Magnetoelectric Field Research Articles

On the Origin of Signal and Bandwidth of Converse Magnetoelectric Magnetic Field Sensors

AbstractConverse magnetoelectric sensors enable the detection of low‐frequency and low‐amplitude magnetic fields over a bandwidth of several kilohertz by combining the electrical excitation of a magnetoelectric resonator via a piezoelectric layer with an inductive readout. Here, a comprehensive sensor model is presented to further foster the development of this promising sensor concept. The model relates the output signal to the device characteristics, taking into account the magnetoelastic and electromechanical properties, the resonator geometry, and operating conditions. The sensor system is thoroughly experimentally analyzed to validate the model. Based on the analysis, the sensor concept is explained in detail, including the origin of its loss and bandwidth and their connection with the magneto‐mechanical loss in the magnetostrictive layer. Significant advances have been made in the comprehensive understanding of converse magnetoelectric sensors, providing a solid basis for future improvements in magnetoelectric sensor systems.

Multiferroic properties of electrospun CoFe2O4–(Ba0.95Ca0.05)(Ti0.89Sn0.11)O3 nanocomposites for magnetoelectric and magnetic field sensing applications

Multiferroic CoFe2O4–Ba0.95Ca0.05Ti0.89Sn0.11O3 composite nanofibers (CFO–BCTSn NFs) were synthesized using a sol–gel electrospinning method. Scanning electron microscopy revealed the morphology of the composites, with fiber diameters ranging from 120 to 150 nm. Transmission electron microscopy confirmed the structure of the nanofibers, while X-ray diffraction, Raman spectroscopy, and high-resolution transmission electron microscopy verified the formation of the spinel structure of CFO and the perovskite structure of BCTSn, with no additional phases detected. The magnetic properties of the CFO–BCTSn NFs were demonstrated by magnetic hysteresis loops (M-H), and piezoresponse force microscopy confirmed their piezoelectricity. Magnetoelectric coupling was evidenced by comparing the M-H hysteresis loops of electrically poled and unpoled CFO–BCTSn NFs samples. These composite nanofibers have the potential to be utilized in innovative, lead-free magnetoelectric and magnetic field sensing technologies at the nanoscale.

The percolation inception of the CNT-polymer nanocomposites with the magneto-electric field effects on the CNT subbands

The percolation inception of CNT-polymer nanocomposites is studied considering the magneto-electric field effects on CNT subbands. The analytical model predicts the electrical conductivity where CNTs are modeled as slender rods with their geometric orientations as randomly distributed or aligned to transfer electrons at tunneling distance range. The tunneling effect takes into account the electron transmission between every linked pair of CNTs when evaluating electrical resistance. The subsequent CNT displacement computation and the resistance change comprise the other phase of the modeling approach. Piezoresistivity results of the analyses agree well with the experimental data when considering tunneling behavior in the percolation transition zone. The magnetic field enhances the field affected subbands and increases the electrical conductivity by enhancing the mobility of the charges. The results reveal that the efficiency of CNT network in transmitting charges is increased with higher aspect ratio CNTs that scaled the sensitivity to lower values.

Magnetoelectric effect in a Metglas–langatate ring heterostructure for current sensing

The magnetoelectric (ME) effect was observed and investigated in a planar ring-type heterostructure containing mechanically coupled rings of magnetostrictive amorphous alloy Metglas and a piezoelectric single crystal langatate. The structure was excited by a circumferential ac magnetic field in the presence of a circumferential dc bias magnetic field. Due to the absence of demagnetization and the high acoustic quality factor of the langatate, a high ME field conversion coefficient of α E ≈ 53 V (Oe cm)−1 was obtained at the frequency 221 kHz of the fundamental radial acoustic resonance mode. The structure can be used as a non-contact ac or dc current sensor. The sensitivity of the structure to the ac current was 1.6 V A−1, whereas for the dc current it reached 4.2 V A−1.

