Regensburg 2010 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 27: CE: Poster Session

TT 27.72: Poster

Wednesday, March 24, 2010, 14:00–18:00, Poster D1

Structural and magnetic properties of the mixed quantum antiferromagnet Cs₂CuCl_4−xBr_x — •P. T. Cong, S. Belz, N. Krüger, F. Ritter, W. Aßmus, B. Wolf, and M. Lang — Physikalisches Institut, Goethe-Universität, SFB/TR 49, D-60438 Frankfurt(M).

The two compounds, Cs₂CuCl₄ and Cs₂CuBr₄, have been classified as quasi-two-dimensional quantum antiferromagnets. Cs₂CuCl₄ shows long-range magnetic order, which can be described as a Bose-Einstein condensation of magnons, i.e., delocalized triplet excitations, whereas the iso-structural compound Cs₂CuBr₄, exhibits plateaus in the magnetization, indicating the localization of triplets. Here we present a systematic study of the magnetic properties in the Cs₂CuCl_4−xBr_x (0 ≤ x≤ 4) mixed system. All crystals were synthesized by a solution-growth method. Two structural variants - an A-type orthorhombic and a B-type tetragonal - were detected in this system depending on the growth conditions. A detailed structural phase diagram has been constructed, based on X-ray Rietveld refinement, SEM and thermal analysis. χ(T) measurements of crystals near the end members of the series reveal a broad maximum at T_max indicative of quasi-2D short range correlations. While for the Cl⁻rich system 0 ≤ x ≤ 0.8, T_max slightly increases with increasing Br⁻, a much stronger increase of T_max.is observed for the Br-rich system for 2.8 ≤ x ≤ 4.0.