Experimental tests of the full spin torque conductivity tensor in epitaxial IrO2 thin films

TL;DR

This study experimentally determines the full spin torque conductivity tensor in IrO2 thin films, demonstrating how symmetry-based predictions can accurately describe both conventional and unconventional spin-orbit torques across different crystal orientations.

Contribution

It provides the first comprehensive measurement of the spin torque conductivity tensor in IrO2 and validates symmetry-based predictions for various orientations.

Findings

All tensor elements consistent with bulk symmetries.

Rotational transformations predict unconventional torques accurately.

Conventional torque measurements can forecast complex torque behaviors.

Abstract

Unconventional spin-orbit torques arising from electric-field-generated spin currents in anisotropic materials have promising potential for spintronic applications, including for perpendicular magnetic switching in high-density memory applications. Here we determine all the independent elements of the spin torque conductivity tensor allowed by bulk crystal symmetries for the tetragonal conductor IrO2, via measurements of conventional (in plane) antidamping torques for IrO2 thin films in the high-symmetry (001) and (100) orientations. We then test that rotational transformations of this same tensor can predict both the conventional and unconventional anti-damping torques for IrO2 thin films in the lower-symmetry (101), (110), and (111) orientations, finding good agreement. The results confirm that spin-orbit torques from all these orientations are consistent with the bulk symmetries of IrO2, and show how simple measurements of conventional torques from high-symmetry orientations of anisotropic thin films can provide an accurate prediction of the unconventional torques from lower-symmetry orientations.