Observation of electric polarization in Gd_1−x Sr_xMnO₃ (x = 0.5, 0.6, 0.7) single crystals

Abstract

In Gd_1−x Sr_xMnO₃ (x = 0.5, 0.6, 0.7) single crystals, a change in electric polarization (ΔP ∼ 100 μK/m²) is found to accompany the suppression of the charge-ordered spin-glass state and the transition to the ferromagnetic conducting phase (H _cr ∼ 100 kOe at 4.5 K). The transition is also characterized by jumps in magnetization and magnetostriction. The sign of the induced polarization depends on the polarity of the electric field in which the sample was preliminarily cooled. This dependence testifies to the presence of spontaneous electric polarization in the system. The effect is maximal at x = 0.5 and decreases by more than an order of magnitude as x increases to 0.7. The phenomenon observed in the experiment may be associated with the new noncentrosymmetric structures with an electric dipole moment that were recently predicted for manganites (x ∼ 0.5) [Nature Materials 3, 853 (2004)]. These structures exhibit charge-orbital ordering such that e _g electrons are not localized by one of the manganese ions but distributed between neighboring ions, thus forming an ordered dimer structure.