Magnetoelectric Research Articles

Large room temperature magnetoelectric response in quasi 1–2 nanocomposite films on mica substrate

AbstractA novel quasi 1–2 type magnetoelectric (ME) nanocomposite films composted of one‐dimensional CoFe2O4 nanofibers and two‐dimensional PbZr0.2Ti0.8O3 films on flexible mica substrate have been designed and fabricated. The ME coupling effects have been greatly enhanced due to the release of the clamping effect and the high strain transfer efficiency between the large aspect ratio of the nanofibers and ferroelectric thin films. The release of the clamping effect was confirmed by reducing the thickness of the mica substrate, in which the piezoelectric coefficient and ME coupling coefficient of the nanocomposite films have been greatly boosted by the decrease in the mica thickness. A large direct ME coupling coefficient of 630 mV/(cm Oe) and a converse ME coupling coefficient of 1.43 × 10−8 s/m have been achieved in the quasi 1–2 nanocomposite film with a substrate thickness of 25 µm. Furthermore, the stain‐mediated ME coupling was revealed by magnetic field/electric field‐induced local ferroelectric/magnetic domain switching dynamics.

Stoner instability-mediated large magnetoelectric effects in 2D stacking electrides

Strong magnetoelectric effects in single-phase two-dimensional (2D) materials are extremely rare in nature. Here by first-principles calculations, we find a strong magnetoelectric coupling in polar stacking bilayer Hf2S that allows the reversal of net magnetic moments with the reversal of electric dipoles. Further analysis shows that such strong magnetoelectric effects benefit from the Stoner instability of surface Hf atoms triggered by polar stacking. Moreover, an unexpectedly large out-of-plane electric polarization (which is at least two times larger than that of bilayer BN) survives in the material, despite its metallicity. The large electric polarization is ascribed to the delocalized interlayer electrons which generally present in layered electride materials. It is quite interesting that large electric polarization, metallicity and magnetism coexist in one single-phase material. Our findings reveal rich physical phenomena to be explored in 2D stacking multiferroics and suggest an alternative way of searching for strong magnetoelectric materials with ultrathin thickness.

Photo-strain induced magnetoresistance modulation in magnetoelectric heterostructure-based devices

The electric-field control of magnetic dynamics and magnetization in magnetoelectric (ME) heterostructures holds promise for energy-efficient beyond-CMOS devices. However, such techniques entail a high-saturation operational electric field near the device breakdown voltage and introduce complexity due to the requirement for electrical contacts. This study circumvents this issue by light-induced magnetoresistance (MR) modulation in a Ni/PMN-PT ME heterostructure driven by photo-strain-induced internal electric field. Reduced MR, especially in the perpendicular mode, is observed, signifying a localized reduction in the external magnetic field required for magnetization alignment, as elucidated by Langevin function analysis. The proposed method could facilitate better integration and scalability of ME-based spintronic devices, paving the way for low-power beyond-CMOS technologies.

A conical beam antenna array with filter characteristics for multi-rotor unmanned aerial vehicle measurement system

ABSTRACT This paper proposed a novel filter antenna with the conical beam, which consists of four magnetoelectric (ME) dipole antennas. By printing parasitic patches and etching open slots on the bottom of the substrate, two radiation nulls near the high frequency of the passband are introduced. Combined with the intrinsic radiation null of the ME-dipole antenna, the filtering response is obtained. In order to verify the design method, a prototype is manufactured and measured. The measurement results show that the impedance bandwidth (VSWR <2) of the antenna is 1.48 ~ 2.61 GHz (55.3%). In addition, the out-of-band suppression is more than 17.4 dB and the maximum radiation direction of the conical beam is stable around to Theta = 30°. The proposed antenna array can be promising candidates for multi-rotor unmanned aerial vehicle (UAV) measurement systems.

