Multiferroic Composites Research Articles

Polarization-induced selective growth of single-crystal heterostructured multiferroic nanoplates with giant magnetoelectric coupling

Single-crystal heterostructured multiferroic (PbTiO3) PTO-(CoFe2O4) CFO nanoplate composites were prepared by a simple two-step hydrothermal process. The CFO nanoparticles with the size of 20–80 nm selectively grow on the positively polarized surface of the single-crystal and single-domain PTO nanoplate. The TEM results demonstrate an epitaxial growth relation between the PTO nanoplates and CFO nanoparticles. The results of the temperature-dependence magnetization of the composites under zero field cooled (ZFC) condition show a novel broad diffuse region around the PTO ferroelectric phase transition (Tc) for the first time. The total change of magnetization (Δ M) near Tc is determined to be (2.71 ± 0.5) × 10−3 emu, a change of 46.2%, implying a giant magnetoelectric coupling in these single-crystal heterostructured multiferroic PTO-CFO nanoplate composites. Such effect has been attributed to the absence of the substrate clamping and single domain in ferroelectric PTO nanoplate.

Nanomechanics of multiferroic composite nanofibers via local excitation piezoresponse force microscopy

Mechanical properties of multiferroic nanostructures are of great importance for their applications, yet their characterization is challenging, especially in a quantitative manner and simultaneously with their piezoelectric properties. In this paper, we show that the widely applied piezoresponse force microscopy, when appropriately carried out and analyzed, can be utilized to quantitatively map the Young's modulus of multiferroic nanofibers with high accuracy and spatial resolution, while their piezoelectricity can be simultaneously determined as usual. The analysis is built on three tightly coupled models, one on contact resonance for the dynamic motion of the cantilever, one for quasi-static contact mechanics between the tip and sample, and the third regarding dynamic tip-sample interaction, with which the mechanical properties of the nanofiber can be deduced from the contact resonance spectrum locally excited by the charged probe, taking advantage of the electromechanical coupling of multiferroic composites. Furthermore, two flexural modes of contact resonances are used in combination with reference material for calibration, so that explicit measurement of some critical model parameters can be avoided. We apply the method to Pb(Zr0.52Ti0.48)O3-CoFe2O4 composite nanofibers with different compositions, and demonstrate its excellent agreement with destructive nanoindentation method, globally excited contact resonance approach, as well as micromechanics rule of mixture. The method can be easily applied to a wide variety of multiferroic nanostructures as well.

Enhanced multiferroic and magnetoelectric properties of Ni0.92(Cu0.05Co0.03)Fe2O4/Ba1-xCaxZr0.10Ti0.90O3 lead-free composite films

The search for lead-free high performance magnetoelectric multiferroic materials at room temperature continues to be stimulated from the perspective of designing environmentally friendly multifunctional devices. In this context, lead-free composite thin films consisting of Ba1-xCaxZr0.10Ti0.90O3 (BCZT, x = 0, 0.10 and 0.15) as the ferroelectric/piezoelectric phase and Ni0.92(Cu0.05Co0.03)Fe2O4 (NCCFO) as the ferromagnetic/magnetostrictive component have been grown on Pt/TiO2/SiO2/Si substrates via chemical solution spin-coating method. The phase and structural evolutions of two distinct pure phases of as grown NCCFO/BCZT composite films were confirmed using X-ray diffractrometry (XRD) and field emission scanning electron microscopy (FE-SEM). The multiferroic, magneto-dielectric and magnetoelectric properties of the NCCFO/BCZT composite films have been investigated. Moreover, significant enhancement of multiferroic properties and magnetoelectric effect was observed in these composite films when compared to those reported recently for other lead-free BCZT based multiferroic composites. The magnetic studies demonstrate that the NCCFO/Ba0.90Ca0.10Zr0.10Ti0.90O3 (NCCFO/BCZT10) composite film exhibits a large saturation and remnant magnetization of Ms ∼ 346.2 emu/cm3 and Mr ∼ 73.5 emu/cm3 respectively having a coercive field of Hc ∼ 73.5 Oe. The NCCFO/BCZT10 composite film also exhibits good ferroelectric properties with saturation polarization Ps ∼26.7 μC/cm2, remnant polarization Pr ∼8.9 μC/cm2 and coercive field Ec ∼82.7 kV/cm. The observed magneto-dielectric effect is of two orders higher than those reported for other lead-free multiferroic composites. A maximum magnetoelectric voltage co-efficient of αME ∼22.4 mVcm−1Oe−1 is obtained for the NCCFO/BCZT10 composite film. The observed results suggest that the NCCFO/BCZT composite films are potential lead-free multiferroic systems at room temperature.

