Magnetic Order and Symmetry in the 2D Semiconductor CrSBr

The advent of two-dimensional (2D) magnets offers unprecedented control over electrons and spins. A key factor in determining exchange coupling and magnetic order is symmetry. Here, we apply second harmonic generation (SHG) to probe a 2D magnetic semiconductor CrSBr. We find that monolayers are ferromagnetically ordered below 146 K, an observation enabled by the discovery of a large magnetic dipole SHG effect in the centrosymmetric structure. In multilayers, the ferromagnetic monolayers are coupled antiferromagnetically, and in contrast to other 2D magnets, the Neel temperature of CrSBr increases with decreasing layer number. We identify magnetic dipole and magnetic toroidal moments as order parameters of the ferromagnetic monolayer and antiferromagnetic bilayer, respectively. These findings establish CrSBr as an exciting 2D magnetic semiconductor and extend the SHG probe of magnetic symmetry to the monolayer limit, opening the door to exploring the applications of magnetic-electronic coupling and the magnetic toroidal moment.

Automated summary

The discovery of ferromagnetic ordering in monolayers of CrSBr, as well as the antiferromagnetic coupling in multilayers, highlights the unique magnetic properties of this 2D material. The Neel temperature of CrSBr increases with decreasing layer number, setting it apart from other 2D magnets. These findings introduce CrSBr as an exciting 2D magnetic semiconductor with potential applications in magnetic-electronic coupling and toroidal moments.