Co K-edge XANES and spin-state transition of RCoO₃ (R = La, Eu)

Co K-edge X-ray absorption near-edge spectra at 300 K and magnetic studies for the rhombohedral LaCoO₃ with low-spin state to intermediate-spin (IS) state transition T_s≃105 K and orthorhombic EuCoO ₃ (T_s≃295 K) are reported. The small pre-edge feature observed is from 1s-3d dipole transition, which is weakly allowed through the hybridization of Co 4p states with 3d states of neighboring Co atoms. For both samples in the IS state, pre-edge can be fitted using three peaks with energy separation P₂ - P₁ = 2.0 eV for R = La and Eu, and P₃ - P₂ = 1.5 eV for R = La and 1.3 eV for R = Eu. Since the thermally excited IS state is a mixed t_2g ⁵e_g¹ and d⁷L (t_2g ⁶e_g¹ or t_2g⁵e _g²), with almost filled t_2g↑ states. From reported band structure calculation, the three peaks P₁, P ₂, P₃ are probably corresponding to the unfilled t _2g↓, e_g↑ and e_g↓ states, respectively.