Magnetic asymmetry induced anomalous spin-orbit torque in IrMn

TL;DR

This study reveals that broken magnetic symmetry in certain phases of IrMn antiferromagnets induces an anomalous out-of-plane spin-orbit torque, with efficiencies varying across different phases, emphasizing the importance of magnetic asymmetry.

Contribution

The paper demonstrates the link between magnetic symmetry breaking in IrMn phases and the generation of anomalous spin-orbit torque, supported by experimental and theoretical analysis.

Findings

Out-of-plane damping-like spin-orbit torque observed in L10 and L12 phases but not in γ phase.

Spin-orbit torque efficiencies measured as 0.61, 1.01, and 0.80 for L10, L12, and γ phases.

Broken magnetic mirror symmetry correlates with the presence of spin-orbit torque.

Abstract

We demonstrate an anomalous spin-orbit torque induced by the broken magnetic symmetry in the antiferromagnet IrMn. We study the magnetic structure of three phases of IrMn thin films using neutron diffraction technique. The magnetic mirror symmetry M' is broken laterally in both L10-IrMn and L12-IrMn3 but not {\gamma}-IrMn3. We observe an out-of-plane damping-like spin-orbit torque in both L10-IrMn/permalloy and L12-IrMn3/permalloy bilayers but not in {\gamma}-IrMn3/permalloy. This is consistent with both the symmetry analysis on the effects of a broken M' on spin-orbit torque and the theoretical predictions of the spin Hall effect and the Rashba-Edelstein effect. In addition, the measured spin-orbit torque efficiencies are 0.61+-0.01, 1.01+-0.03 and 0.80+-0.01 for the L10, L12 and {\gamma} phases, respectively. Our work highlights the critical roles of the magnetic asymmetry in spin-orbit torque generation.