Regensburg 2007 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 22: Low-dimensional Systems - Materials
TT 22.11: Vortrag
Donnerstag, 29. März 2007, 12:15–12:30, H18
Magnetic frustration in one dimension - the distorted diamond chain azurite(Cu3(CO3)2(OH)2) - — •Bernd Wolf1, Andreas Brühl1, Mariano de Souza1, Katharina Removic-Langer1, Yeekin Tsui1, Ulrich Tutsch1, Jürgen Schreuer2, and Michael Lang1 — 1Physikalisches Institut, Universität Frankfurt, 60438 Max-von-Laue-Strasse 1, FOR 412 — 2Institut für Mineralogie, Ruhr-Universität-Bochum, 44780 Universitätsstrasse 150
A simple realization of a frustrated quantum-spin system is the S = 1/2 distorted diamond chain, where the ground state is strongly constrained by the ratio of the three coupling constants Ji. A theoretical phase diagram at T = 0 was examined consisting of a ferrimagnetic -, a dimerized -, as well as a spin fluid (SF) phase. The natural mineral azurite (Cu3(CO3)2(OH)2) represents a distorted diamond chain. We discuss thermodynamic measurements, such as specific heat, thermal expansion, elastic constant and magnetic susceptibility, some of which are also measured under hydrostatic pressure, in a wide-stretched temperature and field range. According to magnetic susceptibility and magnetization measurements, the ground state of azurite is located close to the quantum phase transition, separating the gapless SF phase from the gapped dimerized phase. We find pronounced acoustic anomalies at high fields indicating a significant spin-phonon interaction. From the enormous size of the anomalies in the sound velocity, a large magnetic Grüneisen parameter can be inferred, this possibly resulting from the proximity of the system to a quantum critical point.