Trends in permanent magnet material development

The field of high-energy-density magnets is dominated by the RE-transition metal alloys, which have energy products in the range from 80 to 240 kJ/cu m. The considered alloys belong to two subgroups, including SmCo5 single-phase magnets and (Sm,Ce)(Co,Fe,Cu)6-8 precipitation hardened magnets. It is pointed out that the market for these magnets will be limited to those applications where the extreme energy and high coercivity are worth the price. New in the field of ductile magnets are the Fe-Co-Cr alloys, which have magnetic properties resembling those of alnico, i.e., high remanence and relatively low coercivity. Unlike alnico they can be plastically deformed in certain stages of their heat treatment, which makes them suitable for small and intricate shapes. The field of low-cost magnets is dominated by the ferrite magnets (Ba-hexaferrite and Sr-hexaferrite). These magnets are made from inexpensive raw materials, including iron oxide and Ba- or Sr-carbonate.