Topological Magneto-optical Kerr Effect without Spin-orbit Coupling in Spin-compensated Antiferromagnet

TL;DR

This paper demonstrates a novel magneto-optical Kerr effect in a noncoplanar antiferromagnet without relying on spin-orbit coupling or net magnetization, using scalar spin chirality.

Contribution

It provides the first experimental evidence of large MOKE signals arising solely from scalar spin chirality in a spin-compensated antiferromagnet.

Findings

Large MOKE signals observed without spin-orbit coupling.

Imaging of scalar spin chirality domains and their reversal.

Establishment of a new mechanism for MOKE in compensated magnets.

Abstract

The magneto-optical Kerr effect (MOKE), the differential reflection of oppositely circularly polarized light, has traditionally been associated with relativistic spin-orbit coupling (SOC), which links a particle's spin with its orbital motion. In ferromagnets, large MOKE signals arise from the combination of magnetization and SOC, while in certain coplanar antiferromagnets, SOC-induced Berry curvature enables MOKE despite zero net magnetization. Theoretically, large MOKE can also arise in a broader class of magnetic materials with compensated spins, without relying on SOC - for example, in systems exhibiting real-space scalar spin chirality. The experimental verification has remained elusive. Here, we demonstrate such a SOC- and magnetization-free MOKE in the noncoplanar antiferromagnet Co1/3TaS2. Using a Sagnac interferometer microscope, we image domains of scalar spin chirality and their reversal. Our findings establish experimentally a new mechanism for generating large MOKE signals and position chiral spin textures in compensated magnets as a compelling platform for ultrafast, stray-field-immune opto-spintronic applications.