EFFECT OF Zr ON THE MICROSTRUCTURE, MAGNETIC DOMAIN STRUCTURE, MICROCHEMISTRY AND MAGNETIC PROPERTIES IN Sm(Co_(bal), Cu_(0.088), Fe_(0.01), Zr_x)_(8.5) MAGNETS

摘要

The effect of Zr on the microstructure, microchemistry, and coercivity of Sm(Co_(bal), Cu_(0.088), Fe_(0.01), Zr_x)_(8.5) (x=0-0.10) magnets has been systematically investigated. The presence of Zr is responsible for the formation of lamella structure. With increasing Zr content, a cellular-like structure gradually develops while the density of lamella phase increases. A proper Zr content (0.015-0.060 at%) is a key to form a complete and uniform cellular structure. Less Zr content leads to incomplete cellular structure, while more Zr content leads to inhomogeneous cellular structure and formation of 2:7 phases. 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 morphology. Higher coercivity is obtained in samples where the domain walls are pinned at cell boundaries. For the Zr-free or higher Zr samples, domain walls nucleated at grain boundaries are responsible for the reduction in coercivity. During isothermal aging, at a fixed Zr content, the coercivity is developed with increasing aging time. In higher Zr content sample the coercivity reaches its maximum value early. For lower Zr content samples, both the cell size and density of lamella phase significantly increase with aging time. For the higher Zr content sample, with the exception of a slight increase of cell size, the structure morphology is nearly the same, but the Cu content in the cell boundaries increases with aging time. These results show clearly 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.