Converse Magnetoelectric Research Articles

On the effect of polarization direction on the converse magnetoelectric response of multiferroic composite rings

The application domain of composite multiferroic materials with magnetoelectric coupling has been widening on the nano-, micro- and macro-scales. Generally, a composite multiferroic material consists of two, or more, layers of a piezoelectric material and a magnetostrictive material. In turn, the proliferation of multiferroics in more applications is accompanied by a keen focus on understanding the effect of material phases, geometry, bonding interface and arrangement of phases by performing theoretical, numerical and experimental studies to fundamentally elucidate the response. In this experimental study, a focus is given to exploit the effect of the polarization direction of the piezoelectric phase on the overall converse magnetoelectric (CME) response of a composite concentric PZT/Terfenol-D structure. Specifically, radially and axially polarized PZT rings were concentrically bonded to the outer surface of two Terfenol-D rings, respectively. It was found that the maximum, near resonance, CME coefficient of the axially-poled configuration is 443 mG V−1 when tested at 34 kHz, 80 kV m−1 electric field and 784 Oe bias magnetic field. On the other hand, the near resonance CME value for the radially-poled configuration remained nearly constant at 281.9 ± 5.3 mG V−1 between bias magnetic fields of 532 Oe and 1524 Oe at AC electric field of 80 kV m−1 with a frequency of 36 kHz. Interestingly, the CME coefficient of radially-poled composite structure exhibits a saturation behavior, while the CME coefficient for axially-poled structure is distinguished by a single peak. The difference in the response is attributed to the amount strain transduction due to the polarization direction.

Enhanced converse magnetoelectric effect in cylindrical piezoelectric-magnetostrictive composites

Enhanced converse magnetoelectric (ME) effect has been experimentally observed in cylindrical PZT-Terfenol-D piezoelectric-magnetostrictive bilayered composites, where the piezoelectric and magnetostrictive components are coupled through normal stresses instead of shear stresses that act in most of previous multiferroic composites. A theoretical model based on elastodynamics analysis has been proposed to describe the frequency response of converse ME effect for axial and radial modes in the bilayered cylindrical composites. The theory shows good agreement with the experimental results. The different variation tendency of resonant converse ME coefficient, as well as different variation rate of resonance frequency with bias magnetic field for axial and radial modes is interpreted in terms of demagnetizing effect. This work is of theoretical and technological significance for the application of converse ME effect as magnetic sensor, transducers, coil-free flux switch, etc.

Symmetric relationships between direct and converse magnetoelectric effects in laminate composites

Direct magnetoelectric (DME) and converse magnetoelectric (CME) effects are two opposite processes in magnetoelectric (ME) materials. An ME theoretical model about the longitudinal vibration was proposed to research their relationships in a laminate composite based on equivalent circuit. Following the piezoelectric and magnetostrictive constitutive equations, we deduced magnetic-mechanical-electric equations, and then built a symmetric equivalent circuit about the ME coupling, based on which we analyzed the CME and DMD effects equivalently. A simple laminate composite was prepared by bonding Terfenol-D and Pb(Zr,Ti)O3 plates together for a experimental research. Theoretical calculations meet the experimental results very well. The CME and DME effects exhibit enhanced energy transitions at the resonance frequency with a large phase shift of about π. The ME composite shows CME and DME frequency multiplying behaviors and inhomogeneous CME and DMD responses. The CME and DME as well as their resonance frequencies present nonlinear characteristics with the bias magnetic field. The CME resonance frequency is lower than the DME resonance frequency in a same sample. CME decreases while DME increases with the magnetostrictive layer. The theoretical model plays an important role in the comprehensive understanding of ME properties, especially the CME effect, and design of ME devices such as magnetic-electric field sensors, energy harvesting transducers and solid tunable transformers.

