1. Graduate School of Natural and Applied Sciences, Gazi University, Ankara 06830, Turkey
2. Physics Group, Atilim University, Ankara 06830, Turkey
3. Department of Physics, Gazi University, Ankara 06830, Turkey
4. Department of Physics, Canakkale Onsekiz Mart University, Canakkale 17100, Turkey
5. Department of Physics, Middle East Technical University, Ankara 06830, Turkey