Change In Electric Polarization Research Articles

Effects of a remote binding partner on the electric field and electric field gradient at an atom in a weakly bound trimer

Microwave spectra are reported for the C3v symmetric complexes Kr-SO3 and Kr-SO3-CO. The S-C distance in the trimer, 2.871(9) Å, is the same as that previously determined for SO3-CO to within the estimated uncertainties. The Kr-S distances are 3.438(3) Å and 3.488(6) Å in Kr-SO3 and Kr-SO3-CO, respectively, indicating that the addition of CO to Kr-SO3 increases the Kr-S distance by 0.050(9) Å. Measurements of the (83)Kr nuclear quadrupole coupling constants provide direct probes of the electric field gradient at the Kr nucleus, and a comparison between the two systems reflects the degree to which the CO influences the electronic structure of the krypton atom. Although the Kr and CO in the trimer are on opposite sides of the SO3 and thus are not in direct contact, the addition of CO to Kr-SO3 reduces the electric field gradient at the Kr nucleus by 18%. Calculations using the block localized wavefunction decomposition method are performed to understand the physical origins of this change. While the magnitudes of both the electric field and the electric field gradient at the Kr nucleus decrease upon addition of the CO to Kr-SO3, the changes are shown to arise from rather complex combinations of geometrical distortion, electrostatic, polarization, and electron transfer effects. For the electric field, the electrostatic term accounts for the largest portion of the reduction, while for the electric field gradient, polarization and structural change of the Kr-SO3 moiety make the primary contributions. Despite significant changes in the electronic environment at the Kr nucleus, calculated binding energies indicate that the interactions are largely additive, with the binding energy of the trimer very nearly equal to the sum of the Kr-SO3 and SO3-CO binding energies.

Electric Field Control of Nonvolatile Four-State Magnetization at Room Temperature

We find the realization of large converse magnetoelectric (ME) effects at room temperature in a magnetoelectric hexaferrite Ba0.52Sr2.48Co2Fe24O41 single crystal, in which rapid change of electric polarization in low magnetic fields (about 5 mT) is coined to a large ME susceptibility of 3200 ps/m. The modulation of magnetization then reaches up to 0.62μ(B)/f.u. in an electric field of 1.14 MV/m. We find further that four ME states induced by different ME poling exhibit unique, nonvolatile magnetization versus electric field curves, which can be approximately described by an effective free energy with a distinct set of ME coefficients.

Magneto-electric effects on Sr Z-type hexaferrite at room temperature

In this paper, magnetoelectric effects of Sr Z-type hexaferrite, Sr3Fe24Co2O41, at room temperature is measured. The change in remanence magnetization was measured by applying a DC voltage or electric field across a slab of hexaferrite. Changes of ∼18% in remanence was observed in an electric field of 10 000 V/cm implying a similar change in the microwave permeability at frequencies below 3 GHz. Also, a change in dielectric constant at 1 GHz of ∼16% in a magnetic field of only 320 Oe was measured. In these types of measurements high resistivity is critical in order to reduce current flow in the hexaferrite. The resistivity of the hexaferrite was raised to 4.28 × 108 Ω-cm by annealing under oxygen pressure. The measurements indicate that indeed electric polarization and magnetization changes were induced by the application of magnetic and electric fields, respectively. The implications for microwave applications appear to be very promising at room temperature.

Measurements and ab initio molecular dynamics simulations of the high temperature ferroelectric transition in hexagonal RMnO3

