Effects of the defects on the structural, electronic and magnetic properties of Sr₂FeMoO₆

From the point of view of the half-metallic character and magnetization reduction, the structural, electronic and magnetic properties of the imperfect Sr₂FeMoO₆ compound containing seven different defects of the Fe_Mo or Mo_Fe antisites, Fe–Mo interchange, V_Fe, V_Mo, V_O or V_Sr vacancies have been studied by using first-principles projector augmented wave (PAW) within generalized gradient approximation (GGA) as well as taking into account on-site Coulomb repulsive interaction (GGA + U). No obvious structural changes are observed for the imperfect Sr₂FeMoO₆ compound containing Fe_Mo or Mo_Fe antisites, Fe–Mo interchange or V_Sr vacancy defects. However, the six (eight) nearest oxygen neighbors of the vacancy move away from (close to) V_Fe or V_Mo (V_O) vacancies. The half-metallic character is maintained for the imperfect Sr₂FeMoO₆ compound containing Fe_Mo antisite, V_Fe, V_O or V_Sr vacancies, while it vanishes when Mo_Fe antisite, Fe–Mo interchange or V_Mo vacancy are presented. So the Mo_Fe antisite, Fe–Mo interchange or V_Mo vacancy defects have to be avoided in order to preserve the half-metallic character of the Sr₂FeMoO₆ compound and thus usable in spintronics devices. In Fe_Mo or Mo_Fe antisites, Fe–Mo interchange 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. In V_Fe, V_Mo, V_O or V_Sr vacancies cases, a ferromagnetic coupling is obtained within each cation sublattice, while two cation sublattices are coupled antiferromagnetically. The total magnetic moments μ_tot (μ_B/f.u.) of the imperfect Sr₂FeMoO₆ compound containing seven different defects decrease in the sequence of V_Sr vacancy (4.38), V_Mo vacancy (3.92), V_O vacancy (3.51), V_Fe vacancy (3.40), Fe_Mo antisite (3.40), Mo_Fe antisite (3.33), Fe–Mo interchange (2.47) and the mechanisms of the saturation magnetization reduction have been discussed. - Graphical abstract: The difference or spin charge density of four f.u. Sr₂FeMoO₆ containing seven different defects of (a) Fe antisite (Fe_Mo) at (0.5, 0.5, 0.5) site, (b) Mo antisite (Mo_Fe) at (0, 0.5, 0.5) site, (c) Fe–Mo interchange (Fe–Mo) at (0, 0, 0) and (0, 0, 0.5) sites, (d) Fe vacancy (V_Fe) at (0, 0.5, 0.5) site, (e) Mo vacancy (V_Mo) at (0.5, 0.5, 0.5) site, (f) O vacancy (V_O) at (0.5, 0.5, 0.25) site, and (g) Sr vacancy (V_Sr) at (0.75, 0.75, 0.75) site. The yellow (turquoise) isosurfaces represent positive (negative) charge density of 0.0045/ų and thus up-spin (down-spin) moment. In the (100) cross sections, the colors blue, turquoise and green represent the value of charge density in increasing order. - Highlights: • No structural changes are observed for Fe_Mo, Mo_Fe, Fe–Mo, V_Sr cases. • The 6 (8) nearest O neighbors move away from (close to) V_Fe or V_Mo (V_O) vacancy. • Half-metal maintains for Fe_Mo, V_Fe, V_O, V_Sr, but vanishes for Mo_Fe, Fe–Mo, V_Mo cases. • Spin moment of Fe_Mo (Mo_Fe) is antiferromagnetic coupling with that of regular site Fe (Mo). • Total moments decrease in sequence of V_Sr, V_Mo, V_O, V_Fe, Fe_Mo, Mo_Fe, Fe–Mo