Hard X-ray photoelectron spectroscopy on buried, off-stoichiometric CoxMnyGez (x : z = 2 : 0.38) Heusler thin films

TL;DR

This study investigates the electronic structure of off-stoichiometric CoxMnyGez Heusler thin films using high-energy X-ray photoelectron spectroscopy and first-principles calculations, revealing how stoichiometry adjustments influence their electronic and magnetic properties.

Contribution

It demonstrates how co-sputtering techniques can precisely tune the electronic structure of CoxMnyGez films, impacting their magnetoresistive behavior in tunnel junctions.

Findings

Spectral weight shifts near the Fermi energy in non-stoichiometric films.

Density of states changes align with theoretical predictions.

Stoichiometry adjustments can tune magnetoresistive properties.

Abstract

Fully epitaxial magnetic tunnel junctions (MTJs) with off-stoichiometric Co2-based Heusler alloy shows a intense dependency of the tunnel magnetoresistance (TMR) on the Mn composition, demonstrating giant TMR ratios of up to 1995% at 4.2 K for 1. This work reports on the electronic structure of non-stoichiometric CoxMnyGez thin films with a fixed Co/Ge ratio of x : z = 2 : 0.38. The electronic structure was investigated by high energy, hard X-ray photoelectron spectroscopy combined with first-principles calculations. The high-resolution measurements of the valence band of the non-stoichiometric CoxMnyGez films close to the Fermi energy indicate a shift of the spectral weight compared to bulk Co2MnGe. This is in agreement with the changes in the density of states predicted by the calculations. Furthermore it is shown that the co-sputtering of Co2MnGe together with additional Mn is an appropriate technique to adjust the stoichiometry of the CoxMnyGez film composition. The resulting changes of the electronic structure within the valence band will allow to tune the magnetoresistive characteristics of CoxMnyGez based tunnel junctions as verified by the calculations and photoemission experiments.