Field-induced magnetic ordering and single-ion anisotropy in the quasi-one-dimensional Haldane chain compound SrNi_2V_2O_8: A single-crystal investigation

摘要

Field-induced magnetic ordering in the Haldane chain compound SrNi_2 V_2O_8 and the effect of anisotropy have been investigated using single crystals. Static susceptibility, inelastic neutron scattering, high-field magnetization, and low-temperature heat-capacity studies confirm a nonmagnetic spin-singlet ground state and a gap between the singlet ground state and triplet excited states. The intrachain exchange interaction is estimated to be J ～ 8.9 ± 0.1 meV. Splitting of the dispersions into two modes with minimum energies 1.57 and 2.58 meV confirms the existence of single-ion anisotropy D(S~z)~2. The value of D is estimated to be -0.51 ±0.01 meV and the easy axis is found to be along the crystallographic c axis. Field-induced magnetic ordering has been found with two critical fields (_(μ0)H~(⊥c)_c = 12.0 ± 0.2 T and _(μ0)H~(⊥c)_c = 20.8 ± 0.5 T at 4.2 K). Field-induced three-dimensional magnetic ordering above the critical fields is evident from the heat-capacity, susceptibility, and high-field magnetization study. The phase diagram in the H-T plane has been obtained from the high-field magnetization. The observed results are discussed in the light of theoretical predictions as well as earlier experimental reports on Haldane chain compounds.