Effect of spin-reorientation transition of cell boundary phases on the temperature dependence of magnetization and coercivity in Sm₂Co₁₇ magnets

Four Sm₂Co₁₇ magnets with spin-reorientation transition (SRT) of cell boundary phases (CBPs) are prepared by liquid-phase sintering. The temperature of the SRT of CBPs ($T_{\mathrm{SR}}^{1:5}$) is regulated from 125 K to 195 K by adding 0 wt.%, 3 wt.%, 6 wt.% and 9 wt.% Dy₈₈Cu₁₂ alloy powder. The effect of SRT of Sm₂Co₁₇ magnet CBPs on the temperature dependence of the magnetization (M–T) and coercivity (H–T) is systematically investigated. The temperature dependence of the magnetization is influenced by the SRT of CBPs. The M–T curves measured during the heating process are larger than those measured during the cooling process when $T<T_{\mathrm{SR}}^{1:5}$. When $T=T_{\mathrm{SR}}^{1:5}$ there is a bifurcation point. When $T>T_{\mathrm{SR}}^{1:5}$ the M–T curves overlap and the M–T derivation curve shows that the magnetization of the magnet has low temperature dependence of magnetization above $T_{\mathrm{SR}}^{1:5}$. With increasing $T_{\mathrm{SR}}^{1:5}$, the initial temperature of the low temperature dependence of magnetization shifts towards a higher temperature. The coercivity temperature coefficient becomes positive as the SRT effect increases, and the temperature range of the positive coercivity temperature coefficient moves towards higher temperatures as $T_{\mathrm{SR}}^{1:5}$ increases. This reveals that SRT of CBPs has little effect on the temperature dependence of magnetization above $T_{\mathrm{SR}}^{1:5}$, while the temperature dependence of coercivity is optimized. The temperature range of magnetization and coercivity with low temperature dependence tends towards higher temperatures, which is conducive to the preparation of magnets with a low temperature coefficient at higher temperatures.