Anisotropic interactions opposing magnetocrystalline anisotropy in Sr$_3$NiIrO$_6$

TL;DR

This study investigates the electronic and magnetic excitations of Sr$_3$NiIrO$_6$, revealing how anisotropic interactions and spin-orbit coupling influence its magnetic properties and induce easy-axis magnetism.

Contribution

It provides a detailed analysis of the electronic structure and magnetic interactions in Sr$_3$NiIrO$_6$, highlighting the role of anisotropic interactions opposing magnetocrystalline anisotropy.

Findings

Quantified Ir spin-orbital entanglement.

Observed dispersionless magnetic excitation at 90 meV.

Identified the balance between anisotropic interactions and Ni$^{2+}$ anisotropy leading to easy-axis magnetism.

Abstract

We report our investigation of the electronic and magnetic excitations of Sr$_3$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 IrO$_6$ octahedron, confronted to {\it ab initio} quantum chemistry calculations. The Ir spin-orbital entanglement is quantified and its implication on the magnetic properties, in particular in inducing highly anisotropic magnetic interactions, is highlighted. These are included in the spin-wave model proposed to account for the dispersionless magnetic excitation that we observe at 90 meV. By counterbalancing the strong 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.