Magnetoelectric Effect

Temperature characteristics of resonant magnetoelectric effect in bilayer structures consisting of langatate, lead zirconate titanate, nickel, and amorphous ferromagnetic Metglas layers have been investigated. The measurements were performed in the temperature range of 150-400 K. The influence of the ferromagnetic and piezoelectric layer’s parameters on the temperature dependence of resonant frequency and magnetoelectric coefficient αE has been demonstrated. The results can be used to develop magnetoelectric magnetic field sensors.

The magnetoelectric effect is experimentally studied in a multilayer nickel zinc ferrite-lead zirconate titanate structure at frequencies of 10 -3 -10 Hz that is placed in a harmonically modulated magnetic field of amplitude to 1 kOe. The nonlinearity of the ferrite magnetostriction and the conductivity of the films are shown to double the frequency and distort the shape of the magnetoelectric voltage. The magnetoelectric signal amplitude decreases linearly with decreasing field modulation frequency. The feasibility of using the magnetoelectric effect to detect ultralow-frequency magnetic fields is demonstrated.

Studies on (i) microwave magnetoelectric (ME) interactions in ferrite-piezoelectric bilayers and (ii) electric field tunable ME signal processing devices are discussed. An electric field E applied to the bilayer produces a mechanical deformation in the piezoelectric, resulting in a frequency (δf) or magnetic field shift (δH) in the ferromagnetic resonance (FMR) absorption spectra for the ferrite. Bilayers of single crystal yttrium iron garnet (YIG) and lead zirconium niobate-lead titanate (PMN-PT) were studied. The strength of ME coupling A = δH/E has been measured from FMR absorption profiles at 1-10 GHz for E = 0-10 kV/cm. Variation in δf or δH with E is found to be linear. A decrease in the ME coefficient is measured as the thickness of YIG film is increased. The fabrication and characterization of electric field tunable YIG/PMN-PT resonators are discussed.

Thick film layered magnetoelectric composites consisting of ferromagnetic and ferroelectric phases have been synthesized with nickel ferrite (NFO), cobalt ferrite (CFO), La 0.7 Sr 0.3 MnO 3 (LSMO), or La 0.7 Ca 0.3 MnO 3 (LCMO) and lead zirconate titanate (PZT). Structural, magnetic and ferromagnetic resonance characterization shows evidence for defect free ferrites, but deterioration of manganite parameters. The resistivity and dielectric constants are smaller than expected values. The magnetoelectric effect (ME) is stronger in ferrite-PZT than in manganite-PZT. The ME voltage coefficient α E at room temperature is the highest in NFO-PZT and the smallest for LCMO-PZT. The transverse ME effect is an order of magnitude stronger than the longitudinal effect. The magnitude of α E correlates well with magnetic permeability for the ferrites.

The dependence of the resonant direct magnetoelectric effect on temperature is studied experimentally in planar composite structures. Samples of rectangular shapes with dimensions of 5 mm × 20 mm employed ferromagnetic layers of either an amorphous (metallic glass) alloy or nickel with a thickness of 20-200 µm and piezoelectric layers of single crystalline langatate material or lead zirconate titanate piezoelectric ceramics with a thickness of 500 µm. The temperature of the samples was varied in a range between 120 and 390 K by blowing a gaseous nitrogen stream around them. It is shown that the effective characteristics of the magnetoelectric effect-such as the mechanical resonance frequency f r , the quality factor Q and the magnitude of the magnetoelectric coefficient α E at the resonance frequency-are contingent on temperature. The interrelations between the temperature changes of the characteristics of the magnetoelectric effect and the temperature variations of the following material parameters-Young's modulus Y, the acoustic quality factor of individual layers, the dielectric constant ε, the piezoelectric modulus d of the piezoelectric layer as well as the piezomagnetic coefficients λ (n) of the ferromagnetic layer-are established. The effect of temperature on the characteristics of the nonlinear magnetoelectric effect is observed for the first time. The results can be useful for designing magnetoelectric heterostructures with specified temperature characteristics, in particular, for the development of thermally stabilized magnetoelectric devices.

Self-assembled nanocomposite films containing ferroelectric and ferromagnetic phases have attracted enormous research interest because they are the most promising candidates for practical multiferroic applications. However, obtaining a genuine magnetoelectric (ME) coupling effect is still challenging in this research area. To substantially improve the ME effect, new heterostructure designs with efficient strain control between two phases are urgently needed. Herein, a novel three-dimensional (3D) nanocup architecture of a heterostructure film is developed. To establish the unique architecture, a heavily Co, Fe-doped ferroelectric Bi3.25La0.75Ti3O12(BLT) target was used during the growth of BLT thin films via pulsed laser deposition. Consequently, 3D nanocup-structured CoFe2O4(CFO) particles formed inside the BLT via spontaneous nucleation and agglomeration. The 3D nanocup BLT-CFO film exhibited magnetically controlled reversible dielectric switching, which is direct evidence of stro...

