Magnetization and magnetoresistance in insulating phases of SrFe O3-δ

Abstract

Two insulating phases of SrFe O3-δ have been found by the introduction of oxygen deficiencies in metallic SrFe O3, one with 0.15≤δ≤0.19 (Sample A) and the other above δ=0.19 (Sample B). Sample A shows large negative magnetoresistance around the charge ordering temperature (CO) associated with a magnetic anomaly. A three-dimensional variable range hopping associated with a localized moment antiferromagnetic behavior was seen in Sample B without any measurable CO down to 70 K. Ac and dc susceptibilities (χac and χdc) show multiple magnetic anomalies associated with a frustrated magnetic order with competing ferro- and antiferromagnetic interactions. The frustration decreases with increasing content of Fe3+, the direct consequence of which is the dilution of helical magnetic spin ordering. The competing effects of ferro- and antiferromagnetic phases extend up to high temperatures T∼230 K revealing a characteristic temperature scale not known earlier. These observations are discussed in the context of magnetic interactions associated with Fe4+/Fe3+. © 2005 The American Physical Society.