Piezomagnetic Coefficient Research Articles

Enhancement of the Magnetoelectric Effect in Multiferroic CoFe2O4/PZT Bilayer by Induced Uniaxial Magnetic Anisotropy

In this study we have compared magnetic, magnetostrictive and piezomagnetic properties of isotropic and anisotropic cobalt ferrite pellets. The isotropic sample was prepared by the ceramic method while the sample exhibiting uniaxial anisotropy was made by reactive sintering using Spark Plasma Sintering (SPS). This technique permits to induce a magnetic anisotropy in cobalt ferrite in the direction of the applied pressure during SPS process. Sample with uniaxial anisotropy revealed a higher longitudinal magnetostriction and piezomagnetism compared to the isotropic sample, but the transversal magnetostriction and piezomagnetism were dramatically reduced. In the case of magnetoelectric layered composite, the magnetoelectric coefficient is directly related to the sum of the longitudinal and transversal piezomagnetic coefficients. These two coefficients being opposite in sign, the use of material exhibiting high longitudinal and low transversal piezomagnetic coefficient (or vice versa) in ME devices is expected to improve the ME effect. Hence, ME bilayer devices were made using isotropic and anisotropic cobalt ferrite stuck with a PZT layer. ME measurements at low frequencies revealed that bilayer with anisotropic cobalt ferrite exhibits a ME coefficient three times higher than a bilayer with isotropic cobalt ferrite. We also investigated the behavior of such composites when excited at resonant frequency.

Investigation of the effect of BaTiO3/CoFe2O4 particle arrangement on the static response of magneto-electro-thermo-elastic plates

In this article, a framework based on finite element (FE) methods is proposed for predicting the influence of spatial arrangement of two phase Barium Titanate (BaTiO3) and Cobalt Ferric Oxide (CoFe2O4) particulate composites on the static response of magneto-electro-thermo-elastic (METE) plates. The coupled material properties such as piezoelectric, piezomagnetic, dielectric, magnetic permeability, thermal expansion and pyro co-efficients vary significantly with the spatial arrangement of BaTiO3/CoFe2O4 particulates. The coupled FE governing equations accounting the effect of particle arrangement is presented by incorporating linear coupled constitutive equations of METE composites. Through the condensation technique, the governing equations of METE plates are solved to obtain direct (thermal displacements, electric and magnetic potentials) and derived quantities (stresses, electric displacements and magnetic flux densities). A special attention has been placed on evaluating the pyro-electric and pyro-magnetic coupling effects for different packing arrangement considered namely, Body Centered Cubic (BCC), Face Centered Cubic (FCC) and Simple Cubic (SC) METE particulate composites. Further, parametric studies are carried out to analyse the influence of boundary conditions and aspect ratio. The present study reveals that the multiphysics response of METE plates changes significantly with the packing arrangements of BaTiO3/CoFe2O4 particulates and geometrical parameters. It is believed that the obtained solutions would provide insights into design aspects of METE structures.

Temperature Dependence of the Resonant Magnetoelectric Effect in Layered Heterostructures.

The dependence of the resonant direct magnetoelectric effect on temperature is studied experimentally in planar composite structures. Samples of rectangular shapes with dimensions of 5 mm × 20 mm employed ferromagnetic layers of either an amorphous (metallic glass) alloy or nickel with a thickness of 20–200 μm and piezoelectric layers of single crystalline langatate material or lead zirconate titanate piezoelectric ceramics with a thickness of 500 μm. The temperature of the samples was varied in a range between 120 and 390 K by blowing a gaseous nitrogen stream around them. It is shown that the effective characteristics of the magnetoelectric effect—such as the mechanical resonance frequency fr, the quality factor Q and the magnitude of the magnetoelectric coefficient αE at the resonance frequency—are contingent on temperature. The interrelations between the temperature changes of the characteristics of the magnetoelectric effect and the temperature variations of the following material parameters—Young’s modulus Y, the acoustic quality factor of individual layers, the dielectric constant ε, the piezoelectric modulus d of the piezoelectric layer as well as the piezomagnetic coefficients λ(n) of the ferromagnetic layer—are established. The effect of temperature on the characteristics of the nonlinear magnetoelectric effect is observed for the first time. The results can be useful for designing magnetoelectric heterostructures with specified temperature characteristics, in particular, for the development of thermally stabilized magnetoelectric devices.

