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  • 1995-1999  (5)
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  • 1
    Electronic Resource
    Electronic Resource
    Magnetic properties of the clinopyroxenes aegirine and hedenbergite: a magnetic susceptibility study on single crystals (1997)
    Springer
    Physics and chemistry of minerals 24 (1997), S. 294-300 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract  Two natural clinopyroxene single crystals were investigated, an aegirine-augite (AEG) and a magnesian hedenbergite (HED). Both samples were carefully characterized by electron microprobe, X-ray diffraction, and Mössbauer spectroscopy. Magnetic susceptibility measurements of powdered samples reveal low temperature antiferromagnetic coupling and Curie-Weiss behaviour with T N =7.5(5) K, Θ P =−19(1) K for AEG, and T N =31(1) K, Θ P =+21(1) K for HED, respectively. Low temperature Mössbauer spectra exhibit relaxation phenomena. Magnetic susceptibility measurements of the single crystals show the direction of the magnetic moments to be lying within the a/c plane for both samples: 50(±2)° from a and 57(±2)° from c in AEG, and 45(±2)° from a and 60(±2)° from c in HED, respectively. The antiferromagnetic interchain interaction competes with the ferromagnetic intrachain interaction in both pyroxenes. In the magnesian hedenbergite a field induced magnetic transition is found. Its dependence on temperature, magnetic field and crystallographic direction is investigated and described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002690050041
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    A time-minimizing hybrid method for fitting complex Mössbauer spectra (1999)
    Springer
    Physics and chemistry of minerals 27 (1999), S. 34-40 
    Details
    ISSN: 1432-2021
    Keywords: Key words Fitting of Mössbauer spectra ; Genetic algorithm
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract The present study includes results of the application of a program consisting of a genetic algorithm routine and a conventional refinement part (“hybrid method”) for the evaluation of Mössbauer spectra published elsewhere. It is shown that the saving of total evaluation time compared with conventional refinement routines is very high due to the rapid finding of adequate starting parameters. Contrary to a recently published work on a similar topic our algorithm provides solutions of the combined interaction Hamiltonian with a minimum of conventional input data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002690050237
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Powder- and single crystal Mössbauer spectroscopy on synthetic fayalite (1995)
    Springer
    Physics and chemistry of minerals 22 (1995), S. 259-267 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract Mössbauer measurements on synthetic iron orthosilicate Fe2SiO4 (fayalite) were carried out in the antiferromagnetic spin state below T N ≃65 K. The Mössbauer parameters isomer shift δ, inner magnetic field H(0), angle Θ between H(0) and the z-component of the electric field gradient (efg), quadrupole splitting QS and asymmetry parameter η were determined as a function of temperature. These parameters could be attributed to the two crystallographic sites M1 and M2. The smaller isomer shift on M1 with respect to M2 displays the more covalent character of the Fe-O bond on M1, which is supported by previous neutron diffraction experiments. H(0) shows a Brillouin-type behaviour with different fields on the two crystallographic sites (stronger on M1) and a small discontinuity at T = 23 K which corresponds with previous magnetic measurements. The quadrupole splitting is equal on both sites within error bars, in agreement with previous theoretical results and in contradiction to previous Mössbauer refinements published elsewhere. Single crystal Mössbauer spectroscopy revealed the orientation of the crystallographic c-axis (Pnma) with respect to the axes of the efg. A second parameter set which also holds true for the powder refinement yields the angle between c and H(0) on M1 to be temperature-dependent in quantitative agreement with previous neutron diffraction results and solves an old discrepancy discussed elsewhere. On M2, the angle between c and H(0) is found to be much smaller than 90° in contradiction to symmetry requirements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00202259
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  • 4
    Electronic Resource
    Electronic Resource
    Single crystal Mössbauer spectroscopy on the three principal sections of a synthetic fayalite sample in the antiferromagnetic state (1996)
    Springer
    Physics and chemistry of minerals 23 (1996), S. 432-438 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract The present work reports Mössbauer investigations for several temperatures below T N on fayalite single crystal sections cut perpendicularly to the crystallographic a and b-axis (Pnma). The previously detected correspondence between the c-component of the magnetic moment on M1 from neutron diffraction and our own Mössbauer measurements published elsewhere are confirmed for the other principal sections to a large extent. Small humps in the angular dependence of two components of the internal magnetic field H(0) on T below T=23 K are in good agreement with magnetometric and calorimetric data published elsewhere; a reinterpretation of single reflection neutron data has been possible by our results. Moreover, the axes of the electric field gradient (efg) are oriented within the crystallographic axes for the M1-site at low temperatures. The violation of symmetry on the M2 position as a result of our previous investigations could be confirmed for the section ⊥ a, but not with respect to b. A possible explanation in terms of saturation effects of large line intensities at the expense of the small ones is given in the context.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00202029
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  • 5
    Electronic Resource
    Electronic Resource
    Mössbauer studies of selected synthetic silicates (1998)
    Springer
    Hyperfine interactions 113 (1998), S. 219-248 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Mössbauer spectra of fayalite-, 7#x03B1;-Fe2SiO4, powder and single crystals were taken in the antiferromagnetic temperature region below T N≅65 K. The orientation of the efg and H(0) with respect to the crystallographic axes was determined as function of the temperature and compared to neutron diffraction and magnetic susceptibility data. A similar study was performed with Li‐acmite LiFeSi2O6, whose magnetic structure can be regarded as a model compound for quasi one‐dimensional systems. Synthetic annite KFe3[AlSi3O10(OH)2] has to contain at least about 10% Fe3+ in order to be stable. A comparison of the evaluation of the spectra assuming either Lorentzian line shape of the doublets or quadrupole splitting distributions QSDs shows that Fe3+/Fe2+‐ratios can be determined precisely by both methods. However, M2/M1-site distributions cannot be evaluated with great accuracy. In ilvaite CaFe3[Si2O7/O/(OH)], there is a thermally activated intersite electron hopping between Fe2+ and Fe3+ at temperatures around 300 K in a double octahedron chain. At temperatures above 395 K there is extended electron delocalization in a narrow d‐ or polaron‐band. The substitution of Fe by Mn favours both effects and lowers the temperature of the crystallographic phase transition monoclinic to orthorhombic distinctly. In the solid solution series member acmite(50%)‐hedenbergite(50%) Na0.5Ca0.5Fe2[Si2O6] just intersite electron hopping between Fe2+ and Fe3+ in the M1 octahedron chain and no formation of polaron bands is observed. This is explained by the larger Fe–Fe‐intrachain distances compared to those in ilvaite or magnetite.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1012627817237
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