Electronic structure study of double perovskites A2FeReO6(A = Ba,Sr,Ca) and Sr2MMoO6 (M = Cr,Mn,Fe,Co) by LSDA and LSDA+U -: art. no. 125126

We have implemented a systematic LSDA and LSDA + U study of the double perovskites A(2)FeReO(6) (A = Ba,Sr,Ca) and Sr2MMoO6 (M = Cr,Mn,Fe,Co) for understanding of their intriguing electronic and magnetic properties. The results suggest a ferrimagnetic (FiM) and half-metallic (HM) state of A(2)FeReO(6) (A = Ba,Sr) due to a pdd-pi coupling between the down-spin Re5+/Fe3+ t(2g) orbitals via the intermediate O 2p(pi) ones, also a very similar FiM and HM state of Sr2FeMoO6. In contrast, a decreasing Fe t(2g) component at Fermi level (E-F) in the distorted Ca2FeReO6 partly accounts for its nonmetallic behavior, while a finite pdd-sigma coupling between the down-spin Re5+/Fe3+ e(g) orbitals being present at E-F serves to stabilize its FiM state. For Sr2CrMoO6 compared with Sr2FeMoO6, the coupling between the down-spin Mo5+/Cr3+ t(2g) orbitals decreases as a noticeable shift up of the Cr3+ 3d levels, which is likely responsible for the decreasing T-C value and weak conductivity. Moreover, the calculated level distributions indicate a Mn2+(Co2+)/Mo6+ ionic state in Sr2MnMoO6 (Sr2CoMoO6), in terms of which their antiferromagnetic insulating ground state can be interpreted. While orbital population analyses show that owing to strong intrinsic pd covalence effects, Sr2MMoO6 (M = Cr,Mn,Fe,Co) have nearly the same valence state combinations, as accounts for the similar M-independent spectral features observed in them.