A flexible multiferroic composite with high self-biased magnetoelectric coupling

Polymer-matrix multiferroic composites with self-biased magnetoelectric (ME) coupling hold promises in flexible energy harvester, magnetic field sensors and actuators, etc. Using CoFe2O4 (CFO) nanoparticles and multi-walled carbon nanotubes (CNTs) as fillers to the polyvinylidene fluoride (PVDF) matrix, piezomagnetic films (CFO-CNT-PVDF, also named as M layers) with different volume fractions of CFO and a fixed percentage of CNTs are obtained, which also serve as the electrode. By employing the layer of poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE), named as P layer) sandwiched between the two conductive layers of CFO-CNT-PVDF, and followed by hot-pressing, three-layered multiferroic composite CFO-CNT-PVDF/P(VDF-TrFE)/CFO-CNT-PVDF (named as M/P/M) are prepared. The ME coupling increases with the volume fraction of CFO nanoparticles. The maximum self-biased and peak values of ME coefficient (αME) reach 16.7 mV cm−1 Oe−1 and 25.8 mV cm−1 Oe−1, respectively. Measurements on the relationship between the magnetostriction and static magnetic field (Hs) are performed for the CFO-CNT-PVDF films with different volume fraction of CFO. Based on the equivalent circuit model, the self-biased and peak values of αME are calculated for the ME composites, which fit well with the experimental data. The results imply that it is the high piezomagnetic coefficient, as well as the remnant magnetization of the M layer, contributes to the observed strong self-biased ME coupling for the CFO-CNT-PVDF/P(VDF-TrFE)/CFO-CNT-PVDF composite. Since the mechanical flexibility is also of great importance regarding the practical device applications, the stress-strain behavior for the CFO-CNT-PVDF layers is studied. With the volume fraction of CFO increases, both fracture strength (σf) and fracture strain (εf) decrease. The results offer a guideline for selecting proper ME composites on specified device applications.

Magnetostriction Increase of Polycrystalline Fe-Al-B Thin Sheets after Thermomechanical Process

Magnetostrictive materials are applied in several types of sensors, actuators, and energy harvesting. In particular, for AC devices, thin materials are desired to reduce eddy current losses. It is well known that the magnetostriction of single crystals and textured materials is higher than in polycrystalline ones, however, the cost and manufacture speed are crucial to be used as parts of commercial devices. Therefore, polycrystalline samples are strong candidates for common applications. In this work, (Fe x Al100−x )98.4B1.6 (x = 86.6, 82 and 79.4) alloys were rolled down to 0.7 mm of thickness and annealed at 1473 K (1200 °C) for 2 hours aiming to reduce the thickness of the samples without deteriorating the magnetic properties. The alloys, even with higher contents of Al, were easily deformed to the thickness of 0.7 mm and this ability is attributed to the presence of the Fe2B phase. After the thermomechanical process, new isotropic recrystallized grains emerged and the longitudinal magnetostriction increased to 75.8, 16.9, and 3.2 pct, achieving 28.3, 28.4, and 28.8 ppm, respectively, for x = 86.6, 82, and 79.4. The piezomagnetic coefficient obtained of 4 nm/A is a suitable actuating sensitivity.

Predicting Magnetoelectric Coupling in Layered and Graded Composites.

