Activation of frozen ferroelectric domain wall by magnetic field sweeping in multiferroicCuFeO2

Abstract

In a ferroelectric helimagnetic phase of a spin-driven multiferroic CuFeO2, we have found 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 have revealed 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 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 domains volume fraction by driving the helicity domain wall (DW). Taking into account the results of further detailed P measurements, we propose a possible model of the phenomenon that, instead of simply driving the helicity DW, the variation of q causes the neighborhood of the helicity DWs to store an extra exchange energy and to be sensible for E, and then, these regions and the helicity DWs are reconstructed by applied E so as to enlarge the helicity domain favored by the direction of E. The present study demonstrates the magneto-electric cross correlation in driving multiferroic DW: we could 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.

Influence of nonmagnetic Ga ions on the magnetoelectric coupling in CuFe1−x Ga x O2

“…The magnetization has the same variation tendency with a magnetic field between 0.1 and 7 T, and figure 2(f) shows the details of the lower temper ature region at 1 T. The following discussion uses the temper ature dependence magnetization at 1 T as an example to clarify the magnetization behavior. In CuFe 0.98 Ga 0.02 O 2 , with temperature decreasing from room temperature, magnetization increases, and then a transition from the PM phase to the PD phase is observed at T N1 ~ 14 K, and another sharp transition is observed at 8.3 K, and it is an FEIC phase below 8.3 K [10]. In order to distinguish the T N2 in pure CuFeO 2 , this transition temperature is defined as T L N2 .…”

“…The variation of dielectric polarization with magnetic field in some materials is a representative magnetoelectric coupling effect [5][6][7][8]. Also, the delafossite CuFeO 2 is a particular class of magnetoelectric multiferroic material which has received considerable attention due to the geometrically frustrated magnetic spin systems, in which the dielectric polarization can be modulated by an external magn etic field [9,10].…”