Investigation of biferroic properties in La0.6Sr0.4MnO3/0.7Pb(Mg1/3Nb2/3)O3â0.3PbTiO3 epitaxial bilayered heterostructures

Epitaxial bilayered thin films consisting of La0.6Sr0.4MnO3 (LSMO) and 0.7Pb(Mg1/3Nb2/3)O3â0.3PbTiO3 (PMN-PT) layers of relatively different thicknesses were fabricated on LaNiO3 coated LaAlO3 (100) single crystal substrates by pulsed laser ablation technique. The crystallinity, ferroelectric, ferromagnetic, and magnetodielectric properties have been studied for all the bilayered heterostructures. Their microstructural analysis suggested possible StranskiâKrastanov type of growth mechanism in the present case. Ferroelectric and ferromagnetic characteristics of these bilayered heterostructures over a wide range of temperatures confirmed their biferroic nature. The magnetization and ferroelectric polarization of the bilayered heterostructures were enhanced with increasing PMN-PT layer thickness owing to the effect of lattice strain. In addition, evolution of the ferroelectric and ferromagnetic properties of these heterostructures with changing thicknesses of the PMN-PT and LSMO layers indicated possible influence of several interfacial effects such as space charge, depolarization field, domain wall pinning, and spin disorder on the observed properties. Dielectric properties of these heterostructures studied over a wide range of temperatures under different magnetic field strengths suggested a possible role of elastic strain mediated magnetoelectric coupling behind the observed magnetodielectric effect in addition to the influence of rearrangement of the interfacial charge carriers under an applied magnetic field.

Brillouin Scattering by Phonons Renormalized by Two-Magnon Excitations in Ferromagnetic Dielectrics

Brillouin scattering by one-phonon-two-magnon interacting excitations in ferromagnetic dielectrics is discussed. The basic light scattering mechanism is taken to be the modulation of the density-dependent optical dielectric polarizability of the medium by the dynamic strain field generated by the longitudinal acoustic (LA) phonons. The renormalization effects arising from the scattering of phonons by the two-magnon creation-annihilation processes have, however, been taken into account. Via these interactions, the Brillouin components corresponding to the two-magnon excitations are reflected indirectly in the spectrum of the phonon scattered light as line-broadening of the otherwise relatively sharp Brillouin doublet. The present mechanism is shown to be dominant in a clean saturated ferromagnetic dielectric with large magneto-strictive coupling constant, and with the magnetic ions in the orbitally quenched states. Following the linear response theory, an expression has been derived for the spectral density of the scattered light as a function of temperature, scattering angle, and the strength of the externally applied magnetic field. Some estimates are given for the line-width and line-shift of the Brillouin components for certain typical choice of parameters involved. The results are discussed in relation to some available calculations on the ultrasonic attenuation in ferromagnetic insulators at low temperatures.

Lithium nuclear-magnetic-resonance in lithium acetate dihydrate, Li(CH3COO).2H2O

Li n.m.r, in single crystals of lithium acetate dihydrate is used to determine the quadrupole coupling parameters: (e2qQ/h) and r/. The orientations of the principal z, y and x components of the electric field gradient tensor are determined to be along the crystallographic b, a and c axes respectively. The parameters experimentally determined are (e2qQ/h)= 154"6 kHz; and i/= 0.9. This study indicates a tetrahedral configuration around the Li ion, confirming the recent X-ray and p.m.r, results.

Degenerate surface modes in a magnetized plasma

Electromagnetic surface waves propagating along the plasma-vacuum interface parallel to an applied magnetic field are studied. New modes for which the field components are degenerate, not reported in the earlier investigation of Kotsarenko and Fedorchenko (1969), are found and discussed. These modes, which propagate up to the plasma frequency for all values of the magnetic field, start as forward waves at low frequency but smoothly change into the backward mode as the frequency increases.

Analytical method for solving a set of infinite simultaneous equations

It is shown that a method based on the principle of analytic continuation can be used to solve a set of infinite simultaneous equations encountered in solving for the electric field of a periodic electrode structure.

