Micromagnetic simulations of Nd-Fe-B hot-deformed magnets subjected to eutectic grain boundary diffusion process

The grain boundary diffusion process (GBDP) is one of the most efficient treatments for increasing the coercivity (Hc) of Nd-Fe-B magnets. However, this enhancement typically occurs at the expense of remanence (Mr). In this study, micromagnetic simulations were performed to quantify this tradeoff in hot-deformed Nd-Fe-B magnets subjected to the GBDP using a Nd-based eutectic alloy. The GBDP was imitated in a series of models with a gradually increasing volume fraction of the infiltrated Nd-rich nonmagnetic phase. This infiltration reduced the remanence and grain connectivity via the remaining thin magnetic intergranular phase (IGP), which in turn increased the coercivity. We distinguished between the roles of exchange and magnetostatic interactions in this coercivity enhancement. Furthermore, the simulated Mr vs. Hc curves defined realistic limits for coercivity that depended on the IGP magnetization, which was estimated to be 0.9 ± 0.1 T by reproducing experimental Mr vs. Hc data from the literature.