DOCSLIB.ORG

Computational Investigation of Heusler Compounds for Spintronics Application

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Computational Investigation of Heusler Compounds for Spintronics Application Computational Investigation of Heusler compounds for Spintronics Application A Dissertation Presented to the faculty of the School of Engineering and Applied Science University of Virginia in partial fulfillment of the requirements for the degree Doctor of Philosophy by Jianhua Ma May 2019 Abstract Heusler compounds have become a large family of binary, ternary, and quaternary compounds that shows a variety of diverse properties and attracted tremendous scientific interest in the spintronics. The extensive tunability of the Heusler compounds through chemical substitutions makes the large potential for the family. In this dissertation, we first present first-principles density functional calculations of the electronic structure, magnetism, and structural stability of 378 XYZ half-Heusler compounds (with X = Cr, Mn, Fe, Co, Ni, Ru, Rh; Y = Ti, V, Cr, Mn, Fe, Ni; Z = Al, Ga, In, Si, Ge, Sn, P, As, Sb). We find that a \Slater-Pauling gap" in the density of states, (i.e. a gap or pseudogap after nine states in the three atom primitive cell) in at least one spin channel is a common feature in half-Heusler compounds. We find that the presence of such a gap at the Fermi energy in one or both spin channels contributes significantly to the stability of a half-Heusler compound. We calculate the formation energy of each compound and systematically investigate its stability against all other phases in the Open Quantum Materials Database (OQMD). We represent the thermodynamic phase stability of each compound as its distance from the convex hull of stable phases in the respective chemical space and show that the hull distance of a compound is a good measure of the likelihood of its experimental synthesis. We find low formation energies and mostly correspondingly low hull distances for compounds with X = Co, Rh or Ni, Y = Ti or V, and Z = P, As, Sb or Si. We identify 26 18-electron semiconductors, 45 half-metals, and 34 near half-metals with negative formation energy, that follow the Slater-Pauling rule of three electrons per atom. Our calculations predict several new, as-yet unknown, thermodynamically stable phases which merit further experimental exploration | RuVAs, CoVGe, FeVAs in the half-Heusler structure, and NiScAs, RuVP, RhTiP in the orthorhombic MgSrSi-type structure. In addition, our calculations predict a number of c Abstract d hitherto unreported semiconducting (e.g., CoVSn, RhVGe), half-metallic (e.g., RhVSb), and near half-metallic (e.g., CoFeSb, CoVP) half-Heusler compounds to lie close to the respective convex hull of stable phases, and thus may be experimentally realized under suitable synthesis conditions, resulting in potential candidates for various semiconducting and spintronics applications. The next set of systems studied was inverse-Heusler compounds. First-principles calculations of the electronic structure, magnetism and structural stability of 405 inverse-Heusler compounds with the chemical formula X2YZ are presented and discussed with a goal of identifying compounds of interest for spintronics. Compounds for which the number of electrons per atom for Y exceed that for X and for which X and Y are each one of the 3d elements, Sc-Zn, and Z is one of the group IIIA-VA elements: Al, Ga, In, Si, Ge, Sn, P, As or Sb were considered. The formation energy per atom of each compound was calculated. By comparing our calculated formation energies to those calculated for phases in the Inorganic Crystal Structure Database (ICSD) of observed phases, we estimate that inverse-Heuslers with formation energies within 0.052 eV/atom of the calculated convex hull are reasonably likely to be synthesizable in equilibrium. The observed trends in the formation energy and relative structural stability as the X, Y and Z elements vary are described. In addition to the Slater-Pauling gap after 12 states per formula unit in one of the spin channels, inverse-Heusler phases often have gaps after 9 states or 14 states. We describe the origin and occurrence of these gaps. We identify 14 inverse-Heusler semiconductors, 51 half-metals and 50 near-half-metals with negative formation energy. In addition, our calculations predict 4 half-metals and 6 near-half-metals to lie close to the respective convex hull of stable phases, and thus may be experimentally realized under suitable synthesis conditions, resulting in potential candidates for future spintronics applications. In the following the discovery, a series of half-metallic half-Heusler alloys are combined with MgO to create Heusler-MgO junctions. The electronic and magnetic properties of junctions are investigated. The strong oxidation between metal and oxygen atoms causes the systems with