Grain-boundary effects on the electrical resistivity and the ferromagnetic transition temperature of La0.8Ca0.2MnO3

In this letter, grain-boundary effects on the electrical transport and the ferromagnetic transition temperature were investigated in La0.8Ca0.2MnO3. The different ferromagnetic transition temperature (45 K) and the different metal-semiconductor transition temperature (62 K) were observed in the samples with different grain boundaries. Wide grain boundaries can induce large grain-boundary effects on grain, and small grain size also induces large grain-boundary effects on grain due to the increase of grain boundaries. The possible mechanism of grain-boundary effect is explained as the strain effect of grain induced by the distortion at grain boundaries. The strain of grains should enhance the ferromagnetic double exchange interaction. (C) 2000 American Institute of Physics. [S0003-6951(00)02627-9].