Synthesis-Dependent Properties of Barlowite and Zn-Substituted Barlowite

TL;DR

This paper introduces a new hydrothermal synthesis method for large single crystals of barlowite and Zn-substituted barlowite, revealing how synthesis conditions influence their magnetic and thermodynamic properties, with implications for quantum spin liquid research.

Contribution

A novel hydrothermal synthesis technique for large barlowite and Zn-substituted barlowite crystals, highlighting the impact of synthesis on their magnetic and thermodynamic behaviors.

Findings

Zn-substituted barlowite shows no magnetic order down to 2 K.

Synthesis conditions significantly affect defect chemistry and properties.

Large crystals suitable for neutron scattering were successfully produced.

Abstract

The mineral barlowite, Cu$_4$(OH)$_6$FBr, has been the focus of recent attention due to the possibility of substituting the interlayer Cu$^{2+}$ site with non-magnetic ions to develop new quantum spin liquid materials. We re-examine previous methods of synthesizing barlowite and describe a novel hydrothermal synthesis method that produces large single crystals of barlowite and Zn-substituted barlowite (Cu$_3$Zn$_x$Cu$_{1-x}$(OH)$_6$FBr). The two synthesis techniques yield barlowite with indistinguishable crystal structures and spectroscopic properties at room temperature; however, the magnetic ordering temperatures differ by 4 K and the thermodynamic properties are clearly different. The dependence of properties upon synthetic conditions implies that the defect chemistry of barlowite and related materials is complex and significant. Zn-substituted barlowite exhibits a lack of magnetic order down to T = 2 K, characteristic of a quantum spin liquid, and we provide a synthetic route towards producing large crystals suitable for neutron scattering.