Response of La0.8Sr0.2CoO3- δ to perturbations on the CoO3 sublattice

Emission and transmission Mossbauer studies of La 0.8 Sr 0.2 CoO 3-δ perovskites doped with ∼0.02 stoichiometric units of oxygen vacancy or 2.5% iron corroborate the occurrence of electronic phase separation in these systems. The effect of the small perturbation of the CoO 3 sublattice with either iron ions or oxygen vacancies on the bulk magnetization as well as on the Mossbauer spectra is in good agreement with the double exchange based cluster model. The magnetoresistance does not show any peak near the Curie temperature, but reaches -84% in a field of 7.5 T at T=8 K. Below T C ≈ 180 K the Mossbauer spectra distinctly include the contribution from paramagnetic and ferromagnetic regions, providing direct evidence for phase separation. No contribution to the spectra from Fe 4+ ions can be observed, which is an unambiguous evidence that at low concentration iron (either directly doped or formed from 57 Co by nuclear decay) is accommodated in the cobaltate lattice as Fe 3+ ion. Copyright EDP Sciences/Societa Italiana di Fisica/Springer-Verlag 2007