Grain boundaries and low-field transport properties in colossal magnetoresistance materials

The grain-boundary structure and the temperature dependence of resistivity were investigated for (1-x)LCMO + xYSZ, where LCMO and YSZ represent La_2/3Ca_1/3MnO₃ and yttria-stabilized zirconia, respectively. It is shown that the YSZ doped samples for x<2% show transport and low-field magnetoresistance (LFMR) behaviours different from that for x>2%. The metal-insulator transition temperature (T_p) decreases for x<2% but increases for x>2% as x is increased. LFMR increases with x for x<2% but decreases for x>2%. The experimental observations are discussed on the basis of scanning electron microscopy (SEM) analysis, which reveals YSZ appearing at the grain boundaries of LCMO for x<2%, while presenting itself within the sample in the form of clusters for x>2%.