Permanent magnet materials

Permanent magnets are finding ever-increasing uses as magnet technology develops and materials improve. Permanent magnet materials are evaluated in terms of the geometry and configuration of the application for which they are intended. The origin of the properties of most modern permanent magnet materials is interpreted in terms of fine-particle theory. The fine-particle structures are produced either synthetically or by a solid-state precipitation reaction in an alloy. The preparation and properties of commercial magnets are described. The Alnico alloys are based on magnetically heat-treated iron-nickel-aluminum-cobalt alloys and account for the great majority of present-day production. Ferrites are finding increasing use. Elongated single-domain fine-particle magnets and other materials are used in smaller quantities. A number of interesting, not yet commercial, materials deriving their properties primarily from crystal anisotropy are described.