Modelling of major and minor hysteresis loops in particulate systems

Abstract

In this paper a model for the calculation of major and minor hysteresis loops in particulate systems is described. For the case of a particulate system with aligned easy axes, the model is based on a numerical solution of the rate equation which was modified to take into account particle size distribution and interaction effects. In addition, calculations of minor loops for systems with a distribution of orientation of easy axes have been made. In the model, interaction effects are represented using a mean field approach, i.e. Hi M where M is the average magnetization of the system. The results show that for the non-interacting case, no minor hysteresis loops occur. Interaction formalism in terms of a mean field approach gives minor hysteresis loops only when Hi is positive. This result suggests that the interaction field should be proportional to M2 so as to predict minor loops at positive and negative values of average magnetization similar to experimental observations. In general, the interaction field is an unknown function and should be expressed as a series expansion in terms of M. For the prediction of minor loops we assume that the interaction field is dominated by the quadratic term.