Observation of two-dimensional spin fluctuations in the bilayer ruthenate Sr3Ru2O7 by inelastic neutron scattering

We report an observation of two-dimensional incommensurate magnetic fluctuations in the layered metallic perovskite Sr 3 Ru 2 O 7 . The wave vectors where the magnetic fluctuations are strongest are different from those observed in the superconducting single layer ruthenate Sr 2 RuO 4 and appear to be determined by Fermi surface nesting. No antiferromagnetic ordering is observed for temperatures down to 1.5 K. For temperatures T ≥20 K, the fluctuations become predominately ferromagnetic. Our inelastic neutron scattering measurements provide concrete evidence of the coexistence of competing interactions in Sr 3 Ru 2 O 7 and of the low-energy scale of the fluctuations.