Effect of cerium distribution on Dy-containing grain boundary diffusion in high Ce-content sintered magnets

Obtaining high magnetic properties in high Ce-content magnets is essential to expand the widespread application of low-cost magnets. In this study, high Ce-content magnets with up to 45% Ce substitution for Nd were prepared by combining the single/dual/multi-main-phase processes with the Dy-containing grain boundary diffusion process (GBDP). The effects of base magnets with different Ce distributions on GBDP were systematically investigated. Magnetic properties and microstructure analysis reveal that high-performance multi-main-phase (MMP) diffused magnets with remanence (Br) up to 12.52 kGs, coercivity up to 16.08 kOe, and maximum magnetic energy product up to 36.44 MGOe are obtained, which is attributed to the regulation of Ce by the MMP process, and the optimization of microstructure by Gd-Cu alloy. Meanwhile, the diffusion efficiency is significantly improved because of Ce being restricted to the grain core, which promotes the formation of a continuous structure at the grain boundaries, and the formation of a continuous multilayer shell grain structure with high anisotropy field, while the Br of the diffused magnet is maintained. Besides, magnetic domain analysis shows that the MMP diffused magnet effectively suppresses the nucleation of demagnetized domains and enhances the pinning effect of domain walls. The study establishes an experimental foundation for the development of sintered high Ce-content magnets showcasing superior performance.