Electrically tunable high Curie temperature two-dimensional ferromagnetism in van der Waals layered crystals

Identifying intrinsic low-dimensional ferromagnets with high magnetic transition temperature and electrically tunable magnetism is crucial for the development of miniaturized spintronics and magnetoelectrics. Recently, long-range 2D ferromagnetism was observed in van der Waals crystals CrI₃ and Cr₂Ge₂Te₆, however, their Curie temperature is significantly lowered when reducing down to monolayer/few layers. Herein, using renormalized spin-wave theory and first-principles electronic structure theory, we present a theoretical study of electrically tunable 2D ferromagnetism in van der Waals layered CrSBr and CrSeBr semiconductors with a high Curie temperature of ∼150 K and a sizable bandgap. The high transition temperature is attributed to the strong anion-mediated superexchange interaction and a sizable spin-wave excitation gap due to large exchange and single-ion anisotropy. Remarkably, hole and electron doping can switch the magnetization easy axis from the in-plane to the out-of-plane direction. These unique characteristics establish monolayer CrSBr and CrSeBr as a promising platform for realizing 2D spintronics and magnetoelectrics such as 2D spin valves and spin field effect transistors.