A{sub s} is lowered when a higher pressure is applied. The pressure and magnetic field dependent shift observed in the martensitic transformation has been explained on the basis of thermodynamic calculations. Curie temperature of the phases was found to increase with pressure at a rate of 0.6 K/kbar.

  18. Structural and electronic properties of half-Heusler alloys PtXBi (with X=Mn, Fe, Co and Ni) calculated from first principles

    NASA Astrophysics Data System (ADS)

    Huang, Wenchao; Wang, Xiaofang; Chen, Xiaoshuang; Lu, Wei; Damewood, L.; Fong, C. Y.

    2015-03-01

    First principles calculations with spin polarization based on density functional theory have been performed on half-Heusler alloys PtXBi, with X=Mn, Fe, Co and Ni, in three different atomic configurations (i.e. α, β, and γ phases). For each configuration, their optimized lattice constants are determined. Electronic and magnetic properties are also investigated. The differences reflect the atomic arrangements of the three phases and varied transition metal elements X. Meanwhile, the possibility of having the integer magnetic moment for each phase is explored. PtMnBi in α phase show half-metallic (HM) properties when its lattice constant is reduced from -3.0% to -11.2% with magnetic moment consistent with the values given by the modified Slater-Pauling rule. Additionally, we examined the effects of the spin-orbit (S-O) interaction on half-metal PtMnBi by comparing the relative shifts of the valence bands and the indirect semiconducting gap with respect to the spin polarized results.

  19. Acceleration of ordering transformation of a new Fe{sub 2}(Mn,Cr)Si Heusler-alloy film by very high frequency plasma irradiation process during radio frequency sputter deposition

    SciTech Connect

    Yoshimura, S.; Kobayashi, H.; Egawa, G.; Saito, H.; Ishida, S.

    2011-04-01

    A new Heusler alloy, Fe{sub 2}(Mn,Cr)Si, that is likely to have high spin polarization (P) and high damping constant ({alpha}) was proposed to obtain high magneto-resistance ratio and low spin torque noise in a magnetic read head with a current-perpendicular-to-plane (CPP) giant magneto-resistance (GMR) multilayer. A very high frequency (VHF) plasma irradiation process during radio frequency (RF) sputter deposition was investigated to form the highly ordered structure of the Heusler alloy film with low thermal treatment temperature. The main results are as follows: (1) P and magnetic moment of Fe{sub 2}(Mn{sub 0.5}Cr{sub 0.5})Si with an L2{sub 1} structure were estimated at 0.99 and 2.49 {mu}{sub B}/f.u., respectively, and {alpha} was also estimated to be larger compared with the case of Co{sub 2}MnSi, according to density of states (DOS) calculations. (2) The ordering (at least B2 structure) temperature of Fe{sub 2}(Mn{sub 0.6}Cr{sub 0.4})Si film decreased from 500 to 300 deg. C by using the VHF plasma irradiation process with optimized condition. (3) The surface roughness of Fe{sub 2}(Mn{sub 0.6}Cr{sub 0.4})Si film also reduced from 1.7 to 0.5 nm by using the VHF plasma irradiation process. It is found that the Fe{sub 2}(Mn,Cr)Si Heusler alloy and the VHF plasma irradiation process with optimized condition seems to be applicable for fabrication of high-performance magnetic read head with CPP-GMR device.

  20. Structural and chemical ordering of Heusler CoxMnyGez epitaxial films on Ge (111). Quantitative study using traditional and anomalous x-ray diffraction techniques

    SciTech Connect

    Collins, B. A.; Chu, Y.; He, L.; Haskel, D.; Tsui, F.

    2015-12-14

    We found that epitaxial films of CoxMnyGez grown on Ge (111) substrates by molecular-beam-epitaxy techniques have been investigated as a continuous function of composition using combinatorial synchrotron x-ray diffraction (XRD) and x-ray fluorescence (XRF) spectroscopy techniques. A high-resolution ternary epitaxial phase diagram is obtained, revealing a small number of structural phases stabilized over large compositional regions. Ordering of the constituent elements in the compositional region near the full Heusler alloy Co2MnGe has been examined in detail using both traditional XRD and a new multiple-edge anomalous diffraction (MEAD) technique. Multiple-edge anomalous diffraction involves analyzing the energy dependence of multiple reflections across each constituent absorption edge in order to detect and quantify the elemental distribution of occupation in specific lattice sites. Results of this paper show that structural and chemical ordering are very sensitive to the Co : Mn atomic ratio, such that the ordering is the highest at an atomic ratio of 2 but significantly reduced even a few percent off this ratio. The in-plane lattice is nearly coherent with that of the Ge substrate, while the approximately 2% lattice mismatch is accommodated by the out-of-plane tetragonal strain. Furthermore, the quantitative MEAD analysis reveals no detectable amount (<0.5%) of Co-Mn site swapping, but instead high levels (26%) of Mn-Ge site swapping. Increasing Ge concentration above the Heusler stoichiometry (Co 0.5 Mn 0.25 Ge 0.25 ) is shown to correlate with increased lattice vacancies, antisites, and stacking faults, but reduced lattice relaxation. The highest degree of chemical ordering is observed off the Heusler stoichiometry with a Ge enrichment of 5 at.%.

  1. Structural and chemical ordering of Heusler C oxM nyG ez epitaxial films on Ge (111): Quantitative study using traditional and anomalous x-ray diffraction techniques

    NASA Astrophysics Data System (ADS)

    Collins, B. A.; Chu, Y. S.; He, L.; Haskel, D.; Tsui, F.

    2015-12-01

    Epitaxial films of C oxM nyG ez grown on Ge (111) substrates by molecular-beam-epitaxy techniques have been investigated as a continuous function of composition using combinatorial synchrotron x-ray diffraction (XRD) and x-ray fluorescence (XRF) spectroscopy techniques. A high-resolution ternary epitaxial phase diagram is obtained, revealing a small number of structural phases stabilized over large compositional regions. Ordering of the constituent elements in the compositional region near the full Heusler alloy C o2MnGe has been examined in detail using both traditional XRD and a new multiple-edge anomalous diffraction (MEAD) technique. Multiple-edge anomalous diffraction involves analyzing the energy dependence of multiple reflections across each constituent absorption edge in order to detect and quantify the elemental distribution of occupation in specific lattice sites. Results of this paper show that structural and chemical ordering are very sensitive to the Co : Mn atomic ratio, such that the ordering is the highest at an atomic ratio of 2 but significantly reduced even a few percent off this ratio. The in-plane lattice is nearly coherent with that of the Ge substrate, while the approximately 2% lattice mismatch is accommodated by the out-of-plane tetragonal strain. The quantitative MEAD analysis further reveals no detectable amount (<0.5%) of Co-Mn site swapping, but instead high levels (26%) of Mn-Ge site swapping. Increasing Ge concentration above the Heusler stoichiometry (C o0.5M n0.25G e0.25) is shown to correlate with increased lattice vacancies, antisites, and stacking faults, but reduced lattice relaxation. The highest degree of chemical ordering is observed off the Heusler stoichiometry with a Ge enrichment of 5 at.%.

  2. Production of epoxy compounds from olefinic compounds

    SciTech Connect

    Gelbein, A.P.; Kwon, J.T.

    1985-01-29

    Chlorine and tertiary alkanol dissolved in an inert organic solvent are reacted with aqueous alkali to produce tertiary alkyl hypochlorite which is recovered in the organic solvent and reacted with water and olefinically unsaturated compound to produce chlorohydrin and tertiary alkanol. Chlorohydrin and tertiary alkanol recovered in the organic solvent are contacted with aqueous alkali to produce the epoxy compound, and tertiary alkanol recovered in the organic solvent is recycled to hypochlorite production. The process may be integrated with the electrolytic production of chlorine, with an appropriate treatment of the recycle aqueous stream when required.

  3. Chemicals loading in acetylated bamboo assisted by supercritical CO2 based on phase equilibrium data

    NASA Astrophysics Data System (ADS)

    Silviana, Petermann, M.

    2015-12-01

    Indonesia has a large tropical forest. However, the deforestation still appears annually and vastly. This reason drives a use of bamboo as wood alternative. Recently, there are many modifications of bamboo in order to prolong the shelf life. Unfortunately, the processes need more chemicals and time. Based on wood modification, esterifying of bamboo was undertaken in present of a dense gas, i.e. supercritical CO2. Calculation of chemicals loading referred to ASTM D1413-99 by using the phase equilibrium data at optimum condition by a statistical design. The results showed that the acetylation of bamboo assisted by supercritical CO2 required 14.73 kg acetic anhydride/m3 of bamboo for a treatment of one hour.

  4. Energy or compost from green waste? - A CO(2) - based assessment.

    PubMed

    Kranert, Martin; Gottschall, Ralf; Bruns, Christian; Hafner, Gerold

    2010-04-01

    Green waste is increasingly extracted from the material recycling chain and, as a result of the financial subsidy arising from the German renewable energy law for the generation of energy from renewable raw materials; it is fed into the energy recovery process in biomass power stations. A reduction in climate relevant gases is also linked to the material recovery of green waste - in particular when using composts gained from the process as a new raw material in different types of potting compost and plant culture media as a replacement for peat. Unlike energy recovery, material valorisation is not currently subsidised. Through the analysis of material and energy valorisation methods for green waste, with particular emphasis on primary resource consumption and CO(2)-balance, it could be determined that the use of green waste for energy generation and its recovery for material and peat replacement purposes can be considered to be on a par. Based on energy recovery or material oriented scenarios, it can be further deduced that no method on its own will achieve the desired outcome and that a combination of recycling processes is more likely to lead to a significant decrease of greenhouse gas emissions. PMID:19896819

  5. Crystalline CO2-based polycarbonates prepared from racemic catalyst through intramolecularly interlocked assembly

    PubMed Central

    Liu, Ye; Ren, Wei-Min; Zhang, Wei-Ping; Zhao, Rong-Rong; Lu, Xiao-Bing

    2015-01-01

    The crystalline stereocomplexed polycarbonates can be prepared by mixing enantiopure polymers with opposite configuration, which derived from the asymmetric copolymerization with CO2 using enantiopure catalyst or/and chiral epoxides. Herein, we develop a powerful strategy for producing crystalline intramolecular stereocomplexed polycarbonates from racemic catalysts, which possess similar thermal stability and crystalline behaviour in comparison with the stereocomplexes by mixing opposite enantiopure polymers. Living polymer chains shuttle between catalyst molecules with different configurations to produce diastereomeric active species which is suggested to be responsible for the formation of isotactic multiblock polycarbonates in racemic bimetallic cobalt catalyst-mediated stereoselective copolymerization of CO2 and meso-epoxides. Solid-state NMR spectroscopy study suggests that the interaction in the carbonyl and methine regions is responsible for the strong crystallization capacity and compact package structure in the crystalline polycarbonates. PMID:26469884

  6. The carbon isotope composition of ancient CO2 based on higher-plant organic matter.

    PubMed

    Gröcke, Darren R

    2002-04-15

    Carbon isotope ratios in higher-plant organic matter (delta(13)C(plant)) have been shown in several studies to be closely related to the carbon isotope composition of the ocean-atmosphere carbon reservoir, and, in particular, the isotopic composition of CO(2). These studies have primarily been focused on geological intervals in which major perturbations occur in the oceanic carbon reservoir, as documented in organic carbon and carbonates phases (e.g. Permian-Triassic and Triassic-Jurassic boundary, Early Toarcian, Early Aptian, Cenomanian-Turonian boundary, Palaeocene-Eocene Thermal Maximum (PETM)). All of these events, excluding the Cenomanian-Turonian boundary, record negative carbon isotope excursions, and many authors have postulated that the cause of such excursions is the massive release of continental-margin marine gas-hydrate reservoirs (clathrates). Methane has a very negative carbon isotope composition (delta(13)C, ca. 60 per thousand ) in comparison with higher-plant and marine organic matter, and carbonate. The residence time of methane in the ocean-atmosphere reservoir is short (ca. 10 yr) and is rapidly oxidized to CO(2), causing the isotopic composition of CO(2) to become more negative from its assumed background value (delta(13)C, ca. -7 per thousand ). However, to date, only the Early Toarcian, Early Aptian and PETM are well-constrained chronometric sequences that could attribute clathrate release as a viable cause to create such rapid negative delta(13)C excursions. Notwithstanding this, the isotopic analysis of higher-plant organic matter (e.g. charcoal, wood, leaves, pollen) has the ability to (i) record the isotopic composition of palaeoatmospheric CO(2) in the geological record, (ii) correlate marine and non-marine stratigraphic successions, and (iii) confirm that oceanic carbon perturbations are not purely oceanographic in their extent and affect the entire ocean-atmosphere system. A case study from the Isle of Wight, UK, indicates that the carbon isotope composition of palaeoatmospheric CO(2) during the Mid-Cretaceous had a background value of 3 per thousand, but fluctuated rapidly to more positive (ca. +0.5 per thousand ) and negative values (ca. 10 per thousand ) during carbon cycle perturbations (e.g. carbon burial events, carbonate platform drowning, large igneous province formation). Hence, fluctuations in the carbon isotope composition of palaeoatmospheric CO(2) would compromise our use of palaeo-CO(2) proxies that are dependent on constant carbon isotope ratios of CO(2). PMID:12804297

  7. Ecotoxicology of organofluorous compounds.

    PubMed

    Murphy, Margaret B; Loi, Eva I H; Kwok, Karen Y; Lam, Paul K S

    2012-01-01

    Organofluorous compounds have been developed for myriad purposes in a variety of fields, including manufacturing, industry, agriculture, and medicine. The widespread use and application of these compounds has led to increasing concern about their potential ecological toxicity, particularly because of the stability of the C-F bond, which can result in chemical persistence in the environment. This chapter reviews the chemical properties and ecotoxicology of four groups of organofluorous compounds: fluorinated refrigerants and propellants, per- and polyfluorinated compounds (PFCs), fluorinated pesticides, and fluoroquinolone antibiotics. These groups vary in their environmental fate and partitioning, but each raises concern in terms of ecological risk on both the regional and global scale, particularly those compounds with long environmental half-lives. Further research on the occurrence and toxicities of many of these compounds is needed for a more comprehensive understanding of their ecological effects. PMID:21952849

  8. XAFS Model Compound Library

    DOE Data Explorer

    Newville, Matthew

    The XAFS Model Compound Library contains XAFS data on model compounds. The term "model" compounds refers to compounds of homogeneous and well-known crystallographic or molecular structure. Each data file in this library has an associated atoms.inp file that can be converted to a feff.inp file using the program ATOMS. (See the related Searchable Atoms.inp Archive at http://cars9.uchicago.edu/~newville/adb/) This Library exists because XAFS data on model compounds is useful for several reasons, including comparing to unknown data for "fingerprinting" and testing calculations and analysis methods. The collection here is currently limited, but is growing. The focus to date has been on inorganic compounds and minerals of interest to the geochemical community. [Copied, with editing, from http://cars9.uchicago.edu/~newville/ModelLib/

  9. Thermoelectric performance of nanostructured p-type Zr₀.₅Hf₀.₅Co₀.₄Rh₀.₆Sb1–xSnxhalf-Heusler alloys

    SciTech Connect

    Maji, Pramathesh; Makongo, Julien P.A.; Zhou, Xiaoyuan; Chi, Hang; Uher, Ctirad; Poudeu, Pierre F.P.

    2013-06-01

    Several compositions of the p-type half-Heusler alloys Zr₀.₅Hf₀.₅Co₀.₄Rh₀.₆Sb1–xSnx (0≤x≤0.4) were synthesized by mechanically alloying high purity elemental powders using hardened steel jars and balls on a high energy shaker mill. Powder X-ray diffraction (XRD) investigations of several aliquots taken after regularly spaced milling time suggested that single phase products with half-Heusler (HH) structure can be obtained after 10 h. However, XRD and transmission electron microscopy (TEM) studies of several specimens obtained from compacted polycrystalline powders of Z₀.₅Hf₀.₅Co₀.₄Rh₀.₆Sb1–xSnx alloys using a uniaxial hot press (HP) revealed the presence of CoSb inclusions with various sizes embedded inside the HH matrix. Hall effect, electrical conductivity, and thermopower data collected between 300 K and 775 K on several compositions suggested that electronic transport in the synthesized Zr₀.₅Hf₀.₅Co₀.₄Rh₀.₆Sb1–xSnx/CoSb composites strongly depends on the average size and/or mole fraction of the embedded CoSb inclusions rather than the fraction (x) of Sn substituting for Sb. Among the samples investigated, the nanocomposite with x=0.2, which contains nanometer-scale CoSb inclusions, showed the largest power factor (800 μW/K² m at 775 K) and the lowest lattice thermal conductivity (~2.2 W/m K at 775 K) leading to a six-fold enhancement in the figure of merit when compared to the Zr₀.₅Hf₀.₅Co₀.₄Rh₀.₆Sb₀.₉₉Sn₀.₀₁ bulk matrix. - Graphical abstract: CoSb nanoinclusions embedded into a p-type Zr₀.₅Hf₀.₅Co₀.₄Rh₀.₆Sb1–xSnx half-Heusler matrix simultaneously boost the thermopower and carrier mobility leading to a drastic enhancement of the power factor of the resulting bulk nanostructured materials. Highlights: • The phase composition of half-Heusler (HH) alloy is very sensitive

  10. Preparation of uranium compounds

    DOEpatents

    Kiplinger, Jaqueline L; Montreal, Marisa J; Thomson, Robert K; Cantat, Thibault; Travia, Nicholas E

    2013-02-19

    UI.sub.3(1,4-dioxane).sub.1.5 and UI.sub.4(1,4-dioxane).sub.2, were synthesized in high yield by reacting turnings of elemental uranium with iodine dissolved in 1,4-dioxane under mild conditions. These molecular compounds of uranium are thermally stable and excellent precursor materials for synthesizing other molecular compounds of uranium including alkoxide, amide, organometallic, and halide compounds.

