Transfer-matrix approach to elementary excitations in semi-infinite ferromagnetic superlattice with impurity cell

摘要

A transfer matrix formalism is employed to study the occurrence of the localized modes associated with an impurity cell embedded within a semi-infinite Heisenberg ferromagnetic superlattice with nearest-neighbor exchange interactions. The cell is at arbitrary distance from the deformed surface cell. We find that, in addition to bulk spin waves, there may arise localized modes associated both with the impurity cell and with the surface. Two situations were analyzed numerically: impurity is close to the surface and the impurity is practically in the bulk region. The modes influence each other when the impurity cell is near the surface, modifying spin wave energies.