2020/05/26 by K. Tustain, B. Ward-O'Brien, F. Bert +6 · 2 citations
Physics and Astronomy · #cond-mat.str-el
paper · pdf · doi:10.1038/s41535-020-00276-4
11 pages, 5 figures, supplementary information
arxiv created 2020/05/26 · arxiv updated 2020/10/28
We report a comprehensive muon spectroscopy study of the Zn-barlowite series of 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 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=(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 dynamical behaviour of the widely studied Zn-paratacamite series that contains the quantum spin liquid candidate herbertsmithite.