Analyzing the Local Electronic Structure of Co${}_3$O${}_4$ Using 2p3d Resonant Inelastic X-ray Scattering

We present the cobalt 2p3d resonant inelastic X-ray scattering (RIXS) spectra of Co${}_3$O${}_4$. Guided by multiplet simulation, the excited states at 0.5 and 1.3 eV can be identified as the ${}^4$T${}_2$ excited state of the tetrahedral Co${}^{2+}$ and the ${}^3$T${}_{2g}$ excited state of the octahedral Co${}^{3+}$, respectively. The ground states of Co${}^{2+}$ and Co${}^{3+}$ sites are determined to be high-spin ${}^4$A${}_2$(T${}_d$) and low-spin ${}^1$A${}_{1g}$(O${}_h$), respectively. It indicates that the high-spin Co${}^{2+}$ is the magnetically active site in Co${}_3$O${}_4$. Additionally, the ligand-to-metal charge transfer analysis shows strong orbital hybridization between the cobalt and oxygen ions at the Co${}^{3+}$ site, while the hybridization is weak at the Co${}^{2+}$ site.