Maximum Magnetoelectric Voltage Coefficient Research Articles

Investigation of the magnetoelectric properties of Bi0.9La0.1Fe0.9Mn0.1O3/La0.8Sr0.2MnO3 bilayer: Monte Carlo simulation

In the present work, the magnetic, ferroelectric and magnetoelectric properties of the bilayer composite Bi0.9La0.1Fe0.9Mn0.1O3/La0.8Sr0.2MnO3 (BFO-LM/LSMO) have been studied using Monte Carlo simulation in the framework of the Heisenberg model. The magnetoelectric properties of BFO-LM/LSMO bilayer films with different stacking modes were predicted and analyzed. Furthermore, the effect of interfacial coupling on the magnetoelectric properties was analyzed, and a maximum magnetoelectric voltage coefficient of 195.5 mV/(cm.Oe) was obtained in the BFO-LM/LSMO bilayer films with BL/Mn-interface. The magnetic coupling at the FM/Mn interface provides a novel ferromagnetic state localized at the interface and an improvement in the magnetic properties. The obtained results make BFO-LM/LSMO films a promising material for advanced magnetoelectric applications.

Multifunctional Magnetoelectric Sensing and Bending Actuator Response of Polymer-Based Hybrid Materials with Magnetic Ionic Liquids.

With the evolution of the digital society, the demand for miniaturized multifunctional devices has been increasing, particularly for sensors and actuators. These technological translators allow successful interaction between the physical and digital worlds. In particular, the development of smart materials with magnetoelectric (ME) properties, capable of wirelessly generating electrical signals in response to external magnetic fields, represents a suitable approach for the development of magnetic field sensors and actuators due to their ME coupling, flexibility, robustness and easy fabrication, compatible with additive manufacturing technologies. This work demonstrates the suitability of magnetoelectric (ME) responsive materials based on the magnetic ionic liquid (MIL) 1-butyl-3-methylimidazolium tetrachloroferrate ([Bmim][FeCl4]) and the polymer poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE) for magnetic sensing and actuation device development. The developed sensor works in the AC magnetic field and has frequency-dependent sensitivity. The materials show voltage responses in the mV range, suitable for the development of magnetic field sensors with a highest sensitivity (s) of 76 mV·Oe-1. The high ME response (maximum ME voltage coefficient of 15 V·cm-1·Oe-1) and magnetic bending actuation (2.1 mm) capability are explained by the magnetoionic (MI) interaction and the morphology of the composites.

Significant magnetoelectric enhancement of composite films of CoZnxFe2-xO4 particles and poly (vinylidene fluoride-trifluoroethylene) for AC magnetic sensors

Polymer-based magnetoelectric (ME) nanocomposites exhibit a low ME effect and high bias field at room temperature, which severely limits their application in flexible wearable sensors. To overcome these obstacles, Zn-doped magnetic nanoparticles of CoZnxFe2-xO4 (x = 0, 0.1, 0.2, and 0.3) were prepared by an auto-combustion method in this work. The obtained magnetostrictive curves imply that Zn element doping can improve greatly the piezomagnetic coefficient of magnetic nanoparticles, and among the tested materials, CoZn0.1Fe1.9O4 has the largest piezomagnetic coefficient. Composite films of poly(vinylidene fluoride-trifluoroethylene) and CoZn0.1Fe1.9O4 (P(VDF-TrFE)/CoZn0.1Fe1.9O4) were prepared by spin coating. The maximum ME voltage coefficient of P(VDF-TrFE)/CoZn0.1Fe1.9O4 composite film with a filler weight concentration of 10 wt% is 87.9 mV cm−1 Oe−1 with a bias field of 1050 Oe and a resonance frequency of 46 kHz, which is the highest value reported in the literature of 0–3 type polymer-based ME composite films at present. To evaluate the composite films for application in magnetic sensors, the ME output voltage was measured at a bias field of 1050 Oe with increasing AC magnetic field, demonstrating a good linear relationship with linearity of 0.999. These results indicate that the piezomagnetic coefficient of magnetic materials is an the important factor for the great enhancement of the ME voltage coefficient. This work provides a new approach for the synthesis of more effective polymer-based ME nanocomposites for potential applications in smart wearables.

