Magnetic-Field-Induced Polarization Flop in Multiferroic TmMn2O5

We discovered a reversible electric polarization flop from the a axis (P-a) to the b axis (P-b) in multiferroic TmMn2O5 below 5 K by applying a magnetic field of approximately 0.5 T along the c axis. This phenomenon is the first example of the rare-earth (R) compound RMn2O5. This magnetic-field-induced polarization flop corresponds to a magnetic phase transition from one incommensurate magnetic (ICM) P-a phase to another ICM P-b phase, which is equivalent to an ICM P-b phase above 5 K under no magnetic field. The spin chirality in the bc plane, which was observed in the P-b phase by polarized neutron diffraction, disappeared in the ICM P-a phase. This indicates that the polarization in the ICM phases of TmMn2O5 was induced by an S-i x S-j-type interaction.