pure YY interfaces to be the most stable cases. We concluded that the uniaxial anisotropy can be induced in Heusler layers next to MgO. Type of interface layers determines the half-metallicity and the anisotropy (in-plane or perpendicular) in the Heusler-MgO junctions. The capacity to keep half-metallicity and perpendicular magnetic anisotropy (PMA) in NiMnSb/MgO and CoTiSn/MgO junction with MnMn interface layer makes it be potential candidates as electrode layers in Spin Abstract e Transfer Torque Random Access Memory (STT-RAM) devices. Finally, using first-principles calculations of structural and magnetic properties, we identify several promising ferrimagnetic inverse Heusler half-metal/near half-metals can be the ideal candidate for hosting ultra-small, fast, and room temperature stable skyrmions. Acknowledgments The work presented in this document has been possible because of the support of many people. I want to express my gratitude to my supervisor, Professor Avik Ghosh, whose influence has guided me into the researcher I am today. He has taught me to think simple, to work hard, to make effective presentations and many more important skills to do research. Without his expert-level guidance I could have not achieved the present comfort in bringing this dissertation in its present format. I need to say a 'thank you' to him here, truly. My gratitude also goes to Professor William H. Butler, who as the principal investigator of the DMREF project for Heusler compounds. As a world-famous expert in magnetic materials field, his intelligence and deeply love in science touched my heart greatly. I respect him as my second grandfather forever and I also dream to be a kindly, wise and merry old man as him, in one day. I also want to thank the members of my committee, Professors Joe C. Campbell, Mona Zebarjadi and Sean R. Agnew specially Professors Joseph Poon for mentoring and guiding me along the magnetic skyrmion work. I want to thank the members of my VINO research group for their friendship and all the innumerable enlightening meetings. I want to thank Yaohua Tan, Yunkun Xie, Kamaram Munira, Jingjie Zhang, Mirza M. Elahi, Sheikh Z. Ahmed and Carlos A. Polanco, for their time, interest and collaboration with first principles parameters. I also thank the new students, they given me the chance to share and pass along my research experience. I also need to thank my collaborators from University of Alabama, Northwest University, Southern Illinois University and Virginia Tech. Nariman, Vinay and Jiangang, they really help me so much and it is fortunate for me to work with such smart people. I want to thank all my friends in Charlottesville. Bin Wang, Zan Gao, Yunya Zhang, Naiming f Acknowledgments g Liu, Chao Liu, Haoyi Liang, Puhan Zhang, Zhanyu Yang, Jiyuan Zheng, Keye Sun, Yuan Yuan, Qianhuan Yu and so on. Without your short but significant association, my Ph.D. life could not be filled with such many happiness. I want to thank my beloved friend, Guangchuan "Craig" Yang. I still remember the day I met him for the first time back in 2006. We shared wonderful memories of senior high school together. Then during college and PhD years we stayed connected by WeChat, even half a globe away. It is this bromance that encourages, comforts, and supports me through this long and uneven journey. I believe we will continue to be there for each other in the days to come. Thank you, and love you. Last but not least, I want to thank my father, mother and sister for their unconditional support. My discipline and self-drivability are qualities inherited from them. I thank my parents for their wise counsel and sympathetic ear all along my Ph.D. journey. You are the most important persons to me and I will be back with you in one day. Contents Contents h List of Tables...........................................j List of Figures..........................................l List of Abbreviations.......................................r 1 Introduction 1 1.1 Spintronics Background and Heusler Compounds....................1 1.2 Dissertation Organization.................................5 2 Theoretical Background7 2.1 Density Functional Theory (DFT)............................7 2.1.1 The Hohenberg-kohn Theorems..........................8 2.1.2 The Kohn-Sham Ansatz..............................9 2.1.3 The Exchange-Correlation Function....................... 11 2.1.4 Periodic Boundary Conditions.......................... 13 2.2 DFT Implementations................................... 14 2.2.1 Vienna Ab Initio Simulation Package (VASP).................. 15 2.2.2 Munich SPR-KKR Package............................ 18 2.3 Calculation of Curie Temperature............................. 22 2.3.1 Exchange Coupling Interactions.......................... 22 2.3.2 Mean Field Approximation............................ 24 2.4 Calculation of Gilbert Damping.............................
