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Published online by Cambridge University Press: 01 February 2011
A substitution of La3+ by Sr2+ in LaCoO3 induces holes in the low-spin ground state of the Co ions, which behave like magnetic impurities with a very high spin value (13 μB per hole). In this work, using single-crystal neutron spectroscopy, we prove that the charges introduced by strontium doping do not remain localized at the cobalt sites. Instead, each hole not only creates Co4+ in low-spin state, but it also transforms the six nearest neighboring Co3+ ions to the intermediate-spin state thereby forming a magnetic seven-site (heptamer) polaron. Spin-state polarons behave like magnetic nanoparticles embedded in an insulating nonmagnetic matrix. Therefore, lightly doped La1-xSrxCoO3 is a natural analog to artificial structures composed of ferromagnetic particles in insulating matrices.