Abstract
In a ferroelectric helimagnetic phase of a spin-driven multiferroic, , we find irreversibly additive evolution of electric polarization induced by sweeping magnetic field under an applied electric field , despite a large coercive electric field in the phase. From the unpolarized neutron diffraction experiments with in situ measurements under applied , we reveal that increment of is achieved by the variation of an incommensurate magnetic modulation wave number of the helical magnetic ordering in sweeping regardless of increasing or decreasing . Combining this result with the dependence of the magnetic diffraction intensity and a result of off-bench measurements, we conclude that the evolution of 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 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 sweeping. This is also an achievement of driving an antiferromagnetic DW, which is difficult in conventional antiferromagnets in principle.
2 More- Received 13 October 2015
- Revised 16 March 2016
DOI:https://doi.org/10.1103/PhysRevB.93.174101
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