Multiferroic Composites Research Articles

Ternary composites: A suitable platform for simultaneous improvement of multiferroic characteristics

Here, we report a series of multiferroic composites with general formula 0.8[(1–x)BiFeO3 + xCrFe2O4] + 0.2Cr2O3 (x = 0.0, 0.33, 0.66 and 1.0), prepared using sol–gel based auto-combustion method. Structural analysis helped us to verify the three phases in the composites and confirmed the dominance of spinel phase with introducing the CrFe2O4 contents. Field emission scanning electron microscopy confirmed the distinct, sharp, spherical shaped grains, and the reduction in the grain size with the evolution of spinel phase. Energy dispersive X-ray spectroscopy verified the presence of key elements in the required stoichiometric ratios. Increment in the maximum and remanent polarization with the addition of spinel phase contents was revealed by the ferroelectric analysis. Recoverable energy was observed to be decreased at first, with the increase in CrFe2O4 concentration, but it increased abruptly when the rhombohedral phase was completely replaced by the spinel phase. A systematic analysis of percentage efficiency has been presented and correlated with the crystalline structural phase transformation in the composite series. The successful incorporation of third phase (Cr2O3) has helped to improve the composite phase stability and ferroelectric pursuits. Magnetic analysis showed an increase in magnetization with the increasing concentration of spinel phase, confirming its ferrimagnetic nature and establishing the multifunctional utilization of prepared tri-phase composites. The studies of magneto-polarizability unwrapped the aptitude of these composites for their usage in multi-state devices and illustrated the aptitude of synthesized composite for their applications in energy storage devices.

Impedance spectroscopy and conduction mechanism of xNi.50Zn.40Mn.10Fe2O4.(1- x)Bi0.9La0.1Fe0.93Eu0.07O3 composites

Di-phase multiferroic composites of xNi.50Zn.40Mn.10Fe2O4.(1-x)Bi0.9La0.1Fe0.98Eu0.02O3 was synthesized with the combination of perovskite and ferrite materials. The compounds are synthesized using the solid-state reaction technique. A union of perovskite and ferrite phases has recognized through the X-ray diffraction (XRD) patterns constitutes the composition. Intense and sharp peaks that we observe in XRD patterns reveal that the phases are well crystalline. The morphology of the prepared samples was studied through Scanning Electron Microscopy, which ensured that the compounds were well-distributed in the form of dense and inhomogeneous grain size distribution. The ac conductivity of composites increases with an increase in frequency, signifying that the conduction occurs due to slight polaron springing, and the conductivity trails the Jonschers’ power law. The contribution of grain and grain boundary in the conduction mechanism is also observed from impedance spectroscopy analysis. Particular semicircular curves starting from the origin are visible in all compositions.

A Combination of Calcination and the Spark Plasma Sintering Method in Multiferroic Ceramic Composite Technology: Effects of Process Temperature and Dwell Time.

This study reports a combined technological process that includes synthesis by the calcination powder route and sintering by the Spark Plasma Sintering (SPS) method for multiferroic ceramic composites in order to find the optimal sintering conditions. The effects of temperature on the SPS process and dwell time on the microstructure and dielectric properties of the PF composites were discussed. Research has shown that using the SPS method in the technological process of the multiferroic composites favors the correct densification of powders and allows for obtaining a fine-grained microstructure with good properties and electrophysical parameters in the composite material. The optimal set of parameters and properties is demonstrated by the sample obtained at the temperature of 900 °C for 3 min, i.e., resistivity (6.4 × 108 Ωm), values of the dielectric loss factor (0.016), permittivity at room temperature (753) and permittivity at the phase transition temperature (3290). Moreover, due to the high homogeneity of the microstructure, the strength of the material against electric breakdown increases (when examining the ferroelectric hysteresis loop, the application of a high electric field (3—3.5 kV/mm) is also possible at higher temperatures). In the case of the composite material tested, both the lower and higher temperatures as well as the shorter and longer dwell times (compared to the optimal SPS process conditions) did not contribute to the improvement of the microstructure or the set of usable parameters of the composite materials. The strength of the ceramic samples against electric breakdown has also diminished, while the phenomenon of leakage current increased.

Tuning Exchange Coupling in a New Family of Nanocrystal-Based Granular Multiferroics Using an Applied Electric Field.

