Magnetic, magnetoresistance and electrical transport properties of Ni and Al co-doped ZnO films grown on glass substrates by direct current magnetron co-sputtering

200-nm-thick Zn0.85Al0.04Ni0.11O films were deposited on glass substrates at 300 K and 573 K by co-sputtering ZnO:Al and Ni targets. A temperature dependence of magnetization and resistivity within 50-300 K and a room temperature magnetoresistance (MR) were measured. X-ray photoelectron spectroscopy was used to analyze chemical valences of Ni in the films. The films have the room temperature ferromagnetism. A magnetization of the film grown at 300 K decreases slightly and that of the film grown at 573 K decreases markedly with increasing temperature. The small negative MR is observed for the film deposited at 300 K while the positive MR is obtained for the film prepared at 573 K. For the film grown at 300 K, the carrier transport mechanism is thermally activated band conduction. However, the carrier transport mechanism in the film grown at 573 K is the Mott's variable range hopping in the temperature range below 100 K and the thermally activated band conduction above 140 K. The metallic Ni atoms and Ni2+ ions exist in the films. The ferromagnetism is mainly attributed to the Ni clusters in the Zn0.85Al0.04Ni0.11O film.