Low energy magnetic excitations in Spin-1 honeycomb antiferromagnet Na₃Ni₂BiO₆ using Far-Infrared Magnetospectroscopy.

The spin-½ Kitaev model on a honeycomb lattice is an exactly solvable model for realizing Quantum Spin Liquids (QSLs). The model has been extensively studied in effective spin-½ compounds such as 5d⁷ Iridates and 4d⁷ a-RuCl₃, with recent attention on Co-based systems (3d⁷). We extend this investigation to the 3d⁸ Nickel-based compound Na₃Ni₂BiO₆, a spin-1 antiferromagnet with a honeycomb lattice structure that exhibits Kitaev physics.^[1]

We map the low-energy magnetic excitations of the compound utilizing Far-Infrared Magnetospectroscopy (FIRMS), with energy signatures visible down to 10 cm^-1, in both Faraday and Voigt configurations in magnetic fields up to 17.5T. In the Voigt configuration, we observe a spin-flop transition, marked by a sharp change in optical weight distribution and a kink in a magnon mode. In the Faraday configuration, we observe a magnon mode along with a gradual optical weight transfer when the material gets into fully spin polarized state. We also compare our experimental results with linear spin wave calculations. Our FIRMS measurements show agreement with the B-T phase diagram present in the literature.^[1]

[1] Shangguan, Y., Bao, S., Dong, ZY. et al. Nat. Phys. 19, 1883 (2023).