Light-induced torque in ferromagnetic metals via orbital angular momentum generated by photon-helicity

TL;DR

This study reveals how photon helicity induces both field-like and damping-like torques in ferromagnetic alloys, highlighting the role of orbital angular momentum and spin-orbit interaction in magnetization dynamics.

Contribution

It introduces a model explaining photon-helicity-induced torques via orbital angular momentum and spin-orbit coupling, a novel insight into magnetization control in ferromagnetic metals.

Findings

Observation of large damping-like torque in ferromagnetic alloys

Effective elucidation of torque composition dependence on alloy composition

Enhanced understanding of photon-helicity and magnetization interplay

Abstract

We investigated photon-helicity-induced magnetization precession in Co$_{1-x}$Pt$_{x}$ alloy thin films. In addition to field-like torque, attributable to magnetic field generation owing to {\it the inverse Faraday effect}, we observed non-trivial and large damping-like torque which has never been discussed for single ferromagnetic layer. The composition dependence of those two torques is effectively elucidated by a model that considers mutual coupling via spin-orbit interaction between magnetization and the electronic orbital angular momentum generated by photon-helicity. This work significantly enhances our understanding of the physics relevant to the interplay of photon-helicity and magnetization in magnetic metals.