Investigation of the spin state of Co in $\mathrm{La}\mathrm{Co}{\mathrm{O}}_3$ at room temperature: Ab initio calculations and high-resolution photoemission spectroscopy of single crystals

We investigate the spin state of $\mathrm{La}\mathrm{Co}{\mathrm{O}}_3$ using state-of-the-art photoemission spectroscopy and ab initio band structure calculations. The $\mathrm{GGA}+U$ calculations provide a good description of the ground state for the experimentally estimated value of electron correlation strength $U$. In addition to the correlation effect, spin-orbit interaction is observed to play a significant role in the case of intermediate spin and high spin configurations. The comparison of the calculated $\mathrm{Co}3d$ and $\mathrm{O}2p$ partial density of states with the experimental valence band spectra indicates that at room temperature, Co has dominant intermediate spin state configuration and that the contribution from high spin configuration may not be significant at this temperature. The line shape of the $\mathrm{La}5p$ and $\mathrm{O}2s$ core level spectra could be reproduced well within these ab initio calculations.

Figure 1

(Color online) $\mathrm{O}2p$ (thin solid line) and $\mathrm{Co}3d$ partial densities of states having $t_{2g}$ (dashed line) and $e_g$ (thick solid line) symmetries from (a) LDA and (b) $\mathrm{LDA}+U$ calculations.

Figure 2

(Color online) $\mathrm{Co}3d$ and $\mathrm{O}2p$ partial densities of states calculated using (a) $\mathrm{LDA}+U$ $(U=3.5\mathrm{eV})$, (b) $\mathrm{LDA}+U$ $(U=4\mathrm{eV})$, and (c) $\mathrm{GGA}+U$ $(U=3.5\mathrm{eV})$ methods.

Figure 3

(Color online) Calculated $\mathrm{Co}3d$ and $\mathrm{O}2p$ partial densities of states corresponding to low spin (LS), intermediate spin (IS), and high spin (HS) configurations using the $\mathrm{GGA}+U$ method.

Figure 4

(Color online) $\mathrm{Co}3d$ and $\mathrm{O}2p$ partial densities of states corresponding to low spin (LS), intermediate spin (IS), and high spin (HS) configurations calculated including spin-orbit interactions. All these calculations are performed using the $\mathrm{GGA}+U$ method.

Figure 5

(Color online) Spin-polarized partial density of states corresponding to $\mathrm{Co}{t}_{2g}$ and $e_g$ bands calculated (a) without spin-orbit coupling and (b) with spin-orbit coupling. The inset shows $d_{x^2-y^2}$ and $d_{z^2}$ contributions in the $e_{g\uparrow }$ band.

Figure 6

(Color online) Experimental valence band spectra collected at room temperature using $\mathrm{Al}K\alpha$ and $\mathrm{He}\mathrm{I}$ radiations. The lines denote the calculated $\mathrm{Co}3d$ and $\mathrm{O}2p$ partial densities of states corresponding to the intermediate spin configuration of Co including spin-orbit coupling.

Figure 7

(Color online) (a) Background subtracted $\mathrm{La}5p$ and $\mathrm{O}2s$ core level spectra (symbols) collected at room temperature. The solid line represents the spectrum simulated using PDOS corresponding to IS state configuration. $\mathrm{La}5p$ (solid line) and $\mathrm{O}2s$ (dashed line) PDOSs calculated using (b) LS, (c) IS, and (d) HS configurations of Co.