Control of ferroelectric polarization in multiferroic YMn₂O ₅ by external pressure

We show that the application of external hydrostatic pressure can reverse the ferroelectric polarization of multiferroic YMn₂O₅ at low temperatures. This unique effect is explained by the peculiarities of the highly frustrated magnetic order that is typical for all RMn₂O ₅ (R=rare earth) in the commensurate and incommensurate phases. Our results indicate that the pressure changes the relative phase of adjacent antiferromagnetic spin chains propagating along the orthorhombic a-axis. With further compression the incommensurate phase transforms into the commensurate phase with the highest ferroelectric polarization.