Magnetic and structural properties of Fe‐FeO bilayers

The structural and magnetic properties of sputtered Fe/Fe‐O films were studied by x‐ray photoelectron spectroscopy (XPS), Rutherford backscattering spectroscopy, transmission electron microscopy, and superconducting quantum interference device. XPS studies showed the presence of FeO and Fe2O3 on the surface of as‐made samples. Microstructure studies showed a uniform nanostructure with the grain size in the range of 50–150 A with smaller grains corresponding to thinner films. The coercivity at 10 K was found to increase substantially with decreasing film thickness below 60 A. A high Hc (2.7 kOe) was observed in samples with a thickness about 20 A. Magnetization curves showed a planar anisotropy with a shifted hysteresis loop characteristic of an exchange anisotropy between the Fe and Fe‐O coating. The coercivity was found to drop steeply with increasing temperature. This may be attributed to the superparamagnetic behavior of the Fe‐O surface layer.