Evidence for the singlet-dimer ground state in an S=1 antiferromagnetic bond alternating chain

Susceptibility. ESR: and magnetization measurements have been performed on single crystals of an S = 1 bond alternating chain compound: [Ni(333-tet)(m u -NO2)](ClO4) (333-tet = N, N'-bis(3-aminopropyl)propane-1,3-diamine) and the compound doped with a small amount of Zn. We observed an anomalous angu lar dependence in the Zn-doped sample. These results are well explained by the model based on the valence-bond solid picture for the singlet-dimer pha se. The picture implies that the fi ee spins of S = I with a positive uniax ial single-ion anisotropy are induced at the edges of the chains without fo rming the singlet dimer.