부산대학교 도서관

We have studied effects of the partial substitution of La3+ for A2+ on the magnetic properties of double perovskites A2FeMoO6 (A=Ca, Sr and Ba). Polycrystalline A2-xLaxFeMoO6 (0??x??0.2) samples have been prepared by the conventional solid-state reaction in a stream of 5% H2/Ar gas. The x-ray data indicate that A=Ca is monoclinic with the space group P21/n, A=Sr is tetragonal with the space group I4/mmm, and A=Ba is cubic with the space group Fm3m. The substitution of La3+ for A2+results in a cell volume increase for A=Ca and a cell volume reduction for A=Ba. The decrease of saturation magnetization with increasing x arises from the reduction of magnetic moment associated with the electron doping and the disorder at the Fe and Mo sites. The partial substitution of magnetic La3+ for Ba2+ considerably enhances the Curie temperature Tc from 316 K for x=to 334 K for x=This enhancement of Tc with La3+ doping originates from electron doping effects in addition to ionic size ones.