EXPERIMENTAL AND THEORETICAL STUDIES OF FINITE-SIZE EFFECTS IN AN S = 1/2 ANTIFERROMAGNETIC HEISENBERG CHAIN

Finite-size effects in a spin-$1/2$ one-dimensional (1D) Heisenberg antiferromagnet (HAF) are studied experimentally and theoretically. The calculated susceptibility is compared with that observed in the quasi-1D HAF ${\mathrm{SrCu}}_{1\ensuremath{-}x}{\mathrm{Mg}}_{x}{\mathrm{O}}_{2}$. Excellent agreement between theory and experiment is obtained without any adjustable parameters above about $0.02J$, where $J$ is the dominant exchange interaction constant.