Magnetic and Transport Properties of Quasi Two-Dimensional Ferromagnet Sr₃Fe_2-xCo_xO_7-δ (x=0.2 and 0.5)

Electronic Structure of Sr3Fe2−xCoxO7−δ Studied by Photoemission and X-ray Absorption Spectroscopy

“…This means that the electron density of states near E F dominantly has the Fe 3d character and the Co 3d states are located below the Fe 3d states by ∼1 eV, in agreement with the smaller charge-transfer energy of Co 4+ than that of Fe 4+ [16]. Because the resistivity is insulating but still bad metallic [5], the result implies that with increasing x, rather itinerant-like Fe 3d electrons near E F are replaced by the more localized Co 3d states below E F by 1−3 eV, and that this process may induce a larger magnetic moment at Fe/Co sites. Binding energy (eV) 3) spectra in (e) and (f).…”

“…Moreover, it shows negative magnetoresistance [4,5], reminding us of the colossal magnetoresistive Mn oxides La 2−2x Sr 1+2x Mn 2 O 7 . Nevertheless, Sr 3 Fe 2−x Co x O 7−δ is rather insulating [5] and its ferromagnetism has not yet been completely understood.…”

“…Single crystalline samples of Sr Fe 2−x Co x O 7−δ (x=0.3 and 0.5) were prepared by the standard solid-state reaction. δ was determined to be 0.14 (x=0.3) and 0.16 (x=0.5) with iodometric titration with an accuracy of ±0.02 [5]. This means that the average valence of the Fe/Co site is 3.86+ (x=0.3) and 3.84+ (x=0.5).…”

“…The magnetic moment of Sr 3 Fe 2−x Co x O 7−δ is about 2.5−2.7 µ B per Fe/Co site for x of 0.3−1.0, depending upon synthesis conditions and/or the amount of δ [2,3]. Moreover, it shows negative magnetoresistance [4,5], reminding us of the colossal magnetoresistive Mn oxides La 2−2x Sr 1+2x Mn 2 O 7 . Nevertheless, Sr 3 Fe 2−x Co x O 7−δ is rather insulating [5] and its ferromagnetism has not yet been completely understood.…”

Complex Magnetic Behavior in the PrSr3(Fe1–xCox)3O10−δ n = 3 Ruddlesden–Popper-Type Solid Solution with High Valent Cobalt and Iron

“…This could be due to anisotropic conduction within the RP3 structure and different transport mechanisms along ⟨100⟩ and ⟨001⟩. Such anisotropy has been reported by Chen et al for an RP2Manganite single crystal, by Akahoshi et al in Co-substituted RP2 ferrates, and in cuprate systems . In addition, defects, local inhomogeneities, strain and grain boundaries might lead to departures from the above models.…”