Magnetism in the heavy-electron superconductors UPt3 and URu2Si2

The nature of magnetism in the heavy-electron superconductors UPt3 and URu2Si2 is investigated by using a spin-orbit generalized variant of local-spin-density (LSD) theory to calculate the self-consistent moment-polarized electronic structure and the dynamic (bare-band) susceptibility. It is shown that the direction of the magnetic moment is predicted correctly. The size of the moment, however, is 0.8B in UPt3 and 1.2B in URu2Si2, i.e., a factor of 40 larger than experiment. It is noted, however, that the experimental moment of (0.650.1)B for Th- or Pd-doped UPt3 is close to the theoretical value. The static susceptibility, (q), is predicted to be weakly dependent on q except for UPt3, where a peak is found at q=(/c)(0,0,2)in general agreement with neutron-scattering data at high frequencies. The low-frequency anomalies in the neutron data which lead to magnetic ordering are not seen in the calculated dynamic susceptibility, but can be understood in terms of a moment-moment interaction. An explanation for these conflicting data is offered based on the interaction of itinerant quasiparticle and local-moment degrees of freedom at low temperatures, which leads to a renormalization of the LSD spin-spin response function.