Percolation theory and the critical concentration of a dilute Heisenberg ferromagnet

Abstract

A variational calculation by Murray (see abstrs. A34684 and A34685 of 1966) on spin waves in a disordered ferromagnet is reviewed, shown to contain two errors and corrected. Murray had reached the conclusion that the critical concentration of magnetic atoms obtained by this method was in disagreement with the results of classical percolation theory. By correcting the errors in Murray's calculation the conclusion is reached that her method cannot given an accurate estimate for the critical concentration.