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Temperature dependence of the magnetoelectric (ME) coefficient was studied for FeBSiC/Pb(Zr, Ti)O3(PZT)/FeBSiC laminates over temperature range of -35~85 °C. The variation in ME coefficient as a function of temperature was found to be significantly dependent on the volume fraction of FeBSiC layers and the lateral dimension of the laminate composites. Our results show that minimum number of FeBSiC layer with smaller lateral dimension can provide more stable ME coefficient in wide temperature range, due to the competition of the effects of temperature influenced piezoelectricity, magnetostriction, and mechanical properties of the constituents and the interfacial bonding layer. This finding indicate that it is beneficial to promote miniaturization of the ME composite based devices in view of temperature stability. [ABSTRACT FROM AUTHOR]

Voltage-modified Kerr magnetometer has been widely used to measure the voltage-modulated magnetic properties in multiferroic magnetic/ferroelectric heterostructures, where the Kerr signal change is considered to be in proportion to magnetization change, i.e., the magneto-optical Kerr effect. However, the total Kerr signal changes might also incorporate contribution from the electro-optical effect of the ferroelectric layer in the multiferroic heterostructure. Here, we evaluate quantitatively, by combining analytical calculations with experimental observations, such electro-optical contribution in the total voltage-induced Kerr signal changes with comparison to those from Kerr effect via converse magnetoelectric coupling. Influences of several parameters, including the magnetic film thickness on the Kerr signal changes, are also investigated. [ABSTRACT FROM AUTHOR]

We show that, using phase-field simulations, large voltage-driven perpendicular magnetic domain switching can be realized in magnetic-ferroelectric nanoislands with relieved substrate constraint, which is difficult in continuous multiferroic layered thin films due to significant substrate clamping. The as-grown magnetic and ferroelectric domain structures in the heterostructured nanoislands can be tailored by engineering their respective geometric sizes and/or the underlying substrate strain. Influences of the lateral size of the island on the dynamic voltage-driven magnetic domain switching are addressed, whereby an optimum lateral size is identified for illustration. Thus, such three-dimensional multiferroic nanoislands should provide great flexibilities for designing novel high-density spintronic/microelectronic devices with purely voltage-driven means. [ABSTRACT FROM AUTHOR]

The converse magnetoelectric (ME) effect was investigated in bi-layered Ni/Pb(Zr0.52Ti0.48)O3 (PZT) thin films grown on Si substrates, with different thicknesses of Ni thin layers. By using an AC-mode magneto-optical Kerr effect method, it was revealed that the electric-voltage induced magnetization variation was dependent on the thickness of the Ni thin layer. The results showed that the Ni/PZT bilayered films with thick (about 40 nm) Ni films presented a dominative strain mediated ME coupling, whereas an interface-charge and strain co-mediated ME coupling might coexist in the Ni/PZT bilayered films with decreasing thickness (e.g., about 10 nm) of Ni films. [ABSTRACT FROM AUTHOR]

Switchable voltage modulation of the magnetic properties is reported in different multiferroic bilayers with magnetic films grown on pre-poled ferroelectric substrates, based on the magneto-optical Kerr effect observations. The dynamic voltage control of the magnetic coercive field (Hc) is dependent not only on the materials properties of each ferroic layer, but also on the bias voltage history. The Hc versus electric field behaviors essentially track the dependence of the piezostrains of the substrates on the bias voltage. The observations demonstrate that Hc in such multiferroic bilayers can be controlled by voltage via strain-mediated magnetoelectric coupling and that the Hc change is not an artifact due to a heating effect. [ABSTRACT FROM AUTHOR]

The electric-field-induced in-plane magnetic domain switching in magnetic/ferroelectric (FE) layered heterostructures was studied using phase-field simulations. In particular, we chose the CoFe2O4 (CFO) magnetic film and the Pb(Zn1/3Nb2/3)O3-PbTiO3 (PZN-PT) FE layer as a representative example due to their strong respective magnetoelastic and piezoelectric couplings. In-plane 90° magnetic domain switching in the CFO film was observed when a transverse electric field was applied to the PZN-PT layer. The detailed switching behaviors as well as the corresponding magnetic domain structures are presented for CFO films with different geometric sizes and initial magnetization configurations. The effect of a dynamic electric field on the switching process, i.e., a time-dependent electric-field-induced magnetic domain switching, is also discussed. [ABSTRACT FROM AUTHOR]

