The recent development of permanent magnet materials containing rare earth metals

The prospect that permanent magnets with previously unattainable coercivities and energy products might be made from cobalt-rare earth alloys has caused intense research efforts in the last three years. Alternative ways of preparing magnets from powders and by casting were demonstrated in several laboratories.
(BH)_{\max} \approx 20
MG.Oe and
M
H_{c} > 25 000
Oe have been achieved with SmCo
5
, and the development of manufacturing processes for magnets made from this alloy has begun. This paper reviews the basic concepts, properties of the alloys of interest, and the physical factors influencing the coercive force. Approaches to alloy, powder, and magnet fabrication are discussed, with their merits and drawbacks; also problems incurred in the materials development and their possible solutions. Application areas are reviewed and some economic factors considered. It is concluded that the
R
Co
5
magnets are indeed beginning to live up to their promise, but that more materials research, process development, and circuit redesign are needed if their potential is to be fully utilized.