Abstract
Using Green's function theory and a microscopic model, the multiferroic properties of Co4Nb2O9 are investigated theoretically. There are some discrepancies in the discussion of the electric and dielectric behavior of CNO with and without external magnetic fields. We try to clarify them. It is observed that the polarization and the dielectric constant do not show a peak at the antiferromagnetic phase transition temperature TN without an external magnetic field h. But applying h, there appears a peak around the Neel temperature TN, which increases with increasing h and then shifts to lower temperatures. The magneto-dielectric coefficient MD(T,h) is also calculated. Moreover, the magnetization rises with an increasing external electric field below the Neel temperature. This shows strong magnetoelectric coupling in Co4Nb2O9. The obtained results are compared with the existing experimental data. There is a good qualitative agreement.