Counterrotating magnetic order in the honeycomb layers of ${\mathrm{NaNi}}_{2}{\mathrm{BiO}}_{6−δ}$

The exotic Kitaev spin liquid state emerges from a particular form of anisotropic magnetic exchange on the honeycomb lattice. Here, the authors use neutron scattering, electron spin resonance, and density functional theory to show that bond-anisotropic Kitaev exchange exists in between Ni$3+$ ions in the honeycomb layers of NaNi$2$BiO$5.66$. This magnetic exchange produces a complex counterrotating low-temperature magnetic order with 120° in-plane order in this compound. These results demonstrate that Kitaev physics can be found in 3$d$ transition ion materials.