Spin Dynamics near the Magnetic Percolation Threshold

Abstract

An inelastic neutron-scattering study of spin relaxation in the dilute, two-dimensional Ising antiferromagnet ${\mathrm{Rb}}_{2}{\mathrm{Co}}_{c}{\mathrm{Mg}}_{1\ensuremath{-}c}{\mathrm{F}}_{4}$ has been carried out for $c$ very close to the magnetic percolation threshold ${c}_{p}=0.593$. The dynamical exponent $z$ relating the order-parameter relaxation rate to the magnetic correlation length is found to be ${2.4}_{\ensuremath{-}0.1}^{+0.2}$. It is argued that $z$ has this anomalously high value because of the fractal geometry of percolating networks.