Correlation of microstructure and magnetic properties in Sm(CobalFe0.1Cu0.1Zr0.033)6.93 magnets solution-treated at different temperatures

The correlation of microstructure and magnetic properties in Sm(CobalFe0.1Cu0.1Zr0.033)6.93 magnets solution-treated at different temperatures was systematically investigated. It is found that the magnets solution-treated at 1219 °C possess a single 1:7H phase, exhibiting the homogeneous cellular structure during further aging treatment, leading to the optimum magnetic properties. However, for the magnets solution-treated at 1211 and 1223 °C, 2:17H or 1:5H secondary phase will also form besides 1:7H main phase, which cannot transform into cellular structure, thus deteriorating the magnetic properties greatly. The irreversible magnetization investigations with recoil loops also propose a non-uniform pinning in the magnets induced by the secondary precipitates. At proper solution temperature, Zr is supposed to occupy the Fe–Fe dumbbell sites in the form of Zr-vacancy pairs, leading to the minimum c/a ratio and thus stabilizing the 1:7H phase. Finally, Sm(CobalFe0.1Cu0.1Zr0.033)6.93 magnets with the maximum energy product and intrinsic coercivity at 550 °C up to 60.73 kJ·m−3 and 553.88 kA·m−1 were prepared by powder metallurgy method.