Coercivity enhancement in Nd-Fe-B magnets via Sn-doped DyF3 grain boundary diffusion

Grain boundary diffusion using rare-earth (RE) alloys or compounds is now a popular technique in improving the hard magnet properties of sintered Nd-Fe-B magnets. While DyF 3 serves as a critical industrial diffusion source for coercivity enhancement, its high decomposition temperature and poor penetration efficiency limit practical performance gains. To address this, we propose a Sn-assisted DyF 3 grain boundary diffusion process (GBDP) for sintered Nd-Fe-B magnets. By incorporating cost-effective Sn additives into DyF 3 , we achieved a substantial coercivity increase of 4.77 kOe (reaching 20.61 kOe in 8 mm magnets), overcoming DyF 3 ′s intrinsic diffusion limitations. Systematic characterization via electron probe microanalysis and transmission electron microscopy revealed that Sn increases the distribution range of Dy, forming closure core–shell structures. Micromagnetic simulations further confirmed that defect-free Dy-rich shells suppress reverse domain nucleation, directly correlating with the observed coercivity enhancement. This Sn-mediated GBDP strategy enables efficient utilization of DyF 3 in industrial-scale magnet production, providing a scalable pathway to optimize high-performance magnets while mitigating rare earth cost pressures.