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  • 1
    Electronic Resource
    Electronic Resource
    Electron delocalization in ilvaite, a reinterpretation of its 57Fe Mössbauer spectrum (1984)
    Springer
    Physics and chemistry of minerals 10 (1984), S. 250-255 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract The Mössbauer spectra of ilvaite CaFe 2 2+ Fe3+[Si2O7/O/OH] and their temperature dependence between 298 K and 455 K can be satisfactorily least-squares fitted by a superposition of the resonances for Fe2+(8d), Fe3+(8d) and Fe2+(4c). The relative areas under the three resonances are nearly equal and vary only weakly with temperature. No additional resonances or line broadenings have to be introduced, if we assume that the hyperfine interactions of Fe2+(8d) and Fe3+(8d) fluctuate between their values due to electron hopping between the iron ions at the 8d sites. Hopping can be assumed to occur homogeneously among nearly equivalent sites. The fluctuation rate is described by an Arrhenius law with a pre-exponent of about 9 × 108 s−1 and an activation energy of 0.11 eV indicating non-adiabatic hopping. In addition to the intersite hopping process, the strong decrease of the quadrupole splitting and the isomer shift of Fe2+(8d) between 298 K and 360 K suggests the occurrence of intrinsic charge delocalization from Fe2+(8d) which does not involve the neighbouring Fe3+(8d) ions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00311949
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  • 2
    Electronic Resource
    Electronic Resource
    Crystallographic phase transition and valence fluctuation in synthetic mn-bearing ilvaite CaFe2+ 2-x Mn2+ xFe3+ [Si2O7/O/(OH)] (1992)
    Springer
    Physics and chemistry of minerals 18 (1992), S. 491-496 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract The dependence of the electronic and the crystallographic structure on temperature of synthetic Mnbearing ilvaites CaFe2+ 2-xMn2+ xFe3+ [Si2O7/O/OH] with 0≤x≤0.19 has been investigated. The change of the electronic structure was studied by 57Fe Mössbauer spectroscopy. The spectra show an increasing valence fluctuation rate between Fe2+ and Fe3+ in the double chain of edge-sharing octahedra with increasing temperature resulting in a mixed valent state of iron. The valence fluctuation rate is distinctly increased by the Mnsubstitution. The temperature of the crystallographic phase transition T x as studied by a high temperature Guinier method is distinctly lowered by the Mn-substitution (x = 0.0, T x=390K; x = 0.12, T x =370K; x = 0.19, T x=295K). The reasons for this behaviour are discussed in terms of Fe2 +, Fe3 + cation order-disorder, electronic relaxation rate, and relaxation of the lattice. In the monoclinic phase there is electron hopping between Fe2 +, Fe3 + pairs whereas in the orthorhombic phase there is extended electron delocalization via a narrow, d-band mechanism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00205263
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  • 3
    Electronic Resource
    Electronic Resource
    Electrical and magnetic properties of cronstedtite (1989)
    Springer
    Physics and chemistry of minerals 16 (1989), S. 394-400 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract Two samples of cronstedtite, a mixed valence serpentine with ideal formula {Fe 2 2+ ,Fe3+}[Si,Fe3+]O5(OH)4, have been examined by X-ray and neutron diffraction, thermopiezic analysis, magnetization and susceptibility measurements and Mössbauer spectroscopy. The conductivity is thermally activated, with activation energies of 0.25 eV in the basal plane and 0.37 eV in the perpendicular direction. The shape of paramagnetic Mössbauer spectra above 200 K is influenced by charge fluctuations in octahedral sites and fits of spectra at temperatures up to 410 K with a stochastic relaxation model give an activation energy of 0.19 eV. Static charge ordering sets in progressively below about 100 K. Cronstedtite orders antiferromagnetically below 12 K in a structure with antiferromagnetic octahedral sheets and moments perpendicular to the a-axis. Magnetic and charge-ordered structures are proposed for the ideal composition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00199561
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  • 4
    Electronic Resource
    Electronic Resource
    Mössbauer studies of57Fe doped single crystals of GdBa2Cu3O7-δ (1993)
    Springer
    The European physical journal 91 (1993), S. 139-143 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract 57Fe Mössbauer effect measurements have been performed on single crystals of57Fe doped GdBa2Cu3O7-δ at various c-axis orientations and temperatures. The analysis of the data yields information on the sign and direction of Vzz, the direction of Bhf with respect to Vzz and the anisotropy of the f-factor for the individual observed three quadrupole doublets. From these data we conclude that the quadrupole doublet with ΔEQ ≃1.9 mm/s is due to Fe on a regular Cu(1)-site (4-fold oxygen coordination) with distorted local symmetry (Vzz isnot parallel to the c-axis), while the other quadrupole doublets have higher oxygen coordinations (higher Lamb-Mössbauer-factor).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01315227
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  • 5
    Electronic Resource
    Electronic Resource
    Mössbauer studies of57Fe atoms isolated in CH4 and CO2 matrices (1974)
    Springer
    The European physical journal 270 (1974), S. 31-36 
    Details
