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Title: Magnetism and electronic structure of CoFeCrX (X = Si, Ge) Heusler alloys

Abstract

The structural, electronic, and magnetic properties of CoFeCrX (X = Si, Ge) Heusler alloys have been investigated. Experimentally, the alloys were synthesized in the cubic L2{sub 1} 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 (T{sub C}) significantly above room temperature. The measured T{sub C} 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 μ{sub B}/f.u. and 2.78 μ{sub B}/f.u., respectively, which are close to the theoretically predicted value of 3 μ{sub B}/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.

Authors:
;  [1];  [2];  [3]; ; ;  [4];  [5];  [6]; ; ;  [2];  [2];  [7]; ;  [1];  [3]
  1. Department of Physics and Astronomy, University of Nebraska, Lincoln, Nebraska 68588 (United States)
  2. Department of Physics, South Dakota State University, Brookings, South Dakota 57007 (United States)
  3. (United States)
  4. Department of Physics, University of Northern Iowa, Cedar Falls, Iowa 50614 (United States)
  5. Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, Nebraska 68588 (United States)
  6. Department of Chemistry and Biochemistry, University of Northern Iowa, Cedar Falls, Iowa 50614 (United States)
  7. (China)
Publication Date:
OSTI Identifier:
22597689
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 120; Journal Issue: 5; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; CURIE POINT; DISSOCIATION; ELECTRONIC STRUCTURE; HEAT; HEAT TREATMENTS; HEUSLER ALLOYS; MAGNETIC PROPERTIES; MAGNETISM; MAGNETIZATION; SATURATION; SPIN; TEMPERATURE RANGE 0273-0400 K; TEMPERATURE RANGE 0400-1000 K