Sm substitution induced spin reorientation and stabilization of double perovskite structure resulting in enhanced magnetoelectricity in LaYFe2O6

We report an enhanced magnetoelectric (ME) effect in spin–phonon coupled single-phase La1−xSmxYFe2O6 (0 ≤ x ≤ 1). The structural, electric, magnetic, and ME properties have been investigated to establish their interplay leading to magnetoelectricity. X-ray diffraction study suggests the facilitation of the P21nm phase (double perovskite lattice arrangements) formation and improved structural order due to the substitution of Sm in the lattice. Antiferromagnetic (AFM) transition ∼700 K along with a spin-reorientation transition around room temperature (RT) and below is observed in the thermomagnetic curve. The indication of short range ordering in the magnetization data in the form of a non-Griffiths-like phase (nGP) is observed. The short range ordering could be minimized along with consequent improvement in AFM ordering, due to Sm substitution. An enhanced (∼31% with respect to x = 0) RT first-order ME coupling coefficient ∼0.59 mV cm−1 Oe−1 in x = 0.75 composition is observed. The findings reported here open the door to exercise spin-reorientation transition in the spin–phonon coupled double perovskites for spintronic device applications.

Universal responses in nonmagnetic polar metals

We demonstrate that two phenomena, the kinetic magnetoelectric effect and the nonlinear Hall effect, are universal to polar metals as a consequence of their coexisting and contraindicated polarization and metallicity. We show that measurement of the effects provides a complete characterization of the nature of the polar metal, in that the nonzero response components indicate the direction of the polar axis, and the coefficients change signs on polarization reversal and become zero in the nonpolar phase. We illustrate our findings for the case of electron-doped PbTiO3 using a combination of density functional theory and model Hamiltonian-based calculations. Our model Hamiltonian analysis provides crucial insight into the microscopic origin of the effects, showing that they originate from inversion-symmetry-breaking-induced interorbital hoppings that correlate to an asymmetric charge density quantified by odd-parity charge multipoles. Our paper both heightens the relevance of the kinetic magnetoelectric and nonlinear Hall effects, and broadens the platform for investigating and detecting odd-parity charge multipoles in polar metals. Published by the American Physical Society 2024

FEM-BEM Modeling of Nonlinear Magnetoelectric Effects in Heterogeneous Composite Structures

FEM-BEM Modeling of Nonlinear Magnetoelectric Effects in Heterogeneous Composite Structures

Nonreciprocal superconducting transport and the spin Hall effect in gyrotropic structures

The search for superconducting systems exhibiting nonreciprocal transport and, specifically, the diode effect, has proliferated in recent years. This trend has encompassed a wide variety of systems, including planar hybrid structures, asymmetric SQUIDs, and certain noncentrosymmetric superconductors. A common feature of such systems is a gyrotropic symmetry, realized on different scales and characterized by a polar vector. Alongside time-reversal symmetry breaking, the presence of a polar axis allows for magnetoelectric effects, which, when combined with proximity-induced superconductivity, results in spontaneous non-dissipative currents that underpin the superconducting diode effect. With this symmetry established, we present a comprehensive theoretical study of transport in a lateral Josephson junction composed of a normal metal supporting the spin Hall effect, and attached to a ferromagnetic insulator. Due to the presence of the latter, magnetoelectric effects arise without requiring external magnetic fields. We determine the dependence of the anomalous currents on the spin relaxation length and the transport parameters commonly used in spintronics to characterize the interface between the metal and the ferromagnetic insulator. Therefore, our theory naturally unifies nonreciprocal transport in superconducting systems with classical spintronic effects, such as the spin Hall effect, spin galvanic effect, and spin Hall magnetoresistance. We propose an experiment involving measurements of magnetoresistance in the normal state and nonreciprocal transport in the superconducting state. Such experiment would, on the one hand, allow for determining the parameters of the model and thus verifying with a greater precision the theories of magnetoelectric effects in normal systems. On the other hand, it would contribute to a deeper understanding of the underlying microscopic origins that determine these parameters.

Spin-Reorientation-Driven Linear Magnetoelectric Effect in Topological Antiferromagnet Cu_{3}TeO_{6}.

The search for new materials for energy-efficient electronic devices has gained unprecedented importance. Among the various classes of magnetic materials driving this search are antiferromagnets, magnetoelectrics, and systems with topological spin excitations. Cu_{3}TeO_{6} is a material that belongs to all three of these classes. Combining static electric polarization and magnetic torque measurements with phenomenological simulations we demonstrate that magnetic-field-induced spin reorientation needs to be taken into account to understand the linear magnetoelectric effect in Cu_{3}TeO_{6}. Our calculations reveal that the magnetic field pushes the system from the nonpolar ground state to the polar magnetic structures. However, nonpolar structures only weakly differing from the obtained polar ones exist due to the weak effect that the field-induced breaking of some symmetries has on the calculated structures. Among those symmetries is the PT (1[over ¯]^{'}) symmetry, preserved for Dirac points found in Cu_{3}TeO_{6}. Our findings establish Cu_{3}TeO_{6} as a promising playground to study the interplay of spintronics-related phenomena.

