Field-induced dielectric and magnetic phase transitions in multiferroic compounds of RMn₂O₅ (R = Er, Ho)

A microscopic magnetic phase diagram as functions of temperature and magnetic field was mapped for multiferroic compounds of RMn₂O ₅ (R = Er, Ho) by using neutron diffraction measurements under high magnetic field. The unambiguous relation between the ferroelectric phase transition and the magnetic phase transition from a two-dimensional incommensurate to a commensurate phase, where both the transitions are concomitantly induced by the magnetic field, indicates that the electric polarization is magnetically induced and the commensurate spin state is important for stabilizing the ferroelectricity in the multiferroic RMn ₂O₅ system. The origin of the field-induced magnetic phase transition is discussed based on the magnetic structure.