National Institute Of Materials Physics - Romania

Publications

911 articles found

851. Influence of the Jahn-Teller effect on the linewidth of the Mossbauer spectra of natural spinels

Authors: Kuncser, V; Russo, U; Graziani, R; Della Giusta, A; Filoti, G

Published: FEB 21 2000, JOURNAL OF PHYSICS-CONDENSED MATTER, 12, 1460, DOI: 10.1088/0953-8984/12/7/326

The temperature dependence of the Mossbauer doublet linewidth of tetrahedrally coordinated Fe2+ ions, distorted by the Jahn-Teller effect, was analysed by means of a new mathematical approach. The idea was that the linewidth depends on a distribution of quadrupole splittings that are in turn dependent on temperature. The variation of the quadrupole splitting was supposed to be connected with the temperature dependent population of the ground state E-g orbitals, split by the local Jahn-Teller effect. The model was applied to three sets of experimental data. The barrier splitting Delta between the two E-g electronic states as well as their widths, delta Delta, were obtained.

852. Experimental investigation of the nonlinear optical response in Fe : PVA

Authors: Bulinski, M; Iova, I; Belea, A; Kuncser, V; Filoti, G

Published: JAN 2000, JOURNAL OF MATERIALS SCIENCE LETTERS, 19, 28, DOI: 10.1023/A:1006739412409

853. Non-isothermal pyrolysation of the spray-frozen freeze dried complex nitrate in Bi(Pb)-Sr(Ba)-Ca-Cu system investigated by X-ray diffraction analysis

Authors: Aldica, G; Badica, P; Alexe, G

Published: 2000, EUROPEAN POWDER DIFFRACTION, PTS 1 AND 2, 321-3, 839, DOI: 10.4028/www.scientific.net/MSF.321-324.834

Nitrate powder with cation composition Bi:Pb:Sr:Ba:Ca:Cu= 1.8:0,4:1.8:0.2:2.2:3.0, the precursor powder for synthesis of Bi-2223 superconducting phase, was obtained by spray-frozen, freeze drying technique. Samples of the nitrate precursor powder were placed in a heated furnace and extracted in air when temperature of the powder has attained values of 640, 660, 710, 750, 760, 778, 790, 815 and 850 degrees C. Samples have been investigated by X-ray diffraction analysis. The obtained data allow us to propose and discuss phase formation and decomposition processes and reactions that occur in non-isothermal conditions at different temperatures during thermal decomposition of the nitrate powder.

854. Jahn-Teller configurations in natural spinels

Authors: Kuncser, V; Russo, U; Graziani, R; Della Giusta, A; Palade, P; Bulinski, M; Filoti, G

Published: DEC 1999, PHYSICS AND CHEMISTRY OF MINERALS, 27, 102, DOI: 10.1007/s002690050245

The local configurations and related hyperfine interactions of the tetrahedrally coordinated Fe2+ in two natural spinels were investigated. A special fitting procedure of the Mossbauer spectra is proposed in order to cover the involved mechanisms over the whole temperature range. The behavior of the quadrupole splitting vs temperature was successfully explained in terms of the split of the electronic 3d ground state doublet under a non-cooperative Jahn-Teller effect also providing estimates of the splitting energy for each configuration.

855. Phase formation during nonisothermal decomposition of the freeze-dried Bi : Pb : Sr : Ba : Ca : Cu=1.8 : 0.4 : 1.8 : 0.2 : 1.2 : 2.0 complex nitrate powder

Authors: Badica, P; Aldica, G

Published: OCT 1999, JOURNAL OF SUPERCONDUCTIVITY, 12, 615, DOI: 10.1023/A:1007739716481

Nitrate powder with cation composition Bi:Pb:Sr:Ba:Ca:Cu = 1.8: 0.4:1.8:0.2:1.2:2.0 was obtained by spray-frozen, freeze-drying technique. Samples of the nitrate precursor powder were placed in a heated furnace (heating rate similar to 100 degrees C/min) and extracted in air when temperature of the powdered samples attained values of 439, 495, 550, 600, 640, 647, 717, 766, 814, and 850 degrees C. Samples have been investigated by X-ray diffraction analysis. The obtained data allow us to propose and discuss phase formation and decomposition processes and reactions that occur in non-isothermal conditions at different temperatures during thermal decomposition of the nitrate powder.