Boosting energy harvesting of fully flexible magnetoelectric composites of PVDF-AlN and NiO-decorated carbon nanofibers

The increasing popularity of wearable electronics has sparked interest in flexible energy harvesters as alternatives to conventional batteries. Flexible magnetoelectric (ME) composites, known for converting ambient magnetic field energy into useable power, are emerging as promising autonomous energy sources for integration into wearable devices. In this study, we prepared flexible (PVDF-AlN)–(NiO–CNF) based ME composites using two different methods: solution-casting and electrospinning techniques. The ME coupling was confirmed by measuring the ferroelectric and magnetic properties of the composite, and it was qualitatively characterized through the ME coupling coefficient. The electrospinning fibers-based ME composite exhibited an optimal value of 10.6 V/cm.Oe, significantly higher than the solution-casting films-based ME composite (1.3 V/cm.Oe) under a 1 kHz AC magnetic field (off-resonance condition). Subsequently, a flexible magneto-mechano-electric (MME) generator was designed using electrospun-derived material, harvesting a sinusoidal wave with a maximum output peak-to-peak voltage of 9.02 V. The generator displayed an optimal DC power density of 97 μW/m2 when exposed to a weak AC magnetic field of 6 Oe at a frequency of 50 Hz. Consequently, it holds great promise as an efficient autonomous power supply for medical sensing and various miniature electronic applications.

The Study of Core–Shell Cobalt Ferrite–Barium Titanate Magnetoelectric Nanoparticles in Targeting and Optimized Drug Delivery: An Overview

This review provides a comprehensive understanding of magnetoelectric (ME) nanocomposite, cobalt ferrite–barium titanate (CFO–BTO) as a potential candidate for targeting specific cells. The synthesized core–shell material uses strain-mediated coupling between magnetostrictive and piezoelectric material. CFO–BTO has the competitive advantage of a high ME coefficient and is biocompatible. The shape and size play a pivotal role in passive drug delivery due to the enhanced permeability and retention effect at tumor sites. Surfactants can also enhance drug absorption and influence the interaction with nanoparticle composite. A comparison between external magnetic field–frequency parameters to navigate the ME nanoparticle and trigger release of the drug at site is also reviewed. Coating the nanoparticles with a layer of surfactant can reduce the threshold external magnetic field for navigation and triggering of drug particle release, making the prospect viable for clinical studies.

Direct imaging of the magnetoelectric coupling in multiferroic BaTiO3/La0.9Ba0.1MnO3

We report the direct imaging of the magnetic response of a 4.8 nm La0.9Ba0.1MnO3 film to the voltage applied across a 5 nm BaTiO3 film in a BaTiO3/La0.9Ba0.1MnO3 multiferroic heterostructure using x-ray photoemission electron microscopy (XPEEM). Specifically, we have written square ferroelectric domains on the BaTiO3 layer with an atomic force microscope in contact mode and imaged the corresponding magnetic contrast through the x-ray circular dichroic effect at the Mn L-edge with high spatial lateral resolution using XPEEM. We find a sudden decrease in the magnetic contrast for positive writing voltages above +6 V associated with the switching of the ferroelectric polarization of the BaTiO3, consistent with the presence of a magnetoelectric effect through changes in the hole carrier density at the BaTiO3/La0.9Ba0.1MnO3 interface. Temperature-dependent measurements show a decrease in the Curie temperature and magnetic moment in the areas where a positive voltage above +6 V was applied, corresponding to the hole depletion state and suggesting the onset of a spin-canted state of bulk La0.9Ba0.1MnO3. Our results are the first direct imaging of magnetoelectric coupling in such multiferroic heterostructure.

