  The electric polarization and its magnetic origins in multiferroic RMn2O5,
where R is rare-earth ion, are still issues under debate. In this work, the
temperature-dependent electric polarization of DyMn2O5, the most attractive
member of this RMn2O5 family, is investigated using the pyroelectric current
method upon varying endpoint temperature of the electric cooling, plus the
positive-up-negative-down (PUND) technique. It is revealed that DyMn2O5 at low
temperature does exhibit the unusual ferrielectricity rather than
ferroelectricity, characterized by two interactive and anti-parallel
ferroelectric sublattices which show different temperature-dependences. The two
ferroelectric sublattices are believed to be generated from the symmetric
exchange-striction mechanisms associated with the Mn-Mn spin interactions and
Dy-Mn spin interactions, respectively. The path-dependent electric polarization
reflects the first-order magnetic transitions in the low temperature regime.
The magnetoelectric effect is mainly attributed to the Dy spin order which is
sensitive to magnetic field. The present experiments may be helpful for
clarifying the puzzling issues on the multiferroicity in DyMn2O5 and probably
other RMn2O5 multiferroics.
