Barlowite: A Spin-1/2 Antiferromagnet with a Geometrically Perfect Kagome Motif

TL;DR

This study investigates barlowite, a perfect kagome lattice antiferromagnet, revealing complex magnetic behavior and potential for realizing spin-liquid states with minimal disorder.

Contribution

It provides detailed thermodynamic characterization of barlowite, highlighting its undistorted kagome structure and unique magnetic properties, advancing understanding of frustrated quantum magnets.

Findings

Weak long-range magnetic order at 15 K

Multiple phase transitions at low temperatures

Magnetic entropy indicates nontrivial spin textures

Abstract

We present thermodynamic studies of a new spin-1/2 antiferromagnet containing undistorted kagome lattices---barlowite Cu$_{4}$(OH)$_{6}$FBr. Magnetic susceptibility gives $\theta_{CW}$ = $-$136 K, while long-range order does not happen until $T_{N}$ = 15 K with a weak ferromagnetic moment $\mu$ $<$ 0.1$\mu_{B}$/Cu. A 60 T magnetic field induces a moment less than 0.5$\mu_{B}$/Cu at $T$ = 0.6 K. Specific-heat measurements have observed multiple phase transitions at $T \ll$ $\mid$$\theta_{CW}$$\mid$. The magnetic entropy of these transitions is merely 18% of $k_{B}$ln2 per Cu spin. These observations suggest that nontrivial spin textures are realized in barlowite with magnetic frustration. Comparing with the leading spin-liquid candidate herbertsmithite, the superior interkagome environment of barlowite sheds light on new spin-liquid compounds with minimum disorder. The robust perfect geometry of the kagome lattice makes charge doping promising.