Multiferroic Composites Research Articles

Anisotropic magnetoelectric characteristics in five-layer magnetization-graded multiferroic composites

We investigate the anisotropic magnetoelectric(ME) characteristics for the five-layer magnetization-graded multiferroic composites(MGMC). The magnetic anisotropy and corresponding anisotropic magnetomechanical effect, demagnetization effect and magneto-mechanical damping’s dependence on magnetic field direction result in an obvious anisotropic ME coupling effect. The experimental results show that ME voltage coefficient in H33 mode is remarkably larger than the other ones (H11, H31 and H13) over the whole Hdc range. Correspondingly, ∂VME/∂Hdc arrives about 420mV/Oe at an optimum bias magnetic field of 46Oe, which is approximately 40 times larger than that of the previous reported composite. Furthermore, it also demonstrates an obvious angular dependence on dc magnetic field. Taking advantage of these specifications, the MGMC can be used to detect weak dc magnetic field and its spatial orientation.

An extended constitutive model for nonlinear reversible ferromagnetic behaviour under magnetomechanical multiaxial loading conditions

A constitutive modelling of ferromagnetic materials under combined magnetomechanical multiaxial loading with different boundary conditions and a finite element implementation are presented. The phenomenologically motivated model is capable of predicting magnetisation, strain, and stress and is thus suitable, e.g., for applications in multiferroic composites. The approach covers a reversible nonlinear behaviour as it is observed, e.g., in cobalt ferrite and other soft magnetic alloys. Various examples demonstrate the suitability of the model and its numerical implementation and give an insight into the behaviour of soft magnets, exposed to different boundary conditions or being embedded into other compliant materials.

Electrically driven magnetic antenna based on multiferroic composites

We suggest and demonstrate via large scale numerical simulations an electrically operated spin-wave inducer based on composite multiferroic junctions. Specifically, we consider an interfacially coupled ferromagnetic/ferroelectric structure that emits controllably spin waves in the ferromagnets if the ferroelectric polarization is poled by an external electric field. The roles of geometry and material properties are discussed.

In-plane fracture analysis on the magneto-electro-elastic interfacial region in a multiferroic composite: Effects of volume fraction

Abstract The high temperature and pressure of the hot-pressing process of layered ferromagnetic/ferroelectric (FM/FE) composites inevitably give rise to magneto-electro-elastic (MEE) interfacial regions, where defects such as cracks often aggregate and definitely affect the performance of the composite. Fracture analysis is performed on an MEE interfacial region between an FM layer and an FE layer by the methods of Fourier integral transform and Cauchy singular integral equations. After the numerical computation is verified by the exact solution in a special case and the numerical solutions in existing literature, numerical results of MSERR (mechanical strain energy release rate) and COD (crack opening displacement) are provided to discuss the fracture behavior. The effect of FE volume fraction of the interfacial region on the fracture behavior is demonstrated from three different perspectives. Both material stiffness and constraint effect are used to explain the physical mechanisms. The obtained results may serve as guidelines for the anti-fracture design of FM/FE multiferroic composites. Because the existence of such MEE interfacial regions has been scarcely considered by existing papers, the main novelty of the present work is the incorporation of the MEE interfacial region into the mechanical model of the FM/FE composite.

Magnetoelectric effects in bilayer multiferroic core-shell composites

Abstract We investigate magnetoelectric (ME) effects in bilayer multiferroic core-shell composites in this paper. The composites are driven by the radial magnetic field and the induced radial deformation/vibration is studied. Two configurations are considered in a concise and uniform manner mathematically. One is spherical and the other is cylindrical. For bilayer core-shell composites, we show that the geometric configuration has a significant effect on the ME effect in multiferroic core-shell composites for both low-frequency and electromechanical resonance ranges. At the low-frequency range, except for the mechanically clamped case, the ME effects in spherical multiferroic composites are always stronger than that in cylindrical ones. At the electromechanical resonance range, for traction-free case, the fundamental resonance frequency of the spherical multiferroic composite is higher than that of the cylindrical one and thus the corresponding ME effect in spherical composite is stronger than that in cylindrical one.

