Dependence of anisotropy and coercivity on microstructure in HDDR Nd―Fe―B magnet

Abstract The effect of microstructure on the anisotropy and the coercivity in HDDR Nd–Fe–B magnet has been investigated by putting forward a theoretical anisotropy model influenced simultaneously by both the structure defect and the exchange coupling interaction. The results showed that the coercivity is greatly influenced by both the defect thickness, r 0 , and the anisotropy constant, K 1 (0), at grain surface. Coercivity is determined by the pinning mechanism when K 1 (0) ≤ 0.4 K 1 and r 0 K 1 (0) > 0.4 K 1 . However, it is controlled by the nucleation mechanism when K 1 (0) ≤ 0.4 K 1 and r 0  > 8 nm. For all values of K 1 (0), the coercivity first increases, reaches the maximum and then decreases with increasing r 0 , and its maximum value decreases with increasing K 1 (0). The maximum coercivity is 1102 KA/m while K 1 (0) = 0 and r 0 is close to the thickness of domain wall (∼4 nm), which is consistent with experimental results given by other authors.