Determination of Dy substitution site in Nd 2−x Dy x Fe 14 B by HAADF-STEM and illustration of magnetic anisotropy of “g” and “f” sites, before and after substitution

Nd 2 Fe 14 B and Nd 2−x Dy x Fe 14 B (x = 0.25, 0.50) particles were prepared by the modified co-precipitation followed by reduction–diffusion process. Bright field scanning transmission electron microscope (BF-STEM) image revealed the formation of Nd–Fe–B trigonal prisms in [− 101] viewing zone axis, confirming the formation of Nd 2 Fe 14 B/Nd 2−x Dy x Fe 14 B. Accurate site for the Dy substitution in Nd 2 Fe 14 B crystal structure was determined as “f” site by using high-angle annular dark field scanning transmission electron microscope (HAADF-STEM). It was found that all the “g” sites are occupied by the Nd, meanwhile Dy occupied only the “f” site. Anti-ferromagnetic coupling at “f” site decreased the magnetic moment values for Nd 1.75 Dy 0.25 Fe 14 B (23.48 μB) and Nd 1.5 Dy 0.5 Fe 14 B (21.03 μB) as compared to Nd 2 Fe 14 B (25.50 μB). Reduction of magnetic moment increased the squareness ratio, coercivity and energy product. Analysis of magnetic anisotropy at constant magnetic field confirmed that “f” site substitution did not change the patterns of the anisotropy. Furthermore, magnetic moment of Nd 2 Fe 14 B, Nd 2−x Dy x Fe 14 B, Nd (“f” site), Nd (“g” site) and Dy (“f” site) was recorded for all angles between 0° and 180°.