National Institute Of Materials Physics - Romania

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892 articles found

551. Artificial pinning centres in YBa2Cu3O7-delta thin films by Gd2Ba4CuWOy nanophase inclusions

Authors: Kechik, MMA; Mikheenko, P; Sarkar, A; Dang, VS; Babu, NH; Cardwell, DA; Abell, JS; Crisan, A

Published: MAR 2009, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 22, DOI: 10.1088/0953-2048/22/3/034020

Artificial pinning centres produced by Gd2Ba4CuWOy (2411W) nanophase inclusions in YBa2Cu3Oy (YBCO) thin films grown by pulsed laser deposition (PLD) using a YBCO target containing 1 mol% 2411W have been investigated. For comparison, YBCO thin films have been grown under the same conditions using a pure (commercial) YBCO target. The resulting films were characterized by AC susceptibility (superconducting transition) and SQUID magnetometry (critical current density, J(c)), and by x-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive x-ray (EDX) spectroscopy and atomic force microscopy (AFM) (structure, morphology and chemical composition). J(c) of the film grown from the composite target is practically the same as that measured for the reference sample at 5 K over the whole range of applied field up to 4.5 T. For temperatures higher than 50 K, however, the presence of the nano-inclusions leads to increased J(c). The relative enhancement in J(c) increases with further increase in temperature. J(c) of the film containing nanophase inclusions is between two and three times higher than that of the reference sample at 77.3 K and 1.5 T. This can be explained by considering the dimensions of nanophase inclusions compared with the temperature-dependent coherence length. Susceptibility measurements reveal that, apart from a large and sharp transition at about 91 K, there is a secondary, smaller and broader transition between 88 and 84 K in the YBCO film containing nanophase inclusions. This can be explained by substitutions of compatible atoms between YBCO and the 2411W phase (Gd with Y), which might also create additional pinning centres of delta T-c-type.

552. (001) Bi2Sr2Ca2Cu3O10 Superconducting Thin Films on Substrates with Large Film-Substrate Lattice Mismatch and Different Film-Substrate Lattice Mismatch Anisotropy

Authors: Endo, K; Badica, P

Published: JAN 2009, CRYSTAL GROWTH & DESIGN, 9, 394, DOI: 10.1021/cg800604b

Thin films of (001) Bi2Sr2Ca2Cu3O10 With high zero-resistance critical temperature T(c)0 = 75-95.1 K and low roughness up to three half-c-axis unit cells were grown by metal-organic chemical vapor deposition (MOCVD) on substrates with large film-substrate lattice mismatch and different film-substrate mismatch anisotropy. Comparative analysis of the films on (001) and (110) MgO and NdGaO3 suggests that Bi-2223 films can easily accommodate large mismatch film-substrate differences, while mismatch on different directions, that is, mismatch anisotropy, has a strong influence on the quality of the film. The highest quality (low roughness, high uniformity, and high T-c0(R=O)) is obtained when mismatch anisotropy, taken as the mismatch ratio (r), is given only by compressive or only by tensile mismatch stress, and it is around 1, that is, it is as for the (001) MgO substrate. Mismatch anisotropy (value and sign) is an important parameter and can be used to tune superconducting properties of the film.

553. Nanoblast Synthesis and Consolidation of (La0.8Sr0.2) (Ga0.9Mg0.1)O3-delta Under Spark Plasma Sintering Conditions

Authors: Vasylkiv, O; Borodianska, H; Badica, P; Zhen, Y; Tok, A

Published: JAN 2009, JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 9, 149, DOI: 10.1166/jnn.2009.J008

