Mössbauer detection of magnetic clusters in disordered magnetic materials

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Abstract
Starting from the theories developed by Mørup and coworkers for interpreting the properties of independent or interacting superparamagnetic particles, we show how these theories can be adapted to the detection and study of magnetic clusters (if they exist) in disordered magnetic materials such as reentrant ferromagnets, spin glasses, spinels, amorphous materials, etc. We report preliminary Mössbauer experiments which strongly suggest that ferromagnetic clusters are present in the reentrant ferromagnet Au1 -xFex (x > 15 %) above the magnetic transition temperature Tp in zero field. We also show that T p characterizes the ordering of the (weakly coupled) giant magnetic moments of the clusters and not the ordering of the individual atomic moments. We speculate that the anomalies observed below Tf ∼ 50 K might be associated with a Gabay-Toulouse transition for the giant moments of the clusters