Coefficient αME Research Articles

Synthesis and study of structural, dielectric, magnetic and magnetoelectric properties of K0.5Na0.5NbO3–CoMn0.2Fe1.8O4 composites

Magnetoelectric (ME) composites consisting of K0.5Na0.5NbO3 (KNN) as ferroelectric phase and CoMn0.2Fe1.8O4 (CMFO) as ferrite phase with general formula (x) CoMn0.2Fe1.8O4–(1 − x) K0.5Na0.5NbO3 (x = 10, 20, 30, 40 and 50 wt%) were synthesized using solid state reaction method. X-ray diffraction analysis asserts the existence of component phases including spinel phase of CMFO and orthorhombic phase of KNN. Field emission scanning electron microscopy has been used for studying the morphology and calculation of average grain size. The temperature dependent dielectric properties including dielectric constant ( $$\varepsilon ^{\prime}$$ ) and dielectric loss (tan δ) at different frequencies has been studied and both are found to increase with incorporation of CMFO. Magnetic hysteresis loops have been measured at temperatures of 300 and 5 K. Variation of magnetization versus temperature has been studied in field cooled and zero field cooled modes. Polarization versus electric field (P–E) hysteresis loops are obtained at room temperature indicating presence of ferroelectric ordering in the composites at room temperature. The remnant polarization (2Pr) and coercive field (2Ec) are found to decrease linearly with incorporation of CMFO. ME voltage coefficient (αME) has been measured. The maximum value of αME is found to be 5.941 mV/cm-Oe for 10% CMFO–90% KNN bulk composite.

Magnetoelectric coupling in nanoscale 0-1 connectivity.

The strain-mediated magnetoelectric (ME) coupling between piezoelectric (PE) and magnetostrictive (MS) components are established in various connectivities. Discovering new ME connectivity and elucidating the key factors governing the performance of ME composite are of critical importance to find advanced materials for modern electronics. Reported here is a novel ME coupling in 0-1 connectivity. The unique self-assembling ability of 1-dimension crystalline nanocellulose (CNC) nanowhiskers enables the establishment of ME coupling with 0-dimension cobalt ferrite (CFO) nanoparticles without the use of binder. The developed CFO/CNC 0-1 ME composites display a significant ME voltage coefficient (αME) as high as 0.135 mV cm-1 Oe-1. The CFO nanoparticles are also modified with a cationic surfactant, cetyltrimethylammonium bromide (CTAB), to reduce their dispersion ability. A ME response related to the rearrangement of aggregated MS nanoparticles is observed in the CTAB-CFO/CNC composites, which differs from the typical magnetostriction induced ME effect in nanoparticulate ME composites.

Magnetoelectric effect analysis of magnetostrictive/piezoelectric laminated composites

Based on the finite element analysis software COMSOL5.0,a three-dimensional (3D) model of cantilever beam composed of magnetostrictive/piezoelectric/magnetostrictive laminated composites is established using the piezoelectric module and magnetic field module.The magneto electro coupling coefficient αME of the composite is analyzed.The effect of geometrical parameter on magnetoelectric coefficient is studied,and the geometrical parameters are optimized. Firstly,the stress,strain,displacement and potential distributions of the magnetoelectric layered structure are analyzed by the steady-state solver.The stress and strain concentrate on the fixed terminal while the maximum displacement exists in the free end of the structure.As a result,the potential appears between the upper and lower surface of the piezoelectric layer and the voltage distribution is not uniform.The output voltage in the fixed terminal is larger than that in the free end,which is about 49 V compared with 42 V in the free end.And the dynamic distributions of various variables in magnetoelectric composite structure are analyzed by transient solution.Secondly,the resonance frequency of the structure and the influence of the bias magnetic field on the output voltage are studied by small signal analysis in frequency domain.The results show that the output voltage decreases with the increase of Hdc.Also,the maximum output voltage is about 3.36 V at the second-order resonance frequency,which is far higher than the voltage at the first-order resonant frequency in the condition of bias magnetic fields Hdc=200 Oe and alternating magnetic fields Hac=1 Oe.The reason is that the composite structure has a larger deformation at the second-order resonance frequency.Furthermore,the effect of thickness ratio between magnetostrictive and piezoelectric layers tm/tp on coupling coefficient is analyzed by changing the thickness of magnetostrictive layer and piezoelectric layer,respectively.The results show that the magnetoelectric coefficient increases with the augment of the thickness ratio,but the increasing rate decreases gradually.The research also shows that it has a greater influence on magnetoelectric coefficient to change tp rather than tm.Finally,the variations of magnetoelectric coefficient with the area of composite structure and the aspect ratio are analyzed.The results show that the magnetoelectric coefficient increases gradually with the augment of magnetoelectric composite area,but the increasing rate declines gradually.With the constant composite area,the magnetoelectric coefficient first increases and then drops with the increase of aspect ratio L/W,demonstrating the existence of an optimized value.Besides,the width W acts more importantly than length L because strain concentrates on the fixed terminal along

