Strong Magnetoelectric Research Articles

The shape factor influence on the control process of multiferroic nanoparticle configurations in GHz range

Materials with piezoelectric properties associated with the ferroic phases generate multiferroic structures at microscopic level. Multiferroic core-shell nanoparticles with different configurations were considered: nanospheres versus nanotubes - spherical (magnetostrictive core / piezoelectric shell), respectively cylindrical (magnetostrictive rod / piezoelectric cylindrical coating) The external sphere diameter / cylinder lengths were of 80 - 100 nm to 360 nm, while the inner sphere / rod diameters were of 20 to 60 nm. The influence of the constituents shape on their control process realized by an applied magnetic field, H0 (100 - 270 Oe) was investigated. The nanoparticles were simulated using the HFSS 13.0 program, at frequencies in microwave range (16 - 28 GHz), considering the nanostructures with hexaferrites as magnetic phase (AFe12O19 M-type hexaferrites, with A an alkali earth metal) and the Bi2NiMnO6 perovskite like piezoelectric. The particle configurations response is function of their geometrical shape, modified by the core diameter and the shell thickness. The magnetoelectric (ME) coefficient tensor has been determined using a physical algorithm based on the near-filed values in the particles vicinity, generated by the HFSS, and also the ME voltage coefficient (obtained of tens of mV/cmOe). Performance of the two shapes composite nanoparticles to generate a strong ME response was discussed comparatively and the influence of the shape factor was illustrated on graphs. Each composite configuration presents specific advantages in respect with the control process by the H0 field, considering that the effect of dipolar field generated as response by the electric phase is strongly anisotropic. These features can be elegant illustrated by simulations (non destructive, applied at nanoscale) which help us to decide to the proper nanoparticles shape and the optimal intensity of the applied fields for the desired strength of the ME effect in a defined microscopic area.

Enhanced Magnetoelectric Effect in Permendur/Pb(Zr0.52Ti0.48)O3 Laminated Magnetostrictive/Piezoelectric Composite

In this work, after investigating three typical magneto-electric (ME) composites, Permendur/Pb(Zr0.52Ti0.48)O3(PZT), Metglas/PZT, and Tefenol-D/PZT, with the same dimensions and different saturation magnetostriction and magnetic permeability, the most excellent ME performance is observed in the Permendur/PZT laminates, which agrees well with the predicted results from the figure of merit. The low-frequency and resonance ME coefficients of Permendur/PZT composite are ~23.1 V/Oe.cm and ~309 V/Oe.cm at the optimal dc bias magnetic field of ~250 Oe, respectively. The strong ME effect of Permendur/PZT composite gives it potential in practical magnetic sensitive device applications.

Magnetism-Driven Ferroelectricity in Double Perovskite Y₂NiMnO₆.

We report the discovery of multiferroic behavior in double perovskite Y2NiMnO6. X-ray diffraction shows that the material has a centrosymmetric crystal structure of space group P2(1)/n with Ni(2+)/Mn(4+) ordering. This result is further confirmed by aberration-corrected scanning transmission electron microscopy combined with atomic resolution electron energy loss spectroscopy. The appearance of ferroelectric polarization coincides with the magnetic phase transition (∼67 K), which indicates that the ferroelectricity is driven by magnetism, and this is further confirmed by its strong magnetoelectric (ME) effect. We proposed the origin of the ferroelectricity is associated with the combination of Ni(2+)/Mn(4+) charge ordering and the ↑↑↓↓ spin ordering. When compared with other known magnetic multiferroics, Y2NiMnO6 displays several attractive multiferroic properties, including high polarization (∼145 μC/m(2)), a high multiferroic transition temperature (∼67 K), and strong ME coupling (∼21%).

Electric tuning of magnetization dynamics and electric field-induced negative magnetic permeability in nanoscale composite multiferroics.