Orientation dependence of magnetoelectric coefficient in rhombohedral Pb(Zr0.6Ti0.4)O3-cubic CoFe2O4 composite

In this study, orientation dependences of magnetoelectric coefficient αE33 along arbitrary directions were investigated in 3 m Pb(Zr0.6Ti0.4)O3 (PZT60/40) - m3m CoFe2O4 (CFO) composites with 2–2, 1–3 pm, and 1–3 m/p connectivities using coordinate transformation method. Orientation dependences of parameters of elastic, dielectric, piezoelectric, permeability, and piezomagnetic properties for PZT60/40 and CFO were investigated independently to finally obtain anisotropy characteristics of the magnetoelectric coefficient of composites. Orientation dependence of αE33 in composites is found mainly determined by that of d31 and e31 of PZT60/40 and q31 of CFO for all three investigated connectivities. The greatly enhanced αE33’ of composites along specific orientations of piezoelectric/magnetostrictive phases were presented, which lies in: PZT60/40 ∣∣ [100] - CFO ∣∣ [001] combination for 2–2 laminate (f = 0.43, αE33 = 81 mV cm−1 Oe), PZT60/40 ∣∣ [001] - CFO ∣∣ [001] combination for both 1–3 p/m (f = 0.6, αE33 = 125 mV cm−1 Oe) and 1–3 m/p fiber composites (f = 0.6, αE33 = 121 mV cm−1 Oe). Volume fraction fmax is found unchanged when various orientations of piezoelectric or magnetic phases were applied. The results suggest that the magnetoelectric coefficient of multiferroic composites with various connectivities could be significantly enhanced by adopting specific orientations.

Size-Dependent and Multi-Field Coupling Behavior of Layered Multiferroic Nanocomposites.

The prediction of magnetoelectric (ME) coupling in nano-scaled multiferroic composites is significant for nano-devices. In this paper, we propose a nonlinear multi-field coupling model for ME effect in layered multiferroic nanocomposites based on the surface stress model, strain gradient theory and nonlinear magneto-elastic-thermal coupling constitutive relation. With this novel model, the influence of external fields on strain gradient and flexoelectricity is discussed for the first time. Meanwhile, a comprehensive investigation on the influence of size-dependent parameters and multi-field conditions on ME performance is made. The numerical results show that ME coupling is remarkably size-dependent as the thickness of the composites reduces to nanoscale. Especially, the ME coefficient is enhanced by either surface effect or flexoelectricity. The strain gradient in composites at the nano-scale is significant and influenced by the external stimuli at different levels via the change in materials’ properties. More importantly, due to the nonlinear multi-field coupling behavior of ferromagnetic materials, appropriate compressive stress and temperature may improve the value of ME coefficient and reduce the required magnetic field. This paper provides a theoretical basis to analyze and evaluate multi-field coupling characteristics of nanostructure-based ME devices.

Sm-mediated dielectric characteristics and tunable magneto-electric coefficient of 0.5Bi1-xSmxFe0.95Mn0.05O3-0.5PbTiO3 composites

Magneto-electric multiferroic composites have gained a lot of interest these days mainly due to extensive potential of coupling between ferroelectric and magnetic orders. In this work, we present a series of 0.5Bi1-xSmxFe0.95Mn0.05O3 − 0.5PbTiO3 (x = 0.00, 0.03, 0.06, 0.09, 0.12 and 0.15) composites, prepared by sol-gel auto-combustion and solid state reaction method to explore the tunability of magneto-electric coefficient. X-ray diffraction confirmed the rhombohedraly distorted cubic perovskite and tetragonal structures of BiFeO3 and PbTiO3, respectively. Ferroelectric loops showed that leakage current can be tuned and reduced by Sm-doping. Magnetic analysis showed switching of antiferromagnetic behaviour into weak ferromagnetic behaviour. Saturation and remanent magnetization were also calculated exhibiting an increasing trend with increasing Sm contents. Synthesized composites showed the non-linear frequency dependent dielectric response which was explained on the basis of Maxwell Wagner theory. Time varying conductivity was probed on the basis of polaron mechanism. The optimized composite reveal an enhanced magneto-electric coupling as compared to that of pure BiFeO3 which makes them feasible for the fabrication of multifunctional devices.

