open access

https://hdl.handle.net/2115/89806

Effect of off-stoichiometric composition on half-metallic character of Co2Fe(Ga,Ge) investigated using saturation magnetization and giant magnetoresistance effect

英語

Co2Fe(Ga,Ge)

2022-06-09

IOP Publishing

Journal of Physics D : Applied Physics

55(34)

345003

We investigated the Ge-composition (gamma) dependence of the saturation magnetization of Co2Fe(Ga, Ge) (CFGG) thin films and the magnetoresistance (MR) ratio of CFGG-based current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) devices together with first-principles calculations of the electronic states of CFGG. Theoretical calculations showed that spin polarization is highest at the stoichiometric composition gamma = 0.56 in Co2Fe1.03Ga0.41Ge (gamma) and that it decreases in off-stoichiometric CFGG, mainly due to the formation of Co-Fe antisites for Ge-deficient compositions and Fe-Co antisites for Ge-rich compositions, where Co-Fe (Fe-Co) indicates that Co (Fe) atoms replace the Fe (Co) sites. The saturation magnetic moment (mu (s)) per formula unit decreased monotonically as gamma increased from 0.24 to 1.54 in Co2Fe1.03Ga0.41Ge (gamma) . The mu (s) was closest to the Slater-Pauling value predicted for half-metallic CFGG at the stoichiometric composition gamma = 0.56, indicating that stoichiometric CFGG has a half-metallic nature. This is consistent with the result for the theoretical spin polarization. In contrast, the MR ratio of CFGG-based CPP-GMR devices increased monotonically as gamma increased from 0.24 to 1.10 and reached an MR ratio of 87.9% at the Ge-rich composition gamma = 1.10. Then, the MR ratio decreased rapidly as gamma increased from 1.10 to 1.48. Possible origins for the slight difference between the Ge composition at which the highest MR ratio was obtained (gamma = 1.10) and that at which the highest spin polarization was obtained (gamma = 0.56) are improved atomic arrangements in a Ge-rich CFGG film and the reduction of effective Ge composition due to Ge diffusion in the GMR stacks.

学術雑誌論文

Accepted Manuscript

This is the Accepted Manuscript version of an article accepted for publication in Journal of physics. D, Applied physics. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at http://doi.org/10.1088/1361-6463/ac73c1.

0022-3727

1361-6463

AA00704905