Ferro- and magneto-electric characteristics in YFeO3−Y3Fe5O12 nanocomposites

The magnetoelectric (ME) nanocomposite material contain ferromagnetic phase of yttrium iron garnet (Y3Fe5O12) and ferroelectric phase of yttrium perovskite ferrite (YFeO3) with an equation (x)YFeO3 + (1 − x)Y3Fe5O12 (x = 0.0, 0.25, 0.50, 0.75, 1.0) is synthesized by sol–gel auto combustion method. The composite powder obtained by two phases of composite material sintered at 1100 °C for 6 h. The prepared samples were investigated by using powder X-ray diffraction (XRD) to study the structural properties, that confirm the existence of two phases of Y3Fe5O12 and YFeO3. The crystallite size of material decreased from 23 to 13 nm with increasing the concentration of YFeO3 in composite. The morphological investigation of samples was studied by field emission scanning electron microscopy that gives size, shape and distribution of grains in material and confirmed that material has nano-crystalline in nature. Saturation magnetization (Ms) studied by using vibrating sample magnetometer shows the decrement in its value from 23.9 to 0.48 emu/g with the increase in YFeO3 content. Maximum magnetoelectric coefficient (αME) of 10.711 mv/cm-Oe is observed for composition x = 0.50. Similarly, ferroelectric characteristics of sample such as dielectric constant and dielectric loss were measured in the frequency range 20 Hz to 10 MHz at room temperature. The value of dielectric constant is decreases with increasing frequency and ferroelectric hysteresis loop at room temperature is study by using P-E loop tracer it’s nature is unsaturated due to presence of Y3Fe5O12 phase.

Enhanced magnetoelectric response from lead-free (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 – CoFe2O4 laminate and particulate composites

Lead free multiferroic composite (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 - CoFe2O4 was prepared in two different connectivity schemes, particulate and laminates and their magnetoelectric properties have been investigated in this study. Lead free piezoelectric (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 (BCZT) and ferrimagnetic CoFe2O4 (CFO) phases were synthesized by sol-gel and combustion techniques respectively. Particulate composite was prepared by mechanical mixing of BCZT and CFO phases in equal weight fraction. The laminate structures (bilayer and trilayer) was developed by bonding BCZT with CFO layers by epoxy bonding. High piezoelectric coefficients, d33 ~ 630 pC/N, g33 ~11mVm/N, and magnetostricition ~183ppm were obtained for the laminate composite. Magnetoelectric measurements revealed a large ME response for the trilayer laminate composite especially at high frequency, where the electro-mechanical resonance appears for the composite. A high magnetoelectric coefficient (αME) ~803mVcm−1Oe−1 was obtained for the trilayer laminate composite which was 8 times higher than that of the particulate composite, αME ~ 104mVcm−1Oe−1. Bilayer laminate showed a maximum (αME) coefficient of ~ 615mVcm−1Oe−1. The magnetoelectric behavior of all the three composites is discussed and compared in this study.

