Observation of the Haldane gap in RbNiCl3

Quasi-1D XY antiferromagnet Sr2Ni(SeO3)2Cl2 at Sakai-Takahashi phase diagram

Uniform quasi-one-dimensional integer spin compounds are of interest as a potential realization of the Haldane conjecture of a gapped spin liquid. This phase, however, has to compete with magnetic anisotropy and long-range ordered phases, the implementation of which depends on the ratio of interchain J′ and intrachain J exchange interactions and both uniaxial D and rhombic E single-ion anisotropies. Strontium nickel selenite chloride, Sr₂Ni(SeO₃)₂Cl₂, is a spin-1 chain system which passes through a correlations regime at T_max ~ 12 K to long-range order at T_N = 6 K. Under external magnetic field it experiences the sequence of spin-flop at B_c1 = 9.0 T and spin-flip transitions B_c2 = 23.7 T prior to full saturation at B_sat = 31.0 T. Density functional theory provides values of the main exchange interactions and uniaxial anisotropy which corroborate the experimental findings. The values of J′/J = 0.083 and D/J = 0.357 place this compound into a hitherto unoccupied sector of the Sakai-Takahashi phase diagram.