Magnetoelectric (ME) interaction in magnetostrictive-piezoelectric multiferroic structures consists in inducing the electric field across the structure in an applied magnetic field and is a product property of magnetostriction and piezoelectricity in components. ME voltage coefficient that is the ratio of induced electric field to applied magnetic field is the key parameter of ME coupling strength. It has been known that the ME coupling strength is dictated by the product of the piezoelectric and piezomagnetic coefficients of initial phases. As a result, using the laminates with graded piezoelectric and piezomagnetic parameters are a new pathway to the increase in the ME coupling strength. Recently developed models predict stronger ME interactions in composites based on graded components compared to homogeneous ones. We discuss predicting the ME coupling strength for layered structures of homogeneous and compositionally graded magnetostrictive and piezoelectric components based on the graphs of ME voltage coefficients against composite parameters. For obtaining the graphs, we developed equations for ME output in applied magnetic field for possible modes of operation and layered structure configurations. In particular, our studies have been performed on low-frequency ME coupling, enhanced ME effect in electromechanical resonance (EMR) region for longitudinal and bending modes. Additionally, ME coupling at magnetic resonance in magnetostrictive component and at overlapping the EMR and magnetic resonance is investigated. We considered symmetric trilayers and asymmetric bilayers of magnetostrictive and piezoelectric components and multilayered structures based on compositionally stepped initial components.

Magnetic flux biasing of magnetostrictive sensors

The performance of magnetostrictive materials, especially those with high initial magnetic permeability and associated low magnetic reluctance, is sensitive to not just the amount of magnetic bias but also how the bias is applied. Terfenol-D and Galfenol have been characterized under constant magnetic field and constant magnetomotive force, which require active control. The application of a magnetic flux bias utilizing permanent magnets allows for robust magnetostrictive systems that require no active control. However, this biasing configuration has not been thoroughly investigated. This study presents flux density versus stress major loops of Terfenol-D and Galfenol at various magnetic flux biases. A new piezomagnetic coefficient is defined as the locally-averaged slope of flux density versus stress. Considering the materials alone, the maximum is 18.42 T GPa−1 and 19.53 T GPa−1 for Terfenol-D and Galfenol, respectively. Compared with the peak piezomagnetic coefficient measured under controlled magnetic fields, the piezomagnetic coefficient is 26% and 74% smaller for Terfenol-D and Galfenol, respectively. This study shows that adding parallel magnetic flux paths to low-reluctance magnetostrictive components can partially compensate for the performance loss. With a low carbon steel flux path in parallel to the Galfenol specimen, the maximum increased to 28.33 T GPa−1 corresponding to a 45% improvement compared with the case without a flux path. Due to its low magnetic permeability, Terfenol-D does not benefit from the addition of a parallel flux path.

A multi-impact frequency up-converted magnetostrictive transducer for harvesting energy from finger tapping

Vibration energy harvesting has been a research subject of growing interest over the past few years, and is envisaged as a remedy to the unsatisfactory battery issue in low-power electronic devices. In this study, we propose a new magnetostrictive transducer to harvest energy from finger tapping. Galfenol is selected as the transducing material due to its high piezomagnetic coefficient and excellent machinability. To effectively harness energy in low-frequency conditions, we develop a frequency up-conversion mechanism that succeeds in converting vibration below 10Hz from finger tapping up to the system's resonance of a few hundred Hz. Furthermore, multiple impacts are induced in each working cycle deliberately to boost the efficiency. A comprehensive model is built and solved to analyze the mechanical-magnetic-electrical coupling system. Based on the model, we elucidate the design criteria for high-performance magnetostrictive transducers. A prototype is fabricated with a Galfenol beam of 0.5×5×25mm3 and, under finger tapping, it generates 5.3mW power and instantaneously lights up 10 commercial LEDs and a numeric LCD.

