Magneto-optic Kerr effect (MOKE) is a powerful probe of broken time-reversal symmetry (T), typically used to study ferromagnets. While MOKE has been observed in some antiferromagnets (AFMs) with vanishing magnetization, it is often associated with structures whose symmetry is lower than basic collinear, bipartite order. In contrast, theory predicts a mechanism for MOKE intrinsic to all AFMs of A-type, i.e. layered AFMs in which ferromagnetic layers are antiferromagnetically aligned. Here we report the first experimental confirmation of this mechanism in a bulk AFM. We achieve this by measuring the imaginary component of MOKE as a function of photon energy in MnBi2Te4, an A-type AFM where T is preserved in combination with a translation. By comparing the experimental results with model calculations, we demonstrate that observable MOKE should be expected in all collinear A-type AFMs with out-of-plane spin order, thus enabling optical detection of AFM domains and expanding the scope of MOKE to few-layer AFMs.
@article{arxiv.2504.16167,
title = {Magneto-optical Kerr effect in an A-type antiferromagnet},
author = {V. Sunko and S. Ahsanullah and V. Jain and S. Weber and S. Kumaran and J. -Q. Yan and J. Orenstein and D. Ovchinnikov},
journal= {arXiv preprint arXiv:2504.16167},
year = {2026}
}