Magnetoelectric Research Articles

Effects of W/Co co-doping on the structural, multiferroic, dielectric and optical properties of filled tungsten bronze Ba4Sm2Fe2Nb8O30 ceramics

The structural, magnetic, ferroelectric, dielectric, magneto-dielectric and optical properties of W/Co co-substituted tungsten bronze Ba4Sm2Fe2Nb8-3x(W2Co)xO30 (0 ≤ x ≤ 0.3) ceramics were studied in detail. All the samples can be indexed with the tetragonal structure with the space group of P4bm. The room-temperature ferromagnetism with rather high ferromagnetic Curie temperature Tc was obtained in all compositions. The co-doping of W/Co ions obviously optimized the ferromagnetism and ferroelectricity. The composition x = 0.2 showed a superior multiferroicity with the remnant magnetization Mr of 0.15 emu/g and the remnant polarization Pr of 2.1μC/cm2 as well as the Tc of 886 K. The low-temperature relaxation was related to the thermal process of oxygen vacancies, while the another one around 300 K was ascribed to the localized hopping of electrons. The relative increment of magneto-dielectric constant (MDC) obeyed with the square term of magnetization in Ginzburg-Landau theory, implying the existence of intrinsic magneto-electric coupling effect. A relatively large MDC of 0.17 % was achieved in pure sample. In addition, two direct inter-band transitions with the narrow band gaps of ∼2.0 eV and ∼2.5 eV were demonstrated.

First-principles investigation of the magnetoelectric properties of Ba7Mn4O15

Type-II multiferroics, in which the magnetic order breaks inversion symmetry, are appealing for both fundamental and applied research due their intrinsic coupling between magnetic and electrical orders. Using first-principles calculations we study the ground state magnetic behaviour of Ba7Mn4O15 which has been classified as a type-II multiferroic in recent experiments. Our constrained moment calculations with the proposed experimental magnetic structure shows the spontaneous emergence of a polar mode giving rise to an electrical polarisation comparable to other known type-II multiferroics. When the constraints on the magnetic moments are removed, the spins self-consistently relax into a canted antiferromagnetic ground state configuration where two magnetic modes transforming as distinct irreducible representations coexist. While the dominant magnetic mode matches well with the previous experimental observations, the second mode is found to possess a different character resulting in a non-polar ground state. Interestingly, the non-polar magnetic ground state exhibits a significantly strong linear magnetoelectric (ME) coupling comparable to the well-known multiferroic BiFeO3, suggesting strategies to design new linear MEs.

Axion insulator state in hundred-nanometer-thick magnetic topological insulator sandwich heterostructures

An axion insulator is a three-dimensional (3D) topological insulator (TI), in which the bulk maintains the time-reversal symmetry or inversion symmetry but the surface states are gapped by surface magnetization. The axion insulator state has been observed in molecular beam epitaxy (MBE)-grown magnetically doped TI sandwiches and exfoliated intrinsic magnetic TI MnBi2Te4 flakes with an even number layer. All these samples have a thickness of ~ 10 nm, near the 2D-to-3D boundary. The coupling between the top and bottom surface states in thin samples may hinder the observation of quantized topological magnetoelectric response. Here, we employ MBE to synthesize magnetic TI sandwich heterostructures and find that the axion insulator state persists in a 3D sample with a thickness of ~ 106 nm. Our transport results show that the axion insulator state starts to emerge when the thickness of the middle undoped TI layer is greater than ~ 3 nm. The 3D hundred-nanometer-thick axion insulator provides a promising platform for the exploration of the topological magnetoelectric effect and other emergent magnetic topological states, such as the high-order TI phase.

Monopole-like orbital-momentum locking and the induced orbital transport in topological chiral semimetals

The interplay between chirality and topology nurtures many exotic electronic properties. For instance, topological chiral semimetals display multifold chiral fermions that manifest nontrivial topological charge and spin texture. They are an ideal playground for exploring chirality-driven exotic physical phenomena. In this work, we reveal a monopole-like orbital-momentum locking texture on the three-dimensional Fermi surfaces of topological chiral semimetals with B20 structures (e.g., RhSi and PdGa). This orbital texture enables a large orbital Hall effect (OHE) and a giant orbital magnetoelectric (OME) effect in the presence of current flow. Different enantiomers exhibit the same OHE which can be converted to the spin Hall effect by spin-orbit coupling in materials. In contrast, the OME effect is chirality-dependent and much larger than its spin counterpart. Our work reveals the crucial role of orbital texture for understanding OHE and OME effects in topological chiral semimetals and paves the path for applications in orbitronics, spintronics, and enantiomer recognition.