Micromechanical modeling of thin composite and reinforced magnetoelectric plates – Effective elastic, piezoelectric and piezomagnetic coefficients

A comprehensive asymptotic homogenization model for the analysis of composite and reinforced magnetoelectric plates is developed. The model culminates in a set of unit cell problems via which the relevant expressions for the effective coefficients are derived. The micromechanical and geometrical platform pertinent to the desired model is set up in this paper which also obtains the effective elastic, piezoelectric and piezomagnetic coefficients; the remaining properties, including product properties, are calculated in another work. Examples of structures that can be examined include diagonally- and triangularly-reinforced plates, hexagonal honeycomb sandwich plates and others. The developed model can be used to customize the effective properties of a reinforced plate to the requirements of a particular engineering application by changing some geometric, structural or material parameter of interest. It is shown that in the limiting case of a thin composite plate of uniform thickness whereby electrical conductivity is ignored and all pertinent quantities are time-averaged the presented model converges to the familiar classical plate model. Overall, this paper represents an important addition to the existing literature in terms of the complex geometries that can be designed and analyzed and at the same time constitutes an important refinement over previously published work.

Mechanical-magnetic-electric coupled behaviors for stress-driven Terfenol-D energy harvester

The stress-driven Terfernol-D energy harvester exhibits the nonlinear mechanical-magnetic-electric coupled (MMEC) behaviors and the eddy current effects. To analyze and design the device, it is necessary to establish an accurate model of the device. Based on the effective magnetic field expression, the constitutive equations with eddy currents and variable coefficients, and the dynamic equations, a nonlinear dynamic MMEC model for the device is founded. Comparisons between the measured and calculated results show that the model can describe the nonlinear coupled curves of magnetization versus stress and strain versus stress under different bias fields, and can provide the reasonable data trends of piezomagnetic coefficients, Young’s modulus and relative permeability for Terfenol-D. Moreover, the calculated power results show that the model can determine the optimal bias conditions, optimal resistance, suitable proof mass, suitable slices for the maximum energy extraction of the device under broad stress amplitude and broad frequency.

Electrically modulated magnetoelectric sensors

Magnetoelectric thin film composites have demonstrated their potential to detect sub-pT magnetic fields if mechanical resonances (typically few hundred Hz to a few kHz) are utilized. At low frequencies (1–100 Hz), magnetic field-induced frequency conversion has enabled wideband measurements with resonance-enhanced sensitivities by using the nonlinear characteristics of the magnetostriction curve. Nevertheless, the modulation with a magnetic field with a frequency close to the mechanical resonance results in a number of drawbacks, which are, e.g., size and energy consumption of the sensor as well as potential crosstalk in sensor arrays. In this work, we demonstrate the feasibility of an electric frequency conversion of a magnetoelectric sensor which would overcome the drawbacks of magnetic frequency conversion. This magnetoelectric sensor consists of three functional layers: an exchange biased magnetostrictive multilayer showing a high piezomagnetic coefficient without applying a magnetic bias field, a non-linear piezoelectric actuation layer and a linear piezoelectric sensing layer. In this approach, the low frequency magnetic signal is shifted into the mechanical resonance of the sensor, while the electric modulation frequency is chosen to be either the difference or the sum of the resonance and the signal frequency. Using this electric frequency conversion, a limit of detection in the low nT/Hz1/2 range was shown for signals of low frequency.

Evidence of domain wall pinning in aluminum substituted cobalt ferrites

In the present work spinel structured cobalt ferrites with aluminum substitution having composition CoAlxFe2−xO4 (x=0.0, 0.1, 0.2 and 0.3) have been synthesized using chemical co-precipitation method. Their microstructural, magnetic, magnetostriction and magnetoimpedance properties have been investigated. The piezomagnetic coefficient (dλ/dH) obtained from magnetostriction data is found to enhance with 0.1 Al substitutions in place of iron which decreases with further increase of Al content. It is noticed that 0.3 Al substitutions in place of Fe introduces domain wall pinning as evidenced from magnetostriction, magnetoimpedance and dc magnetization data. It is noted that ferrites so prepared using a simple procedure are magnetostrictive in good measure and with the addition of very small amount of non-magnetic aluminum their magnetostriction has shown saturation at relatively low magnetic fields. Such magnetostrictive ferrites find their applications in magnetic sensors and actuators.

