A mu SR study of high oxidation state iron oxides displaying large magnetoresistance

The magnetic and conducting properties of many transition metal oxides may be drastically altered by doping. This study concerns a family of compounds with compositions intermediate between the itinerant helical antiferromagn et SrFeO3 and the ferromagnetic metal SrCoO3. We have measured the temperat ure-dependent muon-spin relaxation in five compounds in the family SrFe1-xC oxO3 where Co substitution varies from x = 0 to 0.2 and investigated the re lation between the relaxation rate and the magnetic susceptibility above th e ordering temperature. These materials show large magnetoresistance which may be associated with the presence of competing interactions and non-equil ibrium behaviour due to cluster formation. We find a quasistatic local fiel d at the muon site below the magnetic transition temperature indicative of magnetic order in samples with x = 0.15 and 0.2 but not in the sample with x = 0. (C) 2000 Elsevier Science B.V. All rights reserved.