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

Interfacial coupling and its size dependence in PbTiO3 and PbMg1/3Nb2/3O3 multilayers

Multilayers of Pb(Mg1/3Nb2/3)O-3 (PMN)-PbTiO3 (PT) were deposited through pulsed laser ablation deposition with different periodicities (d=10, 20, 30, 40, 50, 60, and 70 nm) for a constant total thickness of the film. The presence of superlattice reflections in the x-ray diffraction pattern clearly showed the superlattice behavior of the fabricated structures over a periodicity range of 20-50 nm. Polarization hysteresis and the capacitance-voltage characteristics of these films show clear size dependent ferroelectric and antiferroelectric (AFE) characteristics. Presence of long-range coupling and strain in multilayers with lower periodicity (similar to 10 nm) exhibited a clear ferroelectric behavior similar to a solid solution of PMN and PT. Multilayers with higher periodicities (20-50 nm) exhibited antiferroelectric behavior, which could be understood from the energy arguments. On further increase of periodicity, they again exhibit ferroelectric behavior. The polarization studies were carried out beyond the Curie temperature T-c of PMN to understand the interlayer interaction. The interaction is changed to a ferroelectric-paraelectric interlayer and tends to lose its antiferroelectric behavior. The behavior of remnant polarization P-r and dP(r)/dT with temperature clearly proves that the AFE coupling of these superlattices is due to the extrinsic interfacial coupling and not an intrinsic interaction as in a homogeneous conventional AFE material. The evidence of an averaged behavior at a periodicity of similar to 10 nm, and the behavior of individual materials at larger periodicities were further confirmed through dielectric phase transition studies. The presence of AFE interfacial coupling was insignificant over the dielectric phase transition of the multilayers.

Observation of a large coupling of a bound dihydrogen ligand to phosphorus ligands in trans-[(dppe)(2)Ru(eta(2)-H-2) (PF(OMe)(2))][BF4](2) complex

A new dicationic dihydrogen complex of the type trans-[(dppe)(2)Ru(eta (2)-H-2)(PF(OMe)(2))]BF4](2) has been prepared and characterized. A large coupling of about 50 Hz between the H-2 and trans-phosphorus ligand in this complex has been observed.

Non-resonant microwave absorption evidence for intrinsic Josephson coupling in Tl2Ba2CaCu2O8 single crystals

We report the results of our non-resonant microwave absorption (NRMA) studies on single crystals of Tl2Ba2CaCu2O8 (Tl 2212) which reflect the occurrence of intrinsic Josephson coupling in these crystals. We have studied the magnetic field induced microwave absorption at various temperatures from 4.2K to T-c (similar to 104K) using a standard CW EPR spectrometer (H-dc parallel to c). We observe the appearance of a characteristic feature in the NRMA signals similar to the ones observed earlier by us in Bi2Sr2CaCu2O8 (Bi 2212) starting a few degrees below T-c, which on cooling passes through a maximum in intensity before disappearing at a further low temperature. This behaviour is attributed to the appearance, strengthening and disappearance of Josephson response consequent to the temperature dependence of the viscosity of the Josephson medium between the CuO2 superconducting sheets.

Scaling behavior of plasmon coupling in Au and ReO3 nanoparticles incorporated in polymer matrices

Polymer nanocomposites containing different concentrations of Au nanoparticles have been investigated by small angle X-ray scattering and electronic absorption spectroscopy. The variation in the surface plasmon resonance (SPR) band of Au nanoparticles with concentration is described by a scaling law. The variation in the plasmon band of ReO3 nanoparticles embedded in polymers also follows a similar scaling law. Sistance dependence of plasmon coupling in polymer composites f metal nanoparticles. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Local structure and magneto-transport in Sr2FeMoO6 oxides

Double perovskite oxides Sr2FeMoO6 have attracted a great interest for their peculiar magneto-transport properties, and, ill particular, for the large values of low-field magneto-resistance (MR) which remains elevated even at room temperature, thanks to their high Curie temperature (T-c > 400 K). These properties are strongly influenced by chemical cation disorder, that is by the relative arrangement of Fe and Mo on their sublattices: the regular alternation of Fe and Mo enhances the M R and saturation magnetization. On the contrary the disorder generally depresses the magnetization and worsen the MR response. In this work the X-ray absorption fine structure (XAFS) technique has been employed in order to probe the cation order from a local point of view. XAFS spectra were collected at the Fe and Mo K edges on Sr2FeMoO6 samples with different degree of long-range chemical order. The XAFS results prove that a high degree of short-range cation order is preserved, despite the different long-range order: the Fe-Mo correlations are always preferred over the Fe-Fe and Mo-Mo ones in the perfectly ordered as well as in highly disordered samples.

