National Institute Of Materials Physics - Romania

Publications

893 articles found

601. Exchange bias and spin valve systems with Fe-Mn antiferromagnetic pinning layers, obtained by the thermo-ionic vacuum arc method

Authors: Kuncser, V; Valeanu, M; Schinteie, G; Filoti, G; Mustata, I; Lungu, CP; Anghel, A; Chiriac, H; Vladoiu, R; Bartolome, J

Published: JUL 2008, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 320, E230, DOI: 10.1016/j.jmmm.2008.02.054

Exchange bias and spin valve systems with Fe-Mn antiferromagnetic layers of different Fe concentrations were obtained by the thermo-ionic vacuum arc method. The adherence of the multilayer system to the Si substrate depends on the Fe-Mn composition. The overall roughness depends on the growing order of the antiferromagnetic/ferromagnetic layers. Very low blocking temperatures for exchange bias were observed for the considered compositions of the Fe-Mn layer. The coercive forces of both the pinned and the free layers of spin valve structures can be considerably modified along a large set of samples simultaneously prepared. (C) 2008 Elsevier B.V. All rights reserved.

602. Magnetoresistiviiy and upper critical field in superconductor Mo3Sb7

Authors: Tran, VH; Bauer, E; Galatanu, A; Bukowski, Z

Published: JUL 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 1632, DOI:

Magnetotransport data on a single crystal of the superconducting Mo3Sb7 are reported for temperatures down to 0.4 K and in magnetic fields up to 12 T. The magnetoresistance data are analyzed in terms of the Ginzburg-Landau fluctuation theory. From the experimental data the upper critical field H-c2(0) and Ginzburg-Landau coherent length xi(O) are determined to be similar to 2.3 T and 12 nm, respectively. The H,2(0) value agrees with that inferred from the Werthamer, Helfand, Hohenberg, and Maki theories for conventional type-II superconductors.

603. Shape memory and associated properties in Fe-Mn-Si-based ribbons produced by melt-spinning

Authors: Valeanu, M; Filoti, G; Kuncser, V; Tolea, F; Popescu, B; Galatanu, A; Schinteie, G; Jianu, AD; Mitelea, I; Schinle, D; Craciunescu, CM

Published: JUL 2008, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 320, E167, DOI: 10.1016/j.jmmm.2008.02.105

Four Fe-Mn-Si alloys, Fe(62)Mn(32)Si(6), Fe(62)Mn(20)Si(5)Cr(8)Ni(5), Fe(62)Mn(16)Si(5)Cr(12)Ni(5) and Fe(65)Mn(9)Si(7)Cr(10)Ni(9), were obtained by the melt-spinning method. The samples were structurally, magnetic and shape memory effect (SME) investigated, both ''as quenched'' and thermally treated. The Mn-rich compositions show different phase, magnetic behavior and SME in comparison with Mn-poor compositions. The thermal treatments generate transformation between the two existing majority phases (alpha and gamma), related magnetization and SME behavior. The features are derived from the corroboration of structural, magnetic interaction and magnitude of SME data. (c) 2008 Elsevier B.V. All rights reserved.

604. Physical properties of the new ferromagnetic Kondo system CeAg1-xNixSb2

Authors: Popescu, B; Birsan, A; Galatanu, A; Royanian, E; Hilscher, G; Bauer, E

Published: JUL 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 1629, DOI:

Structural, magnetic and transport properties of CeAg1-xNixSb2 compounds are investigated on polycrystalline samples. The experimental results show the formation of ferromagnetic compounds with sharp transitions decreasing from 9.5 K in the 100% Ag compound to 8.1 K for 33% Ni substitution, 7 K for 67% Ni substitution to 6 K for the 100% Ni compound. The characteristic temperatures, considered as the temperature of the resistivity maximum To increases from 26 K to 44 K, 54 K and 65 K, respectively. These results indicate Ce(AgNi)Sb2 compounds as a ferromagnetic Kondo system.

605. Pressure response of Ce(Ag, Ni)Sb(2) compounds

Authors: Khan, RT; Galos, R; Bauer, E; Popescu, B; Galatanu, A

Published: JUL 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 1615, DOI:

The pressure response of CeAg(1-x)Ni(x)Sb(2) is Studied by means of electrical resistivity measurements. The ferromagnetic ordering temperatures T(c) of this series decrease as pressure is applied, except CeNiSb(2), showing a pressure driven continuous increase of T(c). This refers to crystalline electric field effects originating distinct different magnetic ground states. Concomitantly, the pressure response of various material dependent parameters also behave in the opposite direction.

