Composition Shift as a Function of Thickness in Fe3-δO4(001) Epitaxial Films

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We report on a thickness-dependent composition shift and a valency change in B-site Fe in Fe3-δO4(001) epitaxial films prepared by ozone-assisted molecular beam epitaxy. Conversion electron Mössbauer spectroscopy (CEMS) measurements for locally inserted 57Fe-enriched probe layers showed that a pure $\gamma$-Fe2O3 film can be obtained only if the film is sufficiently thin, and that the composition shift occurs when the thickness increases. The resistivity of Fe3-δO4 films having different thicknesses exhibited a significant decrease with an increase in the thickness, consistent with the CEMS experiment. These results indicate that $\gamma$-Fe2O3 films do not preferably grow homoepitaxially and that careful control of the growth is necessary to apply $\gamma$-Fe2O3 films to spintronics devices.
2010-08-25