TEM studies of cobalt-rare earth permanent magnets

The microstructures of several cobalt-rare earth magnet alloys from various laboratories were examined by transmission electron microscopy (TEM). The magnets varied in alloying elements and inz, the ratio of transition-metal to rare-earth atoms. Matsushita magnets withz~8had a relatively featureless microstructure. Toshiba magnets withz~7contained a fine cellular microstructure, and Brown-Boveri magnets withz=7.8contained fine isolated precipitates plus a partly-formed cellular structure. These observations are consistent with magnetization hehavior, which indicated nucleation-controlled coercivity for thez~8magnets and pinning-controlled coercivity for thez~7andz=7.8magnets. Results are compared with earlier TEM studies.