Magnetic fluctuations close to an antiferromagnetic quantum critical point in heavy fermion alloys

Neutron scattering spectra of the heavy fermion compounds Ce(Cu,Au)$_6$ and CeNi$_2$Ge$_2$ will be compared to characterize the magnetic correlations and dynamics close to an antiferromagnetic quantum critical point. While the magnetic response in Ce(Cu,Au)$_6$ reveals quantum critical fluctuations which can be consistently described in a simple although unconventional picture, the scenario in CeNi$_2$Ge$_2$ is more complex, both defying the ``ideal'' conventional scenario expected for a three dimensional antiferromagnetic quantum critical point. (Work in collaboration with G. Aeppli, D.F. McMorrow, N. Christensen, M. Adams, O. Tegus, J. Mydosh, Y. Qiu.)