Magnetic and transport properties of Ti _0.96Co _xNi _0.04-xO _2-δ thin films

We investigated the magnetic and transport properties of Co and Ni co-doped TiO ₂ thin films grown by using a sol-gel method with Co and Ni concentrations from 0 % to 4 %. All the samples exhibited ferromagnetism at room temperature, but were highly resistive when annealed in vacuum at 650°C. The magnetic moment per ion increased with the Co concentration. After annealing at 850°C, the electrical conductance and the magnetic moment per ion of the films were enhanced, but a small Co metallic peak was observed in the X-ray diffraction pattern. The Hall effect study showed that the carriers were electrons with densities lower than 10 ¹⁹ cm ^-3 at room temperature for the samples annealed at 850°C. A weak anomalous Hall effect was observed and increased with the Co concentration. We discuss the co-doping effect by comparing the results with those of films singly doped with Ni or Co.