The pressure effect on the ferroelectric (FE) properties of the multiferroic compounds GdMn2O5 and TmMn2O5 was studied up to 18.2 kbars. A new FE phase was observed at a higher temperature in GdMn2O5 above a critical pressure, Pc ≈ 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 Pc. From the dielectric and FE properties of GdMn2O5, a pressureerature phase diagram can be derived. While a new phase was discovered for GdMn2O5, no significant change in polarization was observed for TmMn2O5 up to 16.6 kbars.
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