Three-dimensional magnetization structures revealed with X-ray vector nanotomography
Three-dimensional magnetization structures revealed with X-ray vector nanotomography
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DOI：
10.1038/nature23006
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发表时间：
2017-07-20
期刊：
影响因子：
64.8
通讯作者：
Heyderman, Laura J.
中科院分区：
文献类型：
--
作者：
Donnelly, Claire;Guizar-Sicairos, Manuel;Heyderman, Laura J.
在软铁磁材料中，平滑变化的磁化导致基本图案的形成，例如畴、涡旋和畴壁（1）。这些已经在厚度高达约200纳米的薄膜中进行了广泛的研究，其中磁化可以通过使用电子或软X射线的当前透射成像方法获得。然而，在较厚的样品中，磁化结构在整个厚度上变化，本质上是三维的，直接确定复杂的磁性结构仍然是一个挑战（1，3）。我们已经开发了硬X射线矢量纳米断层扫描，以确定在纳米尺度内的微米尺寸的样品的三维磁配置。我们成像的磁化结构内的直径为5微米的软磁柱的空间分辨率为100纳米，并在散装，观察到一个复杂的磁性配置，包括形成交叉结壁和涡旋壁沿着相交平面的涡旋和反涡旋。在这些结构的交叉点，磁奇点-布洛赫点-发生。这些现象在50多年前就被预测到了（4），但迄今为止还没有被直接观测到。在这里，我们对布洛赫点附近的三维磁结构进行成像，到目前为止，只有通过微磁模拟才能访问该三维磁结构，并确定两种可能的磁化结构：循环磁化结构（5）和扭曲状态，似乎对应于“反布洛赫点”。我们的成像方法使得能够在数十微米量级的系统中对拓扑磁性结构进行纳米级研究。内部纳米磁性纹理的知识对于理解宏观磁性和设计用于技术应用的块状磁体至关重要（7）。
In soft ferromagnetic materials, the smoothly varying magnetization leads to the formation of fundamental patterns such as domains, vortices and domain walls(1). These have been studied extensively in thin films of thicknesses up to around 200 nanometres, in which the magnetization is accessible with current transmission imaging methods that make use of electrons or soft X-rays. In thicker samples, however, in which the magnetization structure varies throughout the thickness and is intrinsically three dimensional, determining the complex magnetic structure directly still represents a challenge(1,3). We have developed hard-X-ray vector nanotomography with which to determine the three-dimensional magnetic configuration at the nanoscale within micrometre-sized samples. We imaged the structure of the magnetization within a soft magnetic pillar of diameter 5 micrometres with a spatial resolution of 100 nanometres and, within the bulk, observed a complex magnetic configuration that consists of vortices and antivortices that form cross-tie walls and vortex walls along intersecting planes. At the intersections of these structures, magnetic singularities-Bloch points-occur. These were predicted more than fifty years ago(4) but have so far not been directly observed. Here we image the three-dimensional magnetic structure in the vicinity of the Bloch points, which until now has been accessible only through micromagnetic simulations, and identify two possible magnetization configurations: a circulating magnetization structure(5) and a twisted state that appears to correspond to an 'anti-Bloch point'. Our imaging method enables the nanoscale study of topological magnetic structures(6) in systems with sizes of the order of tens of micrometres. Knowledge of internal nanomagnetic textures is critical for understanding macroscopic magnetic properties and for designing bulk magnets for technological applications(7).