The spin state transition in LaCoO$_{3}$; revising a revision

TL;DR

This study uses advanced spectroscopic techniques to clarify the spin state transition in LaCoO$_{3}$, revealing a mixed-spin system with significant orbital momentum, challenging previous models.

Contribution

It provides a revised understanding of the spin states in LaCoO$_{3}$, demonstrating the inadequacy of the low-/intermediate-spin model and highlighting the importance of orbital momentum.

Findings

LaCoO$_{3}$ exhibits a low-spin ground state and a triply-degenerate high-spin excited state.

The material is an inhomogeneous mixed-spin-state system at finite temperatures.

Large orbital momentum is observed in the paramagnetic state, contradicting previous models.

Abstract

Using soft x-ray absorption spectroscopy and magnetic circular dichroism at the Co-$L_{2,3}$ edge we reveal that the spin state transition in LaCoO$_{3}$ can be well described by a low-spin ground state and a triply-degenerate high-spin first excited state. From the temperature dependence of the spectral lineshapes we find that LaCoO$_{3}$ at finite temperatures is an inhomogeneous mixed-spin-state system. Crucial is that the magnetic circular dichroism signal in the paramagnetic state carries a large orbital momentum. This directly shows that the currently accepted low-/intermediate-spin picture is at variance. Parameters derived from these spectroscopies fully explain existing magnetic susceptibility, electron spin resonance and inelastic neutron data.