The magnetic properties of Gd-doped ZnO films and nanostructures are important to the development of next-generation spintronic devices. Here, we elucidate the significant role played by Gd-oxygen-deficiency defects in mediating/inducing ferromagnetic coupling in in situ Gd-doped ZnO thin films deposited at low oxygen pressure by pulsed laser deposition (PLD). Samples deposited at higher oxygen pressures exhibited diamagnetic responses. Vacuum annealing was used on these diamagnetic samples (grown at a relatively high oxygen pressures) to create oxygen- deficiency defects with the aim of demonstrating reproducibility of room-temperature ferromagnetism (RTFM). Samples annealed at oxygen environment exhibited super- paramagnetism and blocking-temperature effects. The samples possessed secondary phases; Gd segregation led to superparamagnetism. Theoretical studies showed a shift of the 4f level of Gd to the conduction band minimum (CBM) in Gd-doped ZnO nanowires, which led to an overlap with the Fermi level, resulting in strong exchange coupling and consequently RTFM.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: The authors would like to thank the team involved in this study. In particular, we thank Zhenkui Zhank, Shamima Hussain, Tahani H. Flemban, and Ioannis Bantounas from our group at KAUST. We thank J.B. Franklin, B. Zou, P.K. Petrov, M.P. Ryan, and N.M. Alford from Imperial College London and J-S. Lee from the Stanford Synchrotron Radiation Light- source, SLAC National Accelerator Laboratory. We thank P. Edwards, K.P. O’Donnell, and R.W. Martin for providing access to the EPMA for WDX measurements at the University of Strathclyde. We thank Ratnamal Chatterjees’s group at IIT Delhi, India, for conducting the SQUID experiments.