On the fluctuation field in multidomain barium hexaferrite particles

A complete study of the thermally activated demagnetization phenomenology taking place in multidomain barium hexaferrite sample is presented. From the irreversible magnetization dependence of the fluctuation field, it is concluded that a demagnetization mechanism independent of the magnetization value rules the reversal in samples having large enough particles. Differently from this, in a sample having a broad particle diameter distribution (and including a minority percentage of small, single domain particles), our results clearly indicate the occurrence of two different demagnetization processes. Also, it was observed that the activation volume, in all the samples, was of the same order of magnitude and clearly smaller than the particle volume.