Negative spin-Hall angle and anisotropic spin-orbit torques in epitaxial IrMn

TL;DR

This study reveals a negative spin-Hall angle and anisotropic spin-orbit torques in epitaxial Fe/IrMn bilayers, emphasizing the role of crystalline and magnetic structures in antiferromagnetic spintronics.

Contribution

It reports the first observation of a negative spin-Hall angle in epitaxial IrMn and links spin-orbit torque anisotropy to interface moments and crystallographic orientation.

Findings

Negative spin-Hall angle of a few percent in IrMn

Spin-orbit fields with Rashba symmetry oppose Oersted fields

Torque magnitudes depend on crystallographic direction

Abstract

A spin-torque ferromagnetic resonance study is performed in epitaxial $\mathrm{Fe / Ir_{15}Mn_{85}}$ bilayers with different Fe thicknesses. We measure a negative spin-Hall angle of a few percent in the antiferromagnetic IrMn in contrast to previously reported positive values. A large spin-orbit field with Rashba symmetry opposing the Oersted field is also present. Magnitudes of measured spin-orbit torques depend on the crystallographic direction of current and are correlated with the exchange bias direction set during growth. We suggest that the uncompensated moments at the Fe / IrMn interface are responsible for the observed anisotropy. Our findings highlight the importance of crystalline and magnetic structures for the spin-Hall effect in antiferromagnets.