The Pressure Effect on the Ferroelectricity in Multiferroic $R$Mn$_{2}$O$_{5}$ ($R$=Tb, Dy, Ho)

The effect of isotropic pressure (\textbf{P}) up to 1.7 GPa on the magnetic and ferroelectric phase diagram of $R$Mn$_{2}$O$_{5}$ ($R$=Tb, Dy, Ho) is investigated. Distinctive anomalies of the $b$-axis dielectric constant identifying the critical temperatures for the various magnetic and ferroelectric transitions are monitored as a function of \textbf{P} and the temperature-pressure phase diagram of multiferroic $R$Mn$_{2}$O$_{5}$ was constructed. The magnetic and ferroelectric orders are stabilized under pressure and their respective onset temperatures increase with \textbf{P}. Most notably, the step-like change of the dielectric constant at lower temperatures (T$_{C2})$ that is associated with a drop in the ferroelectric polarization is suddenly quenched upon passing a critical pressure. These results suggest that above the critical pressure the ferroelectric polarization is restored below T$_{C2}$ and the ferroelectric phase in RMn$_{2}$O$_{5}$ is stabilized and extends to the lowest temperatures. $^{\ast }$also at LBNL, Berkeley and HKUST, Hong Kong