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

在磁性系统中，当温度低于临界温度时，存在旋转对称性的破坏，导致磁矩的磁刚度。因为系统抵抗局部扭转磁化，但不抵抗均匀扭转，所以它们具有低能量自旋波激发。因此，自旋波是在磁性材料的有序中传播的扰动。 它们通过实验方法观察到，如：非弹性中子散射，非弹性光散射（布里渊散射，拉曼散射和非弹性X射线散射）等。从实践的角度来看，磁性材料的特征自旋波的最低频率的倒数给出了基于该材料和其他约束（如几何形状和杂质的存在）的器件切换的时间尺度。几何形状和杂质对低维磁性结构的影响的基本理解对于确定它们在高频纳米结构器件和开关等方面的潜力以及理解基础科学和内在材料特性非常重要。例如，薄磁膜具有影响其电子特性的杂质。 因此，操纵这些杂质可以在这些材料中带来新的物理性质的可能性。另一个实验上可行的操纵是磁结构的几何形状。在平面三层磁结构中发现并研究了几个重要现象。然而，在圆柱形几何中的三层结构的研究并不多。低维磁系统的这两个方面（杂质和几何形状）将在本研究项目中进行研究。本研究的理论方法包括多体理论、经典电磁学和蒙特卡罗模拟。非磁性系统，例如碳基材料，也受到杂质和几何约束的影响。因此，调整为磁系统开发的理论模型对于更好地理解这些系统是非常有意义的。这是本提案将涵盖的另一个方面。

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.