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

• X-ray absorption and magnetic circular dichroism spectra are measured and compared to first principles calculations in (Ge,Mn) compounds.
• Standard density functional theory fails in properly describing peculiar features observed in the experiment.
• A new approach to calculate theoretical X-ray absorption and magnetic circular dichroism spectra is proposed.
• Improved modeling of the core levels splitting using the Hartree–Fock approximation allows for a better matching with the experiment.
• This new method could be generalized to any 3d metallic-like system.

X-ray absorption (XAS) and x-ray magnetic circular dichroism (XMCD) spectra at the L2,3 edges of Mn in (Ge,Mn) compounds have been measured and are compared to the results of first principles calculation. Early 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 L3 XMCD spectrum of Mn in Ge3Mn5, 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 2p 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.