Low field magnetoresistance in La0.67Ca0.33MnO3 and Co3O4 combined system

We have studied the magneto-transport properties of the (1 - x) La0.67Ca0.33MnO3/xCo3O4 (x ∼ 0, 0.05, 0.10, 0.15 and 0.20) combined samples, prepared via sol-gel process. The powder X-ray diffraction patterns indicate no evidence of reaction between the La0.67Ca0.33MnO3 and Co3O4. A clear metal to insulator (M-I) transition is observed at 260 K in virgin LCMO sample while that vanishes in the LCMO/Co3O4 combined samples in the measured temperature range (80-300 K). Resistivity of the combined samples increases sharply as a consequence of Co3O4 addition, especially on the low temperatures, and magnetization decreases. An enhancement in low field magnetoresistance (LFMR) is observed at temperatures below 125 K for the composites with lower Co3O4 content, namely, x = 0.05 and 0.10. It is argued that this improved LFMR at low temperature (T < 125 K) arises due to the enhanced spin-polarized tunneling at the grain boundaries in the combined samples