Improving the magnetic properties of sintered Nd-Ce-Fe-B magnets via grain boundary diffusion with Pr60Tb10Cu30 alloy

Grain boundary diffusion process (GBDP) was performed on sintered Nd-Ce-Fe-B magnets with different Ce concentrations, 0 wt.% (Ce0), 5 wt.% (Ce5), 10 wt.% (Ce10) and 15 wt.% (Ce15). After GBDP with Pr60Tb10Cu30 alloy the coercivity increments were 899 kA/m, 646 kA/m, 452 kA/m and 397 kA/m for the Ce0, Ce5, Ce10, and Ce15 magnets, respectively. The corresponding remanence increments were −0.06 T (Ce0), 0 (Ce5), 0.01 T (Ce10) and 0.05 T (Ce15). The demagnetization curve squareness factors of the Ce-containing magnets (Ce5, Ce10 and Ce15) are far higher than that of the Ce-free magnet (Ce0) after GBDP. Interestingly, the demagnetization curve squareness factors of the Ce10 and Ce15 magnets can be improved after GBDP. Microstructure analysis indicates that the (Pr, Tb)-rich shells surrounding the 2:14:1 grains were formed. The enrichments of Pr and Tb in the shells contribute to the coercivity increment while the enrichment of Pr in the shells facilitates the remanence improvement in the Nd-Ce-Fe-B magnets. The enrichment of Tb in the surface coarse grains eliminates the adverse impact of surface grain coarsening on the coercivities and demagnetization curve squareness factors. The enhancement of Ce concentration in sintered Nd-Ce-Fe-B magnets can suppress the lattice diffusion near the surface and improve the distribution homogeneity of the (Pr, Tb)-rich shells.