Magnetic excitations and the search for crystal-field transitions in the heavy-fermion superconductor UPd₂Al₃

We have performed inelastic neutron scattering (INS) experiments to study the spin dynamics and search for crystalline-electric-field (CEF) excitations in the antiferromagnetic heavy-fermion superconductor UPd2Al3. The low-energy-transfer spectra are predominantly characterized by a quasielastic Lorentzian (weighted by the detailed balance factor) with a residual line width of approximately 5 meV. For uranium-based intermetallics, this is an unusually small line width and UPd2Al3 is one of the rare examples of 5f-electron systems whose residual line width corresponds to the macroscopically estimated Kondo lattice temperature. However, significant deviations from this fit suggest additional inelastic contributions that persist up to T = 150 K, i.e. 10T(N). This additional scattering may be attributed to the presence of CEF excitations or intersite magnetic correlations. A survey of the scattering within the whole accessible momentum-energy space provides further evidence for the existence of these inelastic magnetic intensities. We find a surprisingly good agreement between the excitation energies of our neutron scattering spectra and a CEF-level scheme proposed on the basis of magnetic susceptibility and specific heat measurements