In this work, we demonstrate an experimental realization of a granular multiferroic composite, where the magnetic state of a nanocrystal array is modified by tuning the interparticle exchange coupling using an applied electric field. Previous theoretical models of a granular multiferroic composite predicted a unique magnetoelectric coupling mechanism, in which the magnetic spins of the ensemble are governed by interparticle exchange. The extent of these exchange interactions can be controlled by varying the local dielectric environment between grains. We specifically utilize the strong dielectric dependence of ferroelectric materials to modify the interparticle coupling of closely spaced magnetic nanoparticles using either a change in temperature or an electric field. This coupling modifies the ensemble magnetic coercivity and thus the superparamagnetic-to-ferromagnetic phase transition temperature. Through the use of two different ferroelectrics, our results suggest that this magnetoelectric coupling mechanism could be generalized as a new class of multiferroic material, applicable to a broad range of ferroelectric/magnetic nanocrystal composites.

External circular crack problem in magneto–electro-elasticity: Shear mode

Crack problems of multiferroic composites are of engineering significance and academic value. External circular crack is one of the basic configurations in the theoretical analyses. This paper examines an external circular crack on the shear mode embedded in an infinite space of multiferroic composite materials. By the potential theory method, the governing equation for arbitrarily shaped planar cracks under arbitrarily distributed shear loads, are established. The fundamental solution expressed by elementary functions is derived, from which the complex stress intensity factor at the crack tip is further deduced. It is interesting that the crack neck has a “shielding effect” on the physical quantities on the crack plane. The fundamental solution obtained in this work can provide foundations for numerical study and theoretical analysis of many complex boundary value problems.

Flexomagnetic effects on inhomogeneously strained multiferroics composites

Herein, the origin of flexomagnetic effect in Pb[(Zr0.52Ti0.48)0.60(Fe0.67W0.33)0.40]O3]0.80-[CoFe2O4]0.20 (PZTFW–CFO) multiferroic composite is demonstrated. An external inhomogeneous strain on thick composite films significantly changes the crystal lattice constants and phonon wave numbers related to single-phase PZTFW and CFO ceramics. Surface morphology indicates that inhomogeneous strain modified the magnetic dipole moments that partly regain their original position after removing external inhomogeneous strain. The magnitude of magnetic susceptibility increased under inhomogeneous strain for a small probe of the magnetic field. The magnetic anisotropic energy (MAE) supports that under-applied inhomogeneous strain reduces surface spin disorders and is responsible for the enhancement of zero field cooled (ZFC) and field cooled (FC) magnetization. Under a high external magnetic field (>100 Oe), it would be hard to detect the weak flexomagnetic effects. This work provides a framework for the effect of macroscopic inhomogeneous strain gradient on magnetic moments in multiferroics composites suggesting its suitability for the sensors and actuators applications.

Magnetoelectric coupling susceptibility in novel lead-free 0–3 type multiferroic particulate composites of (1-x)Na0.5Bi0.5TiO3 -(x)CoCr0.4Fe1.6O4

Lead-free 0–3 particulate composites of chromium substituted cobalt nano-ferrite CoCr0.4Fe1.6O4 (CCFO) and sodium bismuth titanate Na0.5Bi0.5TiO3 (NBT) having molar ratio of (1-x)Na0.5Bi0.5TiO3 -(x)CoCr0.4Fe1.6O4 (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5& 1) have been investigated. XRD patterns reveal that the composites crystallized with binary rhombohedraland cubic phase, equivalent to room temperature crystal symmetry of host ferroelectric NBT and magnetic CCFO materials, respectively. SEM micrographs depict the presence of both parent phases with different micro-structural symmetries. The observed ferroic properties, derived from isothermal magnetization and polarization measurements, emphasize that all the (1-x)NBT - (x)CCFO compositions exhibit significant sensitivity towards the magnetic field as well as the electric field. To evaluate the degree of magnetoelectric coupling in CCFO-NBT composites, we employed the magneto-dielectric characterization technique as a sensitive probing tool. We note that magneto-dielectric property initially increases with x and is found to be maximum ∼ −0.78% (x = 0.4) and further decreases with x. This unconventional product behaviour of particulate composite system is availed through magnetostrictive nature of magnetic subsystem - CFO and piezoelectric characteristics of ferroelectric- NBT. These lead-free multiferroic composites may provide an opportunity for the miniaturization of environmental-friendly magnetoelectric (ME) devices.