  11. Nitrodifluoraminoterphenyl compounds and processes

    DOEpatents

    Lerom, M.W.; Peters, H.M.

    1975-07-08

    This patent relates to the nitrodifluoraminoterphenyl compounds: 3,3''-bis (difluoramino)-2,2'' 4,4', 4'',6,6',6''-octanitro-m-terphenyl (DDONT) and 3,3''-bis(difluoramino)-2,2',2''4,4',4'',6,6',6''-nonanitro-m-terphenyl (DDNONA). Procedures are described wherein diamino precursors of the indicated compounds are prepared and the final compounds are obtained by a fluorination operation. The compounds are highly energetic and suitable for use as explosives and particularly in exploding bridge wire (EBW) detonators. (auth)

  12. Design and discovery of a novel half-Heusler transparent hole conductor made of all-metallic heavy elements.

    PubMed

    Yan, Feng; Zhang, Xiuwen; Yu, Yonggang G; Yu, Liping; Nagaraja, Arpun; Mason, Thomas O; Zunger, Alex

    2015-01-01

    Transparent conductors combine two generally contradictory physical properties, but there are numerous applications where both functionalities are crucial. Previous searches focused on doping wide-gap metal oxides. Focusing instead on the family of 18 valence electron ternary ABX compounds that consist of elements A, B and X in 1:1:1 stoichiometry, we search theoretically for electronic structures that simultaneously lead to optical transparency while accommodating intrinsic defect structures that produce uncompensated free holes. This leads to the prediction of a stable, never before synthesized TaIrGe compound made of all-metal heavy atom compound. Laboratory synthesis then found it to be stable in the predicted crystal structure and p-type transparent conductor with a strong optical absorption peak at 3.36 eV and remarkably high hole mobility of 2,730 cm(2) V(-1) s(-1) at room temperature. This methodology opens the way to future searches of transparent conductors in unexpected chemical groups. PMID:26106063

  13. Direct observation of the electronic structure in thermoelectric half-Heusler alloys Zr{sub 1−x}M{sub x}NiSn (M = Y and Nb)

    SciTech Connect

    Hattori, Kengo; Miyazaki, Hidetoshi Yoshida, Kento; Inukai, Manabu; Nishino, Yoichi

    2015-05-28

    This study investigates the electronic and local crystal structures of the hole-doped Zr{sub 1−x}Y{sub x}NiSn and electron-doped Zr{sub 1−x}Nb{sub x}NiSn alloys using synchrotron radiation photoemission spectroscopy (SR-PES) and synchrotron radiation X-ray powder diffraction (SR-XRD) measurements, thereby clarifying the mechanisms underlying the thermoelectric performance of the p- and n-type alloys. SR-XRD analysis reveals an interstitial Ni disorder in the half-Heusler structure and the substitution of the dopant Y and Nb atoms at the Zr site. SR-PES result shows that the variation in the electronic structure of the alloys due to doping can be explained on the basis of the rigid band model. The asymmetric pseudo-gap near the Fermi level, which is rather unexpected from the band structure calculation because of the presence of the interstitial Ni disorder, could possibly be the reason underlying poor thermoelectric performance of p-type half-Heusler ZrNiSn alloys when compared with the n-type counterparts.

  14. Enhanced half-metallicity of off-stoichiometric quaternary Heusler alloy C o2(Mn ,Fe )Si investigated through saturation magnetization and tunneling magnetoresistance

    NASA Astrophysics Data System (ADS)

    Moges, Kidist; Honda, Yusuke; Liu, Hong-xi; Uemura, Tetsuya; Yamamoto, Masafumi; Miura, Yoshio; Shirai, Masafumi

    2016-04-01

    We investigated the factors that critically affect the half-metallicity of the quaternary Heusler alloy C o2(Mn ,Fe )Si (CMFS) by examining the film composition dependence of the saturation magnetization per formula unit, μs, of CMFS thin films and the tunneling magnetoresistance (TMR) ratio of CMFS/MgO/CMFS magnetic tunnel junctions (MTJs). We also investigated the origin of the giant TMR ratio of up to 2610% at 4.2 K (429% at 290 K) obtained for CMFS MTJs with Mn-rich, lightly Fe-doped CMFS electrodes. Co antisites at the nominal Mn/Fe sites (C oMn /Fe antisites) can consistently explain the μs for (Mn + Fe)-deficient CMFS thin films being lower than the half-metallic Zt-24 value and the TMR ratio for MTJs with (Mn + Fe)-deficient CMFS electrodes being lower than that for MTJs with (Mn + Fe)-rich CMFS electrodes. It was revealed that the C oMn /Fe antisite is detrimental to the half-metallicity of the CMFS quaternary alloy, as it is in the Co2MnSi (CMS) ternary alloy. It was also shown that (Mn +Fe ) -rich compositions are critical to suppressing these harmful antisites and to retaining the half-metallic electronic state. In addition, a relatively small Fe ratio, rather than a large one, in the total (Mn +Fe ) composition led to a more complete half-metallic electronic state. Half-metallicity was more strongly enhanced by increasing the Mn composition in Mn-rich, lightly Fe-doped CMFS than in Mn-rich CMS. This phenomenon is the cause of the giant TMR ratio recently reported for CMFS MTJs. Our findings indicate that the approach to controlling off-stoichiometry and film composition is promising for fully utilizing the half-metallicity of quaternary CMFS thin films as spin source materials.

  15. Growth of Co2FeAl Heusler alloy thin films on Si(100) having very small Gilbert damping by Ion beam sputtering

    PubMed Central

    Husain, Sajid; Akansel, Serkan; Kumar, Ankit; Svedlindh, Peter; Chaudhary, Sujeet

    2016-01-01

    The influence of growth temperature Ts (300–773 K) on the structural phase ordering, static and dynamic magnetization behaviour has been investigated in ion beam sputtered full Heusler alloy Co2FeAl (CFA) thin films on industrially important Si(100) substrate. The B2 type magnetic ordering is established in these films based on the clear observation of the (200) diffraction peak. These ion beam sputtered CFA films possess very small surface roughness of the order of subatomic dimensions (<3 Å) as determined from the fitting of XRR spectra and also by AFM imaging. This is supported by the occurrence of distinct Kiessig fringes spanning over the whole scanning range (~4°) in the x-ray reflectivity (XRR) spectra. The Gilbert damping constant α and effective magnetization 4πMeff are found to vary from 0.0053 ± 0.0002 to 0.0015 ± 0.0001 and 13.45 ± 00.03 kG to 14.03 ± 0.04 kG, respectively. These Co2FeAl films possess saturation magnetization ranging from 4.82 ± 0.09 to 5.22 ± 0.10 μB/f.u. consistent with the bulk L21-type ordering. A record low α-value of 0.0015 is obtained for Co2FeAl films deposited on Si substrate at Ts ~ 573 K. PMID:27357004

  16. Growth of Co2FeAl Heusler alloy thin films on Si(100) having very small Gilbert damping by Ion beam sputtering

    NASA Astrophysics Data System (ADS)

    Husain, Sajid; Akansel, Serkan; Kumar, Ankit; Svedlindh, Peter; Chaudhary, Sujeet

    2016-06-01

    The influence of growth temperature Ts (300–773 K) on the structural phase ordering, static and dynamic magnetization behaviour has been investigated in ion beam sputtered full Heusler alloy Co2FeAl (CFA) thin films on industrially important Si(100) substrate. The B2 type magnetic ordering is established in these films based on the clear observation of the (200) diffraction peak. These ion beam sputtered CFA films possess very small surface roughness of the order of subatomic dimensions (<3 Å) as determined from the fitting of XRR spectra and also by AFM imaging. This is supported by the occurrence of distinct Kiessig fringes spanning over the whole scanning range (~4°) in the x-ray reflectivity (XRR) spectra. The Gilbert damping constant α and effective magnetization 4πMeff are found to vary from 0.0053 ± 0.0002 to 0.0015 ± 0.0001 and 13.45 ± 00.03 kG to 14.03 ± 0.04 kG, respectively. These Co2FeAl films possess saturation magnetization ranging from 4.82 ± 0.09 to 5.22 ± 0.10 μB/f.u. consistent with the bulk L21-type ordering. A record low α-value of 0.0015 is obtained for Co2FeAl films deposited on Si substrate at Ts ~ 573 K.

  17. Growth of Co2FeAl Heusler alloy thin films on Si(100) having very small Gilbert damping by Ion beam sputtering.

    PubMed

    Husain, Sajid; Akansel, Serkan; Kumar, Ankit; Svedlindh, Peter; Chaudhary, Sujeet

    2016-01-01

    The influence of growth temperature Ts (300-773 K) on the structural phase ordering, static and dynamic magnetization behaviour has been investigated in ion beam sputtered full Heusler alloy Co2FeAl (CFA) thin films on industrially important Si(100) substrate. The B2 type magnetic ordering is established in these films based on the clear observation of the (200) diffraction peak. These ion beam sputtered CFA films possess very small surface roughness of the order of subatomic dimensions (<3 Å) as determined from the fitting of XRR spectra and also by AFM imaging. This is supported by the occurrence of distinct Kiessig fringes spanning over the whole scanning range (~4°) in the x-ray reflectivity (XRR) spectra. The Gilbert damping constant α and effective magnetization 4πMeff are found to vary from 0.0053 ± 0.0002 to 0.0015 ± 0.0001 and 13.45 ± 00.03 kG to 14.03 ± 0.04 kG, respectively. These Co2FeAl films possess saturation magnetization ranging from 4.82 ± 0.09 to 5.22 ± 0.10 μB/f.u. consistent with the bulk L21-type ordering. A record low α-value of 0.0015 is obtained for Co2FeAl films deposited on Si substrate at Ts ~ 573 K. PMID:27357004

  18. Tunnel magnetoresistance effect in magnetic tunnel junctions using Fermi-level-tuned epitaxial Fe2Cr1-xCoxSi Heusler alloy

    NASA Astrophysics Data System (ADS)

    Wang, Yu-Pu; Han, Gu-Chang; Lu, Hui; Qiu, Jinjun; Yap, Qi-Jia; Teo, Kie-Leong

    2014-05-01

    This paper reports a systematic investigation on the structural and magnetic properties of Fe2Cr1-xCoxSi Heusler alloys with various compositions of x by co-sputtering Fe2CrSi and Fe2CoSi targets and their applications in magnetic tunnel junctions (MTJs). Fe2Cr1-xCoxSi films of high crystalline quality have been epitaxially grown on MgO substrate using Cr as a buffer layer. The L21 phase can be obtained at x = 0.3 and 0.5, while B2 phase for the rest compositions. A tunnel magnetoresistance (TMR) ratio of 19.3% at room temperature is achieved for MTJs using Fe2Cr0.3Co0.7Si as the bottom electrode with 350 °C post-annealing. This suggests that the Fermi level in Fe2Cr1-xCoxSi has been successfully tuned close to the center of band gap of minority spin with x = 0.7 and therefore better thermal stability and higher spin polarization are achieved in Fe2Cr0.3Co0.7Si. The post-annealing effect for MTJs is also studied in details. The removal of the oxidized Fe2Cr0.3Co0.7Si at the interface with MgO barrier is found to be the key to improve the TMR ratio. When the thickness of the inserted Mg layer increases from 0.3 to 0.4 nm, the TMR ratio is greatly enhanced from 19.3% to 28%.

  19. Effect of growth temperature on structural, magnetic, and transport properties of Co2Cr0.6Fe0.4Al Heusler alloy sputtered thin films

    NASA Astrophysics Data System (ADS)

    Yadav, Anjali; Chaudhary, Sujeet

    2015-02-01

    The effect of growth temperature TS on crystallographic structure, DC-magnetization, and electrical transport behavior of pulsed dc-magnetron sputtered Co2Cr0.6Fe0.4Al Heusler alloy thin films has been investigated. The increase in TS enhances the crystallite size, structural ordering in these films, eventually resulting in the increase in saturation magnetization to 2.4 μB/f.u. The (220) textured growth of thin films induces an in-plane magnetic anisotropy of ˜2.1 × 104 erg/cc in these films. The improvement in structural ordering is accompanied with the systematic increase in resistivity ratio ρ(300)/ρ(20 K) and also with the change in sign of temperature coefficients of resistivity from negative to positive at TS = 500 °C. In addition, a resistivity minimum is observed at low temperature in the films deposited at TS>400 °C. The resistivity behavior at low temperature is governed by e-e scattering (T2 dependence), one-magnon scattering (T3 dependence), and weak localization effect (T1/2). However at higher temperature, the resistivity behavior is governed by Tn power law, and the value of n was found to be 1.35 and 0.91 for the films grown at 500 and 600 °C, respectively. The anomalous Hall Effect studies revealed the presence of side-jump scattering mechanism in Hall resistivity consistent with the structural, transport, and DC-magnetization measurements. Nearly, temperature independent Hall sensitivity behavior is observed for these samples in a moderate field range from 0 to 0.3 T, which shows the suitability of the material for developing Hall sensors.

  20. First-principles study on the effect of defects on the electronic and magnetic properties of the Ti2NiAl inverse Heusler alloy

    NASA Astrophysics Data System (ADS)

    Zhou, Ying; Chen, Ying; Feng, Yu; Yuan, Hongkuan; Chen, Hong

    2014-12-01

    The effect of atomic antisite and swap defects on the electronic and magnetic properties of Ti2NiAl inverse Heusler alloy is investigated by the first-principles calculations within density functional theory. In the ordered Ti2NiAl alloy, there are eight antisites and five swaps which are established by the replacement of an atom by another and the exchange in positions of atoms, respectively. The NiTi(A) antisite is found to be the most probable defect due to the lowest formation energy, whereas the least probable defects are the AlTi(A)/Ti(B) and NiAl/Ti(B) antisites as well as Ni-Ti(A) and Al-Ti(B) swaps due to the higher formation energies compared with NiTi(A) antisite. The TiNi/Al and AlNi antisites as well as Al-Ti(A)/Ni and Ni-Ti(B) swaps are highly unlikely to be formed due to the positive values of formation energy. Moreover, we deduce from the relative binding energy of the swap with respect to their antisites that the Ni prefers atomic antisite to site swap, while Al prefers site swap to atomic antisite. The spin polarization is markedly reduced in Ni/AlTi(B) antisite as well as Ni-Ti(A) and Al-Ti(B) swaps due to the occurrence of defect states at the Fermi level, while a very high spin polarization is obtained for Ni/AlTi(A) antisites and only the NiAl antisite retains the half-metallicity with a perfect spin polarization. The magnetic moments of all the likely defected structures decrease in comparison to the ordered Ti2NiAl mainly due to the decrease of local magnetic moments of the defect atom and its near neighbors.

  1. Stabilized Lanthanum Sulphur Compounds

    NASA Technical Reports Server (NTRS)

    Reynolds, George H. (Inventor); Elsner, Norbert B. (Inventor); Shearer, Clyde H. (Inventor)

    1985-01-01

    Lanthanum sulfide is maintained in the stable cubic phase form over a temperature range of from 500 C to 1500 C by adding to it small amounts of calcium, barium. or strontium. This novel compound is an excellent thermoelectric material.

  2. Heart testing compound

    DOEpatents

    Knapp, Jr., Furn F.; Goodman, Mark M.

    1985-01-01

    The compound 15-(p-[.sup.125 I]-iodophenyl)-6-tellurapentadecanoic acid is disclosed as a myocardial imaging agent having rapid and pronounced uptake, prolonged myocardial retention, and low in vivo deiodination.

  3. Heart testing compound

    DOEpatents

    Knapp, F.F. Jr.; Goodman, M.M.

    1983-06-29

    The compound 15-(p-(/sup 125/I)-iodophenyl)-6-tellurapentadecanoic acid is disclosed as a myocardial imaging agent having rapid and pronounced uptake, prolonged myocardial retention, and low in vivo deiodination.

  4. Anti-Fog Compound

    NASA Technical Reports Server (NTRS)

    1985-01-01

    Tracer Chemical Corporation's TRX Anti-Fog Composition is an inexpensive product which prevents condensation on plastic and glass surfaces. It was the result from a Tech Briefs article detailing a Johnson Space Center compound.

  5. Compounding a Problem?

    PubMed

    Berlin, Joey

    2016-01-01

    Allergist-immunologists say a U.S. Pharmacopeia proposal will mess with an allergy treatment system that's worked for more than a century. The revised standards, if adopted, would remove a key exemption separating allergen extract preparations from the stricter requirements of other compounds. Immunologists say the exemption has allowed them to compound allergen extracts in their own offices, and they've done so safely and effectively millions of times a year. PMID:27175928

  6. Chemistry of peroxide compounds

    NASA Technical Reports Server (NTRS)

    Volnov, I. I.

    1981-01-01

    The history of Soviet research from 1866 to 1967 on peroxide compounds is reviewed. This research dealt mainly with peroxide kinetics, reactivity and characteristics, peroxide production processes, and more recently with superoxides and ozonides and emphasis on the higher oxides of group 1 and 2 elements. Solid state fluidized bed synthesis and production of high purity products based on the relative solubilities of the initial, intermediate, and final compounds and elements in liquid ammonia are discussed.

