Rare-Earth-Compound Permanent Magnets

Since the discovery of the extremely high magnetocrystalline anisotropy of YCo5 in 1966 there has been rapidly increasing interest in the development of cobalt-rare-earth intermetallic compounds as permanent magnet materials. The observed coercive forces are still only a small fraction of the anisotropy fields, and for some reason the coercive forces attainable with SmCo5 are larger than in other isostructural compounds with comparable anisotropy fields. A number of experiments have shown that the coercive force is very closely related to and can be profoundly influenced by the nature of the particle surface. The processing of these materials into magnets can be approached in several different ways, with due regard to the problem of chemical stability. The long-range prospects of these materials may well be related to the improvement of the properties of compounds other than SmCo5 by influencing the factors that control the magnetization reversal process.