Structural and magnetotransport features in new electron-doped Sr2−xCexFeMoO6 double perovskites

Abstract

A new series of double perovskites of stoichiometry Sr_2−xCe_xFeMoO₆ (0 ≤ x ≤ 1) has been prepared by a wet chemistry procedure yielding very reactive precursors, which were subsequently annealed under reducing conditions. The compounds have been studied by X-ray (XRD), neutron powder diffraction (NPD), Mössbauer spectroscopy, magnetic and magnetotransport measurements in polycrystalline samples, aiming to investigate the effect of electron doping in the parent perovskite Sr₂FeMoO₆. The evolution of the crystal structure has been analyzed from NPD data; a transition from tetragonal (I4/m) to monoclinic (P2₁/n) has been observed at 0.2 ≤ x ≤ 0.4 as a result of the decrease of the tolerance factor due to the electron injection on B sites and the reduction in ionic size at A positions of the ABO₃ perovskite. A bond valence study shows that an important fraction of the injected electrons is localized at Mo sites, which promotes the occurrence of antisite disordering between Fe and Mo cations. The magnetic properties are characteristic of ferromagnetic materials, with an ordering temperature of around 400 K, showing a non-monotonic behavior along the series, which is understood as a compromise between the steric and the electron injection effects. The introduction of a magnetic rare-earth in the Sr sublattice improves the magnetoresistive response at low temperatures, as a result of the polarization of the Ce³⁺ moments: a magnetoresistance (MR) factor of 45% is observed at 5 K for the x = 0.6 sample. For the first time we show that the introduction of a magnetic element in the A sublattice of a double perovskite can be used as an effective way to enhance the magnetoresistive response in this attractive family of oxides.