Spin-State Polarons in Lightly-Hole-Doped LaCoO₃

Inelastic neutron scattering (INS), electron spin resonance (ESR), and nuclear magnetic resonance (NMR) measurements were employed to establish the origin of the strong magnetic signal in lightly-hole-doped La_1-xSr_xCoO₃, x∼0.002. Both INS and ESR low temperature spectra show intense excitations with large effective g factors ∼10–18. NMR data indicate the creation of extended magnetic clusters. From the Q dependence of the INS magnetic intensity, we conclude that the observed anomalies are caused by the formation of octahedrally shaped spin-state polarons comprising seven Co ions. The present INS, ESR, and NMR data give evidence for two regimes in the lightly-hole-doped samples: (i) T<35  K dominated by spin polarons; (ii) T>35  K dominated by thermally activated magnetic Co³⁺ ions.