# Orbital Torque: Torque Generation by Orbital Current Injection

## TL;DR

This paper introduces the concept of orbital torque, generated by orbital current injection in magnetic bilayers, which can induce magnetization switching even with weak spin-orbit coupling, offering a new approach for spin-torque devices.

## Contribution

It proposes a novel orbital torque mechanism in NM/FM bilayers where orbital currents induce magnetization torque without requiring strong SOC in the NM.

## Key findings

- Orbital Hall effect can generate significant orbital currents in NMs.
- Orbital torque can be comparable to spin torque even with weak SOC.
- Potential for new spintronic devices using light elements with large orbital responses.

## Abstract

We propose a mechanism of torque generation by injection of an orbital current, which we call $\textit{orbital torque}$. In a magnetic bilayer consisting of a nonmagnet (NM) and a ferromagnet (FM), we consider a situation where the spin-orbit coupling (SOC) is present only in the FM. Although the SOC is absent in the NM, the orbital Hall effect can arise in the NM. When the resulting orbital Hall current is injected to the FM, the SOC of the FM converts the orbital angular momentum into spin, which exerts torque to the magnetization of the FM. Remarkably, even for small SOC strength comparable to that of $3d$ FMs, the orbital torque can be comparable to the spin torque induced by the spin Hall effect of the NM with strong SOC. This provides a way to experimentally probe the OHE and opens a new venue to achieving spin-torque devices based on light elements that exhibit gigantic orbital response. Experimental implications are discussed.