Anisotropic interactions opposing magnetocrystalline anisotropy inSr3NiIrO6

We report our investigation of the electronic and magnetic excitations of ${\mathrm{Sr}}₃{\mathrm{NiIrO}}₆$ by resonant inelastic x-ray scattering at the Ir ${L}₃$ edge. The intra-${t}_2g$ electronic transitions are analyzed using an atomic model, including spin-orbit coupling and trigonal distortion of the ${\mathrm{IrO}}₆$ octahedron, confronted with ab initio quantum chemistry calculations. The Ir spin-orbital entanglement is quantified and its implications for the magnetic properties, in particular in inducing highly anisotropic magnetic interactions, are highlighted. These are included in the spin-wave model proposed to account for the dispersionless magnetic excitation that we observe at $90\phantom{\rule{0.28em}{0ex}}\mathrm{m}\mathrm{e}\mathrm{V}$. By counterbalancing the strong ${\mathrm{Ni}}²⁺$ easy-plane anisotropy that manifests itself at high temperature, the anisotropy of the interactions finally leads to the remarkable easy-axis magnetism reported in this material at low temperature.