Expansion research on half-metallic materials in double perovskites of Sr₂BB′O₆ (B = Co, Cu, and Ni; B′ = Mo, W, Tc, and Re; And BB′ = FeTc)

Calculations with full structural optimization were conducted by generalized gradient approximation (GGA) with correlation effect correction (GGA + U) based on density functional theory. The stable structures, magnetic stable phases, and electronic structures of the double perovskites of Sr ₂BB′O₆ (B = Co, Cu, and Ni; B′ = Mo, W, Tc, and Re; and BB′ = FeTc) were investigated. All compounds, except for Sr₂NiMoO₆ and Sr₂NiWO₆, can be half-metallic (HM) materials in the GGA scheme; Sr₂NiMoO₆ and Sr₂NiWO₆ are ferromagnetic (FM) insulators. Sr ₂FeTcO₆, Sr₂CoWO₆, and Sr ₂NiTcO₆ are stable ferrimagnetic (FiM)-HM compounds in the GGA and GGA + U schemes. Given the small energy difference between their antiferromagnetic and FiM states, Sr₂CoTcO₆, Sr ₂CuMoO₆, Sr₂NiMoO₆, Sr ₂NiWO₆, and Sr₂NiReO₆ can coexist. The mechanisms of the HM-FiM properties can be described by d-d′ hybridization with double-exchange interaction.