National Institute Of Materials Physics - Romania

Publications

903 articles found

721. A modified airtight two-crucible method for growth of Bi-2212 whiskers from glassy pellets

Authors: Badica, P; Togano, K; Kumakura, H

Published: JUL 2004, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 17, 898, DOI: 10.1088/0953-2048/17/7/011

Bi2Sr2CaCu2Ox, whiskers have been grown by a modified airtight two-crucible method, employing radial and vertical thermal gradients resulting from the relative position of the crucibles. A heating profile with a constant heating rate applied from 842 to 846degreesC allows formation of whiskers up to 2 cm in length for a certain level of Al impurity in the glass. A cation-rich atmosphere is found to be a key intrinsic parameter. Our data confirm the importance of the thermal gradients, but this parameter is a somewhat extrinsic one and from a practical point of view should be correlated to other intrinsic parameters that influence growth atmosphere (i.e. to total and partial pressures). As-grown whiskers have composition Bi:Sr:Ca:Cu = (2.9-3.5):2:(1.7-2.05):(2.4-3.0) (normalized to SrA zero-resistance critical temperature T-c(R=0) = 76-98 K and maximum transport critical current density above J(c) = 10(4) A cm(-2) at 77 K in self-field.

722. Flux lenses in the crossing lattices regime of layered superconductors

Authors: Cole, D; Crisan, A; Bending, SJ; Tamegai, T; van der Beek, K; Konczykowski, M

Published: MAY 1 2004, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 404, 102, DOI: 10.1016/j.physc.2003.09.108

We report here measurements of flux lensing behaviour which have been performed on Bi2Sr2CaCu2O8+delta single crystals placed on top of linear Hall probe arrays. In the crossing lattices regime we observe significant flux focussing as the in-plane field is swept up with a small constant density of pancake vortices. We also observe a sharp discontinous lock-in feature in local magnetic induction when the net field is close to the a-b plane. (C) 2004 Elsevier B.V. All rights reserved.

723. Magnetic interactions and spin structure in composite Fe/Nd2Fe14B systems

Authors: Kuncser, V; Valeanu, M; Lifei, F; Predoi, D; Palade, P; Schinteie, G; Crisan, O; Filoti, G

Published: MAY 2004, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 272, 799, DOI: 10.1016/j.jmmm.2003.12.1279

Local magnetic interactions and spin configurations in alpha-Fe/Nd2Fe14B composite exchange-spring magnets have been investigated by Mossbauer spectroscopy and the magnetic behaviour was analysed by magnetometry. A new method for the evaluation of the coupling strength between soft and hard magnetic phases is proposed. (C) 2003 Elsevier B.V. All rights reserved.

724. Correlation of structure and magnetism of AgCo nanoparticle arrays

Authors: Crisan, O; Angelakeris, M; Nogues, M; Kehagias, T; Komninou, P; Sobal, N; Giersig, M; Flevaris, NK

Published: MAY 2004, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 272, E1254, DOI: 10.1016/j.jmmm.2003.12.304

The bimetallic AgCo nanoparticles synthesized by colloidal chemistry and deposited onto Si(100) substrate are investigated. Size-selective mechanisms of colloidal crystallization during the self-organization are evidenced. The magnetic behavior is studied and correlated with the nanoparticles structure and morphology. (C) 2003 Elsevier B.V. All rights reserved.

725. Magnetic interactions and spin configuration in FeRh and Fe/FeRh systems

Authors: Kuncser, V; Keune, W; Sahoo, B; Duman, E; Acet, M; Radu, F; Valeanu, M; Crisan, O; Filoti, G

Published: MAY 2004, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 272, 350, DOI: 10.1016/j.jmmm.2003.11.199

The magnetic interactions and the Fe spin structure have been studied in Fe(6 nm)/FeRh systems by magnetometry, magneto-optic Kerr effect and conversion electron Mossbauer spectroscopy. A spin-flop coupling mechanism, with the interfacial spins of the ferromagnetic phase perpendicular to the spins of the antiferromagnetic phase was experimentally proved. (C) 2004 Elsevier B.V. All rights reserved.

726. Magnetic nanostructures obtained by colloidal crystallization onto patterned substrates

Authors: Crisan, O; Angelakeris, M; Vouroutzis, N; Crisan, AD; Pavlidou, E; Kostic, I; Sobal, N; Giersig, M; Flevaris, NK

Published: MAY 2004, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 272, E1287, DOI: 10.1016/j.jmmm.2003.12.184

Colloidal solutions of magnetic nanoparticles are regularly dispersed onto patterned substrates in order to form novel magnetic nanostructures. The morphology of these nanostructures is investigated by atomic force microscopy (AFM) and scanning electron microscopy (SEM) and their structure is correlated with magnetic properties. It is shown that, depending on the nature of the substrate, different nanoparticle growth modes are identified during the colloidal crystallization. (C) 2003 Elsevier B.V. All rights reserved.

