High Magnetoelectric Research Articles

Multiple broadband magnetoelectric response in Terfenol-D/PZT structure**Project supported by the National Natural Science Foundation of China (Grant Nos. 11702120, 11372120, 11421062, and 11572143) and the Fundamental Research Funds for the Central Universities, China (Grant No. lzujbky-2016-106).

In this paper, a novel magnetoelectric (ME) composite structure is proposed, and the ME response in the structure is measured at the bias magnetic field up to 2000 Oe (1 Oe = 79.5775 A·m−1) and the excitation frequency of alternating magnetic field ranging from 1 kHz to 200 kHz. The ME voltage of each PZT layer is detected. According to the measurement results, the phase differences are observed among three channels and the multi-peak phenomenon appears in each channel. Meanwhile, the results show that the ME structure can stay a relatively high ME response within a wide bandwidth. Besides, the hysteretic loops of three PZT layers are observed. When the frequency of alternating current (AC) magnetic field changes, the maximum value of ME coefficient appears in different layers due to the multiple vibration modes of the structure. Moreover, a finite element analysis is performed to evaluate the resonant frequency of the structure, and the theoretical calculating results accord well with the experimental results. The experiment results suggest that the proposed structure may be a good candidate for designing broadband magnetic field sensors.

Surface magnetism of gallium arsenide nanofilms

Gallium arsenide (GaAs) is the widest used second generation semiconductor with a direct band gap and increasingly used as nanofilms. However, the magnetic properties of GaAs nanofilms have never been studied. Here we find by comprehensive density functional theory calculations that GaAs nanofilms cleaved along the <111> and <100> directions become intrinsically metallic films with strong surface magnetism and magnetoelectric (ME) effect. The surface magnetism and electrical conductivity are realized via a combined effect of transferring charge induced by spontaneous electric-polarization through the film thickness and spin-polarized surface states. The surface magnetism of <111> nanofilms can be significantly and linearly tuned by vertically applied electric field, endowing the nanofilms unexpectedly high ME coefficients, which are tens of times higher than those of ferromagnetic metals and transition metal oxides.

Theoretical design of high-performance polymer-based magnetoelectric of fibrilar structures

Low-dimensional magnetoelectric (ME) materials are attracting high attention both from the scientific and technological communities due to their interesting electrical, optical and mechanical properties allied to their novel applications in micro and nano smart-devices, drug delivery platforms, heterogeneous catalysis, tissue engineering, biosensors and bio-actuators, among others. Once the low dimensionality of these materials complicate the direct measurement of their performance at a large range of magnetic fields and high filler contents, this work theoretically evaluates low dimensional ME structures from spherical to ellipsoidal and fibre-shaped. The structures are based on CoFe2O4/poly(vinylidene fluoride) composites and the simulations are performed through the finite element method (FEM).Results for 50 wt percentage (wt.%) CoFe2O4 content samples reveal ME coefficients of 182 V/cm at 684 Oe for the spheres and 4241 V/cm at a magnetic field of 208 Oe on the medium eccentricity (of 1200) ellipsoidal structure. These fibre shaped ellipsoids exhibit higher ME values than the spheres and the axisymmetric fibres: 1601 V/cm at 30 Oe for an ellipsoid with eccentricity of 3200. Further, the fibrilar structure strongly decreases the ME performance and operational magnetic field to 14.7 V/cm at 1.38 Oe.These results establish the potential and limits, in terms of magnetic field and electric response, of the use of these composites and structures on technological ME device applications. Further, it demonstrates that suitable tuning of shape and dimensions allow to strongly increase ME response of the composites.

A flexible, high-performance magnetoelectric heterostructure of (001) oriented Pb(Zr0.52Ti0.48)O3film grown on Ni foil

In this study, a flexible magnetoelectric (ME) heterostructure of PZT/Ni was fabricated by depositing a (001) oriented Pb(Zr0.52Ti0.48)O3 (PZT) film on a thin, flexible Ni foil buffered with LaNiO3/HfO2. Excellent ferroelectric properties and large ME voltage coefficient of 3.2 V/cm⋅Oe were realized from the PZT/Ni heterostructure. The PZT/Ni composite’s high performance was attributed to strong texturing of the PZT film, coupled with the compressive stress in the piezoelectric film. Besides, reduced substrate clamping in the PZT film due to the film on the foil structure and strong interfacial bonding in the PZT/LaNiO3/HfO2/Ni heterostructure could also have contributed to the high ME performance of PZT/Ni.