Four-cation nanograined strontium and magnesium doped lanthanum gallate (La0.8Sr0.2) (Ga0.9Mg0.1)O3-delta (LSGM) and its composite with 2 wt% of ceria (LSGM-Ce) were prepared. Morphologcally homogeneous nanoreactors, i.e., complex intermediate metastable aggregates of desired composition were assembled by spray atomization technique, and subsequently loaded with nanoparticles of highly energetic C3H6N6O6. Rapid nanoblast calcination technique was applied and the final composition was synthesized within the preliminary localized volumes of each single nanoreactor on the first step of spark plasma treatment. Subsequent SPS consolidations of nanostructured extremely active LSGM and LSGM-Ce powders were achieved by rapid treatment under pressures of 90-110 MPa. This technique provided the heredity of the final structure of nanosize multimetal oxide, allowed the prevention of the uncontrolled agglomeration during multicomponent aggregates assembling, subsequent nanoblast calcination, and final ultra-rapid low-temperature SPS consolidation of nanostructured ceramics. LaSrGaMgCeO3-delta nanocrystalline powder consisting of similar to 11 nm crystallites was consolidated to LSGM-Ce nanoceramic with average grain size of similar to 14 nm by low-temperature SPS at 1250 degrees C. Our preliminary results indicate that nanostructured samples of (La0.8Sr0.2)(Ga0.9Mg0.1)O3-delta with 2 wt% of ceria composed of similar to 14 nm grains can exhibit giant magnetoresistive effect in contrast to the usual paramagnetic properties measured on the samples with larger grain size.

554. Characterization of Superconducting Wires By Cone-Beam Micro-Tomography

Authors: Tiseanu, I; Craciunescu, T; Badica, P; Aldica, GV; Rindfleisch, M

Published: 2009, 2008 IEEE NUCLEAR SCIENCE SYMPOSIUM AND MEDICAL IMAGING CONFERENCE (2008 NSS/MIC), VOLS 1-9, +, DOI:

Commercial wires of Nb3Sn and NIgB2 were inspected through X-ray cone-beam micro-tomography (mu CT). Details of the architecture of the wires of different topologies were visualized. In the case of MgB2 wires this allowed to compare the geometrical perfection of the component elements between the wires with 18 and 7 superconducting sub-elements heat treated for different conditions. Defects such as 3D voids and interruption of the diffusion barriers were also visualized. High resolution 3D-mu CT observations of the Nb3Sn wire architecture allowed also direct and non-invasive determination of the twist-pitch parameter. 3D tomography shows important advantages over 2D traditional microscopy methods.

555. Magnetism and Structural Phase Transformation in Fe/Fe oxide Nanopowders

Authors: Crisan, O; Crisan, AD; Skorvanek, I; Kovac, J

Published: 2009, 13TH INTERNATIONAL CONFERENCE ON RAPIDLY QUENCHED AND METASTABLE MATERIALS, 144, DOI: 10.1088/1742-6596/144/1/012027

Fe / Fe3O4 (magnetite) powders obtained by ball milling at room temperature, undergo an incomplete redox reaction with formation of FeO. This reaction is favoured due to the high energy developed during the milling and alloying. Concurrent effects of the milling, such as grain refinement down to the nanometric scale lead at the end of the milling processes to a mixed multiphased nanopowder, with a homogeneous dispersion of Fe and Fe oxide grains. Such ferromagnetic - antiferromagnetic systems are extensively studied due to their exchange bias properties, extremely useful in technological applications. We study the phase transformation that leads to a multiphased metal / oxide microstructure with an energy-dispersive in-situ X-ray diffraction experiment using the synchrotron radiation. This study allows direct collection of X-ray spectra after few minutes exposure, at selected temperatures, ranging between 20 degrees C and 1000 degrees C. Magnetic behavior has been studied for as-milled and annealed samples and the obtained magnetic parameters are correlated to the microstructure and phase composition at each stage of annealing. A significant exchange bias effect, related to FeO content, is observed for as-milled sample, the effect being less pronounced upon annealing the nanogranular powder.

