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Durham University

Department of Physics

Staff profile

Publication details for Professor Tom Lancaster

Tustain, Katherine, Ward-O’Brien, Brendan, Bert, Fabrice, Han, Tianheng, Luetkens, Hubertus, Lancaster, Tom, Huddart, Benjamin M., Baker, Peter J. & Clark, Lucy (2020). From magnetic order to quantum disorder in the Zn-barlowite series of S = 1/2 kagomé antiferromagnets. npj Quantum Materials 5(1): 74.

Author(s) from Durham


We report a comprehensive muon spectroscopy study of the Zn-barlowite series of S=12 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=12 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.