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Title: Are Kitaev couplings significant in cobalt honeycomb magnets?
Plain: Theory in 2018 proposed that cobalt honeycomb compounds could realize the Kitaev model with weaker competing couplings than the ruthenium and iridium ones. Neutron studies of BaCo2(AsO4)2 instead fit simpler models without large Kitaev terms, and the magnetic pattern of Na2Co2TeO6 is itself debated.
Precise: For Na2Co2TeO6, Na3Co2SbO6 and BaCo2(AsO4)2 (Co2+ d7 pseudospin-1/2 on honeycomb lattices), determine $|K|/\operatorname{max}(|J1|, |J3|, |\Gamma|)$ from fits of the full magnon spectra, and for Na2Co2TeO6 whether the zero-field order is single-q zigzag in three domains or a triple-q state. An answer gives the exchange set with error bars per compound and the ordering-wavevector content.
Settled by: Inelastic neutron scattering on single-domain or detwinned crystals with field-angle-dependent spectroscopy that distinguishes bond-dependent from XXZ exchange.
Kind: well-posed
Answer type: value
References: (empty)
Literature status: contested
Status note: Halloran et al. (PNAS 2023) fit BaCo2(AsO4)2 with an XXZ $J1-J3$ model with small Kitaev terms, while Kruger et al. (PRL 2023) argued for triple-q order in Na2Co2TeO6 near a hidden-$\mathrm{SU}(2)$-symmetric point.
Posed since: 2018