Spin Torque on Magnetic Textures Coupled to the Surface of a Three-Dimensional Topological Insulator

TL;DR

This paper theoretically analyzes how spin torque induced by surface states of a topological insulator affects the magnetization dynamics of a thin ferromagnetic layer with various magnetic textures, revealing potential for magnetic switching.

Contribution

It introduces a theoretical framework for spin torque effects on magnetic textures on topological insulators, deriving an effective anisotropy field and modified Landau-Lifshitz-Gilbert equation.

Findings

Effective fields are comparable to typical switching fields.

Spin torque significantly influences magnetization dynamics.

Theoretical model applies to domain walls, skyrmions, and vortices.

Abstract

We investigate theoretically the spin torque and magnetization dynamic in a thin ferromagnetic (FM) layer with spatially varying magnetization. The FM layer is deposited on the surface of a topological insulator (TI). In the limit of the adiabatic relaxation of electron spin along the magnetization, the interaction between the exchange interaction and the Rashba-like surface texture of a TI yields a topological gauge field. Under the gauge field and an applied current, spin torque is induced according to the direction of the current. We derived the corresponding effective anisotropy field and hence the modified Landau-Lifshitz-Gilbert equation, which describes the spin torque and the magnetization dynamic. In addition, we study the effective field for exemplary magnetic textures, such as domain wall, skyrmion, and vortex configurations. The estimated strength of the effective field is comparable to the switching fields of typical FM materials, and hence can significantly influence the dynamics of the FM layer.