Structural, optical, and magnetic properties of Co‐doped CeO₂ thin films prepared by radio‐frequency magnetron sputtering

Abstract

Co-doped CeO 2 (Ce 1-x Co x O 2 , x = 0, 0.03, and 0.06) thin films were prepared by radio-frequency magnetron sputtering. The structural, optical, and magnetic properties of these films were characterized by X-ray diffraction (XRD), Raman spectroscopy (Raman), atomic force microscopy (AFM), Fourier transform-infrared spectroscopy (FT-IR), spectroscopic ellipsometry (SE), and superconducting quantum interference magnetometer (SQUID). XRD and Raman studies revealed that all the films exhibited single phase of cubic fluorite structure, with highly ( 111) preferred orientation. No Co and Co-related oxide was detected. Compared with undoped CeO 2 films, the defect concentration of Co-doped films increases. AFM images displayed that the film surface morphology is dependent on the Co-doped content. The vibrational band assignment of undoped and Co-doped CeO 2 films was analyzed by FT-IR. The energy dispersion optical constants (the refractive index n and the extinction coefficient k) of Ce 1-x Co x O 2 thin films were obtained by analyzing the SE spectra in the ultraviolet and visible-near infrared (UV-NIR) region (0.5-5.9 eV). The optical band gap energies E g for these films were determined. The E g values of the Ce 1-x-Co x O 2 thin films are 3.35, 3.27, and 3.25 eV, and the n values at wavelength of 632 nm are about 2.35, 2.38, and 2.42 for Co-doped content x = 0, 0.03, and 0.06, respectively. SQUID measurements show that Co-doped CeO 2 films exhibit room temperature ferromagnetism, and the saturation magnetization (M s ) is 0.0051 and 0.0098 emμ/cm 3 with the Co doping content x = 0.03 and 0.06, respectively. The ferromagnetism of Co-doped CeO 2 films belong to the intrinsic magnetism of the films.