Simultaneous measurements of magnetic neutron diffraction, electrical polarization and permittivity of multiferroic ErMn2O5

In order to determine an exact relationship between magnetic ordering and ferroelectricity in multiferroic rare-earth manganese oxides, we have performed simultaneous measurements of neutron diffraction, ferroelectric D-E hysteresis loops and the permittivity epsilon of ErMn2O5 down to 2.5 K. Special attention was paid to the area around the ferroelectric phase transition temperature. In contrast to previous expectations based on separate measurements, the peak of epsilon was found to coincide with a magnetic incommensurate-commensurate phase transition. However, it was confirmed that electrical polarization appears at the transition to a one-dimensionally incommensurate magnetic phase, which is higher than the peak of epsilon by 1.2 K. A previously unknown low-temperature incommensurate magnetic phase of ErMn2O5 below 8 K was found. The lowest-temperature phase appears to be paraelectric according to the D-E loops, while pyroelectric measurements show that the phase exhibits a small polarization.