First-principles calculations of current-induced spin-transfer torques in magnetic domain walls

TL;DR

This study uses first-principles calculations to analyze current-induced spin-transfer torques in Fe, Co, and Ni domain walls, revealing material-specific behaviors and proposing a higher-order torque model for Fe.

Contribution

It introduces a third-order spatial derivative model of nonadiabatic STT that better captures localized effects in Fe domain walls compared to traditional first-order models.

Findings

Fe DW exhibits localized nonadiabatic STT

Third-order torque better describes Fe DW dynamics

DW velocity with third-order torque is about half of first-order

Abstract

Current-induced spin-transfer torques (STTs) have been studied in Fe, Co and Ni domain walls (DWs) by the method based on the first-principles noncollinear calculations of scattering wave functions expanded in the tight-binding linearized muffin-tin orbital (TB-LMTO) basis. The results show that the out-of-plane component of nonadiabatic STT in Fe DW has localized form, which is in contrast to the typical nonlocal oscillating nonadiabatic torques obtained in Co and Ni DWs. Meanwhile, the degree of nonadiabaticity in STT is also much greater for Fe DW. Further, our results demonstrate that compared to the well-known first-order nonadiabatic STT, the torque in the third-order spatial derivative of local spin can better describe the distribution of localized nonadiabatic STT in Fe DW. The dynamics of local spin driven by this third-order torques in Fe DW have been investigated by the Landau-Lifshitz-Gilbert (LLG) equation. The calculated results show that with the same amplitude of STTs the DW velocity induced by this third-order term is about half of the wall speed for the case of the first-order nonadiabatic STT.