Steering magnetism by electric fields upon interfacing ferromagnetic (FM) and ferroelectric (FE) materials to achieve an emergent multiferroic response bears a great potential for nano-scale devices with novel functionalities. FM/FE heterostructures allow, for instance, the electrical manipulation of magnetic anisotropy via interfacial magnetoelectric (ME) couplings. A charge-mediated ME effect is believed to be generally weak and active in only a few angstroms. Here we present an experimental evidence uncovering a new magnon-driven, strong ME effect acting on the nanometer range. For Co92Zr8 (20 nm) film deposited on ferroelectric PMN-PT we show via ferromagnetic resonance (FMR) that this type of linear ME allows for electrical control of simultaneously the magnetization precession and its damping, both of which are key elements for magnetic switching and spintronics. The experiments unravel further an electric-field-induced negative magnetic permeability effect.

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.

Magnetoelectric effect in shear-mode Pb(Zr,Ti)O3/NdFeB composite cantilever

A magnetoelectric (ME) composite cantilever consisting of two shear-mode Pb(Zr,Ti)O3 unimorphs and a tip NdFeB permanent magnet has been demonstrated to exhibit strong ME coupling based on the superior d15 shear response of the piezoelectric phase. The static ME coefficient and the power density under resonance condition of the fabricated samples reach 300 mV/cm·Oe and 2.25 μW/cm3·Oe2, respectively, without demand for DC bias field, which make it outperform previous designs of shear-mode ME composites. These good properties of the ME composite cantilever promise its prospects as a miniature device for sensing, transducing, and energy harvesting applications.

Interface Effects on the Magnetoelectric Properties of Magnetoelectric Multilayer Composites

The magnetoelectric (ME) effect is studied in the terfenol-D/Pb(Zr, Ti)O3 (PZT) multilayer composites prepared by silver epoxy. A theoretical model reveals that the ME voltage coefficient αE,31 is a constant when the total thickness of the multilayer composites is the same. However, the interface defects exist in multilayer composites in experiments and the interface energy loss increases with increasing the stacking periodicity, which leads to the gradual decrease of the ME voltage coefficient αE,31. The resonant frequency of terfenol-D/PZT multilayer composites is independent of the stacking periodicity and agrees well with the predicted one. One can achieve a strong ME coupling by improving the interface conditions to meet the needs for practical applications.

Investigation of optimized end-bonding magnetoelectric heterostructure for sensitive magnetic field sensor

This paper reports an optimized end-bonding magnetoelectric (ME) heterostructure FeCuNbSiB-PZT-FeCuNbSiB (FPF) for sensitive magnetic field sensor. The heterostructure is made by attaching magnetostrictive Fe73.5Cu1Nb3Si13.5B9 (FeCuNbSiB) foils at the free ends of piezoelectric Pb(Zr1-x,Tix)O3 (PZT) plates. Due to the structural advantages, the FPF has ∼3.12 times larger resonance voltage coefficient (αME,r) than traditional FeCuNbSiB/PZT laminate. And compared with the Metglas-PZT-Metglas heterostructure, the FPF heterostructure has stronger ME responses for the excellent magnetic characteristics of FeCuNbSiB. In experiments, the FPF heterostructure is optimal designed through adjusting the thickness of PZT plate (tp) and the length of FeCuNbSiB foil (L). The results demonstrate that the maximum αME,r of 662.1 (V/cm Oe) is observed at 13 Oe DC bias magnetic field when L = 15 mm and tp = 0.6 mm. Based on the giant ME coupling, the DC magnetic field sensitivity for the optimized FPF heterostructure is 3.89 nT at resonant frequency. These results are very promising for the cheap room-temperature magnetic field sensing technology.

Novel laminated multiferroic heterostructures for reconfigurable microwave devices

Voltage tuning of magnetism is fundamentally and technically important for fast, compact and ultra-low power electronic devices. Multiferroic heterostructures, simultaneously exhibiting distinct ferroelectric and ferromagnetic properties, have caught a lot of attentions because of the capability of controlling magnetism by a voltage via a strain-mediated magnetoelectric (ME) coupling. In these materials, a voltage-induced strain is involved to create an effective magnetic field and change ferromagnetic resonance frequency in the coupled ferromagnetic phases through magnetoelastic interactions. Therefore, the devices made of such materials are compact, ultra-fast and energy efficient, providing new functionalities for microwave components. This paper will review the recent progress of multiferroics and their applications in microwave devices from different aspects, including the creation of the novel laminated multiferroic heterostructures with a strong ME coupling, the realization of the multiferroics based on tunable microwave signal processors and the investigation of nonvolatile tuning of microwave properties using ferroelastic domain switching in multiferroic heterostructures. These tunable multiferroic heterostructures and devices offer great opportunities for realizing the next generation of tunable magnetic microwave components, ultra-low power electronics and spintronics.

