Simultaneous enhancement of coercivity and saturation magnetization in high-performance anisotropic NdFeB thick films with a Dy diffusion layer

Abstract

Generally, the addition of the Dy element leads to a decrease of the saturation magnetization and the remanent magnetization in NdFeB films due to its antiferromagnetic coupling with Fe. However, in this study, upon increasing the ratio of Dy in the Nd–Dy diffusion layers of NdFeB thick films, the saturation magnetization has an anomalously slight enhancement, while the coercivity and remanent magnetization have a large enhancement. The increase of coercivity is attributed to the decoupling between Nd₂Fe₁₄B grains and the enhanced pinning effect. Microstructural analysis revealed a layered structure composed of spherical Nd₂Fe₁₄B grains at the location of the Dy diffusion layer, which is attributed to the Dy diffusion layer reacting with the region of Nd element aggregation during the annealing process, facilitating transformation into Nd₂Fe₁₄B grains. The increase of the proportion of Nd₂Fe₁₄B grains results in a slight enhancement of saturation magnetization. By this method, we obtained a high-performance anisotropic NdFeB thick film of 28.7 μm with a coercivity of 2.46 T and a surface field of 163 Oe. This work establishes a microscale growth model for NdFeB thick films and helps to prepare high-performance NdFeB thick films applicable directly to microelectromechanical systems.