Possible coexistence of cycloidal phases, magnetic field reversal of polarization, and memory effect in multiferroic R0.5Dy0.5MnO3 (R = Eu and Gd)

Abstract

We report the occurrence of both ab and bc cycloidal ordering of Mn-spins at different temperatures and their possible coexistence at low temperatures in the polycrystalline mixed rare-earth compounds, R_0.5Dy_0.5MnO₃ (R = Eu and Gd), which exhibit extraordinary magnetoelectric properties. While the polarization of Gd_0.5Dy_0.5MnO₃ is comparable to TbMnO₃, the compound Eu_0.5Dy_0.5MnO₃ shows high value of polarization. However, both of them show giant magnetic tunability and exhibit large magnetocapacitance whose sign changes across the two cycloidal ordering temperatures. Intriguingly, the electric polarization can be reversed upon ramping up or ramping down the magnetic field, which has not been observed for any of the RMnO₃ system. Most strikingly, these compounds show non-volatile ferroelectric memory effect even in the paraelectric and paramagnetic region (TC ≤ T ≤ 80 K). We attribute these remarkable properties to the coexistence of ab and bc cycloidal ordered phases.