Doping-Driven Antiferromagnetic to Ferromagnetic Phase Transition in Tetragonal Cr₂B₂ Monolayer

Novel two-dimensional (2D) tetragonal (tetra-) (Formula presented.) (X = Mn, V) sheets are studied using density functional theory (DFT) with Monte Carlo (MC) simulations. Both, tetra- (Formula presented.) and tetra- (Formula presented.) sheets exhibit metallic ferromagnetism with great stability at elevated temperatures. The magnetic moment for tetra- (Formula presented.) (1.63 μ _B per unit cell) and tetra- (Formula presented.) ((Formula presented.) μ _B per unit cell) sheets are found to be far less than that of pure tetra- (Formula presented.) ((Formula presented.) μ _B per unit cell). Interestingly, an antiferromagnetic–ferromagnetic (AFM–FM) transition occurs as a result of alloying the pure (Formula presented.) with (Formula presented.) and V atoms. The tetra- (Formula presented.) exhibits a sizable magnetic anisotropy energy (MAE) of 136.25 (Formula presented.) per (Formula presented.) atom, larger than that of tetra- (Formula presented.) (17.5 (Formula presented.) per (Formula presented.) atom), and both the sheets prefer out-of-plane magnetization. The MAE can be tuned via the application of an electric field for both, tetra- (Formula presented.) and tetra- (Formula presented.) cases. MC simulations based on 2D Heisenberg model predict a Curie temperature ((Formula presented.)) of 140 and 20 K for tetra- (Formula presented.) and tetra- (Formula presented.) sheets, respectively. These novel 2D sheets hold promise for controllable spintronic devices application.