Overcoming Refractory REFe ₂ Phase Bottleneck in High‐Ce Nd–Ce–Fe–B Magnets via Praseodymium‐Induced Phase Transformation: Enabling Liquid‐Phase Grain Boundary Diffusion of Dysprosium

Abstract High‐cerium Nd–Ce–Fe–B magnets suffer from severe coercivity degradation, primarily stemming from the poor intrinsic magnetic properties of the Ce ₂ Fe ₁₄ B phase. Although dysprosium (Dy) grain boundary diffusion (GBD) has emerged as a critical strategy for coercivity enhancement, its effectiveness is significantly hindered by the presence of refractory rare‐earth REFe ₂ phases. To address this bottleneck, the Dy _x Pr _80−x Al ₁₀ Ga ₁₀ (x = 0, 20, 40, 80 at.%) diffusion sources are designed, where Pr (praseodymium), Al, and Ga synergistically transform REFe ₂ into low‐melting‐point PrGa‐rich phases, thereby constructing efficient liquid‐phase diffusion pathways for Dy. First‐principles calculations indicate that the positive formation energy of Pr doped CeFe ₂ phase destabilizes the (Pr, Ce)Fe ₂ phase, facilitating the liquid‐phase transformation below the GBD temperature (930 °C). Correlative microstructural analyses demonstrate that these liquid‐phase pathways enable a higher Dy diffusion coefficient and more uniform core–shell structures, effectively suppressing reversed magnetic domains expansion and enhancing coercivity. For magnets with 26, 39, 45, and 61 wt.% Ce‐substitution, the robust coercivity increments of 7.0, 5.4, 5.5, and 3.9 kOe are achieved, respectively, using only ≈0.39 wt.% Dy. This strategy overcomes the long‐standing barrier of REFe ₂ phases in GBD and provides a scalable route for producing Ce‐rich Nd–Ce–Fe–B magnets with high performance.