A different look at the spin state of Co$^{3+}$ ions in CoO$_{5}$ pyramidal coordination

TL;DR

This study uses soft-x-ray absorption spectroscopy to determine that Co$^{3+}$ ions in CoO$_{5}$ pyramids are in a high spin state, challenging previous assumptions about similar layered cobalt compounds.

Contribution

It provides the first unambiguous experimental evidence of the high spin state of Co$^{3+}$ in CoO$_{5}$ pyramids, prompting a re-evaluation of spin state assignments in layered cobalt materials.

Findings

Co$^{3+}$ ions in CoO$_{5}$ pyramids are high spin

Questions previous spin state assignments in layered cobaltates

Calls for revised modeling of cobalt-based materials

Abstract

Using soft-x-ray absorption spectroscopy at the Co-$L_{2,3}$ and O-$K$ edges, we demonstrate that the Co$^{3+}$ ions with the CoO$_{5}$ pyramidal coordination in the layered Sr$_2$CoO$_3$Cl compound are unambiguously in the high spin state. Our result questions the reliability of the spin state assignments made so far for the recently synthesized layered cobalt perovskites, and calls for a re-examination of the modeling for the complex and fascinating properties of these new materials.