Strain and correlation induced half-metallic ferromagnetism in orthorhombic BaFeO${}_3$

Using first-principles calculations, the electronic and magnetic properties of orthorhombic BaFeO${}_3$ (BFO) are investigated with local spin density approximation (LSDA). The calculations reveal that at the optimized lattice volume BFO has a lower energy in ferromagnetic state as compared with antiferromagnetic state. At the equilibrium volume, BFO shows metallic behavior, however, under a large tensile strain ($\sim 25\mathrm{\%}$), BFO shows half-metallic behavior consistent with the integer magnetic moment of $4.0{\mu }_{\mathrm{B}}$/fu mainly caused by the $t_{2g}$ and $e_g$ electrons of Fe. Including a Hubbard-like contribution $U$ (LSDA$+U$) on Fe $d$ states induced half-metallic bahvior without external strain, which indicates that $U$ can be used to tune the electronic structure of BFO. The magnetic moments remained robust against $\sim 10\mathrm{\%}$ compressive and tensile strain. At large compressive (tensile) strain, the half-metallicity of BFO is mainly destroyed by the Fe-$d$ (O-$p$) electrons in agreement with the non-integer value of the magnetic moments of BFO.