Neutron spin echo study of magnetic fluctuations in the kagome antiferromagnet (D3O)Fe3(SO4)2(OD)6

The kagome lattice with antiferromagnetic nearest-neighbour exchange provides a simple example of a geometrically frustrated magnet with a highly degenerate ground state. Theoretical work indicates that the static and dynamic correlations of this magnet are unconventional, with strong fluctuations down to very low temperatures. Deuteronium Jarosite ((D3O)Fe-3(SO4)(2)(OD)(6)) provides a rare example of a suitable model material to test such theory. DC susceptibility studies show strong antiferromagnetic exchange between the S = 5/2 moments (theta(CW) congruent to - 700 K), and a spin-glass transition at T-f congruent to 13 K. We report on neutron spin-echo measurements made on this compound using the polarised neutron spectrometer IN11 at ILL taken with momentum transfer Q = 1.35 Angstrom(-1) for times ranging from 9.7 to 870 ps. The magnetic fluctuations were observed to slow down gradually on cooling through T-f, until they appeared to be static at the shortest experimental timescale at 1.5 K. (C) 1999 Elsevier Science B.V. All rights reserved.