Modelling the irreversible response of magnetically ordered materials:a Preisach-based approach

Abstract

We present a general theoretical framework, based on the Preisach model ofhysteresis, for describing irreversible phenomena in magnetically orderedmaterials, which includes the effects of the critical ordering temperatureTC. The model is based on the premise that the free energy landscape can bedecomposed into an ensemble of bistable Barkhausen elements, eachcharacterized by two energy barriers which are defined by local anisotropy andinteraction fields. The free energy landscape has an explicit temperaturedependence which originates from the critical growth of the spontaneous momentbelow the critical temperature TC, and thermal overbarrier fluctuations areresponsible for relaxing the system towards equilibrium. The theory identifiescertain fundamental characteristic energies which play a primary role indetermining the principal features of the magnetic response. The model is ableto replicate a broad spectrum of behaviour observed experimentally in thefield and temperature dependence of magnetic response functions such as thefield cooled and zero-field cooled moment and the major hysteresisloop, in a wide variety of magnetic materials, including very specificexperimental anomalies and trends, and provides a rigorous theoreticalframework which quantifies the interpretation of the experimental data.