Activation of frozen ferroelectric domain wall by magnetic field sweeping in multiferroic CuFeO2.

In a ferroelectric helimagnetic phase of a spin-driven multiferroic, CuFeO2, we find irreversibly additive evolution of electric polarization P induced by sweeping magnetic field H under an applied electric field E, despite a large coercive electric field in the phase. From the unpolarized neutron diffraction experiments with in situ P measurements under applied E, we reveal that increment of P is achieved by the variation of an incommensurate magnetic modulation wave number q of the helical magnetic ordering in H sweeping regardless of increasing or decreasing H. Combining this result with the H dependence of the magnetic diffraction intensity and a result of off-bench P measurements, we conclude that the H evolution of P is caused by a change in a (ferroelectric) helicity domain volume fraction by driving the helicity domain wall (DW). Taking into account the results of further detailed P measurements, we provide a speculation for microscopic helicity DW motion. The present study demonstrates the magnetoelectric cross correlation in driving a multiferroic DW: we can activate the frozen ferroelectric DW by means of H sweeping. This is also an achievement of driving an antiferromagnetic DW, which is difficult in conventional antiferromagnets in principle. [ABSTRACT FROM AUTHOR]