1995 Volume 64 Issue 10 Pages 3651-3655
Magnetization measurement and inelastic neutron scattering have been performed on a single crystal of a new Haldane system Y2BaNiO5. Magnetic susceptibility shows a weak anisotropy and decreases as temperature decreases, reflecting the singlet ground state at low temperature. The energy gaps were found to be Δ///kB=118, K and Δ⊥ /kB=104, K, parallel and perpendicular to the chain, respectively. Using inelastic neutron scattering magnetic excitations along the chain (a*-) and perpendicular (c*-) directions up to 30, meV energy transfer are studied. Energy gap of about 10, meV (116, K) is observed along the one-dimensional, antiferromagnetic zone center, in good agreement with the magnetization measurement. The observed dispersion relation in the chain direction with the gap can be well described by the exact numerical results of S=1, Heisenberg antiferromagnetic chain yielding an intrachain exchange of J/kB=280± 10, K.
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