Hysteresis models: non-linear magnetism on length scales from the atomistic to the macroscopic

When materials are exposed to high levels of external magnetic field, the response of materials eventually extends beyond the simple linear regime. Under these conditions it is found that the change in response of the materials is no longer reversible. These phenomena are well documented in the experimental literature. However, the theoretical non-linear description of the response of materials is only at a very early stage of development compared to with the low amplitude linear/reversible model theories. High performance computing is enabling researchers to model magnetic devices at smaller and smaller length scales, while at the same time accurate first principles calculations of magnetic properties now extend to systems involving thousands of atoms. The two different approaches, continuum versus discrete, are approaching each other at the mesoscopic length scales. The lecture will discuss some of the model theories that have been developed to describe the properties of magnetic materials. Beginning with first principles theories, the lecture will then trace the development of model theories at increasing length scales through micromagnetics, macroscopic Preisach, domain rotational models and phenomenological models of domain wall motion such as the stochastic process model. (C) 2002 Elsevier Science B.V. All rights reserved.