Crystallization dynamics and magnetoresistance of La0.7Ca0.3MnO3 synthesized by mechanical alloying

Pure, single-phase La0.7Ca0.3MnO3 perovskites with giant magnetoresistance effect have been successfully prepared by mechanical alloying. The amorphou s phase formed in milled samples transforms at about 920 K into perovskite- type phase. Following the law of mass action, crystallization dynamics of t he amorphous phase has been discussed. The activation energy for crystalliz ation transformation is calculated to be about 265 kJ/mol. The characteriza tion of resistivity rho(T) for La0.7Ca0.3MnO3 perovskites has also been inv estigated. At low temperatures T, rho(T) has a direct-proportion dependence on T-2. With increasing annealing temperature, the slope of rho-T-2 curve decreases. The temperature dependent magnetoresistance effect at temperatur es far below the Curie temperature can be well expressed by the equation De lta rho/rho(0) = p(1) - p(2)T(3/2) - p(3)T(5/2).