薄铁磁性纳米条带中携带横向轨道角动量的自旋波

Spin Waves Carrying Transverse Orbital Angular Momentum in Thin Ferromagnetic Nanostrips

摘要: 自旋波是铁磁材料中有序排列的磁矩受到激发而产生的集体运动。涡旋自旋波携带轨道角动量，它的等相位面呈螺旋状。由于轨道角动量方向平行于波矢量的平均方向，因此涡旋自旋波携带的是纵向轨道角动量。本文报道在铁磁性纳米条带中携带横向轨道角动量的自旋波。我们设置纳米带磁矩的初始方向沿其长轴方向，然后在与长轴垂直的平面内施加摆动的脉冲磁场，通过快速傅里叶变换对动态磁矩进行分析，得到自旋波的本征频谱。随后用反傅里叶变换得到了自旋波的模态，我们还研究了摆动场的角度变化范围、摆动场所在平面的方向以及纳米带厚度对微磁模拟结果的影响，还讨论了两列携带横向轨道角动量的自旋波的干涉现象。

Abstract: Spin wave is the collective magnetization oscillation of ferromagnes. Twisted spin waves carry orbital angular momentum, which is characterized with spiral wave front. The orbital angular momentum of twisted spin waves is parallel to the average direction of the wave vector. Therefore, the orbital angular momentum is called longitudinal. Here, we report spin waves carrying transverse orbital angular momentum in ferromagnetic nanostrips. The initial magnetization is uniformly along the long axis of the nanostrip. Then a pulse field, swinging in the plane perpendicular to the long axis of the nanostrip, is applied to the sample. After fast Fourier analysis on the dynamic magnetization oscillation, the spectrum of spin wave mode is obtained. Subsequent inverse fast Fourier analysis obtains the spatial distribution of the spin wave modes. The influences of the swing angle, direction of the plane hosting the swing field and thickness of the nanostrip are also taken into consideration. We also studied the interference of two spin waves carrying transverse orbital angular momentum.