Effect of carrier doping on the formation and collapse of magnetic polarons in lightly hole-doped La1-xSrxCoO3

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, La1-xSrxCoO3. Using single-crystal inelastic neutron scattering and magnetization measurements we show that the lightly doped system exhibits magnetoelectronic phase separation in the form of spin-state polarons. Higher hole doping leads to a decay of spin-state polarons in favor of larger scalemagnetic clusters, due to competing ferromagnetic correlations of Co3+ ions which are formed by neighboring polarons. The present data give evidence for two regimes of magnetoelectronic phase separation in this system: (i) x less than or similar to 0.05, dominated by ferromagnetic intrapolaron interactions, and (ii) x greater than or similar to 0.05, dominated by Co3+ -Co3+ intracluster interactions. Our conclusions are in good agreement with a recently proposed model of the phase separation in cobalt perovskites [C. He et al., Europhys. Lett. 87, 27006 (2009)].