Electron microscopy of some rare earth–cobalt alloy magnets

Transmission electron microscopy is being used to characterize the microstructural features in some 1 : 5 and 2 : 17 RE-Co magnets. In 2 : 17 compounds containing Fe and Mn, lamellae of hexagonal and other polytypic regions embedded in the rhombohedral matrix are observed. It is shown that the interface between the hexagonal and rhombohedral phases can be described as a stacking fault with fault vector normal to the interfacial plane. APB’s parallel to the prism planes in the rhombohedral structure have also been identified and characterized. In contrast, no planar faults have been observed in the 1 : 5 materials containing misch metal as the major rare-earth component. In these alloys extensive twinning and precipitation of a 2 : 17 rhombohedral phase are the major microstructural features observed. The influence of these microstructures on the magnetic properties are discussed.