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Title: Itinerant ferromagnetism and intrinsic anomalous Hall effect in amorphous iron-germanium

Abstract

The amorphous iron-germanium system ( a - Fe x Ge 1 - x ) lacks long-range structural order and hence lacks a significant Brillouin zone. The magnetization of a - Fe x Ge 1 - x is well explained by the Stoner model for Fe concentrations x above the onset of magnetic order around x = 0.4 , indicating that the local order of the amorphous structure preserves the spin-split density of states of the Fe- 3 d states sufficiently to polarize the electronic structure despite k being a bad quantum number. Measurements reveal an enhanced anomalous Hall resistivity ρ x y AH relative to crystalline FeGe; this ρ x y AH is compared to density-functional theory calculations of the anomalous Hall conductivity to resolve its underlying mechanisms. The intrinsic mechanism, typically understood as the Berry curvature integrated over occupied k states but shown here to be equivalent to the density of curvature integrated over occupied energies in aperiodic materials, dominates the anomalous Hall conductivity of a - Fe x Ge 1 - x ( 0.38 x 0.61 ). The density of curvature is the sum of spin-orbit correlations of local orbital states and can hence be calculated with no reference to k space. This effect and the accompanying Stoner-like model for the intrinsic anomalous Hall conductivity establish a unified understanding of the underlying physics of the anomalous Hall effect in both crystalline and disordered systems.

Authors:
ORCiD logo [1];  [2];  [3]; ORCiD logo [4]; ORCiD logo [5];  [6];  [2];  [2];  [7];  [1]
  1. Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Materials Sciences Division
  2. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Materials Sciences Division
  3. Fudan Univ., Shanghai (China)
  4. Univ. of California, Berkeley, CA (United States)
  5. Univ. of Iowa, Iowa City, IA (United States); Univ. of Chicago, IL (United States); Eindhoven Univ. of Technology (Netherlands)
  6. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). Materials Engineering Division
  7. Univ. of California, Irvine, CA (United States). Dept. of Physics and Astronomy
Publication Date:
Research Org.:
Univ. of California, Irvine, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Materials Sciences & Engineering Division
OSTI Identifier:
1599458
Alternate Identifier(s):
OSTI ID: 1599843
Grant/Contract Number:  
[FG02-05ER46237; AC02-05CH11231]
Resource Type:
Accepted Manuscript
Journal Name:
Physical Review B
Additional Journal Information:
[ Journal Volume: 101; Journal Issue: 1]; Journal ID: ISSN 2469-9950
Publisher:
American Physical Society (APS)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 36 MATERIALS SCIENCE

Citation Formats

Bouma, D. S., Chen, Z., Zhang, B., Bruni, F., Flatté, M. E., Ceballos, A., Streubel, R., Wang, L. -W., Wu, R. Q., and Hellman, F. Itinerant ferromagnetism and intrinsic anomalous Hall effect in amorphous iron-germanium. United States: N. p., 2020. Web. doi:10.1103/PhysRevB.101.014402.
Bouma, D. S., Chen, Z., Zhang, B., Bruni, F., Flatté, M. E., Ceballos, A., Streubel, R., Wang, L. -W., Wu, R. Q., & Hellman, F. Itinerant ferromagnetism and intrinsic anomalous Hall effect in amorphous iron-germanium. United States. doi:10.1103/PhysRevB.101.014402.
Bouma, D. S., Chen, Z., Zhang, B., Bruni, F., Flatté, M. E., Ceballos, A., Streubel, R., Wang, L. -W., Wu, R. Q., and Hellman, F. Thu . "Itinerant ferromagnetism and intrinsic anomalous Hall effect in amorphous iron-germanium". United States. doi:10.1103/PhysRevB.101.014402.
@article{osti_1599458,
title = {Itinerant ferromagnetism and intrinsic anomalous Hall effect in amorphous iron-germanium},
author = {Bouma, D. S. and Chen, Z. and Zhang, B. and Bruni, F. and Flatté, M. E. and Ceballos, A. and Streubel, R. and Wang, L. -W. and Wu, R. Q. and Hellman, F.},
abstractNote = {The amorphous iron-germanium system (a-FexGe1-x) lacks long-range structural order and hence lacks a significant Brillouin zone. The magnetization of a-FexGe1-x is well explained by the Stoner model for Fe concentrations x above the onset of magnetic order around x=0.4, indicating that the local order of the amorphous structure preserves the spin-split density of states of the Fe-3d states sufficiently to polarize the electronic structure despite k being a bad quantum number. Measurements reveal an enhanced anomalous Hall resistivity ρxyAH relative to crystalline FeGe; this ρxyAH is compared to density-functional theory calculations of the anomalous Hall conductivity to resolve its underlying mechanisms. The intrinsic mechanism, typically understood as the Berry curvature integrated over occupied k states but shown here to be equivalent to the density of curvature integrated over occupied energies in aperiodic materials, dominates the anomalous Hall conductivity of a-FexGe1-x (0.38≤x≤0.61). The density of curvature is the sum of spin-orbit correlations of local orbital states and can hence be calculated with no reference to k space. This effect and the accompanying Stoner-like model for the intrinsic anomalous Hall conductivity establish a unified understanding of the underlying physics of the anomalous Hall effect in both crystalline and disordered systems.},
doi = {10.1103/PhysRevB.101.014402},
journal = {Physical Review B},
number = [1],
volume = [101],
place = {United States},
year = {2020},
month = {1}
}

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