National Institute Of Materials Physics - Romania

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903 articles found

771. Magnetic properties of gamma-Fe2O3 nanoparticles

Authors: Predoi, D; Kuncser, V; Nogues, M; Tronc, E; Jolive, JP; Filoti, G; Schinteie, G

Published: MAR 2003, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 5, 216, DOI:

The gamma-Fe2O3 nanoparticles with different surface states are investigated by X-ray Diffraction, Electron Microscopy, Differential Thermal Analysis and magnetic: measurements in low applied field. The influence of the adsorbed species (H2O and sulphate complexes) on the inter-particle magnetic interactions is analysed in relation to both the magnetic states of the surface and the inter-particle distance.

772. Easy axis distribution in modern nanoparticle storage media: A new methodological approach

Authors: Kuncser, V; Keune, W; Vopsaroiu, M; Bissell, PR; Sahoo, B; Filoti, G

Published: MAR 2003, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 5, 226, DOI:

Easy axis distribution in metal particle magnetic tapes for linear digital data storage were studied by Mossbauer spectroscopy and magnetometry, for comparison. Qualitative and quantitative agreement between the distribution parameters deduced at room temperature via the two different techniques was found. The proposed methodology based on the interpretation of the Mossbauer data has the advantage that it can be applied at different temperatures and for very thin films. Moreover, angular spin distribution. at low temperatures were obtained by Mossbauer spectroscopy and discussed with respect to the room temperature results. There was evidenced that the room temperature easy axis angular distribution contains both static orientation and dynamical components.

773. Optical and electronic properties of metal doped polymers for integrated optics

Authors: Bulinski, M; Kuncser, V; Cristea, D; Plapcianu, C; Krautwald, S; Franke, H; Wagner, FE; Filoti, G

Published: MAR 2003, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 5, 335, DOI:

The electronic mechanism responsible for the optical behavior of the mixed Fe and Sn doped polymers were studied in comparison with the correspondent single doped (Fe or Sn) ones. Optical absorption as well as Fe-57 and Sn-119 Mossbauer measurements were performed on different UV exposed films. The new data provided the role of each element from the pair on the involved electronic mechanism induced by irradiation.

774. Magnetic properties of Bi1.7Pb0.4Sr1.5Ca2.5Cu3.6Ox/(LiF)(y) superconducting system

Authors: Mihalache, V; Aldica, G; Popa, S; Crisan, A

Published: FEB 15 2003, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 384, 457, DOI: 10.1016/S0921-4534(02)02018-X

AC complex susceptibility (with and without a superimposed DC field) and DC magnetization measurements on (Bi,Pb)-2223 high-temperature superconductors with various amounts of LiF are presented. The results are discussed in the frame of the critical state model. The values of the intra- and inter-granular critical current density as well as of fields for full penetration are estimated. It can be seen that, in Bi1.7Pb0.4Sr1.5Ca2.5Cu3.6Ox/(LiF)(y), various amounts of LiF change the superconducting properties of both the grains and the inter-grain matrix. The intra-granular critical current density has similar values from both AC susceptibility and DC magnetization measurements, its highest value being attained for y = 0.15. For all LiF-doped samples, a split of the peak corresponding to the dissipation in the grains was observed. (C) 2002 Elsevier Science B.V. All rights reserved.

775. Intensification of synthesis and examination of technological parameters influence on the properties and structure of Bi-(Pb)-Sr-Cu-Ca-O ceramics

Authors: Yurchenko, IA; Alekseev, AF; Yurchenko, DO; Badica, P; Gridasova, TY; Morozov, VV; Nemirovsky, AV; Peklun, VF

Published: JAN 15 2003, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 384, 124, DOI: 10.1016/S0921-4534(02)01804-X

Application of active technology factors (for example, the introduction of Bi2Sr2Ca2CU3Oy, (2223) phase additive) and corresponding optimization of synthesis parameters of Bi(Pb)-Sr-Ca-Cu-O (BSCCO) ceramics have allowed reducing the time of oxide precursor sintering from 250 to 25 h. Conditions of positive influence of 2223 phase additives have been investigated. Intensification of BSCCO ceramics synthesis was the basic purpose, but the authors have deliberately conducted broader examinations of the influence of technological parameters on the properties and structure of this material. The complex of the obtained effects (similarly to the solution of an equation set with several unknowns) helps increasing the probability of exact comprehension of the system: technology-processes occurring under ceramics synthesis-phase composition and structure-properties of BSCCO. (C) 2002 Elsevier Science B.V. All rights reserved.

776. TlBa(2)Ca(2)Cu(3)O(y) superconducting films on MgO with different morphologies

Authors: Badica, P; Sundaresan, A; Crisan, A; Nie, JC; Hirai, M; Fujiwara, S; Kito, H; Ihara, H

Published: JAN 1 2003, , DOI: 10.1016/S0921-4534(02)01836-1

TlBa(2)Ca(2)Cu(3)O(y) (Tl-1223) superconducting films were prepared under identical conditions, on MgO substrates with different morphologies resulting from heat treatments at temperatures between 600 and 1350 degreesC. The superconducting films have almost the same morphology, in-plane alignment and composition, but different critical current densities J(c). Critical current density J(c) determined at 77.3 K differs for films with various annealed MgO substrates, by a factor of 5 in zero field and 10 in 1 T. The behavior of J(c) is discussed in relation with the flatness of the MgO surface, and with pinning effects induced by the Ca-segregates. For the present work, the best films were obtained for the un-annealed (as-received) substrates and for substrates treated at 1350 degreesC. In these samples, the substrate's flatness and morphology with regular steps are essential for high quality of the superconducting films. In the films grown on MgO annealed between 800 and 1200 degreesC and showing rough surface and Ca-segregates, J(c) was lower. However, J(c) was increasing with heat treatment temperature of the substrate, possibly due to the Ca-segregates inducing or acting as pinning centers. The effects of Ca-segregates are of interest for maximization of the quality of the high-temperature superconducting films. In the literature, up to now, these effects have not been considered and therefore Ca-segregates removal has been recommended. (C) 2002 Elsevier Science B.V. All rights reserved.