  7. Compound composite odontoma

    PubMed Central

    Girish, G; Bavle, Radhika M; Singh, Manish Kumar; Prasad, Sahana N

    2016-01-01

    The term odontoma has been used as a descriptor for any tumor of odontogenic origin. It is a growth in which both epithelial and mesenchymal cells exhibits complete differentiation. Odontomas are considered as hamartomas rather than true neoplasm. They are usually discovered on routine radiographic examination. Odontomas, according to the World Health Organization, are classified into complex odontoma and compound odontomas. The present paper reports a case of compound composite odontomas. PMID:27194882

  8. Compound composite odontoma.

    PubMed

    Girish, G; Bavle, Radhika M; Singh, Manish Kumar; Prasad, Sahana N

    2016-01-01

    The term odontoma has been used as a descriptor for any tumor of odontogenic origin. It is a growth in which both epithelial and mesenchymal cells exhibits complete differentiation. Odontomas are considered as hamartomas rather than true neoplasm. They are usually discovered on routine radiographic examination. Odontomas, according to the World Health Organization, are classified into complex odontoma and compound odontomas. The present paper reports a case of compound composite odontomas. PMID:27194882

  9. Phenolic Molding Compounds

    NASA Astrophysics Data System (ADS)

    Koizumi, Koji; Charles, Ted; de Keyser, Hendrik

    Phenolic Molding Compounds continue to exhibit well balanced properties such as heat resistance, chemical resistance, dimensional stability, and creep resistance. They are widely applied in electrical, appliance, small engine, commutator, and automotive applications. As the focus of the automotive industry is weight reduction for greater fuel efficiency, phenolic molding compounds become appealing alternatives to metals. Current market volumes and trends, formulation components and its impact on properties, and a review of common manufacturing methods are presented. Molding processes as well as unique advanced techniques such as high temperature molding, live sprue, and injection/compression technique provide additional benefits in improving the performance characterisitics of phenolic molding compounds. Of special interest are descriptions of some of the latest innovations in automotive components, such as the phenolic intake manifold and valve block for dual clutch transmissions. The chapter also characterizes the most recent developments in new materials, including long glass phenolic molding compounds and carbon fiber reinforced phenolic molding compounds exhibiting a 10-20-fold increase in Charpy impact strength when compared to short fiber filled materials. The role of fatigue testing and fatigue fracture behavior presents some insight into long-term reliability and durability of glass-filled phenolic molding compounds. A section on new technology outlines the important factors to consider in modeling phenolic parts by finite element analysis and flow simulation.

  10. Understanding medication compounding issues.

    PubMed

    Hicks, Rodney W

    2014-04-01

    The potential for contamination of compounded products and the resulting infections are a serious threat to patient safety. Immediate use products are used frequently in the perioperative department, and perioperative nurses should be familiar with the guidelines and practices that aim to reduce the contamination that can occur during the sterile compounding process. Four common themes lead to successful compounding: quality (eg, product identification, purity, stability, compatibility, risk level assessment), the environment (eg, using a segregated compounding area with specialized airflow capabilities, reducing particulate matter, practicing proper hand hygiene, performing gloved fingertip sampling, properly cleaning equipment and work areas), personnel activities (eg, familiarity with types of containers used and how often they can be accessed, following expiration dates and the number of times containers can be accessed), and the control process (eg, process monitoring, quality improvement). If a third-party vendor is contracted to handle compounding for a facility, perioperative personnel should be aware of the responsibilities for the facility and the vendor to ensure a quality compounding program. PMID:24674793

  11. Nonpost mold cure compound

    NASA Astrophysics Data System (ADS)

    Hirata, Akihiro

    1997-08-01

    The recent low price trend of electronic products has made IC manufacturing efficiency a top priority in the semiconductor industry. Post mold cure (PMC) process, which generally involves heating the packages in the oven at 175 C for 4 to 8 hours, takes up much longer time than most other assembly processes. If this PMC process can be reduced or eliminated, semiconductor makers will be rewarded with a much higher cost merit. We define the purpose of Non-PMC as 'to get high reliability with suitable physical and electrical properties without PMC'. We compared carious properties of molding compound before and after PMC. We found that curing reaction has almost complete through DSC and C-NMR measurement, but several properties have not stabilized yet, and that not all properties after PMC were better than before PMC. We developed new grade of molding compound considering these facts. And we found that main factors to accomplish non-PMC compound are curability and flowability, and more, increasing of fundamental properties. To accomplish non-PMC, at first, molding compound need to have very high curability. Generally speaking, too high curability causes low flowability, and causes incomplete filing, wire sweep, pad shift, and weak adhesion to inner parts of IC packages. To prevent these failures, various compound properties were studied, and we achieved in adding good flowability to very high curable molding compound. Finally, anti-popcorn property was improved by adding low moisture, high adhesion, high Tg, and high flexural strengths at high temperature. Through this study, we developed new compound grade for various package, especially large QFP using standard ECN resin.

  12. Compound management beyond efficiency.

    PubMed

    Burr, Ian; Winchester, Toby; Keighley, Wilma; Sewing, Andreas

    2009-06-01

    Codeveloping alongside chemistry and in vitro screening, compound management was one of the first areas in research recognizing the need for efficient processes and workflows. Material management groups have centralized, automated, miniaturized and, importantly, found out what not to do with compounds. While driving down cost and improving quality in storage and processing, researchers still face the challenge of interfacing optimally with changing business processes, in screening groups, and with external vendors and focusing on biologicals in many companies. Here we review our strategy to provide a seamless link between compound acquisition and screening operations and the impact of material management on quality of the downstream processes. Although this is driven in part by new technologies and improved quality control within material management, redefining team structures and roles also drives job satisfaction and motivation in our teams with a subsequent positive impact on cycle times and customer feedback. PMID:19502566

  13. Sulfur compounds in coal

    NASA Technical Reports Server (NTRS)

    Attar, A.; Corcoran, W. H.

    1977-01-01

    The literature on the chemical structure of the organic sulfur compounds (or functional groups) in coal is reviewed. Four methods were applied in the literature to study the sulfur compounds in coal: direct spectrometric and chemical analysis, depolymerization in drastic conditions, depolymerization in mild conditions, and studies on simulated coal. The data suggest that most of the organic sulfur in coal is in the form of thiophenic structures and aromatic and aliphatic sulfides. The relative abundance of the sulfur groups in bituminous coal is estimated as 50:30:20%, respectively. The ratio changes during processing and during the chemical analysis. The main effects are the transformation during processing of sulfides to the more stable thiophenic compounds and the elimination of hydrogen sulfide.

  14. Metalloid compounds as drugs

    PubMed Central

    Sekhon, B. S.

    2013-01-01

    The six elements commonly known as metalloids are boron, silicon, germanium, arsenic, antimony, and tellurium. Metalloid containing compounds have been used as antiprotozoal drugs. Boron-based drugs, the benzoxaboroles have been exploited as potential treatments for neglected tropical diseases. Arsenic has been used as a medicinal agent and arsphenamine was the main drug used to treat syphilis. Arsenic trioxide has been approved for the treatment of acute promyelocytic leukemia. Pentavalent antimonials have been the recommended drug for visceral leishmaniasis and cutaneous leishmaniasis. Tellurium (IV) compounds may have important roles in thiol redox biological activity in the human body, and ammonium trichloro (dioxoethylene-O, O’-)tellurate (AS101) may be a promising agent for the treatment of Parkinson’s disease. Organosilicon compounds have been shown to be effective in vitro multidrug-resistance reverting agents. PMID:24019824

  15. Microoptical compound lens

    DOEpatents

    Sweatt, William C.; Gill, David D.

    2007-10-23

    An apposition microoptical compound lens comprises a plurality of lenslets arrayed around a segment of a hollow, three-dimensional optical shell. The lenslets collect light from an object and focus the light rays onto the concentric, curved front surface of a coherent fiber bundle. The fiber bundle transports the light rays to a planar detector, forming a plurality of sub-images that can be reconstructed as a full image. The microoptical compound lens can have a small size (millimeters), wide field of view (up to 180.degree.), and adequate resolution for object recognition and tracking.

  16. Tunable magnetism and half-metallicity in bulk and (1 0 0) surface of quaternary Co2MnGe1-xGax Heusler alloy

    NASA Astrophysics Data System (ADS)

    Wu, Bo; Yuan, Hongkuan; Kuang, Anlong; Feng, Yu; Chen, Hong

    2011-10-01

    The structural, magnetic and half-metallic properties of the bulk and (1 0 0) surface of quaternary Heusler alloy Co2MnGe1-xGax are investigated from the first-principles calculations. For the bulk, the lattice constant and total magnetic moment follow the Vegard law and Slater-Pauling rule well, respectively. Except for Co2MnGa, the Co2MnGe1-xGax series are half-metallic. Because the Fermi level of Co2MnGe0.5Ga0.5 is just located at the middle of the minority-spin gap, we predict that it bears the most robust half-metallicity as against remnant doped alloys. As for the Co2MnGe1-xGax(1 0 0) surface, the analyses on relaxed atomic positions and surface energies reveal that Co-Ge and Co-Ga bonding are more favourable than Co-Mn bonding and the terminations involving surface Mn atoms are more stable than CoCo terminations. By comparing with the bulk values, the surface Co and Mn magnetic moments are enhanced obviously. The calculated PDOS of all accessible 'ideal' surfaces show that the half-metallicity observed in bulk has been destroyed by the surface states, which is a possible reason why the tunnel magnetoresistence steeply drops as temperature increases. However, in the pure atomic terminations the surface properties can be slightly adjusted by the Ga-doped concentrations in bulk through the dipolar interaction. As a result, in the MnMn termination of Co2MnGe0.5Ga0.5(1 0 0) the spin polarization of 1 0 0% is detected, indicating that in the pure Mn atomic termination the half-metallicity of the (1 0 0) surface can remain if the corresponding bulk presents excellent half-metallic stability. Thus we predict that this thin film will present a higher potential for applications in ferromagnetic electrodes.

  17. Urinary Compounds in Autism

    ERIC Educational Resources Information Center

    Alcorn, A.; Berney, T.; Bretherton, K.; Mills, M.; Savery, D.; Shattock, P.

    2004-01-01

    Although earlier claims to identify specific compounds in the urine of people with autism had been discredited, it was subsequently suggested that there might be biochemical characteristics that were specific to early childhood, particularly in those who also did not have a severe degree of intellectual disability This study was to establish…

  18. Aminopropyl thiophene compounds

    SciTech Connect

    Goodman, M.M.; Knapp, F.F.

    1990-04-03

    This patent describes radiopharmaceuticals useful in brain imaging comprising radiohalogenated thienylethylamine derivatives. The compounds are 5-halo-thiophene-2-isopropyl amines able to cross the blood-brain barrier and be retained for a sufficient length of time to allow the evaluation of regional blood flow by radioimaging of the brain.

  19. Fun with Ionic Compounds

    ERIC Educational Resources Information Center

    Logerwell, Mollianne G.; Sterling, Donna R.

    2007-01-01

    Ionic bonding is a fundamental topic in high school chemistry, yet it continues to be a concept that students struggle to understand. Even if they understand atomic structure and ion formation, it can be difficult for students to visualize how ions fit together to form compounds. This article describes several engaging activities that help…

  20. The Onium Compounds

    NASA Astrophysics Data System (ADS)

    Tsarevsky, Nicolay V.; Slaveykova, Vera; Manev, Stefan; Lazarov, Dobri

    1997-06-01

    The onium salts are of a big interest for theoretical and structural chemistry, and for organic synthesis. Some representatives of the group (e.g. ammonium salts) were known from the oldest times. Many onium salts are met the nature: ammonium salts (either as inorganic salts, and organic derivatives, e.g. aminoacids, salts of biogenic amines and alkaloids, etc.); oxonium salts (plant pigments as anthocyans are organic oxonium compounds), etc. In 1894 C. Hartmann and V. Meyer prepared the first iodonium salts - 4-iododiphenyliodonium hydrogensulfate and diphenyliodonium salts, and suggested the ending -onium for all compounds with properties similar to those of ammonium salts. Nowadays onium compounds of almost all nonmetals are synthesised and studied. A great variety of physical methods: diffraction (e.g. XRD) and spectral methods (IR-, NMR-, and UV-spectra), as well as the chemical properties and methods of preparation of onium salts have been used in determination of the structure of these compounds. The application of different onium salts is immense. Ammonium, phosphonium and sulfonium salts are used as phase-transfer catalysts; diazonium salts - for the preparation of dyes, metalochromic and pH-indicators. All the onium salts and especially diazonium and iodonium salts are very useful reagents in organic synthesis.

  1. Analyzing cranberry bioactive compounds.

    PubMed

    Côté, J; Caillet, S; Doyon, G; Sylvain, J-F; Lacroix, M

    2010-10-01

    There is a growing public interest for the North American cranberry (Vaccinium macrocarpon) as a functional food because of the potential health benefits linked to phytochemical compounds present in the fruit--the anthocyanin pigments, responsible for its brilliant red color, and other secondary plant metabolites (flavonols, flavan-3-ols, proanthocyanidins, and phenolic acid derivatives). Isolation of these phenolic compounds and flavonoids from a sample matrix is a prerequisite to any comprehensive analysis scheme. By far the most widely employed analytical technique for the characterization of these compounds has been high-performance liquid chromatography(HPLC) coupled with ultraviolet-visible(UV/Vis) and mass spectrometer(MS) detection. This review covers the cranberry major bioactive compounds, the extraction and purification methods, and the analytical conditions for HPLC used to characterize them. Extraction, chromatographic separation and detection strategies, analyte determinations, and applications in HPLC are discussed and the information regarding methods of specific cranberry analyte analyses has been summarized in tabular form to provide a means of rapid access to information pertinent to the reader. PMID:20924868

  2. Aminopropyl thiophene compounds

    DOEpatents

    Goodman, Mark M.; Knapp, Jr., Furn F.

    1990-01-01

    Radiopharmaceuticals useful in brain imaging comprising radiohalogenated thienylethylamine derivatives. The compounds are 5-halo-thiophene-2-isopropyl amines able to cross the blood-brain barrier and be retained for a sufficient length of time to allow the evaluation of regional blood flow by radioimaging of the brain.

  3. PERSISTENT PERFLUORINATED ORGANIC COMPOUNDS

    EPA Science Inventory

    Perfluorinated compounds (PFCs) have gained notoriety in the recent past. Global distribution of PFCs in wildlife, environmental samples and humans has sparked a recent increase in new investigations concerning PFCs. Historically PFCs have been used in a wide variety of consume...

  4. Zinc and Compounds

    Integrated Risk Information System (IRIS)

    Zinc and Compounds ; CASRN 7440 - 66 - 6 Human health assessment information on a chemical substance is included in the IRIS database only after a comprehensive review of toxicity data , as outlined in the IRIS assessment development process . Sections I ( Health Hazard Assessments for Noncarcinogen

  5. Boron and Compounds

    Integrated Risk Information System (IRIS)

    Boron and Compounds ; CASRN 7440 - 42 - 8 Human health assessment information on a chemical substance is included in the IRIS database only after a comprehensive review of toxicity data , as outlined in the IRIS assessment development process . Sections I ( Health Hazard Assessments for Noncarcinoge

  6. Lead and compounds (inorganic)

    Integrated Risk Information System (IRIS)

    Lead and compounds ( inorganic ) ; CASRN 7439 - 92 - 1 Human health assessment information on a chemical substance is included in the IRIS database only after a comprehensive review of toxicity data , as outlined in the IRIS assessment development process . Sections I ( Health Hazard Assessments for

  7. Barium and Compounds

    Integrated Risk Information System (IRIS)

    Barium and Compounds ; CASRN 7440 - 39 - 3 Human health assessment information on a chemical substance is included in the IRIS database only after a comprehensive review of toxicity data , as outlined in the IRIS assessment development process . Sections I ( Health Hazard Assessments for Noncarcinog

  8. Beryllium and compounds

    Integrated Risk Information System (IRIS)

    Beryllium and compounds ; CASRN 7440 - 41 - 7 Human health assessment information on a chemical substance is included in the IRIS database only after a comprehensive review of toxicity data , as outlined in the IRIS assessment development process . Sections I ( Health Hazard Assessments for Noncarci

  9. Selenium and Compounds

    Integrated Risk Information System (IRIS)

    Selenium and Compounds ; CASRN 7782 - 49 - 2 Human health assessment information on a chemical substance is included in the IRIS database only after a comprehensive review of toxicity data , as outlined in the IRIS assessment development process . Sections I ( Health Hazard Assessments for Noncarcin

  10. 8-fluoropurine compounds

    DOEpatents

    Barrio, Jorge R.; Satyamurthy, Nagichettiar; Namavari, Mohammad; Phelps, Michael E.

    2001-01-01

    An efficient, regiocontrolled approach to the synthesis of 8-fluoropurines by direct fluorination of purines with dilute elemental fluorine, or acetyl hypofluorite, is provided. In a preferred embodiment, a purine compound is dissolved in a polar solvent and reacted with a dilute mixture of F.sub.2 in He or other inert gas.

  11. Noun Compounding in Thai.

    ERIC Educational Resources Information Center

    Fasold, Ralph William August

    The present study, a slightly revised version of the author's 1968 Ph.D. thesis presented to the University of Chicago, investigates compound formation in Thai. Chapter 1 summarizes the transformational generative theory on which the study is based, discusses the concept that Thai is a "simple" language in comparison with English, and briefly…

  12. Compound floating pivot micromechanisms

    DOEpatents

    Garcia, Ernest J.

    2001-04-24

    A new class of tilting micromechanical mechanisms have been developed. These new mechanisms use compound floating pivot structures to attain far greater tilt angles than are practical using other micromechanical techniques. The new mechanisms are also capable of bi-directional tilt about multiple axes.

  13. Enhancement of spin polarization via Fermi level tuning in Co{sub 2}MnSn{sub 1−x}Sb{sub x} (x = 0, 0.25. 0.5, 0.75, 1) Heusler alloys

    SciTech Connect

    Singh, Mukhtiyar Thakur, Jyoti; Kashyap, Manish K.; Saini, Hardev S.

