永久磁石におけるナノ組織と磁気特性

摘要

Interests in the coercivity mechanism of Nd-Fe-B based permanent magnets have recently been revived due to the increasing demand for high coercivity Nd-Fe-B based permanent magnets for automotive applications.This paper reviews our recent investigations on the microstructures of commercial sintered magnets and hydrogen disproportionation desorption recombination (HDDR) powder by high resolution scanning electron microscopy, transmission electron microscopy and atom probe tomography. Continuous thin layers of a Nd- and Cu-rich amorphous phase were found along the grain boundaries of optimally annealed sintered magnets. Although Nd-rich layer was also observed along the grain boundaries of optimally processed HDDR powder, it was crystalline with much less Nd-enrichment. Based on these nanostructure characterization results, we discuss how to enhance the coercivity Nd-Fe-B based magnets without Dy.