ME Response Research Articles

Insights into the novel magnetoelectric coupling mechanism in soft materials due to Maxwell interactions

This study models the novel ME coupling mechanism in soft materials that are inherently non-magnetoelectric (NME). First, the central physical concept for developing ME coupling in soft NME materials is explained. Following this, the stretch of soft materials under magnetic and stress stimuli is solved by using the obtained Euler–Lagrange equations. Finally, the ME coefficients for various operating modes are analytically derived. The numerical results obtained for the ME coefficients of a ME electret system are in good agreement with the experimental data. The nonlinear interplay between the stress, magnetic field, and ME response is investigated. In addition, the key factors for maximizing the ME coupling are discussed. Based on the proposed model, we present physical insights to support the prospects of achieving magnetic energy harvesting and revealing the physical mechanisms of animals' magnetoreception. This work may provide a simple basis to further create soft ME-like materials with good flexibility and strong ME coupling.

Interfacial bonding effect on nonlinear magnetoelectric response of multiferroic composites

Magnetoelectric materials incorporate both ferroelectric and ferromagnetic phases to induce giant magnetoelectric coupling effect, which is one of the most important features and absent in either ferromagnetic or ferroelectric materials alone. ME effects is achieved through elastic deformation between the ferromagnetic and ferroelectric phases. It also depends on the constituent phase properties, the volume concentration and the interfacial conditions. In this paper, we investigate the interfacial effects on the nonlinear ME response of the multiferroic composites consisting both ferromagnetic and ferroelectric through epoxy bonding by using a unified micromechanics model. First, the nonlinear coupling behaviors of each individual ferromagnetic or ferroelectric phase are studied by consideration of evolution of the microstructure due to domain switching. Then, the coated or bonded inclusions are treated as a two-phase composite and a homogenization approach is applied to obtain the equivalent properties of the homogenized coated inclusions. Finally, the micromechanics approach is applied again to investigate the overall effective coupling properties of the multiferroic composites consisting coated inclusions and matrix. With a focus on the Terfenol-D/PZT/Terfenol-D system, we demonstrate how its coupling coefficients α33, and voltage coefficient αE33depend on the interfacial bonding. Comparisons between the theoretical calculations and the existing experimental data agree well.

Magnetoelectric composites of lead-free piezoelectrics and yttrium iron garnet: interfacial reactions and functional properties

A wide range of magnetoelectric composites has been prepared: (100 − x) wt% FE + x wt% YIG (x = 30–70 in steps of 10 wt%), where YIG is yttrium iron garnet and FE is a lead-free ferroelectric material reported in the literature, namely lithium sodium potassium niobate ([Li0.06(Na0.52K0.48)]1.04NbO3, KLNN), modified sodium bismuth titanate ([96 mol.% Bi0.5(Na0.84K0.16)0.5TiO3 + 4 mol.% SrTiO3 + 0.2 wt% La2O3], BNT) or barium calcium zirconate titanate (Ba0.85Ca0.15Ti0.9Zr0.1O3, BCZT). The interfacial reactions and dielectric, piezoelectric, magnetic and magnetoelectric behaviors of the composites have been studied. The high-temperature calcination was found to yield the fergusonite-type impurity phase YNbO4 in KLNN-containing composites and the pyrochlore-like phase Y2Ti2O7 in BNT-containing ones. The BCZT-containing samples remain the only phase-pure materials after heat treatment. As a result, among the materials studied, the samples of (100 − x) wt% BCZT + x wt% YIG show the best magnetoelectric coupling coefficient ΔE/ΔH that reaches ~ 5 mV/(cm Oe) with x = 40. Despite showing significant piezoelectric response, the KLNN-containing ceramics exhibit ΔE/ΔH of 1.2 mV/(cm Oe) or less. The composites containing BNT show weak piezoelectric and almost zero ME response (ΔE/ΔH does not exceed 0.2 mV/(cm Oe)) due to the decomposition of ferroelectric phase caused by high-temperature interfacial reactions. The BCZT-containing composites appeared to be magnetically softer than KLNN-containing materials and magnetically harder than BNT-containing ones.

Magneto‐electric product properties of multiferroic composites

AbstractMagneto‐electric (ME) composite materials enable a coupling between magnetization and electric polarization. This magneto‐electric coupling finds application in sensor technology and data storage devices. Since this coupling is a strain‐induced product property which arises due to the interaction of the different phases, suitable material models for the individual phases as well as microscopic defects, such as pores, have to be considered for precise numerical simulations. In this contribution we implemented suitable material models for both phases describing the behavior on the microscopic level and considered pores which influence the overall ME response. In order to determine the effective properties a two‐scale finite element (FE2) homogenization approach is performed. The remanent magnetization behavior is described using a Preisach operator whereas the remanent electric polarization arises due to a ferroelectric/‐elastic switching criterion based on a change in the free energy.

