Manipulation of Dy-Mn coupling and ferrielectric phase diagram of DyMn2O5: The effect of Y substitution of Dy.

DyMn₂O₅ is an extraordinary example in the family of multiferroic manganites and it accommodates both the 4f and 3d magnetic ions with strong Dy-Mn (4f-3d) coupling. The electric polarization origin is believed to arise not only from the Mn spin interactions but also from the Dy-Mn coupling. Starting from proposed scenario on ferrielectricity in DyMn₂O5 where the exchange-strictions associated with the Mn³⁺-Mn⁴⁺-Mn³⁺ blocks and Dy³⁺-Mn⁴⁺-Dy³⁺ blocks generate the two ferroelectric sublattices, we perform a set of characterizations on the structure, magnetism, and electric polarization of Dy_1-xY_xMn₂O₅ in order to investigate the roles of Dy-Mn coupling in manipulating the ferrielectricity. It is revealed that the non-magnetic Y substitution of Dy suppresses gradually the Dy³⁺ spin ordering and the Dy-Mn coupling. Consequently, the ferroelectric sublattice generated by the exchange striction associated with the Dy³⁺-Mn⁴⁺-Dy³⁺ blocks is destabilized, but the ferroelectric sublattice generated by the exchange striction associated with the Mn³⁺-Mn⁴⁺-Mn³⁺ blocks remains less perturbed, enabling the ferrielectricity-ferroelectricity transitions with the Y substitution. A phenomenological ferrielectric domain model is suggested to explain the polarization reversal induced by the Y substitution. The present work presents a possible scenario of the multiferroic mechanism in not only DyMn₂O₅ but probably also other RMn₂O₅ members with strong 4f-3d coupling. [ABSTRACT FROM AUTHOR]