Crystal structure, magnetic and electrical-transport properties of rare-earth-doped Sr2FeMoO6

Crystal structure, magnetic and electrical-transport properties of the rare-earth-doped compounds (Sr1.85Ln0.15)FeMoO6 (Ln=Sr, La, Ce, Pr, Nd, Sm and Eu) have been investigated by means of X-ray diffraction, magnetic and electric measurements. All the samples are single phase and belong to the I4/m space group. Due to the competing contributions of electron doping and steric effects, the unit-cell volume of the doped compounds changes slightly and does not vary systematically with the ionic radius of the rare-earth ions. The temperature dependence of the magnetization of (Sr1.85Ln0.15)FeMoO6 indicates that the Curie temperature of the doped compounds has increased upon doping, except for the Eu-doped compound. The saturation magnetization of the compounds at 5 K cannot be explained simply by considering the ferrimagnetic arrangement of the magnetic sublattices of Fe and Mo because of the magnetic contribution of rare-earth ions. However, the saturation magnetization at 100 K of the doped compounds exhibits a linear decrease with the increase of the anti-site defect concentration. Comparison of the saturation magnetization of the compounds at 5 and 100 K suggests that at 5 K the magnetic moments of Ce, Pr, Nd and Sm align parallel with that of Fe, while the magnetic moment of Eu is anti-parallel with that of Fe. The normalized resistivities of the parent and the La- and Sm-doped compounds exhibit a semiconductor-metal transition, while the Pr-, Nd- and Eu-doped compounds exhibit semiconducting behavior.