Large training effects in magnetic relaxation and anisotropic magnetoresistance in nanocrystalline exchange-biased Ni_(80)Fe_(20)/Co-O bilayers

摘要

Magnetization curves, magnetic kinetics, and anisotropic magnetoresistance of nanocrystalline Ni_(80)Fe_(20)/CoO bilayers have been studied after field cooling through the blocking temperature of the antifer-romagnetic oxide. Exponential decay together with low magnetoresistance ratio is found to govern the first magnetization reversal after field cooling. Second and consecutive reversals present typical logarithm behavior of a constant distribution of activation energies together with high values of the magnetoresistance ratio. These results are attributed to large training effects that, decreasing the number of noncompensated sites, induce a transition in the reversal magnetization processes from a single wall motion process to multiple rotations