Laser-induced torques in spin spirals

TL;DR

This paper uses ab-initio calculations to show that laser-induced torques in non-collinear spin-spiral ferromagnets can be significantly larger than in collinear systems, impacting ultrafast magnetic processes.

Contribution

It introduces a computational method to evaluate laser-induced torques in spin-spirals, applicable to domain walls and skyrmions, using the generalized Bloch theorem for efficiency.

Findings

Laser-induced torques can be orders of magnitude larger in noncollinear systems.

Torques exist for both linearly and circularly polarized light.

Noncollinear magnetic order significantly influences ultrafast magnetism.

Abstract

We investigate laser-induced torques in magnetically non-collinear ferromagnets with a spin-spiral magnetic structure using \textit{ab-initio} calculations. Since spin-spirals may be used to approximate the magnetization gradients locally in domain walls and skyrmions, our method may be used to obtain the laser-induced torques in such objects from a multiscale approach. Employing the generalized Bloch-theorem we obtain the electronic structure computationally efficiently. We employ our method to assess the laser-induced torques in bcc Fe, hcp Co, and L$_{1}0$ FePt when a spin-spiral magnetic structure is imposed. We find that the laser-induced torques in these magnetically noncollinear systems may be orders of magnitude larger than those in the corresponding magnetically collinear systems and that they exist both for linearly and circularly polarized light. This result suggests that laser-induced torques driven by noncollinear magnetic order or by magnetic fluctuations may contribute significantly to processes in ultrafast magnetism.