Monoclinic crystal structure ofα−RuCl3and the zigzag antiferromagnetic ground state

The layered honeycomb magnet $\ensuremath{\alpha}\ensuremath{-}{\mathrm{RuCl}}_{3}$ has been proposed as a candidate to realize a Kitaev spin model with strongly frustrated, bond-dependent, anisotropic interactions between spin-orbit entangled ${j}_{\mathrm{eff}}=\frac{1}{2}\phantom{\rule{4.pt}{0ex}}{\mathrm{Ru}}^{3+}$ magnetic moments. Here, we report a detailed study of the three-dimensional crystal structure using x-ray diffraction on untwinned crystals combined with structural relaxation cal