Size-dependent effective behaviors of multiferroic fibrous composites with interface stress

The objective of this work is to study the size-dependent effective behaviors of multiferroic fibrous composites with interface stress subjected to generalized in-plane deformation and out-of-plane electromagnetic fields. Using the complex variable approach together with several micromechanical models, closed-form expressions of the effective moduli are obtained. In contrast to the composite with perfect bonding, the effective property formulations show the dependence on the size of the fibers. The derived solutions are applied to several examples to demonstrate the effect of interface stress, and to examine the results among different micromechanical models. Numerical results show that while most of the effective moduli increase as the radius of the fiber decreases, the magnetoelectric voltage coefficient, the figure of merit of the multiferroic material, decreases. Further, when considering the effective transverse shear modulus of composite with interface stress, a higher order approximation is required for the equivalency between an interphase and an imperfect interface if the interphase is not sufficiently thin or is very stiff.

Effects of the volume fraction of piezoelectric particles in the magneto-electro-elastic interfacial region on the fracture behavior of a laminate multiferroic plate

Magneto-electro-elastic (MEE) interfacial regions may be formed in multiferroic composites consisting of alternate piezoelectric (PE) and piezomagnetic layers during the hot-pressing process. The existence of such an MEE region may have effects on the mechanical behavior of the composite, which is an interesting problem deserving studying. The present article proposes an interfacial fracture model for a multiferroic composite that contains an MEE interfacial region. The methods of Fourier integral transform and Green’s functions are employed to convert the crack problem with mixed boundary conditions into Cauchy singular integral equations, which are further numerically solved by the Lobatto–Chebyshev collocation method to determine the stress intensity factors. In the numerical computation, the PE volume fraction is chosen as the only characteristic parameter to calculate the material properties of the MEE interfacial region based on the linear rule of mixture. Finally, parametric studies are conducted to reveal the effects of the volume fraction on the fracture behavior, and two main conclusions are drawn: (a) The effects of the PE volume fraction reflect the effects of the material-property jumps across the interfaces, and (b) the interfacial fracture behavior is mainly dominated by the competition between the property jumps across the interfaces and the thickness of the interfacial region.

Influence of nanoparticulate and fiber reinforcements on the wear response of multiferroic composites processed by powder metallurgy

Nanoparticulates and nanofibres are good candidates to be considered as reinforcements in the design of new multiferroic composites processed by powder metallurgy. As would be expected in any composite material system, the addition of nanoparticles and fibres to the multiferroic composites will influence the wear response of these materials along with other mechanical properties. Also the choice of the processing parameters during the manufacturing of these materials is expected to influence the resulting material properties. The present study reviews the effect of processing parameters such as milling mode, sintering time and temperature on the wear properties of multiferroic composites that can potentially be used in different engineering applications. For this reason, detailed damage analyses due to wear, utilising scratch tests have been carried out on multiferroic composites reinforced with nanoparticles and fibres such as magnetic iron oxide, alumina powder and alumina fibre. Scanning electron microscopy and 3D optical surface scanner were used to assess the damage to the composites.

Effect of Gadolinium doping on structural, ferroic and electrical properties of 0.8BiGdxFe1−xO3-0.2PbTiO3 (x = 0.00, 0.05, 0.10, 0.15 and 0.20) composites

