Electrical transport properties and magnetoresistance of (La0.7Ca0.3MnO3)1−x/(MgO)x composites

(La0.7Ca0.3MnO3)1−x/(MgO)x composites were prepared by traditional solid-state reaction procedure. The electrical transport properties, magnetic properties and low-field magnetoresistance (LFMR) of all samples with different MgO addition were studied systematically. With increasing MgO dopant, the resistivity increases, and the specific magnetic moment σS decreases, but Curie temperature (TC) remains the same as that of the pure LCMO. Some specific effects of Mg dopant on the electrical transport properties were observed. A new metal-insulator (M-I) transition temperature (TP2) was observed at low temperature, except for the normal TP1, which was appeared at high temperature (about 270 K). With increasing the doping, TP2 decreases monotonously. The intensity of resistivity at TP1 becomes weak and then turns to a platform. Furthermore, through the analysis of X-ray diffraction (XRD) and magnetic properties, we can see that MgO does not react with LCMO and only goes into the interface or the surface of LCMO grains. It is interesting to notice that the effect of MgO is to enhance the LFMR of the composites. According to the Double Exchange (DE) interaction theory, we can conclude that the effects of MgO addition on the electrical transport properties and LFMR for all the samples can be explained by the model of the grain boundary effect, the intrinsic transport properties and spin-dependent scattering.