Anomalous temperature dependence of coercivity in precipitation hardened Pr–Co–Cu–Ti magnets

Abstract

The anomalous temperature dependence of coercicity, Hc(T), has been observed in precipitation hardened PrCo6.7−xCuxTi0.3 (x=0.2–1) magnets. Transmission electron microscopy reveals that they exhibit a cellular microstructure. With an increase of Cu content, the Curie temperature of the 2:17 phase remains nearly unchanged whereas that of the 1:5 phase decreases. The peak of Hc(T) becomes higher, broader and shifts towards low temperature while the room temperature coercivity remains low and does not change with an increase of Cu content. There is a strong correlation between the Curie temperature of the 1:5 phase and the peak of Hc(T). The effect of Cu on Hc(T) cannot be explained by a traditional domain wall pinning model. It is highly likely that their magnetization reversal is controlled by the nucleation of reverse domains in isolated 2:17 cells.