Enhanced Low-field Magnetoresistence in the Absence of Mn Content in Polycrystalline La0.67Ca0.33MnO3

Magnetic and electrical transport properties of the La0.67Ca0.33Mn1−x O3 (x=0-0.16), which were prepared by the sol-gel method followed by sintering treatment at 1 450, 1 100 and 900°C, respectively, were investigated. Experimental results show that, with the increase of x, the resistivity of samples increases and the insulator-metal transition temperature shifts towards lower temperature. Meanwhile, the intrinsic megnetoresistance effect is weakened and the extrinsic magnetoresistance is enhanced. For the samples with x=0.16 and 0.10 sintered at 1 100 °C and 900 °C, respectively, low field magnetoresistance as high as about 50% can be observed. Furthermore, for the samples sintered at 1 100 °C and 900 °C, the grain size is not only controlled by about sintering temperature, but also by the absence of Mn content x.