Department of Physics, University of California at San Diego, La Jolla, CA 92093, USA.
Proc Natl Acad Sci U S A. 2011 Aug 16;108(33):13393-8. doi: 10.1073/pnas.1104304108. Epub 2011 Aug 8.
Understanding electronic structure at the nanoscale is crucial to untangling fundamental physics puzzles such as phase separation and emergent behavior in complex magnetic oxides. Probes with the ability to see beyond surfaces on nanometer length and subpicosecond time scales can greatly enhance our understanding of these systems and will undoubtedly impact development of future information technologies. Polarized X-rays are an appealing choice of probe due to their penetrating power, elemental and magnetic specificity, and high spatial resolution. The resolution of traditional X-ray microscopes is limited by the nanometer precision required to fabricate X-ray optics. Here we present a novel approach to lensless imaging of an extended magnetic nanostructure, in which a scanned series of dichroic coherent diffraction patterns is recorded and numerically inverted to map its magnetic domain configuration. Unlike holographic methods, it does not require a reference wave or precision optics. In addition, it enables the imaging of samples with arbitrarily large spatial dimensions, at a spatial resolution limited solely by the coherent X-ray flux, wavelength, and stability of the sample with respect to the beam. It can readily be extended to nonmagnetic systems that exhibit circular or linear dichroism. We demonstrate this approach by imaging ferrimagnetic labyrinthine domains in a Gd/Fe multilayer with perpendicular anisotropy and follow the evolution of the domain structure through part of its magnetization hysteresis loop. This approach is scalable to imaging with diffraction-limited resolution, a prospect rapidly becoming a reality in view of the new generation of phenomenally brilliant X-ray sources.
理解纳米尺度的电子结构对于解决复杂磁性氧化物中相分离和涌现行为等基本物理难题至关重要。能够在纳米长度和亚皮秒时间尺度上超越表面的探针，可以极大地增强我们对这些系统的理解，并无疑会影响未来信息技术的发展。由于其穿透能力、元素和磁性特异性以及高空间分辨率，极化 X 射线是一种很有吸引力的探针选择。传统 X 射线显微镜的分辨率受到制造 X 射线光学器件所需的纳米精度的限制。在这里，我们提出了一种对扩展磁性纳米结构进行无透镜成像的新方法，其中记录并数值反转扫描的一系列二向色相干衍射图案，以绘制其磁畴结构。与全息方法不同，它不需要参考波或精密光学器件。此外，它可以对具有任意大空间尺寸的样品进行成像，其空间分辨率仅受相干 X 射线通量、波长以及样品相对于光束的稳定性限制。它可以很容易地扩展到具有圆二色性或线二色性的非磁性系统。我们通过对具有垂直各向异性的 Gd/Fe 多层膜中的亚铁磁迷宫畴进行成像来证明这种方法，并通过部分磁滞回线跟踪畴结构的演变。这种方法可以扩展到具有衍射极限分辨率的成像，鉴于新一代非凡明亮的 X 射线源，这一前景正在迅速成为现实。
