Regensburg 2004 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 14: FV-internes Symposium ”Orbital Physics”

TT 14.2: Fachvortrag

Dienstag, 9. März 2004, 15:00–15:20, H18

Magnetism, Charge Order and Giant Magnetoresistance in SrFeO_3−δ — •C. Ulrich¹, A. Lebon¹, P. Adler², C. Bernhard¹, A. Boris¹, A. Pimenov¹, A. Maljuk¹, C.T. Lin¹, and B. Keimer¹ — ¹Max-Planck-Institut FKF, Stuttgart — ²Institut für Anorganische Chemie, Universität Karlsruhe

The relationship between spin ordering, charge ordering, and magneto–transport effects has recently received much attention in the context of the colossal magnetoresistance (CMR) phenomenon in manganites. In the 3D perovskite SrFeO₃, Fe⁴⁺ is isoelectric to the Jahn–Teller ion Mn³⁺ in the manganite system. However, while the parent compound of the CMR manganites, LaMnO₃, is insulating and shows a cooperative Jahn–Teller effect, its analogue SrFeO₃ remains metallic at all temperatures and exhibits a helical antiferromagnetic spin structure below 130 K. Therefore, SrFeO₃ is right at the borderline between an itinerant and a strongly localized electron system.

We have studies three single crystals of SrFeO_3−δ with different oxygen content. Cubic SrFeO_3.00 is metallic in the entire temperature range and shows a large negative magnetoresistance effect at 55 K. Tetragonal SrFeO_2.87 shows semiconducting behavior below a second magnetic phase transition at 75 K. Our Mössbauer studies reveal that this phase transition is accompanied by a charge ordering of Fe^3.5+ into Fe³⁺ and Fe⁴⁺. An orthorhombic sample SrFeO_2.81 on the other side showed semiconducting behavior and a pronounced positive MR effect at 70 K.