Insights into the electronic structure of Co2FeSi from x-ray magnetic linear dichroism

TL;DR

This study uses x-ray magnetic linear dichroism to evaluate electronic structure models of Co2FeSi, finding that GGA-based calculations align better with experimental data than LDA+U approaches, challenging previous assumptions about its half-metallicity.

Contribution

It demonstrates that XMLD can effectively distinguish between different electronic structure models of Co2FeSi, favoring GGA over LDA+U methods.

Findings

GGA calculations agree better with experimental XMLD spectra.

LDA+U or GGA+U models are inadequate for describing Co2FeSi.

Constrained GGA with fixed spin moment improves theoretical-experimental match.

Abstract

Experimental evidence both for and against a half-metallic ground-state of the Heusler compound Co2FeSi has been published. Density functional theory based calculations suggest a non half-metallic ground state. It has been argued, that on-site Coulomb interaction of the d electrons has to be taken into account via the LDA+U method, which predicts a half-metallic ground-state for U = 2.5...4.5 eV. X-ray magnetic linear dichroism (XMLD) can be used as a tool to assess the appropriateness of the LDA+U approach: the calculated spectra within the LDA+U or GGA+U schemes are different from those within the LDA or GGA. Due to its ability to separate different orbital symmetries, XMLD allows us to distinguish between different models of the electronic structure of Co2FeSi. In this article we discuss experimental XMLD spectra and compare them with detailed first principles calculations. Our findings give evidence for the inadequacy of the LDA+U or GGA+U band structures, whereas constrained calculations with the GGA and a fixed spin moment of 6 \mu_B give better overall agreement between experiment and theory.