Microstructures and coercivity mechanism of 2:17-type Sm-Co magnets with high remanence

Sm(Co_balFe_0.245Cu_0.07Zr_0.02)_7.8 (at%) sintered magnets with high remanence (B_r ~1.15 T) were prepared using a traditional powder metallurgy method. Tunable magnetic properties, especially intrinsic coercivity (H _cj), were obtained through adjusting isothermal procedure parameters. H _cj of the magnets increases from 305 to 752 kA · m⁻¹ with isothermal annealing time increasing from 3 to 20 h, while B _r of the magnets almost keeps constant. From the bright field transmission electron microscopy (TEM) images, it is found that: (1) there is dispersed precipitated phase with very small size in the magnet annealed for 3 h, while the magnets annealed for 20 h have distinct and intact cellular structure; (2) the number density of Z-phase in magnet annealed for 20 h is bigger than that for 3 h. Besides, the finer microstructures were studied with high-resolution transmission electron microscopy (HRTEM).