Structural phase transition and multiferroic properties of Bi0.8A0.2Fe0.8Mn0.2O3 (A = Ca, Sr)

The multiferroic BiFeO3 and Bi0.8A0.2Fe0.8Mn0.2O3 (A = Ca, Sr) have been synthesized using direct mechanosynthesis. Detailed investigations were made on the influence of Ca–Mn and Sr–Mn co-substitutions on the structure change, electric and magnetic properties of the BFO. Rietveld refinement on the XRD pattern of the modified samples clarifies the structural transition from R3c:H (parent BiFeO3) to the biphasic structure (R3c: H + Pnma). Scanning electron micrographs confirmed the polycrystalline nature of the materials and each of the microstructure comprised of uniformly distributed grains with less porosity. The dielectric measurements reveal that enhancement in dielectric properties due to the reduction of oxygen vacancies by substitutional ions. Studies of frequency-dependence of impedance and related parameters exhibit that the electrical properties of the materials are strongly dependent on temperature, and bear a good correlation with its microstructure. The bulk resistance (evaluated from impedance studies) is found to decrease with increasing temperature for all the samples. The alternating current (ac) conductivity spectra show a typical signature of an ionic conducting system, and are found to obey Jonscher’s universal power law. Preliminary studies of magnetic characteristics of the samples reveal enhanced magnetization for Ca–Mn co-substituted sample. The magnetoelectric coefficient as the function of applied dc magnetizing field under fixed ac magnetic field 15.368 Oe is measured and this ME coefficient αME corresponds to induction of polarization by a magnetic field.

Tuning a sign of magnetoelectric coupling in paramagnetic NH2(CH3)2Al1\u2212xCrx(SO4)2\u2009\xd7\u20096H2O crystals by metal ion substitution

Hybrid organometallic systems offer a wide range of functionalities, including magnetoelectric (ME) interactions. However, the ability to design on-demand ME coupling remains challenging despite a variety of host-guest configurations and ME phases coexistence possibilities. Here, we report the effect of metal-ion substitution on the magnetic and electric properties in the paramagnetic ferroelectric NH2(CH3)2Al1−xCrx(SO4)2 × 6H2O. Doing so we are able to induce and even tune a sign of the ME interactions, in the paramagnetic ferroelectric (FE) state. Both studied samples with x = 0.065 and x = 0.2 become paramagnetic, contrary to the initial diamagnetic compound. Due to the isomorphous substitution with Cr the ferroelectric phase transition temperature (Tc) increases nonlinearly, with the shift being larger for the 6.5% of Cr. A magnetic field applied along the polar c axis increases ferroelectricity for the x = 0.065 sample and shifts Tc to higher values, while inverse effects are observed for x = 0.2. The ME coupling coefficient αME = 1.7 ns/m found for a crystal with Cr content of x = 0.2 is among the highest reported up to now. The observed sign change of αME with a small change in Cr content paves the way for ME coupling engineering.

A flexible multiferroic composite with high self-biased magnetoelectric coupling

Polymer-matrix multiferroic composites with self-biased magnetoelectric (ME) coupling hold promises in flexible energy harvester, magnetic field sensors and actuators, etc. Using CoFe2O4 (CFO) nanoparticles and multi-walled carbon nanotubes (CNTs) as fillers to the polyvinylidene fluoride (PVDF) matrix, piezomagnetic films (CFO-CNT-PVDF, also named as M layers) with different volume fractions of CFO and a fixed percentage of CNTs are obtained, which also serve as the electrode. By employing the layer of poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE), named as P layer) sandwiched between the two conductive layers of CFO-CNT-PVDF, and followed by hot-pressing, three-layered multiferroic composite CFO-CNT-PVDF/P(VDF-TrFE)/CFO-CNT-PVDF (named as M/P/M) are prepared. The ME coupling increases with the volume fraction of CFO nanoparticles. The maximum self-biased and peak values of ME coefficient (αME) reach 16.7 mV cm−1 Oe−1 and 25.8 mV cm−1 Oe−1, respectively. Measurements on the relationship between the magnetostriction and static magnetic field (Hs) are performed for the CFO-CNT-PVDF films with different volume fraction of CFO. Based on the equivalent circuit model, the self-biased and peak values of αME are calculated for the ME composites, which fit well with the experimental data. The results imply that it is the high piezomagnetic coefficient, as well as the remnant magnetization of the M layer, contributes to the observed strong self-biased ME coupling for the CFO-CNT-PVDF/P(VDF-TrFE)/CFO-CNT-PVDF composite. Since the mechanical flexibility is also of great importance regarding the practical device applications, the stress-strain behavior for the CFO-CNT-PVDF layers is studied. With the volume fraction of CFO increases, both fracture strength (σf) and fracture strain (εf) decrease. The results offer a guideline for selecting proper ME composites on specified device applications.

