Spin-wave excitation in the antiferromagnetic bilayer ruthenate Ca ₃Ru₂O₇

We study the spin-wave excitation spectrum of the antiferromagnetic bilayer ruthenate Ca₃Ru₂O₇ through inelastic neutron scattering measurements. The material behaves as a quasi-two-dimensional ferromagnetic bilayer system with very weak interbilayer antiferromagnetic coupling, and its magnetic dispersion can be well described with a nearest-neighbor Heisenberg model. We find that the intrabilayer exchange interaction along the out-of-plane c-axis is much stronger than the in-plane intralayer interaction, in sharp contrast to the previously reported bilayer manganite system. And our study reveals a finite lifetime effect of the magnetic excitation, presumably attributable to the existence of a small number of itinerant charge carriers within the planes.