Adsorption and Unfolding of Lysozyme at a Polarized Aqueous-Organic Liquid Interface

The adsorption of proteins at the interface between two immiscible electrolyte solutions has been found to be key to their bioelectroactivity at such interfaces. Combined with interfacial complexation of organic phase anions by cationic proteins, this adsorption process may be exploited to achieve nanomolar protein detection. In this study, replica exchange molecular dynamics simulations have been performed to elucidate for the first time the molecular mechanism of adsorption and subsequent unfolding of hen egg white lysozyme at low pH at a polarized 1,2-dichloroethane/water interface. The unfolding of lysozyme was observed to occur as soon as it reaches the organic−aqueous interface,which resulted in a number of distinct orientations at the interface. In all cases, lysozyme interacted with the organic phase through regions rich in nonpolar amino acids, such that the side chains are directed toward the organic phase, whereas charged and polar residues were oriented toward the aqueous phase. By contrast, as expected, lysozyme in neat water at low pH does not exhibit significant structural changes. These findings demonstrate the key influence of the organic phase upon adsorption of lysozyme under the influence of an electric field, which results in the unfolding of its structure.

Electron energy distributions and transport coefficients in N2 in E times B fields

Using the concept of energy-dependent effective field intensity, electron transport coefficients in nitrogen have been determined in E times B fields (E = electric field intensity, B = magnetic flux density) by the numerical solution of the Boltzmann transport equation for the energy distribution of electrons. It has been observed that as the value of B/p (p = gas pressure) is increased from zero, the perpendicular drift velocity increased linearly at first, reaches a maximum value, and then decreases with increasing B/p. In general, the electron mean energy is found to be a function of Eavet/p( Eavet = averaged effective electric field intensity) only, but the other transport coefficients, such as transverse drift velocity, perpendicular drift velocity, and the Townsend ionization coefficient, are functions of both E/p and B/p.

Dielectric, Ferroelectric and Relaxor Behavior of BaLaxBi4-xTi4O15 Ceramics

Monophasic BaLaxBi4-xTi4O15 (x = 0, 0.2, 0.4, 0.6 and 0.8) ceramics, fabricated from the powders synthesized via the solid-state reaction route exhibited relaxor behavior. Dielectric properties of the well sintered ceramics were measured in a wide frequency range (1 kHz-1 MHz) at different temperatures (300-750 K). The temperature of dielectri maximum (T-m) was found to decrease significantly from 696 K for an undoped sample (x = 0) to 395 K for the sample corresponding to the composition x = 0.8 accompanied by a decrease in the magnitude ofdielectric maximum (epsilon(m)). The temperature variation of the dielectric constant on the high temperature slope of the peak (T > T-m) was analyzed by using the Lorentz-ype quadratic law and the diffuseness of the peak was found to increase with increasing x. Vogel-Fulcher modelling of dielectric relaxation showed a decrease in freezing temperature (T-VF) (from 678 to 340 K) and an increase in the activation energy (5 to 24 meV) for the frequency dispersion with increase in x (La-3 divided by content). Strength of frequency dispersion of the phase transition increased with lanthanum content. Polarization (P)-electric field (E) hysteresis loops recorded at 373 showed a transition from a nearly squarish to slim loop hysteresis behavior with increasing lanthanum content.

Investigation of true remnant polarization response in heterostructured artificial biferroics

Epitaxial bilayered thin films composed of ferromagnetic La0.6Sr0.4MnO3 and ferroelectric 0.7Pb (Mg1/3Nb2/3)O3-0.3(PbTiO3) were fabricated on LaAlO3 (100) substrates by pulsed laser ablation. Ferroelectric, ferromagnetic and magneto-dielectric characterizations performed earlier indicated the possible existence of strain-mediated magneto-electric coupling in these biferroic heterostructures. In order to investigate their true remnant polarization characteristics, usable in devices, room-temperature polarization versus electric field, positive-up negative-down (PUND) pulse polarization studies and remnant hysteresis measurements were carried out. The PUND and remnant hysteresis measurements revealed the significant contribution of the non-remnant component in the observed polarization hysteresis response of these heterostructures. (C) 2010 Published by Elsevier Ltd

Studies on strontium titanate/barium zirconate superlattices

Artificial superlattices of SrTiO3 and BaZrO3 were grown epitaxially with different periodicities on SrRuO3 coated (00 1) SrTiO3 substrates by pulsed excimer laser ablation. Superlattices were structurally characterized by X-Ray theta-2 theta diffraction data. Electrical characterization was done in metal-insulation-metal configuration. Capacitance-voltage measurements showed limited amount of tunability. The DC field induced tunability has been observed to be sensitive to the periodicity of the superlattices, hence the effective strain present in the layers. Hysteretic behaviour in capacitance-voltage (C-V) and polarization versus electric field (P-E) results from the superlattices also indicate the sensitivity of the interfaces. Interfacial strain is supposed to be the most probable cause for such a behaviour which is also manifested in the variation of dielectric constant with individual layer thicknesses. (c) 2007 Elsevier Ltd. All rights reserved.

