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

Nanocrystalline ferromagnetic La_0.7 Ca_0.3 MnO₃perovskites with magnetoresistance effect have been successfully prepared by mechanical alloying. Thermal transformation of the amorphous phase, resulting from ball milling, to perovskite structure was studied by differential scanning calorimetry. Following the law of mass action, we discuss the crystallization dynamics of the amorphous phase. The activation energy for crystallization transformation is calculated to be about + 1.25 kJ g^-1 . The characterization of resistivity (T) for La_0.7 Ca_0.3 MnO₃perovskites has also been investigated. At low temperature T , (T) has a direct-proportion dependence on T² . With increasing annealing temperature, the slope of the -T²curve decreases. The temperature dependent magnetoresistance effect at temperature far below the Curie temperature can be well expressed as the equation / ₀= p₁- p₂ T^3/2- p₃ T^5/2 .