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

Abstract

We report on the extension of the phase diagram of the magnetic model system zinc paratacamite, Zn xCu 4-x(OH) 6Cl 2 (0≤x≤1), with compositions x>1, up to ∼1.2. This amounts to diamagnetic doping of the kagome lattice of antiferromagnetically coupled Cu2 + with S=1/2 in what was hitherto known as the end member in the series: herbertsmithite of stoichiometry ZnCu 3(OH) 6Cl 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 ∼7% in Cu2 + content, implying that for x=1, ∼7% of the Cu kagome sites is occupied by Zn2 +. (ii) The Zn content can be increased up to x∼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. © 2012 American Physical Society.