Magnetic Correlation Spectroscopy in CrSBr.

CrSBr is an air-stable magnetic van der Waals semiconductor with strong magnetic anisotropy, where the interaction of excitons with the magnetic order enables the optical identification of different magnetic phases. Here, we study the magnetic anisotropy of multilayer CrSBr inside a three-axis vector magnet and correlate magnetic order and optical transitions in emission and absorption. We identify layer-by-layer switching of the magnetization through drastic changes in the optical emission and absorption energy and strength as a function of the applied magnetic field. We correlate optical transitions in reflection spectra with photoluminescence (PL) emission using transfer-matrix analysis and find that ferromagnetic and antiferromagnetic order between layers can coexist in the same crystal. In the multipeak PL emission, the intensity of energetically lower-lying transitions reduces monotonously with increasing field strength, whereas energetically higher-lying transitions around the bright exciton XB brighten close to the saturation field. Using this contrasting behavior, we can therefore correlate transitions with each other.