National Institute Of Materials Physics - Romania
Publications
articles found
831. Mechanically alloyed Cu-Fe studied by Mossbauer spectroscopy
Authors:
Principi, G; Spataru, T; Gupta, R; Enzo, S; Kuncser, V; Filoti, G
Published: AUG 9 2001, JOURNAL OF ALLOYS AND COMPOUNDS, 326, 192, DOI: 10.1016/S0925-8388(01)01301-9
Recent studies of mechanically alloyed Fe-Cu powder mixtures have suggested differences in the local magnetic environment of iron atoms. For a more accurate definition of this point, ball-milled Cu70Fe30 and Cu50Fe50 alloys were investigated by Mossbauer spectroscopy in the, temperature range 4.2-300 K. The low temperature Mossbauer spectra exhibit a broad magnetic pattern. typical of a defect structural configuration. The magnetic splitting strongly decreases with increasing temperature, especially in the case of Cu70Fe30 alloy. But even for this composition there is, at room temperature, an unresolved magnetic pattern. Applying a magnetic field of 3 T, parallel to gamma rays, at 4.2 K a rotation of all magnetic moments along the external field is observed. The samples behave as an alloy with continuously distributed local fields. (C) 2001 Elsevier Science BY. All rights reserved.
832. A magnetic study of magnetoresistive Cu-(SmCo5)-Fe heterogranular alloys
Authors:
Crisan, O; Le Breton, JM; Jianu, A; Maignan, A; Nogues, M; Teillet, J; Filoti, G
Published: AUG 2001, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 234, 99, DOI: 10.1016/S0304-8853(01)00279-7
The magnetic interactions between the nanograins in heterogeneous granular Cu-(SmCo5)-Fe ribbons were evaluated with a classical mean field model to obtain the exchange coupling as well as the magnetic moment per nanoparticle. The samples were subjected to various thermal treatments and a significant magnetoresistive effect was obtained when the optimal annealing conditions had been achieved. (C) 2001 Elsevier Science B.V. All rights reserved.
833. Some superconducting properties of the inter-domain border of melt-textured YBa2Cu3O7-delta
Authors:
Crisan, A; Gordeev, SN; de Groot, PAJ; Beduz, C
Published: JUN 15 2001, PHYSICA C, 355, 237, DOI: 10.1016/S0921-4534(01)00023-5
The resistive transitions R(T) and the current-voltage (I-V) in fields up to 5 T were measured in a melt-textured YBa2Cu7-delta (YBCO) sample consisting of two single-grain domains separated by an inter-domain border, and in a single-grain sample cut from the same pellet and oxygenated in such conditions that ensure the optimum oxygenation of the grains. From comparing the two sets of results, we were able to suggest that the inter-domain border consists of oxygen-deficient YBCO with thickness smaller than 6 mum, having a slightly lower critical temperature, a higher anisotropy factor and without strong pinning centers. From applications point of view, our work shows that, for improving the superconducting properties of large multiple-domain melt-textured pellets. an oxygenation process much longer than that required for optimum grain properties is needed. (C) 2001 Published by Elsevier Science B.V.
834. Fluctuation magnetoconductivity of BSCCO-2212 films in parallel magnetic field
Authors:
Balestrino, G; Crisan, A; Livanov, DV; Manokhin, SI; Milani, E
Published: JUN 1 2001, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 355, 139, DOI: 10.1016/S0921-4534(00)01771-8
The in-plane (delta sigma (ab)(T,H)) and out-of-plane (delta sigma (c)(T,H)) components of the magnetoconductivity tenser of Bi2Sr2CaCu2O8+x films have been simultaneously measured in magnetic fields parallel to the film conducting planes (B less than or equal to 1 T). A negative c-axis magnetoresistance is measured for the first time in this geometry. Both delta sigma (ab) and delta sigma (c) are well described by the fluctuation theory in the temperature range T-c < T < T-c + 20 K, using a single set of microscopical parameters for both directions. The negative c-axis magnetoresistance in the field parallel to conducting layers is shown to be induced by the density of states Zeeman fluctuation contribution. (C) 2001 Elsevier Science B.V. All rights reserved.