A polarized light beam modifies the equilibrium tensors associated with any measurable property of a crystal. The light-induced linear magnetoelectric susceptibility and electric current density of bismuth ferrite (BFO) are investigated theoretically using their expansion in Wigner spherical functions. Under illumination, the interplay between magnetoelectric and photovoltaic properties yields the emergence in the paramagnetic and multiferroic phases of BFO of linear photomagnetoelectric tensor components changing sign in domains with opposite electric polarization or magnetization, and to magnetophotocurrents changing sense in opposite ferroelectric and magnetic domains.

When electric and magnetic fields are applied together on a magnetoelectric antiferromagnet, the domain state is subject to reversal. Although the initial and final conditions are saturated singledomain states, the process of reversal may decompose into local multi-domain switching events. In thin films of Cr2O3, the magnetoelectric coercivity and the switching speed found from experiments are considerably lower than expected from magnetic anisotropy, similar to Brown's paradox in ferromagnetic materials. Multi-domain effects originate because antiferromagnetic domain walls are metastably pinned by lattice defects, not due to reduction of magnetostatic energy, which is negligible. This paper theoretically analyzes domain reversal in thin-film magnetoelectric antiferromagnets in the form of nucleation, domain wall propagation, and coherent rotation. The timescales of reversal mechanisms are modeled as a function of applied magnetoelectric pressure. The theory is assessed with reference to latest experimental works on magnetoelectric switching of thin-film Cr2O3: domain wall propagation is found to be dominant and responsible for switching in the experiments. The results bear implications in the energy-delay performance of ME memory devices utilizing antiferromagnetic insulators, which are prospective for nonvolatile technology.

Spinel ferrites of the chemical formula M x Ni 1-x Fe 2 O 4 (M = Mn, Zn) were prepared by minimum doping or contamination values x = %0, %5 through the co-precipitation process. The samples synthesized by Hydrazine hydrate and ethylene glycol surfactant and were annealed at 800 °C. The XRD, SEM, and TEM analyses were investigated. To investigate the frequency-dependent of magnetic permeability (µ) and magnetic loss in NiFe 2 O 4 ferrite, the eddy current and hysteresis loss were measured by impedance spectroscopy and VSM analysis for all samples. In considering the electrical parameters of impedance spectroscopy in the range of 10-3-10 6 Hz, the frequency-dependent of real (Z') and imaginary (Z'') part of doped specimens increased and consequently conductivity decreased. All three samples exhibit frequency-dependent dielectric parameters and electric modulus, and might have a potential to react to electromagnetic waves. The µ' value extracted from dielectric data, is negative in low frequency regions and approach nearly zero value by enhancing the frequency for all three samples. The magnetic loss enhanced in doped samples that can be explained by the peak point of eddy current loss in the high frequency range for pure and doped samples. M-H hysteresis loop specified that the saturation magnetization (M s) increased by Mn and Zn-doped multi-domain Ni ferrite while the coercivity field (H c) decreased. The hysteresis loss increased in Zn-doped and diminished in Mn-doped Ni ferrite. Other magnetic parameters including: anisotropy constant (K), anisotropy field (H k), magnetic moment (n B) and initial permeability µ i were calculated by hysteresis loop.

In exhibiting the coercivity of permanent magnets, magnetocrystalline anisotropy plays an important role. Since itinerant magnetic states are responsible to direct interactions among magnetic sites, d states are expected to be sensitive to lattice strain. In this work, we report strain effects on magnetic properties theoretically studied by first-principles calculations for Y 2 Fe 14 B, where Y is a prototypical f 0 rare-earth element [1]. To analyze the local magnetic anisotropy, we developed a method to decompose the magnetic-anisotropy energy into contribution from each atomic site as well as from couplings among specific atomic orbitals, where the sum rule is satisfied by including indirect off-site contributions in the second-order perturbation. The OpenMX code is used for first-principles calculations. The lattice constants of Y 2 Fe 14 B are changed from the equilibrium values independently, where we found the uniform compression enhances the perpendicular magnetic anisotropy. Our magnetic-anisotropy decomposition identified dominant magnetic site and orbital couplings. Our method will enable us to study the anisotropy at microstructure interfaces. [1] Z.

