Permanent magnets and hard magnetic materials

This review deals with the definition and development of hard magnetic materials with special emphasis on more recent developments in this field. After discussing the fundamental properties of all hard magnetic materials, based on the intrinsic and extrinsic properties, some remarks on the history of hard magnetic materials and permanent magnets are given. The important hard ferrites are only briefly treated. Emphasis, however, is laid on the rare earth (RE) intermetallics and the hard magnetic materials based on them. Experimental techniques for the measurement of the basic properties of hard magnetic materials, e.g. the ordering temperature, the magnetization, the anisotropy field, the physical and technical hysteresis loop and the properties, derived from this loop are discussed.