Nitrogen as the best interstitial dopant among X = B, C, N, O, and F for strong permanent magnet NdFe11TiX: First-principles study

We study magnetic properties of NdFe11TiX, where X = B, C, N, O, and F, by using first-principles calculations based on density functional theory. Its parent compound NdFe11Ti has the ThMn12 structure, which has the symmetry of space group I4/mmm, No. 139. The magnetization increases by doping B, C, N, O, and F at the 2b site of the ThMn12 structure. The amount of the increase is larger for X = N, O, F than for X = B, C. On the other hand, the crystal field parameter < r(2)> A(2)(0), which controls the axial magnetic anisotropy of the Nd 4f magnetic moment, depends differently on the dopant. With increase of the atomic number from X = B, < r(2)> A(2)(0) increases, takes a maximum value for X = N, and then turns to decrease. This suggests that in NdFe11TiX, nitrogen is the most appropriate dopant among B, C, N, O, and F for permanent magnets in terms of magnetization and anisotropy. The above calculated properties are explained based on the detailed analysis of the electronic structures of NdFe11TiX.