Electronic structure calculations based on density-functional theory with the generalized gradient approximation for 406 double perovskites ${\text{La}}_{2}B{B}^{\prime }{\text{O}}_6$ have been performed using the accurate full-potential linearized augmented plane wave method. ${\text{La}}_2{\text{VTcO}}_6$ and ${\text{La}}_2{\text{VCuO}}_6$ are found to be candidates of half-metallic (HM) antiferromagnets (AFM) among the 406 ordered double perovskites ${\text{La}}_{2}B{B}^{\prime }{\text{O}}_6$ with all the possible $B$ and $B^{\prime }$ pairs from all the $3d$, $4d$, and $5d$ transition metals have been considered. Furthermore, the HM-AFM state in ${\text{La}}_2{\text{VTcO}}_6$ and ${\text{La}}_2{\text{VCuO}}_6$ survive the full lattice constant and atomic position optimizations which were carried out using the frozen-core full-potential projector-augmented wave method. In addition, the $\text{GGA}+U$ electronic structure calculations have also been performed and the HM-AFM state still remains. Their AFM state is attributed to both the superexchange and generalized double exchange mechanisms via the $B\left(t_{2g}\right)\text{-O}\left(2p_{\pi }\right)\text{−}{B}^{\prime }\left(t_{2g}\right)$ coupling, and the latter could also be the origin of their HM.

First-Principle Calculations of Half-Metallic Double Perovskite La2BB´O6(B,B´=3d transition metal) - Volume 14 Issue 1 - Y. P. Liu, S. H. Chen, H. R. Fuh, Y. K. Wang

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.