Correlation of Interface Impurities and Chemical Gradients with High Magnetoelectric Coupling Strength in Multiferroic BiFeO3-BaTiO3 Superlattices.

The detailed understanding of magnetoelectric (ME) coupling in multiferroic oxide heterostructures is still a challenge. In particular, very little is known to date concerning the impact of the chemical interface structure and unwanted impurities that may be buried within short-period multiferroic BiFeO3-BaTiO3 superlattices during growth. Here, we demonstrate how trace impurities and elemental concentration gradients contribute to high ME voltage coefficients in thin-film superlattices, which are built from 15 double layers of BiFeO3-BaTiO3. Surprisingly, the highest ME voltage coefficient of 55 V cm-1 Oe-1 at 300 K was measured for a superlattice with a few atomic percent of Ba and Ti that diffused into the nominally 5 nm thin BiFeO3 layers, according to analytical transmission electron microscopy. In addition, highly sensitive enhancements of the cation signals were observed in depth profiles by secondary ion mass spectrometry at the interfaces of BaTiO3 and BiFeO3. As these interface features correlate with the ME performance of the samples, they point to the importance of charge effects at the interfaces, that is, to a possible charge mediation of ME coupling in oxide superlattices. The challenge is to provide cleaner materials and processes, as well as a well-defined control of the chemical interface structure, to push forward the application of oxide superlattices in multiferroic ME devices.

Evaluation and optimization of the magnetoelectric response of CoFe2O4/poly(vinylidene fluoride) composite spheres by computer simulation

Magnetoelectric (ME) composites exhibiting strain-mediated coupling are gaining increasing interest for applications. The most interesting ones are composed of piezoelectric polymers and magnetostrictive particles. In particular, low dimensional ME materials, such as the ones in the form of micro- and nano-spheres, show strong potentials for improved energy harvesters with higher volume efficiency, sensors and actuators. Nevertheless the ME characterization of such low dimensional ME structures remain a difficult and challenging task and, therefore, the use of mathematical models and simulations are an interesting and viable option to better understand and tailor materials towards applications.In this context, the ME coupling on microspheres based on piezoelectric poly(vinylidene fluoride) (PVDF) and magnetostrictive CoFe2O4 (CFO) particles was theoretically studied based on Finite Element Methods (FEM). The effect of sphere size and filler content on the ME response was evaluated, showing that the ME response of CFO/PVDF microspheres is strongly influenced by the magnetic field intensity, sphere diameter and CFO content, being the highest ME response achieved on composite sphere with 90 wt% of CFO and 1.2 μm.

Switchable 3-0 magnetoelectric nanocomposite thin film with high coupling.

A mixed precursor solution method was used to deposit 3-0 nanocomposite thin films of PbZr0.52Ti0.48O3 (PZT) and CoFe2O4 (CFO). The piezoelectric behavior of PZT and magnetostrictive behavior of CFO allow for magnetoelectric (ME) coupling through strain transfer between the respective phases. High ME coupling is desired for many applications including memory devices, magnetic field sensors, and energy harvesters. The spontaneous phase separation in the 3-0 nanocomposite film was observed, with 25 nm CFO particle or nanophases distributed in discrete layers through the thickness of the PZT matrix. Magnetic-force microscopy images of the nanocomposite thin film under opposite magnetic poling conditions revealed in-plane pancake-like regions of higher concentration of the CFO nanoparticles. The constraints on the size and distribution of the CFO nanoparticles created a unique distribution in a PZT matrix and achieved values of ME coupling of 3.07 V cm-1 Oe-1 at a DC bias of 250 Oe and 1 kHz, increasing up to 25.0 V cm-1 Oe-1 at 90 kHz. Piezo-force microscopy was used to investigate the ferroelectric domain structure before and after opposite magnetic poling directions. It was found that in this nanocomposite, the polarization of the ferroelectric domains switched direction as a result of switching the direction of the magnetization by magnetic fields.

Polymer content and particle size effects on polymer-bonded Terfenol-D/PZT magnetoelectric composites

Polymer-bonded cylindrical Terfenol-D/PZT magnetoelectric (ME) composites have been prepared with varying polymer contents and Terfenol-D particle sizes. The axial ME voltage coefficient, αE,A, was investigated for studying the effects of polymer content and particle size on the composite ME performance. The Terfenol-D particles with four different size ranges (<75µm, 75–100µm, 100–150µm and 150–180µm) were used. Additionally, the epoxy content of the composites was studied with five different weight ratios of 9wt%, 12wt%, 14wt%, 16wt% and 19wt%. The composite with an epoxy content of 0.14wt% and 100–150µm particle range exhibited better overall ME performance. This investigation promotes selecting the appropriate polymer content and particle size to optimize fabrication of the polymer-bonded ME composites for high ME performance to meet practical applications.

