First-principles study of intersite magnetic couplings in NdFe$_{12}$ and NdFe$_{12}$X (X = B, C, N, O, F)

TL;DR

This study uses first-principles calculations to analyze how different interstitial dopants affect magnetic couplings and Curie temperatures in NdFe$_{12}$ compounds, revealing dopant-specific impacts on magnetic properties.

Contribution

It provides detailed insights into how various dopants influence magnetic exchange interactions and Curie temperatures in NdFe$_{12}$, using first-principles methods.

Findings

Nd--Fe couplings are sensitive to dopant X.

Nitrogenation reduces Nd--Fe(8j) coupling significantly.

Dopants enhance Curie temperature through structural and chemical effects.

Abstract

We present a first-principles investigation of NdFe$_{12}$ and NdFe$_{12}$X (X = B, C, N, O, F) crystals with the ThMn$_{12}$ structure. Intersite magnetic couplings in these compounds, so-called exchange couplings, are estimated by Liechtenstein's method. It is found that the Nd--Fe couplings are sensitive to the interstitial dopant X, with the Nd--Fe(8j) coupling in particular reduced significantly for X = N. This suggests that the magnetocrystalline anisotropy decays quickly with rising temperature in the X = N system although nitrogenation has advantages over the other dopants in terms of enhancing low-temperature magnetic properties. The Curie temperature is also calculated from the magnetic couplings by using the mean field approximation. Introduction of X enhances the Curie temperature, with both structural changes and chemical effects found to play important roles in this enhancement.