Magnetic microstructure of candidates for epitaxial dual Heusler magnetic tunnel junctions

Heusler alloys are considered as interesting ferromagnetic electrode materials for magnetic tunnel junctions, because of their high spin polarization. We, therefore, investigated the micromagnetic properties in a prototypical thin film system comprising two different Heusler phases Co2MnSiCo2MnSi (CMS) and Co2FeSiCo2FeSi (CFS) separated by a MgO barrier. The magnetic microstructure was investigated by X-ray photoemission electron microscopy (XPEEM). We find a strong influence of the Heusler phase formation process on the magnetic domain patterns. SiO2/V/CMS/MgO/CFSSiO2/V/CMS/MgO/CFS and SiO2/V/CFS/MgO/CMSSiO2/V/CFS/MgO/CMS trilayer structures exhibit a strikingly different magnetic behavior, which is due to pinhole coupling through the MgO barrier and a strong thickness dependence of the magnetic ordering in Co2MnSiCo2MnSi.