The Sr0.8Y0.2Co1-xFexO3-δ oxygen deficient perovskites:: modulated structure, magnetic properties and magnetoresistance

A series of oxygen deficient perovskites Sr0.8Y0.2Co1-xO3-delta, has been prepared by solid state reaction in close ampoules. The structural study by transmission electron microscopy reveals the existence of extra reflection peaks resulting from ordering phenomenon of the oxygen anions. For x = 0.5 this implies a modulated structure characterized by a vector such as q = 0.45 in the Pm3m space group. Interestingly, the Fe introduction in Sr0.8Y0.2CoO3-delta broadens the ferromagnetic transition, increasing the T-C onset. Despite a lack of metallic-like behavior, the mixed "Co1-xFex" compounds exhibit negative magnetoresistance properties which magnitude increases as T decreases below TC to reach the best effect of -50% in 7 T for Sr0.8Y0.2Co0.5Fe0.5O3-delta. (C) 2006 Elsevier SAS. All rights reserved.