Rare earth-cobalt permanent magnets near the 2-17 composition

The development of permanent magnets based on the rare earth-cobalt 2-17 phases is reviewed. Powdered as well as sintered alloys of Sm2(Co, Fe)17have not shown very good permanent magnet properties. But modifications of these 2-17 phases with other, additional transition metals often exhibit more useful magnetic properties, particularly in sintered form. Detailed studies on one series of such alloys, Cu and Fe-modified nonstoichiometric 2-17 phases, are presented. A grain size of about5-10 was required to obtain an intrinsic coercive force on the order of 10 kOe, or 10% of the anisotropy field, in sintered samples of these "1-8 alloys".