Defects-aggregated cell boundaries induced domain wall curvature change in Fe-rich Sm–Co–Fe–Cu–Zr permanent magnets

Abstract: Raising Fe content has been found to deteriorate the coercivity of the cellular nanostructured Sm–Co–Fe–Cu–Zr 2:17-type permanent magnets because the insufficient 1:5H precipitates cannot occupy all the pyramidal cell boundaries. However, how the defects-aggregated cell boundaries free of 1:5H phase influence the pinning mechanism of magnetic domain walls as well as coercivity remains unknown. Through combined Lorentz and high-resolution transmission electron microscopy investigations, here we found that the magnetic domain walls of a cellular nanostructured Sm₂₅Co_44.9Fe_21.5Cu_5.6Zr_3.0 (wt.%) magnet move from the 1:5H cell boundaries towards cell interiors, repulsed by the surrounding defects-aggregated pyramidal cell boundaries. Further investigations revealed that raising the aging temperature can effectively reduce the density of defects-aggregated cell boundaries and enhance effectively the coercivity H_cj from 5.64 to 9.24 kOe for the Fe-rich Sm₂₅Co_42.9Fe_23.5Cu_5.6Zr_3.0 (wt.%) magnet. The comparative results suggest that the 1:5H-phase-associated attractive domain wall-pinning is more favorable for achieving large coercivity than the defects-associated repulsive domain wall-pinning. These findings add important insights into the domain wall-pinning mechanism in Sm–Co–Fe–Cu–Zr permanent magnets, which may help to achieve better magnetic performance in the Fe-rich magnets. Graphic abstract: Most magnetic domain walls (e.g., dashed blue box in (a) stay at the 1:5H pyramidal cell boundaries (b), some (e.g., dashed red box in a) move towards the cell interiors repulsed by the defects-aggregated cell boundaries (DACBs) (c).[Figure not available: see fulltext.]