Citation Formats

Jin, Y., O'Connell, A., Kharel, P., E-mail: parashu.kharel@sdstate.edu, Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, Nebraska 68588, Lukashev, P., E-mail: pavel.lukashev@uni.edu, Staten, B., Tutic, I., Valloppilly, S., Herran, J., Mitrakumar, M., Bhusal, B., Huh, Y., Yang, K., College of Mechanical and Electrical Engineering, Hohai University, Changzhou, Skomski, R., Sellmyer, D. J., and Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, Nebraska 68588. Magnetism and electronic structure of CoFeCrX (X = Si, Ge) Heusler alloys. United States: N. p., 2016. Web. doi:10.1063/1.4960350.
Jin, Y., O'Connell, A., Kharel, P., E-mail: parashu.kharel@sdstate.edu, Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, Nebraska 68588, Lukashev, P., E-mail: pavel.lukashev@uni.edu, Staten, B., Tutic, I., Valloppilly, S., Herran, J., Mitrakumar, M., Bhusal, B., Huh, Y., Yang, K., College of Mechanical and Electrical Engineering, Hohai University, Changzhou, Skomski, R., Sellmyer, D. J., & Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, Nebraska 68588. Magnetism and electronic structure of CoFeCrX (X = Si, Ge) Heusler alloys. United States. doi:10.1063/1.4960350.
Jin, Y., O'Connell, A., Kharel, P., E-mail: parashu.kharel@sdstate.edu, Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, Nebraska 68588, Lukashev, P., E-mail: pavel.lukashev@uni.edu, Staten, B., Tutic, I., Valloppilly, S., Herran, J., Mitrakumar, M., Bhusal, B., Huh, Y., Yang, K., College of Mechanical and Electrical Engineering, Hohai University, Changzhou, Skomski, R., Sellmyer, D. J., and Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, Nebraska 68588. Sun . "Magnetism and electronic structure of CoFeCrX (X = Si, Ge) Heusler alloys". United States. doi:10.1063/1.4960350.
@article{osti_22597689,
title = {Magnetism and electronic structure of CoFeCrX (X = Si, Ge) Heusler alloys},
author = {Jin, Y. and O'Connell, A. and Kharel, P., E-mail: parashu.kharel@sdstate.edu and Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, Nebraska 68588 and Lukashev, P., E-mail: pavel.lukashev@uni.edu and Staten, B. and Tutic, I. and Valloppilly, S. and Herran, J. and Mitrakumar, M. and Bhusal, B. and Huh, Y. and Yang, K. and College of Mechanical and Electrical Engineering, Hohai University, Changzhou and Skomski, R. and Sellmyer, D. J. and Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, Nebraska 68588},
abstractNote = {The structural, electronic, and magnetic properties of CoFeCrX (X = Si, Ge) Heusler alloys have been investigated. Experimentally, the alloys were synthesized in the cubic L2{sub 1} 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 (T{sub C}) significantly above room temperature. The measured T{sub C} 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 μ{sub B}/f.u. and 2.78 μ{sub B}/f.u., respectively, which are close to the theoretically predicted value of 3 μ{sub B}/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.},
doi = {10.1063/1.4960350},
journal = {Journal of Applied Physics},
number = 5,
volume = 120,
place = {United States},
year = {Sun Aug 07 00:00:00 EDT 2016},
month = {Sun Aug 07 00:00:00 EDT 2016}
}
  • Cited by 6
  • We present first-principles charge- and spin-self-consistent electronic structure computations on the Heusler-type disordered alloys Fe{sub 3{minus}x}V{sub x}X for three different metalloids X=(Si,thinspGa, and Al). In these calculations we use the methodology based on the Korringa-Kohn-Rostoker formalism and the coherent-potential approximation generalized to treat disorder in multicomponent complex alloys. Exchange correlation effects are incorporated within the local spin density approximation. Total energy calculations for Fe{sub 3{minus}x}V{sub x}Si show that V substitutes preferentially on the Fe(B) site, not on the Fe(A,C) site, in agreement with experiment. Furthermore, calculations have been carried out for Fe{sub 3{minus}x}V{sub x}X alloys (with x=0.25, 0.50, and 0.75),more » together with the end compounds Fe{sub 3}X and Fe{sub 2}VX, and the limiting cases of a single V impurity in Fe{sub 3}X and a single Fe(B) impurity in Fe{sub 2}VX. We delineate clearly how the electronic states and magnetic moments at various sites in Fe{sub 3{minus}x}V{sub x}X evolve as a function of the V content and the metalloid valence. Notably, the spectrum of Fe{sub 3{minus}x}V{sub x}X (X=Al and Ga) develops a pseudogap for the majority as well as minority spin states around the Fermi energy in the V-rich regime, which, together with local moments of Fe(B) impurities, may play a role in the anomalous behavior of the transport properties. The total magnetic moment in Fe{sub 3{minus}x}V{sub x}Si is found to decrease {ital nonlinearly}, and the Fe(B) moment to {ital increase} with increasing {ital x}; this is in contrast to expectations of the {open_quotes}local environment{close_quotes} model, which holds that the total moment should vary linearly while the Fe(B) moment should remain constant. The common-band model, which describes the formation of bonding and antibonding states with different weights on the different atoms, however, provides insight into the electronic structure of this class of compounds. {copyright} {ital 1999} {ital The American Physical Society}« less
  • Cited by 7
  • 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 μ B, 866 K and 0.9 μ B, 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 L2 1 disordered structure. The antisitemore » 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.« less
  • We synthesize the polycrystalline Heusler compounds Co{sub 2}Cr{sub 1-x}Fe{sub x}Al (x=0.2-0.6). The x-ray diffraction patterns show A2 structure rather than L2{sub 1} structure. The magnetic moment and the Curie temperature increase with increasing x. The electrical resistivity characterizes the Co{sub 2}Cr{sub 1-x}Fe{sub x}Al compounds to be not typical metals and the temperature dependence of the resistivity changes from metallic to semiconductinglike behavior with increasing Cr concentrations. We attribute the fact, which we observe for most of the compounds smaller magnetic moments than the theoretical values and the low magnetoresistance in these alloys, to the considerably high level of Co-(Cr, Fe)-typemore » disorder.« less