Role of typical elements in Nd$_{2}$Fe$_{14}$$X$ ($X$ = B, C, N, O, F)

TL;DR

This study uses first-principles calculations to investigate how different elements X in Nd₂Fe₁₄X affect magnetic properties and phase stability, revealing B's minor role in magnetocrystalline anisotropy and its importance in phase stabilization.

Contribution

The paper provides a theoretical analysis of the effects of various elements X on Nd₂Fe₁₄X, challenging previous beliefs about B's positive role and clarifying stability trends.

Findings

B reduces magnetic moment and magnetization in Nd₂Fe₁₄B.

B has a minor role in uniaxial magnetocrystalline anisotropy.

B stabilizes the Nd₂Fe₁₄B phase by lowering formation energy.

Abstract

The magnetic properties and structural stability of Nd$_{2}$Fe$_{14}X$ ($X$ = B, C, N, O, F) are theoretically studied by first-principles calculations focusing on the role of $X$. We find that B reduces the magnetic moment (per formula unit) and magnetization (per volume) in Nd$_{2}$Fe$_{14}$B. The crystal-field parameter $A_2^0 \langle r^2 \rangle$ of Nd is not enhanced either, suggesting that B has minor roles in the uniaxial magnetocrystalline anisotropy of Nd. These findings are in contrast to the long-held belief that B works positively for the magnetic properties of Nd$_{2}$Fe$_{14}$B. As $X$ changes from B to C, N, O and F, both the magnetic properties and stability vary significantly. The formation energies of Nd$_{2}$Fe$_{14}X$ and $\alpha$-Fe relative to that of Nd$_{2}$Fe$_{17}X$ are negative for $X$ = B and C, whereas they are positive when $X$ = N, O and F. This indicates that B plays an important role in stabilizing the Nd$_{2}$Fe$_{14}$B phase.