Unlocking high performance in Nd-Ce-Fe-B magnets: a preheating-induced REFe2 diffusion barrier approach to overcome the coercivity-remanence trade-off

: High Ce content in Nd-Ce-Fe-B magnets introduce the low magneto-crystalline anisotropy Ce 2 Fe 14 B phase and the high-melting CeFe 2 phase, which act as barriers to heavy rare earth (HRE) grain boundary diffusion. Conventional approaches attempt to eliminate or modify this phase to mitigate the hindrance. However, this work instead employs a preheating treatment (PHT) to tailor its distribution, thereby transforming the refractory CeFe 2 phase from a physical obstacle into an active regulator of diffusion. The results demonstrate that PHT modifies subsequent diffusion kinetics by thickening the surface CeFe 2 layer. Compared with conventional direct diffusion, PHT significantly restricts the intragranular diffusion of Tb into the matrix phase, thereby mitigating the magnetic moment cancellation induced by Tb-Fe antiferromagnetic coupling. Concurrently, this strategy spatially confines Tb to the grain boundaries, forming a thin, continuous Tb-rich shell and altering the rare-earth element distribution near Zr-rich intergranular regions to yield a steeper concentration gradient. These engineered microstructural features enhance magnetic decoupling between adjacent matrix grains and strengthen domain wall pinning. Regarding thermal stability, the thinner Tb-rich shell and lower Tb content accelerate remanence degradation at elevated temperatures, increasing | α |. Conversely, the continuous intergranular phase and steep gradient stabilize reverse domain nucleation suppression at high temperatures, decreasing | β |. Thus, the PHT+Tb 80 diff. strategy sacrifices remanence thermal stability to gain higher room-temperature remanence and improved coercivity thermal stability.