Anomalous Hall effect in sputter-deposited CoxTi1−xO2–δ films

Abstract Hall effect measurements were performed on epitaxial Co x Ti 1− x O 2– δ thin films grown on (0 0 1) LaAlO 3 by reactive RF magnetron co-sputter deposition. Magnetization measurements reveal ferromagnetic behavior in M – H loop at room temperature for Co x Ti 1− x O 2– δ thin films for which x ⩾0.02. An anomalous Hall effect was observed for Co 0.10 Ti 0.90 O 2− δ films grown with the partial pressure of water P (H 2 O)=4×10 −4 Torr or less. These films exhibit a positive ordinary Hall coefficient and a positive magnetoresistance. X-ray diffraction on films grown under these conditions shows evidence for Ti n O 2 n −1 phase due to the deficiency of oxygen. In contrast, Hall measurements taken for undoped and Co-doped TiO 2 thin films grown under more oxidizing conditions show only the ordinary Hall effect with a negative Hall coefficient consistent with n-type conduction. For these films, the magnetoresistance was positive and increased monotonically with increasing magnetic field. The results suggest that Co-doped Ti n O 2 n −1 may be a dilute magnetic semiconducting oxide for which the carriers couple to the spin polarization.