Enhanced electric field tunable magnetic properties of lead-free Na0.5Bi0.5TiO3–MnFe2O4 multiferroic composites

Strong magnetoelectric (ME) interaction was exhibited at both dc and microwave frequencies in a lead-free multiferroic particulate composites of Na0.5Bi0.5TiO3 (NBT) and MnFe2O4 (MFO) multiferroic, which were prepared by sol–gel route. The room temperature permeability measurements were carried out in the frequency range of 1 MHz–1 GHz. A systematic study of structural, magnetic and ME properties were undertaken. The room temperature ferromagnetic resonance (FMR) was studied. Strong ME coupling is demonstrated in 70NBT–30MFO composite by an electrostatically tunable FMR field shift up to 428 Oe (at E = 4 kV/cm), which increases to a large value of 640 Oe at E = 8 kV/cm. Furthermore, these lead-free multiferroic composites exhibiting electrostatically induced magnetic resonance field at microwave frequencies provide great opportunities for electric field tunable microwave devices.

A theoretical study of the nonlinear thermo-magneto-electric coupling effect in magnetoelectric laminates

For the tri-layer symmetric magnetoelectric (ME) laminates made of giant magnetostrictive materials and piezoelectric materials, we established a theoretical model for the nonlinear thermo-magneto-electric coupling effect in laminates. This model was nonlinear and calculated in an iterative approach. It adopted the nonlinear magneto-thermo-mechanical magnetostrictive constitutive and the linear mechanical-thermo-electric piezoelectric constitutive and introduced the interface coupling factor to describe the strain transfer efficiency between layers. The predictions of ME coefficient versus temperature curves coincide well with experiments qualitatively and quantitatively. This model then was adopted to predict the influences of the temperature, interface coupling factor and thermal expansion coefficient of the giant magnetostrictive materials on ME coupling. It showed that: the laminates had the strongest ME effect at 0 °C; increasing the coupling factor would contribute to obtaining a larger ME coupling in a smaller bias magnetic field and lowering the ME effect attenuation caused by temperature variations; a smaller thermal expansion coefficient was also conducive to obtaining a larger ME coupling in a smaller bias magnetic field and decreasing the ME effect attenuation caused by temperature variations. This model can provide a theoretical basis for the preparation and application of ME devices under different temperature conditions.

High frequency magneto-dielectric effects in self-assembled ferrite-ferroelectric core-shell nanoparticles

Magneto-dielectric effects in self-assembled core-shell nanoparticles of nickel ferrite (NFO) and barium titanate (BTO) have been investigated in the millimeter wave frequencies. The core-shell nano-composites were synthesized by coating 100 nm nickel ferrite and 50 nm barium titanate nanoparticles with complementary coupling groups and allowing them to self-assemble in the presence of a catalyst forming heterogeneous nanocomposites. Magneto-electric (ME) characterization of as-assembled particles has been carried out by measurements of the relative permittivity ɛr as a function of frequency f under an applied static magnetic field H over 16–24 GHz. Measurements show an H-induced decrease in ɛr of 1 to 1.5%. But a giant magneto-dielectric effect with an H-induced change in permittivity as high as 28% is measured under dielectric resonance in the samples. A strong ME coupling was also evident from H-tuning of dielectric resonance in the composites. A theory for the high frequency magneto-dielectric effect has been developed and consists of the following steps. First the Bruggeman model is used to estimate the effective dielectric constant for the shell consisting of the BTO particles and voids considered as spherical air-pores. Then the permittivity for the core and shell is estimated taking into consideration the sample porosity. Finally the H-dependence of the permittivity due to ME interactions is calculated from the free energy considerations. Estimated ɛr vs. H and dielectric resonance frequency vs. H characteristics are in general agreement with the data.

