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TT: Tiefe Temperaturen

TT 6: Postersitzung I: Josephsonkontakte und SQUIDs, Supraleitung: Theorie, Korrelierte Elektronen, Niederdimensionale Systeme, Magnetotransport, Quantenhalleffekt, Kohlenstoff-Nanoröhrchen, Quantenflüssigkeiten

TT 6.70: Poster

Monday, March 26, 2001, 14:30–17:00, Rang S\ 3

CuSiO₃ : a quasi - one - dimensional S=1/2 antiferromagnetic chain system — •M. Baenitz¹, M. Dischner¹, C. Geibel¹, J. Sichelschmidt¹, F. Steglich¹, H.H. Otto², and A.A. Gippius³ — ¹MPI für Chemische Physik fester Stoffe, Nöthnitzer Str. 40, D - 01187 Dresden — ²TU Clausthal, Inst. f. Mineralogie u. Mineralische Rohstoffe, Adolph - Roemer - Straße 2A, 38678 Clausthal — ³Faculty of Physics, Moscow State University, 119899 Moscow

CuSiO₃ , isotypic to the spin - Peierls compound CuGeO₃, was discovered as a metastable decomposition product of the silicate mineral dioptase, Cu₆Si₆O₁₈·6H₂O. We investigated the starting material dioptase and CuSiO₃ using susceptibility χ(T), magnetization, specific heat C(T), NQR and EPR measurements. For the silicate χ(T) and C_m(T) (magnetic contribution) are reproduced very well above T = 8 K by theoretical calculations for an S=1/2 antiferromagnetic Heisenberg chain without frustration (α = 0) and a nearest - neighbor (NN) exchange coupling constant of J/k_B = 21  K, much weaker than in CuGeO₃. The measurements presented indicate an absence of frustration which could be due to a cancellation of the antiferromagnetic and ferromagnetic NN exchange contributions caused by the smaller Cu - O(2) - Cu bond angle in CuSiO₃ (94 ^∘ vs 99 ^∘ in CuGeO₃). The remaining next - nearest - neighbor (NNN) exchange J′ would then transform one atomic chain into two independent spin chains. Furthermore we show that CuSiO₃ undergoes a transition to a long range antiferromagnetic order at T_N = 7.9 K. Temperature dependent ^63,65Cu nuclear quadrupole resonance results (^63,65ν_NQR, ^63,65 △ ν_NQR and 1/T₁) are also discussed.