magnetism. The single phase BiFeO 3 (BFO) has attracted enormous attention due to its multiferroic properties at room temperature. However, BFO has drawbacks such as high leakage current due to the presence of oxygen vacancies and Fe 2+ ions. Another issue is its antiferromagnetic character due to the cycloidal spin structure . Hence, intensive research is being carried out to explore the possibilities to refine and improve its properties in order to make it suitable for applications in memory devices, spintronics and sensors . Attempts have been made to reduce the leakage current density by doping at Bi 3+ site by suitable ions. It is thought that vacancies created by the removal of Bi 3+ ions are compensated by the substitution of rare earth ions, which reduces the conductivity. Replacement of Fe 3+ ions by other transition metal ions such as Cr 3+ , Ti 4+ , Mn 3+ and Sc 3+ is expected to provide better electrical stability by reducing valence fluctuations in Fe ions. There are a few studies on the Gd doped BFO reported so far. Mukherjee et al. experimented that Bi 1-x Gd x FeO 3 with x = 0, 0.01, 0.05 and 0.10 exhibits improved magnetic, electric and magnetoelectric properties. Mohammadi et al. [11] investigated the effects of Gd on the magnetic, electric and structural properties of BiFeO 3 nanostructures synthesized by co-precipitation method followed by microwave sintering. Results of Kim et al. [12] on (Gd,V) doped BFO revealed improved electrical properties with low leakage current density and increased remnant polarization. To the best of author's knowledge, so far there are no reports on (Gd, Cu) doped BFO. So, the main focus in the present work is to study the effect of simultaneous doping of (Gd, Cu) in the BFO lattice on the ferroelectric and dielectric properties. With a rare earth ion Gd and a nonmagnetic ion Cu at Bi and Fe site respectively would reveal the room temperature multiferroic properties of BFO and for comparison effect Abstract The influence of Gd dopant and (Gd, Cu) dopants on the ferroelectric, dielectric and magnetoelectric properties of single phase BiFeO 3 (BFO) were investigated. Nanoparticles of undoped BiFeO 3 , Bi 0.95 Gd 0.05 FeO 3 and Bi 1-x Gd x Fe 0.98 Cu 0.02 O 3 (x = 1, 2, 3, 4 and 5%) were prepared by sol-gel method. X-ray diffraction reveals that all the samples crystallize in rhombohedral phase. The simultaneous Gd and Cu doping at BFO lattice has significantly enhanced the ferroelectric properties of BFO compared to that of BFO. Substitution of Gd alone at the Bi site, gave rise to attractively enhanced remnant polarization. Though the (Gd, Cu) doped BFO samples exhibit relatively less enhancement, their values of remnant polarization are appreciable. Doping of (Gd, Cu) in the BFO lattice leads to an appreciable dielectric properties. An effective magnetoelectric coupling has been recorded for doped BFO when compared to BFO.

We describe theoretically and experimentally a previously unobserved mechanism for the induction of the nonlinear magnetoelectric response in ferromagnet-piezoelectric multiferroic composites. We show that contributions to the nonlinear magnetoelectric effects come not only from the nonlinearity of the magnetostriction coefficient on the dc magnetic field but also from the nonlinear hysteretic dependence of the magnetization of the magnetic phase within the composite. The nonlinearity of the magnetization leads to the self-generation of an additional ac magnetic field oscillating at twice the frequency of the excitation field. In turn, this leads to the strain-mediated activation of the piezocomponent, generating a voltage output response and doubling its frequency relative to that of the excitation field. For the PbZrTiO3/FeBSiC test sample examined in this study, we determined that this mechanism is responsible for an additional contribution of ∼14% to the nonlinear magnetoelectri...

The magnetoelectric (ME) effect induced by a rotating magnetic field, h, in the presence of a dc magnetic field, H 0, is investigated in a disk-shaped ferromagnetic FeBSiC -piezoelectric lead zirconate titanate bilayer structure. It is found that, due to the nonlinear field-dependence of magnetostriction λ(H) in the ferromagnetic layer, voltage harmonics are generated. These harmonics have a specific dependence of their amplitude and phase on H 0 and h, which is different from the case of excitation with a linearly polarized field. A theory is developed that describes characteristics of the ME effect for the cases of weak h <<H 0 and strong h>> H 0 excitation fields. The effect can be employed in designing highly sensitive sensors of permanent and alternating magnetic fields.

Magnetoelectric (ME) response of a multilayer ferrite-piezoelectric structure to short magnetic field pulses has been measured. The frequency spectrum of the ME coefficient α E of the structure in the range from several dozen hertz to 1 MHz has been determined by Fourier analysis of the ME response signal. The α E value shows a general slow monotonic decrease with increasing frequency and exhibits a 7-to 30-fold resonance growth at certain frequencies, which is related to the excitation of intrinsic acoustic oscillations of the multilayer structure. In the low-frequency range, the ME coefficient has a maximum in the region of 1 kHz due to relaxation processes in the piezoelectric and ferrite layers. © 2004 MAIK "Nauka/Interperiodica".

