1. Department of Physics, University of Lucknow, Lucknow, India 226007
2. Department of Materials Science and Nano Engineering, Rice University, Houston, Texas 7005, United States
3. School of Physics, Madurai Kamaraj University, Madurai 625021, Tamil Nadu, India
4. Department of Applied Physics, State University of Campinas, Campinas SP 13083-959, Brazil