Collective instabilities in correlated electron systems are often closely connected to emergent electronic phases, making the characterization of their momentum- and energy-dependent susceptibilities essential for identifying the underlying interactions. In metallic systems, the topology of the Fermi surface can promote a wide range of collective modes, including charge- and spin-density-wave fluctuations, which are frequently associated with unconventional superconductivity. A prominent example is the Sr2RuO4, where the nesting-driven, incommensurate spin fluctuations are believed to play an essential role in the pairing mechanism.

Here, we present a comparative spectroscopic study of the closely related compound Sr2RhO4, using an experimental methodology analogous to that previously established for Sr2RuO4. Despite clear similarities in their electronic structures, we find that the paramagnon excitations characteristic of Sr2RuO4 are suppressed in the rhodate analogue. Comparing the measured response to band-structure calculations, our results show that the collective spin dynamics are highly sensitive to subtle changes in electronic interactions and Fermi surface topology. These results provide new insights into the conditions required for strong spin fluctuations in layered ruthenate and rhodate systems.