Disclosing odd symmetry, strain driven magnetic response of Co on Pt/PMN-PT (0 1 1)

An odd-symmetry magnetic response of multiferroic composites comprising ultrathin Co layers on Pt electrodes on [Pb(Mg0.33Nb0.67)O3](1−x)[PbTiO3]x (PMN-PT) (0 1 1) piezoelectric substrates is observed upon electrical poling of the PMN-PT substrates: the magnetic easy axis of the Co rotates by 90° in-plane between oppositely poled ferroelectric states, mimicking the signature of a surface polarization charge driven effect, which however can be excluded from the presence of the thick Pt interlayer. The origin for this unexpected behavior is as an odd symmetry piezoelectric response of the PMN-PT substrate, as indicated by x-ray diffraction with applied poling, in combination with conventional magnetoelastic coupling. Ferroelectric characterization reveals corresponding features, possibly related to an unswitchable polarization component.

Effects of piezoelectric-phase orientations on magnetoelectric coefficient in AlN–FeCoSiB multiferroic composites

In this study, orientation dependences of ps11′, ps12′, pe33′ and d31′ for piezoelectric phase were investigated along arbitrary directions using relative experimental data and original matrices for AlN with point group of 6mm. Then, effects of various orientations of piezoelectric phase on magnetoelectric coefficient of AlN–FeCoSiB laminated multiferroic composites were studied. It was found that ps11′ is a constant while ps12′, pe33′ and d31′ exhibit high dependence on crystal orientations with their MAX values existing along [001]-axis. The magnetoelectric coefficient αE33′ increases with decreased angle θ apart from c-axis of AlN in range of 90°–0°; the MAX αE33′ = 5405 mV/cm Oe exists in AlN ∥ [001]—FeCoSiB. Along specific preferred orientations of piezoelectric phase, twofold–fivefold of enhancement of αE33 can be obtained compared to randomly arranged composites. Volume fraction is found to be independent of orientations of component phases, and the volume fraction for magnetic phase f around 0.75 obtains the largest αE33. The results suggest an approach of enhancing magnetoelectric coefficient of composite multiferroic materials through crystal-orientation controls of single crystals or textured ceramics.

Magnetoelectric coupling tailored by the orientation of the nanocrystals in only one component in percolative multiferroic composites.

Novel 1–3 type multiferroic composite thin films were prepared via a simple 0–3 composite fabrication process. The orientation of the Ni0.5Zn0.5Fe2O4 (NZFO) nanocrystals in the BaTiO3–Ni0.5Zn0.5Fe2O4 (BTO–NZFO) composite thin films was controlled by magnetron sputtering, and the controlling effect of such orientation on magnetoelectric coupling was investigated in detail. The NZFO lattice in the BTO–NZFO composite thin films grew with (100) orientation under the induction of the (111) plane of Si. The transfer of substrate stress between the closely contacted grains also contributes to the orientation of the NZFO nanocrystals. The 0.6BTO–0.4(100)NZFO multiferroic composite thin film exhibited a magnetization strength of 9.2% at the Curie point of the BTO phase, showing extremely strong magnetoelectric coupling characteristics. This work provides an effective strategy for the development of high-performance multiferroic composites, and brings about new conception of realizing strong magnetoelectric coupling effect from the perspective of physical chemistry.

Magnetoelectric bistability of molecular ferroic solids

Here we report a new magnetoelectric coupling approach through organic multiferroic composites, composed of ferroelectric molecular radical solids.

Ferroelectromagnetic Properties of PbFe1/2Nb1/2O₃ (PFN) Material Synthesized by Chemical-Wet Technology.

