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Title: Enhanced spin polarization of amorphous F e x S i 1 - x thin films revealed by Andreev reflection spectroscopy

Abstract

Point contact Andreev reflection spectroscopy has been utilized to determine the spin polarization of both amorphous and crystalline $$\mathrm{F}{\mathrm{e}}_{x}\mathrm{S}{\mathrm{i}}_{1{-}x}$$ ($0.58<x<0.68$) thin films. The amorphous materials exhibited a substantial spin polarization (generally greater than 60%), despite significant changes in magnetization and resistivity. In particular, the polarization value in the $x=0.65$ amorphous alloy is about 70%, significantly higher than most ferromagnets, including numerous Heusler compounds that are theoretically predicted to be half-metallic ferromagnets. The composition dependence of the spin polarization in the amorphous materials is proportional to (but substantially larger than) the DFT-calculated values. The polarization of a crystalline thin film with $x=0.65$, by contrast, is only 49%, similar to that of common magnetic metals. The enhanced spin polarization in the amorphous structure is attributed to the modification of the local environments. Finally, this work demonstrates that the spin polarization, as well as magnetic moment, anomalous Hall effect, and electrical resistivity, can be tuned by introducing structural disorder as an engineering tool.

Authors:
 [1];  [2];  [3];  [4];  [3];  [3];  [3];  [3];  [3];  [3];  [5];  [3];  [2]
  1. Monash Univ., Melbourne, VIC (Australia). Dept. of Materials Science and Engineering; 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; Univ. of California, Berkeley, CA (United States). Dept. of Physics
  3. Arizona State Univ., Tempe, AZ (United States). Dept. of Physics
  4. Univ. of Electronic Science and Technology of China, Chengdu (China). School of Energy Science and Engineering
  5. Univ. of California, Irvine, CA (United States). Dept. of Physics and Astronomy
Publication Date:
Research Org.:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
OSTI Identifier:
1479419
Alternate Identifier(s):
OSTI ID: 1457499
Grant/Contract Number:  
AC02-05CH11231; SC0012670; FG02-05ER46237
Resource Type:
Accepted Manuscript
Journal Name:
Physical Review Materials
Additional Journal Information:
Journal Volume: 2; Journal Issue: 6; Journal ID: ISSN 2475-9953
Publisher:
American Physical Society (APS)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ferromagnetism; spin injection; spin polarization; spintronics

Citation Formats

Karel, J., Bouma, D. S., Martinez, J., Zhang, Y. N., Gifford, J. A., Zhang, J., Zhao, G. J., Kim, D. R., Li, B. C., Huang, Z. Y., Wu, R. Q., Chen, T. Y., and Hellman, F. Enhanced spin polarization of amorphous FexSi1-x thin films revealed by Andreev reflection spectroscopy. United States: N. p., 2018. Web. doi:10.1103/PhysRevMaterials.2.064411.
Karel, J., Bouma, D. S., Martinez, J., Zhang, Y. N., Gifford, J. A., Zhang, J., Zhao, G. J., Kim, D. R., Li, B. C., Huang, Z. Y., Wu, R. Q., Chen, T. Y., & Hellman, F. Enhanced spin polarization of amorphous FexSi1-x thin films revealed by Andreev reflection spectroscopy. United States. doi:10.1103/PhysRevMaterials.2.064411.
Karel, J., Bouma, D. S., Martinez, J., Zhang, Y. N., Gifford, J. A., Zhang, J., Zhao, G. J., Kim, D. R., Li, B. C., Huang, Z. Y., Wu, R. Q., Chen, T. Y., and Hellman, F. Wed . "Enhanced spin polarization of amorphous FexSi1-x thin films revealed by Andreev reflection spectroscopy". United States. doi:10.1103/PhysRevMaterials.2.064411. https://www.osti.gov/servlets/purl/1479419.
@article{osti_1479419,
title = {Enhanced spin polarization of amorphous FexSi1-x thin films revealed by Andreev reflection spectroscopy},
author = {Karel, J. and Bouma, D. S. and Martinez, J. and Zhang, Y. N. and Gifford, J. A. and Zhang, J. and Zhao, G. J. and Kim, D. R. and Li, B. C. and Huang, Z. Y. and Wu, R. Q. and Chen, T. Y. and Hellman, F.},
abstractNote = {Point contact Andreev reflection spectroscopy has been utilized to determine the spin polarization of both amorphous and crystalline $\mathrm{F}{\mathrm{e}}_{x}\mathrm{S}{\mathrm{i}}_{1{-}x}$ ($0.58<x<0.68$) thin films. The amorphous materials exhibited a substantial spin polarization (generally greater than 60%), despite significant changes in magnetization and resistivity. In particular, the polarization value in the $x=0.65$ amorphous alloy is about 70%, significantly higher than most ferromagnets, including numerous Heusler compounds that are theoretically predicted to be half-metallic ferromagnets. The composition dependence of the spin polarization in the amorphous materials is proportional to (but substantially larger than) the DFT-calculated values. The polarization of a crystalline thin film with $x=0.65$, by contrast, is only 49%, similar to that of common magnetic metals. The enhanced spin polarization in the amorphous structure is attributed to the modification of the local environments. Finally, this work demonstrates that the spin polarization, as well as magnetic moment, anomalous Hall effect, and electrical resistivity, can be tuned by introducing structural disorder as an engineering tool.},
doi = {10.1103/PhysRevMaterials.2.064411},
journal = {Physical Review Materials},
number = 6,
volume = 2,
place = {United States},
year = {2018},
month = {6}
}

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Figures / Tables:

Fig. 1 Fig. 1: (a) Saturation magnetization at 2K versus x for amorphous and crystalline FexSi1-x. The open symbols are theoretical calculations, and the closed symbols are experimental data points. The blue open triangles (blue boxes with cross) are theoretical values for the B2 (D03) structure (note that B2 and D03 havemore » nearly the same M as each other), with solid stars showing the experimental values. The black square divided horizontally is the theoretical result for the A2 structure (also labelled directly); this structure has no experimental value, as it was never successfully fabricated. All experimental data points were measured at 2K. Further details of the theoretical calculations can be found in reference [15]. (b) Cross section HRTEM on a representative x=0.55 amorphous sample.« less

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    Works referencing / citing this record:

    Itinerant ferromagnetism and intrinsic anomalous Hall effect in amorphous iron-germanium
    journal, January 2020


    Effect of structural disordering on magnetic and magneto-optical properties of F e 3 Si
    journal, September 2019


      Figures/Tables have been extracted from DOE-funded journal article accepted manuscripts.