Extension of the zinc paratacamite phase diagram: Probing the effect of spin vacancies in anS=12kagome antiferromagnet

Abstract

We report on the extension of the phase diagram of the magnetic model system zinc paratacamite, Zn${}_{x}$Cu${}_{4\ensuremath{-}x}$(OH)${}_{6}$Cl${}_{2}$ ($0\ensuremath{\le}x\ensuremath{\le}1$), with compositions $x>1$, up to $\ensuremath{\sim}1.2$. This amounts to diamagnetic doping of the kagome lattice of antiferromagnetically coupled Cu${}^{2+}$ with $S=1/2$ in what was hitherto known as the end member in the series: herbertsmithite of stoichiometry ZnCu${}_{3}$(OH)${}_{6}$Cl${}_{2}$. Combining chemical analysis, x-ray diffraction, magnetic susceptibility measurements, Raman spectroscopy and muon spin relaxation spectroscopy we conclude the following: (i) Herbertsmithite can be synthesized in stoichiometric form, but it is affected by antisite disorder of $\ensuremath{\sim}7$% in Cu${}^{2+}$ content, implying that for $x=1$, $\ensuremath{\sim}7$% of the Cu kagome sites is occupied by Zn${}^{2+}$. (ii) The Zn content can be increased up to $x\ensuremath{\sim}1.2$. No qualitatively new behavior is found for the diamagnetically doped kagome lattice, only a continuation of the trends observed for samples with $x<1$ as $x$ is increased.