Coercivity enhancement mechanism of grain boundary diffused Nd-Fe-B sintered magnets by magnetic domain evolution observation

• Published in: Journal of rare earths 2021-06, Vol.39 (6), p.682-688
• Main Authors: Liu, Weiqiang, Li, Yi, Wu, Dan, Yue, Ming, Wang, Zhanjia, Zha, Shanshun, Liu, Youhao, Yi, Xiaofei, Du, Yihui
• Format: Article
• Language: English
• Subjects: Coercivity; Core-shell structure; Grain boundary diffusion; Heavy rare earth; Magnetic domain reversal; Nd-Fe-B sintered magnet
• ISSN: 1002-0721; 2509-4963
• DOI: 10.1016/j.jre.2020.05.011

The grain boundary diffusion (GBD) technology was used to prepare high performance Nd-Fe-B sintered magnets by NdH3 and TbH3 nanoparticle diffusion. The factors affecting the coercivity of GBD magnets include distribution of rare earth rich grain boundary phase and substitution of the heavy rare earth. In order to distinguish the influence of various factors on the coercivity, the microstructure and magnetic domain evolution of the original, reference, Nd-diffused, and Tb-diffused magnets were analyzed. The core-shell structure formed by heavy rare earth substitution is the main factor of coercivity enhancement, and it can transform the magnetic domain reversal mode from easy-nucleation (EN) to difficult-nucleation (DN). With increasing the diffusion depth, the shell of the core-shell structure gradually becomes thinner, DN grains gradually decrease while the EN grains gradually increase, indicating that the magnetic domain reversal mode is directly related to the core-shell structure. The demagnetization curves of original, reference, Nd-diffused, Tb-diffused magnets (a), the microstructure (b) and MOKE images of magnetic domain evolution during demagnetization (c) of Tb-diffused magnets, grains in the blue circle are called easy-nucleation grains, while grains in the red circle are called difficult-nucleation grains. [Display omitted] 1.The contributions of microstructure, GB thickening, and HRE substitution to coercivity were revealed.2.The magnetic domain evolution of GBD magnets at different diffusion depths was obtained.3.The correlation between magnetic domain reversal behavior and microstructure of GBD magnets was established.