Thin film iron oxides prepared by a new pyrolisis technique are studied by means of CEM spectroscopy and Faraday rotation measurements. It is shown that Fe3O4spinel oxides are obtained when the deposition is performed under Ar atmosphere. These spinel-ferrite films present an important magnetization component perpendicular to the film plane. It is also shown that the Fe3O4films are converted to γ-Fe2O3by oxidation in air while retaining a uniaxial magnetic anisotropy. We interpret this induced magnetic anisotropy as arising from a magnetoelastic coupling with the substrate. Faraday rotation hysteresis loops confirm the existence of a strong induced uniaxial magnetic anisotropy in these films.