Giant facet-dependent spin-orbit torque and spin Hall conductivity in the triangular antiferromagnet IrMn ₃

TLDR

Spin‑orbit torques, generated by spin currents from charge currents in materials with strong spin‑orbit coupling, are sought for manipulating ferromagnetic magnetization, but identifying materials with large spin Hall angles remains a key challenge. The study identifies two contributions to the spin Hall effect in IrMn₃: a facet‑independent bulk spin‑dependent scattering mechanism and an intrinsic mechanism arising from its unconventional antiferromagnetic triangular structure. Experiments and ab initio calculations reveal a giant spin Hall angle of ~0.35 in (001)-oriented IrMn₃ films, three times smaller in (111) orientation, and show that the angle can be tuned by domain manipulation through perpendicular field annealing, confirming the larger intrinsic spin Hall conductivity predicted for the (001) facet.

Abstract

There has been considerable interest in spin-orbit torques for the purpose of manipulating the magnetization of ferromagnetic elements for spintronic technologies. Spin-orbit torques are derived from spin currents created from charge currents in materials with significant spin-orbit coupling that propagate into an adjacent ferromagnetic material. A key challenge is to identify materials that exhibit large spin Hall angles, that is, efficient charge-to-spin current conversion. Using spin torque ferromagnetic resonance, we report the observation of a giant spin Hall angle [Formula: see text] of up to ~0.35 in (001)-oriented single-crystalline antiferromagnetic IrMn3 thin films, coupled to ferromagnetic permalloy layers, and a [Formula: see text] that is about three times smaller in (111)-oriented films. For (001)-oriented samples, we show that the magnitude of [Formula: see text] can be significantly changed by manipulating the populations of various antiferromagnetic domains through perpendicular field annealing. We identify two distinct mechanisms that contribute to [Formula: see text]: the first mechanism, which is facet-independent, arises from conventional bulk spin-dependent scattering within the IrMn3 layer, and the second intrinsic mechanism is derived from the unconventional antiferromagnetic structure of IrMn3. Using ab initio calculations, we show that the triangular magnetic structure of IrMn3 gives rise to a substantial intrinsic spin Hall conductivity that is much larger for the (001) than for the (111) orientation, consistent with our experimental findings.