556. Spin configurations and interfacial diffusion in exchange bias and spin valve systems with Ir-Mn antiferromagnetic pinning layers

Authors: Kuncser, V; Schinteie, G; Palade, P; Mustata, I; Lungu, CP; Stefan, N; Chiriac, H; Vladoiu, R; Filoti, G

Published: 2009, ISIAME 2008, +, DOI: 10.1007/978-3-642-01369-0_62

Exchange bias and spin valve structures with Fe as ferromagnetic layers selectively enriched in Fe-57 and Ir-Mn of different compositions as antiferromagnetic pinning layers have been prepared by r.f. sputtering. Conversion Electron Mossbauer Spectroscopy and Magneto Optic Kerr Effect have shown that the local structure and interactions in the whole ferromagnetic layers, with direct influence on their magnetic reversal processes, depend on growing order of the layers and composition of the AF layer. Interfacial atomic diffusion is the main reason of perturbing the local structure of the ferromagnet. Mossbauer Spectroscopy is a powerfool tool which allows a detailed analysis of local configurations, in order to optimize the magnetic and giant magnetoresistive parameters of such multilayers of important technological applications.

557. Fabrication and Transport Properties of Manganite-Polyacrylamide-Based Composites

Authors: Sandu, V; Popa, S; Ivan, I; Plapcianu, C; Sandu, E; Mihailescu, C; Doroftei, F

Published: 2009, JOURNAL OF NANOMATERIALS, 2009, DOI: 10.1155/2009/429430

We present the fabrication and transport properties of a series of composites made of La2/3Sr1/3MnO3 and acrylamide-based copolymers. The most important result is the very narrow transition, of only 27 K, displayed by the peak that appears around the metal-insulator transition of the composites made with poly(acrylamide-vinylacetate). Although the amount of polymer is rather low, different copolymers change drastically the electric transport characteristics. Copyright (C) 2009

558. Characterization of magnetic nano-fluids via Mossbauer spectroscopy

Authors: Filoti, G; Kuncser, V; Schinteie, G; Palade, P; Morjan, I; Alexandrescu, R; Bica, D; Vekas, L

Published: 2009, ISIAME 2008, +, DOI: 10.1007/978-3-642-01369-0_50

The laser pyrolysis became a useful tool, providing various ways, in production of nano materials. The iron Mossbauer spectroscopy is one very accurate method in evidencing the physical properties and related processes in the nano scale compounds. The effect of pressure, laser spot area and induced combustion, of gas mixture and laser power on the phase composition and inside particle distribution, grain size as well as the related phenomena were investigated by temperature dependent Mossbauer spectroscopy. A selection of most relevant properties is presented and discussed in details.

559. Phase diagram of a lattice of pancake vortex molecules

Authors: Tanaka, Y; Crisan, A; Shivagan, DD; Iyo, A; Shirage, PM; Tokiwa, K; Watanabe, T; Terada, N

Published: AUG-OCT 2009, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 469, 1131, DOI: 10.1016/j.physc.2009.05.202

On a superconducting bi-layer with thickness much smaller than the penetration depth, lambda, a vortex molecule might form. A vortex molecule is composed of two fractional vortices and a soliton wall. The soliton wall can be regarded as a Josephson vortex missing magnetic flux (degenerate Josephson vortex) due to an incomplete shielding. The magnetic energy carried by fractional vortices is less than in the conventional vortex. This energy gain can pay a cost to form a degenerate Josephson vortex. The phase diagram of the vortex molecule is rich because of its rotational freedom. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.

560. Polymer functionalization with manganites

Authors: Sandu, V; Popa, S; Ivan, I; Plapcianu, C; Sandu, E; Hurduc, N; Nor, I

Published: 2009, SECOND INTERNATIONAL CONFERENCE ON SMART MATERIALS AND NANOTECHNOLOGY IN ENGINEERING, 7493, DOI: 10.1117/12.843221

We investigated the transport properties of a series of composites made of La2/3Sr1/3MnO3 and different copolymers. The temperature dependence of the electrical resistance of the samples is strongly dependent on the nature of the polymers. We found four types of temperature dependences of the electrical resistance: i) simple current dependence of resistivity for poly(methyl-methacrylate-co-styrene) copolymers, ii) single peaked characteristics for poly(acryl amide-co-vinyl acetate), iii) multipeaked dependence found in poly(methyl-methacrylate-co-butadiene) and star type polysiloxane-g-styrene, and iv) current independent characteristics visible in the samples made with linear polysiloxane-based composites.