Spin wave dynamics in non-trivial magnetic geometries

Magnonics is the study of spin waves: magnetic disturbances propagating in a magnetic material. Magnons are quantum mechanical quasi-particles of the spin waves. Recently, magnonic devices are attracting much attention from researchers as a newly emerging data transport system. Compared to conventional electronic data transport systems, magnon based systems have the following advantages: high energy efficiency, wave based computation system, broad frequency range and small device size.

To control spin waves, it is important to study their behaviors in various structures. In this paper, we first show dynamics of spin waves in magnonic crystals: semi-infinite structures with periodically varying properties. The periodicity introduces band gaps into spin wave dispersion relations and provides information regarding the ranges of frequency that spin waves are allowed to be excited. Secondly, we investigate finite magnetic structures. Unlike infinite structures, the finite structures may have complicated boundary conditions which can be difficult to analyze with analytical calculations. Here, we employ numerical simulations to depict spin wave excitations near the boundaries of the finite structures. Finally, we demonstrate topological properties of the magnonic crystals. Topological band theories explain how bulk properties are related to the topo-logically protected localized excitations. These edge excitations are insensitive to certain crystal imperfections such as defects. Here, we describe the magnonic crystal band topology using both analytical calculations and numerical simulations. We anticipate that the results provide further understanding of the spin wave dynamics in different geometries, and suggest future applications of magnons in data transport systems.