Room temperature ferromagnetism in sol–gel deposited un-doped ZnO films

Dilute magnetic semiconductors are fast emerging spintronic materials where advantage of magnetic properties of semiconductor materials (usually doped with small quantities of magnetic ions) is being explored. Sol–gel technique, being low-cost simple and application oriented method, has been used in the present case. ZnO films of <150 nm thickness have been deposited by spin coating onto single crystal p-type Si substrates. The optimized sol is of paramagnetic nature, whereas, mixed para- dia-magnetic phase is observed for the as-prepared films. A complete ferromagnetic phase transition has been observed after heating the films in vacuum at a temperature of 300 °C. These sol–gel prepared films exhibit hexagonal wurtzite structure as observed by X-ray diffraction. After the magnetic field annealing in vacuum the films showed strengthened magnetic as well as structural properties. This work presents a clear evidence of ferromagnetic behavior of the un-doped ZnO films deposited by sol–gel at room temperature. It is also pointed out that Zn vacancies rather than oxygen deficiency are responsible for ferromagnetism in these sol–gel deposited ZnO thin films, whereas, the experimental evidence has been substantiated with the theoretical calculations using density functional theory.