Overcoming grain boundary diffusion challenges in Ce-based sintered magnets: La substitution as a pathway to enhanced coercivity

This study addresses the challenges of low diffusion efficiency and minimal coercivity enhancement in Ce-based sintered magnets through the grain boundary diffusion (GBD) technique. By conducting a comprehensive experimental and theoretical analysis of La-substituted Ce-based magnets, we have uncovered the detrimental impact of the REFe ₂ phase on grain boundary (GB) structure and the diffusion process. Our findings confirm that an optimal La substitution for Ce effectively mitigates these issues. This substitution reduces the stability and Dy content of the REFe ₂ phase while enhances the continuity of the lamellar GB phases. Consequently, the Dy element utilized in the diffusion process achieves a greater depth of penetration and a more uniform distribution, leading to a significant coercivity increase of 4.28 kOe in the GBD magnet with the ideal La content, an 8.35 % improvement over the La-free magnet. This research reveals the underlying mechanisms and offers a viable solution for enhancing the GBD effect in Ce-based sintered magnets. Furthermore, it underscores the pivotal interplay between phase stability, grain boundary structure, and diffusion dynamics in the advancement of next-generation GBD techniques for permanent magnets.