Magnetic Interactions

This chapter presents a “curio cabinet” of magnetic models and phenomena. Interactions between the sources of the field internally can yield a wide range of magnetic behavior. There is a whole class of spin models that weights nearest neighbor interactions the most strongly. Atoms get their permanent magnetic fields by their electronic spin and unpaired electrons in the outer energy shells. The magnetic moment of an atom appears to arise from the “current-like” components of angular momentum and spin and combined. In the context of condensed matter physics, time reversal symmetry breaking has generally become associated with something in the system behaving like a magnetic field. The chapter illustrates the features of “crystal field theory” with an example. Different mechanisms have been proposed for different materials systems from metals with free electrons to diffuse isolated systems in insulator crystals.