The role of anti-core-shell structure caused by over-saturation diffusion of heavy rare earths in Nd-Fe-B magnets: a micromagnetic simulation study

作者：Liu, Xiangyi; He, Jiayi; Yuan, Bin; Liu, Zhongwu^*

来源：Applied Physics A: Materials Science and Processing , 2023, 129(9): 619.

DOI：10.1007/s00339-023-06905-6

• Nd-Fe-B magnets
• Grain boundary diffusion
• Anti-core-shell structure
• Micromagnetic simulation
• Heavy rare earth

Grain boundary diffusion (GBD) process is an effective method to fabricate high-coercive Nd-Fe-B magnets with less consumption of heavy rare earth (HRE). By this approach, HRE-rich shell forms around the Nd2Fe14B grain, which can hinder the magnetic reversal starting at the edge of the grains and enhance the coercivity of whole magnet. Recently, an anti-core-shell structure was observed in the HRE diffused magnets after over-saturated diffusion, where the HRE concentration in the core is even higher than that in the shell. In this work, the effects of the anti-core-shell structure on the magnetization reversal and magnetic properties of diffused magnet have been clarified by micromagnetic simulations. Three-dimension models were established to analyze the demagnetization process. The results indicate that the anti-core-shell structure leads to a large stray field, which will accelerate the magnetization reversal of the whole magnet. As a result, the beneficial effect of HRE GBD on the coercivity has been reduced. Combined with the existing experimental results, the formation of anti-core-shell structure should be avoided during diffusion. Hence, appropriate diffusion time and diffusion source dosage should be selected for GBD process in order to obtain high-performance products and efficiently use the HRE resources.