Spin wave theory for low-dimensional magnetic systems and excitations in non-magnetic systems

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In magnetic systems when the temperature is lowered below the critical one there is a breaking of rotational symmetry leading to a magnetic stiffness of the magnetic moments. Because the systems resist twisting the magnetization locally, but don't resist a uniform twist, they have low energy spin wave excitations. Therefore, spin waves are propagating disturbances in the ordering of magnetic materials. They are observed through experimental methods like: inelastic neutron scattering, inelastic light scattering (Brillouin scattering, Raman scattering and inelastic X-ray scattering), and others. From the practical point of view, the reciprocal of the lowest frequency of the characteristic spin waves of a magnetic material gives a time scale for the switching of a device based on that material and other constraints like geometry and presence of impurities. A fundamental understanding of the effect of geometry and impurities on low-dimensional magnetic structures is important for identifying their potential for e.g. high-frequency nanostructure devices and switches, as well as for an understanding of the basic science and the intrinsic materials properties. For example, thin magnetic films have impurities that affect their electronic properties. Therefore manipulating these impurities can bring the possibility of new physical properties in these materials. Another experimentally feasible manipulation is the geometry of the magnetic structures. Several important phenomena have been detected and studied in planar trilayer magnetic structures. However, there are not many studies of trilayers in a cylindrical geometry. These two aspects of the low-dimensional magnetic system (impurities and geometry) will be investigated in this research project. The theoretical methods for this study include many body theory, classical electromagnetism, and Monte Carlo simulations. Non-magnetic systems, like for example carbon based materials, are also affected by impurities and geometry constraints. Therefore, to adapt the theoretical models developed for the magnetic systems is of great interest to better understand these systems. This is another aspect that will be covered by this proposal.