Load more

Recommended publications
  • Magnetic and Structural Properties of Co2mnsi Based Heusler Compound
    Magnetic and structural properties of Co2MnSi based Heusler compound S. J. Ahmed†, C. Boyer♯, M. Niewczas†‡∗ † Materials Science and Engineering, McMaster University, Hamilton, Ontario, Canada ♯Canadian Neutron Beam Centre, Canadian Nuclear Laboratories, Chalk River, Ontario, Canada ‡Brockhouse Institute of Materials Research, McMaster University, Hamilton, Ontario. ∗E-mail: [email protected] ABSTRACT The influence of antisite disorder occupancies on the magnetic properties of the half- metallic Co2MnSi compound was studied by experimental techniques and first-principles calculations. The neutron diffraction studies show almost equal amount of Mn and Co dis- orders of 6.5% and 7.6%, which was found to be in good agreement with density functional theory (DFT) calculations of the stable Co2MnSi system with the corresponding disorders. DFT studies reveal that antiferromagnetic interactions introduced by Mn disorder lead to a reduction of the net magnetic moment. The results are discussed in conjunction with neutron diffraction and magnetization measurements. Magnetotransport measurements revealed a positive magnetoresistance for bulk Co2MnSi, which decreases as tempera- ture increases. A Curie temperature of ∼1014 K was determined for the compound by high-temperature electrical resistivity and dilatometry measurements. Keywords: Heusler compounds; Half-metallicity; Antisite disorder; Neutron diffraction; Density Functional Theory; Magnetic properties; Magnetoresistance. 1. Introduction Half-metallicity has been a topic of tremendous scientific attention for the last three decades since the theoretical prediction of a 100 % spin polarization in the half-Heusler NiMnSb [1] and later, on the full-Heusler Co2MnSn [2]. Recent progress on the phe- nomenon has been extended to systems like Weyl semimetal [3–5], Dirac half-metals [6–8], d0-d half-Heusler [9, 10], and also, perovskites [11–13].
    [Show full text]
  • Epitaxy, Exfoliation, and Strain-Induced Magnetism in Rippled Heusler Membranes
    ARTICLE https://doi.org/10.1038/s41467-021-22784-y OPEN Epitaxy, exfoliation, and strain-induced magnetism in rippled Heusler membranes Dongxue Du1, Sebastian Manzo1, Chenyu Zhang 1, Vivek Saraswat1, Konrad T. Genser2, Karin M. Rabe2, ✉ Paul M. Voyles 1, Michael S. Arnold 1 & Jason K. Kawasaki 1 Single-crystalline membranes of functional materials enable the tuning of properties via extreme strain states; however, conventional routes for producing membranes require the 1234567890():,; use of sacrificial layers and chemical etchants, which can both damage the membrane and limit the ability to make them ultrathin. Here we demonstrate the epitaxial growth of the cubic Heusler compound GdPtSb on graphene-terminated Al2O3 substrates. Despite the presence of the graphene interlayer, the Heusler films have epitaxial registry to the underlying sapphire, as revealed by x-ray diffraction, reflection high energy electron dif- fraction, and transmission electron microscopy. The weak Van der Waals interactions of graphene enable mechanical exfoliation to yield free-standing GdPtSb membranes, which form ripples when transferred to a flexible polymer handle. Whereas unstrained GdPtSb is antiferromagnetic, measurements on rippled membranes show a spontaneous magnetic moment at room temperature, with a saturation magnetization of 5.2 bohr magneton per Gd. First-principles calculations show that the coupling to homogeneous strain is too small to induce ferromagnetism, suggesting a dominant role for strain gradients. Our membranes provide a novel platform for tuning the magnetic properties of intermetallic compounds via strain (piezomagnetism and magnetostriction) and strain gradients (flexomagnetism). 1 Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI, USA. 2 Department of Physics and Astronomy, Rutgers University, New ✉ Brunswick, NJ, USA.
