Magnetic domains, energy minimisation and magnetostriction

The magnetic domain structure of a magnetic material determines its magnetic properties. When the domain structure changes, perhaps due to factors such as temperature variation, mechanical stress or the presence of an external magnetic field, magnetic properties also change, in a beneficial or detrimental way. The physics controlling the formation and structure of domains, as well as the dynamics of so-called domain wall motion and domain rotation is quite well understood, but it is very complicated and difficult to apply to materials with complex metallurgical structure such as electrical steels. Magnetic domains of direct relevance to electrical steels are covered in Chapter 1 of Volume 2 of this book. In this chapter their origin and basic structures are explained.