Magnetoelectric Voltage Coefficient Research Articles

Study of enhanced magnetoelectric coupling behavior in asymmetrical bilayered multiferroic heterostructure with two resonance modes

The resonant enhancement of the magnetoelectric coupling effect due to the bending and length modes had been investigated in the asymmetrical bilayered heterostructure consisting of the La0.7Sr0.3MnO3 and BaTiO3 deposited on SrTiO3. The frequency-dependent transverse magnetoelectric voltage coefficient demonstrated two sharp peaks in the vicinity of electromechanical resonant frequencies, which were attributed to the bending and length vibration modes, respectively. The value of the magnetoelectric voltage coefficients for the first peak was higher than that of the second one, which ascribed to the phase shift between the excited magnetic field and induced dielectric polarization. This result demonstrated the asymmetrical bilayered heterostructure has dramatically enhanced magnetoelectric effect when operated near these frequencies, which is likely to provide a tremendous opportunity for configuring the corresponding devices.

The effect of thickness-dependent strain relaxation on magnetoelectric behaviors for highly c-axis oriented BiFeO3 films on Si substrate

The thickness-dependent strain-relaxation behavior and the associated impacts upon the magnetic, electric properties and magnetoelectric coupling effect for the highly c-axis oriented BiFeO3 (BFO) film films grown on (001) oriented Si substrate were studied. The result shown that the value of remnant polarization and coercive field were suppressed as the strain relaxes with increasing thickness. The BFO films also presented typical weak ferromagnetic hysteresis loops with a low coercive field and small remnant magnetization, and the saturated magnetization and remnant magnetization decreasing with increasing film thickness. The room temperature dynamic magnetoelectric coupling was approved by the transverse magnetoelectric voltage coefficients, which also decreased with strain relaxation due to the increase of thickness, and the maximum was around 265 mV/cm.Oe when the film thickness is 50 nm.

Magnetoelectric Ferrite–Piezoelectric Heterostructure With Coil-Free Excitation for DC Magnetic Field Sensing

Abstract The paper describes a new planar multiferroic ferrite-piezoelectric heterostructure that implements the coil-free ex-citation of the direct magnetoelectric (ME) effect. The heterostructure contains a magnetostrictive nickel-zinc ferrite layer with a conducting electrode on its surface and a layer of piezoelectric lead zirconate-titanate, mechanically coupled to each other. The ME effect is excited by passing an alternating current with an amplitude of up to 100 mA through the electrode, which creates an excitation magnetic field in the ferrite layer. A bias dc magnetic field of 0-500 Oe is applied tangentially to the ferrite layer. The ME voltage coefficient of E 42 V/(Oecm) is obtained at the acoustic resonance frequency of the heterostructure of 186 kHz. The sensitivity of the structure to the permanent magnetic field reaches 4.6 mV/Oe and depends on the excitation current and orientation of the bias field. Implementation of heterostructures with coil-free excitation makes it possible reducing of size and power consumption, and improving the electromagnetic compatibility of ME magnetic field sensors.

Low-Frequency Magnetoelectric Effects in Magnetostrictive–Piezoelectric Bilayers: Longitudinal and Bending Deformations

A model for the low-frequency magnetoelectric (ME) effect that takes into consideration the bending deformation in a ferromagnetic and ferroelectric bilayer is presented. Past models, in general, ignored the influence of bending deformation. Based on the solution of the equations of the elastic theory and electrostatics, expressions for the ME voltage coefficients (MEVCs) and ME sensitivity coefficients (MESCs) in terms of the physical parameters of the materials and the geometric characteristic of the structure were obtained. Contributions from both bending and planar deformations were considered. The theory was applied to composites of PZT and Ni with negative magnetostriction, and Permendur, or Metglas, both with positive magnetostriction. Estimates of MEVCs and MESCs indicate that the contribution from bending deformation is significant but smaller than the contribution from planar deformations, leading to a reduction in the net ME coefficients in all the three bilayer systems.

