[1] Visva Bharati Univ, Dept Chem, Santini Ketan 731235, W Bengal, India
[2] SN Bose Natl Ctr Basic Sci, Dept Condensed Matter Phys & Mat Sci, Kolkata 700106, India
[3] Jadavpur Univ, Dept Phys, Kolkata 700032, India
[4] Max Planck Inst Eisenforsch GmbH, D-40237 Dusseldorf, Germany