Consequences of interfacial Fe-O bonding and disorder in epitaxial Fe/MgO/Fe(001) magnetic tunnel junctions

We report on a thorough experimental investigation of the influence of an FeO layer at the Fe/MgO interface on the magnetotransport properties in epitaxial Fe/MgO/Fe(001) magnetic tunnel junctions. Interfacial oxygen is introduced by adsorbing O-2 on the bottom Fe(001) layer. The morphology and composition of the FeO film are investigated by means of scanning tunneling microscopy, reflection high-energy electron diffraction, and x-ray photoelectrons spectroscopy. We show that the amount of interfacial oxygen can be precisely tuned and that either ordered or disordered FeO layers can be grown. Both Fe-O bonding and interfacial disorder strongly alter the conductances of junctions. However, the tunnel magnetoresistance remains large (>85%) even for large oxygen exposure. Interfacial Fe-O bonds are found to lower the parallel conductance in agreement with theoretical predictions.