The processing properties of photocatalysis assisted magnetorheological polishing based on TiO2–CI composite particles

With the development of optoelectronic wafers tend to be high brittleness, high hardness and high chemical stability, a single magnetorheological polishing is difficult to meet the application requirements of optoelectronic wafers. The quality and efficiency of magnetorheological polishing (MRP) of photoelectric wafer can be further improved by electric field assisted polishing or photocatalysis assisted polishing. In this paper, TiO2–CI functional composite particles were synthesized by sol-gel method, and a variety of polishing fluid with magnetic, electric and optical multi field effects were prepared. Silicon wafer and fused silica glass were polished by fixed-point centering polishing method, and the mechanism of photocatalytic assisted magnetorheological polishing (PMRP) was studied by comparing the polishing performance of the polishing fluid under different applied fields. The results show that when the polishing fluids prepared by oil-based liquid, the material removal rate is high under the action of a single magnetic field, but the polishing quality is poor. After polishing for 60 min, the height difference in surface profile ΔRz of fused silica glass is 0.67 μm. When the 2.5 kV/mm electric field is applied, the abrasive distribution can be controlled by electromagnetic composite field, and the stiffness distribution of polishing pad is more uniform, but it will reduce the material removal rate (MRR). Compared with the single magnetic field, the height difference in surface profile ΔRz is reduced by 73.1 % to 0.18 μm under the magnetoelectric compound field, which can obtain a more flattened surface quality. When light field and magnetic field are applied, water-based polishing fluid is used for polishing. Because UV light can induce photocatalytic reaction, the strong oxidation group ·OH generated in the photocatalytic reaction can oxidize the materials of workpiece surface into the lower hardness materials. Therefore, the material removal rate is increased by 249 % to 13.4 mg/h compared with that without light field, and the surface roughness was reduced by 69.32 % to 1.05 nm.

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.

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.

Self-powered elementary hybrid magnetoelectric sensor

There are numerous magnetic field sensors available, but no simple, robust, sensitive sensor for biomedical applications that does not require cryogenic cooling or shielding has yet been developed. In this contribution, a new approach for building a magnetoelectric field sensor is presented, which has the potential to fill this gap. The sensor is based on a resonant cantilever with a piezoelectric readout layer and a pair of opposing permanent magnets. One is attached to the cantilever, and the other one is fixed to a sample holder below. This new concept can be deduced from the most basic composite-based sensor [1], where the magnets interact analog to two particles in a polymer matrix. The bias-free, empirical measurements show a limit-of-detection of 46 pT/√Hz with a sensitivity of 2170 V/T using the sensor’s resonance frequency of 223.5 Hz under ambient conditions. The sensor fabrication is based on low resolution silicon technology, which promises high compatibility and the possibility to be integrated into MEMS devices. The design of this new sensor can be easily altered and adjusted according to the requirements of the specific sensor application. For example, tuning of the operating resonance frequency cannot solely be modified in the production of the cantilever but also by the arrangement of the permanent magnets. In addition, the concept can also be applied to energy harvesters. Beside possible mechanical excitation, the presence of a magnetic stray field alone allows the sensor to convert 20 µT into a power of 1.31 µW/cm³·Oe². The fact that the device does not require any DC bias field makes it very attractive for energy harvesting applications since this allows a purely passive operation. In this manuscript, the sensor assembly, measurements of directional sensitivity, noise level, limit-of-detection, evaluation for energy harvesting applications from magnetic fields and a quantitative sensor model are presented.