Strain-Mediated Magneto-Electric Effects in Coaxial Nanofibers of Y/W-Type Hexagonal Ferrites and Ferroelectrics

Nanofibers of Y- or W-type hexagonal ferrites and core–shell fibers of hexagonal ferrites and ferroelectric lead zirconate titanate (PZT) or barium titanate (BTO) were synthesized by electrospinning. The fibers were found to be free of impurity phases, and the core–shell structure was confirmed by electron and scanning probe microscopy. The values of magnetization of pure hexagonal ferrite fibers compared well with bulk ferrite values. The coaxial fibers showed good ferroelectric polarization, with a maximum value of 0.85 μC/cm2 and 2.44 μC/cm2 for fibers with BTO core–Co2W shell and PZT core–Ni2Y shell structures, respectively. The magnetization, however, was much smaller than that for bulk hexaferrites. Magneto-electric (ME) coupling strength was characterized by measuring the ME voltage coefficient (MEVC) for magnetic field-assembled films of coaxial fibers. Among the fibers with Y-type, films with Zn2Y showed a higher MEVC than films with Ni2Y, and fibers with Co2W had a higher MEVC than that of those with Zn2W. The highest MEVC of 20.3 mV/cm Oe was measured for Co2W–PZT fibers. A very large ME response was measured in all of the films, even in the absence of an external magnetic bias field. The fibers studied here have the potential for use in magnetic sensors and high-frequency device applications.

Magnetoelectric Response of Laminated Cantilevers Comprising a Magnetoactive Elastomer and a Piezoelectric Polymer, in Pulsed Uniform Magnetic Fields.

The voltage response to pulsed uniform magnetic fields and the accompanying bending deformations of laminated cantilever structures are investigated experimentally in detail. The structures comprise a magnetoactive elastomer (MAE) slab and a commercially available piezoelectric polymer multilayer. The magnetic field is applied vertically and the laminated structures are customarily fixed in the horizontal plane or, alternatively, slightly tilted upwards or downwards. Six different MAE compositions incorporating three concentrations of carbonyl iron particles (70 wt%, 75 wt% and 80 wt%) and two elastomer matrices of different stiffness are used. The dependences of the generated voltage and the cantilever’s deflection on the composition of the MAE layer and its thickness are obtained. The appearance of the voltage between the electrodes of a piezoelectric material upon application of a magnetic field is considered as a manifestation of the direct magnetoelectric (ME) effect in a composite laminated structure. The ME voltage response increases with the increasing total quantity of the soft-magnetic filler in the MAE layer. The relationship between the generated voltage and the cantilever’s deflection is established. The highest observed peak voltage around 5.5 V is about 8.5-fold higher than previously reported values. The quasi-static ME voltage coefficient for this type of ME heterostructures is about 50 V/A in the magnetic field of ≈100 kA/m, obtained for the first time. The results could be useful for the development of magnetic field sensors and energy harvesting devices relying on these novel polymer composites.

Component fraction effect on microstructure and properties of CoFe2O4−K0.5Na0.5NbO3 composites

AbstractCoFe2O4−K0.5Na0.5NbO3 (CFO−KNN) composites were sintered in air at 1100°C for 2 h. The relative density of sintered CFO−KNN varied with the KNN/CFO ratio and when the volume fraction of KNN reached 50% or more, the sintered composites had a relative density higher than both of the components (i.e., individually sintered KNN and CFO). The highest relative density (94%) was obtained with the composites of 80 vol% KNN. Transmission electron microscopy did not observe any secondary phase at the interface between CFO and KNN grains. However, elemental analyses showed traces of interdiffusion of Na, K, Co, and Fe ions, which were within the solubility limit of both lattices so that no segregation of other phase occurred. Nevertheless, the interdiffusion altered grain growth kinetics for both phases, resulting in the changes in grain sizes for both KNN and CFO in the composites. The composites of higher CFO content showed lower piezoelectric d33 due to a higher DC conductivity that resulted in an incomplete poling of samples. The attainable magnetoelectric voltage coefficient was 3.6 mV cm−1 Oe−1, which was measured with the composites of 50 vol% KNN.

