Magnetism of Kitaev spin-liquid candidate material RuBr$_3$

Abstract: The ruthenium halide $\alpha$-RuCl${3}$ is a promising candidate for a Kitaev spin liquid. However, the microscopic model describing $\alpha$-RuCl${3}$ is still debated partly because of a lack of analogue materials for $\alpha$-RuCl${3}$, which prevents tracking of electronic properties as functions of controlled interaction parameters. Here, we report a successful synthesis of RuBr${3}$. The material RuBr${3}$~possesses BiI$_3$-type structure (space group: $R\overline{3}$) where Ru$^{3+}$ form an ideal honeycomb lattice. Although RuBr${3}$ has a negative Weiss temperature, it undergoes a zigzag antiferromagnetic transition at $T_\mathrm{N}=34$ K, as does $\alpha$-RuCl$_{3}$. Our analyses indicate that the Kitaev and non-Kitaev interactions can be modified in ruthenium trihalides by changing the ligand sites, which provides a new platform for exploring Kitaev spin liquids.