The role of local anisotropy profiles at grain boundaries on the coercivity of Nd₂Fe₁₄B magnets

We present numerical evidence from atomistic calculations that the coercivity of high-performance NdFeB-sintered-magnets (<20% of the theoretical Stoner–Wolfarth-limit) can be explained by a distorted region of Nd₂Fe₁₄B at grain boundaries, which has a reduced local magnetic anisotropy. We show that depending on the boundary composition of fcc-NdO and hcp-Nd₂O₃, the thickness of this region of reduced anisotropy varies between 0.4 for fcc and 1.6 nm for the hcp phase. For NdO, the distortions are mostly confined in the fcc-NdO-phase but equally distributes in both the hcp-Nd₂O₃ and Nd₂Fe₁₄B. The experimentally measured coercivity of 1.25 T can be understood when taking this distortion and magnetostatic effects into account.