ИСТИНА

An experimental realization of the Haldane conjecture of a gapped spin liquid is of great interested among condensed matter scientists. The conjecture is implemented in the chains of Heisenberg integer spins bounded by identical intrachain exchange interactions J and could be realized in uniform quasi-one-dimensional integer spin compounds [1]. The Haldane phase has to compete with magnetic anisotropy and long-range ordered phases, depending on the ratio of interchain J' and intrachain J exchange interactions and uniaxial D and rhombic E single-ion anisotropy. The critical ratios J'/J and D/J for Haldane phase, easy axis long ordered AFM and easy plane long ordered XY-AFM were first discovered by Sakai and Takahashi [2]. Many compounds, both organic and inorganic, have been studied to verify this idea, some of them have been identified as belonging to the Haldane sector of the Sakai-Takahashi phase diagram. In this work, the position on Sakai-Takahashi phase diagram was determined for the novel integer spin S = 1 chain compound, strontium nickel selenite chloride Sr2Ni(SeO3)2Cl2. The powder sample was obtained by gas transport method. XRD measurements showed that the crystal structure of the compound contains the NiO4Cl2-octahedra bridged by the SeO3-pyramids into uniform spin chains. These chains are well separated by strontium cations and cavities of selenium’s lone pair of electrons that could lead to 1D-dimensionality of magnetic subsystem. Physical properties were investigated in magnetization, heat capacity and thermal expansion measurements. Pulsed-magnetic-field magnetization measurements up to 45 T were provided by Dresden High Magnet Field Lab HLD EMFL. For magnetic structure calculations within the DFT it has been used the GGA+U approach with PBE potential within the VASP code. Thus it was determined that strontium nickel selenite chloride, Sr2Ni(SeO3)2Cl2, is a spin-1 chain system which passes through a correlations regime at Tmax ~ 12 K to long-range order at TN = 6 K. The values of J'/J = 0.083 and D/J = 0.357 place this compound into a hitherto unoccupied XY-AFM sector of the Sakai-Takahashi phase diagram. The authors acknowledge support by the Ministry of Education and Science of the Russian Federation within the framework of the governmental program of Megagrants P-220 and NUST “MISiS” Grant No. K2-2020-039. We also acknowledge the support of the HLD-HZDR member of the European Magnetic Field Laboratory (EMFL).