National Institute Of Materials Physics - Romania

High quality superconducting thin films of HTS have been grown by MOCVD on substrates with artificial steps of predefined height and width. The surface of the films grown on the steps having width equal to the 'double of the migration length' of the atomic species depositing on the substrate is totally free of precipitates: precipitates are gathered at the step edges where the free energy is lowest. The method has several advantages: it is simple, universal (it is independent of the materials, substrates, deposition technique or application) and allows control of precipitates segregates so that the quality and growth conditions of the films are the same as for the films grown on conventional substrates. The method is expected to result in new opportunities for the device fabrication, design and performance.

This paper presents experimental results concerning the influence of the additives on the physical properties of polymer films. Metal oxides/inorganic salts were used as additives in vinyl-polymers solutions. The physical properties of the metal doped polymer films can be significantly modified by the composition of the doping elements and the curing conditions of the polymer. Morphologic, electronic, magnetic and optic properties of the doped polymers were analysed by AFM. SEM. Mossbauer spectroscopy and optical measurements. The film composition and the deposition processes were optimized to allow a better control of the optical parameters (refractive index. transmission). to reduce the processing temperatures and to improve the chemical sensitivity of the films for sensor applications. These compounds can be easily spin coated onto a variety of directly patterned semiconductor substrates. (C) 2005 Elsevier Ltd. All rights reserved.

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.

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 scanning Hall probe microscope (SHPM) with an effective spatial resolution of 1 similar to mu m has been used to study the local induction in high quality superconducting Bi2Sr2CaCu2O8+delta single crystals at high temperatures and low magnetic fields. We observed, for the first time to our knowledge, an anomalous splitting of the peak of first full penetration of magnetic field, We discuss the observed splitting, which is connected to the effects of surface and geometrical barriers on the vortex lattice.

Scanning Hall probe microscopy and magnetometry have been used to study pancake vortices (PV's) in highly anisotropic Bi2Sr2CaCu2O8+delta (BSCCO) thin films. For small perpendicular applied fields we observe well-defined PV stacks which are randomly pinned due to a high density of relatively strong pinning centers in the films. When a strong in-plane magnetic field is added images reveal stripelike flux structures which are quite closely aligned to the in-plane field direction. We conclude that this is a manifestation of Josephson vortex (JV) "decoration" by PV's, which was recently demonstrated in highly ordered BSCCO single crystals in the crossing lattices regime, allowing independent estimates of the anisotropy parameter to be made. This interpretation is supported by the observation that the presence of an in-plane field suppresses the irreversible magnetization of thicker films. Estimates of the JV-PV crossing force and the PV pinning force are found to be comparable in magnitude and fully consistent with this scenario. We believe that this is the first confirmation of the existence of interacting crossing vortex lattices in strongly pinning BSCCO thin films and could find potential applications in superconducting devices.

Growth of such non-superconducting whiskers [Sr2.24Ca0.4Al2Ox, (Ca0.8-0.85Sr0.15-0.1)(2)CuO3, CuO, or Bi2.44Sr2Ca1.3-2Cu6.9-9.95Al0.35-0.46Ox (Cu-rich whiskers)] formed during the growth of Bi-2212 superconducting whiskers from powder or glassy substrates, is discussed. These whiskers are likely to grow from the bottom end, and there is a tight relationship with the growth of the Bi-2212 whiskers. A general reaction-path model for the whisker growth in the BSCCO system, independent of the type of the catalytic impurity and substrate, is proposed. When whiskers are grown under magnetic fields, up to 10 T, changes in the whisker size, aspect ratio, and morphology are observed.

LaNiSn and NdNiSn compounds and their deuterides have been studied by variable temperature Sn-119 Mossbauer spectroscopy. The hyperfine parameters obtained experimentally are in good agreement with those derived from first principle calculations. The enlargement of quadrupole splitting observed for LaNiSn after deuteration confirms the lower symmetry of electron density around tin atoms indicated by the calculation of partial Sn-p density of states (DOS). Magnetic ordering is observed at low temperature in deuterided NdNiSn.

Fe-sheathed tapes of MgB2 with addition of SiC have been prepared by the powder-in-tube (PIT) method using a powder mixture mechanically milled in an argon or hydrogen atmosphere. The reactivity of the component powders in the mixtures, Mg, B and SiC, was significantly enhanced by mechanical milling, so that MgB, formed faster than in tapes fabricated from a hand-milled mixture. At the same time the number of impurity phases was higher, and the impurity phases of Mg2Si and Fe2B were observed only in these tapes. Mechanical milling also induced a lower quality of MgB2, especially for tapes produced from powders milled in a hydrogen atmosphere, with a significant influence on the values of the critical temperature T-C and critical field, J(C). (c) 2005 Published by Elsevier B.V.