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Zigzag magnetic order and possible Kitaev interactions in the spin-1 honeycomb lattice KNiAsO4

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Physical Review Research
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Despite the exciting implications of the Kitaev spin Hamiltonian, finding and confirming the quantum spin-liquid state have proven incredibly difficult. Recently, the applicability of the model has been expanded through the development of a microscopic description of a spin-1 Kitaev interaction. Here we explore a candidate spin-1 honeycomb system, KNiAsO4, which meets many of the proposed criteria to generate such an interaction. Bulk measurements reveal an antiferromagnetic transition at ∼19 K which is generally robust to applied magnetic fields. Neutron diffraction measurements show magnetic order with a k=(32,0,0) ordering vector which results in the well-known “zigzag” magnetic structure thought to be adjacent to the spin-liquid ground state. Field-dependent diffraction shows that while the structure is robust, the field can tune the direction of the ordered moment. Inelastic neutron scattering experiments show a well-defined gapped spin-wave spectrum with no evidence of the continuum expected for fractionalized excitations. Modeling of the spin waves shows that the extended Kitaev spin Hamiltonian is are generally necessary to model the spectra and reproduce the observed magnetic order. First-principles calculations suggest that the substitution of Pd on the Ni sublattice may strengthen the Kitaev interactions while simultaneously weakening the exchange interactions thus pushing KNiAsO4 closer to the spin-liquid ground state.