Barlowite as a canted antiferromagnet: Theory and experiment

Abstract

We investigate the structural, electronic, and magnetic properties of the newly synthesized mineral barlowite ${\mathrm{Cu}}_{4}{(\mathrm{OH})}_{6}\mathrm{FBr}$ which contains ${\mathrm{Cu}}^{2+}$ ions in a perfect kagome arrangement. In contrast to the spin-liquid candidate herbertsmithite ${{\mathrm{ZnCu}}_{3}{(\mathrm{OH})}_{6}\mathrm{Cl}}_{2}$, kagome layers in barlowite are perfectly aligned due to the different bonding environments adopted by ${\mathrm{F}}^{\ensuremath{-}}$ and ${\mathrm{Br}}^{\ensuremath{-}}$ compared to ${\mathrm{Cl}}^{\ensuremath{-}}$. With the synthesis of this material we unveil a design strategy for layered kagome systems with possible exotic magnetic states. Density functional theory calculations and effective model considerations for ${\mathrm{Cu}}_{4}{(\mathrm{OH})}_{6}\mathrm{FBr}$, which has a ${\mathrm{Cu}}^{2+}$ site coupling the kagome layers, predict a three-dimensional network of exchange couplings, which together with a substantial Dzyaloshinskii-Moriya coupling lead to canted antiferromagnetic ordering of this compound in excellent agreement with magnetic susceptibility measurements on single crystals yielding ${T}_{N}=15\phantom{\rule{0.28em}{0ex}}\mathrm{K}$.