Magnetic soft x-ray tomography of magnetic Swiss roll architectures

A further increase in performance of state-of-the-art spin-electronics can be achieved by either miniaturizing its functional components or harnessing the third dimension. The first route, however, faces physical limitations as properties of nanostructures and their response to external stimuli can drastically change in reduced dimensions. An alternative way is to go from planar 2D structures to 3D architectures. Such 3D functional elements can be obtained for example by rolling up initially planar strained thin films into Swiss roll like objects with multiple windings. A major advantage of this technology platform is the possibility to fabricate compact multifunctional 3D architectures with film qualities similar to those of planar systems and peculiar properties only occurring in hollow cylindrical objects. Their magnetic properties are generally characterized by integral techniques, such as ferromagnetic resonance, magneto-robotic probing, anisotropic magneto-impedance/magnetoresistance and cantilever magnetometry, or Kerr and x-ray microscopies. However, the underlying microscopic magnetization configuration can in general not be retrieved by such means. While already established magnetic neutron tomography and electron holography may be applied to probe either microscopic or nanoscopic samples, a technique that provides direct access to the magnetization of 3D-shaped mesoscopic objects with nanometer spatial resolution of the magnetic contrast is highly demanded but not yet developed. Here, we put forth the approach of tomographic imaging of magnetization configurations in 3D-shaped objects relying on x-ray magnetic circular dichroism (XMCD) as element-specific contrast mechanism. A reconstruction of an arbitrary magnetization would require acquiring projections along three orthogonal rotation axes. To minimize experimental affords while exploring the capability of magnetic soft x-ray tomography, we constrain our study to Swiss roll architectures with either i- -plane or out-of-plane magnetic anisotropy that demand recording a set of 2D images of the magnetic patterns taken at different angles along a single rotation axis.