Room-temperature ferroelectricity, superparamagnetism and large magnetoelectricity of solid solution PbFe1/2Ta1/2O3 with (PbMg1/3Nb2/3O3)0.7(PbTiO3)0.3

We report the properties of first synthesized ceramic samples of a perovskite solid solution (PbFe1/2Ta1/2O3)x[(PbMg1/3Nb2/3O3)0.7(PbTiO3)0.3]1−x, x = 0.4, 0.5. The solution is a single-phase material contrary to broadly studied multiphase (magnetic/ferroelectric) composites. Both compounds are ferroelectrics with a diffuse phase transition. An increase in x value results in a decrease in phase transition diffuseness, and an increase in the remnant polarization. 207Pb NMR shows that iron ions are nonuniformly distributed over octahedral sites and tend to random occupation of these sites in the perovskite structure. In particular, the NMR data indicate a tendency to form regions with a higher concentration of iron in the perovskite structure. Magnetic measurements show the coexistence of superparamagnetic and paramagnetic phases in the samples. The paramagnetoelectric (PME) coefficients determined by a dynamic method at room temperature have values β ≈ 0.15 × 10−15 s A−1 (x = 0.4) and 0.54 × 10−15 s A−1 (x = 0.5) at low magnetic fields (± 300 Oe), which are three thousands times larger than that in most single-phase magnetoelectric materials. Our measurements show that the main contribution to the PME response is caused by the superparamagnetic phase. Because the ME response is proportional to dM2/dH, it can be amplified by many orders of magnitude for the multiferroics with the superparamagnetic phase due to a sharp change of magnetization with the field.

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.

Yttrium iron garnet – lead-barium titanate particulate multiferroic composites

ABSTRACTBa1−xPbxTiO3/Y3Fe5O12 particulatecomposites with х = 0–1 were synthesized. The composites (100-y) wt.% Ba0.9Pb0.1TiO3 – y wt.% Y3Fe5O12 with у = 40–50 wt.% exhibit ME coupling coefficient ΔЕ/ΔH of ∼10 mV/(cm·Oe) due to the prominent piezoelectric properties. ME response in Ва1−хPbxTiO3/Y3Fe5O12 ceramics with х = 0.35−1 is precluded by a high content of pyrochlore-type Y2Ti2O7 that forms through chemical interfacial interaction. An increase in sintering temperature to 1300°С was found to be inappropriate to obtain phase-pure ВаTiO3/Y3Fe5O12 ceramics due to the partial decomposition of Y3Fe5O12 to yttrium orthoferrite YFeO3.

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.

Two-range magnetoelectric sensor

In this study, we present a two-range magnetoelectric ME sensor design comprising of permendur (alloy of Fe-Co-V), nickel, and lead zirconate titanate (PZT) laminate composite. A systematic study was conducted to clarify the contribution of magnetostrictive layers variables to the ME response over the applied range of magnetic bias field. The two-range behavior was characterized by opposite sign of the ME response when magnetic dc bias is in different sub-ranges. The ME coefficient as a function of magnetic bias field was found to be dependent on the laminate composite structure.

Unveiling hidden ferrimagnetism and giant magnetoelectricity in polar magnet Fe2Mo3O8.

Magnetoelectric (ME) effect is recognized for its utility for low-power electronic devices. Largest ME coefficients are often associated with phase transitions in which ferroelectricity is induced by magnetic order. Unfortunately, in these systems, large ME response is revealed only upon elaborate poling procedures. These procedures may become unnecessary in single-polar-domain crystals of polar magnets. Here we report giant ME effects in a polar magnet Fe2Mo3O8 at temperatures as high as 60 K. Polarization jumps of 0.3 μC/cm2, and repeated mutual control of ferroelectric and magnetic moments with differential ME coefficients on the order of 104 ps/m are achieved. Importantly, no electric or magnetic poling is needed, as necessary for applications. The sign of the ME coefficients can be switched by changing the applied “bias” magnetic field. The observed effects are associated with a hidden ferrimagnetic order unveiled by application of a magnetic field.

Enhanced Curie temperature and magnetoelectric effects in the BaTiO3-based piezoelectrics and CoFe2O4 laminate composites

In the present work, the 0.65BaTiO3–0.35Bi0.5Na0.5TiO3/CoFe2O4 laminate composites targeting lead-free magnetic field sensor, which can be used at high operating temperatures without depolarizing, were prepared by the conventional solid-state sintering method. Excellent dielectric, piezoelectric, magnetic and magnetoelectric properties can be observed in the 0.65BaTiO3–0.35Bi0.5Na0.5TiO3/CoFe2O4 laminate composites compared with the BaTiO3/CoFe2O4 laminate composites. The ME response is dependent on the relative mass ratio of 0.65BaTiO3–0.35Bi0.5Na0.5TiO3 phase and CoFe2O4 phase and the dc magnetic field. The maximum ME coefficient of the 0.65BaTiO3–0.35Bi0.5Na0.5TiO3/CoFe2O4 laminate composites reaches up to about 113mV/cmOe, which is larger than that of the BaTiO3/CoFe2O4 laminate composites (86mV/cmOe).

