Optimization of microstructures and magnetic properties of Sm(CobalFe0.227Cu0.07Zr0.023)7.6 magnets by sintering treatment

Magnetic properties and microstructures of Sm(CobalFe0.227Cu0.07Zr0.023)7.6 sintered magnets were optimized by sintering treatment. Results show that the knee-point magnetic field, Hknee, is twofold up and the intrinsic coercivity Hcj increases by 40%, ranging from 21.64 to 30.39 kOe at the cost of a little decrease of Br from 10.84 to 10.31 kGs with sintering temperature decreasing from 1488 to 1473 K. And the average domain width is narrower and more uniform for the specimen sintered at 1473 K than that of the specimen sintered at 1488 K. It is impressive that the density of lamellar phase increases from ∼0.050 to ∼0.058 nm−1 with the sintering temperature decreasing from 1488 to 1473 K. Moreover, the average cellular size is about ∼84 nm for the magnets sintered at 1473 K, which is 80% of that of the magnets sintered at 1488 K (∼97 nm). And the cell boundary width of the magnets sintered at 1473 K (∼7 nm) is only half average width of the magnets sintered at 1488 K (∼14 nm). It is found that the Cu content in the cell boundaries is much higher (∼17 at%) in the magnets sintered at 1473 K compared to that of the magnets sintered at 1488 K (∼10 at%). It can be concluded that smaller cells and narrower cell boundaries together with higher gradient of Cu content are key points for obtaining the optimum Hknee and Hcj.