Effects of the defects on the half-metallic characters and magnetic properties in double perovskite Pb2FeMoO6

In point of view of the half-metallic character and magnetization reduction, the structural, electronic and magnetic properties of the disordered Pb2FeMoO6 compound containing seven different defects of FeMo and MoFe antisites, Fe-Mo interchange, and VFe, VMo, VO and VPb vacancies have been studied by using the first-principles projector augmented wave (PAW) potential within the generalized gradient approximation taking into account on-site Coulomb repulsive energy (GGA+U). No obvious structural changes are observed for the cases of the FeMo and MoFe antisites, Fe-Mo interchange, and VPb vacancy, however, the six (eight) nearest oxygen neighbors of the vacancy move away from (close to) VFe or VMo (VO) vacancy. The half-metallic character is maintained for the FeMo antisite, VFe, VO or VPb vacancy cases, while it vanishes in the MoFe antisite, Fe-Mo interchange or VMo vacancy cases even the defect concentration reduces down to C = 6.25%. So the MoFe antisite, Fe-Mo interchange or VMo vacancy defects have to be avoided in order to preserve the half-metallic character of the Pb2FeMoO6 compound and thus usable in magnetoresistive and spintronics devices. In FeMo or MoFe antisite cases, the spin moments of Fe (Mo) cations situated on Mo (Fe) antisites are in an antiferromagnetic coupling with those of Fe (Mo) cations on the regular sites. On the contrary, in Fe-Mo interchange case, the spin moments of Fe (Mo) cations situated on Mo (Fe) antisites are in a ferromagnetic coupling with those of Fe (Mo) cations on the regular sites. In VFe, VO or VPb vacancy cases, a ferromagnetic coupling is observed within each cation sublattice, while the two cation sublattices are coupled antiferromagneticly. But in VMo vacancy case, a ferromagnetic coupling is obtained not only within each cation sublattice but also between Fe and Mo sublattices. The saturation magnetization of the disordered Pb2FeMoO6 compound decreases in the sequence of VPb, VMo, Fe-Mo, VO, VFe, FeMo and MoFe cases.