Magnetoelectric effect in magnetostrictive/piezoelectric laminated composite operating in shear-shear mode

This paper investigates the magnetoelectric (ME) effect of magnetostrictive/piezoelectric laminated composite operating in a shear-shear (S-S) mode, i.e., the magnetostrictive and piezoelectric phases of the laminated composite both operate in thickness shear modes. Theoretical analysis shows that the S-S mode laminated ME composite exhibits stronger ME coupling coefficients, i.e., the ME electric field, voltage, and charge coefficients, than those of a typical L-T mode laminated ME composite (longitudinally magnetized and transversely polarized) because of the higher piezomagnetic and piezoelectric coefficients in thickness shear modes of the magnetostrictive and piezoelectric phases, respectively. Our theoretical analysis provides the optimum design method for practical applications of the S-S mode laminated ME composite.

Shear-mode self-biased magnetostrictive/piezoelectric laminate multiferroic heterostructures for magnetic field detecting and energy harvesting

We report on a shear-mode off-antiresonance and antiresonance magnetoelectric (ME) responses in Tb0.3Dy0.7Fe1.92/Pb(Zr, Ti)O3/SmFe2 laminate multiferroic heterostructures for magnetic detecting and energy scavenging without bias field. A negative shear force as well as large internal anisotropic field is provided by SmFe2 plate due to its ferromagnetic and magnetostrictive properties, while the Terfenol-D plate provides a positive shear force to provoke a higher shear–stress transfer. Consequently, stronger ME coupling with a value of 2.24V/Oe is obtained to be generated from the proposed architecture in the absence of the applied dc magnetic field. Experimental results exhibit an approximately linear sensitivity curve under off-antiresonance and antiresonance conditions, and the minimum stepped variations of input ac magnetic field as low as 2.43×10−8T can be clearly distinguished under 111.5kHz. In addition, a maximum power of 0.323μW with a 2.6MΩ load resistance in series connected to the ME laminate under the conditions of no bias can be achieved. These properties demonstrate that such a miniature multimode ME device is capable of weak magnetic field detecting and spatial magnetic energy scavenging by removing the requirement of dc bias field.

Origin of multiferroicity in the chain cuprate LiCu2O2

Abstract In order to study the multiferroic properties of LiCu 2 O 2 we propose a microscopic model taking into account intra- and inter-chain magnetic interactions, frustration and a linear magnetoelectric (ME) coupling. The real part of the dielectric constant in c direction, ϵ c has two kinks near the magnetic phase transition temperatures T N2 = 22 K and T N1 = 25 K which disappear with increasing of an external magnetic field H c . This behavior is an evidence for a strong ME coupling in agreement with the experimental data. The polarization P c ( T , H ) is also calculated. It is shown that the ferroelectric properties do not uniquely originate from spiral spin order, so the linear ME coupling plays an important role.

In Situ Domain Structure Observation and Giant Magnetoelectric Coupling for PMN‐PT/Terfenol‐D Multiferroic Composites

In situ observations of ferroelectric domain structure evolution, and magnetoelectric (ME) coupling are investigated for PMN‐28PT/Terfenol‐D (abbreviation of Pb(Mg1/3Nb2/3)O3‐28PbTiO3/Tb0.3Dy0.7Fe2) and PMN‐33PT/Terfenol‐D composites under the magnetic loadings. The composite of PMN‐33PT/Terfenol‐D shows stronger ME coupling than that in PMN‐28PT/Terfenol‐D. At a thickness of 0.10–0.12 mm for the single crystal plate, a giant magnetoelectric coefficient (αME) up to 2 V/cm·Oe is obtained for PMN‐33PT/Terfenol‐D at a static magnetic field of 200 Oe and 1 kHz of the alternating magnetic field. In situ domain structure observations reveal the domain morphology change during the applied magnetic loadings. In PMN‐28PT, the domains are of predominantly rhombohedral (R) phase and they change into monoclinic MA phase upon the magnetic loading via the strain transferred between Terfenol‐D plate and PMN‐PT single crystal. In PMN‐33PT, domains of orthorhombic (O), R, and monoclinic MC coexist and phase transitions from O to MC and further to R phase occur upon the magnetic loading. The undulation and diversity of the domain structure makes the domains more susceptible to the magnetic loading via strain transferred between Terfenol‐D plate and PMN‐PT single crystal, and consequently, a strong ME coupling in the composites.

