Barlowite, Cu 4 (OH) 6 FBr, has attracted much attention as the parent compound of a new series of quantum spin liquid candidates, Zn x Cu 4-x (OH) 6 FBr. While it is known to undergo a magnetic phase transition to a long-range ordered state at TN = 15 K, there is still no consensus over either its nuclear or magnetic structures. Here, we use comprehensive powder neutron diffraction studies on deuterated samples of barlowite to demonstrate that the only space group consistent with the observed nuclear and magnetic diffraction at low-temperatures is the orthorhombic P nma space group. We furthermore conclude that the magnetic intensity at T < TN is correctly described by the P n m a magnetic space group, which crucially allows the ferromagnetic component observed in previous single-crystal and powder magnetisation measurements. As such, the magnetic structure of barlowite resembles that of the related material clinoatacamite, Cu 4 (OH) 6 Cl 2 , the parent compound of the well-known quantum spin liquid candidate hebertsmithite, ZnCu 3 (OH) 6 Cl 2 . arXiv:1810.01684v1 [cond-mat.str-el]

We report a comprehensive muon spectroscopy study of the Zn-barlowite series of $$S=\frac{1}{2}$$ S = 1 2 kagomé antiferromagnets, ZnxCu4−x(OH)6FBr, for x = 0.00 to 0.99(1). By combining muon spin relaxation and rotation measurements with state-of-the-art density-functional theory muon-site calculations, we observe the formation of both μ–F and μ–OH complexes in Zn-barlowite. From these stopping sites, implanted muon spins reveal the suppression of long-range magnetic order into a possible quantum spin liquid state upon the increasing concentration of Zn-substitution. In the parent compound (x = 0), static long-range magnetic order below TN = 15 K manifests itself in the form of spontaneous oscillations in the time-dependent muon asymmetry signal consistent with the dipolar fields expected from the calculated muon stopping sites and the previously determined magnetic structure of barlowite. Meanwhile, in the x = 1.0 end-member of the series—in which antiferromagnetic kagomé layers of Cu2+$$S=\frac{1}{2}$$ S = 1 2 moments are decoupled by diamagnetic Zn2+ ions—we observe that dynamic magnetic moment fluctuations persist down to at least 50 mK, indicative of a quantum disordered ground state. We demonstrate that this crossover from a static to dynamic magnetic ground state occurs for compositions of Zn-barlowite with x > 0.5, which bears resemblance to the dynamical behaviour of the widely studied Zn-paratacamite series that contains the quantum spin liquid candidate herbertsmithite.

Here we discuss magnetic hybrid coordination frameworks in relation to the realization of new geometrically frustrated magnets. In particular, we present the nuclear and magnetic structures of one such systemthe Fe 2+ -based oxalate fluoride framework KFe(C 2 O 4 )Fthrough analysis of the powder neutron diffraction and muon spectroscopy data. KFe(C 2 O 4 )F retains an orthorhombic Cmc2 1 structure upon cooling to 2 K composed of quasi-one-dimensional iron fluoride chains connected to a distorted triangular network via oxalate anions. Previous magnetometry measurements of KFe(C 2 O 4 )F indicate that it is a strongly interacting system with a Weiss constant θ ≈ −300 K that undergoes a magnetic ordering transition at T N ≈ 20 K, yielding a frustration index, f = |θ|/T N ≈ 15, reflective of high-spin frustration. We determine the nature of this frustrated antiferromagnetic ordering below T N and show that the resulting magnetic structure is best described by a model in the Cmc′2 1 ′ magnetic space group.

Kagome networks of ferromagnetically or antiferromagnetically coupled S 1 2 1 2= ferromagnetic kagome layers that are coupled antiferromagnetically via their extended organic pillaring linkers.

We present a comprehensive structural and magnetic characterization of the barlowite family of S = 1/2 kagomé magnets, Cu4(OH)6FX, where X = Cl, Br, or I. Through high-resolution synchrotron X-ray and neutron powder diffraction measurements, we reveal two sources of structural complexity within this family of materials, namely, compositional disorder of the halide species that occupy sites in between the kagomé layers and the positional disorder of the interlayer Cu2+ ions that persists well into the Pnma structural ground state. We demonstrate that understanding these inherent structural disorders is key as they correlate with the degree of partial order in the magnetic ground states of these quantum frustrated magnets.