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  • 1990-1994  (38)
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  • 1
    Electronic Resource
    Electronic Resource
    Suppression of superparamagnetism in surface-oxidized nanocrystals (1990)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 12 (1990), S. 35-43 
    Details
    ISSN: 0392-6737
    Keywords: Diamagnetism and paramagnetism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Description / Table of Contents: Riassunto Si sono preparati nanocristalli di Fe (particelle con una dimensione di alcuni nanometri) per mezzo del metodo della condensazione di gas inerti con conseguente ossidazione. La misura media delle particelle nel fine strato di ossido è stata determinata intorno ai 30 Å. Si sono studiati i campioni attraverso la spettroscopia di Mössbauer a varie temperature. In questi esempi il supermagnetismo sembra essere soppresso. Inoltre si è osservata una diminuzione del campo medio iperfino nello strato di ossido. L'anisotropia dell'interfaccia tra ossido di Fe e Fe è proposta come causa di questo fenomeno.
    Abstract: Резюме Используя метод конденсации в инертном газе с последующим окислением, приготовляутся нанокристаллы железа (частицы с размерами порядка нанометров). Средние размеры частиц в тонком слое окисла составляют около 30 Å. Полученные образцы исследуются с помощью Мессбаузровской спектроскопии при различных температурах. Наблюдается двух-ступенчатое уменьшение среднего сверхтонного поля в слоях окисла. Предполагается, что анизотропия границы раздела между окислом железа и железом является ответственной за это явление.
    Notes: Summary Fe nanocrystals (particles with a size of some nanometers) were prepared by the inert-gas condensation method with subsequent oxidization. The average size of the particles in the thin oxide layer was determined to be about 30 Å. The samples were studied by Mössbauer spectroscopy at various temperatures. Superparamagnetism seems to be suppressed in these samples. Furthermore, a two-stage decrease of the average hyperfine field was observed in the oxide layer. The Fe oxide-Fe interface anisotropy is proposed to be responsible for this phenomenon.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02453024
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  • 2
    Electronic Resource
    Electronic Resource
    Mössbauer investigations of mechanical alloying in the Fe-Cu system (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 2768-2770 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A fcc-Fe50Cu50 solid solution was prepared by mechanical alloying of elemental Fe and Cu powder blends. The alloying process was studied by using x-ray diffraction and Mössbauer spectroscopy. Initially, the milling process reduced the crystallite sizes of both elemental powders. After 20 h milling, some Fe particles transformed into the fcc structure. Due to the structural similarity of the fcc-Fe and fcc-Cu phases, composites consisting of coherent Cu and Fe regions were formed. The increasing density of interfaces during further milling resulted in an interdiffusion of Cu and Fe. The alloying process was monitored by Mössbauer investigations which showed an increasing Fe concentration in fcc Cu. After 50 h of milling, the Mössbauer spectra consisted of a broadened sextet caused by a hyperfine field distribution, which demonstrates that the Fe and Cu were alloyed on an atomic level. These observations are in agreement with a model proposed by C. Gente, M. Oehring, and R. Bormann [Phys. Rev. B 48, 13244 (1993)] describing the formation of unstable alloys by mechanical alloying.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.110329
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  • 3
    Electronic Resource
    Electronic Resource
    Thermal stability of the unstable fcc-Fe50Cu50 phase prepared by mechanical alloying (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 1056-1058 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An unstable fcc-Fe50Cu50 alloy has been prepared by milling of elemental powder blends. The structure and the decomposition behavior of the alloy were studied by x-ray diffraction and Mössbauer spectroscopy. A broad distribution of different local environments of the iron atoms was observed in the fcc-FeCu phase. This indicates that Fe and Cu are mixed on an atomic level. In the initial state of decomposition, iron atoms precipitated coherently in the fcc-FeCu matrix as fcc-Fe particles. At higher annealing temperatures the particle size increased during the thermal treatment, and the fcc-Fe precipitates transformed into the bcc-Fe structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.109832
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  • 4
    Electronic Resource
    Electronic Resource
    57Fe Mössbauer study of YBa4Cu2.95Fe0.05O8.5+y (1991)
    Springer
    Applied physics 53 (1991), S. 426-429 
    Details
    ISSN: 1432-0630
    Keywords: 74.70.Vy ; 76.80.+y
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract 57Fe Mössbauer measurements were performed on the Fe-doped YBa4Cu3O8.5+y compound as a function of annealing temperature in vacuum. Mössbauer spectra were analyzed using three different quadrupole split doublets. The resistance measurements showed that the compound is not superconducting. The possible identification of the Cu sites with their nearest neighbor oxygen sites in this compound is suggested. Comparison of the results with data of the presence of the superconductor YBa2Cu3O7 allows us to suppose that the presence of the Cu-chain sites alone does not result in superconductivity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00348157