Measurements of the structure of hexagonal RMnO3 [R = rare earths (Ho) and Y] for temperatures significantly above the ferroelectric transition temperature (TFE) were conducted to determine the nature of the transition. The local and long range structural measurements were complemented by ab initio molecular dynamics simulations. With respect to the Mn sites in YMnO3 and HoMnO3, we find no large atomic (bond distances or thermal factors), electronic structure changes, or rehybridization on crossing TFE from local structural methods. The local symmetry about the Mn sites is preserved. With respect to the local structure about the Ho sites, a reduction of the average Ho–O bond with increased temperature is found. Ab initio molecular dynamics calculations on HoMnO3 reveal the detailed motions of all ions. Above ∼900 K there are large displacements of the Ho, O3, and O4 ions along the z axis which reduce the buckling of the MnO3/O4 planes. The changes result in O3/O4 ions moving to toward central points between pairs of Ho ions on the z axis. These structural changes make the coordination of Ho sites more symmetric thus extinguishing the electric polarization. At significantly higher temperatures, rotation of the MnO5 polyhedra occurs without a significant change in electric polarization. The Born effective charge tensor is found to be highly anisotropic at the O sites but does not change appreciably at high temperatures.

Large electrocaloric effect of highly (100)-oriented 0.68PbMg1/3Nb2/3O3–0.32PbTiO3 thin films with a Pb(Zr0.3Ti0.7)O3/PbOx buffer layer

0.68PbMg1/3Nb2/3O3–0.32PbTiO3 (PMN–PT) thin films with a lead zirconate titanate Pb(Zr0.3Ti0.7)O3 (PZT)/PbOx buffer layer were deposited on Pt/TiO2/SiO2/Si substrates by radio frequency magnetron sputtering technique, and pure perovskite crystalline phase with highly (100)-preferred orientation was formed in the ferroelectric films. We found that the highly (100)-oriented thin films possess not only excellent dielectric and ferroelectric properties but also a large electrocaloric effect (13.4K at 15V, i.e., 0.89K/V) which is attributed to the large electric field-induced polarization and entropy change during the ferroelectric–paraelectric phase transition. The experimental results indicate that the use of PZT/PbOx buffer layer can induce the crystal orientation and phase purity of the PMN–PT thin films, and consequently enhance their electrical properties.

Low-field magnetoelectric effect at room temperature

The discoveries of gigantic ferroelectric polarization in BiFeO(3) (ref. 1) and ferroelectricity accompanied by a magnetic order in TbMnO(3) (ref. 2) have renewed interest in research on magnetoelectric multiferroics, materials in which magnetic and ferroelectric orders coexist, from both fundamental and technological points of view. Among several different types of magnetoelectric multiferroic, magnetically induced ferroelectrics in which ferroelectricity is induced by complex magnetic orders, such as spiral orders, exhibit giant magnetoelectric effects, remarkable changes in electric polarization in response to a magnetic field. Many magnetically induced ferroelectrics showing the magnetoelectric effects have been found in the past several years. From a practical point of view, however, their magnetoelectric effects are useless because they operate only far below room temperature (for example, 28 K in TbMnO(3) (ref. 2) and 230 K in CuO (ref. 11)). Furthermore, in most of them, the operating magnetic field is an order of tesla that is too high for practical applications. Here we report materials, Z-type hexaferrites, overcoming these problems on magnetically induced ferroelectrics. The best magnetoelectric properties were obtained for Sr(3)Co(2)Fe(24)O(41) ceramics sintered in oxygen, which exhibit a low-field magnetoelectric effect at room temperature. Our result represents an important step towards practical device applications using the magnetoelectric effects.

High-Field Study of Strong Magnetoelectric Coupling in Single-Domain Crystals of BiFeO3

Magnetic and dielectric properties of single-domain crystals of BiFeO 3 were studied in pulsed magnetic fields up to 55 T. At low temperatures, metamagnetic transitions accompanied with sharp changes in electric polarization ( P ) were observed at around 18 T. The angular dependence of the transition field coincides with that of the transition from the cycloidal state to the canted antiferromagnetic spin state studied in the framework of the Landau–Ginzburg theory incorporated with the Lifshitz-like invariant. The parasitic P component caused by the cycloidal spin structure amounts to 210±30 µC/m 2 in terms of the projected component on the pseudocubic principal axis, which can be controlled by applying magnetic fields at least up to 500 K. This result indicates that the microscopic magnetoelectric coupling in BiFeO 3 is not weak: In fact, it is rather strong as compared to that in the canonical multiferroic material TbMnO 3 .

