Physical properties in thin films of iron oxides

Abstract

We have grown hematite ( α -Fe 2O 3) thin films on stainless steel substrates and magnetite (Fe 3O 4) thin films on (0 0 1)-Si single crystal substrates by a RF magnetron sputtering process. α -Fe 2O 3 thin films were grown in an Ar atmosphere at substrate temperatures around 400 ∘ C , and Fe 3O 4 thin films in an Ar/O 2 reactive atmosphere at substrate temperatures around 500 ∘ C . Conversion electron Mössbauer ( CEM) spectra of α -Fe 2O 3 thin films exhibit values for hyperfine parameter characteristic of the hematite stoichiometric phase in the weak ferromagnetic state [R.E. Vandenberghe, in: Mössbauer 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 Fe 3O 4 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 Fe 3O 4 [1]. The X-ray diffraction ( XRD) pattern of the polycrystalline thin films also corresponds to α -Fe 2O 3 and Fe 3O 4 [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 211 nm and surface roughness of 45 nm in α -Fe 2O 3 films and an average grain size of 148 nm and surface roughness of 1.2 nm in Fe 3O 4 films.