High- and low-spin transition of ${\mathrm{Ru}}^{4+}$ in the perovskite-related layered system ${\mathrm{Sr}}_{\mathit{n}+1\mathrm{}}$${\mathrm{Ru}}_{\mathit{n}}$${\mathrm{O}}_{3\mathit{n}+1\mathrm{}}$ (n=1, 2, and ∞) with the change in n

The electrical resistivity and magnetic susceptibility of the perovskite-related layered system ${\mathrm{Sr}}_{\mathit{n}+1\mathrm{}}$ ${\mathrm{Ru}}_{\mathit{n}}$ ${\mathrm{O}}_{3\mathit{n}+1\mathrm{}}$ (n=1, 2, and ∞) were measured. The magnetic-susceptibility measurements revealed that tetravalent ruthenium ions take the low-spin and high-spin states in the compounds with n=2 and ∞ and n=1, respectively. The elongation of the Ru-O distance along the c axis in ${\mathrm{Sr}}_2$ ${\mathrm{RuO}}_4$ is attributed to the cooperative Jahn-Teller effect of high-spin ${\mathrm{Ru}}^{4+}$ ions. Among the 4d and 5d transition-metal oxides with perovskite-related structure, the high-spin state is realized only in ${\mathrm{Sr}}_2$ ${\mathrm{RuO}}_4$.