Localized spin wave states in an anisotropic exchange ferromagnet

The localized spin wave states in a linear chain of anisotropic exchange ferromagnet with a substitutional ferromagnetic impurity spin are investigated exactly. Both the cases of an isotropic and anisotropic impurity-host exchange interaction are studied. We calculate the energies and wave functions of localized spin wave modes. Two types of localized s modes above the top of spin wave band are obtained in the anisotropic exchange impurity case. The appearance of these s modes is characteristic of the present system. Hole modes which appear in the gap are also discussed.