Dzyaloshinsky-Moriya Anisotropy in the Spin-1/2 Kagome Compound ${\mathrm{ZnCu}}_3(\mathrm{OH}{)}_6{\mathrm{Cl}}_2$

We report the determination of the Dzyaloshinsky-Moriya interaction, the dominant magnetic anisotropy term in the kagome spin-1/2 compound ${\mathrm{ZnCu}}_3(\mathrm{OH}{)}_6{\mathrm{Cl}}_2$. Based on the analysis of the high-temperature electron spin resonance (ESR) spectra, we find its main component $|D_z|=15(1)\mathrm{K}$ to be perpendicular to the kagome planes. Through the temperature dependent ESR linewidth, we observe a building up of nearest-neighbor spin-spin correlations below $\sim 150\mathrm{K}$.

Figure 1

ESR spectra of ${\mathrm{Zn}}_x{\mathrm{Cu}}_{4-x}(\mathrm{OH}{)}_6{\mathrm{Cl}}_2$ [main panel and inset (a)], measured at 326.4 GHz, and their fits to the powder-averaged Lorentzian (solid lines). The dashed line gives an axial powder spectrum for the same $g$-factor anisotropy ($g_{\parallel }=2.25$, $g_{\perp }=2.14$) in the case of small magnetic-anisotropy broadening. Inset (b): DM vectors connecting the NN ${\mathrm{Cu}}^{2+}$ cites (middle-sized spheres) through ${\mathrm{OH}}^{-}$ groups (big and small spheres), with $D_z$ and $D_p$ as the out-of-plane and the in-plane components.

Figure 2

(a) Scaling of ESR intensity ${\chi }_{\mathrm{ESR}}$ and bulk susceptibility ${\chi }_b$ in ${\mathrm{Zn}}_x{\mathrm{Cu}}_{4-x}(\mathrm{OH}{)}_6{\mathrm{Cl}}_2$ ($x=1$). (b) The out-of-plane $\Delta H_z$ and the in-plane $\Delta H_p$ ESR line width.

Figure 3

The reduced ${\chi }^2$, reflecting the quality of the RT fit in ${\mathrm{ZnCu}}_3(\mathrm{OH}{)}_6{\mathrm{Cl}}_2$. The dashed rectangle gives the optimal parameters $|D_z|=15(1)\mathrm{K}$ and $|D_p|=2(5)\mathrm{K}$.