Designed two dimensional transition metal borides (TM2B12): Robust ferromagnetic half metal and antiferromagnetic semiconductor

Two dimensional transition metal borides have been attracting broad interest due to its rich electronic and magnetic properties. Here, using first-principles calculations, we predict two transition metal boride monolayers, Cr2B12 and Mn2B12, composed of B12 icosahedra and transition metal atoms. It is found that both structures are thermodynamically stable with large cohesive energies and small formation energies. The Cr2B12 monolayer is a ferromagnetic (FM) quasi-half metal, and the Mn2B12 monolayer is an antiferromagnetic (AFM) semiconductor with a bandgap of 0.41 eV. The critical temperature is found to be 145 and 135 K for the Cr2B12 monolayer and the Mn2B12 monolayer, respectively. Moreover, the electronic and magnetic properties of both systems can be tuned by applying external strains. Upon applying biaxial tensile/compressive strain, the (half metallic) bandgap of both systems increases/decreases, and a quasi-half metal to half metal transition is found for the Cr2B12 monolayer under 5% tensile and 4% compressive strain. Furthermore, the critical temperatures of both systems are found to increase with compressive strain and decrease with tensile strain, which reaches 165 and 510 K for the Cr2B12 monolayer and the Mn2B12 monolayer under 5% compressive strain, respectively. The results provide a strategy for designing 2D transition metal borides with potential applications in electronic and spintronic devices.