Response of La0.8Sr0.2CoO3-δ to perturbations on the CoO3 sublattice
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Emission and transmission Mössbauer studies of La0.8Sr0.2CoO3-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 CoO3 sublattice with either iron ions or oxygen vacancies on the bulk magnetization as well as on the Mössbauer 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 TC ≈ 180 K the Mössbauer spectra distinctly include the contribution from paramagnetic and ferromagnetic regions, providing direct evidence for phase separation. No contribution to the spectra from Fe4+ ions can be observed, which is an unambiguous evidence that at low concentration iron (either directly doped or formed from 57Co by nuclear decay) is accommodated in the cobaltate lattice as Fe3+ ion.
PACS.75.47.Gk Colossal magnetoresistance 75.30.Kz Magnetic phase boundaries 75.10.Nr Spin-glass and other random models 71.30.+h Metal-insulator transitions and other electronic transitions 76.80.+y Mossbauer effect; other gamma-ray spectroscopy
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