State of Co and Mn in half-metallic ferromagnet Co$_2$MnSi explored by magnetic circular dichroism in hard X-ray photoelectron emission and soft X-ray absorption spectroscopies

TL;DR

This study investigates the electronic and magnetic properties of Co$_2$MnSi thin films used in spintronic devices, revealing localized Mn moments and itinerant Co electrons through advanced spectroscopic techniques.

Contribution

It provides a detailed spectroscopic analysis of Co$_2$MnSi films, highlighting the localized Mn and itinerant Co contributions to magnetism, which advances understanding of half-metallic ferromagnets.

Findings

Large dichroism effects observed at Co and Mn $2p$ levels.

Mn atoms exhibit localized magnetic moments.

Co electrons contribute itinerant magnetic moments.

Abstract

The half-metallic Heusler compound Co$_2$MnSi is a very attractive material for spintronic devices because it exhibits very high tunnelling magnetoresistance ratios. This work reports on a spectroscopic investigation of thin Co$_2$MnSi films as they are used as electrodes in magnetic tunnel junctions. The investigated films exhibit a remanent in-plane magnetisation with a magnetic moment of about 5~$\mu_B$ when saturated, as expected. The low coercive field of only 4~mT indicates soft magnetic behaviour. Magnetic dichroism in emission and absorption was measured at the Co and Mn $2p$ core levels. The photoelectron spectra were excited by circularly polarised hard X-rays with an energy of of 6~keV and taken from the remanently magnetised film. The soft X-ray absorption spectra were taken in an induction field of 4~T. Both methods yielded large dichroism effects. An analysis reveals the localised character of the electrons and magnetic moments attributed to the Mn atoms, whereas the electrons related to the Co atoms contribute an itinerant part to the total magnetic moment.