Influence of oxygen partial pressure on structural, transport and magnetic properties of Co doped TiO2 films

Pulse laser deposited (PLD) thin films of Co doped TiO2 on silicon and quartz substrates are investigated. A mixture (1:1) of argon and oxygen with various total pressures (6.6 mPa to 53 Pa) is used to vary the oxygen content in the samples. The crystal structure and transport/ magnetic properties of CoxTi1−xO2−δ (x=0.01, 0.03, 0.06) thin films are found to have strong dependence on oxygen stoichiometry. X-ray diffraction (XRD) data reveal mixed phase material containing both anatase and rutile. However, the stability of each phase depends on the amount of oxygen present in the chamber during the growth of the films. X-ray Photoelectron Spectroscopy (XPS) shows the incorporation of Co in TiO2 and is in the 2+ oxidation state. There occurs an enhancement in electrical conductivity and magnetization due to the off stoichiometric oxygen. The resistivity data follow a simple thermal activation model, giving carriers' activation energies in the range of 20 to 140 meV. A bound magnetic polaron model is adopted to explain the observed magnetic behavior of the films.