Superconductivity in chiral cubic Y3Rh4Ge13

Herein, we present the synthesis and experimental characterization of the electronic and structural properties of Y3Rh4Ge13 crystallizing in the chiral cubic space group I213(#199) as confirmed by X-ray diffraction analysis. Resistivity, magnetic susceptibility, and specific-heat measurements confirm bulk superconductivity with a transition temperature TC = 1.45 K. Analyses using the α-model and McMillan’s formula suggest that Y3Rh4Ge13 is a weak-coupling superconductor. Low-energy Einstein phonon modes observed in the specific heat are attributable to the characteristic cage structures in the crystal. Y3Rh4Ge13 possessing the chiral cubic structure provides a promising new platform for exploring the magnetoelectric (or Edelstein) effect in superconductivity.

Detection of inhomogeneous magnetic fields by magnetoelectric composite

Magnetoelectric (ME) composites can be useful due to their wide range of possible applications, especially as sensors of weak magnetic fields at room temperature for magnetocardiography and magnetoencephalography techniques in medical diagnostic equipment. In most works on the topic of ME composites, structures are tested in uniform magnetic fields; however, for practical application, a detailed consideration of the interaction with inhomogeneous magnetic fields (IMF) is necessary. In this work we made measurements of IMF with radial symmetry of individual thin wire with AC voltage with different placements of ME sensor. A ME self-biased structure b-LN/Ni/Metglas with a sensitivity to magnetic field of 120 V/T was created for IMF detection. The necessity of external biasing magnetic field is avoided by a nickel layer and its remanent magnetization. ME composite shows a non-zero ME coefficient of 0.24 V/(cm·Oe) in absence of DC external magnetic field. It is shown that output voltage amplitude from ME composite, which is located in AC IMF, is dependent from relative position of investigated sample and magnetic field lines. Maximum ME signal is obtained when long side of ME sample is perpendicular to the wire, and symmetry plane which divides the long side in two similar pieces contains an axis of the wire. In frequency range from 400 Hz to 1000 Hz in absence of vibrational and other noises a limit of detection has value of (2 ± 0.4) nT/Hz1/2.

CO2 -Induced Spin-Lattice Coupling for Strong Magnetoelectric Materials.

The preparation of 2D magnetoelectric (ME) nanomaterials with strong ME coupling is crucial for the fast reading and writing processes in the next generation of storage devices. Herein, 2D BaTiO3 (BTO)-CoFe2 O4 (CFO) ME nanocomposites are prepared through a substrate-free coupling strategy using supercritical CO2 . Such 2D BTO-CFO with strong coupling is built through alternating in-plane and out-of-plane epitaxy stacking, leading to remarkable mutual biaxial strain effects for spin-lattice coupling. As a results, such strain effect significantly enhances the ferroelectricity of BTO and the ferrimagnetism of CFO, where an unexceptionally high ME coupling coefficient of (325.8mVcm-1 Oe-1 ) is obtained for the BTO-CFO nanocomposites.

Recent progress in MnBi2nTe3n+1 intrinsic magnetic topological insulators: crystal growth, magnetism and chemical disorder.

The search for magnetic topological materials has been at the forefront of condensed matter research for their potential to host exotic states such as axion insulators, magnetic Weyl semimetals, Chern insulators, etc. To date, the MnBi2nTe3n+1 family is the only group of materials showcasing van der Waals-layered structures, intrinsic magnetism and non-trivial band topology without trivial bands at the Fermi level. The interplay between magnetism and band topology in this family has led to the proposal of various topological phenomena, including the quantum anomalous Hall effect, quantum spin Hall effect and quantum magnetoelectric effect. Among these, the quantum anomalous Hall effect has been experimentally observed at record-high temperatures, highlighting the unprecedented potential of this family of materials in fundamental science and technological innovation. In this paper, we provide a comprehensive review of the research progress in this intrinsic magnetic topological insulator family, with a focus on single-crystal growth, characterization of chemical disorder, manipulation of magnetism through chemical substitution and external pressure, and important questions that remain to be conclusively answered.

