Magnetic Compton profiles of disordered Fe$_{0.5}$Ni$_{0.5}$ and ordered FeNi alloys

TL;DR

This study investigates the magnetic Compton profiles of disordered Fe$_{0.5}$Ni$_{0.5}$ and ordered FeNi alloys, highlighting the importance of electronic correlations in accurately modeling experimental spectra and distinguishing between ordered and disordered states.

Contribution

It demonstrates that including local dynamic electronic correlations is essential to accurately describe the MCP spectra and differentiate ordered from disordered FeNi alloys.

Findings

Including local correlations improves agreement with experimental data.

No significant difference in MCP spectra under LSDA for disordered and hypothetical ordered alloys.

Electronic correlations cause notable spectral differences across the Brillouin zone.

Abstract

We study the magnetic Compton profile (MCP) of the disordered Fe$_{0.5}$Ni$_{0.5}$ and of the ordered FeNi alloys and discuss the interplay between structural disorder and electronic correlations. The Coherent Potential Approximation is employed to model the substitutional disorder within the single-site approximation, while local electronic correlations are captured with the Dynamical Mean Field Theory. Comparison with the experimental data reveals the limitation of local spin-density approximation in low momentum region, where we show that including local but dynamic correlations the experimental spectra is excellently described. We further show that using local spin-density approximation no significant difference is seen between the MCP spectra of the disordered Fe$_{0.5}$Ni$_{0.5}$ and a hypothetical, ordered FeNi alloy with a simple cubic unit cell. Only by including the electronic correlations, the spectra significantly separate, from the second Brillouin zone boundary down to zero momenta. The difference between the MCP spectra of ordered and disordered alloys is discussed also in terms of the atomic-type decompositions. Finally based on the presented calculations we predict the shape of the MCP profile for the ordered FeNi alloy along the [111] direction.