Large magnetocapacitance in electronic ferroelectric manganite systems

Abstract

We have observed a sizable positive magnetocapacitance (∼5%–90%) in perovskite Pr_0.55Ca_0.45MnO₃ and bilayer Pr(Sr_0.1Ca_0.9)₂Mn₂O₇ system under 5 T 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_0.1Ca_0.9)₂Mn₂O₇ 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 a typical multiferroic behavior even though the ferroelectric polarization is small in comparison to that of other ferroelectrics.