Prediction of magnetoelectric properties of defect BiFeO3 thin films using Monte Carlo simulations

Magnetoelectric materials have received astonishing attention due to their great potential for nanotechnology and magnetoelectric applications. Herein, the ferroelectric, magnetic and magnetoelectric properties of multiferroic BiFeO3 (BFO) thin films have been carried out using Monte Carlo simulation investigations in the framework of the Heisenberg model. Exchange coupling interactions in magnetic and ferroelectric sublattices that correspond to the experimental critical temperature were estimated. Temperature dependence of the internal energy, specific heat, magnetization, electric polarization and their susceptibilities in BFO thin films have been systematically analyzed. Moreover, the effect of magnetoelectric coupling interaction Jme on M−H and P-H hysteresis loopsand magnetoelectric voltage coefficient were studied. A large magnetoelectric voltage coefficient of 104 mV/(cm.Oe) was predicted in BFO thin films with 25% defects. Furthermore, the defect mechanism can be used to control the polarization switching by the magnetic field in BFO system. The obtained results highlight the large magnetoelectric effect in BFO multiferroic thin films for multifunctional magnetoelectric devices.

Lead-free laminated structures for eco-friendly energy harvesters and magnetoelectric sensors

The ferromagnetic and ferroelectric laminated structure has been utilized to study the magnetoelectric (ME) effect, which holds great potential to fabricate micro-electro-mechanical devices with a high figure of merit. Designed a laminated heterostructure using ribbons of Metglas (Fe–Co–Si–B alloy) having high magnetic permeability and lead-free piezoelectric composites of 0.92(Na0.5Bi0.5)TiO3-0.08BaTiO3 (NBT-BT) to generate the significant magnitude of direct ME voltage. The displacement-voltage measurements of NBT-BT yield a high response showing the nature of the piezoelectricity effect. The strength of ME coupling is determined from the ME voltage coefficient (αME), ME measurements have been carried out in the range of 0–6 kHz frequencies. The magnitude of the direct ME effect was found about 45–50 mV/Oe.cm over a low magnetic field of less than ±8 kOe. The real-time ME effect produced nearly 274.5 and 280.2 mV of ME voltages for the applied field of 200 and 300 Oe, respectively. It shows that the trilayer composite structure may be used as weak magnetic field sensors and energy harvesters.

Effects of post-annealing temperature and micropillar shape on physical properties of micropillar-type multiferroic composite thin films

Microplate (MP) and microrod (MR)-type CoFe2O4/(Bi3.25Nd0.65Eu0.10)Ti3O12 composite thin films were fabricated by a combination of reactive ion etching and metalorganic chemical vapor deposition. The effects of post-annealing temperature on the structural, magnetic, electrical, and magnetoelectric (ME) properties of the films were investigated. Based on the results, the optimal ferroelectric pillar structure to obtain a large ME voltage coefficient (α ME ) was determined. The electrical insulation properties for the films improved with increasing post-annealing temperature. On the other hand, magnetic and ferroelectric properties were degraded at high-temperature. Judging from the structural, magnetic, electric, and ME properties, the optimum post-annealing temperature was 700 °C. The shape of the ferroelectric layer had a significant influence on the ferroelectric properties and consequently on α ME . The MR shape exhibited a smaller clamping effect than the MP shape, producing a greater ME effect. The α ME for the MR-type film post-annealed at 700 °C was 5.5 mV cm−1 Oe−1.

