Intersite interactions in CeRu₂Si₂-_xGe_x alloys

Abstract

CeRu₂Si₂ is a heavy-fermion compound, while CeRu₂Ge₂ has a ferromagnetic ground state below 9 K with a magnetic moment close to that expected from the ground-state wavefunction. The dynamical magnetic response in the pseudo-binary system CeRu₂Si₂ -_xGe_x is characterized by longitudinal spin fluctuations, reflecting the uniaxial nature of the crystal-field ground states in these alloys. The energy widths of the spin fluctuation spectra are shown to be modulated as a function of wave-vector transfer, owing to intersite interactions. A simple analysis using a random-phase approximation response function allows the single-site and intersite components of the response to be separated. The single-site response shows that the hybridization of the 4f electron with the conduction electrons decreases with increasing x. The strength of the intersite interactions appears to be independent of x but, more remarkably, it appears to be strongly temperature dependent.