Evidence for the Singlet-Dimer Ground State in anS=1Antiferromagnetic Bond Alternating Chain

Susceptibility, ESR, and magnetization measurements have been performed on single crystals of an $S=1\mathrm{}$ bond alternating chain compound: $\left[\mathrm{Ni}\right(333-\mathrm{tet}\left)\right(\mu -{\mathrm{NO}}_2\left)\right]\left({\mathrm{ClO}}_4\right)$ $\left(333-\mathrm{tet}{=N,N}^{\prime }-\mathrm{bis}\right(3-\mathrm{aminopropyl})\mathrm{propane}-1,3-\mathrm{diamine})$ and the compound doped with a small amount of Zn. We observed an anomalous angular 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 phase. The picture implies that the free spins of $S=1\mathrm{}$ with a positive uniaxial single-ion anisotropy are induced at the edges of the chains without forming the singlet dimer.