Coherent potential method for a Heisenberg ferromagnet with nonmagnetic impurities

The Heisenberg model at low temperatures and with nonmagnetic substitutional impurities is investigated. The coherent potential method and the properties of a percolation cluster are used. The proposed method of making the solutions self-consistent creates a unified theoretical scheme in which expressions can be obtained for the stiffness coefficient of the spin waves and for the magnetization both at low impurity concentrations and nearly critical concentrations. The region of applicability of the obtained expressions is investigated.