Kent Noah, Reynolds Neal, Raftrey David, Campbell Ian T G, Virasawmy Selven, Dhuey Scott, Chopdekar Rajesh V, Hierro-Rodriguez Aurelio, Sorrentino Andrea, Pereiro Eva, Ferrer Salvador, Hellman Frances, Sutcliffe Paul, Fischer Peter
Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
Physics Department, UC Santa Cruz, Santa Cruz, CA, USA.
Nat Commun. 2021 Mar 10;12(1):1562. doi: 10.1038/s41467-021-21846-5.
Among topological solitons, magnetic skyrmions are two-dimensional particle-like objects with a continuous winding of the magnetization, and magnetic Hopfions are three-dimensional objects that can be formed from a closed loop of twisted skyrmion strings. Theoretical models suggest that magnetic Hopfions can be stabilized in frustrated or chiral magnetic systems, and target skymions can be transformed into Hopfions by adapting their perpendicular magnetic anisotropy, but their experimental verification has been elusive so far. Here, we present an experimental study of magnetic Hopfions that are created in Ir/Co/Pt multilayers shaped into nanoscale disks, known to host target skyrmions. To characterize three-dimensional spin textures that distinguish Hopfions from target skyrmions magnetic images are recorded with surface-sensitive X-ray photoemission electron microscopy and bulk-sensitive soft X-ray transmission microscopy using element-specific X-ray magnetic circular dichroism effects as magnetic contrast. These results could stimulate further investigations of Hopfions and their potential application in three-dimensional spintronics devices.
在拓扑孤子中，磁斯格明子是二维粒子状物体，其磁化强度呈连续缠绕，而磁霍普费子是三维物体，可由扭曲的斯格明子弦的闭环形成。理论模型表明，磁霍普费子可在受挫或手性磁系统中稳定存在，通过调整其垂直磁各向异性，目标斯格明子可转变为霍普费子，但迄今为止其实验验证一直难以实现。在此，我们展示了对在形成为纳米级圆盘的Ir/Co/Pt多层膜中产生的磁霍普费子的实验研究，已知该多层膜中存在目标斯格明子。为了表征区分霍普费子与目标斯格明子的三维自旋纹理，使用元素特异性X射线磁圆二色性效应作为磁对比度，通过表面敏感的X射线光电子发射电子显微镜和体敏感的软X射线透射显微镜记录磁图像。这些结果可能会激发对霍普费子及其在三维自旋电子器件中潜在应用的进一步研究。
