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

Abstract

Susceptibility, ESR, and magnetization measurements have been performed on single crystals of an S = 1 bond alternating chain compound: [Ni(333-tet) (mu-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 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 with a positive uniaxial single-ion anisotropy are induced at the edges of the chains without forming the singlet dimer.

Dynamical structure factors ofS=1bond-alternating Heisenberg chains

“…When −∞ < α < 0 in the S = 1 system, on the other hand, the trivial dimer phase around α ∼ 0 is shown to be smoothly connected to the S = 2 Haldane phase which appears in the limit α → −∞ [20]. Experimentally, using some nickel chain compounds which are regarded as the S = 1 bond-alternating Heisenberg system, magnetic susceptibility, magnetization, and ESR measurements were performed [23,25,26,27,28]. From the comparison between the experimental and numerical results, the strength of the bond-alternation α was evaluated and it was concluded that some compounds are in the singlet-dimer phase [25,26,28] and the other compound is close to the gapless point [23,27].…”

Tomonaga-Luttinger Liquid in a Quasi-One-DimensionalS=1Antiferromagnet Observed by Specific Heat Measurements

“…NTENP has an energy gap between the singlet ground state and the first excited triplet [12], and exhibits an LRO above H c [13,14]. Unlike in NDMAP, the principal axis of the Ni 2 ions in NTENP is nearly parallel to the chain direction.…”

“…The inversion centers are situated in the nitrito groups rather than the Ni 2 ions, so that no staggered components of the magnetic moments are expected to be retained. The critical fields H c parallel and perpendicular to the chain direction are 9.3 and 12.4 T, respectively [12].…”

“…[12] for details. NTENP belongs to a triclinic system (space group P 1), and the Ni 2 ions are bridged along the a axis by nitrito groups having two bond lengths which alternate.…”

“…From the analysis of the magnetic susceptibility data using numerical results with E 0, the following parameter values are known: J=k B 54:2 K, 0:45, D=J 0:25, and g k 2:14 for the component ofg in the chain direction [12]. The ground state of NTENP is expected to be a singlet-dimer phase rather than a Haldane phase on the basis of the bondalternating ratio.…”