1. Department of Physics, Bogazici University, Bebek, 34342 Istanbul, Turkey
2. Department of Physics, Karamanoglu Mehmetbey University, 70100 Karaman, Turkey
3. Department of Electrical and Electronic Engineering, Bogazici University, Bebek, 34342 Istanbul, Turkey
4. Department of Physics, Colombia University, New York, New York 10027, USA
5. HGST, A Western Digital Company, San Jose, California 95135, USA