Role of alkaline metal in the rare-earth triangular antiferromagnet KYbO₂

We report crystal structure and magnetic behavior of the triangular antiferromagnet KYbO₂, the A-site substituted version of the quantum spin liquid candidate NaYbO₂. 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 NaYbO₂, 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 Yb³⁺ 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 KYbO₂ in contrast to the more common 1/3 plateau with the up-up-down order that has been reported in the isostructural Yb³⁺ selenides.