Enhanced multiferroic properties of Bi4Ti3-xCoxO12/La0.67Sr0.33MnO3 layered composite thin films

In this work, Bi4Ti3-xCoxO12/La0.67Sr0.33MnO3 (BITCx/LSMO, x = 0.025, 0.05, 0.10 and 0.15) layered magnetoelectric (ME) composite thin films were successfully synthesized by chemical solution deposition, and the effect of Co2+ doping content on the microstructure, leakage, dielectric property, ferroelectricity, ferromagnetism and ME coupling performance of BITCx/LSMO composite thin films was investigated. Co2+ doping induces improved ferroelectricity and weak ferromagnetism for the BITCx phase. Especially, the single-phase BITC0.05 film exhibits a maximum ME voltage coefficient (αE) of 0.445 mV/cm·Oe at room temperature, suggesting excellent single-phase multiferroic properties. The BITC0.05/LSMO composite thin film possesses the lowest leakage current density, maximum ϵr, minimum tanδ, highest remnant polarization of 24.2 μC/cm2, lowest coercive field of 137 kV/cm and improved saturation magnetization along with a maximum aE value of 27.3 V/cm·Oe. Based on these findings, Co2+-doped Bi4Ti3O12 has excellent single-phase multiferroic properties, and the incorporation of magnetic ion-doped Bi4Ti3O12 with ferromagnetic oxides benefits the improvement of ME composite thin films.

Greener Solvent-Based Processing of Magnetoelectric Nanocomposites.

Polymer-based magnetoelectric (ME) nanocomposites are an enabling material technology for a wide range of applications in the area of digitalization strategies. Due to its highest piezoelectric response among polymers, poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE) is the piezoelectric matrix most used in polymer-based ME materials with over 80% of the total reports, with the resulting composites typically processed from solutions with N,N-dimethylformamide (DMF), a toxic solvent. Nevertheless, environmentally friendlier approaches and sustainable technologies are increasingly being required. This work demonstrates that P(VDF-TrFE)/Co2Fe2O4 nanocomposites can be successfully prepared from solution using three different environmentally friendlier solvents: dimethyl sulfoxide (DMSO), N,N'-dimethylpropyleneurea (DMPU), and triethyl phosphate (TEP) with different dipole moments. It is shown that the prepared composite films, with a maximum ME voltage coefficient of 35 mV cm-1 Oe-1 and a maximum sensitivity of 2.2 mV T-1, are suitable for applications, highlighting the path for a new generation of more sustainable ME sensors.

Rietveld refinement analysis and influence of individual phases on the magnetoelectrically coupled (1-x)BSZT+ xNCZGF multiferroic composites

The magnetoelectric voltage coefficient at room-temperature is realized in various (1-x)BSZT+ xNCZGF composites by studying refined crystal structures, surface morphology, magnetic, electric and ferroeletric properties. The ferroelectric (BSZT) and ferrite (NCZGF) phases of the composites are prepared using standard solid-state reaction technique. Rietveld refinement confirmed that the BSZT phase forms perovskite structure with P4mm space group and NCZGF phase forms spinel structure with Fd3¯m space group. From FESEM surface morphology it was observed that the average grain diameter ranges 0.5–2.21 µm. EDX analysis confirms the formation of respective phases and composites. Initial permeability increases from 55 to 130 with increasing NCZGF content which is consistent with the value calculated theoretically using different models. The saturation magnetization also increases from 12 to 37 emu/g with increasing NCZGF content, consistent with the calculated value using law of approach to saturation technique. The dielectric constant of the composites is found to decrease with increasing NCZGF content which is in line with the Maxwell-Garnett, Bruggeman, Looyenga and Lichteneker theoretical approximations. Frequency dependence of the dielectric constant exhibits dispersion, which can be modeled using a modified Debye function that considers the probability of several ions contributing to the relaxation. The ac conductivity follows the Jonscher’s power law, and the conduction mechanism is attributed to the small polaron hopping. Complex impedance is evaluated using the Cole-Cole plot ensures the dominance of both grain and grain boundary resistances. The P-E hysteresis loops ensure the typical ferroelectric nature at room-temperature for x ≤ 0.2. The simultaneous M-H and P-E hysteresis loops confirm the magnetoelectric coupling between ferrite and ferroelectric phases. Furthermore, the maximum magnetoelectric voltage coefficient for 0.9BSZT+ 0.1NCZGF composite is found to be ~194 mV cm−1 Oe−1 that can be used in multifunctional devices.