Piezomagnetic behaviour in α-Fe2O3 nanofilms grown within nanochannels of Na-4 mica

α-Fe2O3 nanofilms were grown within the 0.6nm width nanochannels of sodium fluorophlogopite mica (Na-4 mica) structure. Due to a large difference in the values of thermal expansion coefficients of Na-4 mica and α-Fe2O3 a huge compressive stress was generated on the latter as the composite was cooled from 1023K to 300K. Magnetization measurements on the composite as a function of temperature showed the presence of piezomagnetic effect in α-Fe2O3. The values of piezomagnetic coefficient were estimated to be in the range 2.3×10−6 to 3.4×10−4emu/gkg/cm2. This is of the same order as that reported earlier by work carried out on single crystals of macrodimensions. Magnetization measurements of α-Fe2O3 particles of diameter ~130nm on the other hand, showed the usual behaviour viz., a magnetic phase transition from antiferromagnetic to ferromagnetic state at 237K.

A mechanical-thermo-magneto model for self-biased magnetoelectric effect in laminated composite

In this paper, a mechanical-thermo-magneto model for self-biased magnetoelectric effect in laminated composite with high-permeability materials is established. Considering the effects of demagnetization, pre-stress and temperature, the effective magnetic field and piezomagnetic coefficient of magnetostrictive layers are calculated. Then, the effects of temperature and pre-stress on ME effect are investigated. Finally, the combined effect of temperature and pre-stress on zero-bias ME voltage coefficient is discussed in detail to achieve a good ME conversion efficiency. The numerical results show that due to the occurrence of the additional magnetic field from high-permeability materials, available self-biased ME effect can be obtained in the proposed model. The operating temperature affects not only the peak value but also the initial value of ME voltage coefficient. Also, pre-stress can change the temperature effect on the zero-bias ME voltage coefficient obviously.

Correlation Between Magnetoelectric and Magnetic Properties of Ferromagnetic–Piezoelectric Structures

The magnetoelectric (ME) effect in composite structures consisting of ferromagnetic (FM) and piezoelectric (PE) layers arises due to combination of magnetostriction and piezoelectricity by means of mechanical coupling between the layers [1]. The structures generate ac voltage u being placed in an external dc bias magnetic field H and ac magnetic field h. Amplitude of the voltage is u ∼qd 31 h, where q = dλ/dH is the piezomagnetic coefficient and λ(H) in the magnetostriction of the FM layer, d 31 is the piezoelectric module of the PE layer, and h is the field amplitude. It has been shown that the magnetostriction is related to the FM layer magnetization as λ ∼ M 2. It follows, that field dependence of the ME voltage u(H) can be explained or predicted by measuring the field dependence of magnetization M(H). The aim of the present work is to demonstrate a correlation between magnetoelectric and magnetic properties of the FM-PE composite structures.

Near-Flat Self-Biased Magnetoelectric Response in Three-Phase Metglas/Terfenol-D/PZT-Laminated Composites

Since the piezoelectric/magnetostrictive laminate composite exhibits a strong magnetoelectric (ME) effect, it provides a novel method for detecting ac magnetic field. There are a number of researches on the development of ME composites and their applications in detecting magnetic fields. Dong et al. demonstrates the possibility of fabricating ac magnetic field sensors with high performances[1]. Especially, ME composite sensor can achieve the passive sensing of magnetic field and possesses high sensitivity, which greatly enhances the competitiveness of ME composite sensor against traditional magnetic sensors. ME voltage coefficient varies with H dc owing to the piezomagnetic coefficient's variation as a function of H dc , which shows a peak behavior near an optimum dc bias magnetic field H dc, opti . Hence, the ME composite sensor requires an external dc bias magnetic field to obtain the high ME sensitivity. However, the bias magnetic field is usually generated by using permanent magnets. It will increase the electromagnetic noise and increase the size of the sensor greatly, which is disadvantageous for the realization of high-sensitivity miniature magnetic sensors. Furthermore, the peak point is sharp and fixed, correspondingly small fluctuations of the optimum dc bias magnetic field will lead to a remarkable decrease of the ME voltage coefficient and degrade the ME composite performance significantly. In addressing these issues, the study of self-biased ME composite has provoked a great number of research activities and made progress [2-3]. However, these efforts have not obtained a wide range of dc bias response.

