Phase separation with charge self-organization in the Tb0.95Bi0.05MnO3, Gd0.75Ce0.25Mn2O5, and Eu0.8Ce0.2Mn2O5 manganite multiferroics

New doped manganite multiferroics Tb0.95Bi0.05MnO3, Gd0.75Ce0.25Mn2O5, and Eu0.8Ce0.2Mn2O5, which are semiconductors, have been grown and studied. The starting dielectric multiferroics TbMnO3 and RMn2O5 (R = Gd and Eu) have close magnetic and ferroelectric ordering temperatures of 30-40 K. The crystals studied are multiferroics in which states with giant permittivity and ferromagnetism coexist at room temperature. An analysis of the dielectric properties suggests that, at temperatures T >= 180 K, these crystals undergo a phase separation involving dynamic periodic alternation of quasi-2D layers of mixed-valence manganese ions, a process accounting for the onset of charge-induced ferroelectricity. At low temperatures (T < 100 K), a small phase volume in the crystals is occupied by as-grown quasi-2D layers containing dopants and carriers. Most of the crystal volume is occupied by the carrier-free dielectric phase. Thermally activated hopping conduction involving carrier self-organization in the crystal matrix with ferroelectric frustrations drives a phase transition to the state of charge-induced ferroelectricity at T approximate to 180 K.