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Heisenberg spin chains: Quantumclassical crossover and the Haldane conjecture J. Appl. Phys. 57, 3319 (1985); 10.1063/1.335134 Field dependent neutron scattering study of the quasi 2D Heisenberg antiferromagnet K2MnF4Our studies of the spin dynamics for two near-Heisenberg antiferromagnets (AFMs) revealed:In CsNiC1 3 (S = 1) at low T < TN we confirm the conclusions given earlier, but disagreement with the spin-wave calculations used is found for the eigenvectors. For T> 1'. .. , the most important result is the observation that ali (sa sa) (a = x,y,z) are identical, demanding another interpretation for the gap observed than the easy axis one. In CsVC1 3 (S =~) we could not observe any inconsistency in the microscopic parameters determined above and below TN' Although there is a striking coincidence with Haldane's conjecture [unexplained gap for S = 1 (CsNiCI 3 ), no such gap for S = ~ (CsVC1 3 )], it is not clear whether this can be considered a prooffor Haldane's conjecture.