    2014-04-24

    Full potential approach has been employed to tune Fermi level in Co{sub 2}MnSn{sub 1−x}Sb{sub x} (x = 0, 0.25, 0.5, 0.75, 1) Heulser alloys for enhancement of spin polarization and finding signature of half metallicity. Present density functional theory (DFT) based calculation indicates that stoichoimetric Heusler alloy, Co{sub 2}MnSn is not a half-metallic ferromagnet but the doping of Sb in it results in the shifting of E{sup F} in well-defined energy gap which leads the 100% spin polarization in the resultant alloys. The magnetism in present alloys is governed by localized moment on Mn atom mainly. The tuning of half-metallicity using doping can be proved as an ideal technique to search the new materials which can accomplish the need of spintronics.

  14. High strain in polycrystalline Ni{sub 48.8}Mn{sub 31.4}Ga{sub 19.8} Heusler alloys under overlapped static and oscillating magnetic fields

    SciTech Connect

    Montanher, D. Z.; Pereira, J. R. D.; Cótica, L. F.; Santos, I. A.; Gotardo, R. A. M.; Viana, D. S. F.; Garcia, D.; Eiras, J. A.

    2014-09-21

    Martensitic polycrystalline Ni{sub 48.8}Mn{sub 31.4}Ga{sub 19.8} Heusler alloys, with a stacking period of 14 atomic planes at room temperature, were innovatively processed by combining high-energy ball milling and powder metallurgy. Bulk samples were mechanically coupled to a piezoelectric material in a parallel configuration, and the mechanical deformation of the studied system due to the twin's variant motion was investigated under overlapped static and oscillating magnetic fields. A reversible and high mechanical deformation is observed when the frequency of the oscillating magnetic field is tuned with the natural vibration frequency of this system. In this condition, a linear deformation as a function of the static magnetic field amplitude occurs in the ±4 kOe range, and a mechanical deformation of 2% at 10 kOe is observed.

  15. Femtosecond laser excitation of multiple spin waves and composition dependence of Gilbert damping in full-Heusler Co{sub 2}Fe{sub 1−x}Mn{sub x}Al films

    SciTech Connect

    Cheng, Chuyuan; Li, Shufa; Lai, Tianshu E-mail: jhzhao@red.semi.ac.cn; Meng, Kangkang; Zhao, Jianhua E-mail: jhzhao@red.semi.ac.cn

    2013-12-02

    Spin-wave dynamics in 30 nm thick Co{sub 2}Fe{sub 1−x}Mn{sub x}Al full-Heusler films is investigated using time-resolved magneto-optical polar Kerr spectroscopy under an external field perpendicular to films. Damon-Eshbach (DE) and the first-order perpendicular standing spin-wave (PSSW) modes are observed simultaneously in four samples with x = 0, 0.3, 0.7, and 1. The frequency of DE and PSSW modes does not apparently depend on composition x, but damping of DE mode significantly on x and reaches the minimum as x = 0.7. The efficient coherent excitation of DE spin wave exhibits the promising application of Co{sub 2}Fe{sub 0.3}Mn{sub 0.7}Al films in magnonic devices.

  16. Determination of the normal and anomalous hall effect coefficients in ferromagnetic Ni{sub 50}Mn{sub 35}In{sub 15-x}Si{sub x} Heusler alloys at the martensitic transformation

    SciTech Connect

    Granovskii, A. B. Prudnikov, V. N.; Kazakov, A. P.; Zhukov, A. P.; Dubenko, I. S.

    2012-11-15

    The magnetization, the electrical resistivity, the magnetoresistance, and the Hall resistivity of Ni{sub 50}Mn{sub 35}In{sub 15-x}Si{sub x} (x = 1.0, 3.0, 4.0) Heusler alloys are studied at T = 80-320 K. The martensitic transformation in these alloys occurs at T = 220-280 K from the high-temperature ferromagnetic austenite phase into the low-temperature martensite phase having a substantially lower magnetization. A method is proposed to determine the normal and anomalous Hall effect coefficients in the presence of magnetoresistance and a possible magnetization dependence of these coefficients. The resistivity of the alloys increases jumpwise during the martensitic transformation, reaches 150-200 {mu}{Omega} cm, and is almost temperature-independent. The normal Hall effect coefficient is negative, is higher than that of nickel by an order of magnitude at T = 80 K, decreases monotonically with increasing temperature, approaches zero in austenite, and does not undergo sharp changes in the vicinity of the martensitic transformation. At x = 3, a normal Hall effect nonlinear in magnetization is detected in the immediate vicinity of the martensitic transformation. The temperature dependences of the anomalous Hall effect coefficient in both martensite and austenite and, especially, in the vicinity of the martensitic transformation cannot be described in terms of the skew scattering, the side jump, and the Karplus-Lutinger mechanisms from the anomalous Hall effect theory. The possible causes of this behavior of the magnetotransport properties in Heusler alloys are discussed.

  17. Arsonium compounds in algae

    PubMed Central

    Benson, A. A.

    1989-01-01

    Search for a precursor of the arsenobetaine discovered in Western Australian rock lobster tail muscle has led to an algal metabolite of radioarsenate having the properties of a trimethylarsoniumriboside derivative of the major arsenicals of aquatic plants, dimethylarsinoylribosylglycerol, its sulfate ester, and the corresponding riboside of phosphatidylglycerol. Such an arsonium compound could serve as metabolic precursor of arsenobetaine, the innocuous arsenical component of many marine food products. The oceanic diatom, Chaetoceros gracilis, cultured in radioarsenate produced a compound whose chemical, chromatographic, and electrophoretic properties are described. It was found to be identical to the trimethylarsonium derivative synthesized from the major algal arsenical, 1-(5′-dimethylarsinoyl-5′-deoxyribosyl)glycerol-3-O -sulfate. PMID:16594059

  18. Organic compounds in meteorites

    NASA Technical Reports Server (NTRS)

    Lawless, J. G.

    1980-01-01

    Recent studies of carbonaceous chondrites provide evidence that certain organic compounds are indigenous and the result of an abiotic, chemical synthesis. The results of several investigators have established the presence of amino acids and precursors, mono- and dicarboxylic acids, N-heterocycles, and hydrocarbons as well as other compounds. For example, studies of the Murchison and Murray meteorites have revealed the presence of at least 40 amino acids with nearly equal abundances of D and L isomers. The population consists of both protein and nonprotein amino acids including a wide variety of linear, cyclic, and polyfunctional types. Results show a trend of decreasing concentration with increasing carbon number, with the most abundant being glycine (41 n Moles/g). These and other results to be reviewed provide persuasive support for the theory of chemical evolution and provide the only natural evidence for the protobiological subset of molecules from which life on earth may have arisen.

  19. Photofunctions of intercalation compounds

    SciTech Connect

    Ogawa, Makoto; Kuroda, Kazuyuki

    1995-03-01

    In this article, the authors review the studies on the photofunctions of intercalation compounds. (The structures and properties of host materials which have been used for immobilizing photoactive species have been summarized in the following section.) some of these studies are for the purpose of characterizing the properties of host materials and host-guest systems, and others are for the purpose of contributing to future practical applications. The well-defined layered structures as well as the ability to accommodate guest species on the surface of the layers are very useful for organizing photoactive species to evaluate and control the photofunctions. Table 1 summarizes the characteristics of typical host-guest systems studied for immobilizing photoactive species. Attention is mainly focused on the role of layered structure on the organization of photoactive species; the photofunctions of intercalation compounds are discussed only in connection with the microscopic structures. 321 refs.

  20. Compound cycle engine program

    NASA Technical Reports Server (NTRS)

    Bobula, G. A.; Wintucky, W. T.; Castor, J. G.

    1986-01-01

    The Compound Cycle Engine (CCE) is a highly turbocharged, power compounded power plant which combines the lightweight pressure rise capability of a gas turbine with the high efficiency of a diesel. When optimized for a rotorcraft, the CCE will reduce fuel burned for a typical 2 hr (plus 30 min reserve) mission by 30 to 40 percent when compared to a conventional advanced technology gas turbine. The CCE can provide a 50 percent increase in range-payload product on this mission. A program to establish the technology base for a Compound Cycle Engine is presented. The goal of this program is to research and develop those technologies which are barriers to demonstrating a multicylinder diesel core in the early 1990's. The major activity underway is a three-phased contract with the Garrett Turbine Engine Company to perform: (1) a light helicopter feasibility study, (2) component technology development, and (3) lubricant and material research and development. Other related activities are also presented.

  1. Antifungal Compounds from Cyanobacteria

    PubMed Central

    Shishido, Tânia K.; Humisto, Anu; Jokela, Jouni; Liu, Liwei; Wahlsten, Matti; Tamrakar, Anisha; Fewer, David P.; Permi, Perttu; Andreote, Ana P. D.; Fiore, Marli F.; Sivonen, Kaarina

    2015-01-01

    Cyanobacteria are photosynthetic prokaryotes found in a range of environments. They are infamous for the production of toxins, as well as bioactive compounds, which exhibit anticancer, antimicrobial and protease inhibition activities. Cyanobacteria produce a broad range of antifungals belonging to structural classes, such as peptides, polyketides and alkaloids. Here, we tested cyanobacteria from a wide variety of environments for antifungal activity. The potent antifungal macrolide scytophycin was detected in Anabaena sp. HAN21/1, Anabaena cf. cylindrica PH133, Nostoc sp. HAN11/1 and Scytonema sp. HAN3/2. To our knowledge, this is the first description of Anabaena strains that produce scytophycins. We detected antifungal glycolipopeptide hassallidin production in Anabaena spp. BIR JV1 and HAN7/1 and in Nostoc spp. 6sf Calc and CENA 219. These strains were isolated from brackish and freshwater samples collected in Brazil, the Czech Republic and Finland. In addition, three cyanobacterial strains, Fischerella sp. CENA 298, Scytonema hofmanni PCC 7110 and Nostoc sp. N107.3, produced unidentified antifungal compounds that warrant further characterization. Interestingly, all of the strains shown to produce antifungal compounds in this study belong to Nostocales or Stigonematales cyanobacterial orders. PMID:25871291

  2. Compound chondrules fused cold

    NASA Astrophysics Data System (ADS)

    Hubbard, Alexander

    2015-07-01

    About 4-5% of chondrules are compound: two separate chondrules stuck together. This is commonly believed to be the result of the two component chondrules having collided shortly after forming, while still molten. This allows high velocity impacts to result in sticking. However, at T ∼ 1100 K, the temperature below which chondrules collide as solids (and hence usually bounce), coalescence times for droplets of appropriate composition are measured in tens of seconds. Even at 1025 K, at which temperature theory predicts that the chondrules must have collided extremely slowly to have stuck together, the coalescence time scale is still less than an hour. These coalescence time scales are too short for the collision of molten chondrules to explain the observed frequency of compound chondrules. We suggest instead a scenario where chondrules stuck together in slow collisions while fully solid; and the resulting chondrule pair was subsequently briefly heated to a temperature in the range of 900-1025 K. In that temperature window the coalescence time is finite but long, covering a span of hours to a decade. This is particularly interesting because those temperatures are precisely the critical window for thermally ionized MRI activity, so compound chondrules provide a possible probe into that vital regime.

  3. Toxic compounds in honey.

    PubMed

    Islam, Md Nazmul; Khalil, Md Ibrahim; Islam, Md Asiful; Gan, Siew Hua

    2014-07-01

    There is a wealth of information about the nutritional and medicinal properties of honey. However, honey may contain compounds that may lead to toxicity. A compound not naturally present in honey, named 5-hydroxymethylfurfural (HMF), may be formed during the heating or preservation processes of honey. HMF has gained much interest, as it is commonly detected in honey samples, especially samples that have been stored for a long time. HMF is a compound that may be mutagenic, carcinogenic and cytotoxic. It has also been reported that honey can be contaminated with heavy metals such as lead, arsenic, mercury and cadmium. Honey produced from the nectar of Rhododendron ponticum contains alkaloids that can be poisonous to humans, while honey collected from Andromeda flowers contains grayanotoxins, which can cause paralysis of limbs in humans and eventually leads to death. In addition, Melicope ternata and Coriaria arborea from New Zealand produce toxic honey that can be fatal. There are reports that honey is not safe to be consumed when it is collected from Datura plants (from Mexico and Hungary), belladonna flowers and Hyoscamus niger plants (from Hungary), Serjania lethalis (from Brazil), Gelsemium sempervirens (from the American Southwest), Kalmia latifolia, Tripetalia paniculata and Ledum palustre. Although the symptoms of poisoning due to honey consumption may differ depending on the source of toxins, most common symptoms generally include dizziness, nausea, vomiting, convulsions, headache, palpitations or even death. It has been suggested that honey should not be considered a completely safe food. PMID:24214851

  4. Offset Compound Gear Drive

    NASA Technical Reports Server (NTRS)

    Stevens, Mark A.; Handschuh, Robert F.; Lewicki, David G.

    2010-01-01

    The Offset Compound Gear Drive is an in-line, discrete, two-speed device utilizing a special offset compound gear that has both an internal tooth configuration on the input end and external tooth configuration on the output end, thus allowing it to mesh in series, simultaneously, with both a smaller external tooth input gear and a larger internal tooth output gear. This unique geometry and offset axis permits the compound gear to mesh with the smaller diameter input gear and the larger diameter output gear, both of which are on the same central, or primary, centerline. This configuration results in a compact in-line reduction gear set consisting of fewer gears and bearings than a conventional planetary gear train. Switching between the two output ratios is accomplished through a main control clutch and sprag. Power flow to the above is transmitted through concentric power paths. Low-speed operation is accomplished in two meshes. For the purpose of illustrating the low-speed output operation, the following example pitch diameters are given. A 5.0 pitch diameter (PD) input gear to 7.50 PD (internal tooth) intermediate gear (0.667 reduction mesh), and a 7.50 PD (external tooth) intermediate gear to a 10.00 PD output gear (0.750 reduction mesh). Note that it is not required that the intermediate gears on the offset axis be of the same diameter. For this example, the resultant low-speed ratio is 2:1 (output speed = 0.500; product of stage one 0.667 reduction and stage two 0.750 stage reduction). The design is not restricted to the example pitch diameters, or output ratio. From the output gear, power is transmitted through a hollow drive shaft, which, in turn, drives a sprag during which time the main clutch is disengaged.

  5. Special Risks of Pharmacy Compounding

    MedlinePlus

    ... Consumer Updates RSS Feed The Special Risks of Pharmacy Compounding Get Consumer Updates by E-mail Consumer ... page: A Troubling Trend What You Can Do Pharmacy compounding is a practice in which a licensed ...

  6. Oligosilanylated Antimony Compounds

    PubMed Central

    2015-01-01

    By reactions of magnesium oligosilanides with SbCl3, a number of oligosilanylated antimony compounds were obtained. When oligosilanyl dianions were used, either the expected cyclic disilylated halostibine was obtained or alternatively the formation of a distibine was observed. Deliberate formation of the distibine from the disilylated halostibine was achieved by reductive coupling with C8K. Computational studies of Sb–Sb bond energies, barriers of pyramidal inversion at Sb, and the conformational behavior of distibines provided insight for the understanding of the spectroscopic properties. PMID:25937691

  7. Titanium alkoxide compound

    DOEpatents

    Boyle, Timothy J.

    2007-08-14

    A titanium alkoxide composition is provided, as represented by the chemical formula (OC.sub.6H.sub.5N).sub.2Ti(OC.sub.6H.sub.5NH.sub.2).sub.2. As prepared, the compound is a crystalline substance with a hexavalent titanium atom bonded to two OC.sub.6H.sub.5NH.sub.2 groups and two OC.sub.6H.sub.5N groups with a theoretical molecular weight of 480.38, comprising 60.01% C, 5.04% H and 11.66% N.

  8. Immunomodulating compounds in Basidiomycetes

    PubMed Central

    Mizuno, Masashi; Nishitani, Yosuke

    2013-01-01

    Mushrooms are distinguished as important food containing immunomodulating and anticancer agents. These compounds belong mostly to polysaccharides especially β-d-glucans. Among them, β-1,3-glucan with side chain β-1,6-glucose residues have more important roles in immunomodulating and antitumor activities. In this review, we have introduced polysaccharide mainly from Lentinula edodes and Agaricus blazei Murill with immunomodulating and antitumor activities. In addition, the mechanism of activation of immune response and signal cascade are also reviewed. PMID:23704809

  9. Boronated porphyrin compounds

    DOEpatents

    Kahl, Stephen B.; Koo, Myoung-Seo

    1992-01-01

    A compound is described having the structure ##STR1## where R preferably is ##STR2## and most preferably R.sup.3 is a closo-carborane and R.sup.2 is --H, an alkyl or aryl having 1 to about 7 carbon atoms, This invention was made with Government support under NIH Grant No. CA-37961 awarded by the Department of Health and Human Services and under the Associated Universities Inc. Contract No. De-AC02-76CH00016 with the U.S. Department of Energy. The Government has rights in this invention.

  10. Boronated porphyrin compounds

    DOEpatents

    Kahl, S.B.; Koo, M.S.

    1992-09-22

    A compound is described having the structure ##STR1## where R preferably is ##STR2## and most preferably R.sup.3 is a closo-carborane and R.sup.2 is --H, an alkyl or aryl having 1 to about 7 carbon atoms, This invention was made with Government support under NIH Grant No. CA-37961 awarded by the Department of Health and Human Services and under the Associated Universities Inc. Contract No. De-AC02-76CH00016 with the U.S. Department of Energy. The Government has rights in this invention.

  11. Turbo compound engine

    SciTech Connect

    Okada, M.; Sekiyama, S.

