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 ε 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 ε 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 ε by 1.2 K. A previously unknown low-temperature incommensurate magnetic phase of ErMn ₂O₅ below 8K 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.