MAGNETIC ORDER AND TRANSPORT IN THE HEAVY-FERMION SYSTEM CECU6-XAUX

We report on extensive elastic neutron scattering to determine the wav e 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 approximate to (0.625 0 0.275) for x = 0.2, nearly unchanged for x = 0.3, and Q approximate to (0.59 0 0) 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 a = 0.1. The or dered magnetic moment is found to increase rapidly for small a, and mo re slowly for the larger a: values. The increase of the specific-heat anomaly at the ordering temperature with x is in qualitative accord wi th this behavior. Finally, data of the electrical resistivity for curr ent how along the three crystallographic directions are presented, sho wing a clear signature of the magnetic order. A theoretical interpreta tion of the interplay of magnetic order and transport in terms of (i) the partial suppression of the Kondo effect by the staggered magnetiza tion and (ii) the anisotropic band structure induced by the staggered field is shown to account well for the data, provided the ordering vec tor Q is close to 2k(F), where k(F) is a typical Fermi momentum.