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 6.26: Poster

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

Magnetic order in the tetrahedral quantum spin system Cu₂Te₂O₅(Br_1−xCl_x)₂ — •H.-H. Klauss¹, P. Lemmens¹, A. Bosse¹, D. Baabe¹, D. Mienert¹, H. Luetkens¹, F.J. Litterst¹, K.-Y. Choi², R. Scheuermann³, and M. Johnsson⁴ — ¹Institut für Metallphysik und Nukleare Festkörperphysik, TU Braunschweig — ²II. Physikalisches Institut, RWTH Aaachen — ³Paul Scherrer Institut, Villigen, Switzerland — ⁴Department of Inorganic Chemistry, Stockholm University, Sweden

We present studies of the magnetic correlations in the weakly coupled spin tetrahedra system Cu₂Te₂O₅(Br_1−xCl_x)₂. Due to quantum fluctuations these systems show strongly reduced magnetic transition temperatures T_N^Cl = 18.2 K and T_N^Br = 11.4 K in comparison with a magnetic exchange of J ≈ 40 K. Susceptibility, specific heat and magnetic raman scattering experiments reveal that the Bromide system (x = 0) is close to a quantum phase transition (P. Lemmens et al. PRL 87 227201 (2001)). We performed muon spin relaxation (µSR) experiments on six samples with 0 ≤ x ≤ 1. All samples show two spontaneous muon spin precession frequencies below their respective ordering temperatures which decrease monotonously with decreasing x. An enhanced longitudinal spin relaxation is attributed to the dominantly low dimensional character of the system.