Structure and magnetic properties of ZnO films doped with Co, Ni or Mn synthesized by pulsed laser deposition under low and high oxygen partial pressures

Zn1-xMxO (M=Co, Ni, Mn) films with different concentrations of transition metal (10-30%)were synthesized by pulsed laser deposition. The substrates were heated at 400 degrees C and the depositions were performed either under secondary vacuum or under an oxygen pressure of 30 Pa. The occurrence of ion channeling in the films during Rutherford Backscattering Analysis, together with X-ray diffraction, optical absorption and transmission electron microscopy, clearly show that the M atoms are in solid solution on Zn sites. Magnetic properties were investigated by means of magnetometry at 5 and 300 K and Electron Spin Resonance. The Zn1-xCoxO and Zn1-xNixO films deposited under low 02 pressure exhibit both a ferromagnetic and a paramagnetic response up to 300 K, while films deposited under high 02 pressure and Zn1-xMnxO films are paramagnetic. Broad spin resonance peaks are recorded at room temperature, from ferromagnetic films only. The nearly isotropic magnetic response of these films, which is observed in ESR when varying the field orientation with respect to the surface, seems to indicate that the crystalline anisotropy oppose the shape anisotropy, because of the strong [001] texture of the films. (C) 2008 Elsevier B.V. All rights reserved.