Near room temperature hexagonal multiferroic (Yb0.25Lu0.25In0.25Sc0.25)FeO3 high-entropy ceramics

In this work, h-RFeO3 multiferroic high-entropy ceramics are designed by introducing high-entropy concept with four elements (Yb, Lu, In, Sc) for R site. (Yb0.25Lu0.25In0.25Sc0.25)FeO3 high-entropy ceramics are prepared by the standard solid-state reaction methods. The samples prepared with precursors were identified to crystalize in the pure hexagonal structure with polar space group (P63cm) at room temperature. By the analysis of the variable XRD patterns, it is speculated that the ferroelectric transition temperature of the sample is above 773 K. Meanwhile, three magnetic anomalies are determined for high-entropy ceramics, which is the antiferromagnetic transition at Néel temperature TÑ280 K, the spin-reorientation temperature TSR∼145 K and the reasonable ferromagnetic-like clusters without long ordering in TN < T < TA (∼397 K). Besides, it is observed that the peak intensity of the pyroelectric current around TN can be tuned by magnetic field, which is indicated the magnetoelectric coupling effect in (Yb0.25Lu0.25In0.25Sc0.25)FeO3 high-entropy ceramics. These results indicate the ferroelectric and antiferromagnetic orders are coexist in the h-RFeO3 high-entropy ceramics as promising near room temperature multiferroic materials, and it is an effective way to obtain a new type single-phase multiferroic materials.

Multiscale Modeling of Magnetoelectric Nanoparticles for the Analysis of Spatially Selective Neural Stimulation.

The growing field of nanoscale neural stimulators offers a potential alternative to larger scale electrodes for brain stimulation. Nanoelectrodes made of magnetoelectric nanoparticles (MENPs) can provide an alternative to invasive electrodes for brain stimulation via magnetic-to-electric signal transduction. However, the magnetoelectric effect is a complex phenomenon and challenging to probe experimentally. Consequently, quantifying the stimulation voltage provided by MENPs is difficult, hindering precise regulation and control of neural stimulation and limiting their practical implementation as wireless nanoelectrodes. The work herein develops an approach to determine the stimulation voltage for MENPs in a finite element analysis (FEA) model. This model is informed by atomistic material properties from ab initio Density Functional Theory (DFT) calculations and supplemented by experimentally obtainable nanoscale parameters. This process overcomes the need for experimentally inaccessible characteristics for magnetoelectricity, and offers insights into the effect of the more manageable variables, such as the driving magnetic field. The model's voltage is compared to in vivo experimental data to assess its validity. With this, a predictable and controllable stimulation is simulated by MENPs, computationally substantiating their spatial selectivity. This work proposes a generalizable and accessible method for evaluating the stimulation capability of magnetoelectric nanostructures, facilitating their realization as wireless neural stimulators in the future.

Low-frequency magnetoelectric capacitively-coupled receiving antenna with enhanced transmission stabilities under low input power density

Exploiting a more stabilized transmission strategy in magnetoelectric (ME) antennas for near-field communication under lower input power density is still challenging since the strain-mediated ME voltage is easily vulnerable to ambient interferences with significant anisotropy. In this work, a low-frequency (LF) receiving ME antenna system, consisting of transmitting coil and Ni0.8Zn0.2Sm0.02Fe1.98O4/PZT/Ni0.8Zn0.2Sm0.02Fe1.98O4 ME laminate, was proposed and established with the quasi-isotropic response, enhanced stabilities and limit of detection (LOD) of communication distance by capacitively-coupled mode. Experimental results showed that a more uniform receiving response in capacitance with 360° rotating of the ME antenna by a nearly circular response. Transmission stabilities were further evaluated by continuous collected data for 100 min, a near-flat capacitance response with standard Gaussian distribution (μ = 27.48nF and σ2 = 6.37 × 10−6nF) was obtained, and the estimated uncertainty shows one order of magnitude lower than that of voltage capturing mode. Under lower input power density of 15 μW/cm3, comparison studies of the LOD in transmission distance of the ME antennas were implemented, and the maximum effective communication distance of 100 cm for the ME antenna can be reached. The findings provide the possibility of using capacitively-coupled receiving mode of the ME antenna with enhanced stabilities under low input power density.

Optical Tellegen metamaterial with spontaneous magnetization

The nonreciprocal magnetoelectric effect, also known as the Tellegen effect, promises a number of groundbreaking phenomena connected to fundamental (e.g., electrodynamics of axion and relativistic matter) and applied physics (e.g., magnetless isolators). We propose a three-dimensional metamaterial with an isotropic and resonant Tellegen response in the visible frequency range. The metamaterial is formed by randomly oriented bi-material nanocylinders in a host medium. Each nanocylinder consists of a ferromagnet in a single-domain magnetic state and a high-permittivity dielectric operating near the magnetic Mie-type resonance. The proposed metamaterial requires no external magnetic bias and operates on the spontaneous magnetization of the nanocylinders. By leveraging the emerging magnetic Weyl semimetals, we further show how a giant bulk effective magnetoelectric effect can be achieved in a proposed metamaterial, exceeding that of natural materials by almost four orders of magnitude.