A screen printed and flexible piezoelectric-based AC magnetic field sensor

A piezoelectric-based flexible magneto-electric (ME) thin film sensor has been developed for the detection of AC magnetic fields (Hac), at room temperature. The sensor was fabricated by screen printing piezoelectric-based polyvinylidene fluoride (PVDF) ink on flexible and magnetic Metglas® substrate. 3D interferometry and X-ray diffraction (XRD) was used to characterize the profile and crystalline contents, respectively of the printed PVDF film. The top electrode was fabricated by depositing silver (Ag) ink on the printed PVDF layer using bar coating technique. The theoretical results demonstrated ME voltage coefficients (αME) of 84.5mV/cmOe and 56.5mV/cmOe for Metglas®/PVDF composite at cross-sectional area (n) of 0.12 (longitudinal direction) and 0.15 (transverse direction), respectively. The performance of the fabricated ME printed sensor was investigated by measuring the induced voltage response towards varying Hac and frequencies. Experimental results demonstrated maximum αME of 685.99V/cmOe, at electromechanical resonance of 50kHz. The result also demonstrated a linear relationship with a sensitivity of 503.3 V/T and correlation coefficient of 0.9994 towards varying Hac.

Induced magnetoelectric coupling and photoluminescence response in solution-processed CoFe2O4/Pb0.6Sr0.4TiO3 multiferroic composite film

ABSTRACTCoFe2O4/(Pb0.6Sr0.4)TiO3 bi-layered composite film exhibits ferromagnetic and ferroelectric responses (Ms ∼ 162 emu/cm3, Hc ∼ 1.8 kOe, 2Pr ∼ 8.6 µC/cm2 and 2Ec ∼ 634 kV/cm) at room temperature. The temperature dependent dielectric anomaly near magnetic phase transition temperature suggests magnetoelectric coupling effect in the composite film. The maximum MD effect can reach as high as ∼49% at 3 kOe applied DC magnetic field. The composite film exhibits magnetoelectric voltage co-efficient αME ∼ 67 mVcm−1Oe−1. The photoluminescence emission bands of the composite film have a significant blue shift as compared to those reported for CFO and PST nanostructures.

Observation of grain size effect on multiferroism and magnetoelectric coupling of Na0.5Bi0.5TiO3 – BaFe12O19 novel composite system

Four novel polycrystalline magnetoelectric composite systems: S1, S2, S3 and S4 having composition [90wt% Na0.5Bi0.5TiO3 (NBT) – 10wt% BaFe12O19 (BaM)] considering the variation of grain size of both the phases [NBT(Lg)-BaM(Lg)-[S1], NBT(Lg)-BaM(Sg)-[S2], NBT(Sg)-BaM(Lg)-[S3] and NBT(Sg)-BaM(Sg)-[S4]] are successfully synthesized by using solid state reaction method. Here, Lg is larger and Sg is smaller grain size respectively. The pure phase formation of desired composite systems is verified by Rietveld refinement of X-ray diffraction pattern. The Field Emission Scanning Electron Micrograph (FESEM) and Transmission Electron Micrograph (TEM) provided the information about the variation of grain size of both the phases. Room temperature ferromagnetic and ferroelectric properties have been estimated by VSM & PE loop tracer. Magnetoelectric coupling coefficient (αME) measurements has been performed by in-house ME setup. From the multiferroic and magnetoelectric data, it is surprisingly found that the composite system having a smaller grain size of NBT matrix and larger grain size of BaM disperse shows highest magnetoelectric coupling (αME) and remnant polarization (Pr) than others. It is also very interesting to observe that the drastic increase (more than 60%) of remnant magnetization (Mr) for composite systems which have smaller grain size of NBT matrix phase.