Lattice‐mediated room temperature magnetoelectric effect in (1‐y)BiFe1‐xCrxO3‐yBaTi1‐xMnxO3 solid solutions

AbstractElectric field (E) control of magnetism is a persistent challenge in low‐power consumption spintronic devices. A promising way to realize this control is to use the converse magnetoelectric (ME) effect in insulating multiferroics. Here, we report considerable and repeatable E‐modulated magnetization (M) at room temperature and even at 350 K via the significantly enhanced converse ME effect near the morphotropic phase boundary (MPB) of the Cr‐Mn co‐doped (1‐y)BiFe1‐xCrxO3‐yBaTi1‐xMnxO3 (0.15 ≤ y ≤ 0.33, 0 ≤ x ≤ 0.03) solid solutions. In situ X‐ray diffraction and Raman scattering experiments at different applied E for the sample near the MPB (i.e., y = 0.27, x = 0.03) show E‐induced shift, broadening, and splitting in the {002}PC reflection, as well as a nearly monotonous variation in intensity of several phonon modes with E, reminiscent of the E‐dependent M behavior. These results indicate that both E‐induced lattice distortion and phase transformation dominate the converse ME effects in these samples. Our demonstration of the E‐regulation of magnetism via the E‐sensitive crystal structures in designed insulating multiferroics near MPB may suggest a potential route to obtain efficient low‐power spintronic devices.

A Flexible Magnetic Field Sensor Based on PZT/CFO Bilayer via van der Waals Oxide Heteroepitaxy.

Magnetoelectric (ME) magnetic field sensors utilize ME effects in ferroelectric ferromagnetic layered heterostructures to convert magnetic signals into electrical signals. However, the substrate clamping effect greatly limits the design and fabrication of ME composites with high ME coefficients. To reduce the clamping effect and improve the ME response, a flexible ME sensor based on PbZr0.2Ti0.8O3 (PZT)/CoFe2O4 (CFO) ME bilayered heterostructure was deposited on mica substrates via van der Waals oxide heteroepitaxy. A saturated magnetization of 114.5 emu/cm3 was observed in the bilayers. The flexible sensor exhibited a strong ME coefficient of 6.12 V/cm·Oe. The local ME coupling has been confirmed by the evolution of the ferroelectric domain under applied magnetic fields. The flexible ME sensor possessed a stable response with high sensitivity to both AC and DC weak magnetic fields. A high linearity of 0.9988 and sensitivity of 72.65 mV/Oe of the ME sensor were obtained under flat states. The ME output and limit-of-detection under different bending states showed an inferior trend as the bending radius increased. A flexible proximity sensor has been demonstrated, indicating a promising avenue for wearable device applications and significantly broadening the potential application of the flexible ME magnetic field sensors.

Magnetoelectric Energy in Electrodynamics: Magnetoelectricity, Bi(an)isotropy, and Magnetoelectric Meta‐Atoms

AbstractMagnetoelectricity denotes the relationship between electric polarization and magnetization. In materials with an intrinsic magnetoelectric (ME) effect, the energy density comprises the polarization, magnetization, and ME energy densities. These three components of energy define local (subwavelength) characteristics of electromagnetic (EM) responses in multiferroic materials. In a subwavelength domain, coupling between the electric and magnetic dipole oscillations forms the ME field structures that are characterized by the violation of both spatial and temporal symmetry. Unlike multiferroics, bi(an)isotropic metamaterials are associated with an EM response characterized only by spatial symmetry breaking. This also applies to chiral materials. Since no “intrinsic magnetoelectricity” is assumed in such structures, any concepts about the stored ME energy are not applicable. This clearly points to the effect of nonlocality. That is why the basic concepts of bi(an)isotropy can only be analyzed by the EM far‐field characteristics. In this paper, it is argued that in the implementation of local (subwavelength) ME meta‐atoms and systems for near‐field probing of chirality, the concept on ME energy is crucial. Real ME energy can occur when ME fields in a singular subwavelength domain are characterized by a violation of both the symmetry of time reversal and spatial reflection.

