We present results of ultrasonic measurements on a single crystal of the distorted diamond-chain compound azurite Cu3(CO3)2(OH)2. Pronounced elastic anomalies are observed in the temperature dependence of the longitudinal elastic mode c22 which can be assigned to the relevant magnetic interactions in the system and their couplings to the lattice degrees of freedom. From a quantitative analysis of the magnetic contribution to c22 the magneto-elastic coupling G = ∂J2/∂ϵb can be determined, where J2 is the intra-dimer coupling constant and ϵb the strain along the intra-chain b axis. We find an exceptionally large coupling constant of ∣G∣∼(3650 ± 150) K highlighting an extraordinarily strong sensitivity of J2 against changes of the b-axis lattice parameter. These results are complemented by measurements of the hydrostatic pressure dependence of J2 by means of thermal expansion and magnetic susceptibility measurements performed both at ambient and finite hydrostatic pressure. We propose that a structural peculiarity of this compound, in which Cu2O6 dimer units are incorporated in an unusually stretched manner, is responsible for the anomalously large magneto-elastic coupling.
@article{arxiv.1402.1306,
title = {Magneto-elastic couplings in the distorted diamond-chain compound azurite},
author = {Pham Thanh Cong and Bernd Wolf and Rudra Sekhar Manna and Ulrich Tutsch and Mariano de Souza and Andreas Brühl and Michael Lang},
journal= {arXiv preprint arXiv:1402.1306},
year = {2014}
}