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  • 75.10.Jm  (2)
  • Oxide superconductors  (1)
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  • 1
    Electronic Resource
    Electronic Resource
    Spin dynamics and spin correlations in the spinS=1 two-dimensional square-lattice Heisenberg antiferromagnet La2NiO4 (1995)
    Springer
    The European physical journal 96 (1995), S. 479-489 
    Details
    ISSN: 1434-6036
    Keywords: 75.10.Jm ; 75.25.tZ ; 75.40.−S ; 75.30.Ds
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The static and dynamic spin fluctuations in the spinS=1, two-dimensional (2D) square-lattice antiferromagnet La2NiO4 have been studied over a wide temperature range using neutron scattering techniques. The spin correlations in La2NiO4 exhibit a crossover from two- to three-dimensional (3D) behavior as the Néel temperature is approached from above. Critical slowing down of the low-energy spin fluctuations is also observed just aboveT N . The correlation length, ξ(T), and the static structure factor,S(0), have been measured and are compared with recent theoretical calculations for the quantum 2D Heisenberg antiferromagnet using microscopic parameters determined from previous spin-wave measurements. Good agreement for ξ(T) is found with the exact low-temperature result of Hasenfratz and Niedermeyer provided that 2π p s is renormalized by ≈20% from the spin-wave value.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01313845
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  • 2
    Electronic Resource
    Electronic Resource
    Neutron scattering study of the two-dimensional spinS=1/2 square-lattice Heisenberg antiferromagnet Sr2CuO2Cl2 (1995)
    Springer
    The European physical journal 96 (1995), S. 465-477 
    Details
    ISSN: 1434-6036
    Keywords: 75.10.Jm ; 75.25.+Z ; 75.40.−S
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have carried out a neutron scattering investigation of the static structure factorS(q 2D ) (q 2D is the in-plane wave vector) in the two-dimensional spinS=1/2 square-lattice Heisenberg antiferromagnet Sr2CuO2Cl2. For the spin correlation length ξ we find quantitative agreement with Monte Carlo results over a wide range of temperature. The combined Sr2CuO2Cl2-Monte Carlo data, which cover the length scale from ≈1 to 200 lattice constants, are predicted without adjustable parameteres by renormalized classical theory for the quantum nonlinear sigma model. For the structure factor peakS(0), on the other hand, we findS(0)∼ξ 2 for the reduced temperature range 0.16〈T/2πρ s 〈0.36, whereas current theories predict that at low temperaturesS(0)∼T 2 ξ 2. This discrepancy has important implications for the interpretation of many derivative quantities such as NMR relaxation rates. In the ordered phase, we have measured the temperature dependence of the out-of-plane spin-wave gap. Its low-temperature value of 5.0 meV corresponds to an XY anisotropyJ XY /J=1.4×10−4. From measurements of the sublattice mangetization we obtain β=0.22±0.01 for the order parameter exponent. This may either reflect tricricality as in La2CuO4, or it may indicate finite-size two-dimensional XY behavior as suggested by Bramwell and Holdsworth. As in theS=1 system K2NiF4, the gap energy in Sr2CuO2Cl2 scales linearly with the order parameter up to the Néel temperature. We also reanalyze static structure factor data for K2NiF4 using the exact low temperature result for the correlation length of Hasenfratz and Niedermayer and including the Ising anisotropy explicitly. Excellent agreement between experiment and theory is obtained for the correlation length, albeit with the spin-stiffnessρ s reduced by ≈20% from the spin-wave value. As in Sr2CuO2Cl2 we find thatS(0)∼ξ 2 for the reduced temperature range 0.22〈T/2πρ s 〈0.47.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01313844
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  • 3
    Electronic Resource
    Electronic Resource
    Local structural instability of high-T c oxide superconductors studied by inelastic neutron scattering (1994)
    Springer
    Journal of superconductivity 7 (1994), S. 415-418 
    Details
    ISSN: 1572-9605
    Keywords: Oxide superconductors ; structural instability ; neutron scattering
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The scattering function,S(Q, E), of superconducting La1.85Sr0.15CuO4 and YBa2Cu3O7 was measured over a wide range ofQ-E space by inelastic neutron scattering. Fine structures in their phonon density of states as well as theQ-dependences ofS(Q, E) were observed. TheQ-dependence ofS(Q, E) is very susceptive atT c , with an anomalous behavior similar to a critical phenomenon. We have found that the anomalous behavior is related to the local structural instability, i.e., the 〈110〉 buckling motion of the Cu-O plane and the shortening of the distance between the apical oxygen and the copper atom in the plane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00724579
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