Extended Kronmüller model for cooperative relaxations in metallic glasses

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Abstract
An atomic model previously proposed by Kronmüller to explain the reversible magnetic after-effect in ferromagnetic amorphous alloys has been extended following the ideas of the coupling scheme for treating relaxation processes in complex systems. In the extended model the elementary atomic mechanism for the relaxation is assumed to be the activated rearrangements of atom pairs proposed by Kronmüller. Correlations among the relaxing units are introduced through the coupling ideas. Due to the inherent randomness of the amorphous metallic alloys, a distribution of the relaxation times corresponding to the elementary processes is also considered. However, the nonexponential character of the relaxation is determined to be mainly due to the correlation. Beyond the stretched-exponential function, the proposed model can explain more experimental facts. In this work we have utilized this model to explain the trend of the change of the relaxation parameters with the metalloid content in ferromagnetic alloys. Moreover we have reanalyzed previously reported data corresponding to the relaxation of magnetization work. From this analysis we have obtained the distribution function of elementary microscopic processes. The distribution function obtained is nearly symmetric and Gaussian-like, as expected from the randomness assumed to exist in amorphous metallic alloys.