The Direct and the Converse Magnetoelectric Effect in Multiferroic Cobalt Ferrite–Barium Titanate Ceramic Composites

We report on a systematic study of the magnetoelectric effect in cobalt ferrite (CoFe2O4)—barium titanate (BaTiO3) ceramic composites with (0‐3) connectivity. Both the converse magnetoelectric coefficient, αC, and the direct voltage magnetoelectric coefficient, αE, were measured in dependence on composition and electric and magnetic bias fields. The strongest ME effect was observed in the composition (1−x) CoFe2O4–xBaTiO3 with x = 0.5 yielding values αC = 25 psm−1 and αE = 3.2 mV/(cm·Oe). We show that the proper conversion between these two coefficients demands knowledge about the dielectric permittivity of the sample. For low BaTiO3 content the dielectric coefficient of the composite yields a better correspondence, whereas for high BaTiO3 content the sample's average dielectric coefficient yields a better match. The influence of mutual orientation of polarization and magnetization on the ME effect is addressed. We found that for measurements performed parallel to the polarization direction (longitudinal effect), the ME coefficient is approximately twice as large and of opposite sign in comparison to the measurements perpendicular to the polarization direction (transverse effect). This difference has been rationalized in terms of the different contributions of the material coefficient tensor components to the ME effect, the demagnetizing factor, and losses. The obtained results provide a better understanding of peculiarities of the ME effect in bulk ceramic composites.

Bidirectional Current–Voltage Converter Based on Coil-Wound, Intermagnetically Biased, Heterostructured Magnetoelectric Ring

We report theoretically and experimentally a passive bidirectional current–voltage ( $I$ – $V$ ) converter, capable of converting input currents into output voltages, and conversely, input voltages into output currents, based on a multiphase heterostructured magnetoelectric (ME) ring. The ME ring has a coil-wound, intermagnetically biased magnetostrictive–piezoelectric (MS–PE) heterostructure, in which an axially polarized PZT PE ceramic ring is bonded between two circumferentially magnetized, intermagnetically biased Terfenol-D short-fiber/NdFeB magnet/epoxy three-phase MS composite rings. In $I$ – $V$ conversion, a current applied to the coil induces a vortex magnetic field to the ME ring, resulting in an open-circuit voltage from the ME ring because of the direct ME effect. In voltage–current ( $V$ – $I$ ) conversion, a voltage applied to the ME ring produces a circumferential magnetic induction due to the converse ME effect, leading to a short-circuit current from the coil. The converter exhibits simultaneously large $I$ – $V$ and $V$ – $I$ conversion factors of $\sim 0.3$ V/A and $\sim 0.2$ mA/V in a broad non-resonance frequency range up to 80 kHz as well as enhanced conversion factors of $\sim 7$ and $\sim 25$ times at the resonance frequency of 122 kHz, respectively.

Converse magneto-electric coefficient of concentric multiferroic composite ring

The converse magnetoelectric (CME) coefficient of an artificial, multiferroic composite cylinder was determined for two interface boundary conditions; specifically epoxy-bonded and shrink-fit. The composite consists of two concentrically bonded rings with the inner and outer rings made from Terfenol-D and lead zirconate titanate, respectively. The diameter of the inner annulus was 25 mm, and the outer ring diameter was 30 mm. Electric fields ranging from 20 kV/m to 80 kV/m with AC components cycling at frequencies from 4 kHz to 50 kHz were applied for actuation of the composite. A magnetic bias field from 0 Oe to 2300 Oe was applied for enhancement of the CME coefficient. It has been found that the maximum CME for epoxy-bonded rings occurs at lower bias magnetic field than shrink-fitted rings. Resonance for the epoxy-bonded composite was found to be 36 kHz whereas the resonant frequency for the shrink-fit structure was 34 kHz. The maximum CME coefficients were approximately 535 mG/V at 100 Vpp and 330 mG/V at 400 Vpp for the epoxy-bonded and shrink-fit configurations, respectively.

Quantification of charge-to-strain mediated interface coupling transfiguration in FE/FSMA multiferroic heterostructures

