The effect of heat treatment on the structural and magnetic properties of bilayered FeOx/Fe thin films grown by pulsed laser deposition on pre-oxidized amorphous SiO2/Si substrates has been studied. Post-deposition vacuum thermal annealing leads to remarkable changes in the structural and magnetic properties of the FeOx layer, which has been investigated by the combination of scanning electron and atomic force microscopy, Raman scattering spectroscopy and conversion electron Mössbauer spectroscopy. FeOx 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 FeOx/Fe stack at T = 500 °C leads to the formation of a polycrystalline Fe3O4/Fe thin film structure with the magnetite nucleation centers of an average size of 100 nm. The formation of the exact magnetite …