The forward and inverse magnetoelectric (ME) effects are experimentally studied in a two layer planar structure containing mechanically coupled Galfenol and PZT plates. The process of production of polycrystalline Galfenol plates and their magnetic and magnetostriction characteristics are described. For the forward ME conversion, the dependences of the amplitude of the voltage generated by the structure on the magnitude and orientation of a dc magnetic field and the frequency and amplitude of a modulating magnetic field are measured. For the inverse ME conversion, the dependences of the amplitude of the change in the magnetic induction of the structure on the dc magnetic field and the frequency of an ac electric field applied to the structure are measured. The efficiencies of the forward and inverse ME conversion are estimated for the case of low frequency field modulation and under conditions of the resonance excitation of bending and longitudinal mechanical vibrations in the structure.

The use of a pulsed magnetic field for studies on frequency characteristics of the magnetoelectric (ME) effect in multilayer composite structures is described. The method is based on the excitation of a ferrite-lead zirconate titanate multilayer with short magnetic field pulses, followed by the measurement and Fourier analysis of the ME response signal. It is shown that the ME voltage coefficient a E generally decreases as the frequency increases from 1 kHz to 1 MHz except (i) at some discrete frequencies where the coefficient increases by an order of magnitude due to electromechanical resonance in the structure and (ii) a local maximum at 2-4 kHz in a E vs. frequency due to relaxation processes caused by the conductivity of individual layers.

Room temperature manipulation of the ferromagnetic state via an electric field is investigated in Ni/BiFe0.95Mn0.05O3 thin film heterostructures. A 600% increase in the magnetic coercive field of the Ni layer is observed at the initial DC electrical poling of the ferroelectric BiFe0.95Mn0.05O3 layer. The magnetoelectric effect is remanent, and the magnetic coercive field can be modulated between a low value and a high value by successively switching the ferroelectric polarization. After the initial poling, the coercive field difference is decreased by subsequent back and forth switching. However, the magnetic bi-stability is preserved at least up to 250 cycles, which is promising for spintronic applications.

A novel low temperature preparation technique (<500ºC) is employed for synthesizing nanoscale Barium Titanate -Nickel ferrite composites, where the particle size is controllable. Two different ratios of hard and soft site composites (BTO-NFO 80:20, BTO-NFO 70:30) are synthesized and characterized to study their unique structural, morphological and magnetic properties. The structural refinement studies using XRD data showed 43 % of hard phase (anorthic structure) and 57% of soft phase (Cubic Structure) for BTO-NFO 80:20 and similarly 76% of hard phase and 24% of soft phase in the BTO-NFO 70:30 composite respectively. The ratio Mr/Ms is much less than 0.5, which states that multidomain grains or single domains are formed and the particle interaction is by magneto-static interaction confirming its superparamagnetic nature

The electric control of magnetic anisotropy has important applications for nonvolatile memory and information processing. By first-principles calculations, we show a large nonvolatile control of magnetic anisotropy in ferromagnetic/ferroelectric CoPt/ZnO interface. Using the switched electric polarization of ZnO, the density-of-states and magnetic anisotropy at the CoPt surface show a large change. Due to a strong Co/Pt orbitals hybridization and a large spin-orbit coupling, a large control of magnetic anisotropy was found. We experimentally measured the change of effective anisotropy by tunneling resistance measurements in CoPt/Mg-doped ZnO/Co junctions. Additionally, we corroborate the origin of the control of magnetic anisotropy by observations on tunneling anisotropic magnetoresistance.

We theoretically investigate the interfacial magnetoelectric effect in the BaTiO3/Ni heterostructure. We find that magnetoelectric coupling, specifically, the dependence of the magnetic moment of Ni on the polarization direction, primarily stems from the flow of the screening charge from Ni into BaTiO3 with a minor contribution coming from interfacial chemical bonding. The estimated change in the magnetic moment from screening with respect to bulk Ni is as high as ∼7%, which is a significant modulation. We also examine the effects of interfacial oxidation on the electronic structures and the strength of magnetoelectric coupling in the BaTiO3/NiO/Ni structure. We find an enhancement of the interfacial bonding contribution, making it unfavorable for interfacial magnetoelectric modulation. In addition, we consider the effect of the Ni magnetic domain wall on interfacial coupling and find it to be negligible to the interfacial magnetoelectric effect.

