Giant spin-driven ferroelectric polarization in TbMnO3 under high pressure

The recent research on multiferroics has provided solid evidence that the breaking of inversion symmetry by spin order can induce ferroelectric polarization P. This type of multiferroics, called spin-driven ferroelectrics, often show a gigantic change in P on application of a magnetic field B. However, their polarization (< similar to 0.1 mu C cm(-2)) is much smaller than that in conventional ferroelectrics (typically several to several tens of mCcm(-2)). Here we show that the application of external pressure to a representative spin-driven ferroelectric, TbMnO3, causes a flop of P and leads to the highest P (approximate to 1.0 mu C cm(-2)) among spin-driven ferroelectrics ever reported. We explain this behaviour in terms of a pressureinduced magnetoelectric phase transition, based on the results of density functional simulations. In the high-pressure phase, the application of B further enhances P over 1.8 mu C cm(-2). This value is nearly an order of magnitude larger than those ever reported in spin-driven ferroelectrics.