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. 2014 Feb 25;7(3):1473-1482.
doi: 10.3390/ma7031473.

The Effect of Cobalt-Sublattice Disorder on Spin Polarisation in Co₂Fe x Mn1- xSi Heusler Alloys

Philip J Hasnip  1 , Christian H Loach  2 , Joseph H Smith  3 , Matthew I J Probert  4 , Daniel Gilks  5 , James Sizeland  3 , Leonardo Lari  6 , James Sagar  3 , Kenta Yoshida  7 , Mikihiko Oogane  8 , Atsufumi Hirohata  9   10 , Vlado K Lazarov  11
Affiliations

The Effect of Cobalt-Sublattice Disorder on Spin Polarisation in Co₂Fe x Mn1- xSi Heusler Alloys

Philip J Hasnip et al. Materials (Basel). .

Abstract

In this work we present a theoretical study of the effect of disorder on spin polarisation at the Fermi level, and the disorder formation energies for Co₂FexMn1-xSi (CFMS) alloys. The electronic calculations are based on density functional theory with a Hubbard U term. Chemical disorders studied consist of swapping Co with Fe/Mn and Co with Si; in all cases we found these are detrimental for spin polarisation, i.e., the spin polarisation not only decreases in magnitude, but also can change sign depending on the particular disorder. Formation energy calculation shows that Co-Si disorder has higher energies of formation in CFMS compared to Co₂MnSi and Co₂FeSi, with maximum values occurring for x in the range 0.5-0.75. Cross-sectional structural studies of reference Co₂MnSi, Co₂Fe0.5Mn0.5Si, and Co₂FeSi by Z-contrast scanning transmission electron microscopy are in qualitative agreement with total energy calculations of the disordered structures.

Keywords: half-metals; heusler alloys; spintronics materials; thin films.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1.
Figure 1.
Schematic of the fully ordered L21 phase, and the XY and XZ disordered phases. (a) L21 ordered phase; (b) Swapping X and Y atoms; (c) Swapping X and Z atoms; For Co2(Fe/Mn)Si the X site is occupied by Co, Y by Fe/Mn and the Z site by Si. Arrows indicate swapped atoms.
Figure 2.
Figure 2.
Z-contrast High Angle Annular Dark Field (HAADF) image of (a) Co2MnSi; (b) Co2(Fe,Mn)Si; and (c) Co2FeSi in (110) direction. Intensity profile along the X (Co site) from corresponding HAADF images.
Figure 3.
Figure 3.
Spin density of states (SDOS) for CMS, CF0.5M0.5S, and CFS. (a–c) SDOS for cells with XZ disorder; i.e., mixing between Co (X) and Si (Z). (d–f) SDOS for cells exhibiting XY disorder; i.e., mixing between Co (X) and Mn/Fe (Y) sites. Dashed (solid) line represents case when Mn (Fe) is mixed with Co. Majority spin states are along the positive axis (red lines in colour), while minority spin states are along the negative axis (blue colour).
See this image and copyright information in PMC

References

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