Magnetoelectric properties of lead-free (80Bi0.5Na0.5TiO3-20Bi0.5K0.5TiO3)-Ni0.8Zn0.2Fe2O4 particulate composites prepared by in situ sol-gel

Lead-free multiferroic ceramics consisting of (1-x) (80Bi0.5Na0.5TiO3-20Bi0.5K0.5TiO3) (BNT-BKT)-xNi0.8Zn0.2Fe2O4 (NZFO) (x = 0, 0.15, 0.25, 0.35, and 0.45) were synthesized by the in situ sol-gel method. The structural, ferroelectric, piezoelectric, ferromagnetic, and magnetoelectric (ME) properties were measured as a function of the NZFO content x. The results showed that the coexistence of BNT-BKT and NZFO phases and the presence of the morphotropic phase boundary in the BNT-BKT phase with a high piezoelectric coefficient d33 (∼131 pC/N) were confirmed. The composites exhibited a homogeneous microstructure and well-combined interfaces between the magnetostrictive and piezoelectric phases, as well as an improved ME response. The largest ME voltage coefficient (αME) of 42.41 mV/cm Oe was achieved for the 0.65(BNT-BKT)-0.35NZFO composite, which is in fact the highest one reported so far for lead-free particulate ME composites fabricated via in situ processing.

Multiferroic and magnetoelectric properties of BiFeO3-CoFe2O4-poly(vinylidene-flouride) composite films

Multiferroic thick nanocomposite films of (1−x)(0.3CoFe2O4-0.7BiFeO3)-xPolyvinylidene difluoride (CFO-BFO/PVDF) with x variations 0.20, 0.30 and 0.40 were synthesized using hot press method. Detailed measurements of structural, dielectric, magnetic and magnetoelectric data have been reported. Structural characterization reveals the presence of all the three distinct phases viz. CFO, BFO and PVDF. The dielectric loss as low as 0.05 has been observed for composite film with 40mol% of PVDF. The AC conductivity (5.9×10−8Ω−1cm−1) of composite film (x=0.40) is found to be much lower as compared to CFO-BFO ceramic. The electric poling of composite film (with x=0.30) leads to substantial increase in saturation (2Ms) and remnant magnetization (2Mr). A significant magnetoelectric effect with magnetoelectric voltage coefficient (αME)∼22.128mV/cm Oe has been observed for composite film with x=0.40, which is possibly a consequence of implicit mechanical interaction between CFO and BFO through PVDF matrix. Hence these nanocomposite films hold a great potential to be promising candidates for multiferroic devices.

Synthesis, characterization, and magneto‐electric properties of (1−x)BCZT‐xCFO ceramic particulate composites

AbstractSynthesis of a new magnetoelectric [(1−x)(Ba0.85Ca0.15)(Zr0.1Ti0.9)O3‐xCoFe2O4] (weight fraction x=0, 0.1, 0.2, 0.3, 0.4, 0.5 and 1) ceramic particulate composites with its structural characterization and magneto‐electric properties have been reported here in this study. Lead free piezoelectric (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 (BCZT) and ferrimagnetic CoFe2O4 (CFO) were synthesized using sol‐gel and combustion methods respectively. (1−x)BCZT‐xCFO magnetoelectric composites were then synthesized by mixing of the calcined individual ferroic phases with required weight fractions. Powder X‐ray diffraction studies indicate the coexistence of BCZT and CFO phases in the composites sintered at 1300°C. 0.5BCZT‐0.5CFO composite showed high strain sensitivity (dλ/dH) of 52×10−9 Oe−1, which is comparable to that of pure CFO (50×10−9 Oe−1). A high piezoelectric voltage constant (g33) of 8×10−3 V m/N was measured for 0.8BCZT‐0.2CFO sample. All the composites showed magnetoelectric effect and a high magnetoelectric coupling coefficient (αME) of 6.85 mV/cm Oe was measured for 0.5BCZT‐0.5CFO composite at 1 kHz and a large ME coefficient of 115 mV/cm Oe at its resonance frequency. The effect of microstructure on the magnetoelectric properties of [(1−x)BCZT‐(x)CFO] composites has been studied and reported here as a function of its piezoelectric (BCZT)/ferrite (CoFe2O4) content.

