Regensburg 2000 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 17: Postersitzung II: Pinning und Vortexdynamik (1-8), Supraleitung: Theorie (9-13), Korrelierte Elektronen (14-48), Niederdimensionale Systeme (49-68), Quantenflüssigkeiten (69-75)

TT 17.61: Poster

Mittwoch, 29. März 2000, 14:30–18:00, A

ESR in (Sr,La,Ca)₁₄Cu₂₄O₄₁ spin-chain spin-ladder compounds — •K.-Y. Choi, V. Kataev, U. Ammerahl, B. Büchner, and A. Freimuth — II. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln

Single crystals of Sr_14−xCa_xCu₂₄O₄₁ (x=0−12) and La_14−xCa_xCu₂₄O₄₁ (x=9−12) were studied by means of electron spin resonance (ESR). We show that in the hole doped Sr-Ca samples the temperature and concentration dependences of the spin relaxation rate in the CuO₂ chains are strongly influenced by the hole dynamics. In particular, we identify a characteristic temperature scale for the onset of charge order in the chains at low Ca doping. With increasing x a rapid destruction of the charge ordered state and a destabilization of the spin dimerized state in the chains is observed. At high Ca doping (x>8) magnetic order at low temperatures is found. The ESR data for La-Ca crystals suggest an unusually large anisotropy of superexchange in the CuO₂ spin chains. In the nearly insulating x=9 sample, which orders magnetically at T_N=9 K, a strong enhancement of antiferromagnetic (AF) spin dynamics is visible already below 50 K. Our results evidence a strong suppression of AF correlations with increasing Ca (i.e. hole) content in these crystals.