Recent Progress in High-Performance Sm₂Co₁₇-Type Magnets

The Sm₂Co₁₇-type (Sm─Co─Fe─Cu─Zr) permanent magnets have drawn growing attention owing to the rapid development of high-efficiency and more miniaturized magnet-associated devices operated at elevated temperatures. Though raising Fe content in the magnets has been known to enable higher theoretical magnetic performance and lower material cost, it is still difficult to achieve high energy product and large coercivity simultaneously in the magnets with high Fe content (in particular, with Fe content above 20 wt.%). This work reviews the recent progress of Fe-rich Sm₂Co₁₇-type magnets over the last decade. This review discusses fundamental issues remaining elusive or controversy in the past, including phase and defects identification, mechanism of forming unique cellular nanostructure, and the role of the nanoscale phases on magnetic properties. It also offers a survey of approaches toward enhancing magnetic performance developed based on a deeper understanding of processing-microstructure-property relationship. Finally, a brief outlook on fundamental research and challenges in mass production is provided.