Determining the Magnetic Structure of the Field-Induced Sloping 1/3 Magnetization Plateau in a Spin-1 Kitaev Candidate Material

A group of 2D layered honeycomb magnets, A3Ni2XO6 (A = Li, Na; X = Sb, Bi), has attracted much attention due to the potentially realizations of higher-spin Kitaev interactions. A 1/3 magnetization plateau phase, considered as evidence for the Kitaev interaction in Na3Ni2BiO6 (NNBO), has been reported more recently. This finding renders A3Ni2XO6 a highly intriguing system with the potential to realize the S = 1 Kitaev interaction. Meanwhile, several theoretical works on 2D magnets suggest the significance of biquadratic exchange interactions in 2D magnets with edge-shared octahedra. Usually, this term was considered to be small and so could be neglected. Motivated by this, we conducted calculations using the spin-1 J1-J3-D-B model (where D and B denote the single-ion anisotropy and biquadratic exchange) and obtained magnetization curves for NNBO. The theoretical curves is distinct from its experimental results. Surprisingly, its sister compound Na3Ni2SbO6 displays a behavior akin to the calculated magnetization curves.These findings hint at the potential influence of biquadratic exchange in NNSO. Its magnetic structure could provide information on the uncommon biquadratic exchange.