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Abstract

A phenomenological model of a system of antiferromagnetically correlated spins is shown to give a good quantitative description of NMR, nuclear-quadrupole-resonance, and Knight-shift measurements on yttrium, planar copper, and planar oxygen sites in ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$. The antiferromagnetic correlation length is estimated to be \ensuremath{\sim}2.5 lattice constants at T=100 K. The temperature dependence of the correlation length ceases at ${\mathit{T}}_{\mathit{x}}$\ensuremath{\simeq}100 K. The enhancement of the observed relaxation rates over what is expected for weakly interacting electrons is calculated and shown to be large. Extension of the calculation to other cuprate superconductors is discussed.