  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)].
