d0 Ferromagnetism in undoped ZnO thin films: Effect of thickness, interface and oxygen annealing

We present a systematic study of the thickness dependency of the structural, electrical and magnetic properties of undoped ZnO thin films. The highest saturation moment (∼36.75 emu cm−3) was observed for the thinnest films. Both the undoped and 5% Co doped ZnO films of different thickness (0.066–1.1 μm) showed a diamagnetic behavior upon annealing in oxygen. Activation energy of quenching of ferromagnetism revealed oxygen vacancies as the key mediating defect in ferromagnetic ZnO thin films.