Magnetoelectric effect and field-induced 'incommensurate-homogeneous' phase transitions in EuMn2O5

The magnetoelectric effect and phase transitions induced by a strong magnetic field (up to 200 kOe) in single crystals EuMn2O2 have been investigated. It is known that these compounds have an incommensurate magnetic structure. The electric polarization of the single crystals were measured, along the a, b-, and c-axes of the crystals, and the magnetic field was oriented along the c-axis. At low magnetic fields (H < 100 kOe), the dependencies of the electric polarization on the magnetic field are practically quadratic ones which correlate well with the above mentioned incommensurate magnetic structure of the compounds. The jump-like anomalies of the curves 'the electric polarization-magnetic field' were discovered. The critical fields H-ef of these jumps are of 100 kOe order and depend more on the temperature. There is in general, a large linear contribution of the electric polarization into the magnetic field dependence at H > H-ef. This favors that the field induced 'incommensurate-homogeneous' phase transition probably takes place at the critical field. (C) 1998 Elsevier Science B.V. All rights reserved.