Structural, Magnetic, and Dielectric Spectroscopy Investigations of Multiferroic Composite Based on Perovskite–Spinel Approach

Multiferroic composite materials with the nominal composition (La0.8Gd0.2FeO3)1−x(Mn0.5Cu0.5Fe2O4)x, x = 0.0≤x≤1 were prepared using the co-precipition method. XRD, FTIR and Raman were utilized to investigate the structure phase, microstructural characteristics, vibrational bands. The optical properties were analyzed; the VSM was used to investigate the magnetic properties of the composites. Broadband dielectric spectroscopy is employed to investigate the dielectric and electrical performance of the prepared multiferroic composites. Rietveld refinement of the XRD patterns confirmed the orthorhombic phase for lanthanum gadolinium iron oxide (La0.8Gd0.2FeO3) and cubic phase for manganese copper ferrite (Mn0.5Cu0.5Fe2O4). The crystallite size of LGFO phase pointed out that it increases with increasing the MCFO phase, while the microstrain found to decline. The FTIR results elucidated the tetrahedral and octahedral bands. The deduced optical properties revealed that the samples have optical energy gap in the range 4.18 −4.5 eV. The magnetic properties revealed that the composites exhibit typical ferromagnetic hysteresis loops, indicating the presence of ordered magnetic structure. The frequency dependence of permittivity ε′(f) and real part of complex conductivity, σ′(f) exhibits a development of a net of micro-capacitors like behavior that stores charge carriers.

Structural, dielectric, magnetic and magnetoelectric properties of the PFN-PT/Co[formula omitted]Ni[formula omitted]Fe2O[formula omitted] multiferroic composites

Structural, magnetic, magnetoelectric (ME), dielectric and ferroelectric properties of multiferroic composites based on ferroelectric PFN-PT and ferrimagnetic Co1−xNixFe2O4 have been studied. By changing the Ni content, we tuned the magnetic anisotropy of the magnetic part and studied its role on the magnetoelectric response of the composite. Our results showed that the ME voltage coefficient in the composites of 0.7(PFN-PT)/0.3(NixCo1−xFe2O4) is highly influenced by the content of Ni. The maximum value of ME voltage coefficient, 11.32 mV/(cm.Oe), was obtained for the composite with x=1 and the minimum value, 5.32 mV/(cm.Oe), was found for the composite with x=0.75. In addition, by changing the Ni content, we observed that the behavior of Hmax, the field in which maximum ME voltage was observed, follows the trend of coercivity Hc. We interpreted the results in the framework of dynamic piezomagnetic coefficient and also cation distribution in the spinel structure of the magnetic phase.

Hot-pressed (1-x)[0.9(0.3CoFe2O4-0.7BiFeO3)-0.1Pb(Zr0.52,Ti0.48)O3]-x poly(vinylidene difluoride) multiferroic composites with magnetically driven polarization

Hot-pressed (1-x)[0.9(0.3CoFe2O4-0.7BiFeO3)-0.1Pb(Zr0.52,Ti0.48)O3]-x poly(vinylidene difluoride) multiferroic composites with magnetically driven polarization

Multiferroic BiFeO3-based hydrophobic polymer composites for polarization rationalization-induced piezo-tribo hybrid energy harvesting and versatile self-powered mechanosensing

Multiferroic BiFeO3-based polymer composites and their suitable combinations by rationalization of polarization have been utilized to design an efficient piezo-tribo hybrid nanogenerator for real life energy harvesting and sensing applications.

Magnetoelectric interaction in molecular multiferroic nanocomposites.

Incorporation of magnetic and electric orders in a form of multiferroics is an interesting topic in materials science. Making a molecular heterogeneous composite by incorporating the molecular magnet vanadium–chromium Prussian blue analogue (V–Cr PBA) and a molecular ferroelectric imidazolium chloride C3N2H5-ClO4 (ImClO4) provides a pathway towards achieving the room temperature magnetoelectric effect. The change of magnetization of about 6% is shown as a result of applying an electric field (21 kV cm−1) to the composite made of the aforementioned molecular crystals at room temperature. In the ferromagnetic resonance measurement (FMR) under the effect of an applied electric field, a shift of the resonance magnetic field is also observed in the nanocomposites. This work provides a pathway towards molecular multiferroic nanocomposites with magnetoelectric coupling interactions at room temperature.

Magnetodielectric coupling in barium titanate–cobalt ferrite composites obtained via thermally-assisted high-energy ball milling

In this work, a magnetodielectric coupling observed in barium titanate–cobalt ferrite composites synthesized using high-energy ball milling assisted via a thermal treatment is discussed. Vibrating sample magnetometry and dielectric spectroscopy showed that multiferroic composites possess both ferromagnetic and dielectric behaviors inherited from the parent ferromagnetic cobalt ferrite and ferroelectric barium titanate phases. The magnetocapacitance (up to 35%) recorded for x = 0.3, (1-x)BaTiO3–xCoFe2O4, can be attributed to the spin-dependent filtering mechanism. The composite with the aforementioned composition exhibited a homogeneous matrix–particle composite microstructure, which was achieved via high-energy ball milling during the mixing stage.

