Magnetoresistance in the ferromagnetic metallic perovskite SrFe1-xCoxO3

The investigation of the magnetic and transport properties of the oxygen deficient perovskites SrFe1-xCoxO3-delta shows that these compounds exhibit both ferromagnetism and metallicity in a wide compositional range (0 less than or equal to x less than or equal to 0.70). Negative magnetoresistance is evidenced for the first time in these oxides, in contrast to SrCoO3-delta. These properties are explained by superexchange interactions between cobalt and iron according to the scheme Fe3+-O-Co4+ <----> Fe4+-O-Co3+. This model is strongly supported by Fe-57 Mossbauer measurements which show the existence of two sites at room temperature, high spin localized Fe4+ and delocalized Fe3+alpha sites, whereas magnetic disordering suggesting spin fluctuations is observed at 5 K as soon as cobalt is introduced into the SrFeO3 structure. (C) 2001 Editions scientifiques et medicales Elsevier SAS. All rights reserved.