Magnetic field tunable piezoelectric resonator for MEMS applications

In this report, the Ni0.50Mn0.35In0.15/Pb0.96La0.04Zr0.52Ti0.48O3 (Ni-Mn-In/PLZT) bulk acoustic wave (BAW) resonator has been fabricated using the sputtering deposition technique. The magnetoelectric effect in the Ni-Mn-In/PLZT resonator has been investigated. The increase in magnetoelectric coupling coefficient (MECC) with the increment in the frequency of applied HAC is observed. The potential of the Ni-Mn-In/PLZT BAW resonator as a magnetic sensor is tested by measuring the shift in the resonant frequency of the reflective (S11 parameter) response in the presence of the externally applied magnetic field. The Ni-Mn-In/PLZT resonator exhibits a frequency shift of 730 MHz in the 1200 Oe magnetic field, among the largest magnetic field-induced frequency shifts in literature. The rarely reported complete dependence of acoustic velocity, coupling coefficients, magnetic sensitivity, and frequency peak shift on the strength of the external magnetic field is investigated. The acoustic velocity increases from 1237 m/s to 1394 m/s, and the electromechanical coupling coefficient increases from 0.0199 % to 0.0206 % after applying the 1200 Oe magnetic field. The reflective responses have been fitted using the Modified-Butterworth Van Dyke (MBVD) model in terms of hardly reported RLC equivalent circuits. The experimental results and extracted parameters from MBVD modeling exhibit high accuracy. This interaction between multiferroic orders and elastic resonance peaks opens a new window for highly sensitive future magnetic field sensors, wireless communication devices, and magnetic field tunable filters.

A low-frequency vibration energy harvester employing self-biased magnetoelectric composite

Global energy shortage puts stringent demand for energy harvesters capable of transforming external green vibration sources into electrical power. Employing a self-biased magnetoelectric (ME) composite of FeCuNbSiB/Ni/PZT (lead zirconate titanate), a prototype of vibration energy harvester is designed and fabricated. The energy harvester has a circular orbit in which a permanent magnetic cylinder reciprocates once an initial kinetic energy is provided. Upon a vibration signal, like handshaking, movement of the permanent magnetic cylinder causes an alternative magnetic field, which was applied on the ME composite. Via magnetic-force-electrical coupling, the ME composite of FeCuNbSiB/Ni/PZT produces output voltage. Finite element simulation is carried out to reveal the underlying mechanism of the harvester. The analysis shows that a maximum output voltage of 7.63 V can be obtained once an original potential energy is applied for the magnet. In particular, the magnet moves back and forth automatically inside the circular orbit with no need to further apply the energy. The effectiveness of the energy output is experimentally verified. When handshaking the energy harvester, a maximum open-circuit voltage of 5.51 V can be generated. The study offers a solution for power supplying some miniaturized or portable devices, such as small hand set and pedometer.

Effect of PEG nanoparticle surface coating on the magnetic and structural properties of CoFe2O4/PVDF composites

This research focuses on the impact of polyethylene glycol (PEG) coating on the magnetic and structural properties of composites consisting of an electroactive polyvinylidene fluoride matrix and CoFe2O4 nanoparticles. The intrinsic piezoelectric and magnetic properties of the constituents fundamentally determine the properties of composites, but the microstructure and particle packing of the composite are equally crucial for enhancing magnetoelectric coupling. Our findings reveal that PEG coating promote a more uniform spatial distribution of particles agglomerates within the polymer matrix, which achieved by strengthening of the interfacial coupling and reducing of the filler density during the solvent casting process. Together with reduced agglomerates size from an average of 28 ± 3 μm to 17 ± 1 μm uniform spatial distribution leads to decrease of magnetic dipolar interactions from ∼ 900 Oe to ∼ 800 Oe - tendence confirmed from the first-order reversal curve (FORC) analysis. Additionally, the root mean square roughness of the composite surface decreases from 185 nm to 74 nm, indirectly confirming increased sample uniformity. Local electrical properties, measured through Piezoresponse Force Microscopy (PFM), show a substantial enhance of the local piezoelectric response by ∼ 40 %. Results can be used for the enhancing of magnetoelectric effect in biocompatible materials, utilized at low frequency.

Effect of crystallization annealing on magnetoelectric properties of amorphous ferromagnet – piezoelectric ceramics – amorphous ferromagnet three-layer composites

Magnetoelectric properties of three-layer symmetrical composites consisting of two layers of Fe0.45Co0.45Zr0.1 amorphous ferromagnetic alloy and a layer of PbZr0.53Ti0.47O3 piezoelectric ceramics were studied. It was revealed that the magnetoelectric coefficients of the composites pass through a maximum depending on a frequency of the alternative magnetic field and strength of the bias magnetic field and decrease as a volume fraction of the piezoelectric and temperature increase. Regularities revealed in the present work are explained in terms of a theory of the magnetoelectric effect. After crystallization annealing in a vacuum, we observed a deterioration of the magnetoelectric properties of the composites which correlates with a weakening of the piezomagnetic properties of Fe0.45Co0.45Zr0.1 and is related to an increase in a force of interaction between domain walls and defects in Fe0.45Co0.45Zr0.1.