The Gadolinium (Gd) doped multiferroic composites of 0.8BiGdxFe1−xO3-0.2PbTiO3 with x = 0.00, 0.05, 0.10, 0.15 and 0.20 were prepared by the conventional solid state reaction technique. The phase formations of the composites were checked by using X-ray diffraction technique and distorted rhombohedral structure was confirmed for all the composites at room temperature. The ferroelectric and ferromagnetic properties were investigated by means of a computer based PE-Scanner and Vibrating- Sample Magnetometer (VSM) respectively. A significant change in the dielectric and magnetic properties were observed by the doping of rare earth (Gd). The dielectric and electrical properties of these composites were analysed by using an impedance analyser for a wide range of temperatures and frequencies (102–106 Hz). The impedance spectroscopy study confirms the presence of bulk effect only. The impedance plots obey non Debye type of relaxation for all the composites. The frequency dependent ac conductivity obeys Jonscher's universal power law. By applying the Correlated Barrier Hopping (CBH) model to ac conductivity data, the density of state at Fermi level and minimum hopping length has been estimated to understand the conduction mechanism within the composites.

Synthesis and Characterization of CoFe2 O 4/BaTiO3 Multiferroic Composites

Three composite modes of CoFe2 O 4/BaTiO3 (CFO/BTO) were created with appropriate stoichiometric proportion. They are nitrate solution of CFO mixed with BTO (SCB), self-propagating precursor of CFO mixed with BTO (PCB), and the made-up CFO mixed with BTO (MCB) separately. The microstructural, ferroelectric, and ferromagnetic properties of SCB, PCB, and MCB bulk composites were investigated. SCB, PCB, and MCB bulk composites with a molar ratio of 2:8 were calcined at 1020, 1120, and 1160 ∘C, respectively. And X-ray diffraction (XRD) analysis showed that they all correspond to the CFO with cubic spinel structure and the BTO with tetragonal perovskite structure. The formation temperature of BTO with hexagonal structure is related to the distance of inter-diffusion and Co 2+ concentration in the CFO/BTO bulk composite. The wet chemical routing is of benefit to inhibit the agglomeration of the BTO in the CFO/BTO bulk composite. The maximum polarization of 5.24 μC/cm 2 was received in the MCB bulk composite sintered at 1160 ∘C with a molar ratio of 1:9. The maximum saturation magnetization of 31.609 emu/g and the remnant magnetization of 10.336 emu/g were obtained in the MCB bulk composite sintered at 1160 ∘C with a molar ratio of 4:6. The threshold ferromagnetic phase content of percolation which has an effect on the MCB bulk composite is less than 40 mol %.

On Eshelby's S-tensor under various magneto-electro-elastic constitutive settings, and its application to multiferroic composites

The magneto-electro-elastic Eshelby S-tensor is the key to the study of linear effective properties of magneto-electro-elastic composites. There are eight different ways to write the constitutive relations, and each is associated with a specific kind of boundary condition and Eshelby S-tensor. In this work, we provide a general procedure to convert the magneto-electro-elastic Eshelby S-tensor from one system to another. As an application, we use it to calculate the magnetoelectric coupling coefficients of a piezoelectric–piezomagnetic multiferroic composite under stress-and strain-prescribed boundary conditions. We demonstrate that the calculated results are significantly different. In particular, it is shown that, under an applied stress, the magnetoelectric coupling coefficient [Formula: see text], is much stronger than that under an applied strain, while for [Formula: see text], the values are positive under a prescribed stress but negative under a prescribed strain. The effects of inclusion shape, volume concentration and geometrical exchange, are also examined. For ready applications, the explicit forms of S-tensor, [Formula: see text] and [Formula: see text], of 1-3 fibrous and 2-2 multilayer composites are also provided at the end.

Constitutive modeling of ferromagnetic and ferroelectric behaviors and application to multiferroic composites

AbstractIn this paper, the constitutive modeling of nonlinear multifield behavior as well as the finite element implementation are presented. Nonlinear material models describing the magneto‐ferroelectric or electro‐ferromagnetic behaviors are presented. Both physically and phenomenologically motivated constitutive models have been developed for the numerical calculation of principally different nonlinear magnetostrictive behaviors. Further, the nonlinear ferroelectric behavior is based on a physically motivated constitutive model. On this basis, the polarization in the ferroelectric and magnetization in the ferromagnetic and magnetostrictive phases, respectively, are simulated and the resulting effects analyzed. Numerical simulations focus on the calculation of magnetoelectric coupling and on the prediction of local domain orientations going along with the poling process, thus supplying information on favorable electric‐magnetic loading sequences. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Enhanced converse magnetoelectric effect in cylindrical piezoelectric-magnetostrictive composites

