Mechanism of sintering in cobalt--rare-earth permanent-magnet alloys

Observations of composition, temperature, and time effects during the sintering of cobalt-samarium permanent-magnet alloys are presented. A correlation between the conditions which lead to the onset of rapid shrinkage during sintering and the conditions which lead to a high Hci is noted. A model for the mechanism of shrinkage during sintering is postulated where the slow step is the diffusion of samarium atoms in the grain-boundary regions via a samarium-atom-cobalt-vacancy cluster exchange mechanism. Furthermore, it is suggested that the ``high'' Hci structures achieved in these alloys would appear to be those with a relatively high concentration of cobalt vacancies in the grain-boundary regions.