Cu and O NMR studies of the magnetic properties of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{6.63}$ (${\mathit{T}}_{\mathit{c}}$=62 K)

The microscopic magnetic properties of the ${\mathrm{CuO}}_2$ planes in ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{6.63}$ (${\mathit{T}}_{\mathit{c}}$=62 K) have been investigated in Cu and O NMR experiments. Unlike the fully oxygenated Y-Ba-Cu-${\mathrm{O}}_7$ (${\mathit{T}}_{\mathit{c}}$≃90 K), the various components of the Cu and O Knight-shift tensors show strong but identical temperature dependences in the normal state. This supports the picture that there is only one spin component in the ${\mathrm{CuO}}_2$ planes. The spin susceptibility deduced from Knight-shift results shows significant reduction with decreasing temperature in the normal state. The temperature dependences of the nuclear-spin-relaxation rates (1/${\mathit{T}}_1$) are very different for the Cu and the O sites. 1/(${\mathit{T}}_1$T) at the O sites is nearly proportional to the spin susceptibility. 1/(${\mathit{T}}_1$T) at the Cu sites shows a broad peak around 150 K. We discuss these relaxation behaviors based on a model of the dynamical spin susceptibility proposed by Millis, Monien, and Pines.