Effects of oxygen pressure on ferromagnetic ordering in Mn-doped ZnO thin films

Magnetic and magnetotransport properties of Mn-doped ZnO thin films grown by pulsed laser deposition are studied. These films are grown at various substrate temperature ranging from 20-800°C. Hysteresis loops of the doped thin films grown at 800°C under oxygen pressures of 0.1 Torr and 0.001 Torr are measured at 4 K and 300 K. Results show that regardless of the oxygen pressure, the Mn-doped ZnO thin films exhibit ferromagnetic ordering at 4 K, although a clear difference between two samples is found in saturation magnetization and coercivity. On the other hand, the ferromagnetic behavior in the film grown under 0.001 Torr is found to disappear. Large magnetoresistance is observed in the film grown at 700°C which indicates that the spin splitting exists and is caused by strong s-d exchange coupling between the conducting carriers and localized spins of Mn ions. Also, extraordinary Hall effect is observed at 4 K in the Mn-doped film grown at 700°C under 0.1 Torr.