The magnetic and crystal structure of azurite Cu$_3$(CO$_3$)$_2$(OH)$_2$ as determined by neutron diffraction

Here we present neutron diffraction results on the mineral azurite. We have found that the crystal structure of azurite can be described in the space group $P2_1$ which is the next lower symmetric group of $P2_1/c$ as found in earlier work. This small change in symmetry does not greatly influence the lattice parameters or atomic fractional coordinates which are presented here for single crystal diffraction refinements. The ordered magnetic moment structure of this material has been determined and is comprised of two inequivalent magnetic moments on copper sites of magnitude 0.68(1) and 0.25(1) $mu_{B}$. This result is discussed in terms of the anisotropic exchange and Dzyaloshinskii-Moriya interactions. It is found that the system is likely governed by one-dimensional behaviour despite the long-range ordered ground state. We also highlight the significance of strain in this material which is strongly coupled to the magnetism.

Magnetoelastic and structural properties of azurite Cu3(CO3)2(OH)2 from neutron scattering and muon spin rotation

Azurite, Cu3(CO3)2(OH)2, has been considered an ideal example of a one-dimensional (1D) diamond chain antiferromagnet. Early studies of this material imply the presence of an ordered antiferromagnetic phase below $T_N sim 1.9$ K while magnetization measurements have revealed a 1/3 magnetization plateau. Until now, no corroborating neutron scattering results have been published to confirm the ordered magnetic moment structure. We present recent neutron diffraction results which reveal the presence of commensurate magnetic order in azurite which coexists with significant magnetoelastic strain. The latter of these effects may indicate the presence of spin frustration in zero applied magnetic field. Muon spin rotation, $mu$SR, reveals an onset of short-range order below 3K and confirms long-range order below $T_N$.