A polarization memory effect of the paramagnetic nonpolar phase is observed in magnetoelectric antiferromagnet Co4Nb2O9, which has a magnetic field induced polarization in the antiferromagnetic phase. Following magnetoelectric poling in the polar phase, the nonpolar paramagnetic state retains a strong memory of polarization. When reentering the polar phase without applying the electric field, a polarization along the initial poling direction is recovered. If the applied magnetic field while staying in the paramagnetic phase is weakened, the memory effect is enhanced. With reversing this magnetic field, the polarization is also reversed when reentering the polar phase. The memory effect can be attributed to the ferroelectric seeds forming in the nonpolar phase due to short-range magnetic ordering as evidenced by magnetic entropy data.

Pyrocurrent and dielectric properties of magnetoelectric antiferromagnet Co4Nb2O9 have been investigated. The sample shows 2 thermally activated dielectric relaxations in the temperature range far above Néel temperature with the low‐ and high‐temperature ones being a dipolar and Maxwell‐Wagner relaxations, respectively. Two types of dipoles: relaxing dipoles and magnetic‐field‐induced dipoles were found in the sample. An internal electric field is formed due to the ordering of relaxing dipoles. Three current peaks were observed. The 2 higher temperature current peaks correspond to the dielectric relaxations. The lowest temperature current peak contains a positive tip and negative dip. The tip and dip are related to the depolarization of ferroelectricity induced by external and internal fields, respectively.

The possibility of switching the magnetically induced polarization (MIP) in magnetoelectric antiferromagnet Co4Nb2O9 by a dielectric-relaxation-related internal electric field was investigated. The MIP at a lower temperature is more difficult to be reversed, and this can be explained based on the Landau-Ginzburg-Devonshire theory as well as the domain nucleation and growth theory.