Long-range order induced by diamagnetic dilution of jarosites, model Kagome antiferromagnets

Members of the jarosite mineral family AFe(3)(OH)(6)(SO4)(2), where A is usually a univalent cation, possess a highly frustrated Kagome lattice of antiferromagnetically coupled S = 5/2 Heisenberg moments. All the members of the family show long-range magnetic order below T-N congruent to 55 K except for the hydronium salt (A = H3O) which displays a spin-glasslike transition at T-f congruent to 15 K. The only clear difference between the two sets of materials is that all the salts except for hydronium salt have a strong tendency to lose iron atoms from the structure when it is synthesised. When 11% of the magnetic sites are removed or replaced with diamagnetic ions in the diluted salt (D3O)Fe3-xAlx(OD)(6)(SO4)(2), T-f rises to 25.5 K and powder neutron diffraction reveals both short-and long-range magnetic correlations at 1.4 K. (C) 1998 Elsevier Science B.V. All rights reserved.