Abstract: Characteristics of magnetic hardening in cast-hot pressed magnet Pr_(19)Fe_(74.5)B_5Cu_(1.5)were stu- died.The microstructure features and virgin magnetization curve reveal a nucleation control- led coercivity mechanism.Regression analysis shows that the intrinsic coercivity varies inversely as the logarithm of the average grain size: _iH_c(MA/m)=1.7312-0.48161nd(μm) which confirms the randomness of nucleation of reversed domains and the statistical nature of coercivity,indicating that the decrease of grain size would reduce the average number of de- fects on its surface and lower the probability of magnetization reversal of a grain and the cu- mulative fraction of the grains that have reversed their magnetization.Coercivity is thus en- hanced.

Key words: Pr-Fe-B magnet, coercivity, grain size, nucleation, cast-hot press