Magnetic properties of epitaxial CoO/Fe(001) bilayers: The onset of exchange bias as a function of sublayer thickness and temperature

We study the magnetic properties of epitaxial double-wedge CoO/Fe bilayers grown on MgO(001). We present a comprehensive set of data derived from the hysteresis loops measured as a function of temperature in a wide range of CoO and Fe thicknesses using Kerr microscopy imaging. We focus on relatively high temperatures and CoO layers with small thicknesses to address the onset of the exchange bias. We identify a characteristic CoO thickness of 30–40 Å, above which the films can be considered bulklike. However, a considerable exchange bias is still observed even for CoO films as thin as 12 Å if the temperature is sufficiently low. From the results of the x-ray photoelectron spectroscopy measurements, we deduce the presence of an interfacial iron oxide layer of mixed stoichiometry and a uniform composition of the CoO layer along the CoO wedge.