Thickness modulated direct, local measurement of magnetoelectric (ME) coupling was executed in a high quality sputter deposited PZT/Ni-Mn-In bilayer system grown on Si(1 0 0) substrate. The additive temperature and magnetic-field-driven shape-memory behavior of bottom ferromagnetic (FM) Ni-Mn-In layer, which vanish at ultra-low regime (8 nm), induce fluctuations in the dielectric and ferroelectric (FE) characteristic of PZT. The prominent magnetic-field-modulated P-E loops registered at room temperature in ±400 kV cm−1 electric field range illustrate the presence of giant strain-mediated direct ME coupling in bilayers. This giant strain-mediated direct ME coupling in bilayers can be imputed to magnetic-field-actuated shape-memory behavior of Ni-Mn-In film. The I–V characteristic depicts that the PZT/Ni-Mn-In bilayer endures transition from Ohmic conduction (dominant at low field) to interface-limited Fowler–Nordheim (FN) tunneling prevailing at high electric field. Magnetic measurements of the bilayer revealed that voltage-attuned magnetic anisotropy variation was strongly dependent on the thickness of the bilayer. The normalized magnetization (M/Ms) versus electric field (ME) plots was sketched to cognize the origin of interfacial converse ME coupling. The occurrence of butterfly-shaped ME loops showed the dominance of strain-mediated coupling in the (200 nm/220 nm) bilayer, in contrast to (40 nm/8 nm) heterostructure coupling which was purely charge mediated. The co-existence of charge- and strain-mediated ME coupling in (80 nm/30 nm) structure was evident from quite asymmetric features of ME curves. In 80 nm/30 nm multiferroic heterostructure two reversible and stable magnetic field states of Ni-Mn-In were observed at zero electric field. Such a non-volatile switching of magnetization accomplished by reversing the electric field could prove useful in future MERAM devices.

Giant Converse Magnetoelectric Effect in PZT/FeCuNbSiB/FeGa/FeCuNbSiB/PZT Laminates Without Magnetic Bias Field

We reported a giant self-biased converse magnetoelectric (CME) effect in laminated composites consisting of gradedmagnetostrictive FeCuNbSiB/FeGa/FeCuNbSiB layers sandwiched between two electro-parallel-connected PZT piezoelectric plates. The great different magnetic characteristics (such as magnetic permeability and coercivity) in FeGa and nanocrystalline foil FeCuNbSiB result in a large internal magnetic field and remanent piezomagnetic coefficient in FeCuNbSiB/FeGa/FeCuNbSiB, which account for the giant self-biased CME effect. The experimental results show that: 1) a large remanent CME coefficient of $ 2.228 \times 10^{-3}$ mGs $\cdot $ cm/V is achieved, which can be used for realizing miniature electrically controlled magnetic flux devices; 2) the dynamic switching of magnetic flux between bistable states in PZT/FeCuNbSiB/FeGa/FeCuNbSiB/PZT through a smaller ac voltage ( $1~V_{\mathrm {rms}}$ ) controlling is realized; and 3) the induced magnetic induction B has an excellent linear relationship with applied ac voltage $V_{\mathrm {in}}$ .

Large Converse Magnetoelectric Properties Without Bias in Composite of Rosen-Type Piezoelectric Transformer and Magnetization-Graded Ferromagnetic Material

We designed a magnetoelectric (ME) composite by bonding the graded-magnetostrictive layers of FeCuNbSiB/FeNi-ferromagnetic constant elasticity (FACE) on the output section of the Rosen-type transformer, in which a much higher self-biased converse magnetoelectric (CME) coefficient is obtained. Due to the different magnetic characteristics of nanocrystalline foil FeCuNbSiB and FeNi-FACE (such as magnetic permeability and coercivity), the FeCuNbSiB/FeNi-FACE layer exhibits an internal magnetic bias field. When the ac voltage is applied on the input section of the transformer, a large strain is mechanically transferred to the graded-magnetostrictive layers due to the stress concentration effect at full-wavelength resonance frequency. Therefore, the large strain in the output section of the Rosen-type transformer associated with the internal magnetic bias field in FeCuNbSiB/FeNi-FACE leads to a large self-biased CME coefficient. The experimental results demonstrate that: 1) a large remnant CME coefficient of 0.02058 mG/V is achieved, which is $\sim 17$ times higher than the previous results; 2) two stable magnetic flux states are generated by switching a smaller electric field of 10 V/cm ON/OFF alternately without magnetic bias field, which can be used as miniature electric-field-written high-density ME memory devices with lower energy consumption; and 3) the composite shows an approximately linear relationship between applied ac voltage $V_{\rm in}$ and induced magnetic induction B .