Electrical tuning of robust layered antiferromagnetism in MXene monolayer

A-type antiferromagnetism, with an in-plane ferromagnetic order and the interlayer antiferromagnetic coupling, owns inborn advantages for electrical manipulations but is naturally rare in real materials except in those artificial antiferromagnetic heterostructures. Here, a robust layered antiferromagnetism with a high Néel temperature is predicted in a MXene Cr2CCl2 monolayer, which provides an ideal platform as a magnetoelectric field effect transistor. Based on first-principles calculations, we demonstrate that an electric field can induce the band splitting between spin-up and spin-down channels. Although no net magnetization is generated, the inversion symmetry between the lower Cr layer and the upper Cr layer is broken via electronic cloud distortions. Moreover, this electric field can be replaced by a proximate ferroelectric layer for non-volatility. The magneto-optic Kerr effect can be used to detect this magnetoelectricity, even if it is a collinear antiferromagnet with zero magnetization.

Low-frequency resonant magnetoelectric effects in a planar heterostructure of ferromagnetic yttrium iron garnet film and piezoelectric quartz

Low-frequency resonant magnetoelectric (ME) effects in a planar heterostructure containing a 50 μm thick single-crystal film of yttrium iron garnet (YIG) and a crystalline quartz platelet were studied. The ME effects in the mechanically coupled composite arise due to a combination of magnetostriction of the YIG film and the piezoelectric effect in quartz. The effects manifest as mutual transformation of ac magnetic and electric fields. When the layered composite was excited by an ac magnetic field (direct ME effect) at a planar acoustic resonance frequency of 128 kHz, the ME field conversion coefficient was 8.8 V/(Oe∙cm). When excited by an ac electric field (converse effect), the ME conversion coefficient was 0.32 G/(V/cm). Nonlinear ME effects caused by the nonlinear magnetostriction of the YIG film were observed as frequency doubling upon excitation of the direct ME effect by a magnetic field at a frequency equal to half the resonant frequency, as well as at the converse ME effect upon excitation by an electric field at the frequency of the resonance of the structure. In spite of weak magnetostriction for YIG, the resonant ME effects in the YIG-quartz composite are comparable in magnitude to the effects in composites with high magnetostriction materials, show high quality factor of Q ∼ 2200 and are observed in weak magnetic fields H ∼ 0–60 Oe. These results demonstrate the potential for YIG film-quartz composites application in electronic devices.

Ultra-low anisotropy magnetoelectric sensor in ferrite/piezoelectric toroidal composites

An ultra-low anisotropy magnetoelectric (ME) magnetic field sensor consisting of strictly concentric toroidal nickel-zinc ferrite/piezoelectric composite with toroidal solenoid was developed, and its sensitivity and resolution under different angles of planar AC/DC magnetic field were systemically characterized. The experimental results demonstrate that the induced voltage output strength was constant along the angles between the ME magnetic sensor and the planar DC/AC magnetic field due to toroidal structure had ultra-low shape-induced anisotropy. Consequently, for the DC case its sensitivity and resolution could reach about 15 mV/Oe and 2 × 10−7T under a low excitation of ƒ=111.42 kHz circumferential AC magnetic field, respectively. Correspondingly, for the AC case its sensitivity and resolution could reach about 56.9 mV/Oe and 7 × 10−9T under a 2.25Oe circumferential DC bias magnetic field. These findings provided more flexibility of the device design for weak magnetic field detection.

Imaging of Love Waves and Their Interaction with Magnetic Domain Walls in Magnetoelectric Magnetic Field Sensors (Adv. Electron. Mater. 6/2022)

Surface Acoustic Wave Magnetic Field Sensors In article number 2200033, Jeffrey McCord and co-workers image the propagating shear wave behavior in magnetoelectric surface acoustic wave (SAW) sensor devices by time-resolved magnetooptical microscopy. The discovered complex spatial magnetoelastic interactions set limits on the sensor's noise performance, which need to be overcome for improved magnetoelectric magnetic field sensors with even lower limit of field detection.

