1. Department of Physics, Sultan Qaboos University, P.O. Box 36, PC 123 Muscat, Oman
2. Department of Physics, South Dakota State University, Brookings, South Dakota 57007, USA
3. Physics Department, University of Gothenburg, 412 96 Gothenburg, Sweden
4. Nebraska Center for Materials and Nanoscience, and Department of Physics and Astronomy, University of Nebraska, Lincoln, Nebraska 68588, USA
5. Materials Physics, School of ICT, Royal Institute of Technology (KTH), 164 40 Kista, Sweden
6. School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore