National Institute Of Materials Physics - Romania

Publications

892 articles found

571. Critical current densities and irreversibility fields of a HgBa2Can-1CunO2n+2+delta sample containing n=6-15 phases

Authors: Shirage, PM; Iyo, A; Shivagan, DD; Crisan, A; Tanaka, Y; Kodama, Y; Kito, H

Published: SEP 15 2008, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 468, 1290, DOI: 10.1016/j.physc.2008.05.049

A recent report on multilayered superconductors establishes unique constant T-c although the number of inner CuO2 plane (IP) increases. Many hypotheses proposed that the irreversibility field (B-irr) and critical current density (J(c)) are depends on the crystal structures. We have measured the J(c) and B-irr of the HgBa2Can-1CunO2n+2+delta sample containing n = 6-15 phases to investigate the effect of the number of IP's on the B-irr and J(c) and its pinning properties. The rate of fall of J(c) increases and irreversible lines (IL's) shift to lower temperatures with increasing the number of IP's, which suggests that anisotropy increases with n. The IL settled in between those for Bi2Sr2CaCu2Oy with high anisotropy value and YBa2Cu3O7 with less anisotropy value. The double logarithmic plot of irreversibility field versus [1 - (T/T-c)] analysis suggests that the flux line melting model is adopted. The flux pinning force density F-p (approximate to J(c)B) exhibits scaling behavior when the magnetic field B is normalized by the irreversibility field B;- Analysis of the normalized pinning force reveals that a surface pinning mechanism is dominant and reduced magnetic field b(max) = 0.2 agree with surface pinning mechanism with closely spaced pins. (C) 2008 Elsevier B.V. All rights reserved.

572. An anelastic spectroscopy, differential scanning calorimetry and X-ray diffraction study of the crystallization process of Mg-Ni-Fe alloys

Authors: Palumbo, O; Paolone, A; Cantelli, R; Giannini, C; Guagliardi, A; Reale, P; Scrosati, B; Lo Russo, S; Maddalena, A; Palade, P; Principi, G; Schinteie, G

Published: SEP 8 2008, JOURNAL OF ALLOYS AND COMPOUNDS, 463, 152, DOI: 10.1016/j.jallcom.2007.08.081

The effects of heating-induced crystallization on the structural and mechanical properties of Mg-Ni-Fe amorphous ribbons were studied by anelastic spectroscopy, differential scanning calorimetry (DSC) and X-ray diffraction. DSC results show that the crystallization occurs through several non-reversible steps, which correspond to significant changes in the Young's modulus and concomitant irreversible elastic energy loss peaks. Moreover, an anelastic peak is found at 215 K, which for the first time indicates the presence of some dynamical process related to the simultaneous presence of different phases. The formation of a metastable Mg(6)Ni phase is detected, which transforms into Mg and Mg(2)Ni stable phases. A quantitative analysis of the different phases present at the different steps was also carried out. (C) 2007 Elsevier B.V. All rights reserved.

573. Vortex melting line and anisotropy of a Ba2Ca3Cu4O8(O1-yFy)(2) multilayered superconductor

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

Published: SEP 2008, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 21, DOI: 10.1088/0953-2048/21/9/095002

We have measured the vortex melting lines of high-pressure-synthesized Ba2Ca3Cu4O8(O1-yFy)(2) (nominal composition, 2y = 1.3, 1.6 and 2.0) F(2y)-0234 multilayered high-T-c superconductor using fundamental and third harmonic susceptibility responses carried out on preferentially oriented crystallites with very low ac field amplitude (5 mu T) and in applied dc fields up to 6 T. The vortex melting lines of all three F-substituted samples show interesting doping dependence and are very well described by the commonly accepted theory of melting lines. Interestingly, we discovered that the models describing the temperature dependence of the in-plane London penetration depth also depend on the doping level: the 3D XY model for the nearly-optimum-doped sample [F(1.3)], the mean-field theory for the under-doped sample [F(1.6)] and the two-fluid model for the heavily-under-doped sample [F(2.0)]. We found that the vortex melting lines in F-0234 are determined by the interplay in the coupling of pancake vortices through the charge reservoir layer (CRL), and through the block of inner CuO2 planes (IPs), respectively. The anisotropy values (47 for the near-optimally-doped sample) derived from experimental vortex melting lines are consistent with the values obtained by first-principles electronic-band-structure calculations.

574. Iron oxide colloids and their heterogenization by silica sol-gel entrapment: Catalytic and magnetic properties

Authors: Neatu, F; Kraynov, A; D'Souza, L; Parvulescu, VI; Kranjc, K; Kocevar, M; Kuncser, V; Richards, R

Published: AUG 31 2008, APPLIED CATALYSIS A-GENERAL, 346, 35, DOI: 10.1016/j.apcata.2008.04.024

Fe3O4 colloids modified by the chiral ligand cinchonidine were prepared with the goal of obtaining a magnetic and catalytic nano-material and were subsequently embedded in silica to form a heterogeneous catalyst. The systems were characterized by TEM and XRD measurements, while the Mossbauer technique was applied for measuring the magnetic properties of the Fe3O4 colloids. The hyperfine magnetic field distribution was consistent with one type of Fe oxide, namely, the magnetite (Fe304). These colloids, both as 'quasi-homogenous catalysts' (or soluble heterogeneous catalysts) and embedded in silica (heterogeneous catalysts) were employed in the selective hydrogenolysis of complex bicyclo[2.2.2]oct-7-enes (bicyclo[2.2.2]oct-2-enes when unsubstituted). (C) 2008 Published by Elsevier B.V.

575. Phase diagram of a lattice of vortex molecules in multicomponent superconductors and multilayer cuprate superconductors

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

Published: AUG 2008, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 21, DOI: 10.1088/0953-2048/21/8/085011

The Abrikosov lattice in the multilayer cuprate superconductor CuBa2Ca3Cu3Oy (Cu-1223) has been experimentally and theoretically demonstrated to be composed of vortex molecules. Cu-1223 is considered to be a typical multicomponent superconductor. We show that in such a system the rotational freedom around the axis of the vortex molecular tube generates orientational disorder and the orientational glass (or crystal) phase, which is never present in conventional vortex lattices consisting of axisymmetric vortices. The emergence of the orientational glass phase and orientational order phase with orthorhombic distortion is a general property of vortex molecule lattices of the multiband type of multicomponent superconductors.

576. A study of the LiNH2-MgH2 system for solid state hydrogen storage

Authors: Barison, S; Agresti, F; Lo Russo, S; Maddalena, A; Palade, P; Principi, G; Torzo, G

Published: JUL 14 2008, JOURNAL OF ALLOYS AND COMPOUNDS, 459, 347, DOI: 10.1016/j.jallcom.2007.04.278

The influence of different high energy milling times and of the addition of catalysts such as Nb2O5, TiCl3 and graphite on the hydrogen absorption/desorption (AID) kinetics of a mixture of 2LiNH(2) + 1.1MgH(2) has been studied in the temperature range 220-240 degrees C. It is found that a prolonged milling time is effective in improving the A/D kinetics, irrespective of the presence or not of any kind of tested additive. The enthalpy of decomposition reaction results to be about 40.4 kJ/mol, as derived from van't Hoff plot using the values of the plateau pressures measured in desorption mode. This thermodynamic parameter fits well with the current literature data. (c) 2007 Elsevier B.V. All rights reserved.

577. 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.

578. 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.

579. 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.

580. 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.