Spin-transfer torque in disordered weak ferromagnets

TL;DR

This paper theoretically investigates spin transfer effects on domain walls in disordered weak ferromagnets, revealing conditions under which efficient wall motion occurs even with small spin splitting energies.

Contribution

It identifies the adiabatic condition for disordered weak ferromagnets and shows that perfect spin-transfer can happen even with weak ferromagnetism.

Findings

Adiabatic condition: λ ≫ √(ħD/Δ) for disordered weak ferromagnets.

Effective β term governs domain wall dynamics.

Efficient wall motion possible even with small spin splitting Δ.

Abstract

We study theoretically the spin transfer effect on a domain wall in disordered weak ferromagnets. We have identified the adiabatic condition for the disordered case as $\lambda \gg \lambda_{\rm D}\equiv \sqrt{{\hbar D}/{\spol}}$, where $D$ and $\spol$ are the diffusion constant and the spin splitting energy due to the $s$-$d$ type exchange interaction, respectively, and found out that perfect spin-transfer effect occurs even in weak ferromagnets as long as this condition is satisfied. The effective $\beta$ term arising from the force turns out to govern the wall dynamics, and therefore, the wall motion can be as efficient as in strong ferromagnets even if $\spol$ is small.