The correlation length of the Heisenberg antiferromagnet with arbitrary spin S

Experiments and numerical data on the correlation length xi(T) for large S disagree strongly with the theoretical prediction based on the effective fi eld theory prescription of the magnon physics. The reason is that for large S, at any accessible xi(T), the cut-off effects from the non-magnon scales become large and can not be treated by an effective field theory. We study these effects in a spin-wave expansion. The corrected prediction on xi(T) connects the renormalized classical and the classical scaling regions smoot hly and comes close to the data.