Temperature-dependent bilayer ferromagnetism in Sr3 Ru2 O7

The ruthenium-based perovskites exhibit a wide variety of interesting collective phenomena related to magnetism originating from the Ru 4d electrons. Much remains unknown concerning the nature of magnetic fluctuations and excitations in these systems. We present results of detailed inelastic neutron scattering measurements of Sr3 Ru2 O7 as a function of temperature, probing the ferromagnetic fluctuations of the bilayer structure. A magnetic response is clearly visible for a range of temperatures, T=3.8 K up to T=100 K, and for energy transfers between ω=2 and 14 meV. These measurements indicate that the ferromagnetic fluctuations manifest in the bilayer structure factor persist to surprisingly large temperatures. This behavior may be related to the proximity of the system in zero magnetic field to the metamagnetic/ferromagnetic transition.