Structural, magnetic and electrical properties of multiferroic xLi0.1Ni0.2Mn0.6Fe2.1O4 – (1-x)Bi0.8Y0.2FeO3 composites

The room temperature magnetoelectric coupling was elucidated by the analysis of structural, magnetic, and electrical properties of xLi0.1Ni0.2Mn0.6Fe2.1O4 – (1-x)Bi0.8Y0.2FeO3 composites. The X-ray diffraction pattern shows that the ferromagnetic phase forms a cubic spinel structure and the ferroelectric phase forms a rhombohedral perovskite structure. The density of the composites decreases with ferrite content. The average grain size slightly decreases with ferrite content for x = 0.1 and increases for further increasing ferrite content. The real part of initial permeability and saturation magnetization increase with increasing ferrite content. The real part of the dielectric constant decreases rapidly with the increase of frequency showing dielectric dispersion at lower frequencies and then remains almost constant at higher frequencies. The dielectric loss of the samples reduces with the increase of the ferrite phase. The ac conductivity of composites increases with frequency, indicating that the conduction is due to small polaron hopping. The study of impedance spectroscopy suggests that grain contribution is effective for the conduction mechanism in the composite. The maximum magnetoelectric voltage coefficient is observed (~182 × 103Vm−1T−1) for the 0.1LNMFO – 0.9BYFO composite which is useful for fabricating magnetic sensors.

Interplay between the ferrimagnetic and ferroelectric phases on the large magnetoelectric coupling of xLi0.1Ni0.2Mn0.6Fe2.1O4–(1 − x)Bi0.8Dy0.2FeO3 composites

The multiferroic composites of ferromagnetic Li0.1Ni0.2Mn0.6Fe2.1O4 (LNMFO) and ferroelectric Bi0.8Dy0.2FeO3 (BDFO) with the general formula xLi0.1Ni0.2Mn0.6Fe2.1O4–(1 − x) Bi0.8Dy0.2FeO3 have been prepared by the solid-state reaction route. The XRD analysis has ensured that the composites are composed of a mixture of cubic spinel LNMFO and orthorhombic perovskite BDFO phases. Field Emission Scanning Electron Microscope is used to investigate the surface morphology of the studied compositions. The average grain size of the composites has reduced slightly with the enhancement of ferrite part up to 20% and after that it has increased again. The real part of the initial permeability $$(\mu^{\prime}_{i} )$$ was found to be increasing with ferrite content. The real part of dielectric constant $$(\varepsilon^{\prime})$$ exhibits dispersion at low-frequency region because of Maxwell–Wagner type interfacial polarization. The complex impedance spectroscopy has been used to separate the grain and grain boundary contribution to the total resistance. Existence of the hopping conduction mechanism has been confirmed through the study of electric modulus. The hysteresis loops of the compositions are studied to confirm the response of ferrite part to the applied magnetic field. The magnetoelectric voltage coefficients of the composites have reduced with the ferrite part. The maximum magnetoelectric voltage coefficient is nearly 158 × 103 Vm−1 T−1 for the 0.1LNMFO–0.9BDFO composite, which is about three times of the reported value compared to other composites.

