Evolution of magnetic oxygen states in Sr-doped LaCoO${}_3$

Abstract

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.

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