Interference Effect between Two Impurity Spins in a Heisenberg Ferromagnet

Abstract

A general and exact theory for the spin wave impurity states associated with two substitutional ferromagnetic impurity spins in a Heisenberg ferromagnet with nearest neighbor exchange interactions only is developed at absolute zero temperature. All possible cases regarding the relative position of the two impurity spins are considered. It is found that the interference effect between the two impurity spins on the in-band spin wave impurity states in the one-dimensional case dose remain even for the infinitely large impurity separation, whereas the effect on the localized spin wave states in this case becomes vanishingly small as the impurity separation becomes large. A brief discussion concerning the interference effect on the spin wave impurity states in the two- and three-dimensional cases is also given.