Effect of Zr on the microstructure, magnetic domain structure, microchemistry and magnetic properties in Sm(CobalCu0.08Fe0.10Zrx)8.5 magnets

Abstract

The effect of Zr on the microstructure, microchemistry and coercivity of Sm(CobalCu0.08Fe0. 10Zrx)8.5 (x = 0–0.10) magnets has been systematically investigated. The presence of Zr is responsible for the formation of the lamella structure. With increasing Zr content, a cellular-like structure gradually develops while the density of the lamella phase increases. A proper Zr content (0.015–0.060 at.%) is the key to form a complete and uniform cellular structure. Microchemistry data show that the Cu content in the cell boundaries in the magnet with 0.04 at.% Zr is higher than that with 0.015 at.% Zr, although both samples have similar microstructure morphologies. Higher coercivity is obtained in samples where the domain walls (DWs) are pinned at cell boundaries. For Zr-free or higher Zr samples, DWs nucleated at grain boundaries are responsible for the reduction in coercivity. During isothermal ageing, at a fixed Zr content, the coercivity is developed with increasing ageing time. These results clearly show that Zr plays an important role in the formation of a uniform cellular structure with the right microchemistry and that a critical amount of Zr is needed for the optimum magnetic properties.