Structural and magnetic properties of CoFe2O4 thin films deposited by laser ablation on Si (001) substrates

Cobalt ferrite (CoFe2O4) thin films have been deposited on Si (001) substrates, with different substrate temperatures (Tdep = 25 °C − 600 °C). The films were prepared by pulsed laser ablation with a KrF excimer laser (wavelength λ = 248 nm). The oxygen pressure during deposition was 2 × 10−2 mbar. The films structure was studied by X-ray diffraction (XRD) and their surface was examined by scanning electron microscopy (SEM). The magnetic properties were measured with a vibrating sample magnetometer (VSM). For low deposition temperatures, the films presented a mixture of a CoFe2O4 phase, with the cubic spinel structure, and cobalt and iron antiferromagnet oxides with CoO and FeO stoichiometries. As the deposition temperature increased, the CoO and FeO relative content strongly decreased, so that for Tdep = 600 °C the films were composed mainly by polycrystalline CoFe2O4. The magnetic hysteresis cycles measured in the films were horizontally shifted due to an exchange coupling field (Hexch) originated by the presence of the antiferromagnetic phases. The exchange field decreased with increasing deposition temperature, and was accompanied by a corresponding increase of the coercivity and remanence ratio of the cycles. This behavior was due to the strong reduction of the CoO and FeO content, and to the corresponding dominance of the CoFe2O4 phase on the magnetic properties of the thin films.