Spin dynamics and magnetic resonance in two-dimensional Heisenberg antiferromagnets

Abstract

High-temperature expansions are calculated and extrapolated to yield estimates of low-order time derivatives of one- and two-point dynamic correlations in the S=1/2 Heisenberg antiferromagnet. Taking this model to describe the spin correlations in Y-Ba-Cu-O, spin-lattice relaxation rates (${\mathit{T}}_1^{\mathrm{-}1}$) for Y and planar Cu and O nuclei are estimated by means of Moriya’s Gaussian approximation. For Y and O, (${\mathit{T}}_1$T${)}^{\mathrm{-}1}$ exhibits a broad plateau in the range 0.7<T/J<1.5, and in that interval their Korringa ratios are also nearly constant, being 0.25 and 1.1 times the free-electron value, respectively.