Spin correlations in heavy fermion systems.

We have used polarized and unpolarized neutron scattering to measure magnetic fluctuations in three heavy fermion systems, CeCu sub 6, U sub 2 Zn sub (17), and UPt sub 3, which at low temperatures are paramagnetic, antiferromagnetic, and superconducting, respectively. Our single crystal experiments demonstrate strong antiferromagnetic correlations in both UPt sub 3 and CeCu sub 6. The inelastic spectra are incompatible with both simple Fermi liquid theory and standard models for magnetic excitations in rare earth compounds. However, an effective Hamiltonian which incorporates both single-impurity Kondo properties and antiferromagnetic RKKY interactions, describes our data for both CeCu sub 6 and UPt sub 3 as well as U sub 2 ZN sub (17). We show that in accord with recent theoretical work, the RKKY coupling, J, undergoes a significant temperature-dependent renormalization.