A Combined Magnetoelectric Sensor Array and MRI-Based Human Head Model for Biomagnetic FEM Simulation and Sensor Crosstalk Analysis.

Magnetoelectric (ME) magnetic field sensors are novel sensing devices of great interest in the field of biomagnetic measurements. We investigate the influence of magnetic crosstalk and the linearity of the response of ME sensors in different array and excitation configurations. To achieve this aim, we introduce a combined multiscale 3D finite-element method (FEM) model consisting of an array of 15 ME sensors and an MRI-based human head model with three approximated compartments of biological tissues for skin, skull, and white matter. A linearized material model at the small-signal working point is assumed. We apply homogeneous magnetic fields and perform inhomogeneous magnetic field excitation for the ME sensors by placing an electric point dipole source inside the head. Our findings indicate significant magnetic crosstalk between adjacent sensors leading down to a 15.6% lower magnetic response at a close distance of 5 mm and an increasing sensor response with diminishing crosstalk effects at increasing distances up to 5 cm. The outermost sensors in the array exhibit significantly less crosstalk than the sensors located in the center of the array, and the vertically adjacent sensors exhibit a stronger crosstalk effect than the horizontally adjacent ones. Furthermore, we calculate the ratio between the electric and magnetic sensor responses as the sensitivity value and find near-constant sensitivities for each sensor, confirming a linear relationship despite magnetic crosstalk and the potential to simulate excitation sources and sensor responses independently.

Radiation of a short linear antenna above a topologically insulating half-space

The topological magnetoelectric effect is a unique macroscopic manifestation of quantum states of matter possessing topological order and it is described by axion electrodynamics. In three-dimensional topological insulators, for instance, the axion coupling is of the order of the fine structure constant, and hence, a perturbative analysis of the field equations is plenty justified. In this paper, we use Green’s function techniques to obtain time-dependent solutions to the axion field equations in the presence of a planar domain wall separating two media with different topological order. We apply our results to investigate the radiation of a short linear antenna near the domain wall.

Atomic-Scale Visualization of Multiferroicity in Monolayer NiI2.

Progress in layered van der Waals materials has resulted in the discovery of ferromagnetic and ferroelectric materials down to the monolayer limit. Recently, evidence of the first purely 2D multiferroic material wasreported in monolayer NiI2. However, probing multiferroicity with scattering-based and optical bulk techniques is challenging on 2D materials, and experiments on the atomic scale are needed to fully characterize the multiferroic order at the monolayer limit. Here, scanning tunneling microscopy (STM) supported by density functional theory (DFT) calculations is used to probe and characterize the multiferroic order in monolayer NiI2. It is demonstrated that the type-II multiferroic order displayed by NiI2, arising from the combination of a magnetic spin spiral order and a strong spin-orbit coupling, allows probing the multiferroic order in the STM experiments. Moreover, the magnetoelectric coupling of NiI2 is directly probed by external electric field manipulation of the multiferroic domains. The findings establish a novel point of view to analyze magnetoelectric effects at the microscopic level, paving the way toward engineering new multiferroic orders in van der Waals materials and theirheterostructures.

Wideband miniaturized circularly polarized magnetoelectric dipole antenna array for millimeter‐wave applications

AbstractA wideband and miniaturized circularly polarized (CP) magnetoelectric (ME) dipole antenna is proposed. Two pairs of rotationally symmetric patch structures replace the rectangular structure of the original linearly polarized ME dipole, generating a rotating electric field that results in CP‐radiated waves. And the magnetic dipole is modified to broaden the impedance bandwidth (IBW) and the axial ratio bandwidth (ARBW). Meanwhile，the simple l‐shaped feed structure makes the antenna more compact. To improve the antenna gain, a 2 × 2 CP ME‐dipole antenna array was designed, completed, and measured. The measured results show that the IBW of the antenna array is 41.5% (from 29.2 to 44.5 GHz), and 3 dB ARBW of 26.7% (from 34.7 to 45.4 GHz) has a peak gain of 13.7 dBic.