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

We present a series expansion study of spin-S square-lattice Heisenber g antiferromagnets. The numerical data are in excellent agreement with recent neutron scattering measurements. Our key result is that the co rrelation 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 o f the experimental and series expansion correlation length data and pr opose a sequence of crossovers from renormalized classical to classica l to Curie-Weiss regimes to explain them.