Multiferroic Bi 0.7Dy 0.3FeO 3 thin films directly integrated on Si for integrated circuit compatible devices

Magnetoelectric multiferroic Bi 0.7Dy 0.3FeO 3 (BDFO) thin films deposited on p-type Si (100) substrate using pulsed laser deposition technique demonstrated a saturated ferroelectric and ferromagnetic hysteresis loop at room temperature. More interestingly, the observed change in electric polarization with applied magnetic field in these films indicated the presence of room temperature magnetoelectric coupling behavior. Using high-frequency capacitance–voltage measurements, the fixed oxide charge density, interface trap density and dielectric constant were estimated on Au/BDFO/Si capacitors. These results suggest the integrated circuit compatible application potential of BDFO films in the field of micro-electro-mechanical systems and non-volatile memories.

Direct measurement of giant electrocaloric effect in BaTiO3 multilayer thick film structure beyond theoretical prediction

The electrocaloric (EC) effect of BaTiO3 multilayer thick film structure was investigated by direct measurement and theoretical calculation. The samples were prepared by the tape-casting method, which had 180 dielectric layers with an average thickness of 1.4 μm. The thermodynamic calculation based on the polarization-temperature curves predicted a peak heat adsorption of 0.32 J/g at 80 °C under 176 kV/cm electric field. The direct measurement via differential scanning calorimeter showed a much higher EC effect of 0.91 J/g at 80 °C under same electric field. The difference could result from the different trends of changes of electric polarization and lattice elastic energy under ultrahigh electric field.

A whirlwind of opportunities

The formation of vortices in multiferroic hexagonal manganites, where the sign of electric polarization changes six times around the vortex core, points towards the origin of composite multiferroic domain walls.

Electric Field Switching of the Magnetic Anisotropy of a Ferromagnetic Layer Exchange Coupled to the Multiferroic CompoundBiFeO3

We report here that a Permalloy layer deposited on top of a multiferroic BiFeO3 single crystal acquires an easy magnetic direction along the propagation vector of the cycloidal arrangement of antiferromagnetic moments in BiFeO3. This anisotropy originates from a direct magnetic coupling with the canted spins forming the cycloid. Moreover, we show that an electric field-induced change of electric polarization is able to toggle the direction of anisotropy in the ferromagnet through the magnetoelectric effect, which links the antiferromagnetic spins to the local polarization in BiFeO3.

Spiral spin structures and origin of the magnetoelectric coupling inYMn2O5

By combining neutron four-circle diffraction and polarized neutron-diffraction techniques we have determined the complex spin structures of a multiferroic ${\text{YMn}}_{2}{\text{O}}_{5}$ that exhibits two ferroelectric phases at low temperatures. The obtained magnetic structure has spiral components in both the low-temperature ferroelectric phases that are magnetically commensurate and incommensurate, respectively. Among proposed microscopic theories for the magnetoelectric coupling, our results are consistent with both the spin-current mechanism and the magnetostriction mechanism. Our results also explain why the electric polarization changes at the low-temperature commensurate-to-incommensurate phase transition.

Magnetoelectric phenomena in manganites R0.6Ca0.4MnO3(R = Pr, Nd) with charge ordering suppressed by a magnetic field

