Half-metallic antiferromagnetic nature of La₂ VTcO₆ and La₂ VCuO₆ from ab initio calculations

Electronic structure calculations based on density-functional theory with the generalized gradient approximation for 406 double perovskites La ₂BB′O₆ have been performed using the accurate full-potential linearized augmented plane wave method. La₂ VTcO ₆ and La₂ VCuO₆ are found to be candidates of half-metallic (HM) antiferromagnets (AFM) among the 406 ordered double perovskites La2 B B^′ O₆ with all the possible B and B^′ pairs from all the 3d, 4d, and 5d transition metals have been considered. Furthermore, the HM-AFM state in La2 VTcO6 and La₂ VCuO₆ 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 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(t_2g) -O (2p_π) - B′ (t_2g) coupling, and the latter could also be the origin of their HM.