Electrochemical oxidation and reduction of the La0.2Sr0.8CoO3−δ phases: Control of itinerant ferromagnetism and magnetoresistance

In order to understand how the magnetotransport properties are related to the oxygen content, the La0.2Sr0.8CoO3−δ perovskite phases have been studied by using electrochemical cycling. The samples, prepared by a sol–gel technique, have been characterized from a structural and chemical point of view concomitantly to their physical properties. Upon reduction, a brownmillerite-type phase La0.2Sr0.8CoO2.65, which presents a weak ferromagnet behavior, is formed and, upon oxidation, a complete stoichiometric phase with a cubic unit cell (a = 3.83Å) could be obtained with a ferromagnetic and metallic behavior. Finally, it is shown that using appropriate cut-off potential upon reduction or oxidation the oxygen content and the cobalt valence can be monitored in such transition metal oxides to reach the fully oxidized or reduced end-members.