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 (oB0.1 mC cm À 2 ) is much smaller than that in conventional ferroelectrics (typically several to several tens of mC cm À 2 ). Here we show that the application of external pressure to a representative spin-driven ferroelectric, TbMnO 3 , causes a flop of P and leads to the highest P (E1.0 mC cm À 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 mC cm À 2 . This value is nearly an order of magnitude larger than those ever reported in spin-driven ferroelectrics.

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The manipulation of domains by external fields in ferroic materials is of major interest for applications. In multiferroics with strongly coupled magnetic and electric order, however, the magnetoelectric coupling on the level of the domains is largely unexplored. We investigated the field-induced domain dynamics of TbMnO3 in the multiferroic ground state and across a first-order spin-flop transition. In spite of the discontinuous nature of this transition, the reorientation of the order parameters is deterministic and preserves the multiferroic domain pattern. Landau-Lifshitz-Gilbert simulations reveal that this behavior is intrinsic. Such magnetoelectric correlations in spin-driven ferroelectrics may lead to domain wall-based nanoelectronics devices.

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