Voltage Control of Perpendicular Magnetic Anisotropy in Multiferroic Composite Thin Films under Strong Electric Fields.

"Ferroelectric/ferromagnetic" multiferroic composites with perpendicular magnetic anisotropy (PMA) are useful for developing power-efficient magnetic memories. Voltage control of PMA has been demonstrated in bulk multiferroic composites based on ferroelectric single crystals, but they are not compatible for integration. Multiferroic composite thin films are useful for developing integrated devices; however, voltage control of PMA in them has not been achieved yet at room temperature due to their low magnetoelectric (ME) coupling coefficient. Here, we demonstrate such functionality and propose to enhance their ME coupling effect under a strong electric field by taking full advantage of the large dielectric strength of ferroelectric thin films. First, the thickness-dependent breakdown of Pb(Zr0.384Ti0.576Nb0.04)O3 (PNZT) thin films was studied, and the two-layer (∼200 nm) samples exhibited the highest breakdown strength (3.68 MV/cm) and small surface roughness (<1 nm). Second, we fabricated "PNZT/(Co/Pt)5" thin films with strong PMA whose breakdown strength is nearly independent of the top electrode materials. Finally, voltage-induced effective magnetic field (Heff) in "PNZT/(Co/Pt)5" was studied. It is comparable to that achieved in bulk composites and will induce magnetization switching under strong electric fields. Multiferroic composite thin films with large breakdown strength will provide a useful platform for enabling integrated multiferroic devices.

Dielectric and magneto-dielectric properties of x [Co0.9Ni0.1Fe2O4] - (1-x) [Ba(Zr0.2Ti0.8)O3] particulate multiferroic composites

Present paper reports on synthesis and characterization of x(Co0.9Ni0.1Fe2O4)-(1-x)(Ba(Zr0.2Ti0.8)O3) multiferroic magneto-dielectric composite of ferrite and ferroelectric phase for x=0.1, 0.2 and 0.3 via hydroxide co-precipitation method. The well compacted disc shape samples of the MD composites are sintered with microwave sintering technique at 1100°C. These composites are investigated for their structural, micro-structural, dielectric, ferroelectric and magneto-dielectric properties. X-ray diffraction shows the presence of the peaks corresponding to both ferroelectric and ferrite phases in the composites. Temperature dependent dielectric spectra gives the two anomalies one at lower temperature (below 50°C) corresponds to the ferroelectric transition temperature and other at the higher temperature (above 350°C) corresponding to magnetic transition. The variation of dielectric constant and loss tangent with applied magnetic field between 0-1 tesla in the frequency range of 500 Hz to 1 MHz are investigated. Dielectric constant possesses contribution due to magnetic field dependent interfacial polarization and variations due to the induced stress which can be explained on the observed MD effect. Copyright © 2016 VBRI Press

On the magnetoelectric performance of multiferroic particulate composite materials

In the current work, quantitative analysis of magnetoelectric particulate composite material system explicated the main mechanisms responsible for the below-optimal performance of this class of materials. We considered compliant particulate composite materials, with constituents relevant to technological and scientific interest, leading to 0–3 Terfenol-D/PVDF–TrFE composite samples. To this objective, thick Terfenol-D/PVDF–TrFE films (10–15 µm) were fabricated and analyzed for chemical, mechanical, and magnetic properties to demonstrate their suitability for energy applications in harsh environmental conditions. The vigorous experimental characterization of the composite exemplified the multifunctional properties, quantifying the interrelationship between the composition and performance. We observed that the addition of magnetic particles to the electroactive copolymer matrix resulted in improvement in the mechanical and electrical properties since the particles acted as pinning sites, hindering the deformation of the chains and enhancing polarization. The effective modulus model was amended to account for the crystallization-induced change in material stiffness. We also measured and computed the magnetic particles motion to explicate the detrimental effect of mobility and migration on the overall magnetoelectric coupling performance of the composite. Thereby, we derived an analytical model based on the magnetic force due to the co-presence of alternating and constant magnetic fields, and the viscous drag force due to the viscoelastic properties of the electroactive copolymer matrix. We demonstrated that the mobility of the particles plays a crucial role in the short and long term performance of magnetoelectric coupling in multiferroic particulate composites, uncovering the underpinnings of the dichotomy in performance between experimentally measured and analytically predicted coupling coefficients, thus allowing for the proposal of new approaches to realize the scientific potential of magnetoelectric particulate composites in energy applications.

