A new model for the coercivity mechanism of Sm2(Co,Fe,Cu,Zr)17 magnets

A two-dimensional model for the coercivity mechanism of [Sm.sub.2][(Co, Fe, Cu, Zr).sub.17] magnets is proposed. The high coercivities of fully heat-treated magnets (> 20 kA/cm) result from pinning sites which are formed by the intersections of the Zr-rich platelet phase (Z-phase) and the Cu-rich Sm[Co.sub.5] (1/5) boundary phase. The pinning strength of this site is assumed to be a result of the large difference between the domain wall energies of the 1/5 phase and the Z-phase. The domain wall energies of almost single phase samples of the Z-phase have been determined by magnetic measurements and by quantitative analysis of domain patterns. The small domain wall energy of the Z-phase of 4 - 11 mJ/[m.sup.2] supports the presented model.