Coercivity of heat-treated Pr-Co power compacts

The variation of coercivity as a function of the temperature of annealing or sintering is reported for compacts of a single-phase PrCo5powder and also for a mixture of PrCo5with an additive richer in Pr. For single-phase PrCo5, the intrinsic coercive force decreases steadily with increasing heat-treating temperature and shows a minor peak near 1000°C. For magnets made with the additive, the curve ofMHcversus has two peaks, one at approximately 1050°C and another at 1120°C. This behavior can be correlated with thermal events in the Pr-Co phase diagram. It is interpreted in terms of a model which assumes that pinning sites for the domain walls exist and are concentrated in shells forming on the surface of PrCo5grains during the sintering. These shell are thought to consist of Pr-Co compounds having lower melting points than PrCo5and to be epitaxial layers on or between the PrCo5grains into which the walls can travel from the latter.