ABSTRACT
This chapter looks at reversible and irreversible changes in magnetization and describes them in terms of the two main mechanisms: domain-wall motion and domain rotation. The changes in magnetization arising from the application of a magnetic field to a ferromagnet can be either reversible or irreversible depending on the domain processes involved. One of the most difficult problems in the field of magnetism is to describe the magnetization curves of a ferromagnet in terms of materials properties. The inclusion theory of domain-wall pinning was suggested by M. Kersten. In general, the critical field for wall motion was much smaller than the anisotropy field so that domain rotation mechanisms could not play a significant role. In fact, domain-wall motion in these materials can be modeled with relatively few parameters, due to the simplicity of the situation, with grain size being the dominant microstructural feature.
