Effects of Sm implantation on the structure and magnetic properties of polar ZnO films

Abstract

The present study reports a large ferromagnetism obtained by implanting Sm ions in Zn-polar and O-polar ZnO films prepared by molecular beam epitaxy (MBE) on sapphire substrates. X-ray diffraction (XRD), Raman spectroscopy, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and superconducting quantum interference device (SQUID) measurements were carried out to characterize the structure, surface morphology, elemental chemical states and magnetic properties of the Sm-doped polar ZnO films. XRD and AFM show that the doped ions in Zn-polar films are located at the grain boundary, while the doping ions in the O-polar films are incorporated into the grains. The magnetic moment for the as-implanted O-polar film is higher than that of the Zn-polar film. After annealing at 600 ℃ for 30 mins., there is a clear reduction in the saturation magnetization for the O-polar film, while the magnetic moment of the Zn-polar film shows little change. Raman and XPS results show that a large number of grain boundaries in the O-polar films are repaired and O vacancy (Vo) defects are reduced. We concluded that the magnetization of polar ZnO film after annealing is attributed to the combined effects of the Vo defects introduced by implantation and the local moments associated with the Sm ions.