Interrelation between the soliton lattice and electric polarization in RMn2O5 oxides

Magnetic transitions from the paramagnetic state to an incommensurate magnetic structure and then to an ordered phase with long-range antiferromagnetic order in RMn2O5 (R is a rare-earth ion) oxides are analyzed. It is shown that a transition from the paramagnetic to the incommensurate phase is associated with exchange as well as relativistic interactions and can be described, apart from the basic magnetic order parameter, by an associated order parameter (viz., electric polarization along the y axis of the crystal). As a result of such a transition, the emergence of electric polarization in the crystal is not accompanied by a change in crystal symmetry.