Low energy excitations in CoO studied by temperature dependent x-ray absorption spectroscopy

TL;DR

This study investigates the temperature-dependent electronic structure of CoO using x-ray absorption spectroscopy, revealing how thermal population of excited states and spin-orbit coupling influence magnetic properties.

Contribution

It provides detailed ligand-field calculations and experimental data showing the role of spin-orbit coupling and magnetic interactions in CoO's temperature-dependent spectra.

Findings

Spectra changes align with ligand-field calculations

Thermal population of excited states affects magnetic susceptibility

Spin-orbit coupling induces non-trivial temperature dependence

Abstract

We have measured the intricate temperature dependence of the Co L2,3 x-ray absorption spectra (2p-3d excitations) of CoO. To allow for accurate total electron yield measurements, the material has been grown in thin film form on a metallic substrate in order to avoid charging problems usually encountered during electron spectroscopic studies on bulk CoO samples. The changes in spectra due to temperature are in good agreement with detailed ligand-field calculations indicating that these changes are mostly due to thermal population of closely lying excited states, originating from degenerate t2g levels lifted by the spin-orbit coupling. Magnetic coupling in the ordered phase, modeled as a mean-field exchange field, mixes in excited states inducing a tetragonal charge density. The spin-orbit coupling induced splitting of the low energy states results in a non-trivial temperature dependence for the magnetic susceptibility.