Quantitative evaluation of site preference in Dy-substituted Nd2Fe14B

We compared site occupancies of Dy ion in (Nd_1−xDy_x)₂Fe₁₄B (x=0.133,0.5$x=0.133,0.5$), derived from powder neutron diffraction data, with theoretical results obtained from a combination of ab initio   and thermodynamic calculations. Neutron diffraction showed that the Dy ion favors the 4f$4f$ site with smaller Wigner-Seitz atomic cell for both samples, as partly reported in literature [Yelon et al., J. Appl. Phys. 60 (1986) 2982]. This site preference was quantitatively reproduced by combining ab initio calculation, giving Gibbs energy at zero temperature, and thermodynamic calculation, considering the entropy effect in the heat treatment process of the samples. The good agreement between experimental and theoretical values confirms the validity of this combined method to evaluate the site preference of (Nd_1−xDy_x)₂Fe₁₄B with arbitrary Dy concentration.

Part of this work was supported by the Elements Strategy Initiative Center for Magnetic Materials(ESICMM) under the outsourcing project of the Ministry of Education, Culture, Sports, Science, andTechnology (MEXT). The sample fabrication has been partly performed under the Magnetic Materialsfor High-Efficient Motors (MagHEM) project. The authors would like to thank Dr. Kazuhiro Hono andDr. Masao Yano for supplying us with samples, and Dr. Thomas Hansen for supporting the experimentat D20. The authors are also indebted to Prof. Hisazumi Akai and Dr. Masako Ogura for stimulatingand helpful discussions.