Orientation-Dependent Properties of CoFe2O4-Bi3.15Nd0.85Ti3O12 Bilayer Multiferroic Films Prepared by a Sol–Gel Method

Lead-free bilayer multiferroic films of CoFe2O4 (CFO) and oriented Bi3.15Nd0.85Ti3O12 (BNT) were deposited on a conventional Pt(111)/Ti/SiO2/Si(100) substrate by use of a sol–gel method. BNT layers with different preferred orientations were grown by use of different spinning and annealing processes. The ferroelectric, ferromagnetic, and magnetoelectric (ME) properties of the CFO–BNT bilayer thin films were investigated at room temperature. a-Axis-oriented bilayer films had larger ME voltage coefficients and larger converse ME response than c-axis-oriented films. This study shows that the orientation of the BNT layer has a stress-mediated interfacial effect which can substantially affect the magnetoelectric coupling behavior of the bilayer structures.

In-plane longitudinal converse magnetoelectric effect in laminated composites: Aiming at sensing wide range electric field

The converse magnetoelectric (CME) effect, a coupling effect resulted from compositing piezoelectric phase and piezomagnetic phase, is explored insightfully concerned with applying chip-scale CME composite into extensive electric field measurement. To establish the in-plane longitudinal CME effect, comparable mathematical models elastomechanical tensile model and elastomechanical flexural model are proposed. Grounded on generalized theoretical frameworks, the models utilized some classical magnetoelectric modeling methods. Furthermore, groups of CME composite are taken as examples to simulate and experiment for consistency verification. What highlights in the proposed models is for the purpose of forecasting and evaluating the most favorable composite and structure for CME effect applied in sensing wide range electric field.

Enhanced self-biased direct and converse magnetoelectric effect in Pb(In1/2Nb1/2)O3–PbTiO3/NiFe2O4 bi-layer laminate composite

The direct magnetoelectric (DME) effect and converse magnetoelectric (CME) effect are investigated in bi-layer ferroelectric [0.65 Pb(In1/2Nb1/2)O3–0.35 PbTiO3]–ferrite [NiFe2O4] laminate composite prepared by epoxy bonding. The magnetoelectric (ME) properties of bi-layer composite is studied at low frequency (1 kHz) and at electromechanical resonance frequencies under external bias field (H dc ). The laminate composite shows a DME coefficient (α DME ) and CME coefficient (α CME ) of 103 mV/(cm Oe) and 0.04 (mG cm)/V respectively at 1 kHz with a H dc of 110 Oe. Moreover the α DME and α CME shows non-zero value in the absence of external bias field, which signifies the presence of self-biased ME effect in this laminate composite. Under resonance condition, ME coupling enhanced two orders of magnitude compared to low frequency value. A large self biased α DME of 8 V/(cm Oe) and α CME of 5 (mG cm)/V is achieved at electromechanical resonance.

Adjustable-Voltage-Ratio Magneto-Electric Transformer

This paper presents a novel adjustable-voltage-ratio (AVR) transformer made using magneto-electric materials. Given a fixed-amplitude alternating current voltage input, the AVR transformer can output an ac voltage whose amplitude can be adjusted continuously from zero volts to the maximum value determined by the design. The core(s) of the AVR transformer are laminated and made of bonded layers of Metglas foils and lead zirconate titanate (PZT) sheets. By adjusting the voltage applied on the PZT sheets of the core, the magnetic reluctance of the core can be altered to control the magnetic flux in the core by utilizing the converse magneto-electric (CME) effect. Thus, the voltages inducted by the time-changing magnetic fluxes can be controlled. This novel concept provides a new solution to electric power control and conversion.

Anisotropy, Magnetostriction and Converse Magnetoelectric Effect in Dy Substituted Ni Ferrite

NiFe2-xDyxO4 (x = 0, 0.1) compounds were prepared by solid state reaction. Room temperature X-ray diffraction confirmed the formation of the compounds in cubic inverse spinel phase with the space group ▪ Increments in the lattice constant were observed upon partial substitution of Fe3+ by Dy3+. While both magnetization and cubic magnetocrystalline anisotropy (K1) decreased with increasing temperature, with Dy3+ substitution, at any given temperature the magnetization decreased and K1 increased. A quantitative observation of direct magnetoelectric (DME) effect and qualitative observation of converse magnetoelectric (CME) effect in NiFe1.9Dy0.1O4 compound, describe its multiferroic nature.

