Ferromagnetism in Ni-doped ZnO films: Extrinsic or intrinsic?

Here we report a detailed study aimed on understanding the origin of ferromagnetism in Ni-doped ZnO films. A pulsed laser deposition technique was used to deposit Ni-doped (5 at. %) ZnO films on sapphire (0001) substrates under different oxygen pressures ranging from 10(-6) to 0.1 Torr. Films were characterized using numerous characterization techniques including x-ray diffraction, x-ray photospectroscopy, energy dispersive x-ray spectroscopy, optical absorption spectroscopy, and electrical transport, magnetotransport, and magnetization measurements. A detailed structure-property correlation and analysis of our results revealed that the ferromagnetism in ZnO:Ni films is not an inherent property of the material but results due to a strong tendency of Ni to precipitate out in the ZnO matrix.