Dependence of the amplitude of mechanical oscillations on the thickness of magnetostrictive-piezoelectric bilayer structure in the form of rectangular plate is presented for the theory of linear magnetoelectric effect. The case of longitudinal orientation of the electric and magnetic fields was considered for structures in the form of a rectangular plate. The frequency dependence of the magnetoelectric effect is obtained using motion equation and electrostatic equations for both phases taking into account the boundary conditions on the interface. The theoretical dependencies of the displacement and stress distributions over the thickness of the sample in the magnetostrictive and piezoelectric phases are presented. These dependencies have a nonlinear character, and their accounting leads to a noticeable contribution to the magnitude of the effect.

Electricity and magnetism play a central role in operation of various nanotechnology devices such radio, receivers, televisions, electric motors, computers, high energy accelerators and most of electronic devices used in medicine. Scientists and researchers have worked hard to develop electromagnetic science and to find out theories to explain properties of the materials. Materials were classified into their interaction with applied magnetic field into diamagnetic, paramagnetic, ferromagnetic, antiferromagnetic and ferrimagnetic. Study of polycrystalline ferrites is important in view of their successively extensively used over a wide range of frequency. This is due to their high initial permeability, large resistivity, high dielectric constant and low dielectric loss. This book divides into two parts. Part I provide: description of ferrimagnetic materials, structure, magnetic and electric properties; and applications of ferrimagnetic. Part II describes structure, magnetic and electric properties of Cu-Zn spinel ferrite. This book should be useful to professionals and students in science, engineering and technology, or anyone else who may be considering utilizing materials science. Samy K.K. Shaath Mr. Samy Shaath has obtained his MSc. degree in Physics in 2004. Since 1997 he has worked in different Academic and Administrative positions. His interesting areas of research are Nanotechnology, specifically, in, Condensed Matter Physics and Materials Science, and Applied Physics. He is the author of several articles published in reputed journal.

Electricity and magnetism play a central role in operation of various nanotechnology devices such radio, receivers, televisions, electric motors, computers, high energy accelerators and most of electronic devices used in medicine. Scientists and researchers have worked hard to develop electromagnetic science and to find out theories to explain properties of the materials. Materials were classified into their interaction with applied magnetic field into diamagnetic, paramagnetic, ferromagnetic, antiferromagnetic and ferrimagnetic. Study of polycrystalline ferrites is important in view of their successively extensively used over a wide range of frequency. This is due to their high initial permeability, large resistivity, high dielectric constant and low dielectric loss. This book divides into two parts. Part I provide: description of ferrimagnetic materials, structure, magnetic and electric properties; and applications of ferrimagnetic. Part II describes structure, magnetic and electric properties of Cu-Zn spinel ferrite. This book should be useful to professionals and students in science, engineering and technology, or anyone else who may be considering utilizing materials science. Samy K.K. Shaath Mr. Samy Shaath has obtained his MSc. degree in Physics in 2004. Since 1997 he has worked in different Academic and Administrative positions. His interesting areas of research are Nanotechnology, specifically, in, Condensed Matter Physics and Materials Science, and Applied Physics. He is the author of several articles published in reputed journal.

The magnetoelectric effect in M-type Ti-Co doped strontium hexaferrite has been studied using a combination of magnetometry and element specific soft X-ray spectroscopies. A large increase (&gt;×30) in the magnetoelectric coefficient is found when Co2+ enters the trigonal bi-pyramidal site. The 5-fold trigonal bi-pyramidal site has been shown to provide an unusual mechanism for electric polarization based on the displacement of magnetic transition metal (TM) ions. For Co entering this site, an off-centre displacement of the cation may induce a large local electric dipole as well as providing an increased magnetostriction enhancing the magnetoelectric effect.

Magnetoelectric coupling is the material based coupling between electric and magnetic fields without recurrence to electrodynamics. It can arise in intrinsic multiferroics as well as in composites. Intrinsic multiferroics rely on atomistic coupling mechanisms, or coupled crystallographic order parameters, and even more complex mechanisms. They typically require operating temperatures much below T = 0 o C in order to exhibit their coupling effects. Room temperature applications are thus excluded. Consequently, composites have been designed to circumvent this limitation. They rely on field coupling between magnetostrictive and piezoelectric materials or in more advanced scenarios on quantum coupling in between both phases. This overview will describe experimental techniques and their particular limitations in accessing these coupling phenomena at different scales. Strain coupling is the dominant coupling mechanism at the macroscale as well as down to the micrometer. At the nanoscale more subtle effects can arise and some care has to be taken when investigating local coupling at interfaces using scanning probe techniques, e. g. due to semiconductor effects, field screening, or gradient and surface effects. At the smallest length scale atomic or molecular coupling can be tested using X-ray dichroism or probe atoms like 57 Fe in Mössbauer spectroscopy. We display a selection of measuring techniques at the different scales and outline possible pitfalls for experimentalists as well as theoreticians when using material parameters extracted from such experimental work.