    [Show full text]
  • Epitaxy, Exfoliation, and Strain-Induced Magnetism in Rippled Heusler Membranes
    Epitaxy, exfoliation, and strain-induced magnetism in rippled Heusler membranes Dongxue Du,1 Sebastian Manzo,1 Chenyu Zhang,1 Vivek Saraswat,1 Konrad T. Genser,2 Karin M. Rabe,2 Paul M. Voyles,1 Michael S. Arnold,1 and Jason K. Kawasaki1, ∗ 1Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI 53706 2Department of Physics and Astronomy, Rutgers University, New Brunswick, NJ (Dated: April 6, 2021) Single-crystalline membranes of functional materials enable the tuning of properties via extreme strain states; however, conventional routes for producing membranes require the use of sacrificial layers and chemical etchants, which can both damage the membrane and limit the ability to make them ultrathin. Here we demonstrate the epitaxial growth of the cubic Heusler compound GdPtSb on graphene-terminated Al2O3 substrates. Despite the presence of the graphene interlayer, the Heusler films have epitaxial registry to the underlying sapphire, as revealed by x-ray diffraction, reflection high energy electron diffraction, and transmission electron microscopy. The weak Van der Waals interactions of graphene enable mechanical exfoliation to yield free-standing GdPtSb membranes, which form ripples when transferred to a flexible polymer handle. Whereas unstrained GdPtSb is antiferromagnetic, measurements on rippled membranes show a spontaneous magnetic moment at room temperature, with a saturation magnetization of 5.2 bohr magneton per Gd. First-principles calculations show that the coupling to homogeneous strain is too small to induce ferromagnetism, suggesting a dominant role for strain gradients. Our membranes provide a novel platform for tuning the magnetic properties of intermetallic compounds via strain (piezomagnetixm and magnetostriction) and strain gradients (flexomagnetism).
    [Show full text]
  • Observation of Unusual Topological Surface States in Half-Heusler Compounds Lnptbi (Ln=Lu, Y)
    Lawrence Berkeley National Laboratory Recent Work Title Observation of unusual topological surface states in half-Heusler compounds LnPtBi (Ln=Lu, Y). Permalink https://escholarship.org/uc/item/14501927 Journal Nature communications, 7(1) ISSN 2041-1723 Authors Liu, ZK Yang, LX Wu, S-C et al. Publication Date 2016-09-27 DOI 10.1038/ncomms12924 Peer reviewed eScholarship.org Powered by the California Digital Library University of California ARTICLE Received 17 Feb 2016 | Accepted 15 Aug 2016 | Published 27 Sep 2016 DOI: 10.1038/ncomms12924 OPEN Observation of unusual topological surface states in half-Heusler compounds LnPtBi (Ln ¼ Lu, Y) Z.K. Liu1, L.X. Yang2, S.-C. Wu3, C. Shekhar3, J. Jiang1,4, H.F. Yang5, Y. Zhang4, S.-K. Mo4, Z. Hussain4,B.Yan1,3, C. Felser3 & Y.L. Chen1,2,6 Topological quantum materials represent a new class of matter with both exotic physical phenomena and novel application potentials. Many Heusler compounds, which exhibit rich emergent properties such as unusual magnetism, superconductivity and heavy fermion beha- viour, have been predicted to host non-trivial topological electronic structures. The coexistence of topological order and other unusual properties makes Heusler materials ideal platform to search for new topological quantum phases (such as quantum anomalous Hall insulator and topological superconductor). By carrying out angle-resolved photoemission spectroscopy and ab initio calculations on rare-earth half-Heusler compounds LnPtBi (Ln ¼ Lu, Y), we directly observe the unusual topological surface states on these materials, establishing them as first members with non-trivial topological electronic structure in this class of materials. Moreover, as LnPtBi compounds are non-centrosymmetric superconductors, our discovery further highlights them as promising candidates of topological superconductors.
    [Show full text]
  • Tuning the Magnetocaloric Response in Half-Heusler/Heusler Mnni1+Xsb Solid Solutions
    Tuning the magnetocaloric response in half-Heusler/Heusler MnNi1+xSb solid solutions Emily E. Levin,∗ Joshua D. Bocarsly, Kira E. Wyckoff, Tresa M. Pollock, and Ram Seshadri Materials Department, University of California, Santa Barbara, California 93106, USA and Materials Research Laboratory, University of California, Santa Barbara, California 93106, USA (Dated: November 30, 2017) Materials with a large magnetocaloric response are associated with a temperature change upon the application of a magnetic field, and are of interest for applications in magnetic refrigeration and ther- momagnetic power generation. The usual metric of this response is the gravimetric isothermal entropy change ∆SM . The use of a simple proxy for the ∆SM that is based on density functional theory (DFT) calculations of the magnetic electronic structure, suggests that half-Heusler MnNiSb should be a bet- ter magnetocaloric than the corresponding Heusler compound MnNi2Sb. Guided by this observation, we present a study of MnNi1+xSb (x = 0, 0.25, 0.5, 0.75, 1.0) to evaluate relevant structural and magnetic properties. DFT stability calculations suggest that the addition of Ni takes place at a symmet- rically distinct Ni site in the half-Heusler structure, and support the observation using synchrotron X-ray diffraction of a homogeneous solid solution between the half-Heusler and Heusler endmembers. There is a maximum in the saturation magnetization at x = 0.5, and the Curie temperature systematically decreases with increasing x. ∆SM for a maximum magnetic field change of ∆H = 5 T monotonically decreases in magnitude from −2.93 J kg−1 K−1 in the half-Heusler to −1.35 J kg−1 K−1 in the Heusler compound.