    1988-06-07

    A turbo compound engine is described comprising: an engine having an exhaust gas passage and a crankshaft; a power turbine disposed in the exhaust gas passage so as to recover the exhaust gas energy; driving power transmission means for drivingly connecting the power turbine and the crankshaft so as to transmit the driving power; a fluid passage connected to a portion of the exhaust passage which lies between the power turbine and the engine; and fluid passage switching means for closing the exhaust passage upstream of the fluid passage while opening the fluid passage during exhaust braking.

  12. Compound allergy. An overview.

    PubMed

    Bashir, S J; Maibach, H I

    1997-04-01

    This review defines the term "compound allergy" in the context of new findings, and discusses evidence that allergenic reaction products have been identified. Material was gathered by searching Index Medicus and the Science Citation Index, and reviewing several standard texts. Issues regarding the validity of patch test results are addressed and we introduce the term "pseudocompound allergy" to cover cases of false-negative patch tests. We present new theories regarding the mechanisms by which new allergens are formed and a means of classification. PMID:9165199

  13. Organometallic chemistry of bimetallic compounds

    SciTech Connect

    Casey, C.P.

    1991-07-01

    This report consists of six sections: heterobimetallic dihydrides, early-late transition metal heterobimetallic compounds, amphiphilic carbene complexes and hydroxycarbene complexes, diiron compounds with bridging hydrocarbon ligands, diphosphine chelates with natural bite angles near 120 degrees, and synthesis and reactions of M=M compounds. (WET)

  14. Potential risks of pharmacy compounding.

    PubMed

    Gudeman, Jennifer; Jozwiakowski, Michael; Chollet, John; Randell, Michael

    2013-03-01

    Pharmacy compounding involves the preparation of customized medications that are not commercially available for individual patients with specialized medical needs. Traditional pharmacy compounding is appropriate when done on a small scale by pharmacists who prepare the medication based on an individual prescription. However, the regulatory oversight of pharmacy compounding is significantly less rigorous than that required for Food and Drug Administration (FDA)-approved drugs; as such, compounded drugs may pose additional risks to patients. FDA-approved drugs are made and tested in accordance with good manufacturing practice regulations (GMPs), which are federal statutes that govern the production and testing of pharmaceutical products. In contrast, compounded drugs are exempt from GMPs, and testing to assess product quality is inconsistent. Unlike FDA-approved drugs, pharmacy-compounded products are not clinically evaluated for safety or efficacy. In addition, compounded preparations do not have standard product labeling or prescribing information with instructions for safe use. Compounding pharmacies are not required to report adverse events to the FDA, which is mandatory for manufacturers of FDA-regulated medications. Some pharmacies engage in activities that extend beyond the boundaries of traditional pharmacy compounding, such as large-scale production of compounded medications without individual patient prescriptions, compounding drugs that have not been approved for use in the US, and creating copies of FDA-approved drugs. Compounding drugs in the absence of GMPs increases the potential for preparation errors. When compounding is performed on a large scale, such errors may adversely affect many patients. Published reports of independent testing by the FDA, state agencies, and others consistently show that compounded drugs fail to meet specifications at a considerably higher rate than FDA-approved drugs. Compounded sterile preparations pose the additional risk

  15. Turbo compound engine

    SciTech Connect

    Kawamura, H.

    1988-05-24

    A turbo compound engine having a first exhaust turbine coupled to an exhaust pipe of an internal combustion engine and a second exhaust turbine coupled to an exhaust port of the first exhaust turbine is described comprising: a first generator drivable by the first exhaust turbine; a second generator drivable by the second exhaust turbine; a motor operatively coupled to an output shaft of the internal combustion engine; speed detecting means for detecting the speed of rotation of the internal combustion engine; and control means for controlling the frequency of electric power, which is the sum of electric power outputs from the first and second generators and supplied to the motor, based on a signal from the speed detecting means, in order to control operation of the motor.

  16. Microoptical telescope compound eye

    NASA Astrophysics Data System (ADS)

    Duparré, Jacques W.; Schreiber, Peter; Matthes, André; Pshenay–Severin, Ekaterina; Bräuer, Andreas; Tünnermann, Andreas; Völkel, Reinhard; Eisner, Martin; Scharf, Toralf

    2005-02-01

    A new optical concept for compact digital image acquisition devices with large field of view is developed and proofed experimentally. Archetypes for the imaging system are compound eyes of small insects and the Gabor Superlens. A paraxial 3x3 matrix formalism is used to describe the telescope arrangement of three microlens arrays with different pitch to find first order parameters of the imaging system. A 2mm thin imaging system with 21x3 channels, 70ºx10º field of view and 4.5mm x 0.5mm image size is optimized and analyzed using sequential and non sequential raytracing and fabricated by microoptics technology. Anamorphic lenses, where the parameters are a function of the considered optical channel, are used to achieve a homogeneous optical performance over the whole field of view. Captured images are presented and compared to simulation results.

  17. Microoptical telescope compound eye.

    PubMed

    Duparré, Jacques; Schreiber, Peter; Matthes, André; Pshenay-Severin, Ekaterina; Bräuer, Andreas; Tünnermann, Andreas; Völkel, Reinhard; Eisner, Martin; Scharf, Toralf

    2005-02-01

    A new optical concept for compact digital image acquisition devices with large field of view is developed and proofed experimentally. Archetypes for the imaging system are compound eyes of small insects and the Gabor-Superlens. A paraxial 3x3 matrix formalism is used to describe the telescope arrangement of three microlens arrays with different pitch to find first order parameters of the imaging system. A 2mm thin imaging system with 21x3 channels, 70 masculinex10 masculine field of view and 4.5mm x 0.5mm image size is optimized and analyzed using sequential and non-sequential raytracing and fabricated by microoptics technology. Anamorphic lenses, where the parameters are a function of the considered optical channel, are used to achieve a homogeneous optical performance over the whole field of view. Captured images are presented and compared to simulation results. PMID:19494951

  18. Epitaxial films of Heusler compound Co{sub 2}FeAl{sub 0.5}Si{sub 0.5} with high crystalline quality grown by off-axis sputtering

    SciTech Connect

    Peters, B.; Hageman, Stephen J.; Yang, F. Y.; Alfonsov, A.; Blum, C. G. F.; Woodward, P. M.; Wurmehl, S.; Büchner, B.

    2013-10-14

    Co{sub 2}FeAl{sub 0.5}Si{sub 0.5} films with a surface roughness of 0.12 nm have been grown epitaxially on lattice-matched MgAl{sub 2}O{sub 4} (001) substrates by off-axis sputtering. X-ray diffraction shows pronounced Laue oscillations, rocking curves as narrow as 0.0043°, and clear Co{sub 2}FeAl{sub 0.5}Si{sub 0.5} (111) peaks indicating L2{sub 1} ordering. Magnetic characterizations show a clear magnetocrystalline anisotropy comprising cubic and epitaxy-induced uniaxial terms. Nuclear magnetic resonance measurements reveal L2{sub 1} order of 81% in the Co{sub 2}FeAl{sub 0.5}Si{sub 0.5} films. Magnetotransport measurements show a distinct separation of anisotropic magnetoresistance and ordinary magnetoresistance. These results demonstrate the state-of-the-art crystalline quality and magnetic uniformity of the Co{sub 2}FeAl{sub 0.5}Si{sub 0.5} films.

  19. Group-IV semiconductor compounds

    SciTech Connect

    Berding, M.A.; Sher, A.; van Schilfgaarde, M.

    1997-08-01

    Properties of ordered group-IV compounds containing carbon, silicon, and germanium are calculated within the local density approximation. Twenty-seven fully relaxed compounds represented by seven different compound structures are compared and, with the exception of SiC, all compounds are found to be metastable. Two trends emerge: carbon-germanium bonds are disfavored, and compounds that have carbon on a common sublattice are the least unbound because of their relatively low strain. When carbon shares a sublattice with silicon or germanium, the large strain results in a narrowing of the band gap, and in some cases the compound is metallic. The most promising structures with the lowest excess energy contain carbon on one sublattice and although they do not lattice match to silicon, they match rather well to silicon carbide. {copyright} {ital 1997} {ital The American Physical Society}

  20. Compound chondrules: an experimental investigation

    NASA Astrophysics Data System (ADS)

    Connolly, H. C., Jr.; Hewins, R. H.; Atre, N.; Lofgren, G. E.

    1994-07-01

    Compound chondrules are considered to be the product of collisions between molten chondrules during chondrule formation Wasson, J. T. et al. (1994) have argued that some compound chondrules are formed when a chondrule with an accretional rim experienced a flash-melting event similar to a chondrule-forming event. We have designed experiments to investigate the formation of compound chondrules by both methods. Experiments were performed on a Deltech vertical muffle tube furnace to form synthetic chondrules to use as accretion rim material. For our experimental conditions, it is clear that compound chondrules can only be made by a collisional event. Our changes maintain their spherical shape and produce distinct boundaries between charges that are similar to natural compound chondrules. Furthermore, collision event(s) between chondrules will cause nucleation if they are molten and undercooled, thus producing chondrule textures. Flash melting chondrules with accretionary rims will not produce compound chondrules but will produce new chondrules with new textures.

  1. Compounding with Silicones.

    PubMed

    Allen, Loyd V

    2015-01-01

    Since the 1940s, methylchlorosilanes have been used to treat glassware to prevent blood from clotting. The use of silicones in pharmaceutical and medical applications has grown to where today they are used in many life-saving devices (pacemakers, hydrocephalic shunts) and pharmaceutical applications from tubing, to excipients in topical formulations, to adhesives to affix transdermal drug delivery systems, and are also being used in products as active pharmaceutical ingredients, such as antiflatulents. About 60% of today's skin-care products now contain some type of silicone where they are considered safe and are known to provide a pleasant "silky-touch," non-greasy, and non-staining feel. Silicones exhibit many useful characteristics, and the safety of these agents supports their numerous applications; their biocompatibility is partially due to their low-chemical reactivity displayed by silicones, low-surface energy, and their hydrophobicity. Silicones are used both as active ingredients and as excipients. In addition is their use for "siliconization," or surface treatment, of many parenteral packaging components. Dimethicone and silicone oil are used as lubricants on stoppers to aid machineability, in syringes to aid piston movement, or on syringe needles to reduce pain upon injection. Silicones are also useful in pharmaceutical compounding as is discussed in this artiele included with this article are in developing formulations with silicones. PMID:26714363

  2. Compounding in synthetic aperture imaging.

    PubMed

    Hansen, Jens Munk; Jensen, Jørgen Arendt

    2012-09-01

    A method for obtaining compound images using synthetic aperture data is investigated using a convex array transducer. The new approach allows spatial compounding to be performed for any number of angles without reducing the frame rate or temporal resolution. This important feature is an intrinsic property of how the compound images are constructed using synthetic aperture data and an improvement compared with how spatial compounding is obtained using conventional methods. The synthetic aperture compound images are created by exploiting the linearity of delay-and-sum beamformation for data collected from multiple spherical emissions to synthesize multiple transmit and receive apertures, corresponding to imaging the tissue from multiple directions. The many images are added incoherently, to produce a single compound image. Using a 192-element, 3.5-MHz, λ-pitch transducer, it is demonstrated from tissue-phantom measurements that the speckle is reduced and the contrast resolution improved when applying synthetic aperture compound imaging. At a depth of 4 cm, the size of the synthesized apertures is optimized for lesion detection based on the speckle information density. This is a performance measure for tissue contrast resolution which quantifies the tradeoff between resolution loss and speckle reduction. The speckle information density is improved by 25% when comparing synthetic aperture compounding to a similar setup for compounding using dynamic receive focusing. The cystic resolution and clutter levels are measured using a wire phantom setup and compared with conventional application of the array, as well as to synthetic aperture imaging without compounding. If the full aperture is used for synthetic aperture compounding, the cystic resolution is improved by 41% compared with conventional imaging, and is at least as good as what can be obtained using synthetic aperture imaging without compounding. PMID:23007781

  3. New England Compounding Center Indictment.

    PubMed

    Cabaleiro, Joe

    2015-01-01

    This article is a review of the lapses in compliance with United States Pharmacopeia standards and pharmacy law as alleged by the New England Compounding Center indictment. This indictment was a result of an outbreak of fungal meningitis traced to fungal contamination of compounded methylprednisolone suspension for epidural steroid injections. This article is also intended as a gap analysis for compounders to review compliance at their own facility, and, if necessary, take the appropriate steps to implement best practices. PMID:26685489

  4. Method of producing cyclohexasilane compounds

    SciTech Connect

    Elangovan, Arumugasamy; Anderson, Kenneth; Boudjouk, Philip R; Schulz, Douglas L

    2015-03-10

    A method of preparing a cyclohexasilane compound from trichlorosilane is provided. The method includes contacting trichlorosilane with a reagent composition to produce a compound containing a tetradecahalocyclohexasilane dianion, such as a tetradecachlorocyclohexasilane dianion. The reagent composition typically includes (a) tertiary polyamine ligand; and (b) a deprotonating reagent, such as a tertiary amine having a pKa of at least about 10.5. Methods of converting the tetradecahalocyclohexasilane dianion-containing compound to cyclohexasilane or a dodecaorganocyclohexasilane are also provided.

  5. Method of preparing metallocene compounds

    DOEpatents

    Rosenblum, Myron; Matchett, Stephen A.

    1992-01-01

    This invention describes a novel method of preparing metallocene compounds. The invention is based on synthesis of novel bis cyclopentadienides that, under appropriate conditions, will either encapsulate a transition metal to produce a metallocene such as ferrocene, or ferrocene derivative, or will yield a polymeric metallocene. Compounds produced by this process are useful as catalysts in propulsion systems, or as anti-knock compounds in gasolines.

  6. Biomedical Compounds from Marine organisms

    PubMed Central

    Jha, Rajeev Kumar; Zi-rong, Xu

    2004-01-01

    The Ocean, which is called the ‘mother of origin of life’, is also the source of structurally unique natural products that are mainly accumulated in living organisms. Several of these compounds show pharmacological activities and are helpful for the invention and discovery of bioactive compounds, primarily for deadly diseases like cancer, acquired immuno-deficiency syndrome (AIDS), arthritis, etc., while other compounds have been developed as analgesics or to treat inflammation, etc. The life-saving drugs are mainly found abundantly in microorganisms, algae and invertebrates, while they are scarce in vertebrates. Modern technologies have opened vast areas of research for the extraction of biomedical compounds from oceans and seas.

  7. Organic Compounds in Carbonaceous Meteorites

    NASA Technical Reports Server (NTRS)

    Cooper, Grorge

    2001-01-01

    Carbonaceous meteorites are relatively enriched in soluble organic compounds. To date, these compounds provide the only record available to study a range of organic chemical processes in the early Solar System chemistry. The Murchison meteorite is the best-characterized carbonaceous meteorite with respect to organic chemistry. The study of its organic compounds has related principally to aqueous meteorite parent body chemistry and compounds of potential importance for the origin of life. Among the classes of organic compounds found in Murchison are amino acids, amides, carboxylic acids, hydroxy acids, sulfonic acids, phosphonic acids, purines and pyrimidines (Table 1). Compounds such as these were quite likely delivered to the early Earth in asteroids and comets. Until now, polyhydroxylated compounds (polyols), including sugars (polyhydroxy aldehydes or ketones), sugar alcohols, sugar acids, etc., had not been identified in Murchison. Ribose and deoxyribose, five-carbon sugars, are central to the role of contemporary nucleic acids, DNA and RNA. Glycerol, a three-carbon sugar alcohol, is a constituent of all known biological membranes. Due to the relative lability of sugars, some researchers have questioned the lifetime of sugars under the presumed conditions on the early Earth and postulated other (more stable) compounds as constituents of the first replicating molecules. The identification of potential sources and/or formation mechanisms of pre-biotic polyols would add to the understanding of what organic compounds were available, and for what length of time, on the ancient Earth.

  8. Antimicrobial Compounds in Tears

    PubMed Central

    McDermott, Alison M.

    2013-01-01

    The tear film coats the cornea and conjunctiva and serves several important functions. It provides lubrication, prevents drying of the ocular surface epithelia, helps provide a smooth surface for refracting light, supplies oxygen and is an important component of the innate defense system of the eye providing protection against a range of potential pathogens. This review describes both classic antimicrobial compounds found in tears such as lysozyme and some more recently identified such as members of the cationic antimicrobial peptide family and surfactant protein-D as well as potential new candidate molecules that may contribute to antimicrobial protection. As is readily evident from the literature review herein, tears, like all mucosal fluids, contain a plethora of molecules with known antimicrobial effects. That all of these are active in vivo is debatable as many are present in low concentrations, may be influenced by other tear components such as the ionic environment, and antimicrobial action may be only one of several activities ascribed to the molecule. However, there are many studies showing synergistic/additive interactions between several of the tear antimicrobials and it is highly likely that cooperativity between molecules is the primary way tears are able to afford significant antimicrobial protection to the ocular surface in vivo. In addition to effects on pathogen growth and survival some tear components prevent epithelial cell invasion and promote the epithelial expression of innate defense molecules. Given the protective role of tears a number of scenarios can be envisaged that may affect the amount and/or activity of tear antimicrobials and hence compromise tear immunity. Two such situations, dry eye disease and contact lens wear, are discussed here. PMID:23880529

  9. Antifungal Compounds from Piper Species

    PubMed Central

    Xu, Wen-Hui; Li, Xing-Cong

    2013-01-01

    This review documents chemical structures and antifungal activities of 68 compounds isolated from 22 Piper species of the plant family Piperaceae. These compounds include amides, flavonoids, prenylated benzoic acid derivatives, lignans, phenylpropanoids, butenolides, and cyclopentendiones. Some of them may serve as leads for potential pharmaceutical or agricultural fungicide development. PMID:24307889

  10. Morphological Dynamics in Compound Processing

    ERIC Educational Resources Information Center

    Kuperman, Victor; Bertram, Raymond; Baayen, R. Harald

    2008-01-01

    This paper explores the time-course of morphological processing of trimorphemic Finnish compounds. We find evidence for the parallel access to full-forms and morphological constituents diagnosed by the early effects of compound frequency, as well as early effects of left constituent frequency and family size. We also observe an interaction between…

  11. Bilingual Reading of Compound Words

    ERIC Educational Resources Information Center

    Ko, In Yeong; Wang, Min; Kim, Say Young

    2011-01-01

    The present study investigated whether bilingual readers activate constituents of compound words in one language while processing compound words in the other language via decomposition. Two experiments using a lexical decision task were conducted with adult Korean-English bilingual readers. In Experiment 1, the lexical decision of real English…

  12. ATMOSPHERIC FREONS AND HALOGENATED COMPOUNDS

    EPA Science Inventory

    Ambient levels of atmospheric Freons, halogenated hydrocarbons, and SF6 were measured at various locations in the U.S.A. Compounds such as CCl3F, CCl2F2, CH3-CCl3, and CCl4 were ubiquitious and generally measured at sub ppb levels. Tropospherically reactive compounds such as C2Cl...

