Thickness-dependent coercivity mechanism and hysteresis loops in hard/soft magnets

Two models are established to reveal the underlying coercivity mechanism for SmCo/Fe films, where one model considers a transition layer between hard and soft layers, while the other model does not consider this layer. Based on the two models, hysteresis loops, nucleation fields and coercivity are obtained by one-dimensional (1D) and three-dimensional (3D) micromagnetic methods. In particular, the calculated nucleation fields (H-N) and coercivity (H-C) match very well with the experimental data. It is found that the increase in the soft phase thickness (L-s) leads to a transition of the coercivity mechanism from nucleation to pinning. Such a pinning is inherently related to nucleation and has both attributes of traditional nucleation and pinning, called as a hybrid coercivity mechanism here. It is general for all hard/soft composites and can be extended to single-phased permanent magnets where defects are inevitable.