The “anomalous” nonmonotonic temperature dependence of coercivity, reported in Sm–Zr–Co–Cu magnets, has also been observed in bulk-hardened Y–Zr–Co–Fe–Cu alloys with a similar microstructure. The phenomenon appears to be universal for all R–Co magnets (R=rare earth) having a microstructure consisting of R2Co17 cells surrounded by the RCo5 phase. The effect of R and Cu on the temperature dependence of coercivity cannot be simply explained by traditional domain-wall pinning model based on the difference in a domain wall energy. Possibility that the coercivity is controlled by nucleation of reversed domains in magnetically isolated R2Co17 cells is discussed.

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Anisotropic nanocomposite R–Fe–B/Fe magnets (R=Pr, Tb) were synthesized by hot pressing and subsequent die upsetting blends of R-rich and R-lean melt-spun ribbons. The magnets have a layered structure, in which alternating layers of the two starting alloys lay perpendicularly to the pressing direction. A crystallographic alignment of the R2Fe14B grains is observed in the R-rich layers, whose microstructure is identical to that of the conventional die-upset magnets. The R-lean layers consisting of exchange-coupled R2Fe14B and α-Fe grains retain the random crystallographic orientation. The obtained bulk R-lean magnets show better properties than magnets of the same overall composition prepared from a single alloy.

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