Structural, Magnetic and Optical Properties CoFe2O4 Thin Films

Cobalt ferrite films were prepared by RF sputtering on glass substrates at ambient temperature and subsequently annealed at 500 degrees C for 3 h in air atmosphere. The influence of variation in Ar gas pressure between 8 and 12 mTorr on the crystal structure and magnetic and optical properties has been studied. The XRD patterns show a single-phase nanocrystalline spinel structure. The FESEM and TEM studies also confirm the nanocrystalline nature of the films and show granular morphology. Surface morphologies of these films, observed by FESEM, indicated the increase in grain size (30-40-63 nm) with increasing Ar pressure. The field-cooled (FC) and the zero-field-cooled (ZFC) magnetization were measured over a temperature interval of 5-350 K, at different applied magnetic fields. The study showed that the post-annealing could significantly improve the magnetic properties of cobalt ferrite films susceptible for temperature sensor applications. The refractive index n was determined from transmittance spectrum in the UV-VIS-NIR regions using envelope method. Film thickness and energy band gap E-g were also calculated from interference of transmittance spectra. The optical band gap of these thin films was found to be between 1.98 and 2.16 eV.