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 PrCo
5
powder and also for a mixture of PrCo
5
with an additive richer in Pr. For single-phase PrCo
5
, 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 of
M
H
c
versus
T
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 PrCo
5
grains during the sintering. These shell are thought to consist of Pr-Co compounds having lower melting points than PrCo
5
and to be epitaxial layers on or between the PrCo
5
grains into which the walls can travel from the latter.