Magnetoelectric memory effect of the nonpolar phase with collinear spin structure in multiferroic MnWO4

Direct Evidence for an Intermediate Multiferroic Phase in LiCuFe2(VO4)3

Magnetic susceptibility, specific heat, dielectric, and electric polarization of LiCuFe₂(VO₄)₃ have been investigated. Two sequential antiferromagnetic transitions at T_N1 ∼ 9.95 K and T_N2 ∼ 8.17 K are observed under zero magnetic field. Although a dielectric peak at T_N1 is clearly identified, the measured pyroelectric current also exhibits a sharp peak at T_N1, implying the magnetically relevant ferroelectricity. Interestingly, another pyroelectric peak around T_N2 with an opposite signal is observed, resulting in the disappearance of electric polarization below T_N2. Besides, the electric polarization is significantly suppressed in response to external magnetic field, evidencing a remarkable magnetoelectric effect. These results suggest the essential relevance of the magnetic structure with the ferroelectricity in LiCuFe₂(VO₄)₃, deserving further investigation of the underlying mechanism.

Interconversion of multiferroic domains and domain walls

Systems with long-range order like ferromagnetism or ferroelectricity exhibit uniform, yet differently oriented three-dimensional regions called domains that are separated by two-dimensional topological defects termed domain walls. A change of the ordered state across a domain wall can lead to local non-bulk physical properties such as enhanced conductance or the promotion of unusual phases. Although highly desirable, controlled transfer of these properties between the bulk and the spatially confined walls is usually not possible. Here, we demonstrate this crossover by confining multiferroic Dy_0.7Tb_0.3FeO₃ domains into multiferroic domain walls at an identified location within a non-multiferroic environment. This process is fully reversible; an applied magnetic or electric field controls the transformation. Aside from expanding the concept of multiferroic order, such interconversion can be key to addressing antiferromagnetic domain structures and topological singularities.

Domains and domain walls can have distinctively different physical properties. Here, the authors show how to transfer domains into domain walls and vice versa while maintaining their physical properties. Thereby the authors tune a multiferroic state between three and two dimensions.

Chirality Memory Stored in Magnetic Domain Walls in the Ferromagnetic State of MnP

Chirality in a helimagnetic structure is determined by the sense of magnetic moment rotation. We found that the chiral information did not disappear even after the phase transition to the high-temperature ferromagnetic phase in a helimagnet MnP. The 2nd harmonic resistivity ρ^{2f}, which reflects the breaking down of mirror symmetry, was found to be almost unchanged after heating the sample above the ferromagnetic transition temperature and cooling it back to the helimagnetic state. The application of a magnetic field along the easy axis in the ferromagnetic state quenched the chirality-induced ρ^{2f}. This indicates that the chirality memory effect originated from the ferromagnetic domain walls.

Antiferromagnetism of Double Molybdate LiFe(MoO4)2

The magnetic properties of the spin-5/2 double molybdate LiFe(MoO₄)₂ have been characterized by heat capacity, magnetic susceptibility, and neutron powder diffraction techniques. Unlike the multiferroic system LiFe(WO₄)₂ which exhibits two successive magnetic transitions, LiFe(MoO₄)₂ undergoes only one antiferromagnetic transition at T_N ∼ 23.8 K. Its antiferromagnetic magnetic structure with the commensurate propagation vector k = (0, 0.5, 0) has been determined. Density functional theory calculations confirm the antiferromagnetic ground state and provide a numerical estimate of the relevant exchange coupling constants.

Electric-Field-Adjustable Time-Dependent Magnetoelectric Response in Martensitic FeRh Alloy

Steady or dynamic magnetoelectric response, selectable and adjustable by only varying the amplitude of the applied electric field, is found in a multiferroic FeRh/PMN-PT device. In-operando time-dependent structural, ferroelectric, and magnetoelectric characterizations provide evidence that, as in magnetic shape memory martensitic alloys, the observed distinctive magnetoelectric responses are related to the time-dependent relative abundance of antiferromagnetic-ferromagnetic phases in FeRh, unbalanced by voltage-controlled strain. This flexible magnetoelectric response can be exploited not only for energy-efficient memory operations but also in other applications, where multilevel and/or transient responses are required.

Comparative study of the field-induced and spontaneous AF2′ multiferroic phases in MnWO4and Mn0.90Co0.10WO4within the magnetic symmetry framework

(Mn,Co)WO4compounds are regarded as reference spin-induced multiferroics. A comparative study is presented here, within the magnetic symmetry framework, of the incommensurate magnetic orders responsible for the ferroelectric phases of (i) MnWO4under a magnetic field (H||b) and (ii) Mn0.90Co0.10WO4in the absence of an external field. On the one hand, although these two ferroelectric phases are stabilized under different external physical conditions, both present the sameXc1′(α0γ)ssmagnetic symmetry and practically the same modulation vector. The magnetic ordering in both phases is an elliptical helix with the magnetic moments (as the polarization vector,P) perpendicular to thebaxis, although in most of the ferroelectric compositions of the (Mn,Co)WO4family the spins rotate in planes containingb(and haveP||b). On the other hand, the anisotropy of the resulting magnetic modulations is extraordinarily different in the two phases. This is described and explained in the light of the different anisotropies of Co and Mn ions.

