Structural, optical and magnetic properties of Ni-Co co-doped ZnO thin films

Abstract

Undoped and Ni-Co co-doped ZnO thin films were successfully prepared by using spray pyrolysis technique. XRD analysis reveals that the secondary phases are not to be formed and confirms that Ni2+ and Co2+ ions are successfully penetrated into ZnO lattice. Raman spectra of undoped and Ni-Co co-doped ZnO thin films show that the films have Raman-active modes of crystalline wurtzite structure and defect vibration depending on Ni-Co co-doping. Furthermore, an additional peak (around ∼560 cm−1) appears with Ni-Co co-doping in Raman analysis, indicating the existence of oxygen vacancy defects. Ultraviolet-visible measurements show a red shift of ZnO band gap with Ni-Co co-doping. The red shift can be attributed to the sp-d exchange interaction between the localized d-electrons of Ni2+ and Co2+ ions and the band electrons in ZnO lattice. The surface morphologies of both thin films were examined by SEM. It is observed that both thin films have homogenous surface. Magnetization curve reveals that Ni-Co co-doped thin film has room temperature ferromagnetic (RTFM) behavior. The RTFM ordering has been elucidated with respect to intrinsic defects in the frame of bound magnetic polaron model. Ni-Co co-doped thin film can be employed as DMS material in spintronic applications.