AC/DC Magnetic Field Sensing Utilizing Mechanically Mediated Product Effect of Ampere Force Caused by Eddy Currents and Piezoelectricity in a Magnetoelectric Disk

The last two decades have witnessed an ever‐increasing research effort devoted to the development and application of magnetoelectric (ME) sensing composites. Herein, the ME effect in a metallic/polymeric composite fabricated by adhering silver electrodes to two surfaces of one poly(vinylidine fluoride) (PVDF) disk is explored. To obtain obvious ME response, the resonance frequency of the experimental setup is measured. Furthermore, it is proved that the ME coupling in the composite (silver/PVDF/silver) originates from the product effect of the piezoelectric effect and ampere force produced by eddy currents under DC bias magnetic fields. By observing measurement results, the ME voltage is approximately considered to be proportional to both AC and DC magnetic fields. Consequently, the average ME voltage coefficient is obtained as 384.73 mV cm−1 Oe at a DC magnetic field value of 1000 Oe. Considering the magnetic fields and eddy current, a theoretical model of ME coupling is developed by combining the ampere force expression and piezoelectric equations, which matches well with measurement results. Without the need of magnetic phase and an external power supply, the proposed disk with excellent linear responses and a considerable ME voltage coefficient has the potential for application in real‐time monitoring sensors.

A phenomenological approach to study the magnetoelectric (ME) response of lead free magnetostrictive NiFe2O4–Piezoelectric BaZr0.2Ti0.8O3 particulate composites

Lead-free magnetoelectric (ME) composites comprises NiFe2O4 (NFO) and BaZr0.2Ti0.8O3 (BZT) were synthesized by using conventional double sintering solid-state reaction technique and it's structural, electric, dielectric, magnetic and ME properties were studied. The spectra of X-ray diffraction displayed the formation of parent phase and presence of two phases within the composites (ferrite-ferroelectric). DC resistivity as a function of temperature has been studied, it indicates the semiconducting behavior. Frequency dependent dielectric spectra of the composites indicates small polaron hopping model of conduction mechanism. Magnetic measurements at room temperature shows the composites are soft magnetic and such materials reveals M-H hysteresis type behavior. The composite with x = 0.3 showed the highest value of ME voltage coefficient ~3.82 mV/cmOe. Such ME composite materials furnish fabulous chances as prospective lead-free systems for multifunctional device applications.

Rietveld refinement analysis and influence of individual phases on the magnetoelectrically coupled (1-x)BSZT+ xNCZGF multiferroic composites

The magnetoelectric voltage coefficient at room-temperature is realized in various (1-x)BSZT+ xNCZGF composites by studying refined crystal structures, surface morphology, magnetic, electric and ferroeletric properties. The ferroelectric (BSZT) and ferrite (NCZGF) phases of the composites are prepared using standard solid-state reaction technique. Rietveld refinement confirmed that the BSZT phase forms perovskite structure with P4mm space group and NCZGF phase forms spinel structure with Fd3¯m space group. From FESEM surface morphology it was observed that the average grain diameter ranges 0.5–2.21 µm. EDX analysis confirms the formation of respective phases and composites. Initial permeability increases from 55 to 130 with increasing NCZGF content which is consistent with the value calculated theoretically using different models. The saturation magnetization also increases from 12 to 37 emu/g with increasing NCZGF content, consistent with the calculated value using law of approach to saturation technique. The dielectric constant of the composites is found to decrease with increasing NCZGF content which is in line with the Maxwell-Garnett, Bruggeman, Looyenga and Lichteneker theoretical approximations. Frequency dependence of the dielectric constant exhibits dispersion, which can be modeled using a modified Debye function that considers the probability of several ions contributing to the relaxation. The ac conductivity follows the Jonscher’s power law, and the conduction mechanism is attributed to the small polaron hopping. Complex impedance is evaluated using the Cole-Cole plot ensures the dominance of both grain and grain boundary resistances. The P-E hysteresis loops ensure the typical ferroelectric nature at room-temperature for x ≤ 0.2. The simultaneous M-H and P-E hysteresis loops confirm the magnetoelectric coupling between ferrite and ferroelectric phases. Furthermore, the maximum magnetoelectric voltage coefficient for 0.9BSZT+ 0.1NCZGF composite is found to be ~194 mV cm−1 Oe−1 that can be used in multifunctional devices.

