  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.
