November 07, 2022
Minneapolis, United States
Revealing 3D Magnetic Textures in [Pt/Co/Cu]15 Multilayers by Coherent X ray Imaging with 5 nm Resolution
In the fields of magnetism and spintronics, magnetic multilayers continue to thrive as pivotal structures to functionalize magnetic interactions, including the interfacial Dzyaloshinskii-Moriya interaction (DMI), and to engineer complex non-trivial spin textures 1-3. However, previous research has focused almost exclusively on 2D structures. The challenge in studying 3D textures is in obtaining the necessary spatial resolution and sensitivity to resolve them. Here we show that this challenge can be met by reference-aided coherent diffractive x-ray imaging combining the robust Fourier Transform Holography with phase retrieval algorithms 4,5. Based on this amplified wide-angle scattering, we achieve 5 nm spatial resolution for spin textures in Pt/Co/Cu magnetic multilayers, which allows us to clearly resolve fine domain walls (Fig.1c). Surprisingly, while conventional low-resolution images only show the well-known stripe domain state characteristic of such multilayers, our high-resolution images additionally reveal several small, mostly circular features of much weaker contrast (Fig. 1a,b), indicating a reduced net magnetization in the out-of-plane direction. Interestingly, while these features are clearly magnetic in nature and interact with the domain walls, they do not annihilate at the largest fields available in our system (220 mT). We associate the features to a localized increased surface roughness, leading to a local loss of perpendicular magnetic anisotropy promoting in-plane spin alignment and of 3D magnetic textures.