1. Department of Physical Sciences, Redeemer’s University, P.M.B. 230, Ede, Nigeria
2. Department of Physics, Lancaster University, Lancaster LA1 4YB, UK
3. School of Engineering, University of Warwick, Coventry CV4 7Al, UK
4. School of Physics, Bharathidasan University, Tiruchirappalli 620 024, Tamilnadu, India