A strain-mediated magnetoelectric random access memory with electric-field-writing is presented, which consists of a magnetic tunnel junction (MTJ) in intimate contact with a ferroelectric (FE) layer. The calculations show that the magnetization vector in the free layer of the MTJ unit can switch in-plane by 90° upon applying an appropriate electric field to the FE layer, as compared to the common 180° reversal induced by magnetic field or spin-current. A perfect interface between the FE layer and the MTJ is assumed. The free layers used for illustration include either (001)-oriented or polycrystalline magnetic films of Fe-Co alloy, CoFe2O4 (CFO), Ni, and Fe3O4. Among them, the (001)-oriented FeCo and CFO films with positive magnetocrystalline anisotropy constant (i.e., K1 >0) show an abrupt magnetization switching, while a gradual magnetization switching takes place in the (001)-oriented Ni and Fe3O3 films with K1<0 as well as the polycrystalline films. Such electric-field-induced in-plane magnetization switching can result in a remarkable change in the MTJ's electric resistance. In particular, hysteretic dependence of the device resistance on the applied electric field is obtained for the cases of the (001)-oriented FeCo and CFO free layers that exhibit the abrupt magnetization switching, whereby a nonvolatile information storage process can be achieved. The influence of the shape of the free layer on both magnetization and resistance switching features is discussed. [ABSTRACT FROM AUTHOR]

An electric-field modulation of the magnetic properties through converse magnetoelectric effect was reported in Fe films directly grown on BiScO3–PbTiO3 (BSPT) ceramics based on the magneto-optical Kerr effect. When an electric field was applied on the piezoelectric BSPT ceramics, the coercive field (Hc) of the ferromagnetic Fe films changed dramatically and an upto 60% change in Hc was observed. The Hc electric field curve essentially tracked the dependence of the piezostrain of the BSPT ceramics on the electric field, which definitely demonstrated the magnetic-mechanical-electric coupling in such film-on-substrate composite structures. [ABSTRACT FROM AUTHOR]

BiFeO3 films with different thicknesses and crystallographic orientations were grown on LaNiO3-buffered Si substrates via a modified chemical route. Remarkable size effect in ferroelectric behavior was observed with thicker films exhibiting a larger polarization value, due to combined depolarization effect and microstructure of the BiFeO3 films. High resolution transmission electron micrograph revealed a complex strain state in the BiFeO3 films, and the net magnetic moment induced by the canting of the antiparallel spins was arranged in disorder in thicker films, presenting a spin-glass state; while in the thinner BiFeO3 films, the disorder spins turned to be orderly arranged to induce a ferromagnetic behavior. Thus there exists a competition between ferroelectric and magnetic behaviors as film thickness changes. Furthermore, magnetoelectric coupling was observed in the BiFeO3 films with a magnetic-field-induced electrical voltage of around 3.5 μV/Oe. [ABSTRACT FROM AUTHOR]

The effect of Mn doping on crystal structure, electric and magnetic properties of BiFeO3 thin films prepared via a chemical deposition method on (111) Pt/Ti/SiO2/Si substrates was studied. The substitution of Fe ions by a small amount (5%) of Mn ions could facilitate the stabilization of Fe3+ in BiFeO3 thin films, while larger substitution (e.g., 10% and 15% Mn substitution) could lead to the increase in Fe2+ concentration. Well saturated polarization hysteresis loops were observed in the Mn-doped BiFeO3 films, with remanent polarization value of 32 μC/cm2 and 53 μC/cm2 for the 5% and 10% Mn-doped BiFeO3 films, respectively. Mn substitution also affect ferroelectric domain structures and microstructures of the films. It was observed that Mn substitution does not affect the intrinsic weak magnetism of BiFeO3. The enhanced ferroelectric and weak magnetic behaviors by Mn substitution were further studied through the analysis of the bonding state of Fe and Mn ions. [ABSTRACT FROM AUTHOR]

