Dresden 2003 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 6: Postersitzung I (Amorphe- u. Tunnelsysteme, Niedrigdimensionale Systeme, Supraleitung: Elektronenstruktur, Phononen, Tunneln, Ordnungsparameter)

TT 6.15: Poster

Montag, 24. März 2003, 14:30–19:00, P2c, P2d

Structural and magnetic properties of a low-dimensional spin magnet InCu_2/3V_1/3O₃ — •V. Kataev¹, A Möller², W Jung², N Schittner¹, M Kriener¹, and A Freimuth¹ — ¹II. Physikalisches Institut, Universität zu Köln — ²Institut für Anorganische Chemie, Universität zu Köln

Polycrystalline samples of InCu_2/3V_1/3O₃ have been obtained from mixtures of In₂O₃, CuO, V₂O₅ (molar ratio 3:4:1) at 900 ^∘C (5d) under a constant flow of O₂ in a Pt crucible. The compound crystallizes in the hexagonal space group P6₃/mmc, a=3.3564(8) Å and c=11.908(3) Å. Non-magnetic V⁵⁺ and magnetic Cu²⁺ (S=1/2) ions share a common site-set with 5-fold triangular-bipyramidal coordination of oxygen ions which is exceptional for Cu²⁺. These polyhedra are corner-connected to form hexagonal layers separated by layers of In³⁺ ions along the c-axis. Measurements of static magnetic susceptibility χ and electron spin resonance (ESR) reveal a strong antiferromagnetic coupling of Cu spins with J∼ 300 K. The compound orders magnetically at 38 K. The T-dependence of χ is reminiscent of low-dimensional spin magnets, suggesting that Cu spins in the hexagonal planes may form e.g. chains or rings. Remarkably, ESR gives evidence that the ground state orbital of Cu²⁺ is d_3z²−r² and not d_x²−y² as in copper oxides with the usual octahedral, square-pyramidal or square-planar coordination. We discuss the origin of such an unusual orbital state of Cu as well as possible spin arrangements in InCu_2/3V_1/3O₃. supported by DFG through SFB 608