Large magnetocapacitance in electronic ferroelectric manganite systems

We have observed a sizable positive magnetocapacitance ($\sim$$5-90\%\() in perovskite Pr\)_{0.55}\(Ca\)_{0.45}\(MnO\)_3\( and bilayer Pr(Sr\)_{0.1}\(Ca\)_{0.9}\()\)_2\(Mn\)_2\(O\)_7\( system under 5T magnetic field across 20-100 K below the magnetic transition point T\)_N\(. The magnetodielectric effect, on the other hand, exhibits a crossover: (a) from positive to negative for the perovskite system and (b) from negative to positive for the bilayer system over the same temperature range. The bilayer Pr(Sr\)_{0.1}\(Ca\)_{0.9}\()\)_2\(Mn\)_2\(O\)_7\( system exhibits a sizable anisotropy as well. We have also noticed the influence of magnetic field on the dielectric relaxation characteristics of these systems. These systems belong to a class of improper ferroelectrics and are expected to exhibit charge/orbital order driven ferroelectric polarization below the transition point T\)_{CO}$. Large magnetocapacitance in these systems shows typical multiferroic behavior even though the ferroelectric polarization is small in comparison to that of other ferroelectrics.