Introduction

When magnetic 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. This phenomenon, known as hysteresis, was first observed by Ewing and he coined the term.

Hysteresis effects are well documented in the experimental literature but the exact description of the non-linear response of materials is a topic at the leading edge of research because of the complexity of the problem, in which many different factors compete to determine the overall response. Therefore the theoretical understanding of hysteresis is only at an early stage of development compared with the understanding of low amplitude, linear/reversible effects.

This lecture will discuss the various different contributions to ferromagnetic hysteresis, how these can be understood and modelled theoretically.