In this work, PbFe1/2Nb1/2O3 (PFN) ceramic samples synthesized by chemically wet method (precipitation from the solution) were obtained. Due to the tendency to form powder agglomerates, the synthesized powder was subjected to ultrasound. The sintering was carried out under various technological conditions, mainly through controlling the sintering temperature. -X-ray powder-diffraction (XRD), scanning electron microscope (SEM) microstructure analysis, as well as the examinations of dielectric, ferroelectric, and magnetic properties of the PFN ceramics were carried out. Studies have shown that hard ceramic agglomerates can be partially minimized by ultrasound. Due to this treatment, closed porosity decreases, and the ceramic samples have a higher density. Optimization and improvement of the technological process of the PFN material extends the possibility of its use for the preparation of multiferroic composites or multicomponent solid solutions based on PFN. Such materials with functional properties find applications in microelectronic applications, e.g., in systems integrating ferroelectric and magnetic properties in one device. The optimal synthesis conditions of PFN ceramics were determined to be 1050 °C/2 h.

Tuning magnetism in 0.25BaTiO3-0.75CoFe2O4 hetero-nanostructure to control ferroelectric polarization

In multiferroic composites, the strain-mediated magnetoelectric coupling is strongly dependent on the characteristics of interface between two (ferroelectric/ferromagnetic) mechanically coupled phases. In this paper, we have studied the magnetic ordering in 0.25BaTiO3-0.75CoFe2O4 (BTO-CFO) nanoparticles and the results are compared with pure CoFe2O4 (CFO) nanoparticles. The cubic spinel structure of CFO and tetragonal BTO is analyzed with X-ray diffraction pattern. The magnetic hysteresis measured at room temperature for both multiferroic BTO-CFO and pure CFO are quite different, that indicate magnetic ordering, which in BTO-CFO composite is changeable. Comparatively higher coercivity in pure CFO than BTO-CFO nanoparticles is observed at room temperature which suggested freezing out of thermal excitations and the onset of stable ferromagnetic ordering. The value of blocking temperature (corresponding to superparamagnetic state), TB is 385 K is observed in pure CFO and 355 K of BTO-CFO. However, the magnetic curve of zero field cooling magnetization is reasonably different than that observed in pure CFO, which is further studied with frequency dependent ac magnetic susceptibility measurement. It results into spin-canting and spin-glass states formation. The spin-glass transition temperature is calculated with both dynamical scaling and Vogel-Fulcher methods. The ferroelectric hysteresis is observed at room temperature is reasonably varied with applied magnetic field of 2, 4, 5, 6 kOe and the variation in the values of polarization and coercive field might be consistent with the observed magnetic hysteresis.

A comparative study on the structural, dielectric and multiferroic properties of Co0.6Cu0.3Zn0.1Fe2O4/Ba0.9Sr0.1Zr0.1Ti0.9O3 composite ceramics

High performance multiferroic composites have attracted great attentions because they are more beneficial to increasing magnetoelectric coupling effect. We report the effects of molar ratio (4:1, 2:1, 1:1, 1:2 and 1:4) on the structural, dielectric and multiferroic properties of Co0.6Cu0.3Zn0.1Fe2O4/Ba0.9Sr0.1Zr0.1Ti0.9O3 (CCZFO/BSZTO) composite ceramics prepared by sol-gel method. The XRD results confirm successful formation of the CCZFO/BSZTO composites without presence of any impurity phase. The mean grain size is about 1.5 mm and it shows double dispersing behavior, the larger grains belong to CCZFO while the smaller ones are ascribed to BSZTO. The maximum dielectric constant and loss appear with the molar ratio is 1:1 due to its more grain boundaries. Two peaks appear in the ε∼T curves, the peak corresponding to the lower temperature corresponds to the Curie temperature of BSZTO, while the other one is resulted by the relaxation polarization. The height of the relaxation peak decreases and the position shifts to higher temperature range with the increase of molar ratio. The maximal remanent polarization is 3.76 μC/cm2, obtained at 1 kHz when the molar ratio is 1:1. An enhanced magnetic properties are observed when the molar ratio is 1:1 due to the stronger interface interaction effect between the two phases. Strong direct magnetoelectric coupling coefficient of 1.53 V/(cm.Oe) is obtained at the field of 8000 Oe for the sample 1:4. These results may provide valuable information for improving the multiferroic properties of composite multiferroic materials.

