Computational analysis of microstructure-coercivity relation in multi-main-phase Nd-Ce-Fe-B magnets

Multi-main-phase (MMP) (Nd, Ce)₂Fe₁₄B magnets containing both Nd-rich shell covering Ce-rich core and Ce-rich shell covering Nd-rich core within the 2:14:1 grains have shown much superior coercivity to the single-main-phase ones with homogeneous Nd/Ce distributions. To understand how these core-shell grains and the microstructure of grain boundaries (GBs) influence the coercivity of MMP Nd-Ce-Fe-B magnets, micromagnetic simulation was carried out through constructing a 3D finite element model. The influences of physical dimension and magnetism of the GBs, Nd or Ce-rich shell thickness, and Ce substitution level on coercivity were all analyzed. It was found that thick and nonmagnetic GB layers play an essential role in enhancing the coercivity as the intergrain exchange coupling can be weakened. Thicker Nd-rich or Ce-rich 2:14:1 grain shells are not necessary for enhancing the coercivity. In addition, with the increase of Ce content, the coercivity does not deteriorate linearly but exhibits an abnormal enhancement around 20 vol.% substitution. The good agreement with the experiments makes these findings as important insights of understanding the coercivity mechanism of MMP RE-Fe-B magnets.