EFFECT OF ANNEALING ON THE GIANT HALL-EFFECT

We studied resistivity, magnetoresistivity, and Hall resistivity for a few percolating granular NiFe-SiO2 films upon thermal annealing. It w as found that both the resistivity and the Hall resistivity decrease b y two orders of magnitude upon annealing at 520 degrees C, accompanied by a crossover from an approximately -lnT dependence of resistivity t o a metallic behavior. On the other hand, transmission electron micros copy study showed that this pattern of resistivity and Hall resistivit y change is not due to any new phases, but is associated with changes in particle size distribution. These results cannot be understood in t he existing theoretical framework.