The iron garnet stripe domain structure “refraction” effect at the electrode location

The new type of magnetoelectric effect observed at the domain walls in iron garnet films is considered. This effect manifests itself as a kind of refraction of the stripe domain structure at the charged stripe electrode. The numerical micromagnetic simulation taking into account inhomogeneity of electric field from the stripe electrode as well as magnetic anisotropy of the (210) iron garnet films reproduces the main features of the shape of the domain walls in the vicinity of the electrode edges.

Structural, Dielectric, Complex Impedance and Magnetoelectric Properties of the (1-x) KNbO3 - xMgFe2O4 Composites

Ferrite-ferroelectric nanoparticle composites have a promising potential for a wider range of applications for the manufacturing of new-generation devices due to the tenability of their electric and magnetic orders. In this present work, room-temperature magnetoelectric (ME) coupling studies of KNbO3/MgFe2O4 composites having a general formula (1-x) KNbO3 - xMgFe2O4 (where x = 0, 0.1, 0.3, 0.5, 0.7, 0.9, 1) is presented. The presence of the cubic spinel-ferrite phase of MgFe2O4 and the orthorhombic ferroelectric phase of KNbO3 were confirmed by the structural analysis which was employed using X-ray diffraction (XRD), Raman spectroscopy, and morphology and grain size using Transmission electron microscopy (TEM). Magnetization versus magnetic field (M-H) measurements conform to ferromagnetic ordering and show improved magnetization with the increase in the ferrite phase. The existence of coupling between ferroelectric and ferromagnetic ordering was performed using a lock-in amplifier ME measurement setup. All the composite samples show good linear magnetoelectric coupling that increases with increasing ferrite content. This composite nanostructure with a well-defined interface provides the possibility of an ideal model of room temperature ME coupling which is significant from the technological point of view for a variety of miniaturized next-generation device applications. 

Dual-wideband radiating surface using interleaved electric and magnetic currents: Underlying physics and experimental verification

Unlike popular multiband antenna array radiation based on either electric or magnetic surface currents, the use of mutually interleaved and tightly coupled electric and magnetic currents results in an aperture-reuse space-efficient multiband radiating surface for highly integrated antenna-frontend architecture and spatial power combining design scenarios. In this work, slot and dipole modes corresponding to magnetic and electric currents are effectively interleaved and excited in a surface to develop a space-efficient dual-wideband aperture-shared radiating surface. In this case, due to an effective reuse of the antenna aperture over both frequency bands, a high aperture-reuse efficiency is achieved. First, we devise a planar magneto-electric (ME)-dipole-alike antenna and analyze it in both the frequency and time domain. The antenna is then studied by the characteristic mode theory and the findings are validated using full-wave simulations. The developed planar ME-dipole-alike antenna is used to realize a dual-wideband radiating surface in which electric and magnetic currents are mutually coupled and interlaced, which is excited by properly oriented and distributed sources on the antenna's surface. Eventually, a highly isolated dual-wideband prototype was developed and fabricated using a cost-effective multi-layer Printed Circuit Board (PCB) process that operates in the Ku-band with both impedance and gain bandwidth of approximately 42% and in the Ka-band with respective impedance and gain bandwidth of 29% and 16.32%.

Electrically Controllable Exchange Bias via Interface Magnetoelectric Effect

Exchange bias is a unidirectional magnetic anisotropy that often arise from interfacial interaction of a ferromagnetic and antiferromagnetic layers. In this article, we show that a metallic layer with spin-orbit coupling can induces an exchange bias via an interface magnetoelectric effect. In linear response regime, the interface magnetoelectric effect is induced by spin-orbit couplings that arises from the broken symmetry of the system. Furthermore, we demonstrate that the exchange bias can be controlled by electric field.

A flexible magnetic detector based on transferred ferroelectric/ferromagnetic thin film heterostructure

A flexible magnetic detector based on ferroelectric/ferromagnetic (PZT/Metglas) thin film heterostructure is developed by using etching and transferring technique. The transferred PZT film still exhibits (001)-oriented or very highly textured structure with good ferroelectricity (P r = 50 μC cm−2 and E c = 150 kV cm−1). Magnetoelectric (ME) voltage coefficient of the PZT/Metglas film heterostructure approaches 5.1 V cm−1 Oe at resonance frequency (57.5 kHz). The flexible detector has a sensitivity of AC 0.3 nT and DC 1 Oe with high stability for magnetic field detection. Our demonstration provides a viable approach for realizing ME thin film transfer technology, which is of great significance for future applications on flexible magnetic detectors.