Actinide 5f Systems: Experimental Determination of the Magnetic Response Function

Understanding of metallic actinide systems is in confusion. Searches for crystal-field levels with neutron spectroscopy have, for the most part, been unsuccessful, despite the acknowledged importance of the 5f electrons in determining the magnetic behavior. In systems such as UAl/sub 2/, USn/sub 3/ and UN a broad response function, S(Q vector,..omega..), reminiscent of that found in intermediate valent compounds, exists. Neutron inelastic scattering experiments on single crystals have shown the small influence of the crystal field. Instead we find an unusual response function dominated by the longitudinal susceptibility chi/sup zz/(Q vector,,..omega..) such that transverse excitations - conventional spin waves - do not exist at low energies. As yet a detailed theoretical interpretation of the measurements does not exist. Indeed, the small, although not necessarily negligible, role of the crystal field presents conceptual difficulties if we anticipate behavior analogous to that found in many lanthanide 4f systems. Some alternate approaches are discussed