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Page 6 of 14 Kautsar et al. Energy Mater. 2025, 5, 500129 https://dx.doi.org/10.20517/energymater.2025.26

Figure 2. (A) BF-TEM image of the hot-pressed (HP) magnet; along with BSE-SEM images of (B) the hot-deformed (HD) magnet; (C)
Dy-Nd-Cu grain boundary diffusion processed (GBDP); (D) Nd-Cu GBDP; and (E) Pr-Cu GBDP HD magnets. BSE-SEM: Backscattered
electron scanning electron microscopy; BF-TEM: bright-field transmission electron microscopy.

Figure 3. STEM-HAADF images and STEM-EDS elemental maps showing the distribution of constituent and diffused elements for (A)
the HD magnet; (B) the Dy-Nd-Cu GBDP HD magnet; (C) the Nd-Cu GBDP HD magnet; and (D) the Pr-Cu GBDP HD magnet. HD:
Hot-deformed; GBDP: grain boundary diffusion process; STEM-HAADF: high-angle annular dark field scanning transmission electron
microscopy; STEM-EDS: STEM-energy dispersive X-ray spectroscopy.

and (Nd,Pr) Fe B phase on the outer surfaces of Nd Fe B grains in the Dy-Nd-Cu and Pr-Cu GBDP
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magnets, respectively [Figure 3B and D]. Since Dy Fe B and Pr Fe B exhibit larger magnetic anisotropy
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[52]
fields than Nd Fe B at room temperature , the formation of Dy-rich and Pr-rich shell regions in the Dy-
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Nd-Cu and Pr-Cu GBDP magnets contributes to a higher coercivity compared to the Nd-Cu GBDP magnet.