Correlations of Structural, Dielectric, Magnetic and Magnetoelectric Properties of Ca<sub>1-x</sub>Sr<sub>x</sub>(Fe<sub>0.5</sub>Ta<sub>0.5</sub>)O<sub>3</sub> Multiferroic Ceramics

Conventional solid state reaction technique was used to synthesize Ca1-xSrx(Fe0.5Ta0.5)O3 multiferroic ceramics (where x = 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5). Powder of ingredients was mixed thoroughly in stoichiometric amount and calcined at 1150°C for 5 h. Disk and toroid shaped samples prepared from each composition were sintered at 1450°C for 5 h. The XRD analysis confirms that all compositions are single phase cubic perovskite structure. The theoretical and bulk density increases with increase of Sr content, which may be attributed to the fact that the atomic weight and density of Sr are larger than those of Ca. The average grain size increased with increasing Sr content up to x = 0.2, and then decreased with further increase of Sr content. Frequency dependent dielectric constant shows usual dielectric dispersion at lower frequencies due to Maxwell-Wagner type interfacial polarization. The higher values of real and imaginary part of impedance at lower frequencies are also due to the fact that all kinds of polarization mechanism are present and increase with Sr content indicating the enhancement property of the composition. The continuous dispersion on increasing frequency contributes to the conduction phenomena. Two semicircles correspond to the grain boundary and grain resistance separately. The complex modulus analysis reveals the polaron hopping and negligibly small contribution of electrode effect. The continuous dispersion on increasing frequency may be contributed to the conduction phenomena. The ac conductivity, σac, was derived from the dielectric measurement and it increases with increase of frequency for all the compositions and can also be explained on the basis of polaron hopping mechanism. At higher frequencies conductive grains are more active, and thereby increases of hopping of charge carrier contribute to rise in conductivity. The real part of initial permeability increased with increasing Sr content up to x = 0.2, and then decreased further increasing the Sr content. Firstly, it increased due to the higher values of grain size, and then decreased with the Sr content due to the lowering the grain size. The saturation magnetization, Ms, increases for x = 0.2 and then decreases with increasing Sr content due to the pore acted as a pinning centre of electron spin; thereby Ms decreases also due to the grain size which is well supported by the permeability results. The decrease of magnetoelectric voltage coefficient αME with content may be attributed to the increased porosity in the sample. The presence of the pores breaks the magnetic contacts between the grains. The highest value of αME is 42.22 mV·cm-1·Oe-1 for the composition x = 0.2 which is attributed to the enhanced mechanical coupling. It was revealed that there is a dramatic influence of Sr with content x = 0.2 and also has strong correlations on grain size as well as magnetic and magnetoelectric properties.

Development of multiferroic polymer nanocomposite from PVDF and (Bi0.5Ba0.25Sr0.25)(Fe0.5Ti0.5)O3

Thin films of some polymer–ceramics multiferroic nanocomposites (in 0–3 connectivity) of compositions (1 − x)PVDF–x((Bi0.5Ba0.25Sr0.25)(Fe0.5Ti0.5)O3 (x = 0.05,0.1,0.15)) have been prepared using a standard solution casting method. The basic structure and surface morphology of the materials were studied using X-ray diffraction and scanning electron microscopy technique respectively. Structural investigation confirms the presence of polymeric electro active β-phase of matrix (PVDF) and nano filler perovskite phase of the incorporated nano-ceramics. The high resolution transmission electron micrograph of the prepared nano-ceramic thin film composite has shown distinct and uniformly distributed particles (with less agglomeration). This has been observed in SEM micrographs also. The flexible nano-composites fabricated with polymer (PVDF), bismuth ferrite (BiFeO3) and ferroelectric (BST) exhibit high dielectric constant and low tangent loss. The electric response investigated by impedance spectroscopy technique in terms of electric circuit has provided some interesting results on contributions of grain and grain boundary in the restive characteristics of the composites. The study of ac conductivity as a function of frequency obeys Jonscher’s power law. The experimentally obtained first order magnetoelectric coefficient (αME) is found to encouraging for multifunctional application. The improved conductivity and dielectric properties suggest some promising applications in the embedded capacitors.

