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

Abstract

Co‐doped CeO2 (Ce1‐xCoxO2, 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 CeO2 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 CeO2 films was analyzed by FT‐IR. The energy dispersion optical constants (the refractive index n and the extinction coefficient k) of Ce1‐xCoxO2 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 Eg for these films were determined. The Eg values of the Ce1‐xCoxO2 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 CeO2 films exhibit room temperature ferromagnetism, and the saturation magnetization (Ms) is 0.0051 and 0.0098 emμ/cm3 with the Co doping content x = 0.03 and 0.06, respectively. The ferromagnetism of Co‐doped CeO2 films belong to the intrinsic magnetism of the films.