Understanding the fundamental dynamics of topological vortex and antivortex naturally formed in microscale/nanoscale ferromagnetic building blocks under external perturbations is crucial to magnetic vortex-based information processing and spintronic devices. All previous studies have focused on magnetic vortex-core switching via external magnetic fields, spin-polarized currents, or spin waves, which have largely prohibited the investigation of novel spin configurations that could emerge from the ground states in ferromagnetic disks and their underlying dynamics. We report in situ visualization of femtosecond laser quenching-induced magnetic vortex changes in various symmetric ferromagnetic Permalloy disks by using Lorentz phase imaging of four-dimensional electron microscopy that enables in situ laser excitation. Besides the switching of magnetic vortex chirality and polarity, we observed with distinct occurrence frequencies a plenitude of complex magnetic structures that have never been observed by magnetic field- or current-assisted switching. These complex magnetic structures consist of a number of newly created topological magnetic defects (vortex and antivortex) strictly conserving the topological winding number, demonstrating the direct impact of topological invariants on magnetization dynamics in ferromagnetic disks. Their spin configurations show mirror or rotation symmetry due to the geometrical confinement of the disks. Combined micromagnetic simulations with the experimental observations reveal the underlying magnetization dynamics and formation mechanism of the optical quenching-induced complex magnetic structures. Their distinct occurrence rates are pertinent to their formation-growth energetics and pinning effects at the disk edge. On the basis of these findings, we propose a paradigm of optical quenching-assisted fast switching of vortex cores for the control of magnetic vortex-based information recording and spintronic devices.

中文翻译：

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通过洛伦兹电子显微镜原位可视化磁涡旋的光学操纵。


了解在外部扰动下微尺度/纳米尺度铁磁构件中自然形成的拓扑涡旋和反涡旋的基本动力学对于基于磁涡旋的信息处理和自旋电子器件至关重要。之前的所有研究都集中在通过外部磁场、自旋极化电流或自旋波进行磁涡核切换，这在很大程度上阻碍了对铁磁盘基态可能出现的新型自旋构型及其潜在动力学的研究。我们通过使用能够实现原位激光激发的四维电子显微镜洛伦兹相位成像，报告了各种对称铁磁坡莫合金盘中飞秒激光淬火引起的磁涡流变化的原位可视化。除了磁涡旋手性和极性的切换之外，我们还以不同的发生频率观察到大量复杂的磁性结构，这些结构从未通过磁场或电流辅助切换观察到。这些复杂的磁结构由许多新创建的拓扑磁缺陷（涡流和反涡流）组成，严格守恒拓扑绕数，证明了拓扑不变量对铁磁盘磁化动力学的直接影响。由于圆盘的几何限制，它们的自旋构型表现出镜像或旋转对称性。微磁模拟与实验观察相结合，揭示了光猝灭引起的复杂磁结构的潜在磁化动力学和形成机制。它们独特的发生率与其形成生长能量学和盘边缘的钉扎效应有关。 基于这些发现，我们提出了一种光学猝灭辅助涡核快速切换的范例，用于控制基于磁涡旋的信息记录和自旋电子器件。