A polarised neutron scattering study of the magnetic correlations in the kagome antiferromagnet AFe3(SO4)2(OD)6 (A = D3O, K)

This paper reports a full three-directional (XYZ) polarisation analysis study of the short- and long-range order in D3OFe3(SO4)(2)(OD)(6) and KFe3(SO4)(2)(OD)(6) performed on the D7 Diffractometer at the ILL. Both compounds belong to the jarosite family of minerals. The Fe3+ ions in these materials are arranged in a two-dimensional kagome lattice which exhibits, in the case of antiferromagnetic superexchange, a strong geometric frustration. Only short-range magnetic correlations down to 1.5 K have been observed in the D3O salt, in contrast to the successive long-range magnetic ordering transitions seen in the K salt at T-N1 approximate to 65 K and T-N2 approximate to 50 K, respectively. The diffuse scattering observed in the deuteronium salt is compared with the theoretical predictions for the magnetic structure factor for a kagome lattice with the nearest-neighbour antiferromagnetic exchange. (C) 1999 Elsevier Science B.V. All rights reserved.