Synthesis, structural and magnetic characterizations of Li₄Cu_1-xNi_xTeO₆ ( x = 0, 0.1, 0.2, 0.5, and 1)

We investigated the effect of Ni doping in a recently proposed quantum spin liquid (QSL) candidate Li₄CuTeO₆. We performed a comprehensive study on the structural and magnetic properties. We find that the anti-site disorder between Li⁺ and Cu²⁺ persists until 50% Ni doping in which Ni and Cu occupy different crystallographic sites. As a result, while Cu sits in both triangular and honeycomb layers in Li₄CuTeO₆, Ni forms only honeycomb layer in Li₄NiTeO₆ and Li₄Cu_0.5Ni_0.5TeO₆. Our magnetic susceptibility measurements show that the Weiss temperature decreases from -145.68 K in Li₄CuTeO₆ to -6.15 K in Li₄NiTeO₆ as Ni doping increases, and find no hint of magnetic ordering or freezing down to 1.8 K. Our analysis implies the existence of abundant low energy excitations in these materials.