Microscale magnetoelectricity: Effect of particles geometry, distribution, and volume fraction

Achieving efficient magnetoelectric coupling of core-shell and particulate multiferroic composites has been a challenging hurdle; however, research has shown unwavering interest to overcome this barrier in pursuit of their implementation into promising potential applications. Herein, a fully coupled computational model of core-shell and particulate composites is developed and verified to investigate the magnetoelectric interactions of the particle and matrix on the microscale. The effects of particle geometry, settling, and agglomeration were exhaustively studied by investigating seven different shapes and a wide range of vertical and lateral particle spacing. Overall, it was found that utilizing particle geometries and positioning that closely resemble a laminate configuration, such as a prolate ellipsoid and horizontal particle alignment, enhances the magnetoelectric coupling of the composite structure. The results coincided with the experimental results concerning settling and agglomeration.

Crystal structure, dielectric and magnetic properties of xBaFe12O19-(1 − x)Na0.5Bi0.5TiO3 composites

Multiferroic composites xBaFe12O19-(1 − x)Na0.5Bi0.5TiO3 were synthesized. Rietveld analysis of XRD patterns of confirms the coexistence of hexagonal (P63/mmc) and rhombohedral (R3c) symmetry. SEM micrographs depict that the average grain size of composites decreases with increase in ferrite phase. The variations of dielectric constant (ε′) and dielectric loss (tanδ) were examined as a function of frequency and at different temperatures. ε′ and tanδ show the dispersion behavior at lower frequencies and become independent at higher frequencies. The magnetic assessment of these composites carried by analyzing M-H hysteresis loop reveals their hard magnetic behavior.

Study of dielectric properties of lead-free multiferroic KNN/22.5 BaFe12 O19 composites

A multiferroic (K_0.5 Na_0.5 NbO_3) -22.5% vol.(〖BaFe〗_12 O_19) composite obtained successfully by conventional sintering (abbreviated as CS) method at 1080 ℃. To compare the dielectric properties of the samples, lead-free K_0.5 Na_0.5 NbO_3 (abbreviated as KNN) piezoceramics were prepared by CS method at 1125℃. The structure and morphology have been determined by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and also the dielectric properties of samples were carried out. In the X-ray spectra of composite samples, all peaks related to the KNN and BFO phases, were observed without any trace of the second phase. In the SEM images of the composite, the distinct cubic morphology of the KNN phase indicating the formation of the perovskite structure of the compound, and the polygonal grains of the BFO phase were observed. The values of relative density, dielectric coefficient, and loss factor of the lead-free KNN ceramic at a sintering temperature of 1125℃ was measured to be 91%, 390, and 0.02, respectively. These values at a sintering temperature of 1080℃ were about 92%, 200 and 0.18 respectively. Although the dielectric properties of KNN-BFO composite are lower than those of pure KNN, the presence of magnetic phase can create the magnetic properties and consequently multiferroicity in the KNN-BFO composite The dielectric properties also confirm that this composite can be considered as a new multiferroic composite.

STRUCTURAL, VIBRATIONAL, OPTICAL, AND MAGNETIC PROPERTIES OF 0-3 TYPE PARTICULATE PbTiO3-NiFe2O4 COMPOSITES

We synthesized 0-3 type (1-x)PbTiO3-xNiFe2O4 (x = 0.0-0.5) multiferroic composites with two independently crystallized parent phases by the sol-gel method. Structural, surface morphology, vibrational, optical, and magnetic characteristics were investigated by X-ray diffraction (XRD), SEM, Raman scattering, UV-vis absorption, and magnetization (M-H) measurements, respectively. The XRD result showed that the lattice parameter a of the PbTiO3 (PTO) phase decreased while lattice parameter c increased after compositing, leading to a decrease in the tetragonal ratio c/a. SEM images indicated that the NiFe2O4 (NFO) crystals that crystallized later are small and adhere to the surface of the large PTO particles. The strong cohesion between the two components was also revealed by the gradual shift of the Raman peaks to the lower wavelength and the reduction of the Raman intensity as the NFO content increased. The UV-vis absorption result showed the co-absorption spectra of the parent phases in the composites. Magnetization curves presented a sharp increase in saturation magnetization MS with NFO content from 0.014 emu/g for the PTO sample to 14.360 emu/g for the composite containing 50 mol% NFO. This study indicates an effective method in the search for multilayer composites.