Ab initio research on a new type of half-metallic double perovskites, A₂CrMO₆ (A = IVA group elements; M = Mo, Re and W)

The research based on density functional theory was carried out using generalized gradient approximation (GGA) for full-structural optimization and the addition of the correlation effect (GGA + U (Coulomb parameter)) in a double perovskite structure, A₂BB'O₆. According to the similar valance electrons between IIA(s²) and IVA(p²), IVA group elements instead of alkaline-earth elements settled on the A-site ion position with fixed BB' combinations as CrM (M = Mo, Re and W). The ferrimagnetic half-metallic (HM-FiM) properties can be attributed to the p-d hybridization between the Cr_d-M_p and the double exchange. All the compounds can be half-metallic (HM) materials, except Si₂CrMoO₆, Ge₂CrMo and Ge₂CrReO₆, because the strong-correlation correction should be considered. For M = W, only A = Sn and Pb are possible candidates as HM materials. Nevertheless, an examination of the structural stability is needed, because Si, Ge, Sn and Pb are quite different from Sr. All compounds are stable, except for the Si-based double perovskite structure.