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/Fe͑001͒ magnetic tunnel junctions. Interfacial oxygen is introduced by adsorbing O 2 on the bottom Fe͑001͒ 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

more »

... facial 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 ͑Ͼ85%͒ even for large oxygen exposure. Interfacial Fe-O bonds are found to lower the parallel conductance in agreement with theoretical predictions.