Complex Dielectric and Impedance Spectroscopic Studies in a Multiferroic Composite of Bi2Fe4O9-BiFeO3

Complex dielectric and impedance spectroscopic studies have been carried out in a detailed manner on the system comprising of Bi2Fe4O9-BiFeO3 composite particles dispersed in a α-Fe2O3 matrix as prepared using ball milling and controlled annealing treatments. This multiferroic composite is observed to exhibit a giant dielectric constant associated with a low tangent loss. A non-Debye type of relaxation has been deduced based on complex modulus analysis. Based on these studies, the important role played by bismuth ferrite nanoshell in the core-shell composite of Bi2Fe4O9-BiFeO3 is elucidated for the observed complex impedance spectroscopic properties of the system. Electron hopping across Fe2+/Fe3+ and oxygen vacancies are deduced to be playing an important role in conduction mechanisms based on activation energy analysis of the complex impedance spectroscopy results.

Comparison of experimental data and FEM simulation for a multiferroic nanocomposite

AbstractThe combination of ferromagnetic and ferroelectric materials, so‐called multiferroic composites, increases the opportunities for technical sensors and data storage devices, see [1]. The magnetic and electric constituents have the property to affect each other e.g. an applied electric field modifies the magnetization of the magnetic phase. In nature also single‐phase materials exist with magneto‐electric properties. Though, the interoperation of the magnetization and the polarization is exclusively activated at very low temperature. Therefore, they are not favorable for most of the known technical applications. Considering this, the magneto‐electric (ME) composites can be seen as a good option since their synergy of the magneto‐electric properties is active at room temperature [2] and can be differentiated in two different effects, the direct and the converse ME effect. We will focus on (1‐3) nanocomposite grounded on the experiments made in [3] and [4]. In the experiments, cobalt ferrite nanopillars, embedded in a barium titanate matrix, are characterized. Then, for the numerical FEM‐simulations the material coefficients from [5] and [6] are taken. The change of the strain‐induced in‐plane polarizations of the ferroelectric matrix around one cobalt ferrite nanopillar is calculated. These computed results are compared to the ones of the experimental measurement outcomes.

Effect of Sequential Heat Impacts on the Formation of a Stable State of the xLPM–(1 – x)PT Multiferroic Composites

The effect of thermal cycling and sintering temperature on the chemical and thermodynamic stability of the bulk multiferroic xLa0.7Pb0.3MnO3–(1 – x)PbTiO3 quasi-ceramic and ceramic composites has been experimentally investigated. It is shown that the limiting temperature of the long-term sample firing should not exceed 1070 K. It has been found that sintering at this temperature and/or short-term exposure of the samples at higher temperatures (up to 1220 K) significantly increase the sample compactness, stabilize the thermal expansion, and enhance the quality of the composites. It has been established that the component grain integrity is violated by shrinkage of the samples and a sharp change in their volume during the phase transition of a ferroelectric component.

Synthesis of type-II based (1-x)Ba0.6(Ca1/2Sr1/2)0.4Ti0.5Fe0.5O3+(x)Ni0.40 Zn0.45Cu0.15Fe1.9Eu0.1O4 composites via standard solid state reaction method and investigation of multiferroic properties

A series of multiferroic composites, (1-x)Ba0.6(Ca1/2Sr1/2)0.4Ti0.5Fe0.5O3+(x)Ni0.4Zn0.45 Cu0.15Fe1.9Eu0.1O4 ((1-x)BCSTFO+(x)NZCFEO) where x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 1.0 have been synthesized by standard double sintering ceramic method sintered for 3 hours at 1200°C in air. The X-ray diffraction patterns reveal that the multiferroics and the parent ceramic samples crystallize in simple cubic structure with a slightly distored lattice parameter. The X-ray and bulk density increase with the increasing ferrite content. Consequently, the porosity decreases indicating better crystallization. A decreasing trend in dielectric constant is observed while the relative quality factor (RQF) increases significantly with the increasing ferromagnetic NZCFEO. At the same time, M–H hysteresis loops reveal that ferromagnetic property enhances with the addition of Ni0.40Zn0.45Cu0.15Fe1.9Eu0.1O4 (NZCFEO). The highest values of coercive field ∼ 92 O and saturation magnetization ∼1.37 emu/g are observed for x = 10% and x = 50% compositions respectively. Additionally, the permeability enhances up-to x = 30% but decreases with further doping. The room temperature resistivity rises due to the decrease in hopping mechanism. The samples exhibit a decreasing trend for resistivity with the increase of temperature. The dopant concentration has also shown an impressive impact on the activation energy. As a result, the multiferroic properties of (1-x)BCSTFO+(x)NZCFEO have been significantly improved considering the measured magnetic and ferroelectric properties.

