Ground state in Sr 3 Ru 2 O 7 : 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 $(\ensuremath{\approx}3 \ensuremath{\mu}\ensuremath{\Omega}\mathrm{cm}$ for in-plane currents) and a nearly ferromagnetic metal with the largest Wilson ratio ${R}_{\mathrm{W}}g~10$ among paramagnets so far. This contrasts with the ferromagnetic order at ${T}_{\mathrm{c}}=104 \mathrm{K}$ 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.