Neutron study of fracton excitations in percolating antiferromagnets

We report the results of an inelastic neutron scattering experiment on nearly percolating Heisenberg antiferromagnets (RbMncMg1-cF3), in which the Mn concentrations (c = 0.31, 0.34 and 0.39) are very close to the percolation threshold (c(p) = 0.312). A broad-peak superimposed on Ising-cluster excitations was observed throughout the Brillouin zone. The intensity of a broad peak increased on approaching the percolation threshold. The origin of this broad peak is attributed to the excitation of fractons in a percolating network. (C) 1998 Elsevier Science B.V. All rights reserved.