Transport properties of La0.8Sr0.2FexCo1-xO3 (0.15 ≤ x ≤ 0.30)

Complete text of publication follows. Spontaneously phase separated perovskite oxides display a couple of unique physical properties, like colossal magnetoresistance effect in manganites and high-temperature superconductivity in cuprates. The hole doped La1-ySryCoO3 cobaltite below the percolation threshold is insulator. Surprisingly, the properties of the low temperature transport of the compound show similarities with characteristics of artificial structures fabricated by depositing nanoscale particles. In order to study the above process, Fe doped La0.8Sr0.-2FexCo1-xO3 (0.15 ≤ x ≤ 0.30) polycrystalline samples were prepared and studied by transport, ac/dc magnetization and 57Fe Moessbauer spectrometry. The quality of the samples was checked by XRD, TEM and SNMS. Magnetization measurements revealed, that the compound undergoes to spin glass freezing at about 50 K, while the amplitude of the ac cusp decreases with Fe doping. Low field magnetization measurements did not show any signs of higher temperature paramagnetic/ferromagnetic phase transition. According to our transport measurements, the resistivity increases with Fe doping. The transport mechanism can be well described by a 'granular metal in insulating matrix' model (ρ α T-1/2), the goodness of fit increases with Fe doping. Magnetoresistance decreased with increasing Fe content and for samples x ≥ 0.2 signalized the setup of magnetic order at 80/90 K. At x=0.15 traces of higher temperature ordering were found. The two transition temperatures can be associated with the setup of short range magnetic coherence and long range magnetic coherence, respectively. The setup of short range magnetic order was approved by the results of Moessbauer spectrometry, as well. (author)