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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Applied physics 29 (1982), S. 1-7 
    ISSN: 1432-0630
    Keywords: 76.80.+y ; 71.55.−i ; 71.70.−d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Mössbauer spectra of LiNbO3: Fe(III)-monocrystals in external magnetic fields of 0.3−7T with various configurations of the γ-direction, c-axis of the crystal, and the magnetic field direction are interpreted by means of a spin Hamiltonian. A consistent set of hyperfine and crystal-field parameters could be least squares fitted for all spectra. Arguments that Fe(III) substitutes Nb(V) are given.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Hyperfine interactions 16 (1983), S. 837-840 
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Lithium niobate monocrystals exhibit many interesting physical phenomena such as ferro-, piezo- and pyroelectricity, low acoustical losses, small optical absorption in the visible region and, especialy after doping with small amounts of transition metal ions, strong photorefraction and photovoltaic effects [1–3]. According to the multitude of the properties there are numerous applications of LiNbO3 for e.g. light modulation, Q-switch, second harmonic generation, fibre optics, acoustic transducers, pyroelectric detectors and holographic data storage. In order to understand in detail the microscopic mechanisms of the bulk photovoltaic effect and the photorefraction, which are strongly enhanced by doping the crystals with iron, an exact knowledge of the not yet unambigously known lattice site and the charge compensation [4,5] as well as the electronic structure of the iron impurities is indispensable. Here the Mössbauer investigation of the hyperfine interaction of57Fe ions probing the crystal field may contribute to clarification. As can be seen from the isomer shift iron enters the LiNbO3-lattice as Fe(II) or Fe(III) [5]. By annealing the samples in oxydizing atmospheres (e.g. ≈p24 hours in air ≈p600
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Hyperfine interactions 42 (1988), S. 1067-1070 
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Mössbauer spectra of LiNbO3: Fe(III)-monocrystals were measured in zero external magnetic field (5mK to 673K). They all show typical lineshapes due to relaxation effects. Below 77K temperature independent and above 77K a temperature-dependent relaxation is observable. In spectra measured in external magnetic fields relaxation effects occur only above 77K. We present least square fits of spectra measured at 300K and external magnetic fields using symmetry invariant reservoir spectral densities. The applied numerical formalism takes the complete electronuclear manifold of57Fe(III) into account. We discuss the problems concerning the interpretation of zero field spectra.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Hyperfine interactions 42 (1988), S. 1071-1074 
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The supermatrix-Liouville formalism to compute Mössbauer relaxation spectra leads, applied to the6S5/2-state of57Fe(III) to a 288-dimensional nonhermitian matrix. Provided that an axial crystal field acts on the electronic states, only few of the states described by the supermatrix are necessary to simulate theoretical spectra and the dimension of this matrix can be reduced to at least 1/3. This confinement implies no approximation for the description of the six electronic states of Fe(III) and for the interactions of them with environment and nucleus.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Single crystal LiNbO3:57Fe(III) Mössbauer absorption spectra at 3 Tesla and 120...300K can be fitted using a dynamical spin Hamiltonian according to spin-lattice relaxation. At high fields (0.9...7 Tesla) and 4.2K the spectra can be fitted using an electronuclear spin Hamiltonian. The area of the subspectra due to each electronic state is not in accordance with a Boltzmann distribution at the bath temperature. From the population we calculate spin temperatures which depend linearly on the external magnetic field.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Hyperfine interactions 28 (1986), S. 785-788 
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Crystal field parameter have been determined from EPR spectra (77K) of LiNbO3∶Fe(III). Anomalous line shapes are described phenomenologically and saturation studies are compared with calculations using a second order dynamic spin-hamiltonian H′. Mössbauer spectra of LiNbO3∶Fe(III) have been interpreted by means of simulations using Liouville superoperators including a static fine-and a hyperfine spin-hamiltonian and H′. Calculations have been performed using an effective spin of 1/2, the supermatrix with dimension 288 and a reduced formalism (supermatrix with dimension 96).
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Hyperfine interactions 56 (1990), S. 1477-1481 
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Mössbauer spectra of LiNbO3:Fe(III)-single crystals at various external fields and temperatures are least-squares fitted using a static spin-Hamiltonian and appropriate relaxation matrices. An electronic secular approximation is used to reduce the number of the relaxation matrix elements. The results forH ext=0 cannot be explained by a dynamical spin-Hamiltonian. The relaxation frequency for the spectra withH ext=1.5 and 3 T is independent of energy and proportional toT 2, thus excluding a direct process.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Hyperfine interactions 66 (1991), S. 141-148 
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The theory of calculating Mössbauer spectra by anab initio method is shortly reviewed. The relaxation supermatrix is calculated in an electronic basis and its dimension is reduced. Spectra are fitted using a dynamical spin-Hamiltonian. A procedure for fitting the spectra in the whole temperature range is suggested.
    Type of Medium: Electronic Resource
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