Pressure-induced polarization reversal in multiferroic $YMn_2O_5$
  The low-temperature ferroelectric polarization of multiferroic $YMn_2O_5$ is completely reversed at a critical pressure of 10 kbar and the phase transition from the incommensurate to the commensurate magnetic phase is induced by pressures above 14 kbar. The high-pressure data correlate with thermal expansion measurements indicating a significant lattice strain at the low-temperature transition into the incommensurate phase. The results support the exchange striction model for the ferroelectricity in multiferroic $RMn_2O_5$ compounds and they show the importance of magnetic frustration as well as the spin-lattice coupling. 
Rajit P. Chaudhury, Clarina R. dela Cruz, Bernd Lorenz, Yanyi Sun,   Ching-Wu Chu, S. Park, and Sang-W. Cheong