    [Show full text]
  • An Enormous Class of Double Half-Heusler Compounds with Low Thermal Conductivity
    An Enormous Class of Double Half-Heusler Compounds with Low Thermal Conductivity Shashwat Anand, Max Wood, Chris Wolverton, and G. Jeffrey Snyder* Department of Materials Science and Engineering Northwestern University Evanston, IL 60208, US E-mail: *[email protected]. Abstract Since their discovery around a century ago, the structure and chemistry of the multi-functional half-Heusler semiconductors have been studied extensively as three component systems. The elemental groups constituting these ternary compounds with the nominal formula XYZ are well established. From the very same set of well-known elements we explore a phase space of quaternary double (X'X''Y2Z2, X2Y'Y''Z2, and X2Y2Z'Z''), triple (X2'X''Y3Z3) and quadruple (X3'X''Y4Z4) half-Heusler compositions which 10 times larger in size. Using a reliable, first- principles thermodynamics methodology on a selection of 347 novel compositions, we predict 127 new stable quaternary compounds, already more than the 89 reported almost exhaustively for ternary systems. Thermoelectric performance of the state-of-the-art ternary half-Heusler compounds are limited by their intrinsically high lattice thermal conductivity (κL). In comparison to ternary half-Heuslers, thermal transport in double half-Heuslers is dominated by low frequency phonon modes with smaller group velocities and limited by disorder scattering. The double half-Heusler composition Ti2FeNiSb2 was synthesized and confirmed to have a significantly lower lattice thermal conductivity (factor of 3 at room temperature) than TiCoSb, thereby providing a better starting point for thermoelectric efficiency optimization. We demonstrate a dependable strategy to assist the search for low thermal conductivity half-Heuslers and point towards a huge composition space for implementing it.
    [Show full text]
  • High-Pressure Investigations on the Semi-Heusler Compound Cumnsb
    PHYSICAL REVIEW B 98, 054431 (2018) High-pressure investigations on the semi-Heusler compound CuMnSb Pallavi Malavi,1 Jing Song,1 Wenli Bi,2,3 Alexander Regnat,4 Linghan Zhu,1 Andreas Bauer,4 Anatoliy Senyshyn,5 Li Yang,1 Christian Pfleiderer,4 and James S. Schilling1,* 1Department of Physics, Washington University, St. Louis, Missouri 63130, USA 2Argonne National Laboratory, Argonne, Illinois 60439, USA 3Department of Geology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA 4Department of Physics, Technical University Munich, D-85748 Garching, Germany 5Heinz Maier-Leibnitz Center, Technical University Munich, D-85748 Garching, Germany (Received 16 February 2018; revised manuscript received 4 June 2018; published 28 August 2018) The antiferromagnetic semi-Heusler compound CuMnSb has been investigated under high pressure by electrical resistivity and angle dispersive synchrotron x-ray diffraction measurements to 53 and 36 GPa, respectively. The Néel temperature at ∼50 K is found to initially increase rapidly with pressure, reaching 83 K at 7 GPa. However, near 8 GPa at ambient temperature a sluggish first-order structural transition begins from a semimetallic cubic phase to a likely semimetallic tetragonal phase; thermal cycling to 355 ◦C at 9.6 GPa serves to complete the transition. In the tetragonal phase no sign of magnetic ordering is visible in the resistivity R(T ) over the measured temperature range 4–295 K. This suggests that magnetic ordering may have shifted to temperatures well above am- bient. Indeed, density functional calculations find the magnetic ground state in the tetragonal phase to be antiferro- magnetic. Following decompression to 1 bar at ambient temperature, the high-pressure tetragonal phase is retained.