In this paper we report on a new approach to synthesize core/shell cobalt iron oxide/barium titanate composite nanoparticles combining the co-precipitation and organosol crystallization techniques. The weight fraction of CoFe 2 O 4 and BaTiO 3 was 20% and 80% respectively. The obtained core/shell powder was used to sinter (0-3) composite multiferroic ceramics. Ferroelectric, magnetic, and magnetoelectric properties of the ceramics were studied. It was found that the value of the converse magnetoelectric coefficient, α c , reaches 4.4•10 -12 s•m -1 at the magnetic field µ 0 H dc = 0.15 T and T = 285 K.

Magnetoelectric coupling is the material based coupling between electric and magnetic fields without recurrence to electrodynamics. It can arise in intrinsic multiferroics as well as in composites. Intrinsic multiferroics rely on atomistic coupling mechanisms, or coupled crystallographic order parameters, and even more complex mechanisms. They typically require operating temperatures much below T = 0 o C in order to exhibit their coupling effects. Room temperature applications are thus excluded. Consequently, composites have been designed to circumvent this limitation. They rely on field coupling between magnetostrictive and piezoelectric materials or in more advanced scenarios on quantum coupling in between both phases. This overview will describe experimental techniques and their particular limitations in accessing these coupling phenomena at different scales. Strain coupling is the dominant coupling mechanism at the macroscale as well as down to the micrometer. At the nanoscale more subtle effects can arise and some care has to be taken when investigating local coupling at interfaces using scanning probe techniques, e. g. due to semiconductor effects, field screening, or gradient and surface effects. At the smallest length scale atomic or molecular coupling can be tested using X-ray dichroism or probe atoms like 57 Fe in Mössbauer spectroscopy. We display a selection of measuring techniques at the different scales and outline possible pitfalls for experimentalists as well as theoreticians when using material parameters extracted from such experimental work.

In this paper we report on a new approach to synthesize core/shell cobalt iron oxide/barium titanate composite nanoparticles combining the co-precipitation and organosol crystallization techniques. The weight fraction of CoFe 2 O 4 and BaTiO 3 was 20% and 80% respectively. The obtained core/shell powder was used to sinter (0-3) composite multiferroic ceramics. Ferroelectric, magnetic, and magnetoelectric properties of the ceramics were studied. It was found that the value of the converse magnetoelectric coefficient, α c , reaches 4.4•10 -12 s•m -1 at the magnetic field µ 0 H dc = 0.15 T and T = 285 K.

Enhancing the magnetoelectric coupling in a strain-mediated multiferroic composite structure plays a vital role in controlling magnetism by electric fields. An enhancement of magnetoelastic coupling between ferroelectric single crystal (011)-cut [Pb(Mg1/3Nb2/3)O3](1-x)-[PbTiO3]x (PMN-PT, x≈ 0.30) and ferromagnetic polycrystalline Ni thin film through an interposed benzocyclobutene polymer thin film is reported. A nearly twofold increase in sensitivity of remanent magnetization in the Ni thin film to an applied electric field is observed. This observation suggests a viable method of improving the magnetoelectric response in these composite multiferroic systems.

We study the effect of pressure on Structural, elastic and electronic properties of Cubic and Tetragonal Perovskite using density function theory. The equilibrium parameters obtained are in good agreement with the available literature both experimental and theoretical. We found out that there is transition from tetragonal to cubic at a pressure of around 30GPa. Both crystals are stable in the pressure range of this study (0 -50 GPa), and the stability increases with increasing pressure. The bulk modulus (B), Young modulus (E) and Shear modulus (G) all increase with increasing pressure. The band-gap increases and decrease around (X-Gamma) and (M-Gamma) for the case of Cubic and decrease for the case of Tetragonal Crystal around (X-Gamma), (Z-Gamma) and (Z-X) which converges at pressure of around 30GPa.

In this work the hyperfine interactions in (BiFeO 3 ) x -(BaTiO 3 ) 1-x solid solutions with relation to their structural properties have been investigated. X-ray diffraction, Mössbauer spectroscopy and magnetoelectric effect measurements have been used for studies of sintered (BiFeO 3 ) x -(BaTiO 3 ) 1-x solid solutions with x = 0.9, 0.8 and 0.7. With increasing contents of BaTiO 3 , the structural transformation from rhombohedral to cubic was observed. The weakening of the hyperfine magnetic fields accompanied by this transformation. On the other hand, the increasing amount of BaTiO 3 caused an increase of the magnetoelectric effect.

