Anisotropic interactions opposing magnetocrystalline anisotropy in Sr3NiIrO6

We report our investigation of the electronic and magnetic excitations of Sr3NiIrO6 by resonant inelastic x-ray scattering at the Ir L3 edge. The intra-t2g electronic transitions are analyzed using an atomic model, including spin-orbit coupling and trigonal distortion of the IrO6 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 90meV. By counterbalancing the strong Ni2+ 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.