Neutron Scattering from Heavy Fermion Systems

We review results of neutron scattering experiments on the heavy fermion systems URu2Si2, U2Zn17 and UPt3. In the antiferromagnetic superconductor URu2Si2 the excitations in the ordered phases are propagating, longitudinal and similar to those in rare earth singlet ground state systems. However, the ordered moment of 0.03 μB is anomalously small and the transverse response is overdamped. In the antiferromagnet U2Zn17, overdamped antiferromagnetic fluctuations dominate the excitation spectrum above and below T.N. In the superconductor UPt3 we have established the existence of spin fluctuations with characteristic energies of 0.5 meV. We discuss a simple model of exchange coupled overdamped responses which gives a consistent description of the diffusive magnetic fluctuations in several heavy fermion systems.