Abstract
Structural, magnetic and Co K-edge X-ray absorption near-edge spectra (XANES) studies for the stoichiometric La1-xEuxCoO3 system (0 £ x £ 1) are reported. Because the reported RCoO3 magnetic data are confused by magnetic rare earth R3+ signal, in order to identify the spin-state transition, La1-xEuxCoO3 (0 £ x £ 1) system is chosen as the best candidate with nonmagnetic Eu3+ ground state (total angular momentum J = 0).The spin-state transition temperature Ts from low-spin (LS) state to intermediate-spin (IS) state increases from ~105 K for x = 0 (LaCoO3), to ~140 K for x = 0.25, ~200 K for x = 0.5 and extrapolated to ~290 K for x = 1 (EuCoO3).The small pre-edge feature observed in room temperature XANES 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 LaCoO3 in IS state, pre-edge can be fitted using three peaks with energy separation DE(P2 - P1) = 2.0 eV and DE(P3 - P2) = 1.5 eV. Since the thermally excited IS state is a mixture of d6 (t2g5eg1) and d7 L (t2g6eg1 or t2g5eg2), with almost filled t2g majority spin states, the three peaks P1, P2, P3 are probably corresponding to unfilled t2g minority, eg majority and eg minority states, respectively.