  Synthesis and extensive structural, pyroelectric, magnetic, dielectric and
magneto-electric characterizations are reported for polycrystalline Co4Nb2O9
towards unraveling the multiferroic state especially in reference to the
magnetic spin flop transition. Magnetic measurements confirm the Co4Nb2O9
becomes antiferromagnetic (AFM) at around 28 K but no clear evidence for
spin-flop effect was found. Associated with the magnetic phase transition, a
sharp peak in pyroelectric current indicates the appearance of the strong
magneto-electric coupling below Neel temperature (TN) with a large coupling
constant upto 17.8 uC/m^2T. Using temperature oscillation technique, we
establish Co4Nb2O9 to be a genuine multiferroic with spontaneous electric
polarization in the anti-ferromagnetic state.
