Localized magnetic excitations of coupled impurities in a Heisenberg ferromagnet: Optical defect modes

► A Green's function method is used to obtain the spectrum of excitations of two neighboring impurities in a semi-infinite ferromagnet. ► The equations of motion for Green's functions are determined in the framework of the Heisenberg model. ► The energies of non-resonant localized modes are calculated as a function of the interaction parameters for the exchange coupling between impurity-spin pairs, host-spin pairs, and impurity-host neighbors, as well as the effective field parameter at the impurity sites.