  The behavior of the low-frequency electromagnon in multiferroic DyMnO3 has
been investigated in external magnetic fields and in a magnetically ordered
state. Significant softening of the electromagnon frequency is observed for
external magnetic fields parallel to the a-axis (BIIa), revealing a number of
similarities to a classical soft mode behavior known for ferroelectric phase
transitions. The softening of the electromagnon yields an increase of the
static dielectric permittivity which follows a similar dependence as predicted
by the Lyddane-Sachs-Teller relation. Within the geometry BIIb the increase of
the electromagnon intensity does not correspond to the softening of the
eigenfrequency. In this case the increase of the static dielectric permittivity
seem to be governed by the motion of the domain walls.