Modulated multiferroic properties of MnWO4via chemical doping

Here we prepare polycrystalline Mn_1−xNi_xWO₄ ceramics with x = 0, 0.02, 0.04, 0.06 for investigating their magnetic, ferroelectric, and multiferroic properties.

Large magnetoelectric coupling in Co4Nb2O9

Magnetoelectric materials which simultaneously exhibit electric polarization and magnetism have attracted more and more attention due to their novel physical properties and promising applications for next-generation devices. Exploring new materials with outstanding magnetoelectric performance, especially the manipulation of magnetization by electric field, is of great importance. Here, we demonstrate the cross-coupling between magnetic and electric orders in polycrystalline Co₄Nb₂O₉, in which not only magnetic-field-induced electric polarization but also electric field control of magnetism is observed. These results reveal rich physical phenomenon and potential applications in this compound.

Voltage-impulse-induced non-volatile ferroelastic switching of ferromagnetic resonance for reconfigurable magnetoelectric microwave devices

A critical challenge in realizing magnetoelectrics based on reconfigurable microwave devices, which is the ability to switch between distinct ferromagnetic resonances (FMR) in a stable, reversible and energy efficient manner, has been addressed. In particular, a voltage-impulse-induced two-step ferroelastic switching pathway can be used to in situ manipulate the magnetic anisotropy and enable non-volatile FMR tuning in FeCoB/PMN-PT (011) multiferroic heterostructures.

Low frequency excitations in multiferroic MnWO4

Dynamic anomalies have been found in the magnetically ordered phases of multiferroic MnWO(4) using polarized Raman scattering. Strong phonon damping is observed for several B(g) modes within the ferroelectric phase and has been attributed to spin-phonon interactions. Moreover, a new low frequency excitation was detected near 33 cm(-1) that grows in intensity on cooling into the antiferromagnetic phases. It is argued that this signal is most probably due to a two-magnon process.

Neutron Laue diffraction study on the magnetic phase diagram of multiferroic MnWO4 under pulsed high magnetic fields

We have combined time-of-flight neutron Laue diffraction and pulsed high magnetic fields at the Spallation Neutron Source to study the phase diagram of the multiferroic material MnWO(4). The control of the field-pulse timing enabled an exploration of magnetic Bragg scattering through the time dependence of both the neutron wavelength and the pulsed magnetic field. This allowed us to observe several magnetic Bragg peaks in different field-induced phases of MnWO(4) with a single instrument configuration. These phases were not previously amenable to neutron diffraction studies due to the large fields involved.

Supramolecular cations of the m-fluoroanilinium(dibenzo[18]crown-6) in ferromagnetic salt

A supramolecular cation of (m-FAni(+))(DB[18]crown-6), where m-FAni(+) and DB[18]crown-6 denote m-fluoroanilinium(+) and dibenzo[18]crown-6, respectively, which is the polar unit rotating in the ferroelectric crystal of (m-FAni(+))(DB[18]crown-6)[Ni(dmit)(2)](-), was introduced into a ferromagnetic [MnCr(oxalate)(3)](-) salt as the counter cation. The crystal structure of (m-FAni(+))(DB[18]crown-6)[MnCr(oxalate)(3)](-)(CH(3)OH)(CH(3)CN) (1) is constructed from alternating layers of a two-dimensional honeycomb layer of [MnCr(oxalate)(3)](-) and (m-FAni(+))(DB[18]crown-6) supramolecular cations. The anionic layer is composed of Mn(II) and Cr(III) ions with S = 5/2 and S = 3/2 spins, respectively, bridged by the oxalate anions, which show ferromagnetic ordering at 5.5 K. The supramolecular structure is formed through the formation of hydrogen bonds between the ammonium hydrogen atoms of the m-FAni(+) cations and the oxygen atoms of the DB[18]crown-6 cavity. No orientational disorder of the fluorine atoms was observed in our X-ray structural analysis, suggesting that a two-fold flip-flop motion of the m-FAni(+) cations does not occur in the salt. The rotational freedom of the m-FAni(+) cations in the salt is restricted by the steric hindrance from neighbouring DB[18]crown-6 molecules. A design strategy for the rotation in a salt is discussed, based on the volume that the supramolecular cations occupy in the unit cell.