  This work reports an experimental investigation of the magneto-elastic
coupling and polarization character of magnetic phases of the orthorhombic
Eu1-xYxMnO3 system at low temperatures. The temperature dependence of the
polarization reversal curves clearly reveals the existence of a reentrant
improper ferroelectric phase for x = 0.2 and 0.3. Although a ferroelectric
phase is also stable for x = 0.4, we have no experimental evidence that it
vanishing at finite temperatures. From these results and those obtained from
other experimental techniques, the corresponding (x,T) phase diagram was
traced, yet yielding significant differences with regard to previous reports.
An expressive magneto-elastic coupling is revealed by changes observed in both
Mn-O bond lengths and Mn-O1-Mn bond angle at the magnetic phase transitions,
obtained by temperature dependence of synchrotron x-ray diffraction
experiments. Furthermore, signatures of the lattice deformations across the
magnetic phase transitions were evidenced by anomalies in the temperature
dependence of the lattice mode involving rotations of the MnO6 octahedra. These
anomalies confirm the important role of the spin-phonon coupling in these
materials.
