Magnetic Properties of the Spin-1 Two-Dimensional J1-J3 Heisenberg Model on a Triangular Lattice

P. Rubina, A. Shermana, M. Schreiberb aInstitute of Physics, University of Tartu, Riia 142, 51014 Tartu, Estonia bInstitut für Physik, Technische Universität, D-09107 Chemnitz, Germany

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Motivated by the recent experiment in NiGa2S4, the spin-1 Heisenberg model on a triangular lattice with the ferromagnetic nearest- and antiferromagnetic third-nearest-neighbor exchange interactions, J1 = -(1 - p)J and J3 = pJ, J > 0, is studied in the range of the parameter 0 ≤ p ≤ 1. Mori's projection operator technique is used as a method, which retains the rotation symmetry of spin components and does not anticipate any magnetic ordering. For zero temperature several phase transitions are observed. At p ≈ 0.2 the ground state is transformed from the ferromagnetic order into a disordered state, which in its turn is changed to an antiferromagnetic long-range ordered state with the incommensurate ordering vector Q' ≈ (1.16, 0) at p ≈0.31. With growing p the ordering vector moves along the line Q' - Qc to the commensurate point Qc = (2π/3, 0), which is reached at p = 1. The final state with the antiferromagnetic long-range order can be conceived as four interpenetrating sublattices with the 120° spin structure on each of them. Obtained results offer a satisfactory explanation for the experimental data in NiGa2S4.

DOI: 10.12693/APhysPolA.126.242 PACS numbers: 75.10.Jm, 67.25.bd