Hall effect in cobalt-doped TiO${}_{2-\delta }$

We report Hall effect measurements on thin films of cobalt-doped TiO${}_{2-\delta }$. Films with low carrier concentrations (10${}^{18}$ - 10${}^{19}$) yield a linear behavior in the Hall data while those having higher carrier concentrations (10${}^{21}$ - 10${}^{22}$) display anomalous behavior near zero field. In the entire range of carrier concentration, n-type conduction is observed. The appearance of the anomalous behavior is accompanied by a possible structural change from rutile TiO${}_2$ to Ti_[n}O${}_{2n-1}$ Magneli phase(s).