Evolution of magnetic oxygen states in Sr-doped LaCoO$_3$
  Magnetism in La$_{1-x}$Sr$_x$CoO$_3$ as a function of doping is investigated with X-ray absorption spectroscopy and X-ray magnetic circular dichroism at the O K edge, and corresponding first principles electronic structure calculations. For small x, the spectra are consistent with the formation of ferromagnetic clusters occurring within a nonmagnetic insulating matrix. Sr-induced, magnetic O-hole states form just above E$_F$ and grow with increasing Sr doping. Density functional calculations for x = 0 yield a nonmagnetic ground state with the observed rhombohedral distortion and indicates that doping introduces holes at the Fermi level in magnetic states with significant O 2p and Co t$_{2g}$ character for the undistorted pseudocubic structure. Supercell calculations show stronger magnetism on oxygen atoms having more Sr neighbors. 
S. Medling, Y. Lee, H. Zhang, J. F. Mitchell, J. W. Freeland, B. N.   Harmon, and F. Bridges
cond-mat.str-el