The electronic and magnetic structure of La
1-xSr
xCoO
3 (0.0≤
x≤0.6) has been studied by X-ray magnetic circular dichroism (XMCD) at the Co
K absorption edge. A negative XMCD peak was clearly observed for pure LaCoO
3 at
E=7.719 keV within the threshold region, suggesting the existence of the intermediate-spin state of Co
3+. A positive XMCD peak at
E=7.723 keV was assigned to Co
4+, having the double-exchange interaction between Co
3+ and Co
4+. In order to verify the origin of XMCD, the electronic structure of ground and is core-hole states was calculated by a DV-Xα Hartree-Fock-Slater method, using several cluster models up to the fifth neighbor shell. The first-principles calculations well reproduced the experimental XMCD spectra, where a hybridization of Co 3
d, 4
p and O 2
p orbits stabilizes a magnetic state of La
1-xSr
xCoO
3.
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