Observation of Orbit-Orbit Torques: Highly Efficient Torques on Orbital Moments Induced by Orbital Currents

TL;DR

This paper demonstrates highly efficient orbit-orbit torques in Cr/Tb bilayers, showing that orbital currents can effectively manipulate orbital moments, opening new avenues in orbitronics.

Contribution

It introduces the concept of orbit-orbit torque (OOT) driven by orbital currents, with experimental evidence in Cr/Tb bilayers showing enhanced torque efficiency.

Findings

Positive dampinglike torque efficiency of ~3.66 in Cr/Tb

Orbital currents injected from Cr interact with Tb's orbital moments

Orbital Hall effect generates orbital currents with negligible interface loss

Abstract

We study the current-induced torques in bilayers composed of a light 3d metal, chromium, and a rare-earth ferromagnet with finite orbital moments, terbium, utilizing second-harmonic Hall-response measurements. The dampinglike torque efficiency of chromium is found to be positive and reaches ~3.66 in this system, in sharp contrast to the negative and subtle dampinglike torque efficiency in general Cr/ferromagnet heterostructures with quenched orbital moment. We suggest that the orbital currents generated by the orbital Hall effect in Cr can be injected into Tb with negligible loss at the interface and then efficiently interact with the orbital moments. We term such an exotic effect as the orbit-orbit torque (OOT). Our work implies that orbital currents could be harnessed to manipulate the orbital magnetization of materials, which would advance the development of orbitronics.