Electronic structure and temperature-induced paramagnetism in ${\mathrm{LaCoO}}_3$

We have studied the electronic structure of ${\mathrm{LaCoO}}_3$ by photoemission spectroscopy and x-ray absorption spectroscopy (XAS). The Co 2p core-level and valence-band photoemission spectra display satellite structures indicating a strong electron-correlation effect. The Co 2p core-level photoemission, the valence-band photoemission, and the O 1s XAS spectra have been analyzed using a configuration-interaction cluster model for the initial-state configurations of the low-spin (LS: ${}_{}{}^1{}_{}{}^{}\mathrm{A}_1^{}{}_{}{}^{}$), intermediate-spin (IS: ${}_{}{}^3{}_{}{}^{}\mathrm{T}_1^{}{}_{}{}^{}$) and high-spin (HS: ${}_{}{}^5{}_{}{}^{}\mathrm{T}_2^{}{}_{}{}^{}$) states and their mixtures. The ground state of ${\mathrm{LaCoO}}_3$ in the LS state is found to have heavily mixed ${\mathrm{d}}^6$ and ${\mathrm{d}}^7$L-̱ character, reflecting the strong covalency. The magnetic susceptibility has been analyzed for various level orderings of the LS, IS, and HS states. From the analyses of the photoemission spectra and the magnetic susceptibility data, the temperature-induced paramagnetism in ${\mathrm{LaCoO}}_3$ above ∼90 K is most likely due to a gradual LS-to-IS transition.