  Cu3Nb2O8 is an unusual multiferroic compound that undergoes a series of
magnetic ordering at low temperatures. Concurrent development of electric
polarization has been reported at TN1 ~25 K corresponding to a non-collinear
helicoidal ordering (Phys. Rev. Lett. 107, 137205 (2011)). But questions remain
on the microscopic origin of such phenomena. In this communication, we report a
detailed study of induced polar ordering in Cu3Nb2O8 by performing
polarization, magnetization, dielectric constant and heat capacity measurements
over a broad range of temperature and magnetic field. The dielectric constant
shows suppression in the magnetic field but it does not shift to lower
temperature with the application of external field. The appearance of
magneto-dielectric effect signifies the contribution of q-dependent magnetic
correlation function with enhanced weightage in the presence of magnetic field.
This magnetic correlation function is associated with the ferro-axial vector
and our overall results support this mechanism for the observation of
muliferroicity in Cu3Nb2O8.
