The effect of heat treatment on the structural and magnetic properties of bilayered FeO x/Fe thin films grown by pulsed laser deposition on pre-oxidized amorphous SiO 2/Si substrates has been studied. Post-deposition vacuum thermal annealing leads to remarkable changes in the structural and magnetic properties of the FeO x layer, which has been investigated by the combination of scanning electron and atomic force microscopy, Raman scattering spectroscopy and conversion electron Mössbauer spectroscopy. FeO x layer deposited at room temperature on top of the polycrystalline Fe underlayer is amorphous with the smooth surface (root mean square roughness~ 0.5 nm). Vacuum thermal annealing of the FeO x/Fe stack at T= 500° C leads to the formation of a polycrystalline Fe 3 O 4/Fe thin film structure with the magnetite nucleation centers of an average size of 100 nm. The formation of the …