Ground state inSr3Ru2O7:Fermi liquid close to a ferromagnetic instability

We show that single-crystalline ${\mathrm{Sr}}_3{\mathrm{Ru}}_2{\mathrm{O}}_7$ grown by a floating-zone technique is an isotropic paramagnet and a quasi-two-dimensional metal, as spin-triplet superconducting ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ is. The ground state is a Fermi liquid with very low residual resistivity $(\approx 3\hspace{0.5em}\mu \Omega \mathrm{cm}$ for in-plane currents) and a nearly ferromagnetic metal with the largest Wilson ratio $R_{\mathrm{W}}>~10$ among paramagnets so far. This contrasts with the ferromagnetic order at $T_{\mathrm{c}}=104\mathrm{}\hspace{0.5em}\mathrm{K}$ 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.