Abstract
We investigate spin precession in the presence of randomly distributed magnetic moments which reorient by thermally activated transitions. Based on analytical calculations and scaling arguments, we find that the polarisation decay of a spin ensemble exhibits a rich behaviour characterised by stretched exponentials and power laws. The anomalous relaxation laws result from heavy-tailed local field distributions and are verified by computer simulations. The general problem is discussed in the context of μSR in random assemblies of superparamagnetic clusters.
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