The unconventional excitations and critical behavior in actinide compounds

The low lying electronic states of the uranium ion, at present imperfectly understood, have been probed by neutron inelastic scattering methods. In the rock‐salt structure pnictides and chalcogenides the character of the magnetic excitations and the magnitudes of the ordered moments are highly sensitive to the U‐U distance. For example, in the ferromagnetic chalcogenides, US with the smallest U‐U distance exhibits only a broad distribution of scattering at low temperatures, whereas UTe with the largest U‐U spacing exhibits several distinct branches of excitations. Similarly, for the antiferromagnetic pnictides those with small U‐U distance (UN, UAs) exhibit only a broad magnetic response with no sign of the sharp collective features seen in USb. The pnictides exhibit very anisotropic longitudinal spin correlations above Tn. For UN a dynamical scaling model has been obtained which incorporates the anisotropy and describes the linewidths of the critical scattering accurately.