Enhanced converse magnetoelectric (ME) effect has been experimentally observed in cylindrical PZT-Terfenol-D piezoelectric-magnetostrictive bilayered composites, where the piezoelectric and magnetostrictive components are coupled through normal stresses instead of shear stresses that act in most of previous multiferroic composites. A theoretical model based on elastodynamics analysis has been proposed to describe the frequency response of converse ME effect for axial and radial modes in the bilayered cylindrical composites. The theory shows good agreement with the experimental results. The different variation tendency of resonant converse ME coefficient, as well as different variation rate of resonance frequency with bias magnetic field for axial and radial modes is interpreted in terms of demagnetizing effect. This work is of theoretical and technological significance for the application of converse ME effect as magnetic sensor, transducers, coil-free flux switch, etc.

Ferroelectric and Magnetic Properties of CoFe 2 O 4/BaTiO 3 Prepared by Microwave-Assisted Sol-Gel Method

The xCoFe 2O4/(1 −x)BaTiO 3 (x= 0.1 ∼ 0.5) multiferroic composites were prepared by microwave-assisted sol-gel method. The theoretical densities and actual densities of CoFe 2O4/BaTiO 3 were compared. The structural, ferroelectric, and magnetic properties were studied. At room temperature, the multiferroic composites exhibited good ferroelectric and magnetic properties. The maximum polarization 2.52 μC/cm 2 was obtained at x= 0.1 and the minimum polarization 1.21 μC/cm 2 was achieved at x= 0.5. The maximum saturation magnetization 35.020 emu/g and remnant magnetization 15.587 emu/g were obtained at x= 0.5.

Electric control of magnetism and magnetocaloric effects in LaFe11.4Si1.6H1.5 using ferroelectric PMN–PT

The alloy with first-order magnetic phase transition has an advantage to exhibit large magnetoelectric effect in strain-mediated multiferroic composites, since the strain can drive its phase transition and consequently lead to a large magnetic change. In the present paper, we investigate the electric field manipulation of magnetic and magnetocaloric properties in LaFe11.4Si1.6H1.5/Pb(Mg1/3Nb2/3)O3–PbTiO3 laminate. By applying an electric field on the ferroelectric substrate, the relative change of magnetization has a peak value of −8% around the Curie temperature, showing a large converse magnetoelectric effect. As for the magnetocaloric performance, the peak temperature of magnetic entropy change (ΔSM) has a shift of 3 K to low temperature and the maximal value of ΔSM keeps almost unchanged under an electric field of 8 kV cm−1. Moreover, the thermal and magnetic hysteresis can be reduced as well with the application of the electric field.

Tuning magnetoelectric coupling using porosity in multiferroic nanocomposites of ALD-grown Pb(Zr,Ti)O3 and templated mesoporous CoFe2O4

In this manuscript, we examine ways to create multiferroic composites with controlled nanoscale architecture. We accomplished this by uniformly depositing piezoelectric lead zirconate titanate (PZT) into templated mesoporous, magnetostrictive cobalt ferrite (CFO) thin films to form nanocomposites in which strain can be transferred at the interface between the two materials. To study the magnetoelectric coupling, the nanostructure was electrically poled ex situ prior to magnetic measurements. No samples showed a change in in-plane magnetization as a function of voltage due to substrate clamping. Out-of-plane changes were observed, but contrary to expectations based on total PZT volume fraction, mesoporous CFO samples partially filled with PZT showed more change in out-of-plane magnetization than the sample with fully filled pores. This result suggests that residual porosity in the composite adds mechanical flexibility and results in greater magnetoelectric coupling.

