铁磁性纳米圆柱中携带轨道角动量的自旋波的激发和传播

Excitation and Propagation of Spin Waves with Orbital Angular Momentum in Ferromagnetic Nano-Cylinder

摘要: 铁磁材料中有序磁性排列的磁矩受到激发而产生的集体运动，称为自旋波。而在传播过程中不仅具有动量，还具有轨道角动量的自旋波称为涡旋自旋波。涡旋自旋波在传播过程中它的等相位面沿着传播轴扭转，呈现出呈螺旋状的波阵面，表明涡旋自旋波带有轨道角动量。本文采用微磁学模拟方法研究涡旋自旋波在坡莫合金纳米圆柱中涡旋自旋波的激发和传播。研究了在铁磁纳米圆柱中的涡旋自旋波的本征模式，通过在纳米圆柱底部施加一个朝着x方向的sinc函数脉冲磁场，再利用快速傅里叶变换对动态磁矩分量平均值＜m_x＞进行分析，得到拓扑荷数l = 1的涡旋自旋波的本征频谱，最后利用反傅里叶变换得到涡旋自旋波的模态。并且，利用施加一个面内的旋转场，可以激发出拓扑荷数l = 1的涡旋自旋波。

Abstract: When the magnetic moment lined order in the magnetic materials generates collective movement, we call this phenomenon as spin wave. The spin wave that not only has momentum but also has orbital angular momentum in the propagation process is called twisted spin wave. Different from the plane wave, twisted spin wave will twist alone the central axis during its propagating. Finally, the twisted spin wave will distribute in spiral way, meanwhile the spin wave always possesses angular momentum. This paper studies eigenmodes of twisted spin waves in ferromagnetic nanocylinder; through applying a sinc pulse magnetic field in the bottom of the nanocylinder and using FFT, analyzes the component of dynamic magnetic moment; and gets the resonant spectrum of twisted spin waves. Then we use inverse Fast Fourier Transform to acquire the mode of twisted spin wave with l = 1. Moreover, by applying an in-plane rotating field, a twisted spin wave with topological charge l = 1 can be excited.