Inverse bilayer magnetoelectric thin film sensor

Prior investigations on magnetoelectric (ME) thin film sensors using amorphous FeCoSiB as a magnetostrictive layer and AlN as a piezoelectric layer revealed a limit of detection (LOD) in the range of a few pT/Hz1/2 in the mechanical resonance. These sensors are comprised of a Si/SiO2/Pt/AlN/FeCoSiB layer stack, as dictated by the temperatures required for the deposition of the layers. A low temperature deposition route of very high quality AlN allows the reversal of the deposition sequence, thus allowing the amorphous FeCoSiB to be deposited on the very smooth Si substrate. As a consequence, the LOD could be enhanced by almost an order of magnitude reaching 400 fT/Hz1/2 at the mechanical resonance of the sensor. Giant ME coefficients (αME) as high as 5 kV/cm Oe were measured. Transmission electron microscopy investigations revealed highly c-axis oriented growth of the AlN starting from the Pt-AlN interface with local epitaxy.

Magnetoelectric Effect in Ceramics Based on Bismuth Ferrite.

Solid-state sintering method was used to prepare ceramic materials based on bismuth ferrite, i.e., (BiFeO3)1 − x–(BaTiO3)x and Bi1 − xNdxFeO3 solid solutions and the Aurivillius Bi5Ti3FeO15 compound. The structure of the materials was examined using X-ray diffraction, and the Rietveld method was applied to phase analysis and structure refinement. Magnetoelectric coupling was registered in all the materials using dynamic lock-in technique. The highest value of magnetoelectric coupling coefficient αME was obtained for the Bi5Ti3FeO15 compound (αME ~ 10 mVcm−1 Oe−1). In the case of (BiFeO3)1 − x–(BaTiO3)x and Bi1 − xNdxFeO3 solid solutions, the maximum αME is of the order of 1 and 2.7 mVcm−1 Oe−1, respectively. The magnitude of magnetoelectric coupling is accompanied with structural transformation in the studied solid solutions. The relatively high magnetoelectric effect in the Aurivillius Bi5Ti3FeO15 compound is surprising, especially since the material is paramagnetic at room temperature. When the materials were subjected to a preliminary electrical poling, the magnitude of the magnetoelectric coupling increased 2–3 times.

Influences of the shape of magnetic material on the magnetoelectric properties of the PZT/Metglas composite

In this paper, the influences of the shape of magnetic material on the magnetoelectric (ME) properties of PZT/Metglas magnetoelectric (ME) composites have been investigated. The results indicate that, with the decrease of the waist length (L w) of the dumbbell-shaped Metglas, the magnetic flux density in the center region and ME coefficients(α ME) of the composites increase, while the optimal bias magnetic field H dc decreases on the contrary. In an AC magnetic field of 1 kHz, the maximum α ME (α Max) of the composite with L w= 20 mm exhibits 1.3 times larger than that of the one with L w=50 mm, and the optimal H dc deceases by 15%. At the resonant frequencies of each composites, α Max is enhanced by 1.3 times as L w decreases from 50 to 20 mm. The simulation made by Comsol Multiphysics and the theoretical analysis based on an equivalent magnetic circuit confirm the experimental results.

Epitaxial Coherence at Interfaces as Origin of High Magnetoelectric Coupling in Multiferroic BaTiO3–BiFeO3 Superlattices

Multiferroic superlattices consisting of 15 double layers BaTiO3–BiFeO3 show a very high magnetoelectric voltage coefficient αME of up to 49 V cm−1 Oe−1 at 300 K, measured at 1 kHz with zero direct current (DC) bias magnetic field. However, the microscopic origins of such high αME values, and the temperature and DC magnetic field dependencies of αME are not understood up to now. Therefore, in this study two superlattices grown at high/low oxygen partial pressures having high/low αME values, respectively, are compared. While at high growth pressure the strain contrast in high‐resolution transmission electron microscopy images is limited to few layers at the substrate interface, the low‐pressure sample shows much more pronounced microstrain. This is additionally visualized in Fourier transformed images, and the out‐of‐plane lattice parameter of the single BaTiO3 layer is increased near the interface. In addition to a low density of oxygen vacancies, it seems to be important to avoid micromechanical clamping of the 2D single‐phase nanolayers of the multiferroic BaTiO3–BiFeO3 superlattices to achieve high magnetoelectric coupling.