    [Show full text]
  • Structural, Electronic and Magnetic Properties of the Manganese Telluride Layers Amnte2 (A=K, Rb, Cs) from First-Principles Calc
    Structural, electronic and magnetic properties of the Manganese telluride layers AMnTe2 (A=K, Rb, Cs) from first-principles calculations 1, 2 3 4 2 5 A. Benmakhlouf , Y. Bourourou , A. Bouhemadou , A. Bentabet , F. Khemloul , S. Maabed5, M. Bouchenafa5 , I. Galanakis6* 1Département de Sciences Technique, Faculté de Technologie, université de Laghouat, Algérie 2Laboratoire de Recherche : Caractérisation et Valorisation des Ressources Naturelles, Université de Bordj Bou Arreridj, 34000, Algérie 3 Laboratoire de Modélisation et Simulation en Sciences des Matériaux (LMSSM) Université Djilali Liabes de Sidi Bel Abbes 22000 / Algérie 4 Laboratory for Developing New Materials and their Characterization, University of Setif 1, Setif 19000, Algeria 5Faculty of sciences, Sciences de la matière département, Laghouat University, 03000, Algeria 6 Department of Materials Science, School of Natural Sciences, University of Patras, Patras 26504, Greece *Corresponding author: [email protected] Abstract Using first-principles electronic structure calculations based on density functional theory (DFT), we investigate the structural, electronic and magnetic properties of the layered ternary manganese tellurides: AMnTe2 (A = K, Rb, and Cs). Calculations are accomplished within the full-potential linearized augmented plane wave (FP-LAPW) using the generalized gradient approximation GGA formalism for the exchange correlation term. We have treated all ferromagnetic, antiferromagnetic and non-magnetic phases and found that the ferromagnetic is the ground-state for all studied compounds. Moreover, all three compounds under study are half-metals with a total spin magnetic per formula unit of 4 휇퐵 which is mainly localized at the Mn atoms. We express for these compounds a new version of the Slater-Pauling rule and discuss in detail the origin of the minority-spin gap.
    [Show full text]
  • Journal of Science the Electronic and Magnetic Properties Of
    Research Article GU J Sci 31(3): 940-952 (2018) Gazi University Journal of Science http://dergipark.gov.tr/gujs The Electronic and Magnetic Properties of New Full-Heusler Compounds: M2IrSi (M=Ti, Cr and Mn) Ziya MERDAN1*, Evren G. OZDEMIR2 1 Gazi University, Sciences Faculty, Department of Physics, 06500, Ankara, Turkey 2 Gazi University, Polatli Sciences and Arts Faculty, Department of Physics, 06900, Polatli, Ankara, Turkey Article Info Abstract The structural and magnetic properties of M2IrSi (M=Ti, Cr and Mn) full-Heusler compounds Received: 12/12/2017 were investigated using WIEN2k program. The ferromagnetic states (FM) were compared to the Accepted: 01/06/2018 non-magnetic states in the Hg2CuTi and Cu2MnAl structures to determine more stable state as energetically using the optimization curves. For all compounds, FM states are the most stable states in the Hg2CuTi type structure. The electronic calculations show that the majority Keywords electrons of Ti2IrSi, Cr2IrSi and Mn2IrSi compounds have metallic feature. For Ti2IrSi and Half-metal Mn2IrSi compounds, the minority electrons have semiconducting nature with an energy gap of Electronic structure 0.89 and 0.41 eV, respectively. Finally, Ti2IrSi compound is a conventional half-metallic, Ferromagnet Cr2IrSi compound is metallic and Mn2IrSi is a half-metallic ferromagnet within 2.73,1.0 and 3.0 Magnetic property µB/f.u. magnetic moment, respectively. DFT 1. INTRODUCTION The NiMnSb compound is the first Heusler compound which was introduced by de Groot et al. in 1983 [1]. According to this prediction, NiMnSb compound was half-metal material. While one band of half- metallic materials exhibits semiconducting qualities, the other band exhibits metallic properties [2,3].
    [Show full text]
  • Creep of Heusler-Type Alloy Fe-25Al-25Co
    crystals Article Creep of Heusler-Type Alloy Fe-25Al-25Co Ferdinand Dobeš 1, Petr Dymáˇcek 1,2 and Martin Friák 1,2,* 1 Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Žižkova 22, CZ-61662 Brno, Czech Republic; [email protected] (F.D.); [email protected] (P.D.) 2 CEITEC IPM, Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Žižkova 22, CZ-61662 Brno, Czech Republic * Correspondence: [email protected]; Tel.: +420-532-290-400 Received: 20 December 2019; Accepted: 16 January 2020; Published: 20 January 2020 Abstract: Creep of an alloy based on the intermetallic compound Fe2AlCo was studied by compressive creep tests in the temperature range from 873 to 1073 K. The stress exponent n and the activation energy of creep Q were determined using the multivariable regression of the creep-rate data and their description by means of sinh equation (Garofalo equation). The evaluated stress exponents indicate that the dislocation climb controls creep deformation. The estimated apparent activation energies for creep are higher than the activation enthalpy for the diffusion of Fe in Fe3Al. This can be ascribed to the changes in crystal lattice and changing microstructure of the alloy. Keywords: iron aluminides; Heusler alloy; creep; stress exponent; activation energy 1. Introduction Fe–Al-based alloys are potential candidates for new structural materials due to their outstanding corrosion resistance in various hostile environments, relatively low density and the low cost of both the basic constituting elements [1–3]. Insufficient creep resistance has been identified as an obstacle for their extensive application at high temperatures [4,5].