  13. METHOD OF REDUCING PLUTONIUM COMPOUNDS

    DOEpatents

    Johns, I.B.

    1958-06-01

    A method is described for reducing plutonium compounds in aqueous solution from a higher to a lower valence state. This reduction of valence is achieved by treating the aqueous solution of higher valence plutonium compounds with hydrogen in contact with an activated platinum catalyst.

  14. Bilayer Effects of Antimalarial Compounds.

    PubMed

    Ramsey, Nicole B; Andersen, Olaf S

    2015-01-01

    Because of the perpetual development of resistance to current therapies for malaria, the Medicines for Malaria Venture developed the Malaria Box to facilitate the drug development process. We tested the 80 most potent compounds from the box for bilayer-mediated effects on membrane protein conformational changes (a measure of likely toxicity) in a gramicidin-based stopped flow fluorescence assay. Among the Malaria Box compounds tested, four compounds altered membrane properties (p< 0.05); MMV007384 stood out as a potent bilayer-perturbing compound that is toxic in many cell-based assays, suggesting that testing for membrane perturbation could help identify toxic compounds. In any case, MMV007384 should be approached with caution, if at all. PMID:26551613

  15. Macrocyclic compounds as corrosion inhibitors

    SciTech Connect

    Quraishi, M.A.; Rawat, J.; Ajmal, M.

    1998-12-01

    The influence of three macrocyclic compounds on corrosion of mild steel (MS) in hydrochloric acid (HCl) was investigated using weight loss, potentiodynamic polarization, alternating current (AC) impedance, and hydrogen permeation techniques. All the investigated compounds showed significant efficiencies and reduced permeation of hydrogen through MS in HCl. Inhibition efficiency (IE) varied with the nature and concentrations of the inhibitors, temperature, and concentrations of the acid solutions. The addition of iodide ions (I{sup {minus}}) increased IE of all the tested compounds as a result of the synergistic effect. Potentiodynamic polarization results revealed that macrocyclic compounds acted as mixed inhibitors in 1 M HCl to 5 M HCl. Adsorption on the metal surface obeyed Temkin`s adsorption isotherm. Auger electron spectroscopy (AES) of the polished MS surface, exposed with tetraphenyldithia-octaazacyclotetradeca-hexaene (PTAT) proved adsorption of this compound on the surface through nitrogen and sulfur atoms.

  16. Assimilation of Unusual Carbon Compounds

    NASA Astrophysics Data System (ADS)

    Middelhoven, Wouter J.

    Yeast taxa traditionally are distinguished by growth tests on several sugars and organic acids. During the last decades it became apparent that many yeast species assimilate a much greater variety of naturally occurring carbon compounds as sole source of carbon and energy. These abilities are indicative of a greater role of yeasts in the carbon cycle than previously assumed. Especially in acidic soils and other habitats, yeasts may play a role in the degradation of carbon compounds. Such compounds include purines like uric acid and adenine, aliphatic amines, diamines and hydroxyamines, phenolics and other benzene compounds and polysaccharides. Assimilation of purines and amines is a feature of many ascomycetes and basidiomycetes. However, benzene compounds are degraded by only a few ascomycetous yeasts (e.g. the Stephanoascus/ Blastobotrys clade and black yeastlike fungi) but by many basidiomycetes, e.g. Filobasidiales, Trichosporonales, red yeasts producing ballistoconidia and related species, but not by Tremellales. Assimilation of polysaccharides is wide-spread among basidiomycetes

  17. Antiparasitic Compounds That Target DNA

    PubMed Central

    Wilson, W. David; Tanious, Farial A.; Mathis, Amanda; Tevis, Denise; Hall, James Edwin; Boykin, David W.

    2008-01-01

    Designed, synthetic heterocyclic diamidines have excellent activity against eukaryotic parasites that cause diseases such as sleeping sickness and leishmania and adversely affect millions of people each year. The most active compounds bind specifically and strongly in the DNA minor groove at AT sequences. The compounds enter parasite cells rapidly and appear first in the kinetoplast that contains the mitochondrial DNA of the parasite. With time the compounds are also generally seen in the cell nucleus but are not significantly observed in the cytoplasm. The kinetoplast decays over time and disappears from the mitochondria of treated cells. At this point the compounds begin to be observed in other regions of the cell, such as the acidocalcisomes. The cells typically die in 24–48 hours after treatment. Active compounds appear to selectively target extended AT sequences and induce changes in kinetoplast DNA minicircles that cause a synergistic destruction of the catenated kinetoplast DNA network and cell death. PMID:18343228

  18. Bilayer Effects of Antimalarial Compounds

    PubMed Central

    Ramsey, Nicole B.; Andersen, Olaf S.

    2015-01-01

    Because of the perpetual development of resistance to current therapies for malaria, the Medicines for Malaria Venture developed the Malaria Box to facilitate the drug development process. We tested the 80 most potent compounds from the box for bilayer-mediated effects on membrane protein conformational changes (a measure of likely toxicity) in a gramicidin-based stopped flow fluorescence assay. Among the Malaria Box compounds tested, four compounds altered membrane properties (p< 0.05); MMV007384 stood out as a potent bilayer-perturbing compound that is toxic in many cell-based assays, suggesting that testing for membrane perturbation could help identify toxic compounds. In any case, MMV007384 should be approached with caution, if at all. PMID:26551613

  19. Devices for collecting chemical compounds

    DOEpatents

    Scott, Jill R; Groenewold, Gary S

    2013-12-24

    A device for sampling chemical compounds from fixed surfaces and related methods are disclosed. The device may include a vacuum source, a chamber and a sorbent material. The device may utilize vacuum extraction to volatilize the chemical compounds from a fixed surface so that they may be sorbed by the sorbent material. The sorbent material may then be analyzed using conventional thermal desorption/gas chromatography/mass spectrometry (TD/GC/MS) instrumentation to determine presence of the chemical compounds. The methods may include detecting release and presence of one or more chemical compounds and determining the efficacy of decontamination. The device may be useful in collection and analysis of a variety of chemical compounds, such as residual chemical warfare agents, chemical attribution signatures and toxic industrial chemicals.

  20. Half-metallic and magnetic properties of full-Heusler alloys Zr2CrZ (Z=Ga, In) with Hg2CuTi-type structure: A first-principles study

    NASA Astrophysics Data System (ADS)

    Deng, Zun-Yi; Zhang, Jian-Min

    2016-01-01

    The half-metallic and magnetic properties of Heusler alloys Zr2 CrZ (Z=Ga, In) with Hg2 CuTi -type structure have been investigated by using the first-principles projector augmented wave (PAW) potential within the generalized gradient approximation (GGA). The equilibrium lattice constants are 6.635 and 6.875 Å for Zr2 CrGa and Zr2 CrIn, respectively. Under compression and expansion deformations within lattice constant ranges of 6.515-7.100 and 6.371-7.126 Å for Zr2 CrGa and Zr2 CrIn, respectively, the Zr2 CrZ (Z=Ga, In) maintain a half-metallic nature with a fixed total magnetic moment of -1 μB / f.u ., following the Slater-Pauling rule μt = Zt - 18, but the absolute values of the local magnetic moments on Zr and Cr atoms increase with increasing lattice constant.

  1. Magnetic and chemical order-disorder transformations in Co2Fe(Ga1-xSix) and Co2Fe(Al1-ySiy) Heusler alloys

    NASA Astrophysics Data System (ADS)

    Umetsu, Rie Y.; Okubo, Akinari; Kainuma, Ryosuke

    2012-04-01

    The concentration dependence of the order-disorder phase transformation temperature from the L21 to the B2 phase (TtL21/B2) and magnetic properties of Co2Fe(Ga1-xSix) and Co2Fe(Al1-ySiy) Heusler alloys were investigated. In the phase diagrams, a crossover of the Curie temperature (TC) and TtL21/B2 was confirmed at around y = 0.45 in Co2Fe(Al1-ySiy), whereas the TC and TtL21/B2 monotonically changed with x in Co2Fe (Ga1-xSix). The slopes of the linear concentration dependence of TtL21/B2 for Co2Fe(Al1-ySiy) drastically changed at about y = 0.45, suggesting that the chemical interchange energy between Fe and Al in Co2FeAl alloy is affected by the magnetic ordering.

  2. Tunnel Magnetoresistance and Spin-Transfer-Torque Switching in Polycrystalline Co2FeAl Full-Heusler-Alloy Magnetic Tunnel Junctions on Amorphous Si /SiO2 Substrates

    NASA Astrophysics Data System (ADS)

    Wen, Zhenchao; Sukegawa, Hiroaki; Kasai, Shinya; Inomata, Koichiro; Mitani, Seiji

    2014-08-01

    We study polycrystalline B2-type Co2FeAl (CFA) full-Heusler-alloy-based magnetic tunnel junctions (MTJs) fabricated on a Si /SiO2 amorphous substrate. Polycrystalline CFA films with a (001) orientation, a high B2 ordering, and a flat surface are achieved by using a MgO buffer layer. A tunnel magnetoresistance ratio up to 175% is obtained for a MTJ with a CFA /MgO/CoFe structure on a 7.5-nm-thick MgO buffer. Spin-transfer-torque-induced magnetization switching is achieved in the MTJs with a 2-nm-thick polycrystalline CFA film as a switching layer. By using a thermal activation model, the intrinsic critical current density (Jc0) is determined to be 8.2×106 A /cm2, which is lower than 2.9×107 A /cm2, the value for epitaxial CFA MTJs [Appl. Phys. Lett. 100, 182403 (2012), 10.1063/1.4710521]. We find that the Gilbert damping constant (α) evaluated by using ferromagnetic resonance measurements for the polycrystalline CFA film is approximately 0.015 and is almost independent of the CFA thickness (2-18 nm). The low Jc0 for the polycrystalline MTJ is mainly attributed to the low α of the CFA layer compared with the value in the epitaxial one (approximately 0.04).

  3. Crystal orientation dependence of current-perpendicular-to-plane giant magnetoresistance of pseudo spin-valves with epitaxial Co{sub 2}Fe(Ge{sub 0.5}Ga{sub 0.5}) Heusler alloy layers

    SciTech Connect

    Chen, Jiamin; Hono, K.; Li, Songtian; Furubayashi, T. Takahashi, Y. K.

    2014-06-21

    The magnetoresistive (MR) properties of Co{sub 2}Fe(Ge{sub 0.5}Ga{sub 0.5}) (CFGG) Heusler alloy-based current-perpendicular-to-plane giant magnetoresistance pseudo-spin-valves (PSVs) are investigated. The PSV films are epitaxially grown on a sapphire (112{sup ¯}0) substrate with an Ag or Cu spacer layer, and their magnetoresistive properties are compared with those of PSV grown on MgO(001) substrates. For substrates with an Ag spacer, the PSV with the (001)[110]{sub CFGG}//(001)[010]{sub Ag} interface grown on MgO(001) exhibits a higher MR output compared with the (110)[001]{sub CFGG}//(111)[11{sup ¯}0]{sub Ag} interface grown on sapphire (112{sup ¯}0). In contrast, a higher MR output is obtained using a Cu spacer with the (110)[001]{sub CFGG}//(111)[11{sup ¯}0]{sub Cu} interface. These results demonstrate that the MR outputs depend upon the crystal orientation at the interface, and that interfaces with a small misfit tend to exhibit a larger MR output. This indicates the influence of crystal orientation as well as lattice mismatch upon the interfacial spin scattering asymmetry.

  4. Magnetic ordering and physical stability of X2Mn1+xSn1-x (X=Ru, Os, Co, Rh, Ni, Pd, Cu, and Ag) Heusler alloys from a first-principles study

    NASA Astrophysics Data System (ADS)

    Li, Chun-Mei; Hu, Qing-Miao; Yang, Rui; Johansson, Börje; Vitos, Levente

    2013-07-01

    The magnetic ordering and its effect on the physical stability of X2Mn1+xSn1-x (0≤x≤0.5, and X=Ru, Os, Co, Rh, Ni, Pd, Cu, and Ag) Heusler alloys are investigated systematically by the use of first-principles method. It is found that the ferromagnetic (FM) coupling between Mn on Mn sublattice (Mn1) and Mn on Sn sublattice (Mn2) is favorable over the antiferromagnetic (AFM) coupling for X with the number of valence electrons [Nv(X)] of 8 and 9, and vice versa for X with Nv(X)=10 and 11, originated from the competition of the exchange interactions between X-Mn2 and Mn1-Mn2. In comparison with the FM Mn1-Mn2 coupling, the AFM coupling decreases significantly the shear elastic constant C' but increases slightly C44, which results in increasing elastic anisotropy (A=C44/C') and consequently may facilitate the tetragonal shear lattice deformation. The hybridization of the minority electronic states between X d and Sn p plays a dominant role on the orientation of the magnetic coupling. The smaller change of the density of states in the Fermi level, induced by the lattice distortion for C', corresponds to the softer C' as well as the larger A in the AFM state than the FM one.

  5. Neutron diffraction study of the martensitic transformation and chemical order in Heusler alloy Ni1.91Mn1.29Ga0.8

    SciTech Connect

    Ari-Gur, Pnina; Garlea, Vasile O.; Cao, Huibo; Ge, Y.; Aaltio, I.; Hannula, S. P.; Koledov, V.

    2015-11-05

    In this study, Heusler alloys of Ni-Mn-Ga compositions demonstrate ferromagnetic shape memory effect in the martensitic state. The transformation temperature and the chemical order depend strongly on the composition. In the current work, the structure and chemical order of the martensitic phase of Ni1.91Mn1.29Ga0.8 were studied using neutron diffraction; the diffraction pattern was refined using the FullProf software. It was determined that the structural transition occurs around 330 K. At room temperature, 300 K, which is below the martensite transformation temperature, all the Bragg reflections can be described by a monoclinic lattice with a symmetry of space group P 1 2/m 1 and lattice constants of a = 4.23047(7) [Å], b = 5.58333(6) [Å], c = 21.0179(2) [Å], beta = 90.328(1). The chemical order is of critical importance in these alloys, and it was previously studied at 363 K. Analysis of the neutron diffraction in the monoclinic phase shows that the chemical order is maintained during the martensitic transformation.

  6. Vertical profiling of CH4 and CO2 based on high resolution ground-based NIR heterodyne spectro-radiometry

    NASA Astrophysics Data System (ADS)

    Klimchuk, Artem; Rodin, Alexander V.; Nadezhdinskii, Alexander; Spiridonov, Maxim; Churbanov, Dmitriy

    A compact, lightweight heterodyne NIR spectro-radiometer suitable for ground-based atmospheric sounding by direct spectro-radimetry of Sun spectrum with spectral resolution lambda / deltalambda=5*10 (7) has been used for precise measurements and vertical profiling of methane and carbon dioxide. Highly stabilized DFB laser was used as local oscillator, while single model quartz fiber Y-coupler served as a diplexer. Radiation mixed in the single mode fiber was detected by quadratic detector using p-i-n diode within the bandpass of 10 MHz. Wavelength coverage of spectral measurement was provided by sweeping local oscillator frequency in the range 1,1 cm (-1) . With the exposure time of 15 min, the absorption spectrum of the atmosphere over Moscow has been recorded with S/N=300. We retrieved methane vertical profile using Tikhonov method of smooth functional, which takes into account a priori information about first guess profile. The reference to model methane profile means that the regularization procedure always selects a priori values unless the measurements contradict this assumption. The retrieved methane profile demonstrates higher abundances in the lower scale height compared to the assumed model profile, well expected in the megalopolis center. The retrievals sensitivity is limited by 10 ppb, with the exception of the lower part of the profile where the tendency to lower values is revealed. Thus the methane abundance variations may be evaluated with relative accuracy better than 1%, which fits the requirements of greenhouse gas monitoring. The CO2 profile has also been retrieved with the accuracy sufficient for analyzing regional sources of greenhouse gases.

  7. Transparent Films from CO2 -Based Polyunsaturated Poly(ether carbonate)s: A Novel Synthesis Strategy and Fast Curing.

    PubMed

    Subhani, Muhammad Afzal; Köhler, Burkhard; Gürtler, Christoph; Leitner, Walter; Müller, Thomas E

    2016-04-25

    Transparent films were prepared by cross-linking polyunsaturated poly(ether carbonate)s obtained by the multicomponent polymerization of CO2 , propylene oxide, maleic anhydride, and allyl glycidyl ether. Poly(ether carbonate)s with ABXBA multiblock structures were obtained by sequential addition of mixtures of propylene oxide/maleic anhydride and propylene oxide/allyl glycidyl ether during the polymerization. The simultaneous addition of both monomer mixtures provided poly(ether carbonate)s with AXA triblock structures. Both types of polyunsaturated poly(ether carbonate)s are characterized by diverse functional groups, that is, terminal hydroxy groups, maleate moieties along the polymer backbone, and pendant allyl groups that allow for versatile polymer chemistry. The combination of double bonds substituted with electron-acceptor and electron-donor groups enables particularly facile UV- or redox-initiated free-radical curing. The resulting materials are transparent and highly interesting for coating applications. PMID:27028458

  8. Bringing High-Rate, CO2-Based Microbial Electrosynthesis Closer to Practical Implementation through Improved Electrode Design and Operating Conditions.

