Two-dimensional ferromagnetic semiconductor VBr3 with tunable anisotropy

Two-dimensional (2D) ferromagnets (FMs) have attracted widespread attention due to their prospects in spintronic applications. Here we explore the electronic structure and magnetic properties of the bulk and monolayer of VBr$_{3}$ in the honeycomb lattice, using first-principles calculations, crystal field level analyses, and Monte Carlo simulations. Our results show that VBr$_{3}$ bulk has the $e'_{g}$$^2$ ($S$=1) ground state and possesses a small orbital moment and weak in-plane magnetic anisotropy. Those results well explain the recent experiments. More interestingly, we find that a tensile strain on the semiconducting VBr$_{3}$ monolayer tunes the ground state into $a_{1g}$$^1$$e'_{g}$$^1$ and thus produces a large orbital moment and a strong out-of-plane anisotropy. Then, the significantly enhanced FM superexchange and single ion anisotropy (SIA) would raise $T_{\rm C}$ from 20 K for the bare VBr$_{3}$ monolayer to 100-115 K under a 2.5$\%$-5$\%$ strain. Therefore, VBr$_{3}$ would be a promising 2D FM semiconductor with a tunable anisotropy.