Magnetic Properties of Ce₈₅Al₁₅ Doped NdFeB Sintered Magnet by Grain Boundary Diffusion of Tb₇₀Cu₃₀ Powders

Magnetic properties' modification and coercivity enhancement of NdFeB sintered magnets prepared by the dual-alloy (DA) sintering together with grain boundary diffusion (GBD) treatment are demonstrated. For the original NdFeB magnet, ( BH ) _max of 51.4 MGOe and ${_{i}}H_{\mathrm {c}}$ of 14.9 kOe are obtained. For the magnet made with the same composition as the former but doped with Ce ₈₅ Al ₁₅ (CeAl) powders, magnetic isolation due to the distribution of Ce and Al at GB increases the coercivity effectively, yet few Ce entering into grain interior decreases $B_{\mathrm {r}}$ , ( BH ) _max , and Curie temperature slightly. In addition, the coercivity of the above magnets can be further enhanced to 22.7–25.1 kOe by GBD with different amounts of Tb ₇₀ Cu ₃₀ (TbCu) powders. The clear core–shell structure, which consists of (Nd, Tb) ₂ Fe ₁₄ B phase with higher magnetocrystalline anisotropy field ( $H_{\mathrm {A}}$ ) as the shell and Nd ₂ Fe ₁₄ B phase as the core, is observed. CeAl helps to form a continuous and smooth GB. The diffusion source of TbCu could infiltrate into the magnet along such smooth GB and form a homogeneous core–shell structure. As a result, coercivity is remarkably enhanced from 14.9 kOe for DA sintered magnet with 2 wt% CeAl to 25.1 kOe for the magnet GBD with TbCu. Most importantly, various levels of NdFeB magnets, such as 52M, 35–50SH, and 45UH, could be easily attained by modifying the amounts of CeAl for DA sintered magnets and/or GBD with TbCu powders.