Pressure Effect on Ferroelectric Properties of GdMn2O5 and TmMn2O5

The pressure effect on the ferroelectric (FE) properties of the multiferroic compounds GdMn
₂
O
₅
and TmMn
₂
O
₅
was studied up to 18.2 kbars. A new FE phase was observed at a higher temperature in GdMn
₂
O
₅
above a critical pressure, P
_c
≈10 kbars. Our results indicate that pressure decouples the Gd moment from Mn spin system and splits the FE phase. Thermal expansion measurements reveal a large increase of the c-axis at the ambient-pressure FE transition. The pressure-induced contraction of the c lattice parameter is considered to be the origin of the decoupling of both spin systems above P
_c
. From the dielectric and FE properties of GdMn
₂
O
₅
, a pressure-temperature phase diagram can be derived. While a new phase was discovered for GdMn
₂
O
₅
, no significant change in polarization was observed for TmMn
₂
O
₅
up to 16.6 kbars.