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 Fe 2O3 on the surface of as-made samples. Microstructure studies showed a uniform nanostructure with the grain size in the range of 50-150 Å with smaller grains corresponding to thinner films. The coercivity at 10 K was found to increase substantially with decreasing film thickness below 60 Å. A high Hc (2.7 kOe) was observed in samples with a thickness about 20 Å. 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.