Half-Metallic Property Induced by Double Exchange Interaction in the Double Perovskite Bi₂BB' O₆ (B, B' = 3d Transitional Metal) via First-Principles Calculations

In this paper, we identify three possible candidate series of half-metals (HM) from Bi-based double perovskites Bi₂BB'O₆ (BB' = transition metal ions) through calculations utilizing the density functional theory (DFT) and full-structural optimization, in which the generalized gradient approximation (GGA) and the strong correlation effect (GGA + U) are considered. After observing the candidate materials under four types of magnetic states, i.e., ferromagnetic (FM), ferrimagnetic (FiM), antiferromagnetic (AF), and nonmagnetic (NM), we found eight promising candidates for half-metallic materials. Under the GGA scheme, there are three ferromagnetic-half-metal (FM-HM) materials, Bi₂CrCoO₆, Bi₂CrNiO₆ and Bi₂FeNiO₆, and three FiM-HM materials, Bi₂FeZnO₆, Bi₂CrZnO₆ and Bi₂CoZnO₆. With implementation of the Coulomb interaction correction (GGA + U), we find two stable half-metallic materials: Bi₂CrNiO₆ and Bi₂CrZnO₆. We determine that the stability of some of these materials are tied to the double exchange interaction, an indirect interaction within the higher powers of localized spin interaction among transition metals via oxygen ions. Found in half-metallic materials, and especially those in the ferromagnetic (FM) state, the double exchange interaction is recognized in the FM-HM materials Bi₂CrCoO₆ and Bi₂FeNiO₆.