[P1] RE-Fe-B Magnets

[P1-10] A macroscopic perspective on the sintered Nd-Fe-B magnets prepared by Tb grain boundary diffusion

*Jinghui Di¹, Hui Meng², Chaoyue Zhang³, Min Zou⁴ (1. Hangzhou Magmax Technology Co., Ltd. (China), 2. Hangzhou Foresee Group Holdings Co., Ltd. (China), 3. Hangzhou Kede Magnetic Components Co., Ltd. (China), 4. Lab Magnetics Inc. (United States of America))

Keywords:

Nd-Fe-B,grain boundary diffusion,macroscopic demagnetization,thick GBD magnets

Heavy rare earths grain boundary diffusion in sintered Nd-Fe-B has attracted tremendous amount of attention due to the achieved broader demagnetization curves and competitive cost efficiency of Dy/Tb[1, 2]. The enhanced magnetic performance of the GBD magnets can be attributed to their unique composition and distribution of materials. Within the microstructure, a GBD magnet is characterized by the presence of (Tb/Dy,Nd)2Fe14B shells enveloping the Nd2Fe14B cores. This arrangement serves to enhance the local anisotropy within the material. While at the macroscale, it is augmented by the gradation of Tb/Dy concentration from the surface inward, resulting in a differentiated coercivity within the material. Despite these advancements, lingering challenges remain in pinpointing the exact locations where magnetic nucleation begins during demagnetization, a pivotal aspect in fine-tuning magnetic performance. Prior studies using magnetic force microscopy and magneto-optical Kerr effect microscopy have investigated potential nucleation sites, tending toward the edges of the core or the (Tb/Dy)2Fe14B shells that exhibit a higher anisotropy field [3]. In this context, the interaction between the high coercivity layers, which ostensibly act as shields, and the lower coercivity layers, where magnetization reversal is likely to initiate, has been a topic of extensive debate [4]. Nevertheless, investigations into macroscopic demagnetization processes have been conspicuously absent and a comprehensive examination of the underlying coercivity mechanisms in GBD magnets is still needed. In this study, we report the macroscopic demagnetization [5] of the Tb GBD magnets and a method to make thick GBD blocks. The broader application area can be achieved together with a verification method for the high-performance and GBD magnets.

References
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[2] K. Loewe, D. Benke, C. Kübel, T. Lienig, K.P. Skokov, O. Gutfleisch, Grain boundary diffusion of different rare earth elements in Nd-Fe-B sintered magnets by experiment and FEM simulation. Acta Materialia 124 (2017) 421-429.
[3] J. Fliegans, C. Rado, R. Soulas, L. Guetaz, O. Tosoni, N.M. Dempsey, G. Delette, Revisiting the demagnetization curves of Dy-diffused Nd-Fe-B sintered magnets. Journal of Magnetism and Magnetic Materials 520 (2021) 10.
[4] T. Helbig, K. Loewe, S. Sawatzki, M. Yi, B.X. Xu, O. Gutfleisch, Experimental and computational analysis of magnetization reversal in (Nd,Dy)-Fe-B core shell sintered magnets. Acta Materialia 127 (2017) 498-504.
[5] J. Di, H. Liu, H. Meng, C.H. Chen, M. Zou, X. Wu, C. Yu, C. Zhang, S. Jia, Q. Wei, B. Zhang, Macroscopic demagnetization of the sintered Nd-Fe-B magnets prepared by Tb grain boundary diffusion. Scripta Materialia 247 (2024) 116113.