We present a specific heat and inelastic neutron scattering study in magnetic fields up into the 1/3 magnetization plateau phase of the diamond chain compound azurite Cu3(CO3)2(OH)2. We establish that the magnetization plateau is a dimer-monomer state, {\it i.e.}, consisting of a chain of S=1/2 monomers, which are separated by S=0 dimers on the diamond chain backbone. The effective spin couplings Jmono/kB=10.1(2) K and Jdimer/kB=1.8(1) K are derived from the monomer and dimer dispersions. They are associated to microscopic couplings J1/kB=1(2) K, J2/kB=55(5) K and a ferromagnetic J3/kB=−20(5) K, possibly as result of dz2 orbitals in the Cu-O bonds providing the superexchange pathways.
@article{arxiv.0709.2560,
title = {Nature of the spin dynamics and 1/3 magnetization plateau in azurite},
author = {K. C. Rule and A. U. B. Wolter and S. Süllow and D. A. Tennant and A. Brühl and S. Köhler and B. Wolf and M. Lang and J. Schreuer},
journal= {arXiv preprint arXiv:0709.2560},
year = {2009}
}