Tunable Magnetoelectric Response in Cofired (Bi0.5Na0.5TiO3-Bi0.5K0.5TiO3)/CoFe2O4 Laminated Composite

Magnetoelectric (ME) composites exhibiting strain-mediated coupling are gaining increasing interest for applications. In this paper, an enhancement of ME response on simple lead-free laminated composites (80Bi0.5Na0.5TiO3-20Bi0.5K0.5TiO3)/CoFe2O4 (BNKT/CFO) prepared by a modified cofiring processing were demonstrated, by analyzing the effect of thickness variation on ME properties. The coexistence of independent BNKT and CFO phase and the presence of a clear and well-bonded interface were confirmed. Specifically, the maximum ME voltage coefficient of laminated composite reached up to 74.59 mV/(cm·Oe) with an optimized BNKT/CFO layer thickness ratio of 1:2. The static elastic model and the equivalent circuit model were used to determine the interface coupling. Also, there is a large magnetodielectric (MD) response up to 5.1% in a magnetic field of 8 kOe. Tuning the layer thickness, the ME response of laminated composite is further optimized, which is of significance in development of magnetic-field-tuned electronic devices.

Investigation of magnetoelectric effect in Bi0.5Na0.5TiO3–CoMn0.2Fe1.8O4 composites

In the present work Bi 0.5 Na 0.5 TiO 3 (BNT) and CoMn 0.2 Fe 1.8 O 4 (CMFO) composites, (1-x) BNT/(x) CMFO with x = 0.10, 0.20, 0.30, 0.40 and 0.50 have been synthesized using solid state reaction method. X-ray diffraction exhibits the peaks akin to constituent BNT and CMFO phases suggesting the effective development of the desired composites. The variation of dielectric constant with temperature reveals their diffuse phase transition behaviour and existence of two dielectric anomalies in vicinity of ferroelectric to antiferroelectric and from antiferroelectric to paraelectric transition temperatures. Remnant polarization (2P r ) and Coercive field (2E C ) found to decrease with addition of CMFO. Furthermore, magnetization vs. magnetic field (M-H) hysteresis loops shows an increment in magnetization with increase in CMFO content. Complex impedance spectroscopy confirms the existence of grain (bulk) effect and temperature dependent electrical relaxation processes in the composites. Magnetoelectric analysis shows maximum magnetoelectric voltage coefficient, α ME for x = 0.10 and the value of, α ME decreases from 6.765 mV/cm-Oe to 2.780 mV/cm-Oe for the composites x = 0.10 to 0.50.

The effects of the soft magnetic alloys’ material characteristics on resonant magnetoelectric coupling for magnetostrictive/piezoelectric composites

The resonant magnetoelectric (ME) effects are investigated in Terfenol-D/PZT laminates with various soft magnetic alloys (i.e. FeCuNbSiB, FeSiB and CoNiFeSiB). The soft magnetic alloys with high magnetic permeability and magnetization produces an additional magnetostatic field in the Terfenol-D, which changes the effective magnetic field distribution within the Terfenol-D and plays an important role at the large zero bias ME response. Meanwhile, the magnetostrictive strain of soft magnetic alloys can produce a pre-stress on the Terfenol-D layer due to its low saturation field, which enhances the maximum ME voltage coefficient and reduces the required optimal dc magnetic field Hopt,dc. The experimental results indicate that the largest zero bias ME voltage coefficient is obtained for Terfenol-D/PZT composite with FeCuNbSiB (i.e. the soft magnetic alloy with the highest magnetization), which is about 7.3 times more than that of Terfenol-D/PZT at zero bias. The maximum ME voltage coefficient is obtained for Terfenol-D/PZT composite with FeSiB (i.e. the soft magnetic alloy with the largest magnetostriction constant) at Hopt,dc = 175 Oe, which is about 1.15 times greater than that of Terfenol-D/PZT composite (at Hopt,dc = 598 Oe) and also happens at a much smaller bias field.

