Phase Structure and Properties of Fe-Rich 2:17-Type Sm-Co Sintered Magnets

The effect of Fe-rich content on the microstructure, phase structure, elements distribution, and magnetic properties of Sm(Co
$_{0.91-\mathit {x}}$
Fe
_x
Cu
_0.07
Zr
_0.02
)
_7.6
(
$x$
= 0.22, 0.30, and 0.35) magnets has been investigated systematically. With the increase of Fe content, the 2:17H, 2:17R, and 1:3R phases appeared in the Fe-rich solid solution. The different phase structures in the high-resolution transmission electron microscopy (HRTEM) images showed a locally short-range ordered state with dislocations. The presence of 2:17R phase and 1:3R phase was negative to the spinodal decomposition during the aging stage. In addition, the high Fe content caused Cu element enrichment in some area of the final state magnet, which further affected the formation of cellular structure. The Fe content increased from
$x$
= 0.22 to
$x$
= 0.35, the average cell size increased from 83.67 to 112.46 nm, the thickness of cell boundary increased from 9.6 to 18.25 nm, and the density of Zr-rich platelets increased from 0.036 to 0.06 nm. Furthermore, the defective cellular structures in the magnet (
$x$
= 0.35) with incomplete and discontinuous cell boundaries had weak pinning field and poor coercivity. Moreover, the magnetooptical Kerr optical microscope observation revealed that the domain width of magnet (
$x$
= 0.35) was significantly higher than that of magnet (
$x$
= 0.22), and the reversal magnetic domain was formed first in the magnet (
$x$
= 0.35), which caused a poor coercivity.