Lorentz electron microscopy of Co-Sm permanent-magnet materials

The magnetic domain structure and microstructure of several Co-Sm magnet alloys were examined by transmission electron microscopy. This study reveals that the investigated single-phase magnets exhibit a low defect density within the grains. The coercivity is determined by the nucleation of reverse domains at soft magnetic inclusions. Precipitation - hardened magnets contain a fine-scale precipitation structure. From the wavy nature of the domain walls we conclude a strong pinning at the precipitates.