Structure, magnetic and optical properties of polycrystalline Co-doped TiO2 films

Co-doped TiO2 films were fabricated under different conditions using reactive facing-target magnetron sputtering. Co doping improves the transformation of TiO2 from anatase phase to rutile phase. The chemical valence of doped Co in the films is +2. All the films are ferromagnetic with a Curie temperature above 340 K. The average room-temperature moment per Co of the Co-doped TiO2 films fabricated at 1.86 Pa decreases from 0.74 μB at x=0.03 to 0.02 μB at x=0.312, and decreases from 0.54 to 0.04 μB as x increases from 0.026 to 0.169 for the Co-doped TiO2 films fabricated at 0.27 Pa. The ferromagnetism originates from the oxygen vacancies created by Co2+ dopants at Ti4+ cations. The optical band gaps value (Eg) of the Co-doped TiO2 films fabricated at 1.86 Pa decreases linearly from 3.35 to 2.62 eV with the increasing x from 0 to 0.312. For the Co-doped TiO2 films fabricated at 1.86 Pa, the Eg decreases linearly from 3.26 to 2.53 eV with increasing x from 0 to 0.350.