Giant Magnetoelectric Effect in PZT Thin Film Deposited on Nickel

Abstract The magnetoelectric (ME) effect has been investigated in lead zirconate titanate (PZT) thin film deposited on nickel foil using chemical solution deposition (CSD) technique. The synthesized PZT thin films are found to possess perovskite structure without presence of any intermediate layer. PZT thin film deposited on nickel foil exhibits a good ferroelectric property with a high remnant polarization of about 86 µC/cm2.The ferroelectric loop has been modeled using domain wall theory to verify the behavior of the ferroelectric domains. It is observed that deposition conditions, specially annealing temperature, play a crucial role in enhancing the magnetoelectric effect. A high ME coefficient of 220 mVcm–1Oe–1 at a bias magnetic field of 50 Oe has been obtained due to enhanced magnetoelectric coupling between PZT film and nickel foil.

Optimization design for magnetoelectric coupling property of the magnet/bimorph composite

Magnetoelectric (ME) composite as one kind of ME material that can yield a strong coupling effect between magnetic and electric fields at room temperature, has drawn widespread attention for decades due to its rich physics contents and significant technological prospect. Except for traditional magnetostrictive/piezoelectric based ME composites, other ME composites have been reported, among which the magnet/piezo-cantilever composites show super strong ME coupling effect. The magnet/piezo-cantilever composite is generally composed of a piezoelectric cantilever and magnets attached at the free end of the cantilever, which realizes ME coupling by force moment-mediated magnetic torque effect and piezoelectric effect. Recently, various configurations of the magnet/piezo-cantilever composites for obtaining higher ME coupling coefficients have been proposed and demonstrated experimentally. However, few theoretical researches of these magnet/piezo-cantilever composites of different configurations have been carried out, which is of great importance for optimizing the design of ME coupling property of the magnet/piezo-cantilever composites. Here in this paper, a theoretical expression for the low-frequency ME coupling coefficient in the magnet/piezo-cantilever composite is deduced based on piezoelectric constitutive equations by using the theory of elastic mechanics. The typical magnet/bimorph composite is chosen as the theoretical model. Based on the deduced theoretical expression, the dependences of the lowfrequency ME coupling coefficients in the magnet/bimorph composite on material and structural parameters are numerically calculated. The results show that there are optimal thickness values of the piezoelectric layers in the magnet/bimorph composite with different metal thickness values and material constituents for achieving maximal lowfrequency ME coupling coefficients. The thicker the metal layer in the magnet/bimorph composite, the less insensitive the low-frequency ME coupling coefficient to the thickness of the piezoelectric layer will be. And the low-frequency ME coupling coefficient of the magnet/bimorph composite decreases when a metal with higher elastic module is selected for bimorph. For the magnet/bimorph composite consisting of hard piezoelectric ceramics (PZT-4), the low-frequency ME coupling coefficient is higher than that of the composite consisting of the soft counterpart ones (PZT-5 H), which is due to the hard piezoelectric ceramics with higher piezoelectric voltage coefficient than the soft counterpart ones. What is more interesting is that when the piezoelectric material in the magnet/bimorph composite is changed into relaxor ferroelectric single crystals Pb(Zn1/3 Nb2/3)O3-PbTiO3 (PZN-PT), an extremely high low-frequency ME coupling coefficient can be obtained, which is 3.8 and 5 times those of the 13 composites with hard and soft piezoelectric ceramics, respectively. This research gives a theoretical guidance for optimal design and practical applications of the magnet/Bimorph composite.

Enhanced magnetoelectric efficiency of the Tb1 − xDyxFe2 − y/Pb(Zr,Ti)O3 cylinder multi-electrode composites

Cylinder layered magnetoelectric (ME) Tb1−xDyxFe2−y/Pb(Zr,Ti)O3 (T–P), Pb(Zr,Ti)O3/Tb1−xDyxFe2−y/Pb(Zr,Ti)O3 (P–T–P) and Tb1−xDyxFe2−y/Pb(Zr,Ti)O3/Tb1−xDyxFe2−y/Pb(Zr,Ti)O3 (T–P–T–P) composites with the same overall dimensions, but different structures and layers were designed and prepared for enhancing magnetoelectric efficiency. The ME effect in the vertical mode was studied. Compared with the T–P and T–P–T–P composites, the hollow P–T–P composite with a multi-electrode cylinder structure has higher ME effect and uses less Tb1−xDyxFe2−y (Terfenol-D, a piezomagnetic material). The ME efficiency factor of P–T–P is more than two times higher than the other two composites. The reason for the improvement can be ascribed to the effective working surface conditions and the series multi-electrode effect. The results of the study indicate that this type of hollow multi-electrode cylinder ME composite can enhance the efficiency of piezomagnetic materials, particularly Terfenol-D. This finding demonstrates that creating similar structural designs not only reduces the weight, but also provides a cost effective way to manufacture ME devices for practical applications.

