Novel method for preparation of high-performance SmFe12/α-Fe nanocomposite magnets by rapid thermal processing

SmFe12-based magnets have attracted considerable attention because of their high intrinsic magnetic properties. The metastable ThMn12-type SmFe phase can be easily decomposed into the α-Fe phase during heat treatment process. The nanocomposite theory of soft and hard magnetic phases is used to improve the magnetic properties of SmFe12-based magnets. At present, it is difficult to obtain strong exchange coupling in SmFe12/α-Fe nanocomposite magnets prepared by melt spinning or melt spinning followed by isothermal heat treatment. This study proposes a SmFe12/α-Fe nanocomposite magnet with a maximum energy product of 84.5 kJ/m3 by melt spinning followed by rapid thermal processing (RTP). The effects of RTP time on the phase composition, microstructure, and exchange coupling of the magnets were systematically studied. The results showed that a suitable RTP time benefitted the formation of fine and uniform 1:12 phase grains in the magnet. Henkel curves, magnetic domains and quantitative analysis based on the exchange coupling volume were employed to study the exchange coupling of the magnets, which indicated that the enhanced hard/hard-exchange coupling strength originating from the uniform and fine hard magnetic 1:12 phase grains is the main reason for the improvement in the overall exchange coupling strength. We believe this study provides a new technology for preparing high-performance SmFe12/α-Fe nanocomposite magnets with a high exchange coupling strength.