The investigation of the magnetic and transport properties of the oxygen de
ficient perovskites SrFe1-xCoxO3-delta shows that these compounds exhibit b
oth ferromagnetism and metallicity in a wide compositional range (0 less th
an 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 cobal
t and iron according to the scheme Fe3+-O-Co4+ <----> Fe4+-O-Co3+. This mod
el is strongly supported by Fe-57 Mossbauer measurements which show the exi
stence of two sites at room temperature, high spin localized Fe4+ and deloc
alized Fe3+alpha sites, whereas magnetic disordering suggesting spin fluctu
ations is observed at 5 K as soon as cobalt is introduced into the SrFeO3 s
tructure. (C) 2001 Editions scientifiques et medicales Elsevier SAS. All ri
ghts reserved.