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  • 1
    ISSN: 1434-6036
    Keywords: PACS. 75.30.Mb Valence fluctuation, Kondo lattice, and heavy-fermion phenomena - 75.25.+z Spin arrangements in magnetically ordered materials - 72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: We report on extensive elastic neutron scattering to determine the wave vector of the magnetic order in CeCu6-xAux single crystals for x 〉 0.1. For all values of x investigated (0.2, 0.3, 0.5, 1.0) we find long-range incommensurate antiferromagnetic order with an ordering vector (0.625 0.275) for x =0.2, nearly unchanged for x =0.3, and (0.59) for x =0.5, staying roughly the same for x =1.0. In addition, short-range correlations are observed for x =0.2, reminiscent of those found previously for x =0.1. The ordered magnetic moment is found to increase rapidly for small x, and more slowly for the larger x values. The increase of the specific-heat anomaly at the ordering temperature with x is in qualitative accord with this behavior. Finally, data of the electrical resistivity for current flow along the three crystallographic directions are presented, showing a clear signature of the magnetic order. A theoretical interpretation of the interplay of magnetic order and transport in terms of (i) the partial suppression of the Kondo effect by the staggered magnetization and (ii) the anisotropic band structure induced by the staggered field is shown to account well for the data, provided the ordering vector is close to 2 k F, where k F is a typical Fermi momentum.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 41 (2004), S. 471-478 
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. From measurements of the specific heat of $\mathrm{NdBa_2Cu_3O_{6 + \mathnormal{x}}}$ in the temperature range between 20 K and 300 K the electronic contribution C e (T)/T has been derived. The results depend strongly on the assumptions made for the normal-state reference, especially the phonon contribution. Taking into account entropy conservation between the superconductor and a hypothetical normal-state reference, we found a temperature independent electronic contribution of this normal-state reference without any sign of a pseudogap for both optimum doped and underdoped samples. For oxygen concentrations between x = 0.79 and x = 0.89 a broad hump in C e (T)/T is observed around 120 K, which we ascribe to pair formation above T c . The dependence of the hole concentration n h in the copper oxide planes on the oxygen concentration x in the copper oxide chains was calculated by means of bond-valence sums. We found that the optimum doping of the copper oxide planes is n h,opt = 0.24 for $\mathrm{\mathnormal{R}Ba_2Cu_3O_{6 + \mathnormal{x}}}$ (R = Nd, Y) irrespective of the element on the rare-earth site.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of low temperature physics 117 (1999), S. 951-955 
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The specific heat of Nd(Y)Ba 2 Cu 3 O x single crystals without substitution of Nd for Ba has been measured for various oxygen contents. In comparison with YBa 2 Cu 3 O x , the maximum attainable transition temperature of the crystals is about 4 K higher and shifted from x = 6.92 to x = 7.0, the highest possible oxygen content. In spite of the difference in the T c (x) dependences, the jump in the specific heat ΔC/T c at T c in both systems increases continuously being maximum at x = 7.0. Bond valence sum calculations based on neutron diffraction data point to a retarded generation of holes with increasing oxygen content in the Nd system and a different hole distribution between the chains and the planes in comparison to YBa 2 Cu 3 O x accounting for the different behaviour of both systems.
    Type of Medium: Electronic Resource
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