Multilayered heterostructures, BaTiO3/(NiFe2O4/BaTiO3)n (n=1,2,3,4), with alternating ferroelectric BaTiO3 and ferrimagnetic NiFe2O4 layers were epitaxially grown on (001)-SrTiO3 substrates via pulsed laser deposition technique. The multilayered heterostructures with a total thickness of about 120 nm preserved ferromagnetic and ferroelectric properties at room temperature, strongly depending on the number n due to interface and thickness size effect. The influence of the interface on the magnetoelectric coupling effect in the multilayered thin films were further confirmed by observed increasing magnetoelectric coefficients with the number n. [ABSTRACT FROM AUTHOR]

Multiferroic bilayered thin films consisting of Pb(Zr0.52Ti0.48)O3 (PZT) and CoFe2O4 (CFO) layers of different relative thicknesses were prepared on a general Pt/Ti/SiO2/Si substrate via a simple solution processing. The influence of the thickness fraction on their properties including ferroelectric, ferromagnetic, and magnetoelectric properties in the PZT-CFO bilayered thin films was investigated. Our results showed that the thickness fractions (or relative thicknesses) of the layers have a significant effect not only on the magnetic and electric properties of the bilayered films but also on their magnetoelectric response. The bilayered thin films with the intermediate thickness fraction of around 0.6 exhibited a maximum magnetoelectric effect. [ABSTRACT FROM AUTHOR]

BaTiO3 films were grown on highly dense CoFe2O4 ceramics via pulsed laser deposition. Microstructural characterization showed that polycrystalline BaTiO3 thin films with grain size of about 70 nm were grown on the CoFe2O4 ceramics. BaTiO3 films showed good ferroelectric feature. An obvious magnetoelectric response, which had the same bias-dependent trend as the piezomagnetic coupling coefficient of CoFe2O4 ceramics, was observed in the multiferroic film-ceramic composites. Phenomenological theoretical analysis shows that there is plenty of room for further enhancing the magnetoelectric response of such film-substrate composites. [ABSTRACT FROM AUTHOR]

The residual stresses due to high-temperature processing in micromultilayer ceramic capacitors (MLCCs) with various thicknesses and numbers of dielectric ceramic layers were investigated by using a three-dimensional elastoplastic finite element model with temperature-dependent material properties taken into account. For comparison, an explicit analytical solution for the in-plane residual stress in the dielectric ceramic layer was derived. Both the numerical results and the analytical model showed that the thickness ratio of the dielectric layer to electrode layer has a dominant impact on the residual stress states. There exists a critical thickness for the dielectric ceramic layer in MLCCs in the case of a given thickness of the electrode layer, below which both high tensile out-of-plane stresses and high compressive in-plane stresses could cause the cracking of the brittle dielectric layers near the electrode tips and/or the debonding of the electrode/dielectric interface. [ABSTRACT FROM AUTHOR]

An expression for the description of the frequency-dependent magnetoelectric response in hybrid magnetostrictive-piezoelectric multiferroic composites is presented by using constitutive and motion equations. The calculations show that the values of the magnetoelectric voltage coefficient of the composites in the region of an electromechanical resonance sharply increase and exceed a low-frequency value by more than two orders of magnitude, which is in reasonable agreement with recent experimental data. The enhanced magnetoelectric response at the electromechanical resonance is dependent on the interface losses. [ABSTRACT FROM AUTHOR]

