Comparison of nuclear spin relaxation rates at Y and O sites in YBa2Cu3O7-y

We report a detailed comparison of the Y89 and the planar O17 NMR shifts K and spin-lattice relaxation rates 1/T1 in oriented YBa2Cu3O7-y powder with y0 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 Tc and T1TK at Y sites is not constant, which suggests that the antiferromagnetic spin correlations between adjacent CuO2 layers grow with decreasing temperature. The magnitude of R in both y=0.37 and y0 is smaller than evaluated from an ionic model of the hyperfine Hamiltonian. © 1993 The American Physical Society.