ABSTRACT
GG = (44.1) The influence of an applied field on a solid has been discussed in Chapter 40, where the solid was treated as an assembly of free electrons. Experiments have shown, however, that solids where the electrons are localized on isolated atoms and described by the tightbinding approximation display larger magnetic effects than those with nearly-free electrons, described by the weak-binding model. This suggests that magnetism is of atomic origin and can be understood by treating the solid as a system of isolated atoms. If any interaction between atoms is negligible, the solids exhibit just diamagnetic or paramagnetic behaviour. If there is a cooperative interaction between the atoms, the solids may be in a state that shows spontaneous magnetization, corresponding to ferromagnetism, antiferromagnetism or ferrimagnetism.
