Wide ferromagnetic domain walls can host both adiabatic reflectionless spin transport and finite nonadiabatic spin torque: A time-dependent quantum transport picture

Abstract

The key concept in spintronics of current-driven noncollinear magnetic textures, such as magnetic domain walls (DWs), is adiabaticity, i.e., how closely electronic spins track classical localized magnetic moments (LMMs) of the texture. When mistracking occurs nonadiabatic effects arise, the salient of which is nonadiabatic spin transfer torque (STT) where spin angular momentum is exchanged between electrons and LMMs to cause their dynamics and enable DW motion without any current threshold. The microscopic mechanisms behind nonadiabatic STT have been debated theoretically for nearly two decades, but with unanimous conclusion that they should be significant only in narrow DWs. However, this contradicts sharply experiments [O.