1H-NMR of S=1 antiferromagnets with bond alternation

The nuclear spin-lattice relaxation times T-1 of H-1 in three model substances of the S = 1 Heisenberg antiferromagnetic chains with bond alternation were measured at temperatures between 1.7 and 180 K. At low temperatures, T-1(-1) of two compounds with a finite spin gap decreased exponentially with decreasing temperature reflecting the presence of the spin gap, whereas the field- and temperature dependencies of T-1(-1) of the gapless compound were completely different from gapped compounds. (C) 2003 Elsevier B.V. All rights reserved.