    PubMed

    Jourdin, Ludovic; Freguia, Stefano; Flexer, Victoria; Keller, Jurg

    2016-02-16

    The enhancement of microbial electrosynthesis (MES) of acetate from CO2 to performance levels that could potentially support practical implementations of the technology must go through the optimization of key design and operating conditions. We report that higher proton availability drastically increases the acetate production rate, with pH 5.2 found to be optimal, which will likely suppress methanogenic activity without inhibitor addition. Applied cathode potential as low as -1.1 V versus SHE still achieved 99% of electron recovery in the form of acetate at a current density of around -200 A m(-2). These current densities are leading to an exceptional acetate production rate of up to 1330 g m(-2) day(-1) at pH 6.7. Using highly open macroporous reticulated vitreous carbon electrodes with macropore sizes of about 0.6 mm in diameter was found to be optimal for achieving a good balance between total surface area available for biofilm formation and effective mass transfer between the bulk liquid and the electrode and biofilm surface. Furthermore, we also successfully demonstrated the use of a synthetic biogas mixture as carbon dioxide source, yielding similarly high MES performance as pure CO2. This would allow this process to be used effectively for both biogas quality improvement and conversion of the available CO2 to acetate. PMID:26810392

  9. Environmentally Benign CO2-Based Copolymers: Degradable Polycarbonates Derived from Dihydroxybutyric Acid and Their Platinum-Polymer Conjugates.

    PubMed

    Tsai, Fu-Te; Wang, Yanyan; Darensbourg, Donald J

    2016-04-01

    (S)-3,4-Dihydroxybutyric acid ((S)-3,4-DHBA), an endogenous straight chain fatty acid, is a normal human urinary metabolite and can be obtained as a valuable chiral biomass for synthesizing statin-class drugs. Hence, its epoxide derivatives should serve as promising monomers for producing biocompatible polymers via alternating copolymerization with carbon dioxide. In this report, we demonstrate the production of poly(tert-butyl 3,4-dihydroxybutanoate carbonate) from racemic-tert-butyl 3,4-epoxybutanoate (rac-(t)Bu 3,4-EB) and CO2 using bifunctional cobalt(III) salen catalysts. The copolymer exhibited greater than 99% carbonate linkages, 100% head-to-tail regioselectivity, and a glass-transition temperature (Tg) of 37 °C. By way of comparison, the similarly derived polycarbonate from the sterically less congested monomer, methyl 3,4-epoxybutanoate, displayed 91.8% head-to-tail content and a lower Tg of 18 °C. The tert-butyl protecting group of the pendant carboxylate group was removed using trifluoroacetic acid to afford poly(3,4-dihydroxybutyric acid carbonate). Depolymerization of poly(tert-butyl 3,4-dihydroxybutanoate carbonate) in the presence of strong base results in a stepwise unzipping of the polymer chain to yield the corresponding cyclic carbonate. Furthermore, the full degradation of the acetyl-capped poly(potassium 3,4-dihydroxybutyrate carbonate) resulted in formation of the biomasses, β-hydroxy-γ-butyrolacetone and 3,4-dihydroxybutyrate, in water (pH = 8) at 37 °C. In addition, water-soluble platinum-polymer conjugates were synthesized with platinum loading of 21.3-29.5%, suggesting poly(3,4-dihydroxybutyric acid carbonate) and related derivatives may serve as platinum drug delivery carriers. PMID:26974858

  10. Investigation on the Dielectric Properties of CO2 and CO2-Based Gases Based on the Boltzmann Equation Analysis

    NASA Astrophysics Data System (ADS)

    Sun, Hao; Wu, Yi; Rong, Mingzhe; Guo, Anxiang; Han, Guiquan; Lu, Yanhui

    2016-03-01

    In this paper, the dielectric properties of CO2, CO2/air, CO2/O2, CO2/N2, CO2/CF4, CO2/CH4, CO2/He, CO2/H2, CO2/NH3 and CO2/CO were investigated based on the Boltzmann equation analysis, in which the reduced critical electric field strength (E/N)cr of the gases was derived from the calculated electron energy distribution function (EEDF) by solving the Boltzmann transport equation. In this work, it should be noted that the fundamental data were carefully selected by the published experimental results and calculations to ensure the validity of the calculation. The results indicate that if He, H2, N2 and CH4, in which there are high ionization coefficients or a lack of attachment reactions, are added into CO2, the dielectric properties will decrease. On the other hand, air, O2, NH3 and CF4 (ranked in terms of (E/N)cr value in increasing order) have the potential to improve the dielectric property of CO2 at room temperature. supported in part by the National Key Basic Research Program of China (973 Program) (No. 2015CB251002), the Science and Technology Project Funds of the Grid State Corporation of China (No. SGSNK00KJJS1501564), National Natural Science Foundation of China (Nos. 51221005, 51577145), the Fundamental Research Funds for the Central Universities of China, and the Program for New Century Excellent Talents in University, China

  11. A circular dichroism sensor for Ni(2+) and Co(2+) based on L-cysteine capped cadmium sulfide quantum dots.

    PubMed

    Tedsana, Wimonsiri; Tuntulani, Thawatchai; Ngeontae, Wittaya

    2015-03-31

    A new circular dichroism sensor for detecting Ni(2+) and Co(2+) was proposed for the first time using chiral chelating quantum dots. The detection principle was based on changing of circular dichroism signals of the chiral quantum dots when forming a chiral complex with Ni(2+) or Co(2+). L-Cysteine capped cadmium sulfide quantum dots (L-Cyst-CdS QDs) were proposed as a chiral probe. The CD spectrum of L-Cyst-CdS QDs was significantly changed in the presence of Ni(2+) and Co(2+). On the other hand, other studied cations did not alter the original CD spectrum. Moreover, when increasing the concentration of Ni(2+) or Co(2+), the intensity of the CD spectrum linearly increased as a function of concentration and could be useful for the quantitative analysis. The proposed CD sensor showed linear working concentration ranges of 10-60 μM and 4-80 μM with low detection limits of 7.33 μМ and 1.13 μM for the detection of Ni(2+) and Co(2+), respectively. Parameters possibly affected the detection sensitivity such as solution pH and incubation time were studied and optimized. The proposed sensor was applied to detect Ni(2+) and Co(2+) in real water samples, and the results agreed well with the analysis using the standard ICP-OES. PMID:25813022

  12. Membrane rejection of nitrogen compounds

    NASA Technical Reports Server (NTRS)

    Lee, S.; Lueptow, R. M.

    2001-01-01

    Rejection characteristics of nitrogen compounds were examined for reverse osmosis, nanofiltration, and low-pressure reverse osmosis membranes. The rejection of nitrogen compounds is explained by integrating experimental results with calculations using the extended Nernst-Planck model coupled with a steric hindrance model. The molecular weight and chemical structure of nitrogen compounds appear to be less important in determining rejection than electrostatic properties. The rejection is greatest when the Donnan potential exceeds 0.05 V or when the ratio of the solute radius to the pore radius is greater than 0.8. The transport of solute in the pore is dominated by diffusion, although convective transport is significant for organic nitrogen compounds. Electromigration contributes negligibly to the overall solute transport in the membrane. Urea, a small organic compound, has lower rejection than ionic compounds such as ammonium, nitrate, and nitrite, indicating the critical role of electrostatic interaction in rejection. This suggests that better treatment efficiency for organic nitrogen compounds can be obtained after ammonification of urea.

  13. New syntheses of diazo compounds.

    PubMed

    Maas, Gerhard

    2009-01-01

    Diazo compounds (R1R2C=N2) are known as versatile and useful substrates for an array of chemical transformations and, therefore, diazo chemistry is still far from losing anything of its long-standing fascination. In addition to many studies on the subsequent chemistry of the diazo group, the inventory of methods for the preparation of diazo compounds is continuously supplemented by new methods and novel variations of established procedures. Several of these synthetic approaches take into account the lability and remarkable chemical reactivity of certain classes of diazo compounds, and environmentally more benign procedures also continue to be developed. PMID:19790217

  14. Regulation of Compound Leaf Development

    PubMed Central

    Wang, Yuan; Chen, Rujin

    2013-01-01

    Leaf morphology is one of the most variable, yet inheritable, traits in the plant kingdom. How plants develop a variety of forms and shapes is a major biological question. Here, we discuss some recent progress in understanding the development of compound or dissected leaves in model species, such as tomato (Solanum lycopersicum), Cardamine hirsuta and Medicago truncatula, with an emphasis on recent discoveries in legumes. We also discuss progress in gene regulations and hormonal actions in compound leaf development. These studies facilitate our understanding of the underlying regulatory mechanisms and put forward a prospective in compound leaf studies. PMID:27135488

  15. Polishing compound for plastic surfaces

    DOEpatents

    Stowell, Michael S.

    1995-01-01

    A polishing compound for plastic surfaces. The compound contains by weight approximately 4 to 17 parts at least one petroleum distillate lubricant, 1 to 6 parts mineral spirits, 2.5 to 15 parts abrasive particles, and 2.5 to 10 parts water. The abrasive is tripoli or a similar material that contains fine particles silica. Preferably, most of the abrasive particles are less than approximately 10 microns, more preferably less than approximately 5 microns in size. The compound is used on PLEXIGLAS.TM., LEXAN.TM., LUCITE.TM., polyvinyl chloride (PVC) and similar plastic materials whenever a smooth, clear polished surface is desired.

  16. Polishing compound for plastic surfaces

    DOEpatents

    Stowell, M.S.

    1995-08-22

    A polishing compound for plastic surfaces is disclosed. The compound contains by weight approximately 4 to 17 parts at least one petroleum distillate lubricant, 1 to 6 parts mineral spirits, 2.5 to 15 parts abrasive particles, and 2.5 to 10 parts water. The abrasive is tripoli or a similar material that contains fine particles silica. Preferably, most of the abrasive particles are less than approximately 10 microns, more preferably less than approximately 5 microns in size. The compound is used on PLEXIGLAS{trademark}, LEXAN{trademark}, LUCITE{trademark}, polyvinyl chloride (PVC) and similar plastic materials whenever a smooth, clear polished surface is desired. 5 figs.

  17. Polishing compound for plastic surfaces

    SciTech Connect

    Stowell, M.S.

    1993-01-01

    A polishing compound for plastic surfaces is disclosed. The compound contains by weight approximately 4 to 17 parts at least one petroleum distillate lubricant, 1 to 6 parts mineral spirits, 2.5 to 15 parts abrasive particles, and 2.5 to 10 parts water. The abrasive is tripoli or a similar material that contains colloidal silica. Preferably, most of the abrasive particles are less than approximately 10 microns, more preferably less than approximately 5 microns in size. The compound is used on PLEXIGLAS{sup TM}, LEXAN{sup TM}, LUCITE{sup TM}, polyvinyl chloride (PVC) and similar plastic materials whenever a smooth, clear polished surface is desired.

  18. Compound cuing in free recall.

    PubMed

    Lohnas, Lynn J; Kahana, Michael J

    2014-01-01

    According to the retrieved context theory of episodic memory, the cue for recall of an item is a weighted sum of recently activated cognitive states, including previously recalled and studied items as well as their associations. We show that this theory predicts there should be compound cuing in free recall. Specifically, the temporal contiguity effect should be greater when the 2 most recently recalled items were studied in contiguous list positions. A meta-analysis of published free recall experiments demonstrates evidence for compound cuing in both conditional response probabilities and interresponse times. To help rule out a rehearsal-based account of these compound cuing effects, we conducted an experiment with immediate, delayed, and continual-distractor free recall conditions. Consistent with retrieved context theory but not with a rehearsal-based account, compound cuing was present in all conditions, and was not significantly influenced by the presence of interitem distractors. PMID:23957364

  19. Polishing compound for plastic surfaces

    DOEpatents

    Stowell, M.S.

    1991-01-01

    This invention is comprised of a polishing compound for plastic materials. The compound includes approximately by approximately by weight 25 to 80 parts at least one petroleum distillate lubricant, 1 to 12 parts mineral spirits, 50 to 155 parts abrasive paste, and 15 to 60 parts water. Preferably, the compound includes approximately 37 to 42 parts at least one petroleum distillate lubricant, up to 8 parts mineral spirits, 95 to 110 parts abrasive paste, and 50 to 55 parts water. The proportions of the ingredients are varied in accordance with the particular application. The compound is used on PLEXIGLAS{trademark}, LEXAN{trademark}, LUCITE{trademark}, polyvinyl chloride (PVC), and similar plastic materials whenever a smooth, clear polished surface is desired.

  20. Crystallographic properties of fertilizer compounds

    SciTech Connect

    Frazier, A.W.; Dillard, E.F.; Thrasher, R.D.; Waerstad, K.R.; Hunter, S.R.; Kohler, J.J.; Scheib, R.M.

    1991-02-01

    This bulletin is a compilation of crystallographic data collected at NFERC on 450 fertilizer-related compounds. In TVA's fertilizer R and D program, petrographic examination, XRD, and infrared spectroscopy are combined with conventional chemical analysis methods in identifying the individual compounds that occur in fertilizer materials. This handbook brings together the results of these characterization studies and supplemental crystallographic data from the literature. It is in one-compound-per-page, loose-leaf format, ordered alphabetically by IUPAC name. Indexes provided include IUPAC name, formula, group, alternate formula, synonyms, x-ray data, optical data. Tables are given for solids, compounds in commercial MAP and DAP, and matrix materials in phosphate rock.

  1. Crystallographic properties of fertilizer compounds

    SciTech Connect

    Frazier, A.W.; Dillard, E.F.; Thrasher, R.D.; Waerstad, K.R.; Hunter, S.R.; Kohler, J.J.; Scheib, R.M.

    1991-02-01

    This bulletin is a compilation of crystallographic data collected at NFERC on 450 fertilizer-related compounds. In TVA`s fertilizer R and D program, petrographic examination, XRD, and infrared spectroscopy are combined with conventional chemical analysis methods in identifying the individual compounds that occur in fertilizer materials. This handbook brings together the results of these characterization studies and supplemental crystallographic data from the literature. It is in one-compound-per-page, loose-leaf format, ordered alphabetically by IUPAC name. Indexes provided include IUPAC name, formula, group, alternate formula, synonyms, x-ray data, optical data. Tables are given for solids, compounds in commercial MAP and DAP, and matrix materials in phosphate rock.

  2. Detection of chlorinated aromatic compounds

    DOEpatents

    Ekechukwu, Amy A.

    1996-01-01

    A method for making a composition for measuring the concentration of chloated aromatic compounds in aqueous fluids, and an optical probe for use with the method. The composition comprises a hydrophobic polymer matrix, preferably polyamide, with a fluorescent indicator uniformly dispersed therein. The indicator fluoresces in the presence of the chlorinated aromatic compounds with an intensity dependent on the concentration of these compounds in the fluid of interest, such as 8-amino-2-naphthalene sulfonate. The probe includes a hollow cylindrical housing that contains the composition in its distal end. The probe admits an aqueous fluid to the probe interior for exposure to the composition. An optical fiber transmits excitation light from a remote source to the composition while the indicator reacts with chlorinated aromatic compounds present in the fluid. The resulting fluorescence light signal is reflected to a second optical fiber that transmits the light to a spectrophotometer for analysis.

  3. Detection of chlorinated aromatic compounds

    DOEpatents

    Ekechukwu, A.A.

    1996-02-06

    A method for making a composition for measuring the concentration of chlorinated aromatic compounds in aqueous fluids, and an optical probe for use with the method are disclosed. The composition comprises a hydrophobic polymer matrix, preferably polyamide, with a fluorescent indicator uniformly dispersed therein. The indicator fluoresces in the presence of the chlorinated aromatic compounds with an intensity dependent on the concentration of these compounds in the fluid of interest, such as 8-amino-2-naphthalene sulfonate. The probe includes a hollow cylindrical housing that contains the composition in its distal end. The probe admits an aqueous fluid to the probe interior for exposure to the composition. An optical fiber transmits excitation light from a remote source to the composition while the indicator reacts with chlorinated aromatic compounds present in the fluid. The resulting fluorescence light signal is reflected to a second optical fiber that transmits the light to a spectrophotometer for analysis. 5 figs.

  4. Sulfated compounds from marine organisms.

    PubMed

    Kornprobst, J M; Sallenave, C; Barnathan, G

    1998-01-01

    More than 500 sulfated compounds have been isolated from marine organisms so far but most of them originate from two phyla only, Spongia and Echinodermata. The sulfated compounds are presented according to the phyla they have been identified from and to their chemical structures. Biological activities, when available, are also given. Macromolecules have also been included in this review but without structural details. PMID:9530808

  5. Volatile Organic Compounds in Uremia

    PubMed Central

    Seifert, Luzia; Slodzinski, Rafael; Jankowski, Joachim; Zidek, Walter; Westhoff, Timm H.

