Properties Of Defect States In Two-dimensional Magnonic Crystals With Bend Line Defects

Due to the rapid progress of the fabricating technology for artificial micro- and nano-structure, some periodic nanostructure composite materials have been produced, such as semiconductor lattice, photonic crystal and phonon crystals. These composite materials have some special properties which can not be found in the natural crystals, and so they have been widely used as the production. These artificial composite materials will put the research into a new field of materials science, and they will provide more effective help for live and work.Magnonic crystal is a new artificial micro- or nano-composite system after phononic crystals and photonic crystal, and it is a periodic structure composed of two kinds of ferromagnetic materials. Spin waves propagating in the magnonic crystal can be modulated by the periodic structure, and so the band gaps will be generated, and the spin wave locating in the gap can not propagate through the magnonic crystal. Furthermore, if defect states would be introduced into magnonic crystals, the gaps can be designed according to different requirements, and then the propagation of spin waves can be controlled, which is very interesting to the investigation of magnonic gaps. According to these characteristics of magnonic crystals, spin-wave waveguide, filter, signal processor, logical drive and others can be designed, and these will be valuable in the fields of digital communication, environment protection, and others.In this thesis, bend line defects are introduced into two-dimensional magnonic crystals at the first time. Band structures and field distributions of defect states in two-dimensional magnonic crystals composed of Fe circle rods embedded in EuO matrix are calculated by using the plane-wave expansion method under the supper-cell approximation. The results show that some defect states with non-zero slope can be generated in the gap, and the energies of spin waves are localized near the defect bodies. And so, spin waves of defect modes can propagate along the bend directions. Besides, the frequency position of defect states in gaps can be adjusted by changing the size of defect bodies. All of these properties of defect states will provide some helpful theoretical foundations.