Microscopic nature of the electron doping effects in the double perovskite Sr2−xLaxFeMoO6 (0 ≤ x ≤ 1) series

Abstract

Electron doping effects on Sr₂FeMoO₆ have been investigated in the title series by X-ray diffraction (XRD), neutron powder diffraction (NPD) and magnetic measurements in polycrystalline samples. XRD patterns show that the anti-site defects concentration increases with x, giving rise to highly disordered samples at the B positions, for the highest doping levels. The study of the evolution of structural parameters and valence state of Fe and Mo cations with doping, followed by NPD, sheds some light on the observed changes in the magnetic properties, in particular the ferromagnetic ordering temperature (T_c). An important fraction of the injected electrons is localized at Mo sites, which is harmful concerning the potential applicability, since it promotes the occurrence of anti-site disordering between Fe and Mo cations. Our results suggest that the competition between steric and electronic effects gives rise to a non-monotonic behavior of T_c, which tends to decrease at low doping levels and increases in highly doped samples. However, we have found that a higher T_c is accompanied by a frustrated ferromagnetism probably associated with the AFM correlations emerging at the anti-sites.