[1] Bharath Univ, Dept Phys, Madras 600073, Tamil Nadu, India
[2] Sriram Engn Coll, PG & Res Dept Phys, Perumalpattu 602024, India
[3] Presidency Coll, Dept Phys, Chennai 600005, Tamil Nadu, India
[4] Easwari Engn Coll, Dept Phys, Chennai 600089, Tamil Nadu, India