Motivated by the recently synthesized insulating nickelate Ni2Mo3O8, which has been reported to have an unusual non-collinear magnetic order of Ni2+S=1 moments with a nontrivial angle between adjacent spins, we construct an effective spin-1 model on the honeycomb lattice, with the exchange parameters determined with the help of first principles electronic structure calculations. The resulting bilinear-biquadratic model, supplemented with the realistic crystal-field induced anisotropy, favors the collinear N\'eel state. We find that the crucial key to explaining the observed noncollinear spin structure is the inclusion of the Dzyaloshinskii--Moriya (DM) interaction between the neighboring spins. By performing the variational mean-field and linear spin-wave theory (LSWT) calculations, we determine that a realistic value of the DM interaction D≈2.78 meV is sufficient to quantitatively explain the observed angle between the neighboring spins. We furthermore compute the spectrum of magnetic excitations within the LSWT and random-phase approximation (RPA) which should be compared to future inelastic neutron measurements.
@article{arxiv.1906.02215,
title = {Noncollinear Antiferromagnetic Order and Effect of Spin-Orbit Coupling in Spin-1 Honeycomb Lattice},
author = {Shuyi Li and Manh Duc Le and Vaideesh Loganathan and Andriy H. Nevidomskyy},
journal= {arXiv preprint arXiv:1906.02215},
year = {2021}
}