Terahertz spin dynamics driven by an optical spin-orbit torque

TL;DR

This paper investigates an optical spin-orbit torque induced by circularly polarized laser pulses, demonstrating its comparable strength to Zeeman torque and its temperature dependence in ferromagnetic systems.

Contribution

It introduces and analyzes the relativistic optical spin-orbit torque, highlighting its dependence on light helicity, intensity, and temperature, and compares it with traditional Zeeman torque.

Findings

Optical spin-orbit torque can exert a measurable torque on spins.

The torque scales with laser intensity and depends on light helicity.

The effect persists above the Curie temperature, decreasing with temperature.

Abstract

Spin torques are at the heart of spin manipulations in spintronic devices. Here, we examine the existence of an optical spin-orbit torque, a relativistic spin torque originating from the spin-orbit coupling of an oscillating applied field with the spins. We compare the effect of the nonrelativistic Zeeman torque with the relativistic optical spin-orbit torque for ferromagnetic systems excited by a circularly polarised laser pulse. The latter torque depends on the helicity of the light and scales with the intensity, while being inversely proportional to the frequency. Our results show that the optical spin-orbit torque can provide a torque on the spins, which is quantitatively equivalent to the Zeeman torque. Moreover, temperature dependent calculations show that the effect of optical spin-orbit torque decreases with increasing temperature. However, the effect does not vanish in a ferromagnetic system, even above its Curie temperature.