ABSTRACT
Magnetically ordered solids have atomic magnetic moments due to unpaired electrons. The atomic moments are coupled by exchange interactions which may give a net magnetization at all temperatures below the Curie point. Magnetization creates a magnetic field, and is itself a nonlinear and irreversible function of an externally applied field, represented on the hysteresis loop. The key concept in solid-state magnetism is the magnetic dipole moment m. Almost all the moments that concern are associated with atomic electrons, which are the elementary magnets in solids. The local, spontaneous magnetization of iron is greater than that of any commercial permanent magnet, but the demagnetizing field makes it impossible to retain the fully magnetized state which usually breaks up into domains. Much of the art of making magnets consists in realizing a suitable shape or microstructure which will allow a metastable, highly magnetized state to persist after saturating the magnetization in an external field.
