Fluctuation-mediated spin-orbit torque enhancement in the noncollinear antiferromagnet Mn3Ni0.35Cu0.65N

TL;DR

This paper demonstrates that spin-orbit torques in a noncollinear antiferromagnet are significantly enhanced near the Ne9el temperature due to spin fluctuations, revealing a new mechanism involving orbital currents for potential memory device applications.

Contribution

It uncovers a novel fluctuation-mediated mechanism for SOT enhancement in noncollinear antiferromagnets, emphasizing the role of orbital currents triggered by spin chirality.

Findings

Maximum SOT efficiency of 30% observed.

Strong temperature dependence peaking near Ne9el temperature.

Orbital Hall effect explains the SOTs, not the spin Hall effect.

Abstract

The role of spin fluctuations near magnetic phase transitions is crucial for generating various exotic phenomena, including anomalies in the extraordinary Hall effect, excess spin-current generation through the spin-Hall effect (SHE), and enhanced spin-pumping, amongst others. In this study, we experimentally investigate the temperature dependence of spin-orbit torques (SOTs) generated by Mn3Ni0.35Cu0.65N (MNCN), a member of the noncollinear antiferromagnetic family that exhibits unconventional magnetotransport properties. Our work uncovers a strong and nontrivial temperature dependence of SOTs, peaking near the N\'eel temperature of MNCN, which cannot be explained by conventional intrinsic and extrinsic scattering mechanisms of the SHE. Notably, we measure a maximum SOT efficiency of 30%, which is substantially larger than that of commonly studied nonmagnetic materials such as Pt. Theoretical calculations confirm a negligible SHE and a strong orbital Hall effect that can explain the observed SOTs. We propose a previously unidentified mechanism wherein fluctuating antiferromagnetic moments trigger the generation of substantial orbital currents near the N\'eel temperature due to the emergence of scalar spin chirality. Our findings present an approach for enhancing SOTs, which holds promise for magnetic memory applications by leveraging antiferromagnetic spin fluctuations to amplify both orbital and spin currents.