Imaging of Love Waves and Their Interaction with Magnetic Domain Walls in Magnetoelectric Magnetic Field Sensors

AbstractThe complex behavior of horizontally polarized surface shear waves in magnetoelectric surface acoustic wave based magnetic field sensor devices is revealed by time‐resolved magnetooptical microscopy with picosecond temporal and submicron spatial resolution. The imaging of the propagating waves in the magnetoelectric composites is realized through the functional soft‐magnetic layer by coupled magnetoelastic interactions. Partial surface wave reflections, wave front dephasing, and secondary wave generation occur, which originate from structures and magnetic domain walls. Closure domain structures bend and reflect the magnetic surface waves. Strain stimulated magnetic domain walls display dynamic periodic expansions, which propagate along the domain walls and change the magnetomechanical response also in the surrounding regions. The revealed spatial and temporally varying nondeterministic response restricts the noise performance of the surface acoustic wave based magnetic field sensors and thus confines the sensor's limit of detection. Magnetic time‐resolved optical imaging is shown to be a powerful method for the operando characterization of magnetoelectric devices and in‐plane displacement surface acoustic wave fields that are not accessible by other methods.

Basic exploration and research on magnetoelectric synergistic rheological finishing

Both the magnetorheological effect and the electrorheological effect can effectively constrain and clamp abrasives for polishing processing. This paper proposes a magneto-electric synergy rheological finishing (MERF) method. Based on a magnetoelectric composite field simulation, magnetoelectric synergistic rheological finishing equipment is built. A polishing slurry with both electrorheological and magnetorheological effects is prepared for processing a 2-inch single-crystal silicon wafer. Comb-type electrodes and cylindrical flat-bottomed magnetic poles are used to construct magnetoelectric composite fields. Under the action of a magnetoelectric composite field, a hemispherical polishing pad with abrasives distributed in strips can be obtained. By conducting a test, a smooth and gentle arc cross section of the removed contour can be obtained. The removal rate of MERF was 4.04 mg/h, which was between those of electrorheological finishing (ERF) and magnetorheological finishing (MRF). The surface roughness Ra reached 1.80 nm, and the depth and width of the machining traces were the largest. Magnetoelectric synergistic rheological finishing equipment can realize processing under electric fields, magnetic fields, and magnetoelectric composite fields. The MERF method can effectively enhance the semifixed binding force and distributional uniformity of the abrasive and achieve a more efficient and uniform planarization process.

Recent Progress in Devices Based on Magnetoelectric Composite Thin Films.

The strain-driven interfacial coupling between the ferromagnetic and ferroelectric constituents of magnetoelectric (ME) composites makes them potential candidates for novel multifunctional devices. ME composites in the form of thin-film heterostructures show promising applications in miniaturized ME devices. This article reports the recent advancement in ME thin-film devices, such as highly sensitive magnetic field sensors, ME antennas, integrated tunable ME inductors, and ME band-pass filters, is discussed. (Pb1−xZrx)TiO3 (PZT), Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT), Aluminium nitride (AlN), and Al1−xScxN are the most commonly used piezoelectric constituents, whereas FeGa, FeGaB, FeCo, FeCoB, and Metglas (FeCoSiB alloy) are the most commonly used magnetostrictive constituents in the thin film ME devices. The ME field sensors offer a limit of detection in the fT/Hz1/2 range at the mechanical resonance frequency. However, below resonance, different frequency conversion techniques with AC magnetic or electric fields or the delta-E effect are used. Noise floors of 1–100 pT/Hz1/2 at 1 Hz were obtained. Acoustically actuated nanomechanical ME antennas operating at a very-high frequency as well as ultra-high frequency (0.1–3 GHz) range, were introduced. The ME antennas were successfully miniaturized by a few orders smaller in size compared to the state-of-the-art conventional antennas. The designed antennas exhibit potential application in biomedical devices and wearable antennas. Integrated tunable inductors and band-pass filters tuned by electric and magnetic field with a wide operating frequency range are also discussed along with miniaturized ME energy harvesters.

