Ferroics

Ferroics is the general framework for ferroelectricity and ferromagnetism. Ferroelectrics are materials where the polarization exhibits nonlinear behaviour and hysteresis. They may have a strong permanent polarization but only if the temperature lies below a characteristic temperature, called the Curie temperature. In this chapter, a nonlinear approach to ferroelectrics is investigated and then a general setting is established for the modelling of hysteretic effects. The leading idea is that the entropy production is, per se, a non-negative function here involving the time derivative of the electric field. Also, the GLD theory is examined to describe the transition between linear paraelectric properties and hysteretic behaviours. Further, a nonlinear theory is developed for nonlinear behaviour and hysteresis in ferromagnetic materials.