Samarium-cobalt magnets resistant to 750°C

Hcilosses in high coercivity plasma-sprayed samarium-cobalt magnets (at temperatures of 700 to 800°C) are much less severe than those observed for sintered magnets. Magnets with initial coercivities of about 60 kOe show values of 35 to 50 kOe, after exposures of several hundred hours to temperatures of 700 and 750°C. The data collected on sprayed magnets indicates that Hcilosses at these temperatures can be related to a narrowing SmCo5homogeneity range and to processes involving oxygen dissolution and precipitation. These losses do not result from eutectoid decomposition of the SmCo5phase as is widely accepted. The findings of this study will find extensive use in the development of thermal processing techniques that will employ slow cooling of magnets from elevated temperatures.