Bimetal chalcogenide TM₂TM'X₄ monolayers: stable room temperature ferromagnetic semiconductors

Two-dimensional (2D) ferromagnetic semiconductors (FMSs), which combine ferromagnetism and semiconducting properties, have long been highly desired in the field of spintronics. Here, we predicted a class of stable 2D FMSs based on transition metal chalcogenides by mixing the metal atoms, TM₂TM'X₄ (TM = V/Ti, TM' = Ni/Ti/V, X = Se/Te). It is revealed that the V₂NiTe₄ monolayer is a bipolar ferrimagnetic (FIM) semiconductor with an indirect bandgap of 0.40 eV, while V₂TiTe₄ and Ti₂VSe₄ monolayers are indirect bandgap FMSs with bandgaps of 0.62 eV and 0.24 eV, respectively. Particularly, all the TM₂TM'X₄ monolayers prefer in-plane magnetization and the magnetic orders can be survived at room temperature with Curie temperatures of 715 K, 347 K and 297 K for V₂NiTe₄, V₂TiTe₄ and Ti₂VSe₄ monolayers, respectively. Moreover, the electronic and magnetic stabilities are sensitive to biaxial strains. Interestingly, Ti₂VSe₄ and V₂NiTe₄ monolayers can be tuned to be room temperature FM half metals under biaxial 3% tensile strain and -6% compressive strain, separately. Our results provide a platform to design promising candidates for spintronic devices.