Sintered NdFeB magnets with Tb - Dy double-layer core/shell structure were fabricated by double alloy method and grain boundary diffusion

The high magnetocrystalline anisotropy of the Dy or Tb core shell structure formation can greatly improve the coercivity of sintered NdFeB magnets. In this work, we fabricated the base NdFeB magnet with Dy core-shell structure by double alloy method, and then diffusion TbH₂ on the base NdFeB magnet. The result showed that compared with the base magnets, the coercivity of diffusion magnet increased by 7.6 kOe with a slight reduction in remanence. The thermal stability and the microstructure of the diffused magnet improved significantly. Microstructure analysis found that a Tb - Dy double-layer core-shell structure formed around Nd₂Fe₁₄B grains after diffusion. The double-layer core-shell structure can effectively prevent the reversed magnetic domain nucleation, and improve the utilization of heavy rare earths. This work may shed light on developing low heavy rare earth NdFeB magnets with high coercivity through controlling core-shell structure.