INFLUENCE OF THE DISTRIBUTION OF MAGNETIC-MOMENTS ON THE MAGNETIZATION AND MAGNETORESISTANCE IN GRANULAR ALLOYS

In granular solids, the magnetoresistance is directly related to the m acroscopic magnetization, but this relationship is extremelly complex due to the distribution of grain sizes and the intergranular magnetic interactions. The dependence of the magnetoresistance on the magnetiza tion is here investigated by means of a theoretical. model that is dev eloped taking explicitly into account the magnetic moment distribution and the spin-dependent electron-impurity scattering within magnetic g rains and at the interface between the grains and the metallic matrix. Using this model, one can explain large experimental deviations from the parabolic behavior of the magnetoresistance vs magnetization curve s that are typically expected for equal noninteracting superparamagnet ic grains. The expressions for the magnetization and magnetoresistance , obtained for general distribution functions, are tested considering a log-normal-type distribution function by fitting on data obtained fr om melt-spun Cu90Co10 ribbons after annealing by de Joule heating. The experimental data are well traced using just three parameters that de termine the particle size distribution, the particle density, and the ratio of the scattering cross section at the boundaries of the grains to the scattering cross section within the grains.