Interface-induced field-like optical spin torque in a ferromagnet/heavy metal heterostructure

TL;DR

This study investigates how interface effects in ferromagnet/heavy metal heterostructures enhance optical spin torque, revealing a significant in-plane field-like torque linked to the optical Rashba-Edelstein effect, aiding optical control of nanomagnets.

Contribution

It demonstrates the interfacial origin of optical spin torque in heterostructures and links it to the optical Rashba-Edelstein effect, advancing understanding of optical magnetization control.

Findings

In-plane field-like optical spin torque increases with decreasing ferromagnet thickness.

Interfacial optical Rashba-Edelstein effect explains the observed torque.

Work supports optical manipulation of thin film nanomagnets.

Abstract

The manipulation of magnetization in a metallic ferromagnet by using optical helicity has been much attracted attention for future opto-spintronic devices. The optical helicity induced torques on the magnetization, {\it optical spin torque}, have been observed in ferromagnetic thin films recently. However, the interfacial effect of the optical spin torque in ferromagnet/nonmagnetic heavy metal heterostructures have not been addressed so far, which are widely utilized to efficiently control magnetization via electrical means. Here, we studied optical spin torque vectors in the ferromagnet/nonmagnetic heavy metal heterostructures and observed that in-plane field-like optical spin torque was significantly increased with decreasing ferromagnetic layer thicknesses. The interfacial field-like optical spin torque was explained by the optical Rashba-Edelstein effect caused by the structural inversion symmetry breaking. This work will aid in the efficient optical manipulation of thin film nanomagnets using optical helicity.