Despite decades-long fascination, the difficulty of maintaining high lattice symmetry in frustrated nonbipartite $S=\frac{1}{2}$ materials that can also be made into high-quality single crystals has been a persistent challenge. Here we report magnetization studies of a single-crystal sample of barlowite, ${\mathrm{Cu}}_4{\left(\mathrm{OH}\right)}_6\mathrm{FBr}$, which has a geometrically perfect kagome motif. At $T\le 4.2$ K and $35\le {\mu }_{0}H\le 65$ T, the interlayer spins are fully polarized, and the kagome-intrinsic magnetization is consistent with a Heisenberg model having $J/k_{\mathrm{B}}=-180$ K. Several field-driven anomalies are observed, having varied scalings with temperature. At an applied field, kagome disorder caused by the interlayer spins is smaller than that in herbertsmithite. At $T\le$ 15 K, the bulk magnetic moment comes from the interlayer spins. An almost coplanar spin order suggests that the magnitude of in-plane Dzyaloshinskii-Moriya interaction is smaller than 0.006(6) $J$. On the other hand, the possibility of a spin-liquid state in the kagome lattice coexisting with ordered interlayer spins is left open.

• Received 18 March 2015
• Revised 11 May 2016

DOI:https://doi.org/10.1103/PhysRevB.93.214416