Effect of cobalt substitution on structural, impedance, ferroelectric and magnetic properties of multiferroic Bi2Fe4O9 ceramics

Structural, impedance, ferroelectric and magnetic properties were examined in multiferroic Bi2Fe4(1-x)Co4xO9 (0 <= x <= 0.02) ceramics synthesized via solid-state reaction method. X-ray diffraction analysis and Rietveld refinement showed secondary phase formation (for x >= 0.01) which was subsequently confirmed from room temperature Raman spectroscopy study. The frequency dependence of impedance and electric modulus of the material showed the presence of non-Debye type relaxation in all the samples. The values of the activation energies calculated from imaginary impedance and modulus lay in the range of 0.92-0.99 eV which confirmed that the oxygen vacancies play an important role in the conduction mechanism. Moreover, suitable amount of Co substitution significantly enhanced the remnant polarization (2P(r)) from 0.1193 mu C/cm(2) (x=0) to 0.2776 mu C/cm(2) (x=0.02). Besides, room temperature M-H measurement showed improved ferromagnetic hysteresis loop for all the modified samples. The remnant magnetization (M-r) and coercive field (H-c) increased from 0.0007 emu/gm and 42 Oe for x=0-0.1401 emu/gm and 296 Oe for x=0.02. The improved ferroelectricity was due to Co 3d-O 2p hybridization and enhanced magnetization originated from the partial substitution of Co3+ ions leading to breakdown of balance between the anti-parallel sub lattice magnetization of Fe3+ ions. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.