HYbO2: A Jeff = 12 anisotropic triangular lattice

Highly frustrated magnets exhibit unusually ordered and disordered quantum ground states. The two-dimensional (2D) antiferromagnetic triangular lattice is one of the simplest models to explore unconventional excitations. A family of compounds AYbX₂ (A = Na, K, and X = O, S, Se) hold the 2D isotropic triangular lattices and exhibit the ground state of quantum spin liquid with gapless excitations originating from the Spinon-Fermi surface. The compound HYbO₂ has a chemical formula similar to the AYbX₂ family, but the crystal structure has an anisotropic 2D triangular lattice. We successfully synthesized HYbO₂ polycrystalline samples using the hydrothermal synthesis method and confirmed the single phase using powder X-ray diffraction measurements. Magnetic susceptibility and specific heat measurements confirm that Yb${}^{3+}$ hosts the $J_{\mathrm{eff}}$ = $\frac{1}{2}$ state at low temperatures. The magnetic moments interact antiferromagnetically with ${\theta }_{\mathrm{CW}}$ = −3.8 K at low temperatures. The system exhibits magnetic long-range order at 1.18 K, possibly due to the non-negligible inter-layer interactions between the anisotropic triangular lattice layers. The electronic structure calculations further evidence anisotropy in the effective spin space due to the involvement of strong spin–orbit coupling. Overall, the system HYbO₂ is anisotropic in both spatial and spin space.