  Anomalous Hall effect (AHE) of a ferromagnetic semiconductor anatase \cotio
thin film is studied from 10K to 300K. Magnetic field dependence of anomalous
Hall resistance is coincident with that of magnetization, while the anomalous
Hall resistance decreases at low temperature in spite of nearly
temperature-independent magnetization. Anomalous Hall conductivity sigma_AHE is
found to be proportional to the square of Hall mobility, suggesting that charge
scattering strongly affects the AHE in this system. The anatase Ti1-xCoxO2 also
follows a scaling relationship to conductivity sigma_xx as sigma_AHE ~
sigma_xx^1.6, which was observed for another polymorph rutile Ti1-xCoxO2,
suggesting an identical mechanism of their AHE.