A change in electric polarization (up to 300 {mu}C/m{sup 2}) upon magnetic-field suppression of a charge-ordered antiferromagnetic state upon a transition to the ferromagnetic conducting phase (H{sub cr} {approx} 65-80 kOe at 4.2 K) is discovered in Pr{sub 0.6}Ca{sub 0.4}MnO{sub 3} and Nd{sub 0.6}Ca{sub 0.4}MnO{sub 3} single crystals. The transition is also accompanied by a jump in magnetization and magnetostriction. The dependence of the induced polarization sign on the polarity of the electric field in which the sample was preliminarily cooled indicates the existence of spontaneous electric polarization. The effect is the strongest in Nd{sub 0.6}Ca{sub 0.4}MnO{sub 3} and is weaker by a factor of 5-10 in Pr{sub 0.6}Ca{sub 0.4}MnO{sub 3}, for which the tolerance factor is higher. The observed effect may be associated with recently predicted noncentrosymmetric structures in doped manganites with x {approx} 0.5 (see D.V. Efremov, J. van den Brink, and D.I. Khomskii, Nature Materials 3, 853 (2004)), in which e{sub g} electrons are not localized upon charge and orbital ordering at one manganese ion, but are distributed among neighboring ions, thus forming an ordered polar dimer structure.

A modified sol-gel process for multiferroic nanocomposite films

Multiferroic CoFe2O4–Pb(Zr,Ti)O3 (CFO-PZT) composite films with nanoscale mixture of the two phases were prepared by a modified sol-gel process, in which a mixed precursor solution of both CFO and PZT was used. X-ray diffraction and transmission electron microscopy examinations revealed the coexistence of perovskite PZT and spinel CFO that were mixed in nanoscale with mean grain sizes of 5–10nm. Magnetic properties of the CFO-PZT nanocomposite were examined, which were consistent with their microstructures. The magnetoelectric coupling between CFO and PZT was demonstrated by an external magnetic field induced electric polarization change. This modified sol-gel processing provides an alternative for multiferroic composite films, which is simpler and easier to control compared to the conventional layer-layer sol-gel process for multiferroic composite films.

Observation of electric polarization in Gd1−x SrxMnO3 (x = 0.5, 0.6, 0.7) single crystals

In Gd1−xSrxMnO3 (x = 0.5, 0.6, 0.7) single crystals, a change in electric polarization (ΔP ∼ 100 μK/m2) is found to accompany the suppression of the charge-ordered spin-glass state and the transition to the ferromagnetic conducting phase (Hcr ∼ 100 kOe at 4.5 K). The transition is also characterized by jumps in magnetization and magnetostriction. The sign of the induced polarization depends on the polarity of the electric field in which the sample was preliminarily cooled. This dependence testifies to the presence of spontaneous electric polarization in the system. The effect is maximal at x = 0.5 and decreases by more than an order of magnitude as x increases to 0.7. The phenomenon observed in the experiment may be associated with the new noncentrosymmetric structures with an electric dipole moment that were recently predicted for manganites (x ∼ 0.5) [Nature Materials 3, 853 (2004)]. These structures exhibit charge-orbital ordering such that e g electrons are not localized by one of the manganese ions but distributed between neighboring ions, thus forming an ordered dimer structure.

Specificity of magnetoelectric effects in a new GdMnO3 magnetic ferroelectric

A complex study of the magnetic, electric, magnetoelectric, and magnetoelastic properties of GdMnO3 single crystals has been performed in the low-temperature region in strong pulsed magnetic fields up to 200 kOe. An anomaly of the dielectric constant along the a axis of a crystal has been found at 20 K, where a transition from an incommensurate modulated phase to a canted antiferromagnetic phase, as well as electric polarization along the a and b axes of the crystal induced by the magnetic field H‖ b (Hcr ∼ 40 kOe), is observed. Upon cooling the crystal in an electric field, the magnetic-field-induced electric polarization changes its sign depending on the sign of the electric field. The occurrence of the electric polarization is accompanied by anisotropic magnetostriction, which points to a correlation between the magnetoelectric and magnetoelastic properties. Based on these results, it has been stated that GdMnO3 belongs to a new family of magnetoelectric materials with the perovskite structure.

