Antiferromagnetic transitions in polymorphous minerals of the natural cuprates atacamite and botallackite ${\mathrm{Cu}}_2\mathrm{Cl}{\left(\mathrm{O}\mathrm{H}\right)}_3$

A systematic study on pure-phase samples of the polymorphous natural cuprates ${\mathrm{Cu}}_2\mathrm{Cl}{\left(\mathrm{O}\mathrm{H}\right)}_3$, atacamite and botallackite, is carried out using synchrotron x-ray-diffraction, magnetic susceptibility, and muon spin rotation/relaxation $\left(\mu \mathrm{SR}\right)$ measurements. Atacamite and botallackite are found to undergo antiferromagnetic transition at $T_{\mathrm{N}}=9.0$ and $T_{\mathrm{N}}=7.2\mathrm{K}$, respectively. Contrasting results are obtained in the $\mu \mathrm{SR}$. Atacamite is suggested to have a distribution in the internal (electron-spin) field, favoring a picture of a disordered ground state, while botallackite shows distinct muon-spin rotation, indicating a long-range magnetic order. The different magnetic properties exhibited by the two polymorphs are consistently explained by inspection into the coordination of Cu and the $\mathrm{Cu}-\mathrm{O}-\mathrm{Cu}$ bond angles in the polymorphs.

Figure 1

Field-emission scanning electron microscopy for botallackite.

Figure 2

(Color online) Observed and calculated synchrotron x-ray-diffraction spectra for atacamite.

Figure 3

(Color online) Observed and calculated synchrotron x-ray-diffraction spectra for botallackite.

Figure 4

Crystal structure of atacamite ${\mathrm{Cu}}_2\mathrm{Cl}{\left(\mathrm{O}\mathrm{H}\right)}_3;$ (a) viewed from $b$ axis, (b) viewed from $c$ axis, and (c) local coordination.

Figure 5

Crystal structure of botallackite ${\mathrm{Cu}}_2\mathrm{Cl}{\left(\mathrm{O}\mathrm{H}\right)}_3;$ (a) viewed from $b$ axis, (b) viewed from $a$ axis, and (c) local coordination.

Figure 6

Temperature dependence of the magnetic susceptibility at $10\mathrm{kOe}$ for atacamite and botallackite.

Figure 7

Temperature dependence of the reciprocal magnetic susceptibility for atacamite and botallackite.

Figure 8

(Color online) Time evolution of zero-field $\mu \mathrm{SR}$ asymmetry $a\left(t\right)$ for atacamite (KEK-MSL). Solid lines for $T>9$show the Kubo-Toyabe fit with $\sigma =0.44\mu {\mathrm{s}}^{-1}$.

Figure 9

(Color online) Time evolution of zero-field $\mu \mathrm{SR}$ asymmetry $a\left(t\right)$ for botallackite (KEK-MSL). Solid line shows the Kubo-Toyabe fit with $\sigma =0.44\mu {\mathrm{s}}^{-1}$.

Figure 10

(Color online) Muon spin rotation seen in the high time resolution zero-field asymmetry spectra (TRIUMF) for botallackite, the solid lines are fitted curves.

Figure 11

(Color online) Temperature dependence of the muon spin precession in zero field for botallackite (TRIUMF).

Figure 12

(Color online) Longitudinal-field $\mu \mathrm{SR}$ asymmetries for atacamite at $2\mathrm{K}$ (TRIUMF).

Figure 13

(Color online) Temperature dependence of the fitted parameters from the $\mathrm{ZF}\text{−}\mu \mathrm{SR}$ for atacamite.