Large magnetoelectric response in lead free BaTi1−xSnxO3/NiFe2O4 bilayer laminated composites

Magnetoelectric studies on BaTi1−xSnxO3/NiFe2O4 (x = 0.07, 0.08, 0.09 and 0.10) lead-free bilayer laminated composites were investigated at 1 kHz and resonance frequencies. The pure phase formation of BaTi1−xSnxO3 and NiFe2O4 samples was confirmed by X-ray diffraction technique. The ferroelectric BaTi1−xSnxO3 layers of different compositions having large piezocoefficient were used for the ME studies. The composites displayed their maximum magnetoelectric voltage coefficient at resonance peaks related to the 1st radial mode. The thickness dependent magnetoelectric studies on composites with x = 0.08 revealed a giant magnetoelectric voltage coefficient of 24.53 V cm−1 Oe−1 at 285 kHz under bias field condition. Remarkably, a large self-biased magnetoelectric response of the order of ~ 2–5 V cm−1 Oe−1 at resonance was exhibited by the composites. The observed large and self-biased magnetoelectric response in BaTi1−xSnxO3/NiFe2O4 composites enables them to be a useful lead-free alternative for several magnetoelectric related applications.

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.

Large magnetoelectric coupling in 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3) TiO3 film on Ni foil

Lead-free, high piezocoefficient 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 film is fabricated on soft magnetic Ni foil as a substrate using a pulse laser deposition technique for the magnetoelectric studies. The x-ray diffraction analysis confirms the phase pure formation of polycrystalline ferroelectric film along with the presence of NiO formed during the high temperature growth process. The obtained lattice parameters suggest that the native oxide could favour the coherent growth of a ferroelectric layer. The film exhibits ferroelectric characteristics with a polarization value of 23 µC cm−2 at 225 kV cm−1. The fabricated heterostructure displayed a high magnetoelectric coupling coefficient with the maximum magnetoelectric voltage coefficient (α31) value of 1.08 V cm−1 Oe−1 at low field of 44 Oe. It is noteworthy to mention that the observed α31 is comparable to the earlier reported toxic lead-based similar systems. The comparison between the experimental and calculated α31 values suggests that the strain transfer percentage efficiency is around 69%, which is responsible for the observed large ME coupling. These experimental findings give a way to achieve high magnetoelectric coefficients by fabricating the oxide piezoelectric layer directly on the clamping free magnetic substrate.

Structural, microstructural, electromagnetic and magnetoelectric properties of (1 − y) [Ba0.85Ca0.15Zr0.1Ti0.9O3] + (y) [Ni0.92Co0.03Mn0.05Cu0.05Fe1.95−xAlxO4] composites

In the present study, polycrystalline (1 − y) [Ba0.85Ca0.15Zr0.1Ti0.9O3] (BCZTO) + (y) [Ni0.92Co0.03Mn0.05Cu0.05Fe1.95−xAlxO4] (NCMCFAlxO) (where x = 0, 0.1, 0.3, 0.5, 0.7, 0.9 and y = 0.5) composites were synthesized via solid state reaction route. The samples were characterized through the standard techniques. X-ray diffraction (XRD) analysis revealed the successful formation of the BCZTO–NCMCFAlxO composites without any extra phases and diffusion. The lattice parameter of BCZTO and NCMCFAlxO decreases as the concentration of Al3+ increases. SEM analysis reveals that the microstructure exhibits nonuniform grain size distribution with Al3+ concentration. The dispersion of dielectric constant is well consistent with Maxwell–Wagner interfacial polarization and the dielectric constant decreases as the concentration of Al3+ ions increases due to the difference of ionic radii. The electrical conductivity is due to the small polaron hopping according to Austin–Mott model. The decrement in saturation magnetization with increasing Al3+ concentration because exchange interactions is weakened through the substitution of Fe3+ by Al3+ ions. Permeability decreases with Al3+ concentration and exhibits good frequency stability over the entire measured frequency domain. The magnetoelectric coupling coefficient decreases as the concentration of Al3+ increases at both sintering temperatures which is due to the variation of grain size. The maximum magnetoelectric voltage coefficient of 0.72 V Oe−1 cm−1 was obtained for the pristine composite at 1373 K.