Zero-Biased Magnetoelectric Effects in Five-Phase Laminate Composites With FeCoV Soft Magnetic Alloy

Magnetoelectric (ME) response has attracted continuously increasing interest in the past decades due to its potential applications in many new multifunctional devices, including magnetic storage, magnetic sensors, current sensors, and energy harvesters.[1] In general, single-phase ME materials are difficult to be utilized in such devices because the ME responses are weak and mostly appear at low temperature. Compared to single-phase ME materials, Magnetoelectric composites consisting of piezoelectric materials (e.g., PZT and PMN-PT) and magnetostrictive materials (e.g., Terfenol-D and Metglas) exhibit strong ME responses at room temperature, and meet the demands of practical application. However, in order to obtain high piezomagnetic coefficient and ME response, most of the reported ME composites require an external bias magnetic field (H bias ) that increases their sizes and costs.[2] To overcome these limitations, more and more researchers have focused on zero-biased ME effects in the composites. Recently, some studies have attempted to achieve high zero-biasd ME response with different methods. For example, Mandal et al. have reported that ME composite of PZT and graded NZFO show an enhancement in the ME coefficient at zero bias. [3]Yang et al. demonstrated a methodology for achieving zero-biased ME response by changing the electrical connections in a sandwiched ME structure of NKNLS-NZF/Ni/NKNLS-NZF. These methods are difficult to realize and require special synthesis process. In fact, utilizing an internal magnetic bias of the magnetostrictive materials in ME composite is a feasible way to solve thisproblem. In this paper, a new zero-biased five-phase laminate composite consists of FeCoV/Terfenol-D/Pb(Zr 1 - x , Ti x )O 3 (PZT)/Terfenol-D/FeCoV (FMPMF) is presented, whose magnetoelectric (ME) coupling characteristics have been investigated. Due to the different magnetic characteristics between FeCoV and Terfenol-D (such as permeability, saturation magnetization and magnetostriction), an internal magnetic field is formed in the compound magnetostrictive layers. It is found that the resonant ME voltage coefficient of five-phase laminate composite is much larger than that of traditional Terfe-nol-D/PZT/Terfenol-D (MPM) laminate composite at zero bias. The experimental results show that the zero-biased resonant ME voltage coefficient strongly depends on the thickness of FeCoV layers as shown in Fig.1. When the thickness of FeCoV layers is 90μm, we obtain the optimum resonant ME voltage cofficient of 1.96 V/Oe at the zero magnetic bias field, which is 1.75 times as great as that of MPM laminate composite. Furthermore, a low-frequency ME voltage coefficient of 50.4 mV/Oe is achieved, which is 2.1 times higher than that of the MPM laminate composite. Meanwhile, the induced zero-bias ME voltage of FMPMF laminate composite shows an excellent linear relationship to ac magnetic field both at the low frequency (1kHz) and the resonant frequency (115.14kHz) as shown in Fig.2. It indicates that the proposed zero-biased five-phase laminate composite shows promising applications for high sensitive dc magnetic field sensors, zero-biased ME transducers and small-size energy harvesters.

Giant Converse Magnetoelectric Effect in PZT/FeCuNbSiB/FeGa/FeCuNbSiB/PZT Laminates Without Magnetic Bias Field

