Effect of carrier doping on the formation and collapse of magnetic polarons in lightly hole-doped La_{1-x}Sr_xCoO_3

We investigate the doping dependence of the nanoscale electronic and magnetic inhomogeneities in the hole-doping range 0.002<x<0.1 of cobalt based perovskites, La{1-x}Sr_xCoO_3. Using single crystal inelastic neutron scattering and magnetization measurements we show that the lightly doped system exhibits magneto-electronic phase separation in form of spin-state polarons. Higher hole doping leads to a decay of spin-state polarons in favor of larger-scale magnetic clusters, due to competing ferromagnetic correlations of Co^{3+} ions which are formed by neighboring polarons. The present data give evidence for two regimes of magneto-electronic phase separation in this system: (i) x<0.05, dominated by ferromagnetic intrapolaron interactions, and (ii) x>0.05, dominated by Co^{3+}-Co^{3+} intracluster interactions. Our conclusions are in good agreement with a recently proposed model of the phase separation in cobalt perovskites [He et al., Europhys. Lett. 87, 27006 (2009)].