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

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We have investigated the magnetic and dielectric properties of orthorhombic Eu1-yYyMnO3 (0 \leq y \leq 0.6) single crystals without the presence of the 4f magnetic moments of the rare-earth ions. In y \geq 0.2, the magnetic-structure driven ferroelectricity is observed. The ferroelectric transition temperature is steeply reducing with increasing y. In y \geq 0.52, two ferroelectric phases (P \parallel a and P \parallel 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 bc-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.
2011-09-15