Influence of Al2O3 on low-field spin-polarized tunneling magnetoresistance of (1 − x) La0.7Ca0.3MnO3 + x Al2O3 composites

In this study we report the effect of Al2O3 on the low field magnetoresistance (LFMR) of (1 − x) La0.7Ca0.3MnO3 + x Al2O3 composite synthesized through a solid-state reaction method combined with an energy milling method. Based upon a spin-polarized tunneling of conduction electrons at the grain boundaries, we have proposed a phenomenological model to explain the observed electrical transport behavior over the whole temperature range (5  300 K), especially the gradual drop of metal-insulator transition temperature (Tp = Tmax) as a function of increasing Al2O3 content, while the ferromagnetic–paramagnetic transition temperature (TC) remains almost constant (TC = 250 K).