1. Department
of Applied Physics, The Hong Kong Polytechnic University, Hong Kong, China
2. Interdisciplinary
Materials Science Program, Vanderbilt University, Nashville, Tennessee 37235-0106, United States
3. Centre
for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973, United States
4. Central
European Institute of Technology, Brno University of Technology, Technická
10, 61669 Brno, Czech Republic
5. Institut Néel,
CNRS UPR2940, 25 rue des Martyrs BP166, 38042 Grenoble Cedex 9, France
6. Department
of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235-1807, United States
7. Department
of Physics, Imperial College London, London SW7 2AZ, United Kingdom