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The Mössbauer absorption spectra of matrix isolated57Fe atoms have been measured in the inert matrices CH4 and CO2 with matrix temperatures between ∼3.3 and ∼46 K. The isomer shift of the observed resonances is (−0.79±0.02) mm/s and (−0.76±0.05) mm/s with respect to iron metal at 300 K for57Fe in CH4 and for CO2 respectively. This is within the experimental errors the same isomer shift as that of rare-gas matrix isolated57Fe atoms. All spectra show quadrupole doublets due to the noncubic point symmetry of the lattice site occupied by the57Fe atoms. The effective Debye temperatures as obtained from the temperature dependence of the resonance absorption areas are (46±4) K for the CH4 matrix and (121±6) K for the CO2 matrix annealed at ∼20 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01676790
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  • 6
    Electronic Resource
    Electronic Resource
    Mössbauer study of the mixed ferrimagnetic-spin glass phase in SrFe12−x CrxO19 hexagonal ferrites (1986)
    Springer
    Hyperfine interactions 28 (1986), S. 569-572 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract It is shown from zero magnetic field Mössbauer spectroscopy that the mixed ferrimagnetic-spin glass phase observed in SrFe12−x CrxO19 hexagonal ferrites is characterized by longitudinal spin components contributing to the ferrimagnetic long range magnetic ordering and transverse spin components contributing to the spin glass ordering. It is argued as well that different sublattices could behave in a different way owing to their different degree of magnetic frustration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02061513
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  • 7
    Electronic Resource
    Electronic Resource
    Quasielastic resonance absorption of57Fe in the hydrides and deuterides of vanadium and niobium (1986)
    Springer
    Hyperfine interactions 28 (1986), S. 1009-1012 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The anomalous temperature dependence ot the f-factor arising from the diffusion of interstitials has been studied for57Fe in hydrides and deuterides of vanadium and niobium at temperatures between 6 and 500K. Isotope effects in both the diffusion rate of the interstitials and the magnitude of the displacements of the probes are observed. The centre shift and quadrupole splitting of the patterns provide further information on the hydrogen distribution near the probes and on phase transition temperatures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02061615
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  • 8
    Electronic Resource
    Electronic Resource
    Spin dynamics in crystalline and amorphous DyAg (1986)
    Springer
    Hyperfine interactions 31 (1986), S. 303-308 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Crystalline (cr-) Dyag [CsC] structure] orders antiferro-magnetically with TN≅60K; amorphous (am-) DyAg ferro-magnetically with TC≈-18K. We measured the longitudinal field (LF) μ+SR relaxation functions GZZ(t) for 5K〈T〈300K using surface muons. In the paramagnetic state. cr-DyAg gives an exponential GZZ (t) in the relaxation rate rising first slowly then more rapidlynear TN; no decoupling is observed in LF up to 0.4T. In the ordered state we see a Lorentzian Kubo-Toyabe GZZ(t), becoming nearly static at the lowest temperatures. Its static width is very narrow (Δ≈-7 MHz), and full dceoupling is achieved here in 0.1 T. On approaching TN, the fluctuation rate and the static width increase mootonically bt the field distribution remains Loratzian. A LF of 0.4T is then insufficient to quench the fast exponential relaxation. In paramagnetic am-DyAg, the μ+ depolarization is always much faster then in cr-DyAg. At lower temperatures it is better described by a root-exponential than an exponential GZZ(t). Below TC an exponentially relaxing signal with 1/3 amplitude is seen. The decoupling effect of LF up to 0.4T was negligible at all temperatures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02401572
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  • 9
    Electronic Resource
    Electronic Resource
    μSR measurements on UAl2 (1986)
    Springer
    Hyperfine interactions 31 (1986), S. 309-312 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The cubic Laves Phase UAl2 is known to exhibit unusual magnetic and transport properties at low temperatures which have been explained by a narrow 5f-band in connection with strong spin fluctuations. Transverse and longitudinal μSR spectra taken between 300 K and 2 K show little variation in damping rate and muonic Knight shift. The fact that the weak damping seen in zero field can fully be decoupled by a longitudinal field of less than 10 mT shows that its origin lies in the interactions between the muon and the27Al nuclear moments, rather than in an influence of the uranium magnetic moments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02401573
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  • 10
    Electronic Resource
    Electronic Resource
    Muon spin relaxation in different samples of DyAl2 (1986)
    Springer
    Hyperfine interactions 31 (1986), S. 337-338 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Two samples of DyAl2 were studied by longitudial μSR in the paramagnetic and ferromagnetic regime. In a region Tc±40 K the samples give different signals although X-ray analysis can not detect any impurity phase in either of them.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02401578
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