We report on the growth and properties of magnetite, Fe3O4, thin films on spinel substrates. Raman studies confirmed growth of single-phase magnetite, but X-ray diffraction analysis reveals a non-uniform structure of the films with a strained pseudomorphic layer. Transport properties of the films are well satisfied to the magnetite ones, but magnetization is significantly reduced than it can be expected for a high quality magnetite. We explain these results within the concept of dead magnetic layer situated close to the film/substrate interface resulting in the coexistence of different magnetic phases within a uniform crystal phase of magnetite.