    [Show full text]
  • High-Throughput Machine-Learning-Driven Synthesis of Full-Heusler
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Apollo 1 High-Throughput Machine-Learning-Driven Synthesis of Full-Heusler Compounds Anton O. Oliynyk,† Erin Antono,‡ Taylor D. Sparks,§ Leila Ghadbeigi,§ Michael W. Gaultois,¶ Bryce Meredig,‡,* and Arthur Mar†,* † Department of Chemistry, University of Alberta, Edmonton, AB T6G 2G2 Canada ‡ Citrine Informatics, Redwood City, CA 94063 USA § Department of Materials Science and Engineering, University of Utah, Salt Lake City, UT 84112 USA ¶ Department of Chemistry, University of Cambridge, Cambridge CB2 1EW United Kingdom 2 Abstract A machine-learning model has been trained to discover Heusler compounds, which are intermetallics exhibiting diverse physical properties attractive for applications in thermoelectric and spintronic materials. Improving these properties requires knowledge of crystal structures, which occur in three subtle variations (Heusler, inverse Heusler, and CsCl-type structures) that are difficult, and at times impossible, to distinguish by diffraction techniques. Compared to alternative approaches, this Heusler discovery engine performs exceptionally well, making fast and reliable predictions of the occurrence of Heusler vs non-Heusler compounds for an arbitrary combination of elements with no structural input on over 400,000 candidates. The model has a true positive rate of 0.94 (and false positive rate of 0.01). It is also valuable for data sanitizing, by flagging questionable entries in crystallographic databases. It was applied to screen candidates with the formula AB2C and predict the existence of 12 novel gallides MRu2Ga and RuM2Ga (M = Ti–Co) as Heusler compounds, which were confirmed experimentally. One member, TiRu2Ga, exhibited diagnostic superstructure peaks that confirm the adoption of an ordered Heusler as opposed to a disordered CsCl-type structure.
    [Show full text]
  • Structural Characterization and Thermoelectric Performance of Zrnisn Half-Heusler Compound Synthesized by Mechanical Alloying
    University of New Orleans ScholarWorks@UNO University of New Orleans Theses and Dissertations Dissertations and Theses 5-14-2010 Structural Characterization and Thermoelectric Performance of ZrNiSn Half-Heusler Compound Synthesized by Mechanical Alloying Jeffrey Germond University of New Orleans Follow this and additional works at: https://scholarworks.uno.edu/td Recommended Citation Germond, Jeffrey, "Structural Characterization and Thermoelectric Performance of ZrNiSn Half-Heusler Compound Synthesized by Mechanical Alloying" (2010). University of New Orleans Theses and Dissertations. 1197. https://scholarworks.uno.edu/td/1197 This Thesis is protected by copyright and/or related rights. It has been brought to you by ScholarWorks@UNO with permission from the rights-holder(s). You are free to use this Thesis in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights- holder(s) directly, unless additional rights are indicated by a Creative Commons license in the record and/or on the work itself. This Thesis has been accepted for inclusion in University of New Orleans Theses and Dissertations by an authorized administrator of ScholarWorks@UNO. For more information, please contact [email protected]. Structural Characterization and Thermoelectric Performance of ZrNiSn Half-Heusler Compound Synthesized by Mechanical Alloying A Thesis Submitted to the Graduate Faculty of the University of New Orleans In partial fulfillment of the requirements for the degree of Master of Science in Engineering Mechanical Engineering By Jeffrey D Germond B.S. University of Michigan, 2004 May 2010 © 2010, Jeffrey D Germond ii TABLE OF CONTENTS Abstract .............................................................................................................................
    [Show full text]