Abstract
Abstract The microstructure and magnetic domain structure of single-phase sintered Co5Sm permanent magnets has been studied by means of transmission electron microscopy. The materials contain coherent inclusions of different sizes within single-crystal Co5Sm grains. Inclusions with diameters less than 200 nm are characterized as Co7Sm2. The bordering α fringes correspond to a boundary fault vector of . Electron-diffraction analysis reveals that the large inclusions (> 300 nm) consist of a rhombohedral Co17Sm2 phase. Besides inclusions, grains with numerous fringe patterns perpendicular to the [0001] direction are also observed. These grains contain overlapping stacking faults with different crystallographic shear vectors of the type . The coercivity of the single-phase Co5Sm magnets is limited by the nucleation of reverse domains at soft magnetic inclusions. It is found that precipitates act as weak pinning centres for domain walls, and grain boundaries as strong ones.
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