Trends in permanent magnet material development

The pressure of requirements concerning mass, size, temperature coefficient, resistance to demagnetization, price, machinability, etc., has given rise to three trends in magnet development: a) high energy-density magnets, notably RE-Co alloys; b) ductile magnets, notably Fe-Cr-Co alloys; c) low-cost magnets, notably Mn-Al attoys. For each of these materials we consider how the present state relates to what can be obtained theoretically, how further progress can be made and what the constraints are concerning availability of raw materials and commercial feasibility.