Neutron scattering study of linear-chain Haldane compounds NDMAZ and NDMAP

Abstract

Neutron scattering experiments were carried out for the new Haldane compounds Ni(C 5H 14N 2) 2N 3(ClO 4) (NDMAZ) and Ni(C 5H 14N 2) 2N 3(PF 6) (NDMAP) in the magnetic field up to 10 T in order to investigate the field-induced long-range ordering and the spin excitation. For NDMAZ, the triplet excited state (1.61, 1.76, and 3.2 meV) and field dependence of these levels were observed at Q=(0 0 0.5). From these data, the intra-chain coupling constant≈4.3 meV and the anisotropic parameters D≈0.76 meV and | E|≈0.038 meV were estimated. For NDMAP the gap was observed at about 0.48 and 0.64 meV at Q=(0 0 0.5). By applying the field of 5 T, the first excited state shifted below the resolution less than 0.13 meV. Above the critical field H C, the intensities of singlet–triplet excitation becomes very weak. This work is the first neutron scattering study on a Haldane system above the critical fields.