Structural, chemical and electronic properties of the Co2MnSi(001)/MgO interface

TL;DR

This study investigates the atomic and electronic properties of the Co2MnSi/MgO interface, revealing how MgO thickness and annealing influence surface quality, defects, and spin polarization relevant for magnetic tunnel junctions.

Contribution

It provides detailed analysis of interface formation, crystalline distortions, and spin polarization in Co2MnSi/MgO structures, highlighting the effects of MgO thickness and annealing on interface quality.

Findings

Thin MgO layers show surface distortions and adsorbates.

Thicker MgO layers have improved crystalline structure.

Positive spin polarization observed near the Fermi energy.

Abstract

The performance of advanced magnetic tunnel junctions build of ferromagnetic (FM) electrodes and MgO as insulating barrier depends decisively on the properties of the FM/insulator interface. Here, we investigate interface formation between the half-metallic compound Co2MnSi (CMS) and MgO by means of Auger electron spectroscopy, low energy electron diffraction and low energy photoemission. The studies are performed for different annealing temperatures TA and MgO layer coverages (4, 6, 10, 20 and 50 ML). Thin MgO top layers (t_MgO<=10 ML) show distinct surface crystalline distortions, which can only be partly healed out by annealing and furthermore lead to distinct adsorption of carbon species after the MgO surface is exposed to air. For t_MgO> 10 ML the MgO layer surface exhibits clearly improved crystalline structure and hence only marginal amounts of adsorbates. We attribute these findings to MgO misfit dislocations occurring at the interface, inducing further defects throughout the MgO layer for up to at least 10 ML. Furthermore, spin-polarized photoemission spectra of the CMS/MgO interface are obtained for MgO coverages up to 20 ML, showing a clear positive spin polarization near the Fermi energy in all cases.