We reported a giant self-biased converse magnetoelectric (CME) effect in laminated composites consisting of gradedmagnetostrictive FeCuNbSiB/FeGa/FeCuNbSiB layers sandwiched between two electro-parallel-connected PZT piezoelectric plates. The great different magnetic characteristics (such as magnetic permeability and coercivity) in FeGa and nanocrystalline foil FeCuNbSiB result in a large internal magnetic field and remanent piezomagnetic coefficient in FeCuNbSiB/FeGa/FeCuNbSiB, which account for the giant self-biased CME effect. The experimental results show that: 1) a large remanent CME coefficient of $ 2.228 \times 10^{-3}$ mGs $\cdot $ cm/V is achieved, which can be used for realizing miniature electrically controlled magnetic flux devices; 2) the dynamic switching of magnetic flux between bistable states in PZT/FeCuNbSiB/FeGa/FeCuNbSiB/PZT through a smaller ac voltage ( $1~V_{\mathrm {rms}}$ ) controlling is realized; and 3) the induced magnetic induction B has an excellent linear relationship with applied ac voltage $V_{\mathrm {in}}$ .

Magnetoelectric Coupling Characteristics of Multiphase Laminate Heterostructures Based on FeCuNbSiB Nanocrystalline Soft Magnetic Alloy

Over the last decade, multiferroic laminate heterostructures, consisting of the piezoelectric layer (such as PZT) and the magnetostrictive layer (such as Terfenol-D), have attracted considerable attention due to their high Curie or Neel temperature and large magnetoelectric (ME) effect at room temperature. The ME laminate materials have demonstrated potential in many applications such as transducers, actuators, magnetic field sensors, energy harvesters, and other devices [1]. ME effect in the multiferroic laminated heterostructures is essentially attributed to the elastic coupling between the piezoelectric and magnetostrictive layers [2]. The effective piezomagnetic coefficient and effective mechanical quality factor play a key role in the performance of the ME materials. However, owing to the small values of the mechanical quality factor and relative permeability, the ME voltage coefficient of the traditional Terfenol-D/PZT (MP) composites is difficult to increase [3, 4]. The nanocrystalline FeCuNbSiB soft magnetic alloy would be a good solution, according to the large interface stress-strain coupling effects. In this paper, a series of FeCuNbSiB/Terfenol-D/PZT (F/M/P) multi-phase laminate heterostructures are presented (Fig. 1), whose ME coupling characteristics have been investigated. Compared to traditional MPM, the ME coupling characteristics of the proposed FMPMF heterostructures were significantly improved. The resonant and low-frequency ME voltage coefficient of the proposed F/M/P heterostructures could be tuned by controlling the layer numbers N. When N is 7 (FMPMPMF), the maximum value of resonant ME voltage coefficient achieves 8.69 V/Oe, which is about 3.65 times higher than that for FMP, 1.81 times higher than that for FMPMF (Fig. 2(a)). Meanwhile, the maximum value of low-frequency ME voltage coefficient for FMPMPMF heterostructures achieves 69.6 mV/Oe at H b =378 Oe (Fig. 2(b)). Remarkably, it indicates that the F/M/P heterostructures have great potential as far as its application in highly sensitive dc magnetic field sensing and vibration energy harvesting.

High strain-rate magnetoelasticity in Galfenol

This paper presents the experimental measurements of a highly magnetoelastic material (Galfenol) under impact loading. A Split-Hopkinson Pressure Bar was used to generate compressive stress up to 275 MPa at strain rates of either 20/s or 33/s while measuring the stress-strain response and change in magnetic flux density due to magnetoelastic coupling. The average Young's modulus (44.85 GPa) was invariant to strain rate, with instantaneous stiffness ranging from 25 to 55 GPa. A lumped parameters model simulated the measured pickup coil voltages in response to an applied stress pulse. Fitting the model to the experimental data provided the average piezomagnetic coefficient and relative permeability as functions of field strength. The model suggests magnetoelastic coupling is primarily insensitive to strain rates as high as 33/s. Additionally, the lumped parameters model was used to investigate magnetoelastic transducers as potential pulsed power sources. Results show that Galfenol can generate large quantities of instantaneous power (80 MW/m3), comparable to explosively driven ferromagnetic pulse generators (500 MW/m3). However, this process is much more efficient and can be cyclically carried out in the linear elastic range of the material, in stark contrast with explosively driven pulsed power generators.