National Institute Of Materials Physics - Romania

Publications

5781 articles found

4211. 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.

4212. 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.

4213. Hydrothermal synthesis and structural characterization of (1-x)alpha-Fe2O3-xSnO(2) nanoparticles

Authors: Sorescu, M; Diamandescu, L; Tarabasanu-Mihaila, D; Teodorescu, VS; Howard, BH

Published: MAY 2004, JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 65, 1029, DOI: 10.1016/j.jpcs.2003.10.062

Structural and morphological characteristics of (1 - x)alpha-Fe2O3-xSnO(2) (x = 0.0- 1.0) nanoparticles obtained under hydrothermal conditions have been investigated by X-ray diffraction (XRD), transmission Mossbauer spectroscopy, scanning and transmission electron microscopy as well as energy dispersive X-ray analysis. On the basis of the Rietveld structure refinements of the XRD spectra at low tin concentrations, it was found that Sn4+ ions partially substitute for Fe3+ at the octahedral sites and also occupy the interstitial octahedral sites which are vacant in alpha-Fe2O3 corundum structure. A phase separation of alpha-Fe2O3 and SnO2 was observed for x greater than or equal to 0.4 : the alpha-Fe2O3 Structure containing tin decreases simultaneously with the increase of the SnO2 phase containing substitutional iron ions. The mean particle dimension decreases from 70 to 6 DID, as the molar fraction x increases up to x = 1.0. The estimated solubility limits in the nanoparticle system (1 - x)alpha-Fe2O3-xSnO(2) synthesized under hydrothermal conditions are: x less than or equal to 0.2 for Sn4+ in alpha-Fe2O3 and x greater than or equal to 0.7 for Fe3+ in SnO2. (C) 2003 Elsevier Ltd. All rights reserved.

4214. Influence of powder precursors on reaction sintering of Al2TiO5

Authors: Stanciu, L; Groza, JR; Stoica, L; Plapcianu, C

Published: MAY 2004, SCRIPTA MATERIALIA, 50, 1262, DOI: 10.1016/j.scriptamat.2004.01.034

Al2TiO5 has been obtained by reaction sintering of precursor powders synthesized by three powder processing methods. A field activated sintering technique has been used for the process, with 100 degreesC/min heating rate and short holding plateaus (minutes) at the maximum temperature. SEM, XRD, and density measurements were performed after sintering. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

4215. 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.

4216. 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.

4217. 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.

4218. 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.

4219. 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.

4220. Systematic study related to the role of initial impurities and irradiation rates in the formation and evolution of complex defects in silicon for detectors in HEP experiments

Authors: Lazanu, S; Lazanu, I

Published: MAY 2004, PHYSICA SCRIPTA, 69, 384, DOI: 10.1238/Physica.Regular.069a00376

The influence of oxygen and carbon impurities on the concentrations of defects in silicon for detector uses, in complex fields of radiation, characteristic to high energy physics experiments, is investigated in the frame of the quantitative phenomenological model developed previously by the authors and extended in the present paper. Continuous irradiation conditions are considered, simulating realistically the environments for these experiments. The generation rate of primary defects is calculated starting from the projectile-silicon interaction and from the recoil energy redistribution in the lattice. The mechanisms of formation of complex defects are explicitly analysed. Vacancy-interstitial annihilation, interstitial and vacancy migration to sinks, divacancy, vacancy- and interstitial-impurity complex formation and decomposition are considered. Oxygen and carbon impurities present in silicon could monitor the concentration of all stable defects, due to their interaction with vacancies and interstitials. Their role in the mechanisms of formation and decomposition of the following stable defects: V-2, VO. V2O, C-i, CiOi, CiCs, and VP, is studied. The model predictions cover a generation rate of primary defects between 10(2) pairs/cm(3)/s and 10(11) pairs/cm(3)/s, and could be a useful clue in obtaining harder materials for detectors for space missions, at the new generation of accelerators, as, e.g. LHC, Super-LHC and Eloisatron, or for industrial applications.