Role of alkaline metal in the rare-earth triangular antiferromagnet KYbO${}_2$

We report crystal structure and magnetic behavior of the triangular antiferromagnet KYbO${}_2$, the A-site substituted version of the quantum spin liquid candidate NaYbO${}_2$. The replacement of Na by K introduces an anisotropic tensile strain with 1.6% in-plane and 12.1% out-of-plane lattice expansion. Compared to NaYbO${}_2$, both Curie-Weiss temperature and saturation field are reduced by about 20% as the result of the increased Yb–O–Yb angles, whereas the $g$-tensor of Yb${}^{3+}$ becomes isotropic with $g=3.08(3)$. Field-dependent magnetization shows the plateau at 1/2 of the saturated value and suggests the formation of the up-up-up-down field-induced order in the triangular AYbO${}_2$ oxides (A = alkali metal), in contrast to the isostructural selenides that exhibit the 1/3 plateau and the up-up-down field-induced order.