Influence of Ho spontaneous aggregation on the coercivity and magnetic domain movement of sintered NdY-Fe-B magnets

Development of NdY-Fe-B magnets not only reduces the cost of Nd-Fe-B type magnets but also promotes the balanced utilization of rare-earth resources. However, the lower coercivity of NdY-Fe-B magnets hinders their further development. This study investigated the coercivity of NdY-Fe-B magnets via intergranular doping of Ho76Al12Ga12 powders. Although this process improved the coercivity, the remanence substantially deteriorated with the increasing content of the Ho76Al12Ga12 alloy. A coercivity of 1.37 T was achieved in a NdY-Fe-B magnet with a Ho76Al12Ga12 alloy doping of 7 wt%, showing a coercivity increment (Delta Hcj) of 0.64 T compared to the original magnet. This can be attributed to the observed microstructural and elemental distributions, as well as the analysis of the magnetic domain wall movement. An abnormal Ho-biased layer is observed between the Y-rich core and the Ho-rich shell in the matrix grains, exhibiting a higher anisotropy field compared than the shell layer. Further analysis revealed that the movement of magnetic domain wall movement was obstructed by the Hobiased layer, demonstrating a domain-wall pinning effect within the matrix grains. Additionally, the formation of a Ho-rich shell in the outer area of the 2:14:1 matrix grain and the presence of a continuous uniform grain boundary phase were found to be important for improving both coercivity and thermal stability.