Crystallization dynamics and magnetoresistance of perovskite-like manganate synthesized by mechanical alloying

Nanocrystalline ferromagnetic La0.7Ca0.3MnO3 perovskites with magnetoresist ance effect have been successfully prepared by mechanical alloying. Thermal transformation of the amorphous phase, resulting from ball milling, to per ovskite structure was studied by differential scanning calorimetry. Followi ng the law of mass action, we discuss the crystallization dynamics of the a morphous phase. The activation energy for crystallization transformation is calculated to be about +1.25 kJ g(-1). The characterization of resistivity rho(T) for La0.7Ca0.3MnO3 perovskites has also been investigated. At low t emperature T, rho(T) has a direct-proportion dependence on T-2 With increas ing annealing temperature, the slope of the rho-T-2 curve decreases. The te mperature dependent magnetoresistance effect at temperature far below the C urie temperature can be well expressed as the equation Delta rho/rho(0) = p (1) - p(2) T-3/2 - p(3)T(5/2).