777. TlBa2Ca2Cu3Oy superconducting films on MgO with different morphologies

Authors: Badica, P; Sundaresan, A; Crisan, A; Nie, JC; Hirai, M; Fujiwara, S; Kito, H; Ihara, H

Published: JAN 1 2003, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 383, 490, DOI: 10.1016/S0921-4534(02)01836-1

TlBa2Ca2Cu3Oy (Tl-1223) superconducting films were prepared under identical conditions, on MgO substrates with different morphologies resulting from heat treatments at temperatures between 600 and 1350 degreesC. The superconducting films have almost the same morphology, in-plane alignment and composition, but different critical current densities J(c). Critical current density J(c) determined at 77.3 K differs for films with various annealed MgO substrates, by a factor of 5 in zero field and 10 in 1 T. The behavior of J(c) is discussed in relation with the flatness of the MgO surface, and with pinning effects induced by the Ca-segregates. For the present work, the best films were obtained for the un-annealed (as-received) substrates and for substrates treated at 1350 degreesC. In these samples, the substrate's flatness and morphology with regular steps are essential for high quality of the superconducting films. In the films grown on MgO annealed between 800 and 1200 degreesC and showing rough surface and Ca-segregates, J(c) was lower. However, J(c) was increasing with heat treatment temperature of the substrate, possibly due to the Ca-segregates inducing or acting as pinning centers. The effects of Ca-segregates are of interest for maximization of the quality of the high-temperature superconducting films. In the literature, up to now, these effects have not been considered and therefore Ca-segregates removal has been recommended. (C) 2002 Elsevier Science B.V. All rights reserved.

778. Electron-doped superconductivity induced by oxygen vacancies in as-grown Sr0.6Ca0.4CuO2-delta infinite-layer films

Authors: Nie, JC; Badica, P; Hirai, M; Sundaresan, A; Crisan, A; Kito, H; Terada, N; Kodama, Y; Iyo, A; Tanaka, Y; Ihara, H

Published: JAN 2003, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 16, L3, DOI: 10.1088/0953-2048/16/1/101

Thin films of the infinite-layer compound Sr0.6Ca0.4CuO2-delta have been prepared by off-axis rf magnetron sputtering on SrTiO3 (001). For an opt mum level of oxygen vacancy superconductivity was observed (T-c onset = 42 K and T-c(rho=0) = 11 K). Structural and transport data suggesting n-type superconductivity are presented and discussed. Infinite-layer thin films of Sr0.5Ca0.4CuO2-delta, without trivalent cation doping and showing n-type superconductivity, are reported for the first time.

779. Magnetism and phase structure of crystallized Sm-Fe-B melt spun ribbons

Authors: Crisan, O; Le Breton, JM; Nogues, M; Machizaud, F; Filoti, G

Published: DEC 2 2002, JOURNAL OF PHYSICS-CONDENSED MATTER, 14, 12609, DOI: 10.1088/0953-8984/14/47/331

The crystallization of amorphous SmxFe80-xB20 melt spun ribbons is studied over an extended range of composition (0 < x < 8). Differential scanning calorimetry scans reveal different endo- and exothermic effects depending upon the composition. X-ray diffraction and Mossbauer studies for samples annealed at temperatures close to the onset of the first exothermic effect prove that, during the primary crystallization of the amorphous ribbons, both alpha-Fe and Fe3B phases appear-with Sm ions randomly accommodating the Fe sites in the tetragonal Fe3B lattice-while the subsequent exothermic reactions correspond to the decomposition of the metastable Fe3B phase into alpha-Fe and Fe2B and to the formation of the ternary Sm1.1Fe4B4 phase. Fully crystallized ribbons with Sm contents lower than about 7 at.% show the co-existence between alpha-Fe and Fe2B soft magnetic phases and the Sm2Fe14B magnetic one. The enhancement of magnetic properties with increasing relative proportion of magnetic phase is discussed and correlated with exchange coupling and spin wave stiffness data obtained from the magnetic measurements.

780. The "in-plane" angular spin distribution in layered systems as obtained by Fe-57 Mossbauer spectroscopy

Authors: Kuncser, V; Keune, W; Vopsaroiu, M; Bissell, PR

Published: NOV 2002, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS, 196, 147, DOI: 10.1016/S0168-583X(02)01274-0

A practical approach for in-plane angular spin distributions in layered systems, as obtained by Mossbauer spectroscopy, is discussed. The line intensity ratio R-23 of a Mossbauer pattern is expressed versus particular distribution parameters in unidirectional, step-shaped and ellipse-type models. The distribution parameters are deduced from experimental spectra taken by rotating the sample in its own plane. Three-dimensional spin distributions with small out-of-plane components can be analysed using the same method. The procedure is exemplified on four samples containing metallic nano-particles. The in-plane angular magnetic moment distributions derived with this method are compared with the results from bulk vector vibrating sample magnetometry in order to prove the accuracy of the described technique. (C) 2002 Elsevier Science B.V. All rights reserved.