The performance of sintered NdFeB magnets, critical for green energy technologies, hinges on enhancing their coercivity without sacrificing remanence. A breakthrough lies in the synergistic diffusion of Dy and Tb, two heavy rare-earth elements that “unlock” the grain boundary channel. Thermodynamically, Dy and Tb exhibit a strong preference for substituting Nd sites in the Nd2Fe14B lattice, driven by negative substitution energies. This atomic-level affinity is amplified by concentration gradients during diffusion, where Tb—with its higher supply in a 3 μm Dy/11 μm Tb bilayer structure—initially outcompetes Dy at the magnet surface, creating a dynamic interplay of elemental distribution. Equally pivotal is the role of melting point differences: Tb has a lower melting point than Dy (1356°C vs. 1407°C), which facilitates the earlier formation of a liquid grain boundary phase. This liquid pathway accelerates the migration of both elements along grain boundaries. Together, these effects yield magnets with optimized coercivity and diffusion efficiency, paving the way for high-performance NdFeB magnets. (http://doi.org/10.1002/rar2.70238)
Chang et al. (Mon,) studied this question.