Signature of half-metallicity in [formula omitted]: A DFT study

Abstract

BiFeO3 has drawn great attention over the last several decades due to its promising multiferroic character. In the ground state, the bulk BiFeO3 is found to be in the rhombohedral phase. However, it has been possible to stabilize BiFeO3 with a tetragonal structure. The importance of the tetragonal phase is due to its much larger value of the electric polarization and the possible stabilization of ferromagnetism as in the rhombohedral phase. Furthermore, the tetragonal structure of BiFeO3 has been reported with different c/a ratios, opening up the possibility of a much richer set of electronic phases. In this work, we have used the density functional theory based first-principle method to study the ferromagnetic phase of the tetragonal BiFeO3 structure as a function of the c/a ratio. We have found that, as the c/a ratio decreases from 1.264 to 1.016, the tetragonal phase evolves from a ferromagnetic semiconductor to a ferromagnetic metal, passing through a half-metallic phase. This evolution of the electronic properties becomes even more interesting when viewed with respect to the volume of each structure. The most stable half-metallic phase initially counter-intuitively evolve to the magnetic-semiconducting phase with a reduction in the volume, and after further reduction in the volume, it finally becomes a metal. So far, this type of metal to insulator transition on compression was known to exist only in alkali metals, especially in lithium, in heavy alkaline earth metals, and in some binary compounds.