Strain mediated magnetoelectric coupling in a NiFe2O4–BaTiO3 multiferroic composite

In this paper we demonstrate significant magnetoelectric coupling in ferrimagnetic, NiFe2O4, and ferroelectric, BaTiO3, multiferroic composite bulk materials by measuring temperature dependent magnetization. X-ray diffraction, scanning electron microscopy and high resolution transmission electron microscopy data show that the two phases coexist with a highly crystalline and sharp interface without any detectable impurities, which enables significant magnetoelectric (ME) coupling. The temperature dependent magnetization data of the composite clearly show the jumps in magnetization curves at the structural phase transitions of BaTiO3, thereby indicating their origin in ME coupling. The change in coercivity of composite sample in different ferroelectric phases of BaTiO3 has been observed compared to the NiFe2O4 sample. The different lattice strains corresponding to different ferroelectric phases of BaTiO3 could be the driving force for modulating the magnetization and coercivity of the composite material. This is clear evidence of strain mediated ME coupling in ferrimagnetic and ferroelectric composite materials.

Various properties of the 0.6BaTiO 3 –0.4Ni 0 . 5 Zn 0 . 5 Fe 2 O 4 multiferroic nanocomposite

Structural, magnetic and ferroelectric properties of 0.6BaTiO3–0.4(Ni0.5Zn0.5Fe2O4) multiferroic nanocomposite are presented here. The structural properties of the samples were studied by XRD and Raman spectroscopy which confirm the formation of BaTiO3 (BTO) phase with a tetragonal perovskite structure and a small secondary spinel phase due to the ferrite content. The magnetic and electric orderings were investigated by vibrating sample magnetometer (VSM) and ferroelectric (P–E) loop tracer at room temperature. The inception of ferroelectric properties is due to barium titanate. The remnant polarization increases ∼5 times for the composite with Ni0.5Zn0.5Fe2O4 (NZFO) substitution compared to BTO. The remnant polarization is conducive for switching applications of multiferroic composite.

Ultra-Low-Energy Electric Field-Induced Magnetization Switching in Multiferroic Heterostructures

Electric field-induced magnetization switching in multiferroics is intriguing for both fundamental studies and potential technological applications. Here, we review the recent developments on electric field-induced magnetization switching in multiferroic heterostructures. Particularly, we study the dynamics of magnetization switching between the two stable states in a shape-anisotropic single-domain nanomagnet using stochastic Landau–Lifshitz–Gilbert (LLG) equation in the presence of thermal fluctuations. For magnetostrictive nanomagnets in strain-coupled multiferroic composites, such study of magnetization dynamics, contrary to steady-state scenario, revealed intriguing new phenomena on binary switching mechanism. While the traditional method of binary switching requires to tilt the potential profile to the desired state of switching, we show that no such tilting is necessary to switch successfully since the magnetization’s excursion out of magnet’s plane can generate a built-in asymmetry during switching. We also study the switching dynamics in multiferroic heterostructures having magnetoelectric coupling at the interface and magnetic exchange coupling that can facilitate to maintain the direction of switching with the polarity of the applied electric field. We calculate the performance metrics like switching delay and energy dissipation during switching while simulating LLG dynamics. The performance metrics turn out to be very encouraging for potential technological applications.

Influences of imperfect interfaces on effective properties of multiferroic composites with coated inclusion

In order to predict the effective properties of multiferroic composite materials, the effective material constants of multiferroic composites with the coated inclusion and imperfect interface are investigated. Based on the generalized self-consistent theory, the closed-form solutions of the effective material constants are derived. For the composites with piezomagnetic inclusion, piezoelectric coating and polymer matrix, numerical calculations are performed to present the influences of the imperfect interface cooperating with the coating on the effective material constants. From the results, it can be observed that the effective constants can be enhanced by the coating but reduced by the imperfect interface. Moreover, the coating has the shielding effects on the imperfect interface for the composite structures with its higher filling ratio.