2 0 Fe b 19 98 Magnetic order and transport in the heavy - fermion system

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 Q ≈ (0.625 0 0.275) for x = 0.2, nearly unchanged for x = 0.3, and Q ≈ (0.59 0 0) for x = 0.5, staying roughly the same for x = 1.0. In addition, short-range correlations are observed at 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 Q is close to 2kF , where kF is a typical Fermi momentum. 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