Enhanced ferroelectric and magnetoelectric properties of the laminated 0.65BiFeO3–0.35BaTiO3/BiY2Fe5O12 composite

In the present work, the laminated 0.65BiFeO3–0.35BaTiO3/BiY2Fe5O12 composite targeting low cost lead-free magnetic field sensor, which was prepared by the conventional solid-state sintering method, was reported. Excellent ferroelectric, magnetic and magnetoelectric properties can be observed in the laminated composite. The ME response was characterized as the functions of frequency and dc magnetic field. The maximum ME coefficient of the composite reaches up to about 0.87mV/cmOe.

High-temperature polymer based magnetoelectric nanocomposites

The use of polymer based magnetoelectric materials for sensing and actuation applications has been the subject of increasing scientific and technological interest. One of the drawbacks to be overcome in this field is to increase the temperature range of application above 100°C. In this way, a nanocomposite material composed by a mixture of two aromatic diamines, 1,3-bis-2-cyano-3-(3 aminophenoxy)phenoxybenzene (diamine 2CN) and 1,3-bis(3-aminophenoxy)benzene (diamine 0CN) and CoFe2O4 (CFO) nanoparticles was designed, fabricated and successfully tested for high temperature magnetoelectric applications.Results revealed that CFO nanoparticles are well distributed within the 0CN2CN polymer matrix and that the addition of CFO nanoparticles does not significantly alter the polyimides structure.The magnetization response of the composite is determined by the CFO nanoparticle content. The piezoelectric response of the 0CN2CN polymer matrix (≈11pCN−1) and the maximum α33 value (0.8mVcm−1Oe−1) are stable over time and decrease only when the composite is subjected to temperatures above 130°C. Strategies to further improve the ME response are also discussed.

Magnetoelectric coupling tuned by competing anisotropies inMn1−xNixTiO3

A flop of electric polarization from $P$$\parallel$$c$ ($P_c$) to $P$$\parallel$$a$ ($P_a$) is observed in MnTiO$_3$ as a spin flop transition is triggered by a $c$-axis magnetic field, $H_{\|c}$=7 T. The critical magnetic field $H_{\|c}$ for $P_a$ is significantly reduced in Mn$_{1-x}$Ni$_x$TiO$_3$ (x=0.33). $P_a$ and $P_c$ have been observed with both $H_{\|c}$ and $H_{\|a}$. Neutron diffraction measurements revealed similar magnetic arrangements for the two compositions where the ordered spins couple antiferromagnetically with their nearest intra- and inter-planar neighbors. In the x=0.33 system, the uniaxial and planar anisotropies of Mn$^{2+}$ and Ni$^{2+}$ compete and give rise to a spin reorientation transition at $T_R$. A magnetic field, $H_{\|c}$, aligns the spins along $c$ for $T_R$$<$$T$$<$$T_N$. The rotation of the collinear spins away from the $c$-axis for $T$$<$$T_R$ alters the magnetic point symmetry and gives rise to a new ME susceptibility tensor form. Such linear ME response provides satisfactory explanation for the behavior of the field-induced electric polarization in both compositions. As the Ni content increases to x=0.5 and 0.68, the ME effect disappears as a new magnetic phase emerges.

Strong Enhancement of Bending-Mode Magnetoelectric Effect by Layer Sequence Choice in Thin Film Bilayer Composites on a Substrate

ABSTRACTMagnetoelectric (ME) effects in bilayer composite cantilevers of magnetostrictive (MS) and piezoelectric (PE) materials on a substrate (Sub) are investigated theoretically for the FeCoBSi-AlN-Si system in open circuit mode and compared for different MS-PE-Sub layer thickness ratios and layer sequence choices. Static and resonant magnetic field excitations, the latter with resonance-enhanced cantilever oscillation, are investigated. Greatly differing behavior of the ME response with layer thicknesses is found for alternate layer sequences and excitation modes with the greatest resonant ME effect for the MS and PE layers on opposite sides of the substrate and the highest static effect for non-central substrates. The unexpected layer sequence systematics of the ME response are explained by the behaviour of the neutral (zero strain) plane in the strain coupled elastic layer stack.

