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

Abstract

We investigate the exchange coupling constant Jij in NdxFe1−x amorphous alloys with different compositions within the framework of first-principles calculation. We observed a strong atomicdependence of Jij and its fluctuations. We show that the composition strongly affects the distance dependence of Jij . 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 Jij 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.