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The magnetoelectric response in composites of barium titanate (BTO) and cobalt ferrite (CFO) has been determined by measuring the magnetoelectric susceptibility coefficient. This was done by two different methods: magnetocapacitance measurements and magnetoelectric voltage measurement using a lock-in technique. These composites were prepared by the sol-gel method. Four different compositions with different molar ratios of the magnetostrictive phase (CFO) embedded in a piezoelectric matrix of BTO were studied to investigate the effect of the magnetostrictive content and the number density of interfaces on the magnetoelectric response. It was found from both techniques that the magnetoelectric coupling effect increases with the increase of applied field and it had a non-linear dependence on the percentage of magnetostrictive content in the composites.

We report giant magnetoelectric coupling at room temperature in a self-assembled nanocomposite of BiFeO3-CoFe2O4 (BFO-CFO) grown on a BaTiO3 (BTO) crystal. The nanocomposite consisting of CFO nanopillars embedded in a BFO matrix exhibits weak perpendicular magnetic anisotropy due to a small out-of-plane compression (∼0.3%) of the magnetostrictive (CFO) phase, enabling magnetization rotation under moderate in-plane compression. Temperature dependent magnetization measurements demonstrate strong magnetoelastic coupling between the BaTiO3 substrate and the nanocomposite film, which has been exploited to produce a large magnetoelectric response in the sample. The reorientation of ferroelectric domains in the BTO crystal upon the application of an electric field (E) alters the strain state of the nanocomposite film, thus enabling control of its magnetic anisotropy. The strain mediated magnetoelectric coupling coefficient α=μodM/dE  calculated from remnant magnetization at room temperatur...

In strong magnetic fields up to 20 T quasistatic measurements of the magnetic-field-induced electric polarization have been performed in LiNiPO 4 single crystals between 4.2 and ϳ25 K. The magnetoelectric ͑ME͒ effect has been studied in detail near the Ne ´el temperature. The temperature hysteresis of the polarization induced by a magnetic field was found. An anomalous temperature dependence of the magnetoelectric susceptibility during the phase transition and the ME ''butterfly loop'' were observed. The phenomenological theory of the magnetoelectric effect in LiCoPO 4 and LiNiPO 4 has been developed. A tentative explanation of the existence of the magnetoelectric ''butterfly loop'' is given. It is shown that there is a non-Lifshitz invariant in the free energy expansion which is linear in the spatial derivatives. Hence the phase transition to a spacemodulated spin structure is possible. The influence of such a structure on the linear magnetoelectric effect is examined.

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During the synthesis by flux evaporation in KCl at 930°C of KCr 11 P0 4 an oxidation of chromium II was observed leading to the formation of chromium pyrophophate KCr m P 2 0 7 • The crystal lattice of KCr Iii P 2 0 7 , was found to be of monoclinic centrosymmetric space group P2 11 c with a=7.3470(7), b=9.9090(10), c=8.1730(8)A, /9= 106.806(11) 0 , Z=4 and VM=569.59(10)A 3 • The magnetic susceptibility has been measured between 3.6 and 300K at different magnetic field strengths. The negative value of the Curie-Weiss temperature and the behaviour of magnetic susceptibility indicate an antiferromagnetic spin order in this compound with a Nee! temperature TN=8.5 K.

The results of the comprehensive magnetoelectric interaction research in three-layer structure Ni–piezoceramic BaTiO3–Ni are presented. It has been theoretically shown and experimentally confirmed that, in the general case, the dependence of the magnetoelectric response has non-linear character. At low bias magnetic field, a quadratic dependence magnetoelectric response from an AC magnetic field is observed then there is a linear section, as well as at high values of the field magnetoelectric response has saturation. The obtained values of the magnetoelectric characteristics (αEmax = 32 V(cmOe) for resonance and 437 mV/(cmOe) for field dependence) for lead-free three-layer structure barium–titanate–piezoceramic nickel are comparable with the magnetoelectric characteristics for similar structures, based on lead-containing ceramics.