Diameter and sequence effects on magnetoelectric effect in FeCo/Pb(Zr,Ti)O3/Ni trilayered long cylindrical composite structures

Here we studied the magnetoelectric (ME) effect of FeCo/Pb(Zr,Ti)O3/Ni and Ni/Pb(Zr,Ti)O3/FeCo trilayered long cylindrical composites made up of negative magnetostrictive Ni layers, positive magnetostrictive FeCo layers and piezoelectric Pb(Zr,Ti)O3 (PZT) cylinders. Magnetostrictive layers were directly deposited on the PZT by electroless deposition. The bias magnetic field and the frequency dependences of ME effect were studied in both the axial and the vertical modes. The mean diameter of the trilayered long cylindrical composites has a strong impact on the ME effect. Keeping the height fixed, the resonant frequency and the maximum ME voltage coefficient decrease with the mean diameter of the cylinder increasing, while the optimal bias magnetic field HDC approximately remains constant. Besides, the ME effect is also influenced by the sequence of Ni and FeCo layers. The FeCo/Pb(Zr,Ti)O3/Ni cylinder obtains larger ME voltage coefficients, superior to those of the Ni/Pb(Zr,Ti)O3/FeCo in both modes. This work is significant for optimizing ME performance of the cylindrical layered ME composites in practical application such as magnetic field sensors and energy harvesters.

Enhanced magnetoelectric response in 2-2 bilayer 0.50Pb(Ni1/3Nb2/3)O3–0.35PbTiO3–0.15PbZrO3/NiFe2O4 thin films

In this work, room temperature magnetoelectric (ME) properties of 0.50Pb(Ni1/3Nb2/3)O3–0.35PbTiO3–0.15PbZrO3 (PNNZT)/NiFe2O4 (NFO) 2-2 bilayer thin films grown on Pt/Ti/SiO2/Si substrate, using pulsed laser deposition technique, are reported. Structural studies confirm single phase PNNZT/NFO 2-2 bilayer structure formation. PNNZT/NFO 2-2 bilayer thin film shows a maximum ME voltage coefficient (αE) of ~0.70 V cm−1. Oe–1 at a frequency of 1 kHz. The present study reveals that PNNZT/NFO bilayer thin film can be a potential candidate for technological applications.

Equivalent circuit model for plate-type magnetoelectric laminate composite considering an interface coupling factor

We describe the modeling of magnetoelectric (ME) effect in the plate-type Terfenol-D/PZT laminate composite by introducing a newly proposed interface coupling factor into the equivalent circuit model, aiming at providing a guidance for designing, fabricating and using the ME laminate composite based devices, such as current sensor, magnetic sensor, energy harvester, and wireless energy transfer system. Considering that the strains of the magnetostrictive and piezoelectric layers are not equal in actual operation due to the epoxy resin adhesive bonding condition, the equivalent circuit models of magnetostrictive and piezoelectric layers are created based on the constitutive equation and the equation of motion, respectively. An interface coupling factor kc is introduced which physically reflects the strain transfer condition between the magnetostrictive and piezoelectric phases. Specifically, the respective equivalent circuit models of magnetostrictive and piezoelectric layers are combined with an ideal transformer whose turn-ratio is just the interface coupling factor. Furthermore, the theoretical expressions containing kc for the longitudinal ME voltage coefficient v and the optimum thickness ratio noptim to which the maximum ME voltage coefficient corresponds are derived from the modified equivalent circuit model of ME laminate, where the interface coupling factor acts as an ideal transformer. To explore the influence of mechanical load on the interface coupling factor kc, two sets of weights, i.e., 100 g and 500 g, are placed on the top of the ME laminates, each with the same thickness ratio n in the sample fabrication for comparison. A total of 12 L-T mode plate-type ME laminate samples with different-thickness configurations are fabricated. The interface coupling factors determined from the measured v and the DC bias magnetic field Hbias are 0.15 for 500 g pre-mechanical load and 0.10 for 100 g pre-mechanical load, respectively. Furthermore, the measured optimum thickness ratios are 0.57 for kc=0.15 and 0.50 for kc=0.10, respectively. Both the measured ME voltage coefficient v and optimum thickness ratio containing kc agree well with the corresponding theoretical predictions. The relationship between the optimum thickness ratios under two different mechanical loads remains unchanged, i.e., the measured optimum thickness ratio for kc=0.15 is larger than for kc=0.10. The experimental results verify the reasonability and correctness of the introduction of kc in the modified equivalent circuit model. The possible reasons for different interface coupling factors under different loads are also qualitatively discussed in this paper.

