1. Materials and Physics Research Group, School of Science, Engineering and Environment, University of Salford, Salford M5 4WT, United Kingdom
2. University College London, London Centre for Nanotechnology, Gower Place, London WC1E 6BT, United Kingdom
3. Berlin Joint EPR Lab, Fachbereich Physik, Freie Universität Berlin, D-14195 Berlin, Germany
4. Institut Néel-CNRS-UJF-INPG, UPR2940, 25 rue des Martyrs, BP 166, 38042 Grenoble Cedex 9, France
5. Advanced Technology Institute, Faculty of Engineering and Physical Sciences, University of Surrey, Guildford GU2 7XH, United Kingdom
6. School of Materials Science and Engineering, Hubei University, Wuhan 430062, People's Republic of China
7. Department of Electrical and Electronic Engineering, University of Surrey, Guildford GU2 7XH, United Kingdom