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Optical manipulation of magnetic vortices visualized in situ by Lorentz electron microscopy

机译：洛伦兹电子显微镜原位可视化磁涡旋的光学操纵

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Understanding the fundamental dynamics of topological vortex and antivortex naturally formed in microscaleanoscale 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.
机译：理解在外部扰动下在微尺度/纳米尺度的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。以前的所有研究都集中于通过外部磁场，自旋极化电流或自旋波进行的磁涡旋-铁心切换，这在很大程度上阻止了对可能自铁磁盘基态及其潜在动力学中出现的新型自旋结构的研究。我们通过使用能够进行原位激光激发的四维电子显微镜的Lorentz相成像，报告了飞秒激光淬火引起的各种对称铁磁坡莫合金磁盘中磁涡旋变化的原位可视化。除了磁涡旋手性和极性的切换外，我们还观察到在不同的出现频率下，大量复杂的磁性结构从未被磁场或电流辅助切换所观察到。这些复杂的磁性结构由许多新创建的拓扑磁缺陷（涡旋和反涡旋）组成，这些缺陷严格保留了拓扑绕组数，证明了拓扑变量对铁磁盘磁化动力学的直接影响。由于磁盘的几何限制，它们的自旋配置显示镜像对称或旋转对称。将微磁模拟与实验观察相结合，揭示了光学猝灭诱导的复杂磁结构的潜在磁化动力学和形成机理。它们的不同发生率与它们在磁盘边缘的形成增长能量和钉扎效应有关。基于这些发现，我们提出了一种光学猝灭辅助涡芯快速切换的范例，用于控制基于磁涡的信息记录和自旋电子设备。

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