Enhanced magnetic properties and thermal stability of spark plasma sintered multi-main-phase Nd-Ce-Fe-B magnet via co-adding DyF₃ and Cu

Low coercivity and poor thermal stability are still the main challenges for practical application of low-cost Nd-Ce-Fe-B magnet. To solve these challenging problems, a strategy to simultaneously improve the coercivity and thermal stability of Nd-Ce-Fe-B magnet through combining the nanocrystalline multi-main-phase (MMP) structure and grain boundary engineering is demonstrated. In this study, nanocrystalline MMP Nd-Ce-Fe-B magnet was grain boundary engineered by co-adding DyF₃ and Cu powders. The results show that the intrinsic coercivity H_cj is significantly improved, and meanwhile optimum maximum energy product (BH)_max is achieved at 2 wt% DyF₃-Cu. Moreover, the superior reversible temperature coefficients of H_cj (β) and B_r (α) are both achieved, implying the improved thermal stability for the DyF₃-Cu added magnet. Microstructural and compositional characterizations indicate that the modified RE-rich phase, the inhibited abnormal grain growth near the flake boundary, and the diffused Dy towards main phase grains are the main reasons for simultaneously enhanced magnetic properties and thermal stability. Thus, combining the nanocrystalline MMP structure and grain boundary engineering will be a promising approach for preparing thermally-stable high-performance Nd-Ce-Fe-B magnet.