Enhanced Magnetic Field Sensitivity in Magnetoelectric Composite Based on Positive Magnetostrictive/Negative Magnetostrictive/Piezoelectric Laminate Heterostructure

Resonance magnetoelectric (ME) responses are investigated for the ME laminate heterostructure consisting of positive magnetostrictive material FeCuNbSiB, negative magnetostrictive material Ni and piezoelectric material PZT-8. On one hand, both a built-in magnetic field induced by the strong magnetic interactions between positive magnetostrictive and negative magnetostrictive materials and an intrinsic anisotropic field with obvious hysteresis and remnant magnetization in Ni layer result in a large zero-biased ME effect. The corresponding zero-biased ME voltage coefficient reaches 10.12 V/Oe (126.5 V/cm Oe), which is about 3 times larger than that of traditional Ni/PZT-8 (NP) laminate. On the other hand, the additional stress produced by the high magnetic permeability FeCuNbSiB layer enhances the magnetostriction of Ni layer and ME response. The corresponding maximum ME voltage coefficient (dVME/dHac) is 12.09 V/Oe (150.87 V/cm Oe) at bias magnetic field $H_{\mathrm {dc}} = 4$ Oe. It is further found that even a step change of ac magnetic field less than 10−10 T can be clearly distinguished by the proposed ME composite. The value of ME voltage sensitivity to dc magnetic fields (dVME/dH $_{\mathrm {dc}})$ reaches ~76.7 mV/Oe at $H_{\mathrm {dc}}= 5$ Oe and $H_{\mathrm {ac}} =0.1$ Oe. Correspondingly, the proposed laminate heterostructure is able to possess both strong ac and dc magnetic field sensitivities.

Magnetoelectric Effect in Cofired Lead‐Free Laminated (Bi0.5Na0.5TiO3‐Bi0.5K0.5TiO3)/(Ni0.8Zn0.2)Fe2O4 Composites

Lead‐free magnetoelectric (ME) laminated (80Bi0.5Na0.5TiO3‐20Bi0.5K0.5TiO3)/(Ni0.8Zn0.2)Fe2O4 (BNKT/NZFO) composites are prepared via a modified cofiring processing, combining grain refinement and liquid phase sintering with low sintering aid content. The microstructure, dielectric, ferroelectric, magnetic, and magnetoelectric properties are investigated by varying the thickness of NZFO layer. The results show that the coexistence of independent BNKT and NZFO phase and the presence of the morphotopic phase boundary in BNKT phase with high piezoelectric coefficient d33 of 131 pC/N are confirmed. Laminated composites have clear and well‐bonded interfaces across the two layers, as well as improved ME properties. The maximum ME voltage coefficient (αE31) of the laminated composite reach 115.1 mV cm−1 Oe−1 with an optimized BNKT/NZFO layer thickness ratio of 1/2. In addition, a zero‐biased ME response was observed in BNKT/NZFO laminated composites.