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.

A method to decrease the harmonic distortion in Mn-Zn ferrite/PZT and Ni-Zn ferrite/PZT layered composite rings exhibiting high magnetoelectric effects

We have investigated the magnetoelectric (ME) effect in layered composite rings subjected to circumferential AC magnetic fields and DC magnetic fields in radial, axial, or circumferential directions. Bilayer samples were obtained combining different grades of commercial Mn-Zn ferrites or Ni-Zn ferrites with commercial lead zirconate titanate (PZT). Mn-Zn ferrites with low magnetostriction saturation (λs&amp;lt;10−6) and low magneto-crystalline anisotropy constants show high ME capabilities when associated with PZT in ring structures. In certain conditions, these ME effects are higher than those obtained with Terfenol-D/PZT composites in the same layered ring structure. Magnetostrictive and mechanical characterizations have given results that explain these high ME performances. Nevertheless, Mn-Zn ferrite/PZT composites exhibit voltages responses with low linearity especially at high signal level. Based on the particular structure of the ME device, a method to decrease the nonlinear harmonic distortion of the ME voltages is proposed. Harmonic distortion analysis of ME voltages measured in different configurations allows us to explain the phenomenon.

Room temperature magnetoelectric effect of YFeO3–Y3Fe5O12 ferrite composites

We report the room temperature magnetoelectric (ME) behavior of microwave ferrite composites consisting of ferroelectric phase YFeO3 (YIP) and ferromagnetic phase Y3Fe5O12 (YIG). These ferrite composites were fabricated by traditional solid–state reaction method. The structure, magnetic and ferroelectric measurements indicate that the composites are of two phase crystalline structures, revealing significant magnetic, ferroelectric properties and ME interaction. Room temperature ME effects were demonstrated for composites xYFeO3-(1−x) Y3Fe5O12(x = 0.1, 0.3, 0.5, 0.7), yielding a highest ME coefficient, αME = 11.568 mV/cm-Oe for x = 0.3. The results have shed light on the challenge in ME-based tunable electronic devices. The ME investigation on YIG microwave ferrites is of great importance in the exploration of next generation multifunctional devices and integrated circuits.

Lithium sodium potassium niobate-modified nickel ferrite lead-free magnetoelectric composite ceramics

The variety of compositions and weight ratios of components has strong effect on dielectric, piezoelectric, and magnetoelectric (ME) properties of хwt% [Li0.06(Na0.52K0.48)0.94+у]NbO3+(100-х)wt% Ni0.9Cо0.1Cu0.1Fe1.9O4-δ (у=0.015, 0.05, 0.10; х=30, 40, 50, 60, 70wt%) lead-free particulate composites. Composites based on [Li0.06(Na0.52K0.48)0.94+у]NbO3 (у=0.1) piezoelectric material, which exhibits significant piezoelectric voltage coefficient g33=40mVm/N, have maximal piezoelectric parameters and the highest ME response. ME coupling coefficient ΔЕ/ΔН of composition with x=60 was found to be 120mV/(cmOe) at DC bias field of 80–90kА/m and reached value of 140mV/(cmOe) in the best samples.

Magnetoelectric effect in layered ferrite/PZT composites. Study of the demagnetizing effect on the magnetoelectric behavior

We report the use of high magnetomechanical coupling ferrites in magnetoelectric (ME) layered composites. Bilayer samples combining (Ni0.973 Co0.027)1−xZnxFe2O4 ferrites (x = 0–0.5) synthesized by non conventional reactive Spark Plasma Sintering and commercial lead zirconate titanate (PZT) were characterized in term of ME voltage coefficients measured at sub-resonant frequency. Strong ME effects are obtained and we show that an annealing at 1000 °C and a quenching in air improve the piezomagnetic behavior of Zn-rich compositions. A theoretical model that predicts the ME behavior was developed, focusing our work on the demagnetizing effects in the transversal mode as well as the longitudinal mode. The model shows that: (i) high ME coefficients are obtained when ferrites with high magnetomechanical coupling are used in bilayer ME composites, (ii) the ME behavior in transversal and longitudinal modes is quite similar, and differences in the shapes of the ME curves are mainly due the demagnetizing effects, (iii) in the transversal mode, the magnetic field penetration depends on the ferrite layer thickness and the ME coefficient is affected accordingly. The two later points are confirmed by measurements on ME samples and calculations. Performances of the ME composites made with high magnetomechanical coupling ferrites are compared to those obtained using Terfenol-D materials in the same conditions of size, shape, and volume ratio. It appears that a ferrite with an optimized composition has performances comparable to those obtained with Terfenol-D material. Nevertheless, the fabrication processes of ferrites are quite simpler. Finally, a ferrite/PZT based ME composite was used as a current sensor.

