Effect of Fe on Microstructure and Coercivity of SmCo-Based Magnets

High-temperature permanent magnets have an important application in the aerospace and other high-tech fields, among which 2:17-type SmCo magnets have become the first choice for hightemperature permanent magnets due to the strong magnetic anisotropy and high Curie temperature. Although there are studies on the effect of Fe on the remanence and coercivity, the role that Fe plays on coercivity mechanism of SmCo magnets is still unclear. In this work, Sm(Co_balFe_xCu_0.08~0.10Zr_0.03~0.033)_z (x=0.10~0.16, z=6.90 and 7.40) magnets are prepared and the magnetic properties under different temperatures are investigated. The magnets with an intrinsic coercivity of 603.99 kA/m and a maximum energy product of 87.30 kJ/m³ at 500℃ are obtained. It is revealed that at room temperature the coercivity of the magnets increases with increasing Fe content, however, at 500℃ the coercivity shows an opposite dependency on Fe content. Moreover, the effect of Fe on coercivity is more obvious at low z value. The phase structure and composition analyses were characterized by XRD and TEM. The results show that with the increase of Fe content, the size of the 2:17R cell phase increases, the volume ratio of cell boundary 1:5H phase decreases, and furthermore, both Fe content in the 2:17R phase and Cu content in the 1:5H phase increase. The variations of Fe and Cu contents in both phases lead to the change of the domain wall energy difference. With the increase of Cu content of 1:5H phase, the domain wall energy of 1:5H phase (γ_1:5) drops faster at room temperature, the coercivity is determined by γ_2:17-γ_1:5, so the coercivity increases with increasing Fe content. While at 500℃, due to γ_1:5 at its Curie temperature, the coercivity is mainly determined by the domain wall energy of 2:17R phase (γ_2:17), which decreases with increasing Fe content. The increase of Fe content at the low z value results in a smaller growth of cell size, which leads to a more significant change in coercivity.