PbTiO3–Ni0.5Co0.5Fe2O4 multiferroic nanocomposites: Impact of ball-milling on dielectric, magnetic and ferroelectric properties

The structural, dielectric, ferroelectric and magnetoelectric (ME) properties of multiferroic [PbTiO3-Ni0.5Co0.5Fe2O4] (PT-NCF) composites have been discussed at room temperature. The uniformly distributed two-phase composites of PbTiO3 (ferroelectric) dispersed into nano-sized Ni0.5Co0.5Fe2O4 (ferromagnetic) of different particle size were synthesized by employing high energy ball milling for 12, 24 and 48 h respectively. The phase and morphology of composites were confirmed by XRD and SEM analysis respectively. The dielectric properties were determined at different frequencies (i.e. from 1 kHz to 1 MHz) and it is observed that the dielectric constant and ferroelectric transition temperature (TC) decreases with particle size. Further, the ferroelectric behavior of the composites was discussed at room temperature by examining the P-E loops. The magnetic and magnetoelectric measurements were performed to analyze the effect of particle size on ferromagnetic and magnetoelectric properties of PT-NCF composites. The coexistence of ferroelectric and ferromagnetic properties in composites with strong ME coupling is essential for a good multiferroic composites material and its applications.

Temperature Dependent Electric Properties and Magnetoelectric Effects in Ferroelectric rich Ni0.8Mg0.2Fe2O4 + BaZr0.2Ti0.8O3 Magnetoelectric Composites

The magnetoelectric composites with the compositions of ferrites & ferroelectrics having the general chemical formula (x) Ni0.8Mg0.2Fe2O4 + (1-x) BaZr0.2Ti0.8O3 (in which x = 0.1, 0.2, 0.3) were synthesized by using double sintering ceramic technique. From XRD, the phase formation of ferrites with cubic structure and ferroelectrics with tetragonal perovskite structure was confirmed through the measurement of XRD. The two phase ME composites have larger saturation magnetization and dielectric constant; it is because of the effect of interfacial strain on BaZr0.2Ti0.8O3 ferroelectric phase. Furthermore, the ME response 4.262 mVcm−1Oe−1 was observed for (30%) Ni0.8Mg0.2Fe2O4 + (70%) BaZr0.2Ti0.8O3 composites at 5.0 kOe applied DC magnetic field; it shows the success of magnetic control of the dielectric response via the mechanical coupling which can be exploited in the future applications of multiferroic composites.

Enhanced multiferroic properties of lead-free (1-x)GaFeO3-(x)Co0.5Zn0.5Fe2O4 composites

Multiferroic composites of (1-x)GaFeO3-(x)Co0.5Zn0.5Fe2O4 with x = 0.0, 0.1, 0.2, and 1 were prepared using a conventional solid state reaction method. The X-ray diffraction patterns confirmed that the composites consisted of cubic spinel Co0.5Zn0.5Fe2O4 and orthorhombic GaFeO3 phases. The coexistence of both magnetic and ferroelectric orderings at ambient temperature was confirmed by measuring M-H and P-E loops. The inclusion of Co0.5Zn0.5Fe2O4 enhanced magnetization and dielectric constant, as well as improved the ferroelectric properties of GaFeO3. The leakage current (9.33 × 10−8 A/cm2) of composite (x = 0.20) is found to be much lower as compared to pure GaFeO3. The value of saturation magnetization increased to 30.6 emu/g at 300 K. This large enhancement of magnetization, as well as the presence of ferroelectricity, is promising for enabling future magnetoelectric applications.