Evidence for FeO formation at the Fe/MgO interface in epitaxial TMR structure by X-ray photoelectron spectroscopy

Epitaxial Fe/ MgO/ Fe tunnelling magnetoresistance ( TMR) structure was grown on the MgO substrate by molecular beam epitaxy, characterized in- situ by reflection high- energy electron diffraction and ex- situ by high- resolution transmission electron microscopy. The chemical states at the Fe/ MgO interface have been investigated by X- ray photoelectron spectroscopy ( XPS) and peak decomposition technique. The results show that there is FeO formation at interface of Fe/ MgO, clearly identified by the existence of Fe2+ and Fe3+ peaks at 708.2 and 710.4 eV, respectively, which locate at the high- energy side of the main metallic Fe peak. The presence of FeO layer at the Fe/ MgO interface proved by XPS is likely to have considerable influence on its MR value and hence on its application in spintronics. (c) 2006 Elsevier B. V. All rights reserved.