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Magnetic properties of the Haldane-gap material NENB

Research paper by E. Cizmar, M. Ozerov, O. Ignatchik, T. P. Papageorgiou, J. Wosnitza, S. A. Zvyagin, J. Krzystek, Z. Zhou, C. P. Landee, B. R. Landry, M. M. Turnbull, J. L. Wikaira

Indexed on: 12 Sep '07Published on: 12 Sep '07Published in: Physics - Other



Abstract

Results of magnetization and high-field ESR studies of the new spin-1 Haldane-chain material [Ni(C2H8N2)2NO2](BF4) (NENB) are reported. A definite signature of the Haldane state in NENB was obtained. From the analysis of the frequency-field dependence of magnetic excitations in NENB, the spin-Hamiltonian parameters were calculated, yielding Delta = 17.4 K, g_parallel = 2.14, D = 7.5 K, and |E| = 0.7 K for the Haldane gap, g factor and the crystal-field anisotropy constants, respectively. The presence of fractional S = 1/2 chain-end states, revealed by ESR and magnetization measurements, is found to be responsible for spin-glass freezing effects. In addition, extra states in the excitation spectrum of NENB have been observed in the vicinity of the Haldane gap, which origin is discussed.