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  • 2010-2014
  • 2000-2004  (5)
  • 1820-1829
  • 1800-1809
  • 2001  (5)
  • PACS. 32.80.Pj Optical cooling of atoms; trapping – 34.50.Rk Laser-modified scattering and reactions  (3)
  • PACS. 61.12.-q Neutron diffraction and scattering – 61.66.Fn Inorganic compounds – 75.25.+z Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.) – 75.30.Et Exchange and superexchange interactions  (2)
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  • 2010-2014
  • 2000-2004  (5)
  • 1820-1829
  • 1800-1809
Year
  • 2001  (5)
Keywords
  • 1
    Electronic Resource
    Electronic Resource
    Crystal and magnetic structures of the oxyphosphates MFePO 5 (M = Fe, Co, Ni, Cu). Analysis of the magnetic ground state in terms of superexchange interactions (2001)
    Springer
    The European physical journal 22 (2001), S. 429-442 
    Details
    ISSN: 1434-6036
    Keywords: PACS. 61.12.-q Neutron diffraction and scattering – 61.66.Fn Inorganic compounds – 75.25.+z Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.) – 75.30.Et Exchange and superexchange interactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: We have studied in detail the crystal and magnetic structures of the oxyphosphates MFePO5 (M: divalent transition metal) using neutron powder diffraction as a function of temperature. All of them are isomorphic to the mixed valence compound α-Fe2PO5 with space-group Pnma. No disorder exists between the two metallic sites. The M2+O6 octahedra share edges between them and faces with Fe3+O6 octahedra building zigzag chains running parallel to the b-axis that are connected by PO4 tetrahedra. The topology of this structure gives rise to a complex pattern of super-exchange interactions responsible of the observed antiferromagnetic order. The magnetic structures are all collinear with the spin directed along the b-axis except for M = Co. The experimental magnetic moments of Cu+2 and Ni2+ correspond to the expected ionic value, on the contrary the magnetic moment of Fe3+ is reduced, probably due to covalence effects, and that of Co2+ is greater than the spin-only value indicating a non negligible orbital contribution. Using numerical calculations we have established a magnetic phase diagram adapted for this type of crystal structure and determined the constraints to be satisfied by the values of the exchange interactions in order to obtain the observed magnetic structure as the ground state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100510170093
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  • 2
    Electronic Resource
    Electronic Resource
    Neutron diffraction study of the magnetic ordering in the series R 2 BaNiO 5 (R = Rare Earth) (2001)
    Springer
    The European physical journal 24 (2001), S. 59-70 
    Details
    ISSN: 1434-6036
    Keywords: PACS. 61.12.-q Neutron diffraction and scattering – 61.66.Fn Inorganic compounds – 75.25.+z Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.) – 75.30.Et Exchange and superexchange interactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: A neutron diffraction study, as a function of temperature, of the title compounds is presented. The whole family (space group Immm, a ≈ 3.8Å, b ≈ 5.8Å, c ≈ 11.3Å) is structurally characterised by the presence of flattened NiO6 octahedra that form chains along the a-axis, giving rise to a strong Ni-O-Ni antiferromagnetic interaction. Whereas for Y-compound only strong 1D correlations exist above 1.5 K, presenting the Haldane gap characteristic of 1D AF chain with integer spin, 3D AF ordering is established simultaneously for both R and Ni sublattices at temperatures depending on the rare earth size and magnetic moment. The magnetic structures of R2BaNiO5 ( R = Nd, Tb, Dy, Ho, Er and Tm) have been determined and refined as a function of temperature. The whole family orders with a magnetic structure characterised by the temperature-independent propagation vector = (1/2, 0, 1/2). At 1.5 K the directions of the magnetic moments differ because of the different anisotropy of the rare earth ions. Except for Tm and Yb (which does not order above 1.5 K), the magnetic moment of the R3+ cations are close to the free-ion value. The magnetic moment of Ni2+ is around 1.4 , the strong reduction with respect to the free-ion value is probably due to a combination of low-dimensional quantum effects and covalency. The thermal evolution of the magnetic structures from T N down to 1.5 K is studied in detail. A smooth re-orientation, governed by the magnetic anisotropy of R3+, seems to occur below and very close to T N in some of these compounds: the Ni moment rotates from nearly parallel to the a-axis toward the c-axis following the R moments. We demonstrate that for setting up the 3D magnetic ordering the R-R exchange interactions cannot be neglected.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100510170022
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  • 3
    Electronic Resource
    Electronic Resource
    Inversion analysis of K 2 coupled electronic states with the Fourier grid method (2001)
    Springer
    The European physical journal 17 (2001), S. 319-328 
    Details
    ISSN: 1434-6079
    Keywords: PACS. 32.80.Pj Optical cooling of atoms; trapping – 34.50.Rk Laser-modified scattering and reactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: We present a new determination of the potential curves and interactions of the coupled electronic states A 1 Σ + u and b 3 Π u of the potassium dimer, based on new laser spectroscopy measurements within a molecular beam, combined with data available in the literature. We used a new global deperturbation approach, involving the Fourier Grid Hamiltonian method for energy level calculation. A standard deviation of 1.2 is obtained corresponding to a variance of 7.5×10 -3 cm-1, representing a significant improvement compared to the standard deviation of 4 yielded by the traditional local deperturbation approach.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100530170006
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  • 4
    Electronic Resource
    Electronic Resource
    Cold rubidium molecule formation through photoassociation: A spectroscopic study of the 0 g - long-range state of 87 Rb 2 (2001)
    Springer
    The European physical journal 15 (2001), S. 189-198 
    Details
    ISSN: 1434-6079
    Keywords: PACS. 32.80.Pj Optical cooling of atoms; trapping – 34.50.Rk Laser-modified scattering and reactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: We report the detailed analysis of translationally cold rubidium molecule formation through photoassociation. Cold molecules are formed after spontaneous decay of photoexcited molecules from a laser cooled atomic sample, and are detected by selective mass spectroscopy after two-photon ionization into Rb 2 + ions. A spectroscopic study of the 0 g - (5 S + 5 P 3/2 ) pure long-range state of 87Rb2 is performed by detecting the ion yield as a function of the photoassociation laser frequency; the spectral data are theoretically analyzed within the semiclassical RKR approach. Molecular ionization is resonantly enhanced through either the 2 3 Π g or the 2 3 Σ + g intermediate molecular states. Some vibrational levels of the latter electronic state are observed and assigned here for the first time. Finally, cold molecules formation rates are calculated and compared to the experimentally measured ones, and the vibrational distribution of the formed molecules in the a 3 Σ + u ground triplet state is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100530170165
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  • 5
    Electronic Resource
    Electronic Resource
    Penning collisions of laser-cooled metastable helium atoms (2001)
    Springer
    The European physical journal 14 (2001), S. 15-22 
    Details
    ISSN: 1434-6079
    Keywords: PACS. 32.80.Pj Optical cooling of atoms; trapping – 34.50.Rk Laser-modified scattering and reactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: We present experimental results on the two-body loss rates in a magneto-optical trap of metastable helium atoms. Absolute rates are measured in a systematic way for several laser detunings ranging from -5 to -30 MHz and at different intensities, by monitoring the decay of the trap fluorescence. The dependence of the two-body loss rate coefficient β on the excited state ( 23 P 2) and metastable state ( 23 S 1) populations is also investigated. From these results we infer a rather uniform rate constant K sp = (1±0.4)×10-7 cm3/s.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100530170228
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    Paper (German National Licenses)
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