The relationship between the composition and the abnormal temperature dependence of coercivity in Sm(Co,Fe,Cu,Zr)z

The abnormal temperature dependence of coercivity with a positive temperature coefficient is characteristic in Sm-Co magnets with a cellular (or cellular-like) microstructure. The H_c(T) exhibits a transformation from abnormal to normal behavior with an increase in the ratio of z from 7.0 to 8.5. For a given z, there exists a critical Cu amount below which the abnormal H_c(T) is observed. This critical amount of Cu increases with decreasing z ratio. Additionally, the temperature of the H_c peak at high temperature decreases with increasing Cu content. The magnets below the critical Cu value with different Zr also exhibit an abnormal H_c(T) behavior. However, Zr does not cause an obvious change of H_c(T). In the magnets with different Fe, the room temperature coercivity increases, but the peak of H_c at high temperature decreases with increasing Fe content. An increase in the amount of Fe lowers the anisotropy field and the Curie temperature of the 2:17 matrix phase, resulting in a change of H_c(T).