Ferromagnetism In ZnO Thin Films Research Articles

Tuning of optical bandgap and magnetization of C-implanted ZnO thin films

The present study demonstrates that one can tune the bandgap and ferromagnetism in ZnO thin films by carbon implantation. The X-ray diffraction (XRD) study infers that at lower concentration, C ions prefer to occupy substitutional sites whereas at higher concentration it occupies partially interstitial sites. Combined with ferromagnetic behaviour, the results demonstrate that lower bandgap induces stronger magnetization and reverse in the case of wider bandgap. The optical and magnetic results are well supported by XRD and XPS measurements. These experimental results provide new evidence that ferromagnetic behaviour in these systems is closely related with the distribution of carbon ions in the host lattice.

Defects Induced Room Temperature Ferromagnetism in ZnO Thin Films

Polycrystalline ZnO thin films are prepared by the co-sputtering method under different oxygen partial pressures. Films deposited in pure argon gas exhibit ferromagnetism, whereas other films deposited under different oxygen partial pressures are diamagnetism. XPS results show the presence of Zn interstitial and oxygen vacancy in all of samples. Further analysis indicates that Zn interstitial may play an important role in triggering magnetic order on the undoped ZnO thin films by inducing an alteration of electronic configuration.

Reversible Ferromagnetism Study in Un-Doped ZnO Thin Films

Room temperature ferromagnetism in pure ZnO thin films prepared by spin-coating method was observed. X-ray photoelectron spectroscopy and inductively coupled plasma-mass spectrometry showed no or extremely little presence of impurities, which were unlikely to be responsible for the large magnetization moment observed. In order to study the origin of ferromagnetism, ZnO thin films were rapidly annealed in N2 and O2 ambient in a repetitive way. Electrical and magnetic performance after each annealing was measured. It is found that ferromagnetism is diminished and re-appeared, in accordance with the decrease and increase of conductivity. Cathodoluminescence spectra show evidence of reversible variation of oxygen vacancy defect in the annealing process. These results provide strong evidence that oxygen vacancies play a significant role in inducing ferromagnetism in ZnO thin films.