Structural and magnetoelectric properties ofGa2−xFexO3single crystals grown by a floating-zone method

Lattice-structural, magnetic, and magnetoelectric (ME) properties have been investigated for single crystals of prototypical polar ferrimagnet ${\mathrm{Ga}}_{2\ensuremath{-}x}{\mathrm{Fe}}_{x}{\mathrm{O}}_{3}$ $(0.8\ensuremath{\leqslant}x\ensuremath{\leqslant}1.4)$ as melt-grown by a floating-zone (FZ) method. Magnetization measurements show that the saturated magnetization as well as the ferrimagnetic phase transition temperature $({T}_{C})$ increases with as increase of $\mathrm{Fe}$ content $x$, while the coercive force decreases. A neutron powder diffraction study indicates fairly low ordering of $\mathrm{Ga}$ and $\mathrm{Fe}$ arrangement at cation sites, which is likely related to the lower ${T}_{C}$ in the FZ crystals than in the corresponding flux-grown crystals. Coefficients of linear and quadratic ME effects have been obtained with measurements of change in electric polarization induced by sweeping a magnetic field. Electric polarization was largely modulated in a magnetic field applied parallel to the direction of spontaneous magnetization, but not in a field parallel to that of the spontaneous polarization. A simple model to explain the sharp contrast is presented.

States of orientation of pyridine and 1,4-pyrazine as a function of electrode potential and surface charge at a high-area, porous C electrode

In the course of earlier work on development of electrochemical procedures for adsorptive removal of noxious organic impurities from waste waters, using high specific-area carbon-cloth electrodes, we have found a major promoting influence of electrode potential applied through galvanostatic or potentiostatic polarization. In the present paper, those effects are examined more quantitatively using pyridine and 1,4-pyrazine as model adsorbates. The effects of electrode-potential changes are followed by means of double-layer capacitance measurements and related changes of surface charge-density with variation of electrode potential. Extents of adsorption as a function of potential and time are directly evaluated by means of in situ UV–Vis spectrometry in a combined electrochemical optical absorbance cell. The effects of changes of electric polarization of the C electrode surface are interpreted in terms of an Esin and Markov type of effect through evaluations of surface-potential ( χ) changes due to adsorption and interfacial orientation of the organic adsorbates in the double-layer interphase, coupled with changes of the solvent–water orientation. The results obtained for C are analogous to those found at Hg.

Pyroelectric activity of aromatic-substituted copolysiloxane/ eicosylamine alternate-layer Langmuir-Blodgett films

The pyroelectric behaviour of alternate-layer Langmuir-Blodgett (LB) films containing monomelic eicosylamine and a linear copolysiloxane substituted with ×omega;-(4-alkoxyphenyl)alkanoic acid side-groups has been investigated. A quasi-static detection method has been used to measure the rate of change of electric polarization with respect to temperature, i.e. the pyroelectric coefficient of these molecular thin films. The coefficient measured at 303 K is 6·4 μCm−2 K−2, which is one of the highest values ever reported for an LB film device.

Structural Changes Occurring in the Phase Transition of Ferroelectric Liquid Crystals [I Temperature Dependence of the X-Ray Diffraction and FTIR/Raman Spectra

Abstract Structural changes in the ferroelectric liquid crystal of chiral 4-n-hexyloxyphenyl 4′-[2-methylheptyloxy - biphenyl-4-carboxylate were analyzed by means of X-ray diffraction, FTIR, Raman and DSC measurements. Many different types of crystal modifications were found to be generated depending on the crystallization conditions such as the cooling rate from the isotropic phase, the type of solvents, etc. These crystal phases experience crystal-to-crystal and crystal-to-liquid crystal phase transitions, in which the interlamellar spacing and the packing fashion of the molecules change drastically, as revealed by the X-ray diffraction data. The Raman and FTIR spectral measurements clarified that the molecular conformations were thermally agitated during the phase transitions: the alkyl chains are disordered and the biphenyl groups are twisted in the liquid-crystalline and isotropic phases. In the ferroelectric phase transition between the chiral smectic C and cholesteric phases, the electric dipoles locating around the part are considered to change their orientation directions through the internal rotation of the biphenyl groups, resulting in the change in bulk electric polarization.