Charge carrier self-organization in ferroelectromagnetic semiconductors Eu₀.₈Ce₀.₂Mn₂O₅

Abstract

The state with a giant permittivity (ε~10⁴) and ferromagnetism has been observed above 185 K (including room temperature) in single crystals of diluted semiconductor manganite–ferroelectromagnetic Eu₀.₈Ce₀.₂Mn₂O₅ in the investigations of x-ray diffraction, dielectric and magnetic properties, conductivity. X-ray diffraction study has revealed a layered superstructure along the c axis at room temperature. A model of the state with a giant ε including as-grown 2D layers with doping impurities, charge carriers, and double-exchange coupled Mn³⁺–Mn⁴⁺ ion pairs is suggested. At low temperatures these layers form isolated electrically neutral small-size 1D superlattices, in which de Haas van Alphen oscillations were observed. As temperature grows and hopping conductivity increases, the charge carrier self-organization in the crystal cause formation of a layered superstructure consisting of charged layers (with an excess Mn³⁺ concentration) alternating with dielectric layers of the initial crystal — the ferroelectricity state due to charge ordering. Ferromagnetism results from double exchange between Mn³⁺ and Mn⁴⁺ ions through of charge carriers in the charged layers.