Spin states of cobalt ions in the bulk and on the surface of LaCoO$_3$ probed by x-ray absorption, emission, and photoelectron spectra

We present X-ray photoelectron, Co $L_{2,3}$ and O $K \mathrm{X}$-ray absorption, as well as Co $K\beta_{1,3}\mathrm{X}$-ray emission spectroscopy results of studies of the spin states of trivalent cobalt ions in single-crystal cobaltite LaCoO$_3$. We show that at room temperature, in the bulk of a LaCoO$_3$ single crystal, Co$^{3+}$ ions are in the low-spin state, while high-spin Co$^{2+}$, high-spin Co$^{3+}$, low-spin Co$^{3+}$, and probably also intermediate-spin Co$^{3+}$ ions are located on the surface.