Giant self-biased converse magnetoelectric effect in multiferroic heterostructure with single-phase magnetostrictive materials

Giant self-biased converse magnetoelectric (CME) effects with obvious hysteretic behaviors are systematically investigated in two-phase SmFe2/PZT [Pb(Zr1−x, Tix)O3] multiferroic laminates at room temperature. Taking advantage of the huge anisotropic field of SmFe2 plate, large remnant CME coupling is provoked by this field instead of permanent magnets to bias the laminate. Consequently, bitable magnetization status switching is realized through a smaller ac voltage far below the electric coercive field in the absence of magnetic bias field. Experiments demonstrate that a large remnant CME coefficient (αCME) of 0.007 mG/V is achieved, exhibiting ∼50 times higher CME coefficient than the previous laminate composite multi-phase magnetostrictive plates. These results provide promising applications for realization of high-density magnetoelectric random access memories (MERAMs) devices with lower energy consumption.

Uniformity of direct and converse magnetoelectric effects in magnetostrictive–piezoelectric composites

In this paper, we theoretically and experimentally confirmed the uniformity of magnetoelectric (ME) coupling coefficients for the direct and converse ME (DME and CME) effects in longitudinal-transverse (L-T) mode magnetostrictive–piezoelectric two-phase composites, both at low frequencies and in the electromechanical resonance region. We also discussed the flaws in previous measurements of the ME coupling coefficients, which led to misunderstandings in the uniformity between the DME and CME effects. Our current work provided a correct method to correctly understand ME coupling in magnetostrictive-piezoelectric two-phase composites.

Converse magnetoelectric effect in laminated composite of Metglas and Pb(Zr,Ti)O3 with screen-printed interdigitated electrodes

In this study, we investigate the converse magnetoelectric (CME) effect in a laminated composite consisting of Metglas ribbons and Pb(Zr,Ti)O3 (PZT) plate with screen-printed interdigitated electrodes and operating in longitudinal magnetization and longitudinal polarization (L-L) mode. Large CME coefficients of 0.134 G·cm/V at frequency of 1 kHz and 2.75 G·cm/V at resonance frequency of 43.5 kHz under a small bias magnetic field of 7 Oe are achieved. The large CME effect can be attributed to the L-L mode and low mechanical loss of the Metglas/PZT laminated composite.

Film size-dependent voltage-modulated magnetism in multiferroic heterostructures.

The electric-voltage-modulated magnetism in multiferroic heterostructures, also known as the converse magnetoelectric (ME) coupling, has drawn increasing research interest recently owing to its great potential applications in future low-power, high-speed electronic and/or spintronic devices, such as magnetic memory and computer logic. In this article, based on combined theoretical analysis and experimental demonstration, we investigate the film size dependence of such converse ME coupling in multiferroic magnetic/ferroelectric heterostructures, as well as exploring the interaction between two relating coupling mechanisms that are the interfacial strain and possibly the charge effects. We also briefly discuss some issues for the next step and describe new device prototypes that can be enabled by this technology.

Inequivalence of direct and converse magnetoelectric coupling at electromechanical resonance

Resonant direct and converse magnetoelectric (ME) effects have been investigated experimentally and theoretically in FeGa/PZT/FeGa sandwich laminate composites under the same electric and magnetic bias conditions. Resonant direct ME effect (DME) occurs at antiresonance frequency while resonant converse ME effect (CME) occurs at resonance frequency. The antiresonance and resonance frequencies have close but different values under identical bias conditions. The magnitudes of resonant effective ME coefficients for direct and converse ME effects are also not equal. A model was developed to describe the frequency response of DME and CME in laminate composite, which was in good agreement with experimental results.

The Low‐Temperature Cosintering of Cobalt Ferrite and Lead Zirconate Titanate Ceramic Composites

Magneto‐electric (ME) ceramic composites of cobalt ferrite (CoF) and lead zirconate titanate (PZT) were prepared by mechanical mixing of the constituent powders followed by cosintering. The cosintering conditions for nano‐sized CoF and submicrometer‐sized PZT powders were studied in detail. It was found that the CoF powder needs to be presintered at 700°C for 2 h to minimize the differences in the sintering kinetics of the constituent powders. Despite the low cosintering temperatures (900°C–1000°C) the interdiffusion of the cations from both phases was confirmed with energy‐dispersive X‐ray analysis and X‐ray diffraction. Efforts were made to optimize the cosintering conditions to prepare dense ceramic ME composites, which showed the converse ME effect.