  Thin films of Co-TiO2 are deposited on silicon and quartz substrates using
Pulse Laser Deposition (PLD) process at various oxygen partial pressures
ranging from 6.6 x 10-3 Pascals (Pa) to 53 Pa. Crystal structure, transport and
magnetic properties of reduced CoxTi(1-x)O2 (0 <x< 0.03) thin films are
investigated and are found to have a strong dependence on the oxygen partial
pressure. X-ray diffraction (XRD) data reveals the presence of mixed phase
material containing both anatase and rutile. However, these phases
intertransform with the change in the oxygen partial pressure in the chamber
during the growth of the films. X-ray Photoelectron Spectroscopy (XPS) shows no
Co or CoO related peaks for samples with Co concentration up to x=0.03.
However, the oxygen 1s peaks are asymmetric suggesting the presence of oxygen
vacancies. The transport and magnetic measurements show a clear dependence on
the concentration of oxygen vacancies. There is an enhancement in the
electrical conductivity and the magnetization as more vacancies are created in
the material. The resistivity as a function of temperature rho(T) follows the
polaronic behavior and the activation energies obtained, ~100 to 150meV, are
within the range that is typical for semiconducting materials.
