Excitonic fingerprints of magnetic configurations and switching in multilayer CrSBr

Abstract: The coupling between electronic states and magnetism provides a route towards optical readout and control of magnetic information. In the magnetic semiconductor CrSBr, excitons are coupled to magnetic order, making their optical response sensitive to the underlying magnetization. Here, we show that the energy and oscillator strength of bulk and surface excitons provide distinct spectroscopic fingerprints of magnetic configurations and switching pathways. We distinguish domain-wall-mediated magnetization reversal, manifested by continuous spectral evolution as a domain wall traverses the optical spot, from abrupt, large-area magnetization reversal. Using the resulting excitonic fingerprints, we reconstruct successive magnetic configurations in 4- and 5-layer CrSBr during the transition from ferromagnetic to antiferromagnetic order. We further find that the sensitivity to magnetic order is strongly exciton-dependent: low-energy excitons resolve intermediate and surface-related configurations, whereas a higher-energy exciton predominantly exhibits a transfer of oscillator strength between ferromagnetic and antiferromagnetic resonances. These results establish excitonic spectroscopy as a sensitive probe of layer-dependent magnetic configurations and their switching pathways in layered magnetic semiconductors.