Permanent magnet properties of rapidly quenched rare earth-iron alloys

Recent studies have demonstrated the potential of producing rare earth-iron permanent magnets by rapid quench processing. High coercivity, unachievable by traditional powder-metallurgy methods, has been obtained either by crystallization of an amorphous or rapidly quenched precursor or by direct-quenching. Results obtained by both techniques on a variety of rare earth-iron alloys are discussed. In particular, melt-spun Nd-Fe and Pr-Fe alloys develop an appreciable maximum (7-9 kOe) in room temperature coercivity (Hci) as a function of quench rate, which is controlled by varying the surface velocity of the melt-spinner substrate. Even higher Hci(>20 kOe) has been observed in Sm-Fe. Magnetic and crystallization properties suggest that the coercive force of these materials is related to the formation of one or more metastable rare earth-iron phases.