Time-resolved x-ray microscopy is used in a low-alpha synchrotron operation mode to image spin dynamics at an unprecedented combination of temporal and spatial resolution. Thereby, nanoscale spin waves with wavelengths down to 70 nm and frequencies up to 30 GHz are directly observed in ferromagnetic thin film microelements with spin vortex ground states. In an antiparallel ferromagnetic bilayer system, we detect the propagation of both optic and acoustic modes, the latter exhibiting even a strong non-reciprocity. In single-layer systems, quasi-uniform spin waves are observed together with modes of higher order (up to the 4th order), bearing precessional nodes over the thickness of the film. Furthermore, the effects of magnetic material properties, film thickness, and magnetic fields on the spin-wave spectrum are determined experimentally. Our experimental results are consistent with numerical calculations from a micromagnetic theory even on these so-far unexplored time- and length scales.

中文翻译：

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使用低 α 同步加速器操作在多 GHz 频率下对纳米级自旋波动力学进行时间分辨 X 射线成像


时间分辨 X 射线显微镜用于低 α 同步加速器操作模式，以前所未有的时间和空间分辨率组合对自旋动力学进行成像。因此，在具有自旋涡旋基态的铁磁薄膜微元件中可以直接观察到波长低至 70 nm、频率高达 30 GHz 的纳米级自旋波。在反平行铁磁双层系统中，我们检测到光学和声学模式的传播，后者甚至表现出很强的非互易性。在单层系统中，观察到准均匀的自旋波与高阶模式（最高 4 阶）一起出现，在薄膜厚度上承载进动节点。此外，通过实验确定了磁性材料特性、薄膜厚度和磁场对自旋波谱的影响。我们的实验结果与微磁理论的数值计算一致，即使在这些迄今为止尚未探索的时间和长度尺度上也是如此。