Laser-driven non-local electron dynamics in ultrathin magnetic samples on a sub-10 nm length scale is a key process in ultrafast magnetism. However, the experimental access has been challenging due to the nanoscopic and femtosecond nature of such transport processes. Here, we present a scattering-based experiment relying on a laser-induced electro- and magneto-optical grating in a Co/Pd ferromagnetic multilayer as a new technique to investigate non-local magnetization dynamics on nanometer length and femtosecond timescales. We induce a spatially modulated excitation pattern using tailored Al near-field masks with varying periodicities on a nanometer length scale and measure the first four diffraction orders in an x-ray scattering experiment with magnetic circular dichroism contrast at the free-electron laser facility FERMI, Trieste. The design of the periodic excitation mask leads to a strongly enhanced and characteristic transient scattering response allowing for sub-wavelength in-plane sensitivity for magnetic structures. In conjunction with scattering simulations, the experiment allows us to infer that a potential ultrafast lateral expansion of the initially excited regions of the magnetic film mediated by hot-electron transport and spin transport remains confined to below three nanometers.

中文翻译：

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纳米尺度的瞬态磁性光栅

低于10 nm长度尺度的超薄磁性样品中的激光驱动非局部电子动力学是超快磁性的关键过程。然而，由于这种传输过程的纳米级和飞秒性质，实验访问一直具有挑战性。在这里，我们提出了一种基于散射的实验，该实验依赖于Co / Pd铁磁多层膜中的激光感应电光和磁光光栅，作为研究纳米长度和飞秒时标上的非局部磁化动力学的新技术。我们使用量身定制的Al近场掩模在纳米级尺度上以变化的周期来诱导空间调制的激发图案，并在自由电子激光设备FERMI上利用磁圆二色性对比在X射线散射实验中测量前四个衍射级，的里雅斯特。周期性激励掩模的设计导致了强烈增强的特征瞬态散射响应，从而为磁性结构提供了亚波长面内灵敏度。结合散射模拟，该实验使我们可以推断出，由热电子传输和自旋传输介导的磁性膜初始受激区域的潜在超快横向扩展仍被限制在3纳米以下。