856. Nanostructure and phase distributions in (Cu0.80Fe0.20)(100-x)B-x melt spun ribbons studied by Mossbauer spectroscopy

Authors: Kuncser, V; Rosenberg, M; Yavari, AR; Filoti, G

Published: JUL 20 1999, JOURNAL OF ALLOYS AND COMPOUNDS, 289, 276, DOI: 10.1016/S0925-8388(99)00163-2

The analysis of the Mossbauer spectra of (Cu0.8Fe0.2)(100-x))B-x the melt spun ribbons taken at several temperatures between 4.2 K and room temperature allowed us to identify the occurring Fe-containing phases: alpha-Fe, gamma-Fe and <(Cu)under bar>Fe solid solutions. The presence of B inhibits the phase transformation from fee to bcc Fe. For x = 0 and 1, the amount of Fe in the <(Cu)under bar>Fe solid solution is close to 3 at.% solubility limit, while for x=3 besides crystalline Fe3B, a supersaturated phase of 9.7 at.% Fe in the <(Cu)under bar>Fe solid solution was found, showing a strong deviation from the binary equilibrium phase diagram. (C) 1999 Elsevier Science S.A. All rights reserved.

857. Structural refinement effect on the magnetoresistive properties of annealed melt spun Cu-Co-(Fe-Si) ribbons

Authors: Crisan, O; Le Breton, JM; Maignan, A; Machizaud, F; Jianu, A; Teillet, J; Filoti, G

Published: MAY 1999, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 195, 436, DOI: 10.1016/S0304-8853(99)00160-2

Structural and magnetic properties of melt-spun Cu-Co-(Fe-Si) ribbons, as-quenched and after appropriate annealing, are investigated and correlated with their magnetoresistive properties. The effect of structural refinement of the magnetic phases and of the coexistence of multiple magnetic phases on the magnetoresistance is discussed. The existence of an optimum in the annealing conditions for obtaining a significant magnetoresistive effect, is inferred. (C) 1999 Elsevier Science B.V. All rights reserved.

858. Intermediate frustration in [Fe3O(CH3COO)(6)(H2O)(3)] NO3 center dot 4(H2O) trinuclear cluster

Authors: Filoti, G; Bartolome, J; Dickson, DPE; Rillo, C; Prisecaru, I; Jovmir, T; Kuncser, V; Turta, C

Published: MAY 1999, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 196, 563, DOI: 10.1016/S0304-8853(98)00825-7

The frustration of the trinuclear clusters with antiferromagnetic intracluster interaction was investigated at low temperature and in applied magnetic field, by Mossbauer, susceptibility and magnetisation measurements. The spin configuration and the electronic state are described as a function of the temperature and the intensity of the applied field. The values of the exchange integrals are provided. (C) 1999 Elsevier Science B.V. All rights reserved.

859. Structural and magnetic properties of magnetoresistive Cu-Co-Fe ribbons

Authors: Crisan, O; Le Breton, JM; Jianu, A; Maignan, A; Nogues, M; Teillet, J; Filoti, G

Published: MAY 1999, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 196, 469, DOI: 10.1016/S0304-8853(98)00822-1

Melt-spun Cu80Co10Fe10 ribbons are shown to exhibit a nanogranular structure with magnetic alpha-Fe(Co) grains segregated from the Cu-rich matrix after appropriate annealing. The Cu matrix purification as well as the magnetic properties of the alpha-Fe(Co) grains existing in a range of sizes are studied using X-ray diffraction, Mossbauer spectrometry and magnetic measurements. There is an optimum annealing for obtaining a high magnetoresistive effect. (C) 1999 Elsevier Science B.V. All rights reserved.

860. Fe-57 Mossbauer study of Pr-m(Fe, MO)(n) compounds with m : n=2 : 17 and 1 : 12

Authors: Morariu, M; Lazar, DP; Galatanu, A; Plugaru, N; Kuncser, V; Filoti, G; Hilscher, G; Kottar, A

Published: MAR 30 1999, JOURNAL OF ALLOYS AND COMPOUNDS, 285, 47, DOI: 10.1016/S0925-8388(98)01055-X

The effects of Mo substitution in Pr2Fe17-xMox and PrFe12-xMox compounds were investigated by X-ray diffraction, magnetic measurements and Mossbauer spectroscopy. Different fitting procedures, using magnetic sextets at low temperature, magnetic sextets and quadrupole doublets at room temperature and paramagnetic doublets well above the Curie points, had to be considered in order to analyze the Mossbauer spectra. The Mossbauer data obtained on the Mo-containing compounds stand for distributions of the hyperfine fields due to the random distributions of Mo over the 6c sites in the 2:17 and 8i sites in the 1:12 compounds. The variations in the isomer shifts and hyperfine fields with composition are discussed in relationship to the local environment details at the different iron sites. Site-specific information on the electronic effects due to Fe(Sd)-Mo(4d) states hybridization are derived. (C) 1999 Elsevier Science S.A. All rights reserved.