Coercive force in heat-treated R-Co alloys

Abstract

The variation of coercive force as a function of annealing temperature is reported for some compacts of Co₅Sm and Co₅Pr alloys with the compositions of 63∼64 wt% Co‐Sm and 60∼64 wt% Co‐Pr, respectively. For the magnets made of these alloys, the curves of intrinsic coercive force against annealing temperature have two peaks; one at around 1080 °C and the other at 1190 °C in the Co‐Sm sintered magnets. The curves of coercive force in sintered Pr‐Co alloys have also two peaks; one near 1040 °C and the other near 1125 °C. This behavior can be correlated with the peritectic temperatures in the Co‐Sm and Co‐Pr phase diagrams. It is interpreted in terms of a model which assumes the existence of the pinning sites for the domain walls and their concentration at boundaries between the precipitates and grains of Co₅R during the sintering. These precipitates are thought to consist of other R‐Co compounds with lower melting points than RCo₅.