Photo-induced magnetoresistance of nanocrystalline ZnO thin film

Nanocrystalline zinc oxide thin film has been prepared by conventional spray method. The optical energy gap is about 3.39 eV, which is greater than the energy gap of bulk ZnO. The prepared thin film has semiconductor behavior in dark measurements, while it has metallic behavior under ultraviolet illumination. There is a negative magnetoresistance effect for the prepared film under ultraviolet radiation. Furthermore, there is a magnetic transition from diamagnetic to paramagnetic state under ultraviolet radiation. The results has been explained in terms of the band conduction theory and spin polaron model. (author)