SPIN DEPENDENCE OF CORRELATIONS IN 2-DIMENSIONAL SQUARE-LATTICE QUANTUM HEISENBERG ANTIFERROMAGNETS

We present a series expansion study of spin-S square-lattice Heisenberg antiferromagnets. The numerical data are in excellent agreement with recent neutron scattering measurements. Our key result is that the correlation length xi for S > 1/2 strongly deviates from the exact T --> 0 (renormalized classical) scaling prediction for all experimentally and numerically accessible temperatures. We note basic trends with S of the experimental and series expansion correlation length data and propose a sequence of crossovers from renormalized classical to classical to Curie-Weiss regimes to explain them.