Topological magneto-optics in the non-coplanar antiferromagnet Co_{1/3}NbS_2: Imaging and writing chiral magnetic domains

TL;DR

This study demonstrates that magnetic circular dichroism (MCD) can effectively image and manipulate chiral antiferromagnetic domains in Co$_{1/3}$NbS$_2$, revealing topological magnetic order through optical methods spanning ultraviolet to infrared wavelengths.

Contribution

It introduces optical MCD techniques for imaging and writing chiral AFM domains in a topologically non-trivial antiferromagnet, linking quantum geometry to optical properties.

Findings

MCD provides a direct probe of topological AFM order.

Scanning MCD microscopy images chiral AFM domains.

Chiral AFM domains can be optically written.

Abstract

Despite its tiny net magnetization, the antiferromagnetic (AFM) van der Waals material Co$_{1/3}$NbS$_2$ exhibits a large transverse Hall conductivity $\sigma_{xy}$ even at zero applied magnetic field, which arises, as recently shown, from the topological nature of its non-coplanar ``tetrahedral'' AFM order. This triple-Q magnetic order can be regarded as the short-lengthscale limit of a magnetic skyrmion lattice, and has an intrinsic spin chirality. Here we show, using optical wavelengths spanning the ultraviolet to infrared (400-1000 nm), that magnetic circular dichroism (MCD) provides an incisive optical probe of the topological AFM order in Co$_{1/3}$NbS$_2$. Measurements as a continuous function of photon energy are directly compared with first-principles calculations, revealing the influence of the underlying quantum geometry on optical conductivity. Leveraging the power and flexibility of optical methods, we use scanning MCD microscopy to directly image chiral AFM domains, and demonstrate writing of chiral AFM domains.