Nitrogen as the best interstitial dopant among $X$=B, C, N, O and F for strong permanent magnet NdFe$_{11}$Ti$X$: First-principles study

TL;DR

This study uses first-principles calculations to identify nitrogen as the optimal interstitial dopant in NdFe$_{11}$Ti$X$ for enhancing magnetization and magnetic anisotropy, crucial for permanent magnet applications.

Contribution

It provides a comparative first-principles analysis of B, C, N, O, and F doping effects on NdFe$_{11}$Ti, highlighting nitrogen's superior performance for magnetic properties.

Findings

Nitrogen doping maximizes magnetic anisotropy.

Magnetization increases with doping, especially for N, O, F.

Electronic structure analysis explains the dopant effects.

Abstract

We study magnetic properties of NdFe$_{11}$Ti$X$, where $X$=B, C, N, O, and F, by using the first-principles calculation based on the density functional theory. Its parent compound NdFe$_{11}$Ti has the ThMn$_{12}$ 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 ThMn$_{12}$ 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 $\langle r^{2} \rangle A_{0}^{2}$, 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, $\langle r^{2} \rangle A_{0}^{2}$ increases, takes a maximum value for $X$=N, and then turns to decrease. This suggests that in NdFe$_{11}$Ti$X$, 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 NdFe$_{11}$Ti$X$.