First-principles study of exchange coupling constants in Nd$_x$Fe$_{1-x}$ amorphous alloy

TL;DR

This study uses first-principles calculations to analyze how exchange coupling constants in Nd_xFe_{1-x} amorphous alloys depend on atomic environment, composition, and local structure, revealing key factors influencing magnetic properties.

Contribution

It provides a detailed first-principles analysis of exchange interactions in Nd-Fe amorphous alloys, highlighting the atomic dependence and environmental effects on magnetic coupling.

Findings

Exchange coupling constants show strong atomic dependence and fluctuations.

Composition influences the distance dependence of exchange interactions.

Curie temperatures are mainly determined by average exchange constants and coordination numbers.

Abstract

We investigate the exchange coupling constant $J_{ij}$ in Nd$_x$Fe$_{1-x}$ amorphous alloys with different compositions within the framework of first-principles calculation. We observed a strong atomic-dependence of $J_{ij}$ and its fluctuations. We show that the composition strongly affects the distance dependence of $J_{ij}$. Composition dependence of calculated Curie temperatures is modest for $x<0.5$. To examine the effect of the local environment on the exchange couplings, we demonstrate combined analyses of the coordination structure and exchange coupling constants using the Gabriel graph. Our study reveals that the Curie temperatures are mostly dominated by the averaged $J_{ij}$ and coordination numbers determined by the pairs of neighboring atoms. We also observed that the exchange couplings between Fe--Fe and Fe--Nd become stronger with increasing the number of surrounding Nd atoms.