Modelling of major and minor hysteresis loops in particulate systems

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. H-i proportional to 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 H-i is positive. This result suggests that the interaction field should be proportional to M-2 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.