Magnetoresistance effects in Zn0.90Co0.10O films

Zn0.90Co0.10O films of different thicknesses (689, 408, 355 nm) doped with 0.5 at. % Al were prepared by pulsed laser deposition on a-plane sapphire substrates. At 290 K the resistivity increases drastically with decreasing film thickness, while the electron concentration and mobility decrease. Magnetoresistance (MR) effects were measured in the temperature range of 5–290 K. At low temperature, the positive MR increases with decreasing film thickness. Positive MR decreases rapidly with increasing temperature. With increasing temperature, the MR of the thicker film changes to negative, while positive MR was still observed for the 355 nm thick film at 290 K. Anomalous Hall effect was observed in the 355 nm thick film at 20 K, indicating the possible ferromagnetism in Zn0.90Co0.10O.