NMR study of internal motions in certain iron group fluosilicates

NMR study of ferrous fluosilicate hexahydrate indicated the presence of motion of both proton and fluorine nuclei. Only a single narrow line was observed for protons for any arbitrary orientation of a single crystal with respect to the applied magnetic field. This can be interpreted in terms of a phase-correlated flip motion of the interproton vectors between two disordered orientations or in terms of a hindered rotation of the Fe(H2O) 6 octahedron about the fourfold axes, together with the flip motion. The fluorine second moment indicated that the SiF6 octahedron also is undergoing reorientation. The temperature variation of the powder linewidth showed a transition around 195°K and led to rather low values for the potential barriers hindering the motions. No significant temperature variation of the linewidth was observed for hexahydrated cobalt fluosilicate in the temperature range between 90°K and room temperature. Similar observations in a powder sample of tetrahydrated copper fluosilicate also showed the presence of internal motions. The linewidth transition in this case took place at about 220°K and was found to be rather abrupt. The potential barrier for the motion was found to be relatively high.

Quantum theoretic explanation of the Schwarz-Hora effect

Following the path-integral approach we show that the Schwarz-Hora effect is a one-electron quantum-mechanical phenomenon in that the de Broglie wave associated with a single electron is modulated by the oscillating electric field. The treatment brings out the crucial role played by the crystal in providing a discontinuity in the longitudinal component of the electric field. The expression derived for the resulting current density shows the appropriate oscillatory behaviour in time and distance. The possibility of there being a temporal counterpart of Aharonov-Bohm effect is briefly discussed in this context.

Epoxy resin chamber for high voltage breakdown studies in high vacuum

As the study of electrical breakdown phenomena in vacuum systems, gains more importance, a thorough understanding of the breakdown mechanism at high voltages necessitates a chamber for experimental studies. An epoxy-resin chamber has been constructed by casting ring sections which were joined together. The advantages of such a chamber over the conventional metal or glass chamber are given especially as regards the electric field configuration, high voltage lead-in, and the ease of construction. Special facilities can be incorporated while constructing the chamber which makes it more versatile; for example, in pre-breakdown current measurements, electron beam focusing studies, etc.

Observation of reduced activation energy and the possible existence of decoupled pancake vortices in superconductor/ferromagnet bilayers

Investigations of different superconducting (S)/ferromagnetic (F) heterostructures grown by pulsed laser deposition reveal that the activation energy (U) for the vortex motion in a high T-c superconductor is reduced remarkably by the presence of F layers. The U exhibits a logarithmic dependence on the applied magnetic field in the S/F bilayers suggesting the existence of decoupled two-dimensional (2D) pancake vortices. This result is discussed in terms of the reduction in the effective S layer thickness and the weakening of the S coherence length due to the presence of F layers. In addition, the U and the superconducting T-c in YBa2Cu3O7-delta/La0.5Sr0.5CoO3 bilayers are observed to be much lower than in the YBa2Cu3O7-delta/La0.7Sr0.3MnO3 ones. This in turn suggests that the degree of spin polarization of the F layer might not play a crucial role for the suppression of superconductivity due to a spin polarized induced pair-breaking effect in S/F bilayers.

Double diffusive unsteady free convection on two-dimensional and axisymmetric bodies in a porous medium

The unsteady laminar free convection flow of an incompressible electrically conducting fluid over two-dimensional and axisymmetric bodies embedded in a highly porous medium with an applied magnetic field has been studied. The unsteadiness in the flow field is caused by the variation of the wall temperature and concentration with time. The coupled nonlinear partial differential equations with three independent variables have been solved numerically using an implicit finite-difference scheme in combination with the quasilinearization technique. It is observed that the skin friction, heat transfer and mass transfer increase with the permeability parameter but decrease with the magnetic parameter. The results are strongly dependent on the variation of wall temperature and concentration with time. The skin friction and heat transfer increase or decrease as the buoyancy forces from species diffusion assist or oppose the thermal buoyancy force. However, the mass transfer is found to be higher for small values of the ratio of the buoyancy parameters than for large values