Submitted for the MAR17 Meeting of The American Physical Society Giant Magnetoelectric Energy Conversion Utilizing Inter-Ferroelectric Phase Transformations in Ferroics PETER FINKEL, MARGO STARUCH, US Naval Research Laboratory -Phase transition-based electromechanical transduction permits achieving a non-resonant broadband mechanical energy conversion see ( Finkel et al Actuators, 5 [1] 2. ( )) , the idea is based on generation high energy density per cycle , at least 100x of magnitude larger than linear piezoelectric type generators in stress biased [011]cut relaxor ferroelectric Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) single crystal can generate reversible strain >0.35% at remarkably low fields (0.1 MV/m) for tens of millions of cycles. Recently we demonstrated that large strain and polarization rotation can be generated for over 40 x 10 6 cycles with little fatigue by realization of reversible ferroelectric-ferroelectric phase transition in [011] cut PIN-PMN-PT relaxor ferroelectric single crystal while sweeping through the transition with a low applied electric field <0.18 MV/m under mechanical stress. This methodology was extended in the present work to propose magnetoelectric (ME) composite hybrid system comprised of highly magnetostrictive alloymFe81.4Ga18.6 (Galfenol), and lead indium niobate-lead magnesium niobate-lead titanate (PIN-PMN-PT) domain engineered relaxor ferroelectric single crystal. A small time-varying magnetic field applied to this system causes the magnetostrictive element to expand, and the resulting stress forces the phase change in the relaxor ferroelectric single crystal. ME coupling coefficient was fond to achieve 80 V/cm Oe near the FR-FO phase transition that is at least 100X of magnitude higher than any currently reported values.

A novel conductive anionic hydrogel was synthesized for use as a solid electrolyte for electrochemical impedance spectroscopy (EIS) characterization of the barrier properties of protective coatings on outdoor metalworks, such as bronze sculptures. The AMPS-co-PAA hydrogel was soaked in a variety of aqueous salt solutions and characterized by swelling capacity and conductivity in order to determine the most appropriate gel/liquid electrolyte combination for use on culturally significant objects. K 2 PIPES-equilibrated hydrogels were selected as the preferred electrodes for this particular application and were used to measure the impedance of a coated substrate, yielding spectra similar to those from standard liquid cells.

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The temperature dependent stability of the magnetic phases of FeRh were investigated by means of total energy calculations with magnetic disorder treated within the uncompensated disordered local moment (uDLM) approach. In addition, Monte Carlo simulations based on the extended Heisenberg model have been performed, using exchange coupling parameters obtained from first principles. The crucial role and interplay of two factors in the metamagnetic transition in FeRh has been revealed, namely the dependence of the Fe-Fe exchange coupling parameters on the temperature-governed degree of magnetic disorder in the system and the stabilizing nature of the induced magnetic moment on Rh-sites. An important observation is the temperature dependence of these two competing factors.

We give a number of equivalent conditions for a topos to be homotopically trivial and then relate these conditions to the logic of the topos. This is accomplished by constructing a family of intervals that can detect complemented, regular subobjects of the terminals. It follows that these conditions generally are weaker than the Stone condition but are equivalent to it if they hold locally. As a consequence we obtain an extension of Johnstone's list of conditions equivalent to DeMorgan's law. Thus, for example, the fact that there is no nontrivial homotopy theory in the category of sets is equivalent to the fact, among others, that maximal ideals in commutative rings are prime. Moreover, any topos has a 'best approximation' by a locally homotopically trivial topos.

Multiferroics, where (anti-) ferromagnetic, ferroelectric and ferroelastic order parameters coexist, enable manipulation of magnetic ordering by an electric field through switching of the electric polarization. It has been shown that realization of magnetoelectric coupling in a single-phase multiferroic such as BiFeO(3) requires ferroelastic (71 degrees, 109 degrees) rather than ferroelectric (180 degrees) domain switching. However, the control of such ferroelastic switching in a single-phase system has been a significant challenge as elastic interactions tend to destabilize small switched volumes, resulting in subsequent ferroelastic back-switching at zero electric field, and thus the disappearance of non-volatile information storage. Guided by our phase-field simulations, here we report an approach to stabilize ferroelastic switching by eliminating the stress-induced instability responsible for back-switching using isolated monodomain BiFeO(3) islands. This work demonstrates a cri...

Nanopowders of the 0.8BaTiO 3 /0.2Ni (1-x) Co x Fe 2 O 4 (x= 0, 0.25, 0.5, 0.75, and 1) were synthesized by the in situ sol-gel method using poly(acrylic acid) (PAA1800) as a chelating agent. The synthesis developed using PAA1800 ensured the simultaneous crystallization of two phases. The results provided a reliable method for producing biphasic nanopowders in all the compositions of Co-Ni-ferrite with an average particle size of less than 50 nm with a potential application in lead-free magnetoelectric particulate composites. The XRD results indicated the formation of only BaTiO 3 and Ni (1-x) Co x Fe 2 O 4 phases, verifying that there was no interdiffusion between the perovskite BaTiO 3 and spinel Co-NiFe 2 O 4 phases during the crystallization phase. A detailed analysis of the crystalline structures was conducted to quantify the phases using the Rietveld method, and thus ensure the success of the in situ sol-gel synthesis. Keywords: in situ sol-gel, 0.8BaTiO 3 /0.2Ni (1-x) Co x Fe 2 O 4 , nanopowders, biphasic system.