Recent progress in high temperature permanent magnetic materials

Permanent magnetic materials capable of operating at high temperature up to 500 A degrees C have wide potential applications in fields such as aeronautics, space, and electronic cars. SmCo alloys are candidates for high temperature applications, since they have large magnetocrystalline anisotropy field (6-30 T), high Curie temperature (720-920 A degrees C), and large energy product (> 200 kJ center dot m(-3)) at room temperature. However, the highest service temperature of commercial 2:17 type SmCo magnets is only 300 A degrees C, and many efforts have been devoted to develop novel high temperature permanent magnets. This review focuses on the development of three kinds of SmCo based magnets: 2:17 type SmCo magnets, nanocrystalline SmCo magnets, and nanocomposite SmCo magnets. The oxidation protection, including alloying and surface modification, of high temperature permanent magnets is discussed as well.