X-ray magnetic circular dichroism in (Ge,Mn) compounds: experiments and modeling

TL;DR

This paper investigates the electronic and magnetic properties of (Ge,Mn) compounds using X-ray absorption and dichroism measurements, and improves theoretical modeling by combining DFT and Hartree-Fock methods to accurately reproduce experimental spectra.

Contribution

It demonstrates that combining DFT for valence states with Hartree-Fock for core states enhances the accuracy of XMCD spectral simulations in (Ge,Mn) compounds.

Findings

DFT accurately describes valence band properties

Hartree-Fock improves core state exchange splitting

Combined approach reproduces experimental XMCD sign change

Abstract

X-ray absorption (XAS) and x-ray magnetic circular dichroism (XMCD) spectra at the L$_{2,3}$ edges of Mn in (Ge,Mn) compounds have been measured and are compared to the results of first principles calculation. Early \textit{ab initio} studies show that the Density Functional Theory (DFT) can very well describe the valence band electronic properties but fails to reproduce a characteristic change of sign in the L$_{3}$ XMCD spectrum of Mn in Ge$_3$Mn$_5$, which is observed in experiments. In this work we demonstrate that this disagreement is partially related to an underestimation of the exchange splitting of Mn 2$p$ core states within the local density approximation. It is shown that the change in sign experimentally observed is reproduced if the exchange splitting is accurately calculated within the Hartree-Fock approximation, while the final states can be still described by the DFT. This approach is further used to calculate the XMCD in different (Ge,Mn) compounds. It demonstrates that the agreement between experimental and theoretical spectra can be improved by combining state of the art calculations for the core and valence states respectively.