The field rate dependence of coercivity in fine particle ferromagnets and the applicability of the critical volume approach

A thermally activated Stoner Wohlfarth model is used to calculate coercivity as a function of field rate for systems in which a distribution of particle volumes and easy axis orientations is possible. The analytical treatment of M. El-Hilo, A. M. de Witte, K. O'Grady and R. W. Chantrell [J. Magn. Magn. Mater., vol. 117, pp. L307-L310, 1992] which was based on a critical volume assumption is found to be in excellent agreement with the model calculations for aligned systems with a distribution of particle volumes. The limitations of any analytical theory are shown when a distribution of orientations is included.