Influence of lattice distortion on the Curie temperature and spin-phonon coupling in LaMn0.5Co0.5O3

Two distinct ferromagnetic phases of LaMn0.5Co0.5O3 having monoclinic structure with distinct physical properties have been studied. The ferromagnetic ordering temperature T-c is found to be different for both the phases. The origin of such contrasting characteristics is assigned to the changes in the distance(s) and angle(s) between Mn-O-Co resulting from distortions observed from neutron diffraction studies. Investigations on the temperature dependent Raman spectroscopy provide evidence for such structural characteristics, which affects the exchange interaction. The difference in B-site ordering which is evident from the neutron diffraction is also responsible for the difference in T-c. Raman scattering suggests the presence of spin-phonon coupling for both the phases around the T-c. Electrical transport properties of both the phases have been investigated based on the lattice distortion.

Broad-Band Coupling of High-Q Resonant Loads

Considering the method of broad-band coupling a series resonant RLC load to a resistive source using a uniform quarter-wave transmission-line inverter, it is shown that the 3-dB bandwidth of the network insertion loss reckoned with respect to a 0-dB loss attains a maximum for a particular value of the center frequency insertion loss in the range 0-3 dB. The center frequency Ioss and the corresponding value of the maximum 3-dB bandwidth are calculated for various loads and the results graphically presented.

Coupling of surface acoustic waves propagating in two separated piezoelectric media

The coupling of surface acoustic waves propagating in two separated piezoelectric media is studied using the perturbation theory of Auld. The results of the analysis are applied to two configurations using Bi12GeO20 and CdS crystals. It is found that the loss due to coupling is about 7 dB at 50 MHz in the cases of (111)-cut, [110]-prop. Bi12GeO20 and Y-cut, 60°-X prop. CdS combination. On étudie le couplage des ondes acoustiques de surface se propageant sur deux milieux piezo-eléctriques par la théorie de perturbation de Auld. Les resultats d'analyse sont appliqué's aux deux configurations des cristanx Bi12GeO20 et CdS. On trouve que la perte par couplage est environ de 7 dB a 50 MHz dans le cas de combination de (111)-coupe, [110]-prop. Bi12GeO20 et Y-coupe, 60°-X prop. CdS.

Psi-angle dependence of geminal proton–carbonyl-13C coupling constants in peptides. A theoretical investigation†

Theoretical calculations of the geminal carbonyl-13C- proton coupling constant, 2J(C′H), in α-amino acids have been carried out using Dirac Vector model and Penney-Dirac bond order formulations. The results indicate that the couplings are dependent on the backbone torsion angle psi (ψ) of the amino acid residues in peptides. The meagre available experimental data seem to support the theoretical findings.

A geodesic constant method for computing high-frequency mutual coupling between antennas on general quadric cylinders

A Geodesic Constant Method (GCM) is outlined which provides a common approach to ray tracing on quadric cylinders in general, and yields all the surface ray-geometric parameters required in the UTD mutual coupling analysis of conformal antenna arrays in the closed form. The approach permits the incorporation of a shaping parameter which permits the modeling of quadric cylindrical surfaces of desired sharpness/flatness with a common set of equations. The mutual admittance between the slots on a general parabolic cylinder is obtained as an illustration of the applicability of the GCM.

Padé approach to potential transients: Part 1. Electron transfer without and with coupling to first-order homogeneous reactions at planar electrodes

Potential transients are obtained by using “Padé approximants” (an accurate approximation procedure valid globally — not just perturbatively) for all amplitudes of concentration polarization and current densities. This is done for several mechanistic schemes under constant current conditions. We invert the non-linear current-potential relationship in the form (using the Lagrange or the Ramanujan method) of power series appropriate to the two extremes, namely near reversible and near irreversible. Transforming both into the Pad́e expressions, we construct the potential-time profile by retaining whichever is the more accurate of the two. The effectiveness of this method is demonstrated through illustrations which include couplings of homogeneous chemical reactions to the electron-transfer step.

Analysis of the evanescent field coupling between a fiber and a planar waveguide using the explicit finite difference method with a nonuniform mesh (Journal Paper)

We investigate an optical waveguide system consisting of an unclad fiber core suspended at a constant distance parallel to the surface of a planar waveguide. The coupling and propagation of light in the combined system is studied using the three-dimensional explicit finite difference beam propagation method with a nonuniform mesh configuration. The power loss in the fiber and the field distribution in the waveguide are studied as a function of various parameters, such as index changes, index profile, and propagation distance, for the combined system.