National Institute Of Materials Physics - Romania

Investigations on coupling coefficients in a stargeometry filter with defected ground are presented in this paper. The device is compact, requiring a surface area of more than 6 times smaller than the area needed for a conventional patch dual mode resonator.

In this paper we present a penetration depth study on the newly discovered superconductors Li2Pd3B and Li2Pt3B. Surprisingly, the low-temperature penetration depth lambda(T) demonstrates distinct behavior in these two isostructural compounds. In Li2Pd3B, lambda(T) follows an exponential decay and can be nicely fitted by a two-gap BCS superconducting model with a small gap Delta(1)=3.2K and a large gap Delta(2)=11.5K. However, linear temperature dependence of lambda(T) is observed in Li2Pt3B below 03T(c), giving evidence of line nodes in the energy gap.

Giant magnetoresistive (GMR) coatings on silicon, glass and Kapton were prepared by simultaneous thermionic vacuum are (TVA) discharges in high vacuum conditions. The magnetic metal or alloy (Fe, Co, Ni, Permalloy) together with the noble non magnetic metal were deposited on substrates having different positions relative to the discharges. Local magnetic interactions and Fe-phase composition were obtained by Mossbauer spectroscopy whereas the magnetoresistance effects were measured by a dc method using a four-point configuration with perpendicular to plane magnetic fields up to 0.8 T. The surface morphology of the coatings was characterized by atomic force microscopy (AFM) in contact mode.

The use of a variationnal perturbation method combined with finite element analysis is presented here to simulate the influence of mass-loading effects on the resonance frequency of bulk acoustic wave resonator. Computations are conducted on 2D and 3D and any shape of resonator can be considered. Predictions are compared to experimental data.

The spin dynamics and thermodynamic properties of micro- and nanostructured lanthanum manganites La0.67Ca0.33Mn1-xMeO3 (Me = Al; x = 0-0.05) have been studied in order to evidence new features related to the effect of different compositional variables on the thermodynamic and magnetic behaviour. By electron paramagnetic resonance (EPR) spectroscopy, the influence of the grain size and the Mn substitution effects on the spin dynamics were investigated. A solid state electrochemical method was used to obtain the relative partial molar free energies, enthalpies and entropies of oxygen dissolution in the perovskite phase, as well as the equilibrium partial pressures of oxygen. The influence of the oxygen stoichiometry change on the thermodynamic properties has been investigated. The results were correlated with the average Mn valence values as determined by redox titration. In this paper an alternative method is proposed to estimate the contribution made by oxygen vacancies in balancing the local charge in CMR manganites. (c) 2006 Elsevier Ltd. All rights reserved.

Nd-doped strontium and lanthanum (ASL) crystals Sr1-xLax-yNdyMgxAl12-xO19 (0.05 <= x <= 0.5; y = 0.05) were grown by Czochralski pulling technique. Up to 1.67W of 900mn rR output laser power for an absorbed power of 2.53W was obtained under Ti:sapphire pumping at 792nm. Intracavity second harmonic generation experiments led to 320mW of blue laser power at 450mn with a 10mm-long BiB3O6 nonlinear crystal. Other nonlinear crystals were also evaluated such as LBO.

In-plane conductivity sigma(ab) curves of Y0.54Pr0.46Ba2Cu3O7 single crystals, measured at constant temperature T in magnetic fields H tilted with an angle theta relative to the c-axis, were found to map onto a single curve in a sigma(ab) vs Hcos theta plot. This scaling occurs both below and above the critical temperature T-c, maintaining the same convexity, and is consistent with the dissipation caused by the motion of two-dimensional (2D) vortices. This indicates the presence of 2D vortices above T-c. A second scaling sigma(ab)(Hcos theta) takes place at higher T-c with an opposite convexity. This scaling is consistent with the dissipation of quasiparticies. There is a T range between these two regimes where no scaling is found. We attribute the absence of scaling in this intermediate regime to a 2D to 3D crossover in the vortex matter.

Magnetization M(H,T) and M(T,H) curves with magnetic field approximately parallel and perpendicular to the c-axis of Na0.35CoO2.1.3H(2)O superconducting crystals have been measured (T-c = 3.7 K). The shape of the M(H,T) loops resembles Bi-based high-T-c superconductors (HTS), but the superconducting anisotropy is below that of Bi-system; this parameter is as for HTS with middle or moderately high anisotropy. (c) 2006 Elsevier Ltd. All rights reserved.

A microscopic theory is applied to study carrier-carrier Coulomb scattering in nitride-based quantum dots. Kinetic equations for the carrier population are used to define capture and relaxation rates. For the states involved in the scattering processes, the combined influence of the quantum-confined Stark effect and many-body renormalizations is taken into account. It is shown that the charge separation due to the built-in field is accompanied with strong Hartree energy shifts, which can increase the scattering efficiency. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.