Improved magneto-electric response in Na0.5Bi0.5TiO3–MnFe2O4 composites

Magneto-electric composites comprising Na0.5Bi0.5TiO3 (NBT) and MnFe2O4 (MFO) were fabricated using their fine powders obtained via sol–gel method. X-ray diffraction and scanning electron microscopy results confirmed the single-phase formation of NBT and MFO and the composite nature when these were mixed and sintered at appropriate temperatures. The dielectric constant (er) and dielectric loss (D) decreased with increase in frequency (40–110 MHz). Room temperature magnetization measurements established these composites to be soft magnetic. Further, the nature of these composites were established to be magneto-electric at 300 K. The highest ME response of 0.19 % was observed in 30NBT–70MFO composite. The ME coefficient (α) was 240 mV/cm Oe for the same composition. The present study demonstrated the effectiveness of NBT/MFO as a lead-free multiferroic composite and provides an alternative for environment-friendly ME device applications.

Enhanced Magnetoelectric Response and Phonon Abnormality of Self-assembled Feather-like CoFe2O4-BaTiO3 Nanostructures

ABSTRACTMagnetoelectric (ME) (CoFe2O4)0.3-(BaTiO3)0.7 (CFO-BTO) nanostructures have been synthesized by a combinative using of hydrothermal reaction and polymer-assisted deposition. The feather-like nanostructures have an average diameter of 250nm and lengths up to 5μm, with the single-crystal CFO nanopillars embedded in the BTO matrix. The CFO-BTO nanostructures exhibit good magnetic (Ms=21.0emu/g, Mr=10.4emu/g and Hc=560.7Oe) and ferroelectric properties (Ps=10.5μC/cm2, Pr=5.6μC/cm2), as well as a large ME coefficient of 51.8mV/cmOe. A prominent phonon abnormality has also been detected between 110°C and 140°C. With emphasis on the novel microstructure, the ME response and phonon abnormality of the CFO-BTO nanostructures have been discussed.

Fabrication and magnetoelectric effect of 1–3 type composites with microscale (K,Na)NbO 3-based Pb-free piezoceramic pillars embedded in CoFe 2O 4-epoxy matrix

Microscale magnetoelectric composites with 1–3 connectivity structure were fabricated by a dice-and-fill method. Mechanically sliced microscale pillar arrays of (K,Na)NbO 3-based ceramics were used as the piezoelectric phase, which were embedded in a hybrid matrix composed of ferromagnetic CoFe 2O 4 particles bonded with epoxy. Commercial CoFe 2O 4 nano-powder and CoFe 2O 4 particles derived from a sol–gel method during the filling process were used in two sets of samples, respectively. Obvious ME response signals were detected to be switched with the applied magnetic field. It was deduced that the different ME coefficient values of the two composites were mainly due to the interface morphology between the piezoelectric pillars and the matrix.

Thermodynamic theory of strain-mediated direct magnetoelectric effect in multiferroicfilm–substrate hybrids

A nonlinear thermodynamic theory is developed for the strain-mediated directmagnetoelectric (ME) effect displayed by ferroelectric–ferromagnetic nanostructures. Thiseffect results from transmission of magnetic-field-induced deformations of a thickferromagnetic substrate to a thin ferroelectric overlayer, where the polarization changesdue to lattice strains. The strain-dependent polarization and permittivity of anepitaxial nanolayer (few tens of nm thick) are calculated using the thermodynamictheory of single-domain ferroelectric films. The substrate magnetostrictivedeformations are described phenomenologically, taking into account their nonlinearvariation with magnetic field. The calculations show that ME polarization andvoltage coefficients strongly depend on the initial strain state of the film. ForBaTiO3 andPbTiO3 filmsdeposited on Co0.8Zn0.2Fe2O4, the out-of-plane polarization and related ME coefficients are calculated numerically as afunction of magnetic field parallel to the interface. For films stabilized in themonoclinic phase, this transverse ME response depends on the orientation ofmagnetic field relative to their in-plane crystallographic axes. The longitudinalME coefficient is also evaluated and, for a substrate geometry minimizing thedemagnetizing field, predicted to be comparable to the transverse one. ForBaTiO3 andPbTiO3 films deposited on Terfenol-D, the calculations yield high ME polarization coefficients ∼ 10 − 7 s m − 1 and giant MEvoltage coefficients ∼ 50 V cm − 1 Oe − 1.

Magnetoelectric properties of CoFe 2O 4–BaTiO 3 core-shell structure composite studied by a magnetic pulse method

A new method using a magnetic pulse field in order to measure the ME effect of CoFe 2O 4–BaTiO 3 core-shell structure composite has been developed. This new method combines advantages of both quasi-static and dynamic ones and allows quantifying the whole ME response of the materials. The maximum ME coefficient of this composite is 5.5 and 4.2 mV/cm Oe for longitudinal and transverse measurements, respectively. These values are bigger than those measured by the lock-in technique and can be attributed to the fact that the pulse field method determines the full magnetoelectric coefficient whereas the AC method determines only the part that corresponds to the amplitude of the AC field. Both pulse duration and field sweep rate dH/ dt are found to affect the ME response of the composite.