We report ${}_{}{}^{89}{}_{}{}^{}\mathrm{Y}$ NMR shift (K) and spin-lattice relaxation (${\mathit{T}}_1$) data on oriented ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{6+\mathit{x}}$ powders, with x=1 and 0.64. The anisotropy of K is shown to be dominated by that of the spin susceptibility on the oxygen sites ${\mathrm{\chi }}_{\mathit{c}}^{\mathrm{}\left(\mathrm{O}\right)\mathrm{}}$/${\mathrm{\chi }}_{\mathit{a}\mathit{b}}^{\mathrm{}\left(\mathrm{O}\right)\mathrm{}}$=1.2±0.05, which agrees with that expected on the Cu sites, and with a single-spin fluid picture for the ${\mathrm{CuO}}_2$ band. The anisotropy of ${\mathit{T}}_1$ is compatible with a nearly isotropic spin lifetime in the q∼0 dynamic susceptibility. Deviations from ${\mathit{T}}_1$TK∼const are found at high T for both the underdoped (x=0.64) and the overdoped sample (x=1).

• Received 21 August 1992

DOI:https://doi.org/10.1103/PhysRevLett.70.1171