Ferromagnetism in Gd-doped ZnO thin films mediated by defects

Defects play an inevitable role in controlling the optical and magnetic properties of ZnO. In this study, defects were introduced in gadolinium (Gd)-doped ZnO films by depositing in pure argon atmosphere. The pristine- and Gd-doped (0.05, 0.1 and 1 at%) films were deposited on Si(111) substrate by radio frequency magnetron sputtering at a substrate temperature of 450°C under Ar pressure of 0.02 mbar. Structural, morphological, chemical, optical and magnetic properties of the deposited films were studied by X-ray diffraction and Raman spectroscopy, atomic force microscopy, X-ray photoelectron spectroscopy, photoluminescence and vibrating sample magnetometer, respectively. It is confirmed that oxygen-deficient growth condition leads to the formation of oxygen vacancy (VO+) and zinc interstitial (Zni+) defects in the films. It is shown that a critical amount of Zni+ and VO+ along with the appropriate amount of Gd3+ ions are required to induce room temperature ferromagnetism in Gd-doped ZnO thin film deposited on Si(111) substrate. A possible mechanism has been proposed based on bound magnetic polaron model to explain the observed ferromagnetism.