Anomalous Coexistence of Ferroelectric Phases (P ∥a and P ∥c) in Orthorhombic Eu1-yYyMnO3 (y > 0.5) Crystals

We have investigated the magnetic and dielectric properties of orthorhombic Eu 1- y Y y MnO 3 (0 ≤ y ≤0.6) single crystals without the presence of the 4 f magnetic moments of the rare-earth ions. In y ≥0.2, the magnetic-structure driven ferroelectricity is observed. The ferroelectric transition temperature is steeply reducing with increasing y . In y ≥0.52, two ferroelectric phases ( P ∥ a and P ∥ c ) are coexistent at low temperatures. In these phases, ferroelectricity has different origin, which is evidenced by the distinctive poling-electric-field dependence of electric polarization. Namely, the electric polarization along the c -axis ( P c ) is easily saturated by a poling electric field, therefore P c is caused by the b c -spiral antiferromagnetic order. On the other hand, the electric polarization along the a -axis ( P a ) is probably attributed to the collinear E -type antiferromagnetic order, because P a is unsaturated even in a poling field of 10 6 V/m.