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

Neutron scattering experiments were carried out for the new Haldane compounds Ni(C₅H₁₄N₂)₂N ₃(ClO₄) (NDMAZ) and Ni(C₅H₁₄Nj) ₂N₃(PF₆) (NDMAP) in the magnetic field up to 10T 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 = (000.5). From these data, the intra-chain coupling constant = 4.3 meV and the anisotropic parameters D = 0.76meV and |E| = 0.038 meV were estimated. For NDMAP the gap was observed at about 0.48 and 0.64 meV at Q = (000.5). By applying the field of 5 T, the first excited state shifted below the resolution less than 0.1.3 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