Cobalt-induced ferromagnetic interactions and magnetoresistance in charge-ordered Sr2/3La1/3FeO3

Sr2/3La1/3FeO3 is a perovskite-type oxide with formally 67% Fe4+ and 33% Fe3+ ions revealing a charge disproportionation of Fe4+ and concomitant Fe3+Fe3+Fe5+ charge ordering below its Neel temperature of similar to200 K. Co-doped materials Sr2/3La1/3Fe1-xCoxO3 (0.15 less than or equal to x less than or equal to 0.33) were synthesized and investigated by X-ray powder diffraction, Fe-57 Mossbauer spectroscopy, magnetization measurements, and magnetotransport studies in order to explore the relation between charge ordering, magnetic properties, and magnetoresistance effects in this system. Cobalt substitution induces the formation of charge disordered ferromagnetic clusters (x = 0.15, 0.24) and finally leads to complete suppression of the charge disproportionation (x = 0.33). Spin-glass like magnetic properties are observed. Pronounced negative magnetoresistance effects up to -20% at 5 K and 7 T are attributed to reduced scattering of charge carriers due to parallel spin alignment of ferromagnetic regions in an applied magnetic field. (C) 2003 Editions scientifiques et medicales Elsevier SAS. All fights reserved.