1. Center for Memory and Recording Research, University of California, San Diego, La Jolla, California 92093-0401, USA
2. Department of Physics, School of Sciences, National Institute of Technology, Andhra Pradesh-534102, India
3. Radboud University, Institute for Molecules and Materials, Heyendaalseweg 135, Nijmegen 6525 AJ, The Netherlands
4. Department of Physics, Lancaster University, Bailrigg, Lancaster LA1 4YW, United Kingdom