Comparison of nuclear spin relaxation rates at Y and O sites in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathit{y}}$

We report a detailed comparison of the ${}_{}{}^{89}{}_{}{}^{}\mathrm{Y}$ and the planar ${}_{}{}^{17}{}_{}{}^{}\mathrm{O}$ NMR shifts K and spin-lattice relaxation rates 1/${\mathit{T}}_1$ in oriented ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathit{y}}$ powder with y≃0 and y=0.37. For y=0.37, the ratio R of the O relaxation rate to the Y relaxation rate increases with decreasing temperature above ${\mathit{T}}_{\mathit{c}}$ and ${\mathit{T}}_1$TK at Y sites is not constant, which suggests that the antiferromagnetic spin correlations between adjacent ${\mathrm{CuO}}_2$ layers grow with decreasing temperature. The magnitude of R in both y=0.37 and y≃0 is smaller than evaluated from an ionic model of the hyperfine Hamiltonian.