835. The influence of BaZrO3 on the magnetic response of (Bi,Pb): 2223 high-temperature superconductors
Authors:
Mihalache, V; Aldica, G; Popa, S; Nita, P; Crisan, A
Published: JUN 2001, JOURNAL OF SUPERCONDUCTIVITY, 14, 386, DOI: 10.1023/A:1011174321955
DC magnetization and AC complex susceptibility measurements on (Bi,Pb) : 2223 high-temperature superconductors impurified with various amounts of BaZrO3 are presented. The results are discussed in the frame of the critical state model. and the values of the inter- and intragranular critical current density as well as of the field for full penetration are estimated. The values of the intergranular critical current density are consistent with those obtained from transport measurements. The intragranular critical current density and the field for full penetration have similar values from both DC magnetization and AC susceptibility measurements. It was shown that, in the (Bi,Pb) : 2223 system. BaZrO3 impurification changes only the properties of the intergrain matrix, while the superconducting properties of the grains are not modified.
836. Improvement of the superconducting transport properties of YBa2Cu3O7-delta by BaZrO3 doping
Authors:
Aldica, G; Bradea, I; Jaklovszky, J; Crisan, A
Published: JUN 2001, JOURNAL OF SUPERCONDUCTIVITY, 14, 409, DOI: 10.1023/A:1011186724681
We have doped the YBa2Cu3O7-delta,S superconducting ceramics with BaZrO3 up to 75 wt.% and studied the changes of some physical properties. The most important finding is the enhancement of the critical current density, which has a maximum at around 5 wt.% doping level. Compared with the undoped samples, the critical current density is four times higher if the doping compound is introduced prior to the calcination treatment, or two times higher if BaZrO3 is introduced prior to the sintering treatment, The dependence of the critical current density on the doping level is consistent with the dependence of the Seebeck coefficient. We also observed a very small decrease of the critical temperature. The real density of the samples decreases with increasing doping level as expected from the ratio between the theoretical densities of YBa2Cu3O7-delta and BaZrO3, the effect being important for doping levels higher than 25 wt.%.
837. Superconducting properties from AC susceptibility and harmonic generation in CuBa2Ca3Cu4Oy bulk superconductors
Authors:
Crisan, A; Iyo, A; Tanaka, Y; Hirai, M; Tokumoto, M; Ihara, H
Published: MAY 15 2001, PHYSICA C, 353, 240, DOI: 10.1016/S0921-4534(00)01744-5
We measured for the first time the fundamental and higher harmonic components of AC susceptibility of CuBa2Ca3Cu4Oy superconductor produced by the high-pressure technique, in various experimental conditions (temperature, DC magnetic field, AC held amplitude and frequency). The results are discussed qualitatively in the frame of the critical state and other models in the literature. By using a very simple frequency-dependent critical state model, we estimated the parameters of practical interest, critical current density and pinning potential at various DC fields and temperatures and the irreversibility field. We also extrapolated our estimations to both practical temperature of 77 K and longer time scale as of DC magnetization and transport measurements. The results appeared to be quite self-consistent. (C) 2001 Published by Elsevier Science B.V.
838. The influence of BaZrO3 on the transport properties of the (Bi,Pb)2223 superconducting system
Authors:
Mihalache, V; Aldica, G; Crisan, A
Published: MAY 2001, JOURNAL OF MATERIALS SCIENCE LETTERS, 20, 891, DOI: 10.1023/A:1010912429361
839. A Mossbauer study of the new phases Th4Fe13Sn5 and ThFe0.22Sn2
Authors:
Principi, G; Spataru, T; Maddalena, A; Palenzona, A; Manfrinetti, P; Blaha, P; Schwarz, K; Kuncser, V; Filoti, G
Published: APR 12 2001, JOURNAL OF ALLOYS AND COMPOUNDS, 317, 572, DOI: 10.1016/S0925-8388(00)01389-X
Two new phases Th4Fe13Sn5 and ThFe0.22Sn2 have been studied by Fe-57 and Sn-119 Mossbauer spectroscopy. The Fe-57 Mossbauer spectra of Th4Fe13Sn5, measured at room temperature and 4.2 Ii without and with applied magnetic field up to 5.5 T, exhibit four sextets. Our measurements prove that all four Ft: sub-lattices are collinear. The Sn-119 Mossbauer spectra of Th4Fe13Sn5 show two sextets with different B-eff, reflecting the influence of ferromagnetic nn iron atoms. The results obtained from full-potential linear augmented plane wave (LAPW) calculations are in agreement with the experimental data and confirm the assignment of Mossbauer spectra, The Mossbauer data for the ThFe0.22Sn compound prove the existence of two different sites both for Fe and Sn, all having icosahedral co-ordination. (C) 2001 Elsevier Science B.V, All rights reserved.
Copyright © 2025 National Institute of Materials Physics. All Rights Reserved