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The main aspects of hysteresis in magnetic materials are reviewed, and some theoretical methods for their description are discussed. Particular emphasis is given to Preisach-type models of hysteresis, which yield a unified treatment of rate-independent phenomena, eddy-current dissipation and thermal relaxation. Expressions for the free energy and the entropy production are given, which provide a proper general basis for the interpretation of magnetization curves, losses, thermal relaxation. In particular, they permit one to clarify the nature of the states of minimum Gibbs energy and their relationship to the anhysteretic magnetization curve. Lines of possible development, concerning in particular the connection between microstructural and magnetic properties, are indicated.

In this work we studied temperature dependent magnetization processes in nanocrystalline Fe86Zr7B6Cu1. Ribbons produced by melt-spinning in air, were submitted to fast de Joule heating in vacuum to induce a nanocrystalline α-Fe phase. In order to investigate the untrivial interplay between structural and magnetic properties, hysteresis curves were measured as a function of temperature, with particular attention to the magnetic hardening effect. Details of the magnetization process were analyzed by using the Preisach model of hysteresis.