Optical Properties of Magnetoelectric Gallium Ferrite

Effect of Site-disorder, Off-stoichiometry and Epitaxial Strain on the 1 Optical Properties of Magnetoelectric Gallium Ferrite 2 3 Amritendu Roy, Somdutta Mukherjee, Surajit Sarkar, Sushil Auluck, Rajendra 4 Prasad, Rajeev Gupta 4 and Ashish Garg 5 6 Department of Materials Science & Engineering, Indian Institute of Technology, 7 Kanpur-208016, India 8 Department of Physics, Indian Institute of Technology, Kanpur 208016, India 9 National Physical Laboratory, Dr. K. S. Krishnan Marg, New Delhi-110012, India 10 Materials Science Programme, Indian Institute of Technology, Kanpur 208016, India 11 12 ABSTRACT 13 14 We present a combined experimental-theoretical study demonstrating the role of site 15 disorder, off-stoichiometry and strain on the optical behavior of magnetoelectric gallium 16 ferrite. Optical properties (band-gap, refractive indices and dielectric constants) were 17 experimentally obtained by performing ellipsometric studies over the energy range 0.8 – 18 4.2 eV on pulsed laser deposited epitaxial thin films of stoichiometric gallium ferrite with 19 b-axis orientation and the data was compared with theoretical results. Calculations on the 20 ground state structure show that the optical activity in GaFeO3 arises primarily from O2p21 Fe3d transitions. Further, inclusion of site disorder and epitaxial strain in the ground state 22 structure significantly improves the agreement between the theory and the room 23 temperature experimental data substantiating the presence of site-disorder in the 24 experimentally derived strained GaFeO3 films at room temperature. We attribute the 25 modification of the ground state optical behavior upon inclusion of site disorder to the 26 corresponding changes in the electronic band structure, especially in Fe3d states leading 27 to a lowered band-gap of the material. 28 29 30