PERMANENT MAGNETS BASED ON RARE EARTH-TRANSITION METAL COMPOUNDS

A large number of binary, rare earth (RE) transition metal (TM) inter­ metallic compounds have been studied (1,2), Of these, the RECos and RE2Cot7 alloys form the basis for materials with excellent permanent­ magnetic properties. These intermetallic compounds possess an ideal combination of magnetic and structural properties for applications. Nesbitt, Wernick, and co-workers were the first to establish the struc­ ture, magnetic moment, and high Curie temperature of RECos com­ pounds (3-6). An appreciable coercive field, [He, was reported in GdCos soon afterwards (7) and attributed to a high magneto-crystalline aniso­ tropy. However, it remained for Strnat and coworkers (8-10) to point out the high permanent-magnetic potential of the light RECos, based on their estimates of the anisotropy fields, HA, and to report the first [He values. Their investigations of the magnetic properties showed further­ more that SmC05 was clearly the most promising of these compounds (11). This fact was further justified by the results published in the following years by a number of laboratories (12-15). Das '(12) reported the first dense SmCos magnet with an energy product of 20 MGOe. Simul­ taneously, investigations began on precipitation-hardened copper­ containing RECos (16,17). By now SmCos magnets have become com­ mercially available with hard magnetic properties that are in many respects superior to those of the traditional alternatives, namely Alnico, Ferrites, and Pt-Co. The technology necessary for the production of SmCos has been fully developed (18,19) and the magnets have found a wide range of applica-