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 5K 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 100K 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 100K suggests that at 5K 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.