    2012-01-01

    Background Although “uremic fetor” has long been felt to be diagnostic of renal failure, the compounds exhaled in uremia remain largely unknown so far. The present work investigates whether breath analysis by ion mobility spectrometry can be used for the identification of volatile organic compounds retained in uremia. Methods Breath analysis was performed in 28 adults with an eGFR ≥60 ml/min per 1.73 m2, 26 adults with chronic renal failure corresponding to an eGFR of 10–59 ml/min per 1.73 m2, and 28 adults with end-stage renal disease (ESRD) before and after a hemodialysis session. Breath analysis was performed by ion mobility spectrometryafter gas-chromatographic preseparation. Identification of the compounds of interest was performed by thermal desorption gas chromatography/mass spectrometry. Results Breath analyses revealed significant differences in the spectra of patients with and without renal failure. Thirteen compounds were chosen for further evaluation. Some compounds including hydroxyacetone, 3-hydroxy-2-butanone and ammonia accumulated with decreasing renal function and were eliminated by dialysis. The concentrations of these compounds allowed a significant differentiation between healthy, chronic renal failure with an eGFR of 10–59 ml/min, and ESRD (p<0.05 each). Other compounds including 4-heptanal, 4-heptanone, and 2-heptanone preferentially or exclusively occurred in patients undergoing hemodialysis. Conclusion Impairment of renal function induces a characteristic fingerprint of volatile compounds in the breath. The technique of ion mobility spectrometry can be used for the identification of lipophilic uremic retention molecules. PMID:23049998

  6. Sensing acetylcholine and anticholinesterase compounds.

    PubMed

    Schena, Alberto; Johnsson, Kai

    2014-01-27

    Acetylcholine is a key neurotransmitter, and anticholinesterase agents are essential compounds used as medical drugs, pesticides, and chemical warfare agents. A semisynthetic fluorescence-based probe for the direct, real-time detection of acetylcholine and anticholinesterase compounds is introduced. The probe possesses good sensitivity, tunable detection range, and can be selectively targeted to cell surfaces, thereby making it an attractive tool for applications in analytical chemistry and quantitative biology. PMID:24339043

  7. Aza compounds as anion receptors

    DOEpatents

    Lee, H.S.; Yang, X.Q.; McBreen, J.

    1998-01-06

    A family of aza-ether based compounds including linear, multi-branched and aza-crown ethers is provided. When added to non-aqueous battery electrolytes, the family of aza-ether based compounds acts as neutral receptors to complex the anion moiety of the electrolyte salt thereby increasing the conductivity and the transference number of Li{sup +} ion in alkali metal batteries. 3 figs.

  8. Aza compounds as anion receptors

    DOEpatents

    Lee, Hung Sui; Yang, Xiao-Qing; McBreen, James

    1998-01-06

    A family of aza-ether based compounds including linear, multi-branched and aza-crown ethers is provided. When added to non-aqueous battery electrolytes, the family of aza-ether based compounds acts as neutral receptors to complex the anion moiety of the electrolyte salt thereby increasing the conductivity and the transference number of Li.sup.+ ion in alkali metal batteries.

  9. Photochemical dimerization of organic compounds

    SciTech Connect

    Crabtree, R.H.; Brown, S.H.; Muedas, C.A.; Ferguson, R.R.

    1992-04-14

    This patent describes improvement in a Group IIb photosensitized vapor phase dimerization of an organic compound in which a gaseous mixture of a Group IIB metal and the organic compound is irradiated in a reaction zone with a photosensitizing amount of radiant energy. The improvement comprises: a continuous stream of the gaseous mixture is passed as a vapor phase in a single pass through the reaction zone at a temperature at which the thus-produced dimer condenses immediately upon the formation thereof; the starting gaseous mixture comprises hydrogen and two ethylenically unsaturated compounds selected from the group consisting of alkenes of at least six carbon atoms, unsaturated nitriles, unsaturated epoxides, unsaturated silanes, unsaturated amines, unsaturated phosphines, and fluorinated alkenes; the gaseous mixture comprises nitrous oxide and the organic compound is a saturated compound with C-H bond strengths greater than 100 kcal/mol or a mixture of the saturated compound and an alkene; or the starting gaseous comprises an activating amount of hydrogen and the dimerization is a dehydrodimerization or cross-dimerization of a saturated hydrocarbon.

  10. Miniature curved artificial compound eyes

    PubMed Central

    Floreano, Dario; Pericet-Camara, Ramon; Viollet, Stéphane; Ruffier, Franck; Brückner, Andreas; Leitel, Robert; Buss, Wolfgang; Menouni, Mohsine; Expert, Fabien; Juston, Raphaël; Dobrzynski, Michal Karol; L’Eplattenier, Geraud; Recktenwald, Fabian; Mallot, Hanspeter A.; Franceschini, Nicolas

    2013-01-01

    In most animal species, vision is mediated by compound eyes, which offer lower resolution than vertebrate single-lens eyes, but significantly larger fields of view with negligible distortion and spherical aberration, as well as high temporal resolution in a tiny package. Compound eyes are ideally suited for fast panoramic motion perception. Engineering a miniature artificial compound eye is challenging because it requires accurate alignment of photoreceptive and optical components on a curved surface. Here, we describe a unique design method for biomimetic compound eyes featuring a panoramic, undistorted field of view in a very thin package. The design consists of three planar layers of separately produced arrays, namely, a microlens array, a neuromorphic photodetector array, and a flexible printed circuit board that are stacked, cut, and curved to produce a mechanically flexible imager. Following this method, we have prototyped and characterized an artificial compound eye bearing a hemispherical field of view with embedded and programmable low-power signal processing, high temporal resolution, and local adaptation to illumination. The prototyped artificial compound eye possesses several characteristics similar to the eye of the fruit fly Drosophila and other arthropod species. This design method opens up additional vistas for a broad range of applications in which wide field motion detection is at a premium, such as collision-free navigation of terrestrial and aerospace vehicles, and for the experimental testing of insect vision theories. PMID:23690574

  11. Miniature curved artificial compound eyes.

    PubMed

    Floreano, Dario; Pericet-Camara, Ramon; Viollet, Stéphane; Ruffier, Franck; Brückner, Andreas; Leitel, Robert; Buss, Wolfgang; Menouni, Mohsine; Expert, Fabien; Juston, Raphaël; Dobrzynski, Michal Karol; L'Eplattenier, Geraud; Recktenwald, Fabian; Mallot, Hanspeter A; Franceschini, Nicolas

    2013-06-01

    In most animal species, vision is mediated by compound eyes, which offer lower resolution than vertebrate single-lens eyes, but significantly larger fields of view with negligible distortion and spherical aberration, as well as high temporal resolution in a tiny package. Compound eyes are ideally suited for fast panoramic motion perception. Engineering a miniature artificial compound eye is challenging because it requires accurate alignment of photoreceptive and optical components on a curved surface. Here, we describe a unique design method for biomimetic compound eyes featuring a panoramic, undistorted field of view in a very thin package. The design consists of three planar layers of separately produced arrays, namely, a microlens array, a neuromorphic photodetector array, and a flexible printed circuit board that are stacked, cut, and curved to produce a mechanically flexible imager. Following this method, we have prototyped and characterized an artificial compound eye bearing a hemispherical field of view with embedded and programmable low-power signal processing, high temporal resolution, and local adaptation to illumination. The prototyped artificial compound eye possesses several characteristics similar to the eye of the fruit fly Drosophila and other arthropod species. This design method opens up additional vistas for a broad range of applications in which wide field motion detection is at a premium, such as collision-free navigation of terrestrial and aerospace vehicles, and for the experimental testing of insect vision theories. PMID:23690574

  12. Method for purifying bidentate organophosphorus compounds

    DOEpatents

    Schulz, Wallace W.

    1977-01-01

    Bidentate organophosphorus compounds useful for extracting actinide elements from acidic nuclear waste solutions are purified of undesirable acidic impurities by contacting the compounds with ethylene glycol which preferentially extracts the impurities found in technical grade bidentate compounds.

  13. Host compounds for red phosphorescent OLEDs

    SciTech Connect

    Xia, Chuanjun; Cheon, Kwang -Ohk

    2015-08-25

    Novel compounds containing a triphenylene moiety linked to an .alpha..beta. connected binaphthyl ring system are provided. These compounds have surprisingly good solubility in organic solvents and are useful as host compounds in red phosphorescent OLEDs.

  14. Extraterrestrial Organic Compounds in Meteorites

    NASA Technical Reports Server (NTRS)

    Botta, Oliver; Bada, Jeffrey L.; Meyer, Michael (Technical Monitor)

    2003-01-01

    Many organic compounds or their precursors found in meteorites originated in the interstellar or circumstellar medium and were later incorporated into planetesimals during the formation of the solar system. There they either survived intact or underwent further processing to synthesize secondary products on the meteorite parent body. The most distinct feature of CI and CM carbonaceous chondrites, two types of stony meteorites, is their high carbon content (up to 3% of weight), either in the form of carbonates or of organic compounds. The bulk of the organic carbon consists of an insoluble macromolecular material with a complex structure. Also present is a soluble organic fraction, which has been analyzed by several separation and analytical procedures. Low detection limits can be achieved by derivatization of the organic molecules with reagents that allow for analysis by gas chromatography/mass spectroscopy and high performance liquid chromatography. The CM meteorite Murchison has been found to contain more than 70 extraterrestrial amino acids and several other classes of compounds including carboxylic acids, hydroxy carboxylic acids, sulphonic and phosphonic acids, aliphatic, aromatic and polar hydrocarbons, fullerenes, heterocycles as well as carbonyl compounds, alcohols, amines and amides. The organic matter was found to be enriched in deuterium, and distinct organic compounds show isotopic enrichments of carbon and nitrogen relative to terrestrial matter.

  15. Cytotoxic Compounds from Brucea mollis

    PubMed Central

    Tung, Mai Hung Thanh; Đuc, Ho Viet; Huong, Tran Thu; Duong, Nguyen Thanh; Phuong, Do Thi; Thao, Do Thi; Tai, Bui Huu; Kim, Young Ho; Bach, Tran The; Cuong, Nguyen Manh

    2013-01-01

    Ten compounds, including soulameanone (1), isobruceine B (2), 9-methoxy-canthin-6-one (3), bruceolline F (4), niloticine (5), octatriacontan-1-ol (6), bombiprenone (7), α-tocopherol (8), inosine (9), and apigenin 7-O-β-D-glucopyranoside (10), were isolated from the leaves, stems, and roots of Brucea mollis Wall. ex Kurz. Their structures were determined using one-and two-dimensional NMR spectroscopy and mass spectrometry. All compounds were evaluated for their cytotoxic activity against KB (human carcinoma of the mouth), LU-1 (human lung adenocarcinoma), LNCaP (human prostate adeno-carcinoma), and HL-60 (human promyelocytic leukemia) cancer cell lines. Compound 2 showed significant cytotoxic activity against KB, LU-1, LNCaP, and HL-60 cancer cells with IC50 values of 0.39, 0.40, 0.34, and 0.23 μg/mL, respectively. In addition, compounds 3 and 5 showed significant cytotoxic activity against KB, LU-1, LNCaP, and HL-60 cancer cells with IC50 values around 1–4 μg/mL. Compounds 9-methoxycanthin-6-one (3) and niloticine (5) have been discovered for the first time from the Brucea genus. PMID:24106661

  16. The structural, electronic, magnetic and mechanical properties of quaternary Heusler alloys ZrTiCrZ (Z  =  Al, Ga, In, Si, Ge, Sn): a first-principles study

    NASA Astrophysics Data System (ADS)

    Yan, Peng-Li; Zhang, Jian-Min; Zhou, Bo; Xu, Ke-Wei

    2016-06-01

    The structural, electronic, magnetic and mechanical properties of the quaternary Heusler alloys ZrTiCrZ (Z  =  Al, Ga, In, Si, Ge, Sn) have been investigated firstly by using the first-principles calculations. The preferred configurations of the ZrTiCrZ alloys are all Y-type (I). At their equilibrium lattice constants, the ZrTiCrZ alloys are half-metallic (HM) ferrimagnets for Z  =  Al, Ga and In, while spin-gapless semiconductor (SGS) antiferromagnets (AFM) for Z  =  Si, Ge and Sn. The total magnetic moments {μt} of the ZrTiCrZ alloys are  ‑1 {μ\\text{B}}/\\text{f}\\text{.u}\\text{.} for Z  =  Al, Ga and In, while 0 {μ\\text{B}}/\\text{f}\\text{.u}\\text{.} for Z  =  Si, Ge and Sn, both linearly scaled with the total number of valence electrons {{Z}\\text{t}} by Slater–Pauling rule {μ\\text{t}}={{Z}\\text{t}}-18 . The elastic constants {{C}11} , {{C}12} and {{C}44} of the single crystal and the related elastic moduli G , B , E , \\upsilon and A of the polycrystalline aggregates are also calculated and used to study the mechanical stability of these alloys. Although the Curie temperatures {{T}\\text{C}} of the ZrTiCrZ alloys are overestimated by using the mean field approximation (MFA), they can be better estimated by including the exchange interactions. Finally, the HM stabilities as well as the total and atomic magnetic moments of the ZrTiCrZ alloys (Z  =  Al, Ga, In) under either hydrostatic strain or tetragonal strain are also discussed.

  17. Tunnel magnetoresistance effect in magnetic tunnel junctions using Fermi-level-tuned epitaxial Fe{sub 2}Cr{sub 1−x}Co{sub x}Si Heusler alloy

    SciTech Connect

    Wang, Yu-Pu; Han, Gu-Chang; Qiu, Jinjun; Yap, Qi-Jia; Lu, Hui; Teo, Kie-Leong

    2014-05-07

    This paper reports a systematic investigation on the structural and magnetic properties of Fe{sub 2}Cr{sub 1−x}Co{sub x}Si Heusler alloys with various compositions of x by co-sputtering Fe{sub 2}CrSi and Fe{sub 2}CoSi targets and their applications in magnetic tunnel junctions (MTJs). Fe{sub 2}Cr{sub 1−x}Co{sub x}Si films of high crystalline quality have been epitaxially grown on MgO substrate using Cr as a buffer layer. The L2{sub 1} phase can be obtained at x = 0.3 and 0.5, while B2 phase for the rest compositions. A tunnel magnetoresistance (TMR) ratio of 19.3% at room temperature is achieved for MTJs using Fe{sub 2}Cr{sub 0.3}Co{sub 0.7}Si as the bottom electrode with 350 °C post-annealing. This suggests that the Fermi level in Fe{sub 2}Cr{sub 1−x}Co{sub x}Si has been successfully tuned close to the center of band gap of minority spin with x = 0.7 and therefore better thermal stability and higher spin polarization are achieved in Fe{sub 2}Cr{sub 0.3}Co{sub 0.7}Si. The post-annealing effect for MTJs is also studied in details. The removal of the oxidized Fe{sub 2}Cr{sub 0.3}Co{sub 0.7}Si at the interface with MgO barrier is found to be the key to improve the TMR ratio. When the thickness of the inserted Mg layer increases from 0.3 to 0.4 nm, the TMR ratio is greatly enhanced from 19.3% to 28%.

  18. Microbial Identification in Pharmaceutical Compounding.

    PubMed

    Hyde, Tiffany; Anstead, James; Schade, Lisa; Zellner, James

    2016-01-01

    Compounding pharmacies and contract testing laboratories can readily utilize critical information that microbial identification methods provide. Rapidly identifying the genus and species of environmental isolates and sample contaminates provides pharmacies and laboratories the opportunity to determine the possible source and implement corrective actions to improve compounding and testing processes. The microbial identification data collected from a compounding environment is critical. It is important to have accurate and specific microbial information to guide environmental collection practices, validation studies, and troubleshooting initiatives. The different technologies available provide varying levels of identification. They range from phenotypic assays to more accurate molecular-based techniques, including macromolecular methods and whole genome sequencing. Selecting the appropriate identification methodology requires evaluating multiple factors including the level of information required (genus only, genus and species, etc.) and the pharmacy's tolerance for unidentified or incorrectly identified isolates. PMID:27125052

  19. Antitumor Compounds from Marine Actinomycetes

    PubMed Central

    Olano, Carlos; Méndez, Carmen; Salas, José A.

    2009-01-01

    Chemotherapy is one of the main treatments used to combat cancer. A great number of antitumor compounds are natural products or their derivatives, mainly produced by microorganisms. In particular, actinomycetes are the producers of a large number of natural products with different biological activities, including antitumor properties. These antitumor compounds belong to several structural classes such as anthracyclines, enediynes, indolocarbazoles, isoprenoides, macrolides, non-ribosomal peptides and others, and they exert antitumor activity by inducing apoptosis through DNA cleavage mediated by topoisomerase I or II inhibition, mitochondria permeabilization, inhibition of key enzymes involved in signal transduction like proteases, or cellular metabolism and in some cases by inhibiting tumor-induced angiogenesis. Marine organisms have attracted special attention in the last years for their ability to produce interesting pharmacological lead compounds. PMID:19597582

  20. Antimicrobial Compounds from Drypetes staudtii.

    PubMed

    Grace, David; Khan, Madiha S; Friesen, Kenneth; Ata, Athar

    2016-07-01

    Antimicrobial-directed phytochemical investigation of the MeOH extract of Drypetes staudtii afforded two new compounds, 4,5-(methylenedioxy)-o-coumaroylputrescine (1), 4,5-(methylenedioxy)-o-coumaroyl-4'-N-methylputrescine (2), along with seven known natural products 4α-hydroxyeremophila-1,9-diene-3,8-dione (3), drypemolundein B (4), friedelan-3β-ol (5), erythrodiol (6), ursolic acid (7), p-coumaric acid (8), and β-sitosterol (9). Structures of compounds 1 - 9 were elucidated with the aid of extensive NMR and mass spectral studies. All of the isolates exhibited antibacterial activity against Gram-positive and Gram-negative bacteria with minimum inhibitory concentration (MIC) in the range of 8 - 128 μg/ml. Compounds 1 - 2 were also moderately active against Candida albicans with an MIC value of 32 μg/ml. PMID:27288642