Anomalous Coexistence of Ferroelectric Phases (P [par]a and P [par]c) in Orthorhombic Eu sub( 1-y)Y sub( y)MnO sub( 3) (y > 0.5) Crystals

We have investigated the magnetic and dielectric properties of orthorhombic Eu ... Y ... MnO ... (0 less than or equal to y less than or equal to 0.6) single crystals without the presence of the 4 f magnetic moments of the rare-earth ions. In y greater than or equal to 0.2, the magnetic-structure driven ferroelectricity is observed. The ferroelectric transition temperature is steeply reducing with increasing y . In y greater than or equal to 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 ... ) is easily saturated by a poling electric field, therefore P ... is caused by the b c -spiral antiferromagnetic order. On the other hand, the electric polarization along the a -axis ( P ... ) is probably attributed to the collinear E -type antiferromagnetic order, because P ... is unsaturated even in a poling field of 10 ... V/m. (ProQuest: ... denotes formulae/symbols omitted.)