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By using broadband linear and non-linear dielectric spectroscopy we studied the magnetoelectric dynamics in the chiral antiferromagnet MnWO4. In the multiferroic phase the dielectric response is dominated by the dynamics of domains and domain walls which is strongly dependent on the stimulating electric field. The mean switching time reaches values in the minute range in the middle of the multiferroic temperature regime at T ≈ 10 K but unexpectedly decays again on approaching the lower, first-order phase boundary at TN1 ≈ 7.6 K. The switchability of the ferroelectric domains denotes a pinning-induced threshold and can be described considering a growth-limited scenario with an effective growth dimension of d ≈ 1.8. The rise of the effective dynamical coercive field on cooling below the TN2 is much stronger compared to the usual ferroelectrics and can be described by a power law Ec ∝ ν 1/2 . The latter questions the feasibility of fast switching devices based on this type of material.PACS numbers: 75.85.+t, 75.30.Mb, 75.60.Ch A. IntroductionIn recent years magnetoelectric multiferroics have attracted considerable interest within the community of correlated transition-metal compounds 1,2 . In these compounds ferroelectric order and magnetism do not only coexist in a single phase but exhibit strong coupling of the ferroic order parameters. Among other mechanisms the probably most established magnetoelectric coupling scenario is based on the inverse Dzyaloshinskii-Moriya (DM) interaction in partially frustrated spiral magnets 3,4 . This type of magnetically driven ferroelectricity is the underlying mechanism, e.g., in the numerously studied family of multiferroic manganites such as TbMnO 3 5,6 and in principle is now well understood. In these compounds a non-collinear cycloidal spin-structure is directly coupled to a ferroelectric polarization resulting from the coherent distortion of the Mn-O-Mn bonds perpendicular to the propagation vector of the spin-cycloid. However, the manifestation of a magnetoelectrically coupled multiferroic phase and the formation of the complex, magnetoelectric order parameter raises questions concerning the corresponding dynamics.One aspect is given by the elementary excitations within the ordered multiferroic phase, the so called electromagnons, as they were detected, e.g., in perovskite manganites in a typically sub-phononic region below terahertz frequencies 7-9 . Another aspect is the low frequency dielectric response originating from intrinsic or extrinsic sample inhomogeneities. In materials with a residual conductivity, which in addition may be dependent on external fields, contributions of contacts or grain boundaries may add capacitive or even magneto-capacitive contributions, which will cover the intrinsic sample properties 10-13 . Also one may find relaxational features resulting from localized polarons at defect states as, e.g., demonstrated for the case of perovskite rare-earth manganites above and within the multiferroic phase 14 . But even though one avoids these latter...

Abstract. The control of multiferroic domains through external electric fields has been studied by dielectric measurements and by polarized neutron diffraction on singlecrystalline TbMnO 3 . Full hysteresis cycles were recorded by varying an external field of the order of several kV/mm and by recording the chiral magnetic scattering as well as the charge in a sample capacitor. Both methods yield comparable coercive fields that increase upon cooling.

Polarized neutron scattering experiments reveal that type-II multiferroics allow for controlling the spin chirality by external electric fields even in the absence of long-range multiferroic order. In the two prototype compounds TbMnO 3 and MnWO 4 , chiral magnetism associated with soft overdamped electromagnons can be observed above the long-range multiferroic transition temperature T MF , and it is possible to control it through an electric field. While MnWO 4 exhibits chiral correlations only in a tiny temperature interval above T MF , in TbMnO 3 chiral magnetism can be observed over several kelvin up to the lock-in transition, which is well separated from T MF . DOI: 10.1103/PhysRevLett.119.177201 Multiferroic materials with coupled magnetic and ferroelectric order bear considerable application potential [1,2]. In type-II multiferroics, magnetic order directly induces ferroelectric polarization and giant magnetoelectric coupling. External magnetic fields imply a flop of electric polarization, and electric fields can control chiral magnetic domains [1][2][3][4][5]. Various neutron experiments [6][7][8][9][10][11][12] as well as resonant and nonresonant x-ray studies [13,14] show that cooling in electric fields enforces a monodomain chiral state, and varying external electric fields at constant temperature drives the chiral magnetic order [9][10][11][12], which corresponds to the most promising application as a data storage medium. In addition, time resolved soft x-ray diffraction showed that chiral magnetism can be manipulated by THz-radiation pulses at an electromagnon energy [15].So far, studies of the multiferroic coupling and hysteresis curves were restricted to the phases with long-range magnetic order on bulk or film materials [16], while only small multiferroic blocks would be vital for applications. Also, from the fundamental point of view, one may ask whether multiferroic hysteresis and control can be achieved in short-range systems above the long-range static multiferroic transition, and how far spin chirality persists above the static and long-range multiferroic order. The mixed system Ni 0.42 Mn 0.58 TiO 3 already indicates that magnetoelectric coupling can persist in cluster systems with competing magnetic structures [17], but until now there has been no information about the control and multiferroic coupling of chiral ordering that is limited in space and time. Here, we study two prototype type-II multiferroics, TbMnO 3 [1, 3,4] and MnWO 4 [18-20], above the long-range ferroelectric transition at zero electric field T MF , where it is still possible to pole and control chiral magnetic correlations. Although the two materials exhibit a similar sequence of magnetic transitions, it turns out that only in TbMnO 3 can chiral scattering be controlled over a large temperature interval of several kelvin.TbMnO 3 (MnWO 4 ) both exhibit a first magnetic transition at T N ¼ 42 K (13.5 K), followed by a second transition at lower temperature, at which cycloid order develops at T MF ¼ 27.6 K (12.6 K). For ...

The compound [Formula: see text] is magnetoelectric but not multiferroic with an erythrosiderite-related structure. We present a comprehensive investigation of its structural and antiferromagnetic phase transitions by polarization microscopy, pyroelectric measurements, x-ray diffraction and neutron diffraction. At about [Formula: see text] K, the compound changes its symmetry from Cmcm to I2/c, with a doubling of the original c-axis. This transformation is associated with rotations of the [Formula: see text] octahedra and corresponds to an ordering of the [Formula: see text] molecules and of the related [Formula: see text] bonds. A significant ferroelectric polarization can be excluded for this transition by precise pyrocurrent measurements. The antiferromagnetic phase transition occurring at [Formula: see text] results in the magnetic space group [Formula: see text], which perfectly agrees with previous measurements of the linear magnetoelectric effect and magnetization.