Giant circumferential magnetoelectric effect in Pb(Zr,Ti)O3/Mn-Zn-ferrite cylindrical composite

Giant magnetoelectric effect was observed in Pb(Zr,Ti)O3(PZT)/Mn-Zn-ferrite cylindrical composite with both DC bias and AC magnetic fields along circumferential direction. The circumferential magnetoelectric voltage coefficient αME,C-C at low frequency f = 1 kHz and resonance frequency fr = 73.9 kHz reaches 1 Vcm−1 Oe−1 and 381 Vcm−1 Oe−1, respectively, at low optimum bias field H DC= 0.40 Oe, which is the highest values of circumferential magnetoelectric voltage coefficient in all kinds of magnetoelectric structures reported ever. Combining constitutive equations for piezoelectric phase and magnetic phase under circumferential excitation with equation of motion for continuous medium, the frequency dependence of αME,C-C was derived as a function of material parameters and geometrical sizes, which agrees well with the experimental results. The achieved high circumferential magnetoelectric effect originates from low compliance of Mn-Zn-ferrite, improved interface mechanical coupling and self-bound effect due to cylindrical structure, and absence of effect of demagnetization factor with circumferential excitation and bias. The distinct features including giant circumferential ME effect, extremely low bias field and cheap cost of Mn-Zn-ferrite promise the PZT/Mn-Zn-ferrite cylindrical composite as a competitive device for vortex magnetic field detection and transducers.

Theory of magnetic force driven magnetoelectric effect in piezo-bimorph/ferrite cantilever composite

A theoretical model is proposed for the frequency response of the magnetic force driven (MFD) magnetoelectric (ME) effect in a piezo-bimorph/ferrite cantilever based on the elastodynamics method, which agrees well with the experimental results for Pb(Zr, Ti)O3-bimorph/Mn–Zn-ferrite cantilever composites. Based on the theoretical model, the dependences of the resonant ME voltage coefficient on geometrical and material parameters of the piezo-bimorph/ferrite cantilever composite are numerically calculated. The results show that an optimum resonant ME effect can be achieved by adjusting the structural and material parameters in the piezo-bimorph/ferrite cantilever composite. This research lays a theoretical basis for understanding the resonant ME effect in the piezo-bimorph/ferrite composite and optimal design of the MFD-ME device based on this configuration.

Effective moduli of multiferroic fibrous composites with strain gradient and electromagnetic field gradient effects

This paper studies the effective moduli of multiferroic fibrous composites with strain gradient and electromagnetic field gradient effects subjected to generalized anti-plane shear deformation. Using the energy variational formulation and the generalized self-consistent method, we can determine the effective moduli of the heterogeneous material. The derived solutions are then applied to a BaTiO3–CoFe2O4 composite to demonstrate the effect of strain gradient, electric field gradient, and magnetic field gradient. Numerical results show that the gradient effects have significant influence on the effective moduli of the multiferroic composite. We show that the magnetoelectric voltage coefficient, the figure of merit of the multiferroic material, can be enhanced many-fold than that of the classical solution. In addition, most of the effective moduli increase as the radius of the fiber decreases (or equivalently the characteristic length increases).

Advances in magneto-ionic materials and perspectives for their application

The possibility of tuning magnetic material properties by ionic means is exciting both for basic science and, especially in view of the excellent energy efficiency and room temperature operation, for potential applications. In this perspective, we shortly introduce the functionality of magneto-ionic materials and focus on important recent advances in this field. We present a comparative overview of state-of-the-art magneto-ionic materials considering the achieved magnetoelectric voltage coefficients for magnetization and coercivity and the demonstrated time scales for magneto-ionic switching. Furthermore, the application perspectives of magneto-ionic materials in data storage and computing, magnetic actuation, and sensing are evaluated. Finally, we propose potential research directions to push this field forward and tackle the challenges related to future applications.

