Cu and O NMR studies of the magnetic properties of YBa2Cu3O6.63 (Tc=62 K).

Abstract

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-${\mathrm{O}}_{7}$ (${\mathit{T}}_{\mathit{c}}$\ensuremath{\simeq}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.