Magnetization curves, magnetic kinetics, and anisotropic magnetoresistance of nanocrystalline ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}/\mathrm{CoO}$ bilayers have been studied after field cooling through the blocking temperature of the antiferromagnetic 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

• Received 10 June 2003

DOI:https://doi.org/10.1103/PhysRevB.69.052402