Structural, magnetic and electrical properties of multiferroic xLi0.1Ni0.2Mn0.6Fe2.1O4 – (1-x)Bi0.8Y0.2FeO3 composites

The room temperature magnetoelectric coupling was elucidated by the analysis of structural, magnetic, and electrical properties of xLi0.1Ni0.2Mn0.6Fe2.1O4 – (1-x)Bi0.8Y0.2FeO3 composites. The X-ray diffraction pattern shows that the ferromagnetic phase forms a cubic spinel structure and the ferroelectric phase forms a rhombohedral perovskite structure. The density of the composites decreases with ferrite content. The average grain size slightly decreases with ferrite content for x = 0.1 and increases for further increasing ferrite content. The real part of initial permeability and saturation magnetization increase with increasing ferrite content. The real part of the dielectric constant decreases rapidly with the increase of frequency showing dielectric dispersion at lower frequencies and then remains almost constant at higher frequencies. The dielectric loss of the samples reduces with the increase of the ferrite phase. The ac conductivity of composites increases with frequency, indicating that the conduction is due to small polaron hopping. The study of impedance spectroscopy suggests that grain contribution is effective for the conduction mechanism in the composite. The maximum magnetoelectric voltage coefficient is observed (~182 × 103Vm−1T−1) for the 0.1LNMFO – 0.9BYFO composite which is useful for fabricating magnetic sensors.

Enhanced Energy Conversion Performance of a Magneto–Mechano–Electric Generator Using a Laminate Composite Made of Piezoelectric Polymer and Metallic Glass

AbstractMagneto–mechano–electric (MME) generators, which convert ubiquitous stray magnetic field into electricity, have attracted significant attention as a permanent power source for innumerable sensors. In this study, a MME generator based on magnetostrictive metallic substrate and piezoelectric polymer is reported. After the metallic glass sheets are stacked using adhesives, ferroelectric poly(vinylidene fluoride‐co‐trifluoroethylene) is spin‐casted onto Metglas lamination. The fabricated MME generator harvests an output peak voltage of ≈12.5 V under the applied alternating current magnetic field of 7 Oe at 38.2 Hz. A high magnetoelectric voltage coefficient of 910.14 V cm−1 Oe−1 obtained from the energy device is higher than those reported earlier in inorganic and polymeric piezoelectric components‐based MME generators. Moreover, finite element analysis using the multiphysics simulation is carried out to theoretically investigate the magnetoelectric energy harvesting of the fabricated MME generator. This research results achieve low cost, mechanical stability, eco‐friendliness, and high performance for MME generators, which is anticipated to provide a future direction for magnetoelectric energy harvesting.

Thermal treatment effect on the magnetoelectric properties of (Ni0.5Zn0.5)Fe2O4/Pt/Pb(Zr0.3Ti0.7)O3 heterostructured thin films

Magnetoelectric (ME) property modulation in heterostructured (Ni0.5Zn0.5)Fe2O4/Pt/Pb(Zr0.3Ti0.7)O3 (NZFO/Pt/PZT) thin films on platinized Si substrate by thermal annealing condition variation was studied. In an attempt to prevent interfacial reaction between NZFO and PZT layers during high temperature annealing, thin Pt layer was deposited which can serve as inter-diffusion barrier as well as electrode. The ferroelectric, magnetic, and ME properties of the heterostructured film were noticeably modulated due to microstructural evolution and clamping relaxation developed during thermal annealing process. Room temperature ME voltage coefficient of the heterostructured thin films was enhanced with increasing annealing temperature and reached to 29 mV/cm·Oe when annealed at 650 °C.