The coercivity mechanism of sintered SM(CobalFe0.245Cu0.07Zr0.02)7.8 permanent magnets with different isothermal annealing time

Precipitation-hardened 2:17-type SmCo permanent magnet has attracted much attention due to its high Curie temperature and excellent magnetic properties. Sm(CobalFe0.245Cu0.07Zr0.02)7.8 (at%) sintered magnets with high remanence (Br ~1.15 T) were prepared using a traditional powder metallurgy method. The intrinsic coercivity Hcj of the magnets was increased from 429 to 994 kA m−1 with isothermal annealing time increasing from 10 to 40 h, which is different from the phenomenon that increasing aging time leads to a reduced coercivity mentioned in the Ref. [16]. In consideration of rarely report about the microstructure of the final magnet isothermally annealed for 40 h, we have tried to originally analyze the relationship between the microstructure and the magnetic properties. Besides, the lattice constants of sintered Sm(CobalFe0.245Cu0.07Zr0.02)7.8 permanent magnet isothermally annealed for 40 h have been given by indexing the HRTEM results including the selected area electron diffraction (SAED) and HRTEM images.