Possible room-temperature ferromagnetic semiconductor in monolayer MnSe2 through a metal-semiconductor transition

To realize room-temperature ferromagnetic semiconductors is still a challenge in spintronics. Recent experiments have obtained two-dimensional (2D) room-temperature ferromagnetic metals, such as monolayer ${\mathrm{MnSe}}_2$. In this paper, we proposed a way to obtain room-temperature ferromagnetic semiconductors through metal-semiconductor transition. By the density-functional theory calculations, a room-temperature ferromagnetic semiconductor is obtained in monolayer ${\mathrm{MnSe}}_2$ with a few-percent tensile strain, where a metal-semiconductor transition occurs with 2.2% tensile strain. The tensile strains raise the energy of $d$ orbitals of Mn atoms and $p$ orbitals of Se atoms near the Fermi level, making the Fermi-level sets in the energy gap of bonding and antibonding states of these $p$ and $d$ orbitals, and opening a small band gap. The room-temperature ferromagnetic semiconductors are also obtained in the heterostructures ${\mathrm{MnSe}}_2$/X (X = ${\mathrm{Al}}_2{\mathrm{Se}}_3$, GaSe, SiH, and GaP), where metal-semiconductor transition happens due to the tensile strains by interface of heterostructures. In addition, a large magneto-optical Kerr effect (MOKE) is obtained in monolayer ${\mathrm{MnSe}}_2$ with tensile strain and ${\mathrm{MnSe}}_2$-based heterostructures. Our theoretical results pave a way to obtain room-temperature magnetic semiconductors from experimentally obtained 2D room-temperature ferromagnetic metals through metal-semiconductor transitions.