We have grown hematite (a-Fe2O3) thin films on stainless steel substrates and magnetite (Fe3O4) thin films on (0 0 1)-Si single crystal substrates by a RF magnetron sputtering process. a-Fe2O3 thin films were grown in an Ar atmosphere at substrate temperatures around 400 C, and Fe3O4 thin films in an Ar/O2 reactive atmosphere at substrate temperatures around 500 C. Conversion electron Mo¨ssbauer (CEM) spectra of a-Fe2O3 thin films exhibit values for hyperfine parameter characteristic of the hematite stoichiometric phase in the weak ferromagnetic state [R.E. Vandenberghe, in: Mo¨ ssbauer Spectroscopy and Applications in Geology, University Gent, Belgium, 1990. [1]. Furthermore, the relative line intensity ratio suggests that the magnetization vector of the polycrystalline film is aligned preferentially parallel to the surface. The CEM spectra of Fe3O4 thin films show the presence of only the stoichiometric phase, and the values for the hyperfine fields and isomer shifts of the A and B sites are consistent with bulk Fe3O4 [1]. The X-ray diffraction (XRD) pattern of the polycrystalline thin films also corresponds to a-Fe2O3 and Fe3O4 [JCPDS, X-ray diffraction data cards, 2001. [2]]. The samples were also analyzed by atomic force microscopy (AFM) and they reveal a grain morphology common for polycrystalline films. We found an average grain size of 211nm and surface roughness of 45nm in a-Fe2O3 films and an average grain size of 148nm and surface roughness of 1.2nm in Fe3O4 films.