Ground State Properties of Antiferromagnetic Chains with Unrestricted   Spin: Integer Spin Chains as Realisations of the O(3) Non-Linear Sigma Model
  A continuum limit treatment of planar spin chains with arbitrary S is presented. The difference between integer and half-integer spins is emphasised. While isotropic half-integer spin chains are gapless,and have power-law decay of correlations at T = 0 with exponent eta = 1, integer spin systems have a singlet ground state with a gap for S=1 excitations and exponential decay of correlations. The easy-plane to easy-axis transition is described.   Note: this is a verbatim transcription of ILL preprint SP-81/95, which is cited in a number of places, but was rejected for publication in 1981, and remained unpublished in this original form, which gives somewhat different arguments for the central result as compared to the later paper finally published in Phys. Lett. 93A, 464 (1983); many thanks to Jeno Solyom for preserving this historical document. 
F.D.M. Haldane
cond-mat.other cond-mat.str-el