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Evidence for an unconventional magnetic instability in the spin-tetrahedra system Cu_2Te_2O_5Br_2

P. Lemmens·K. -Y. Choi·E. E. Kaul·Ch. Geibel·K. Becker·W. Brenig·R. Valenti·C. Gros·M. Johnsson·P. Millet·F. Mila
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Abstract

Thermodynamic experiments as well as Raman scattering have been used to study the magnetic instabilities in the spin-tetrahedra systems Cu_2Te_2O_5X_2, X=Cl and Br. While the phase transition observed in the Cl system at T_o=18.2 K is consistent with 3D AF ordering, the phase transition at T_o=11.3 K in the Br system has several unusual features. We propose an explanation in terms of weakly coupled tetrahedra with a singlet-triplet gap and low lying singlets.

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P. Lemmens, K. -Y. Choi, E. E. Kaul, Ch. Geibel, K. Becker, W. Brenig, R. Valenti, C. Gros, M. Johnsson, P. Millet, F. Mila. 2001-07-03. Evidence for an unconventional magnetic instability in the spin-tetrahedra system Cu_2Te_2O_5Br_2. https://doi.org/10.1103/physrevlett.87.227201

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