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  • 5
    Electronic Resource
    Electronic Resource
    Study of the crystallization kinetics in amorphous Fe73.5Cu1Nb3Si13.5B9 alloy (1994)
    Springer
    Journal of materials science 29 (1994), S. 1213-1216 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The kinetics of the crystallization of Fe73.5Cu1Nb3Si13.5B9 amorphous alloy was studied using Mössbauer spectroscopy and X-ray diffractometry. During isothermal annealing of the samples, two phases were observed: a crystalline D03-FeSi alloy with fine grains and an amorphous phase enriched with niobium, boron and copper. It was found that the growth rate of the particles of the crystalline alloy was controlled by diffusion. For longer annealing time or at higher annealing temperature the growth process was found to be suppressed, probably by the niobium atoms. The activation energy obtained for the crystallization was about 143 kJ mol−1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00975066
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  • 6
    Electronic Resource
    Electronic Resource
    Laser remelting of cast iron: a Mössbauer study (1991)
    Springer
    Journal of materials science 26 (1991), S. 5019-5024 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The Mössbauer spectroscopy in backscattering technique (CXMS) was used to analyse cw-CO2 laser-treated samples of cast iron. The depth profile as revealed by Mössbauer phase analysis is discussed in connection with the initial microstructure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00549886
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  • 7
    Electronic Resource
    Electronic Resource
    The effect of oxidized surface layers on the inner core of fine iron particles (1992)
    Springer
    Hyperfine interactions 68 (1992), S. 373-376 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Mössbauer measurements on fine iron particles with the size ranging from 150 to 350 Å with oxidized surface layer are carried out between 81 and 300K. The spectra consist of two components, a component due to metallic iron and a second component with a larger hyperfine field. The thickness of the oxide surface layer calculated from the area ratio of the subspectra is about 19 Å, and is independent of the average diameter of the particles. A slight enhancement of the hyperfine field of the iron core with a decrease of particle size has been observed. It results from the contribution of the atoms at the interface layer and the dipole interaction between the particles. The dipole interaction decreases owing to the effects of the oxide surface layer on the dipole field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02396513
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  • 8
    Electronic Resource
    Electronic Resource
    The activation energy for γ-Fe precipitates inCuFe (1990)
    Springer
    Hyperfine interactions 54 (1990), S. 811-816 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The precipitation of the fcc γ-phase of iron has been studied by a systematic series of isothermal and isochronal (0–48 h) heat treatments (300–800°C) on a supersaturated solution ofCuFe containing 3 at% Fe. The optimal conditions (450–600°C) for precipitation of the maximum fraction (90%) of iron attainable within 48 h in the form of γ-Fe have been delineated from analysis of the room temperature spectra. The time dependence for formation of γ-Fe precipitates is well described by the equation for long term annealing. An activation energyE a ≈0.6 eV for the formation of γ-Fe in Cu is obtained. It indicates short range rather than long range diffusion in theCuFe sample studied.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02396133
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  • 9
    Electronic Resource
    Electronic Resource
    Experience with a toroidal proportional detector for backscattered Mössbauer ψ-rays and X-rays (1990)
    Springer
    Hyperfine interactions 58 (1990), S. 2541-2545 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Because backscattering geometry in Mössbauer spectroscopy is particularly useful for non-destructive testing interesting technical applications arise. The reported toroidal proportional detector for backscattered Mössbauer ψ-rays and X-rays enables non-destructive testing of technical surfaces since no sample preparation is required. Improvements in assembling, shielding, wire-fixing and gas-filling-in comparison to the first version of the detector-are reported. The performance of the improved detector is demonstrated by measurements of steel surfaces which are modified by plasma nitriding and laser irradiation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02398374
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  • 10
    Electronic Resource
    Electronic Resource
    ESR measurements on hydrogenated Zr2Ni (1990)
    Springer
    Hyperfine interactions 60 (1990), S. 813-816 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract X-band magnetic resonance measurements have been carried out on Zr2NiHx (x=0–5). The room temperature results indicate the presence of Ni atom clusters which form during the hydrogenation process. The intensity of the resonance signal depends on the hydrogenation treatment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02399876
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