727. Influence of Gd addition on the magnetism and structure of Finemet-type nanocrystalline alloys

Authors: Crisan, O; Le Breton, JM; Crisan, AD; Machizaud, F

Published: MAY 2004, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 272, 1397, DOI: 10.1016/j.jmmm.2003.12.1284

The effect of rare earth addition in the structure and magnetism of melt spun nanocrystalline Finemet-type alloys devitrified from amorphous precursor ribbons is discussed. Starting with the initial composition Fe73.5Cu1Nb3Si13.5B9 an amount of 5 at% Gd is introduced into the primary alloy. The purpose is to enable after appropriate recrystallization the occurrence of hard and soft magnetic, suitably dispersed, exchange-coupled nanograins and to determine the transformation sequences of the crystallization process and the obtained crystallization products. (C) 2003 Elsevier B.V. All rights reserved.

728. Effects of Zr and Ti substitutions on the crystallization processes of Fe3B/Nd2Fe14B nanocomposite magnetic system

Authors: Jianu, A; Valeanu, M; Lazar, DP; Lifei, F; Bunescu, C; Pop, V

Published: MAY 2004, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 272, 1494, DOI: 10.1016/j.jmmm.2003.12.1005

The influence of Zr and Ti substitutions on the formation of a nanocomposite magnet was studied by high-temperature X-ray diffraction and magnetic measurements. It has been shown that Ti and especially Zr additions favorably change the crystallization temperatures and the sequence of phase transformations which leads to an exchange coupled magnet, even in a composition range that promotes the precipitation of the detrimental Nd2Fe23B3 phase. (C) 2003 Elsevier B.V. All rights reserved.

729. Anomalies of AC susceptibility losses in the doped [Bi(Pb)](2)Sr2Ca2CU3Ox superconductor

Authors: Mihalache, V; Aldica, G; Badica, P; Crisan, A

Published: APR 2004, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 17, 730, DOI: 10.1088/0953-2048/17/4/030

AC susceptibility measurements have been performed on Bi1.7Pb0.4Sr1.5Ca2.5Cu3.6Ox (Bi-2223) samples doped with different Li-based compounds and prepared by the solid-state method. As-prepared samples and/or samples annealed in oxygen or argon, ground or unground, have been investigated in detail in order to understand the occurrence, nature and evolution of the anomalous peaks observed in chi " (T) curves versus the measuring parameters; we have detected up to four peaks instead of the usual two peaks observed in the non-doped samples. It was found that intrinsic physical-chemical properties, such as the melting temperature of the doping compound, are no less important for the final properties of the superconductor than their insertion properties into the crystal lattice of Bi-2223. Doping compounds with melting temperatures below or close to the phase formation temperature of the Bi-2223 phase can act as flux, changing the growth conditions. Intensification of some processes against others (e.g. decomposition-recovery of the BI-2223 phase, solubilization-precipitation of the secondary phases, changes in the properties of the liquid phase, etc) can lead to the formation of the Bi-2223 phase with different properties than for the non-doped superconductor. Generally, when using flux-type doping compounds, anomalous AC losses peaks are detected and the intra-granular critical current density is enhanced.

730. The first specimen of tetranuclear (Fe-III, Ln(III)) clusters assembled by carboxylate ligands: synthesis, structure, Mossbauer spectra, and magnetic properties of [Fe3EuO2(CCl3COO)(8)H2O(THF)(3)]center dot THF

Authors: Turta, C; Prodius, D; Mereacre, V; Shova, S; Gdaniec, M; Simonov, YA; Kuncser, V; Filoti, G; Caneschi, A; Sorace, L

Published: APR 2004, INORGANIC CHEMISTRY COMMUNICATIONS, 7, 579, DOI: 10.1016/j.inoche.2004.02.025

The reaction of the neutral cluster [Fe2BaO(CCl3COO)(6)(THF)(6)] with Eu(NO3)(3) . 6H(2)O in methanol affords novel tetra-nuclear Fe-Eu complex [Fe3EuO2(CCl3COO)(8)H2O(THF)(3)] . THF (1), which displays interesting Mossbauer spectra and magnetic behaviour. (C) 2004 Elsevier B.V. All rights reserved.