First-principles calculations to investigate structural, elastic, electronic and magnetic properties of novel d0 half metallic half Heusler alloys XSrB (X=Be, Mg)

The structural, elastic, electronic properties and magnetism of new d0 half Heusler alloys XSrB (X = Be, Mg) were investigated by means of first-principles calculation based on the density functional theory (DFT). The exchange correlation functional is treated by the generalized gradient approximation proposed by Perdew-Burke-Ernzerhof (GGA-PBE). The Tran-Blaha modified Becke-Johnson (TB-mBJ) exchange potential, which can compute accurately the band gap of solids, is adopted to improve the calculations of the electronic structure and magnetic properties. We found that the two alloys are energetically and mechanically stable in the alpha phase presenting ductile nature with negative cohesive energies. It was found that MgSrB compound can be experimentally synthesized because of its negative formation energy. The two compounds are half-metallic ferromagnets with total magnetic moment of 1.000 mu(B) per formula unit, in well agreement with Slater-Pauling rule (M-tot = (8 - Z(tot)) mu(B)). Our calculations show that BeSrB and MgSrB have majority band gaps of 1.024 eV (1.387 eV) and 0.831 eV (1.277 eV) with half-metallic gaps of 0.165 eV (0.613 eV) and 0.311 eV (0.626 eV), respectively, by GGA-PBE (TB-mBJ). The origin of these gaps is well discussed. It was also found that BeSrB and MgSrB are robust half-metallic alloys with respect to the variation of lattice constants. They kept their half-metallicity in relatively wide range of lattice constants of 5.90-7.00 angstrom and 6.18-7.28 angstrom, respectively. The obtained results reveal also that BeSrB and MgSrB compounds are considered as nearly gapless half-metallic ferromagnets for lattice parameters range of 7.03-7.88 angstrom and 7.50-8.40 angstrom, respectively, which makes them promising candidates for potential applications.