The giant magnetoelectric effect in Fe73.5Cu1Nb3Si13.5B9/PZT thick film composites

The Fe73.5Cu1Nb3Si13.5B9/PZT thick film composites with excellent magnetoelectric (ME) coupling effect were synthesized by electrostatic spray depositing. The ME coupling characteristics of Fe73.5Cu1Nb3Si13.5B9/PZT thick film composites were investigated. It is found that the appropriate thickness ratio between magnetostrictive layers and piezoelectric layers (tm/tp) will be favorable to raise the resonance ME field output performance. The resonance frequency of ME field coefficient can be tuned by controlling tm/tp. The optimum resonance ME field coefficient of Fe73.5Cu1Nb3Si13.5B9/PZT thick film composites achieves 259.2 V/cm Oe at mechanical resonance frequency at 11.5 kHz with the dc bias magnetic field is 60 Oe. Remarkably, the proposed composites exhibit a giant ME effect and a higher ME voltage coefficient than the previous Terfenol-D/PZT laminated composites. It indicates that the mentioned Fe73.5Cu1Nb3Si13.5B9/PZT thick film composites have great potential for the application of highly sensitive magnetic field sensing and vibration energy harvesting.

Size effects on the magnetoelectric response on PVDF/Vitrovac 4040 laminate composites

Tri-layered and bi-layered magnetoelectric (ME) flexible composite structures of varying geometries and sizes consisting on magnetostrictive Vitrovac and piezoelectric poly(vinylidene fluoride) (PVDF) layers were fabricated by direct bonding. From the ME measurements it was determined that tri-layered composites structures (magnetostrictive–piezoelectric–magnetostrictive type), show a higher ME response (75 V cm−1 Oe−1) than the bi-layer structure (66 V cm−1 Oe−1). The ME voltage coefficient decreased with increasing longitudinal size aspect ratio between PVDF and Vitrovac layers (from 1.1 to 4.3), being observed a maximum ME voltage coefficient of 66 V cm−1 Oe−1. It was also observed that the composite with the lowest transversal aspect ratio between PVDF and Vitrovac layers resulted in better ME performance than the structures with higher transversal size aspect ratios. It was further determined an intimate relation between the AreaPVDF/AreaVitrovac ratio and the ME response of the composites. When such ratio values approach 1, the ME response is the largest. In addition the ME output value and magnetic field response were controlled by changing the number of Vitrovac layers, which allows the development of magnetic sensors and energy harvesting devices.

Improved magnetoelectric performance of the Ni-P/Ni/Pb(Zr,TiO)3 cylindrical layered composites

The Ni-P/Ni/Pb(Zr,TiO)3 (PZT) cylindrical layered magnetoelectric (ME) composites have been prepared by electroless deposition and electrodeposition. The ME effect in the axial mode was researched in this paper. Compared with that of the Ni/PZT and Ni-P/PZT composites, the Ni-P/Ni/PZT composites have both lower optimal magnetic field and higher ME voltage coefficient. The reason for the ME improvement can be ascribed to the flux concentration effect and the compressive stress in the Ni layers induced by the high permeability Ni-P layers. These results open up a suitable way to enhance the sensitivity and optimize the design of ME devices for practical application.

Height-related magnetoelectric performance of PZT/Ni layered composites

The effect of height on performance of the PZT/Ni cylindrical bilayered magnetoelectric (ME) composites was studied in situ in this paper. Multiple resonant peaks appear between 1 and 300 kHz frequency for cylinders of different heights. The first resonance frequency does not change with the cylinder height decreasing, but the second and the third resonant frequencies increase. The first three resonant modes are attributed to the cylinder radial, first-order height resonance, and second-order height resonance, respectively. The appropriate size and resonance frequency were chosen to obtain the highest ME voltage coefficient when designing cylindrical bilayered magnetoelectric devices. This article provides reference to design cylindrical magnetoelectric devices.