Abstract
The question of localisation of spin wave states is considered in a dilute Heisenberg ferromagnet with nearest-neighbour exchange near the percolation threshold. Using a geometrical model of the percolating cluster introduced by de Gennes (1976) which assumes that it is connected by effectively one-dimensional chains, together with Dyson's solution (1953) for the properties of states on a disordered chain. The authors find that the mobility edge drops to zero energy as p to pc like exp(-A/(p-pc)xi 2/).