Determination of Dy substitution site in Nd_2−xDy_xFe₁₄B by HAADF-STEM and illustration of magnetic anisotropy of “g” and “f” sites, before and after substitution

Nd₂Fe₁₄B and Nd_2−xDy_xFe₁₄B (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 Nd₂Fe₁₄B/Nd_2−xDy_xFe₁₄B. Accurate site for the Dy substitution in Nd₂Fe₁₄B 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_1.75Dy_0.25Fe₁₄B (23.48 μB) and Nd_1.5Dy_0.5Fe₁₄B (21.03 μB) as compared to Nd₂Fe₁₄B (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 Nd₂Fe₁₄B, Nd_2−xDy_xFe₁₄B, Nd (“f” site), Nd (“g” site) and Dy (“f” site) was recorded for all angles between 0° and 180°.