Optical Characterizations of Magnetic Phases in Two-Dimensional Ferromagnetic Semiconductor CrSBr

The advent of two-dimensional (2D) magnetic materials has not only altered our understanding of magnetism in low-dimensional systems, but invites numerous applications in nanoscale transport, optoelectronics, and quantum devices. However, the library of materials has been limited to metals and insulators with strong air-sensitivity, limiting the potential scope of utilization. Here, we present 2D ferromagnetic semiconductor CrSBr, which possesses in-plane magnetic anisotropy and interlayer antiferromagnetic coupling. Magnetic phase transitions in CrSBr are probed with second- and third-harmonic generations in various thicknesses to the monolayer limit. With decreasing number of layers, CrSBr displays unconventional increase in magnetic transition temperature. Linear spectroscopy and transport measurements demonstrate the semiconducting nature of the material. Lastly, Raman spectroscopy reveals complex magnetic phases in bulk CrSBr, some of which are suppressed at the atomically thin limit.