Ground state in Sr3Ru2O7:: Fermi liquid close to a ferromagnetic instability

We show that single-crystalline Sr3Ru2O7 grown by a floating-zone technique is an isotropic paramagnet and a quasi-two-dimensional metal, as spin-tripler superconducting Sr2RuO4 is. The ground state is a Fermi liquid with very low residual resistivity (approximate to 3 mu Omega cm for in-plane currents) and a nearly ferromagnetic metal with the largest Wilson ratio R(W)greater than or equal to 10 among paramagnets so far. This contrasts with the ferromagnetic order at T-c = 104 K reported on single crystals grown by a flux method [Cao et al., Phys. Rev. B 55, R672 (1997)]. However, we have found a dramatic changeover from paramagnetism to ferromagnetism under applied pressure. This suggests the existence of a substantial ferromagnetic instability in the Fermi-liquid state.