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

We present a general theoretical framework, based on the Preisach model of hysteresis, for describing irreversible phenomena in magnetically ordered materials, which includes the effects of the critical ordering temperature T_C. The model is based on the premise that the free energy landscape can be decomposed into an ensemble of bistable Barkhausen elements, each characterized by two energy barriers which are defined by local anisotropy and interaction fields. The free energy landscape has an explicit temperature dependence which originates from the critical growth of the spontaneous moment below the critical temperature T_C, and thermal overbarrier fluctuations are responsible for relaxing the system towards equilibrium. The theory identifies certain fundamental characteristic energies which play a primary role in determining the principal features of the magnetic response. The model is able to replicate a broad spectrum of behaviour observed experimentally in the field and temperature dependence of magnetic response functions such as the field cooled and zero-field cooled moment and the major hysteresis loop, in a wide variety of magnetic materials, including very specific experimental anomalies and trends, and provides a rigorous theoretical framework which quantifies the interpretation of the experimental data.