Facet-dependent giant spin orbit torque in single crystalline antiferromagnetic Ir-Mn / ferromagnetic permalloy bilayers

TL;DR

This study demonstrates that single crystalline IrMn3/Permalloy bilayers exhibit a giant, facet-dependent spin Hall angle, with the (100) orientation showing significantly larger spin-orbit torque efficiency than the (111) orientation, influenced by AF domain manipulation.

Contribution

It reveals a large, orientation-dependent spin Hall angle in IrMn3 thin films and links it to the AF structure and domain control, advancing spintronic material understanding.

Findings

Giant spin Hall angle of ~0.35 in (100) IrMn3 films.

Spin Hall angle is about three times smaller in (111) films.

Manipulating AF domains significantly alters the spin Hall angle.

Abstract

There has been considerable interest in spin-orbit torques for the purpose of manipulating the magnetization of ferromagnetic (FM) films or nano-elements for spintronic technologies. Spin-orbit torques are derived from spin currents created from charge currents in materials with significant spin-orbit coupling that diffuse into an adjacent FM material. There have been intensive efforts to search for candidate materials that exhibit large spin Hall angles, i.e. efficient charge to spin current conversion. Here we report, using spin torque ferromagnetic resonance, the observation of a giant spin Hall angle of up to ~0.35 in (100) oriented single crystalline antiferromagnetic (AF) IrMn3 thin films, coupled to ferromagnetic permalloy layers, and a spin Hall angle that is about three times smaller in (111) oriented films. For the (100) oriented samples we show that the magnitude of the spin Hall angle can be significantly changed by manipulating the populations of the various AF domains through field annealing. Using ab-initio calculations we show that the triangular AF structure of IrMn3 gives rise to a substantial intrinsic spin Hall conductivity that is three times larger for the (100) than for the (111) orientations, consistent with our experimental findings.