Dielectric and phonon properties of the multiferroic ferrimagnet Cu2OSeO3

We propose a microscopic model in order to study the multiferroic properties of Cu2OSeO3 taking into account the ferrimagnetic interaction, frustration, linear magnetoelectric (ME) coupling, and anharmonic spin-phonon interaction. We have shown that the dielectric constant and the phonon energy and damping have a kink near the magnetic phase transition TC = 58 K which disappears with increasing of an external magnetic field. This behavior is an evidence for a strong ME coupling and in qualitative agreement with the experimental data.

Dynamical magnetic charges and linear magnetoelectricity

Magnetoelectric (ME) materials are of fundamental interest and have been investigated for their broad potential for technological applications. The search for, and eventually the theoretical design of, materials with large ME couplings present challenging issues. First-principles methods have only recently been developed to calculate the full ME response tensor $\alpha$ including both electronic and ionic (i.e., lattice-mediated) contributions. The latter is proportional to both the Born dynamical electric charge $Z^{\rm e}$ and its analogue, the dynamical magnetic charge $Z^{\rm m}$. Here we present a theoretical study of the magnetic charge $Z^{\rm m}$ and the mechanisms that could enhance it. Using first-principles density-functional methods, we calculate the atomic $Z^{\rm m}$ tensors in $\rm{Cr_2O_3}$, a prototypical magnetoelectric, and in KITPite, a fictitious material that has previously been reported to show a strong ME response arising from exchange striction effects. Our results confirm that in $\rm{Cr_2O_3}$, the $Z^{\rm m}$ values and resulting ME responses arise only from spin-orbit coupling (SOC) and are therefore rather weak. In KITPite, by contrast, the exchange striction acting on the non-collinear spin structure induces much $Z^{\rm m}$ values that persist even when SOC is completely absent.

Thickness and frequency dependence of magnetoelectric effect for epitaxial La0.7Sr0.3MnO3/BaTiO3 bilayer

The epitaxial La0.7Sr0.3MnO3/BaTiO3 (LSMO/BTO) bilayer films were grown on (001) oriented (LaAlO3)0.3(SrAl0.5Ta0.5O3)0.7 (LSAT) substrate by pulsed laser deposition technique. The effect of film thickness on its ferromagnetic properties, ferroelectric properties and magnetoelectric (ME) effect was investigated. Measurements of thickness and frequency dependence (0.1—100KHz) of the ME voltage coefficient (αE) and phase angle (Δθ) demonstrated a strong ME coupling at room temperature for all bilayer films. The value of αE approached the maximum (140mV/cm Oe) when the thickness of LSMO and BTO films was all equal to 100nm, which was at least one order of magnitude higher than previous reported similar structure due to a rather low dielectric constant of BTO film. The value of αE decreased with the increasing bilayer film thickness when both the LSMO and BTO film thickness were higher than 100nm. It was a combined effect of the thickness dependence for the magnetic and electric properties.

Theory of frequency response of magnetoelectric effects in radially polarized thin cylindrical composites

A theoretical model for the frequency response of magnetoelectric (ME) effect in thin cylindrical piezoelectric-magnetostrictive composites is presented by using constitutive and elastodynamic equations. The calculated results show that there is a resonant enhancement peak of ME voltage coefficient in the electromechanical resonance region and the ME voltage coefficient at resonance frequency exceeds that at low frequency by one or two orders of magnitude. The resonance frequency is predicted to increase with decreasing average diameter D$ \bar{D}$ and increasing thickness of magnetostrictive layer t M of the cylindrical composite, which is in good agreement with the experimental results reported in literatures. The corresponding resonance ME voltage coefficient increases with increasing t M , but reaches to a peak value and then decreases with increasing D$ \bar{D}$. It is indicated that the ME effect of trilayered cylindrical composite is less than that of bilayered one, possibly due to its symmetric structure. Under clamped condition, the resonance frequency will shift to a very high value for both trilayered and bilayered cylindrical composites, while the ME effect has different performance, enhanced in bilayered but suppressed in trilayered cylindrical composite. Our model shows that one can obtain strong ME effect and proper resonance frequency by selecting suitable materials, optimizing its geometry structure and varying mechanical boundary conditions for the cylindrical composite structure