Effect of cobalt substitution on structural, impedance, ferroelectric and magnetic properties of multiferroic Bi_2Fe_4O_9 ceramics

TL;DR

This study investigates how cobalt substitution affects the structural, electrical, ferroelectric, and magnetic properties of Bi2Fe4O9 ceramics, revealing enhanced multiferroic behavior and magnetic properties with Co doping.

Contribution

It provides new insights into the effects of low-level Co substitution on multiferroic Bi2Fe4O9 ceramics, including phase formation, improved ferroelectricity, and magnetic properties.

Findings

Cobalt substitution induces secondary phase formation at x≥0.01.

Enhanced remnant polarization with increasing Co content.

Improved ferromagnetic hysteresis and magnetization with Co doping.

Abstract

Structural, impedance, ferroelectric and magnetic properties were examined in multiferroic Bi_{2}Fe_{4(1-x)}Co_{4x}O_{9} (0$\leq$x$\leq$0.02) ceramics synthesized via solid-state reaction method. X-ray diffraction analysis and Rietveld refinement showed secondary phase formation (for x$\geq$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 lie 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 polarisation (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 to 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 Co^{3+} ions leading to breakdown of balance between the anti-parallel sub lattice magnetization of Fe^{3+} ions.