Magnetoelectric (ME) Pb(Zr0.52Ti0.48)O3 (PZT)–NiFe2O4 bulk composites with various PZT volume fractions were prepared. The ME coupling coefficient, impedance, and flux density versus the frequency were measured. The magnetic bias and PZT volume fraction in the composites are investigated to optimize the ME output. It is revealed that ME resonances are caused by electromechanical resonance in the piezoelectric phase and magnetomechanical resonance in the magnetostrictive phase. Maximum magnetoelectric voltage coefficient resonance values of 6.7 V/cm Oe at 132.6 kHz and 6.12 V/cm Oe at 427.2 kHz for the composite with optimized PZT volume fraction of 0.55 were obtained at optimized magnetic bias of 0.6 kOe. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report on a systematic experimental investigation of a class of multiferroic, three-phase particulate composite of Tb–Dy–Fe alloy, lead–zirconate–titanate (PZT), and polymer, in which a small volume fraction f of Tb–Dy–Fe alloy particles without and with the particle surfaces modified by an inactive surfactant are dispersed in PZT/polymer mixture. The measured electrical properties demonstrate that a percolation transition occurs in the three-phase composite as in normal two-phase metal–insulator continuum media. Our piezoelectric measurements also show a percolation transition which provides an experimental test of the critical behavior of the piezoelectric composites with conductive fillers in the percolation regime. Accordingly, the multiferroic composite exhibits increasing magnetoelectric response in the low f range, but such magnetoelectric response sharply drops when f approaches the percolation threshold above which the composite becomes a conductive, magnetostrictive composite only. The inactive interface between the alloy particles and the PZT/polymer matrix induced by coating surfactant on the alloy particles produces a negative effect on the piezo- and magnetoelectric properties of the composite. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The effective magnetostriction of a two-phase fibrous composite and a two-dimensional polycrystal assembled from cylindrical magnetostrictive cubic crystals is studied. For the considered systems, we show that there exist exact microstructure-independent relations between the effective magnetostriction and the effective elastic moduli. The fibers could be aligned identically or randomly oriented in the transverse plane. There is no restriction on the cross-sectional shapes of the fibers, nor on the arrangement of transverse geometry of the composite aggregate. These connections imply that knowledge of the effective elastic moduli will readily provide the effective magnetostriction of the composite medium. [ABSTRACT FROM AUTHOR]

A magnetoelectric (ME) hybrid structure is constructed by an efficient coupling between magnetostrictive Terfenol-D (Tb[SUB0.27-0.30]Dy[SUB0.73-0.70]Fe[SUB1.90-1.95])/epoxy and piezoelectric lead-zirconate-titanate [(Pb(Zr[SUB0.52]Ti[SUB0.48])O[SUB3]]/epoxy composites. Significant ME effect produced by the piezoelectric k[SUB31] coupling with the longitudinal vibration of the magnetostrictive component over a wide range of frequency is observed. It is revealed that the ME effect can be enhanced by applying an optimized magnetic bias. A magnetoelectric voltage coefficient as high as 8700 mV/cm Oe is recorded at the resonance frequency of 59.2 kHz for the structure with an optimized magnetic bias of 0.7 kOe. Our measurement confirms that the eddy current loss remains negligibly small at an operating frequency as high as ∼200 kHz, predicting very promising applications of the present ME structure. [ABSTRACT FROM AUTHOR]

A class of multiferroic, three-phase particulate composite of Tb-Dy-Fe alloy, lead-zirconate-titanate (PZT) and polymer are systematically investigated. A small volume fraction f of Tb-Dy-Fe alloy particles without and with the particle surfaces modified by an inactive surfactant is dispersed in the PZT/polymer mixture.

A novel characterization method is presented to directly observe the pure converse magnetoelectric (ME) effect, i.e., the electric-field modification of magnetization, in composite magnetic/ferroelectric (FE) layered thin films. A low-frequency AC electric-voltage, rather than DC voltage bias, is applied to the FE thin films to minimize the leakage current, whereby the possible side effect of heating can be avoided. In particular, by synchronizing the frequency of the Kerr signal detector to the AC actuation voltage bias, the voltage-induced change of the magnetization in the magnetic films can be in situ recorded even under zero external magnetic fields. For illustration, this method is applied to two similar magnetic/FE composite thin films, with significant strain-mediated converse ME coupling being demonstrated in both cases. [ABSTRACT FROM AUTHOR]