Magnetic fluctuations in CeCu6-xAux at the nonmagnetic-magnetic quantum phase transition

When the heavy-fermion system CeCu6 is doped with Au, long-range antiferrom agnetic order develops above a threshold concentration x = 0.1, with T-N re aching 2.3 K for x = 1. The magnetic ordering vector of CeCu6-xAux as deter mined from elastic neutron scattering is almost independent of x for x = 0. 15, 0.2 and 0.3, Q approximate to (0.63 0 0.26), and jumps to the a* axis f or = 0.5. At the quantum critical point x = 0.1, the specific heat C exhibi ts a divergence of C/T similar to - In(T/T-0) towards low temperatures T, a nd the electrical resistivity varies linearly with T. Inelastic neutron sca ttering experiments were carried out at the ILL Grenoble and at Riso in ord er to investigate whether the critical fluctuations for x = 0.1 can account for this anomalous behavior. We review some salient features of the both d ata sets. The observed reduced dimensionality of the critical fluctuations indeed leads to the above anomalous behavior. A detailed study of the energ y and temperature dependence of the dynamic structure factor reveals unusua l dynamics. The orthorhombic-monoclinic distortion in CeCu6 is suppressed r apidly with increasing x and is shown to be unrelated to the quantum phase transition. (C) 2000 Elsevier Science S.A. All rights reserved.