606. Thermally-induced self-assembling nanotechnology of gold nano-dots on CeO2-buffered sapphire for superconducting films

Authors: Crisan, A; Wordenweber, R; Hollmann, E; Kutzner, R; Button, TW; Abell, JS

Published: JUN 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 1373, DOI:

A typical facility for fabrication of devices based on high temperature superconducting (HTS) films grown on the less-expensive CeO2-buffered sapphire substrates comprises a transfer chamber, a chamber for CeO2 growth, a chamber for YBa2Cu3Oy (YBCO) growth, and a chamber for Au deposition at room temperature. Here we present the adaptation of our previously-reported method to create artificial pinning centres in HTS films through self-assembled nano-scale islands for this type of facility without making any modifications. We succeeded to grow Au nano-dots from an ultra-thin layer of Au grown at room temperature subsequently annealed in the chamber for YBCO deposition, in the same conditions as for YBCO growth. AFM and RBS were used to investigate the formation of Au nano-dots, while XRD and susceptibility measurements were used to study the properties of nano-structured YBCO films.

607. Microstructural and magnetic characterization of CuNb/Nb3Sn wires with different architectures

Authors: Sandim, MJR; Cangani, MP; Sandim, HRZ; Ghivelder, L; Awaji, S; Badica, P; Watanabe, K

Published: JUN 2008, IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, 18, 1025, DOI: 10.1109/TASC.2008.920575

In this work we focus on the microstructural and magnetic characterization of CuNb/Nb3Sn wires with different architectures (design and reinforcement). The microstructural characterization was performed using scanning electron microscopy. AC magnetic susceptibility was measured with field applied both parallel and perpendicular to the wire axis. The heat treatment performed to form the A-15 superconducting phase leads to partial spheroidization followed by coarsening of the Nb filaments in the reinforcement material. The differences concerning the microstructure of the reinforcement material among the investigated wires were reflected in the broadening of the superconducting transition of Nb, more evident for a field applied parallel to the wire axis. From the magnetic data the wires were also compared in terms of the superconducting volume fraction.

608. Influence of deviatoric strain for superconducting parameters of Nb3Sn wires

Authors: Oguro, H; Awaji, S; Nishijima, G; Badica, P; Shikanai, F; Kamiyama, T; Katagiri, K; Watanabe, K

Published: JUN 2008, IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, 18, 1050, DOI: 10.1109/TASC.2008.921907

The tensile strain dependence of the upper critical field B-c2 for Nb3Sn wires was measured using a new apparatus for applying tension at low temperature. The critical current I-c calculated from the strain-dependent B-c2 measurements is the almost consistent with the measured I-c. In the measurements by a new apparatus, the axial and the lateral applied strains were examined by the strain gauges attached onto the wire. The deviatoric strain epsilon(dev) and the hydrostatic strain epsilon(hyd) were estimated by the axial and the lateral strain. We found the deviatoric strain dependence of B-c2 is different between the tensile and compressive strain states. This means that the hydrostatic strain also should be taken into account in order to understand the strain effects on the superconducting properties of Nb3Sn.

609. Pancake vortex molecules in HgBa2Can-1CunOy (n > 6) superconductors

Authors: Crisan, A; Iyo, A; Tanaka, Y; Matsuhata, H; Shivagan, DD; Shirage, PM; Tokiwa, K; Watanabe, T; Button, TW; Abell, JS

Published: APR 1 2008, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 468, 717, DOI: 10.1016/j.physc.2007.11.085

HgBa2Can-1CunOy (Hg: 12(n -1)n) phases have the same T-c independent of n and the same vortex melting line for n >= 6. In these materials, there are two types of pancake pairs: those separated by the thick block of (n-2) inner CuO2 planes, which are weakly coupled by the magnetic interaction, and, respectively, those separated by the thin HgBa2Ox charge reservoir layer, which are much stronger coupled by the Josephson coupling. The vortex melting line common to all Hg:12(n-1)n phases (n >= 6), separates two new vortex phases, pancake-molecule-glass, and pancake-molecule-liquid. (c) 2008 Elsevier B. V. All rights reserved.

610. Vortex imaging with varying temperature revealed by SHPM on Bi(2)Sr(2)CaCu(2)O8+y

Authors: Mihalache, V; Dede, M; Oral, A; Sandu, V

Published: APR 1 2008, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 468, 836, DOI: 10.1016/j.physc.2007.11.059

Scanning Hall probe microscopy with an effective spatial resolution of similar to 1 mu m has been used to investigate the vortex structures in superconducting Bi2Sr2CaCu2O8+delta single crystals in the temperature range 77.3-81.3 K and zero applied field (in the presence of the earth field). The vortex images were obtained in real time mode as the temperature increased slowly for 3.36 h. At 77.3 K, the vortices were arranged in a chain structure. With the increase of the temperature, two jumps in the vortex array occur at 77.3 K, immediately when the temperature starts to rise, and at 79.2 K with a good stability between jumps. The second jump is accompanied by the jump in the average magnetic induction when bundles of 4-5 additional vortices enter the scanning area and the vortex array get disordered. These directly visualized transitions in the vortex lattice are consistent with a vortex creep over the surface barriers at high temperatures. A short movie is presented. (c) 2008 Elsevier B.V. All rights reserved.