Application of magnetoelectric sensors in biomedicine

The prospects of applying highly sensitive magnetic field sensors based on the magnetoelectric effect in biomedicine are discussed in this paper. When developing highly sensitive magnetic field sensors, it is necessary to take into account the magnitude of the equivalent magnetic noise, as well as the mass and size dimensions and ease of use of the system that the sensor is included in. One of the most relevant areas discussed in the article is the application of magnetoelectric magnetic field sensors for magnetocardiography, magnetoencephalography, etc. These methods are non-invasive, have high sensitivity and are easy to use. They also have wide opportunities in detecting weak biomagnetic signals when examining the state of the human body and providing the necessary assistance.

Quadratic magnetoelectric effect during field cooling in sputter grown Cr2O3 films

${\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$ is the archetypal magnetoelectric (ME) material, which has a linear coupling between electric and magnetic polarizations. Quadratic ME effects are forbidden for the magnetic point group of ${\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$, due to space-time inversion symmetry. In ${\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$ films grown by sputtering, we find a signature of a quadratic ME effect that is not found in bulk single crystals. We use Raman spectroscopy and magnetization measurements to deduce the removal of space-time symmetry and corroborate the emergence of the quadratic ME effect. We propose that metastable site-selective trace dopants remove the space, time, and space-time inversion symmetries from the original magnetic point group of bulk ${\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$. We include the quadratic ME effect in a model describing the switching process during ME field cooling and estimate the effective quadratic susceptibility value. The quadratic magnetoelectric effect in a uniaxial antiferromagnet is promising for multifunctional antiferromagnetic and magnetoelectric devices that can incorporate optical, strain-induced, and multiferroic effects.

Magnetoelectric Induced Switching of Perpendicular Exchange Bias Using 30-nm-Thick Cr2O3 Thin Film

Magnetoelectric (ME) effect is a result of the interplay between magnetism and electric field and now, it is regarded as a principle that can be applied to the technique of controlling the antiferromagnetic (AFM) domain state. The ME-controlled AFM domain state can be read out by the magnetization of the adjacent ferromagnetic layer coupled with the ME AFM layer via exchange bias. In this technique, the reduction in the ME layer thickness is an ongoing challenge. In this paper, we demonstrate the ME-induced switching of exchange bias polarity using the 30-nm thick ME Cr2O3 thin film. Two typical switching processes, the ME field cooling (MEFC) and isothermal modes, are both explored. The required ME field for the switching in the MEFC mode suggests that the ME susceptibility (α33) is not deteriorated at 30 nm thickness regime. The isothermal change of the exchange bias shows the hysteresis with respect to the electric field, and there is an asymmetry of the switching field depending on the switching direction. The quantitative analysis of this asymmetry yields α33 at 273 K of 3.7 ± 0.5 ps/m, which is comparable to the reported value for the bulk Cr2O3.

Influence of the piezoelectric material on the signal and noise of magnetoelectric magnetic field sensors based on the delta-E effect

Magnetoelectric thin-film sensors based on the delta-E effect have widely been reported for the detection of low frequency and small amplitude magnetic fields. Such sensors are usually fabricated with microelectromechanical system technology, where aluminum nitride (AlN) is the established piezoelectric material. Here, we present aluminum scandium nitride (AlScN) for delta-E effect sensors instead and compare it with AlN using two sensors of identical design. The sensors are experimentally and theoretically analyzed regarding sensitivity, noise, limit of detection (LOD), and resonator linearity. We identify the influence of the dominating piezoelectric coefficients dij and other material parameters. Simulations and measurements demonstrate that, in contrast to the conventional direct operation of magnetoelectric sensors, a sensitivity increase ∝dij2 and a LOD improvement ∝dij−1 can be achieved if thermal–mechanical noise is dominant. In the present case, an 8× improved sensitivity and LOD are measured with AlScN at small excitation amplitudes. This factor decreases with increasing amplitude and resonator nonlinearities. The overall minimum LOD does not change due to an earlier onset of magnetic noise in the AlScN sensor. All in all, this study reveals the influence of the piezoelectric material on the signal and noise of delta-E effect sensors and the potential of AlScN to significantly improve sensitivity.