High temperature stability of SmTM magnets

To meet the demand for permanent magnet materials usable up to 350-500 degr ees C, we investigated and reported that a SmTM magnet with a low temperatu re coefficient of coercivity and a moderately high coercivity has substanti ally lower irreversible losses at elevated temperatures than conventional S m2TM17 magnets. We have continued our studies on the high temperature magne tic behavior of these magnets. The magnetic properties, particularly coerci vity, of the SmTM7 alloy magnets are reduced much more slowly than the Sm2T M17 alloy magnets as temperature increases, As a result, the H-ci of SmTM7 remains greater than 5 kOe at 500 degrees C and thus maintains its high-ene rgy product, while the Sm2TM17 magnet has only about 1.7 kOe at the same te mperature and has a low energy product. SmTM7 alloy magnets undergoing a lo ng-term stability test at 500 degrees C exhibit irreversible flux losses of less than 5% after 1240 h, These results indicate that SmTM7 alloy magnets can be usable up to 500 degrees C for an extended period of time. This wil l expand the application temperature range of high performance permanent ma gnets. (C) 1998 American Institute of Physics. [S0021-9979(98)41811-5].