Point defect states of exchange spin waves in all-ferromagnetic two-dimensional magnonic crystals

Abstract

Using the plane-wave expansion method under supercell approximation, band structures of exchange spin waves propagating in all-ferromagnetic two-dimensional magnonic crystals with point defects are calculated. The results indicate that the point defects in these structures can create localized states inside the bandgap. The characteristics and the magnetization distributions of these localized states are studied. The results show that the group velocities of the localized states almostequal zero in the whole first Brillouin zone, and numbers of localized states and their frequency-positions in the bandgap are related to the size of the point defect. Magnonic crystalswith such defect states can be used as fabricating materials of narrow bandpass spin-wave filters.