Dresden 2009 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 29: Correlated Electrons: Low-dimensional Systems - Materials 2
TT 29.3: Vortrag
Mittwoch, 25. März 2009, 14:30–14:45, HSZ 301
Ultrasonic investigations on the 1D diamond chain compound Azurite — •Cong T. Pham1, Andreas Brühl1, Mariano de Souza1, Bernd Wolf1, Jürgen Schreuer2, Stefan Süllow3, and Michael Lang1 — 1Physikalisches Institut, Universität Frankfurt, SFB/TR49, 60438 Frankfurt(M — 2Institut für Mineralogie, Ruhr-Universität, 44780 Bochum — 3Institut für Physik der kondensierten Materie, TU Braunschweig, 38106 Braunschweig
The natural mineral Azurite has been considered a model substance for the 1D distorted antiferromagnetic (AFM) diamond chain. The unusual magnetic properties were believed to arise from the competition between quantum fluctuations and spin frustration and have been modelled by assuming three AFM exchange-coupling constant J1,J2,J3 > 0. However, the microscopic magnetic structure and the detailed phase diagram are unknown or disputed. Recent inelastic neutron scattering experiments suggest a non-frustrated structure with J3 < 0 and J1 ~ 0 below the Néel-temperature of 1.8 K. In this contribution, we present results of ultrasonic investigations on a high-quality single crystal. The longitudinal elastic constant has been studied as a function of temperature down to 80 mK and magnetic fields up to 12 Tesla. The data reveal clear signatures of the magnetic energy scales involved and disclose distinct anomalies at the magnetic phase transition. Based on these results a detailed B-T phase diagram is obtained which includes an additional phase boundary of unknown origin at low temperature (T < 0.6 K). The latter is accompanied by a pronounced softening of the elastic constant.