Cr 2 XTe 4 (X = Si, Ge) monolayers: a new type of two-dimensional high- T C Ising ferromagnetic semiconductors with a large magnetic anisotropy.

Two-dimensional (2D) ferromagnetic semiconductor (FMS) provides the ideal platform for the development of quantum information technology in nanoscale devices. However, most of them suffer from low Curie temperature and small magnetic anisotropic energy (MAE), severely limiting their practical application. In this work, by using first-principles calculations, we predicted two stable 2D materials, namely, Cr 2 SiTe 4 and Cr 2 GeTe 4 monolayers. Interestingly, both of them are intrinsic direct band gap FMSs (∼1 eV) with a large magnetization (8 µ B f.u. -1 ) and sizable MAE (∼500 μ e V Cr -1 ). Monte Carlo simulations based on Heisenberg model suggest markedly high Curie temperatures of these monolayers (∼200 K). Besides, their high mechanical, dynamical, and thermal stabilities are further verified by elastic constants, phonon dispersion calculations, and ab initio molecular dynamics simulations. The outstanding attributes render Cr 2 XTe 4 (X = Si, Ge) monolayers broadening the candidates of 2D FMS for a wide range of applications.