Stability of magnetic properties of Sm/sub 2/Co/sub 17/-type magnets at operating temperatures higher than 400(degree)C

The stability of the magnetic properties of Sm/sub 2/Co/sub 17/-type magnets at high operating temperatures was investigated by magnetic measurements at room temperature (RT) and high temperatures (HTs). The coercivity at RT is changed by the HT measurement and starts to decrease after measurements above 400(degree)C. These changes in coercivity are attributed to microchemical changes in the bulk. The losses, however, can be fully recovered when the last segment of the original heat treatment of the magnet (550(degree)C-400(degree)C with 0.7K/min and 3 h at 400(degree)C) was repeated. It was also found that prolonged exposure to air at high operating temperatures leads to a gradual decrease in remanence. Thus, coating the magnets is essential for the application of the magnets at high operating temperature in air.