Anisotropy: Spin order and magnetization of single-crystalline Cu4(OH)6FBr barlowite

Despite decades-long fascination, the difficulty of maintaining high lattice symmetry in frustrated nonbipartite S = 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, Cu-4(OH)(6)FBr, which has a geometrically perfect kagome motif. At T <= 4.2 K and 35 <= mu H-0 <= 65 T, the interlayer spins are fully polarized, and the kagome-intrinsic magnetization is consistent with a Heisenberg model having J/k(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 <= 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.