Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe

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 J_i. 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.