Features of the magnetoelectric behavior of the family of multiferroics RMn2O5 at high magnetic fields (Review)

The family of multiferroics comprised of the orthorhombic manganates RMn2O5 (R=Eu,Gd,Er,Y), in which the coexistence of antiferromagnetism and ferroelectricity has been reported previously, is investigated at high magnetic fields. These compounds, unlike the members of the family RMnO3 (where R=Eu,Ge,Tb,Dy) have two subsystems of magnetic mixed-valence d ions Mn3+ and Mn4+, the direct and indirect interactions between which, being of the ferro- or antiferromagnetic type, depending on the particulars of the environment and properties of the rare-earth ions, enhance substantially the role of the frustrations observed in RMnO3 compounds. These systems, as a consequence of the specific combination of the additional magnetic degeneracy realized in them (due to competition between nearest- and next-nearest-neighbor interactions of nearly equal magnitude) and their strong magnetoelastic coupling, display a cascade of magnetic phase transitions, with the appearance/disappearance of incommensurate (modulated) magnetic structure independently along the a and c axes. The substantial magnetoelectric interactions observed in these systems provide the prerequisites not only for efficiently influencing the phase transitions by means of a magnetic field but also hold forth the possibility of magnetic control of electrical polarization effects.