  Triplet pairing in Sr2RuO4 was initially suggested based on the hypothesis of
strong ferromagnetic spin fluctuations. Using polarized inelastic neutron
scattering, we accurately determine the full spectrum of spin fluctuations in
Sr2RuO4. Besides the well-studied incommensurate magnetic fluctuations we do
find a sizeable quasiferromagnetic signal, quantitatively consistent with all
macroscopic and microscopic probes. We use this result to address the
possibility of magnetically-driven triplet superconductivity in Sr2RuO4. We
conclude that, even though the quasiferromagnetic signal is stronger and
sharper than previously anticipated, spin fluctuations alone are not enough to
generate a triplet state strengthening the need for additional interactions or
an alternative pairing scenario.
