Pressure induced enhancement of ferroelectricity in multiferroic $R$Mn$_2$O$_5$($R$=Tb,Dy, and Ho)

TL;DR

This study demonstrates that applying hydrostatic pressure enhances ferroelectricity in $R$Mn$_2$O$_5$ compounds by inducing a phase transition to a commensurate magnetic structure, as shown through detailed pressure-temperature phase diagrams.

Contribution

It provides the first detailed pressure-temperature phase diagrams for $R$Mn$_2$O$_5$ ($R$=Tb,Dy,Ho), revealing pressure-induced stabilization of ferroelectricity linked to magnetic structure changes.

Findings

Pressure quenches dielectric anomalies at low temperatures.

High ferroelectric polarization correlates with commensurate magnetic order.

Pressure induces a phase transition to a more stable ferroelectric state.

Abstract

Measurements of ferroelectric polarization and dielectric constant were done on $R$Mn$_2$O$_5$ ($R$=Tb, Dy, and Ho) with applied hydrostatic pressures of up to 18 kbar. At ambient pressure, distinctive anomalies were observed in the temperature profile of both physical properties at critical temperatures marking the onset of long range AFM order (T$_{N1}$), ferroelectricity (T$_{C1}$) as well as at temperatures when anomalous changes in the polarization, dielectric constant and spin wave commensurability have been previously reported. In particular, the step in the dielectric constant at low temperatures (T$_{C2}$), associated with both a drop in the ferroelectric polarization and an incommensurate magnetic structure, was shown to be suddenly quenched upon passing an $R$-dependent critical pressure. This was shown to correlate with the stabilization of the high ferroelectric polarization state which is coincident with the commensurate magnetic structure. The observation is suggested to be due to a pressure induced phase transition into a commensurate magnetic structure as exemplified by the pressure-temperature ($p$-$T$) phase diagrams constructed in this work. The $p$-$T$ phase diagrams are determined for all three compounds.