Influence of Film Thickness and Oxygen Partial Pressure on Cation-Defect-Induced Intrinsic Ferromagnetic Behavior in Luminescent p-Type Na-Doped ZnO Thin Films

In this article, we have investigated the effect of oxygen partial pressure (P-O2) and film thickness on defect-induced room-temperature (RT) ferromagnetism (FM) of highly c-axis orientated p-type Na-doped ZnO thin films fabricated by pulse laser deposition (PLD) technique. We have found that the substitution of Na at Zn site (Na-Zn) can be effective to stabilize intrinsic ferromagnetic (FM) ordering in ZnO thin films with Curie temperature (T-C) as high as 509 K. The saturation magnetization (M-S) is found to decrease gradually with the increase in thickness of the films, whereas an increase in M-S is observed with the increase in P-O2 of the PLD chamber. The enhancement of ferromagnetic signature with increasing P-O1 excludes the possibility of oxygen vacancy (V-O) defects for the magnetic origin in Na-doped ZnO films. On the other hand, remarkable enhancement in the green emission (I-G) are observed in the photoluminescence (PL) spectroscopic measurements due to Na-doping and that indicates the stabilization of considerable amount of Zn vacancy (V-Zn)-type defects in Na-doped ZnO films. Correlating the results of PL and X-ray photoelectron spectroscopy (XPS) studies with magnetic measurements we have found that V-Zn and Na substitutional (Na-Zn) defects are responsible for the hole-mediated FM in Na-doped ZnO films, which might be an effective candidate for modern spintronic technology.