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Regensburg 2002 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 22: Postersitzung III: Syst. korr. Elektr.: Theorie II (1-15), Metall-Isol.- und Phasenüberg
änge (16-33), SL: Massivmat., Bandl., Pinning, Vortexdyn., Transport, Korngr. (34-43), Niedrigdim. Syst., Magnetotransport (44-63)

TT 22.55: Poster

Donnerstag, 14. März 2002, 14:00–17:30, A

Synthesis, structure and magnetic properties of the transition metal compound FeCl2(NH3)2 — •V. Kataev1, A. Möller2, S. Bremm2, M. Kriener1, G. Meyer2, and A. Freimuth11II. Physikalisches Institut, Universität zu Köln — 2Institut für Anorganische Chemie, Universität zu Köln

In search for new low dimensional spin systems with strong electronic correlations we have synthesized single phase FeCl2(NH3)2. The compound crystallizes orthorhombic, space group Cmmm. Fe atoms in the formal oxidation state +2 (3d6-configuration) are octahedrally coordinated by four Cl atoms in the equatorial bc-plane and by two NH3 molecules at the apexes along the a-axis. The octahedra share trans-edges via Cl ligands and form chains along the c-axis. In contrast to oxides, where the octahedron of a 3d6-complex is usually elongated, we observe a compression in this case. This is due to shorter bond lengths of Fe–NH3 compared to Fe-Cl. Therefore, one may expect a completely different magnetic ground state of iron which cannot be achieved in oxides. We present results of optical, magnetization and electron spin resonance measurements of FeCl2(NH3)2. The data give evidence for strong intra- and interchain magnetic correlations which lead to antiferromagnetic order at low temperatures. We discuss the interplay between structure, spin and orbital degrees of freedom in FeCl2(NH3)2 and propose a scheme of the low energy states of iron.

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