Effect of TbF3 diffusion on the demagnetization behavior and domain evolution of sintered Nd–Fe–B magnets by electrophoretic deposition


 We studied the magnetic properties and domain evolution of the annealed and TbF3-diffused sintered Nd–Fe–B magnets using electrophoretic deposition method. After TbF3 diffusion, the coercivity increased significantly and the increment was 9.9 kOe, and microstructure analysis suggested that Tb favored to form the (Nd, Tb)2Fe14B shell phase in the outer region of the matrix grains. The first magnetization reversal and the dynamic successive domain propagation process was detected through the magneto-optical Kerr microscope. For the TbF3-diffused magnet, the magnetization reversal appeared at a larger applied field and the degree of simultaneous magnetization reversal decreased compared to the annealed magnet. During demagnetization after being fully magnetized, the formation of domain wall motion (DWM) in reproduced multi-domain regions was observed by the step method. And the maximum polarization change resulted from the reproduced DWM was inversely related to the coercivity. The increment of coercivity for the diffused magnet was mainly attributed to the harder nucleation of the magnetic reversed region owing to the improved magnetocrystalline anisotropy field by Tb diffusion.