Microstructure and properties of Fe-doped SnO₂ nanocrystalline films

Fe-doped SnO₂ films were grown on Si (100) substrates at 270°C by reactive magnetron sputtering. The sputtering atmosphere was a mixture of argon and oxygen. The samples were prepared under three different oxygen partial pressures. XRD, AFM, VSM were used to investigate the crystalline structure, surface morphology and room temperature ferromagnetism (RTFM) of the samples, respectively. The film deposited under oxygen partial pressure of 0.12Pa exhibits a clear ferromagnetism at room temperature. The chemical composition of the film is Sn_0.975Fe_0.025O_2-δ, and the saturated magnetic moment is about 1.8μ_B/Fe. The microstructure and element distribution of this sample were examined by HRTEM and EDS, respectively. It shows that the films are composed of tetragonal rutile SnO₂ nanocrystals with diameter of 3-7 nm. Fe atoms are uniformly distributed in the films. No Fe metallic clusters or iron oxides are observed; the measurement of the resistivity indicates insulating characteristic of the film, therefore RTFM of the film can not be attributed to secondary phase or spin-charge carriers interaction. It shows that RTFM is closely related to a great number of structural defects in the film.