3D quantification of Skyrmion properties in device-related structures
Funding period: 2018 - 2021

Magnetic skyrmions are stable topological defects with a complex non-coplanar spin structure which distinguishes them from magnetic domain walls and vortices. Low critical electric currents are needed to set skyrmions into motion and the stability of these nanosized solitons opened a new active field of research - skyrmionics, which has the goal to use skyrmions as information bits in data storage and to perform logical operations by moving them in magnetic nanostructures.
The concept has transformed our approach to spintronics because it provides an example of how nanometer scale magnetic inhomogeneities may address fundamental challenges of high data rate, low energy electronics for information technologies. Recent advances in skyrmionics depend upon the ability to build a fundamental understanding of the full 3D spin texture including its coupling to surfaces and interfaces. Unlike homogeneous bulk materials, device-related skyrmionic structures will usually be nanoscopically small, laterally and/or vertically heterogeneously composed of different elements and materials and exhibit arbitrary, complex structures including local confinements, surfaces, and interfaces.
As a consequence, the details of the 3D magnetic texture of the skyrmions, determining the stability and dynamics of the skyrmion state in such device-related structures, is currently unknown, which is mainly due to the lack of tomographic magnetic imaging techniques facilitating the reconstruction of all three Cartesian components of the magnetic field within a skyrmion state.
Within this project, we seek to develop a hitherto not available high-resolution 3D mapping technique of skyrmionics spin textures, addressing several technological and conceptual challenges. More specifically, we first extend single-tilt-axis Electron Holographic Tomography of one in-plane component of the magnetic field B in thin films to be applicable under cryogenic conditions including the application of a rotationable external magnetic field. In a second approach, we further develop Electron-energy-loss Magnetic Chiral Dichroism (EMCD) to measure the out-of-plane component of the magnetization in skyrmionic thin films.
Finally, we will employ these techniques in combination with micro-nmagnetic modelling to characterize the influence of these device-related boundary conditions on the 3D skyrmion structure in several systems. We anticipate new discoveries emerging in the course or as a direct consequence of this project, such as the Bloch-Néel character mixing in surface layers of FeGe thin films as found in preparation to this project. Here, due to the characteristic difference in how the spin-transfer-torque and the spin-Hall-effect affect Bloch and Néel skyrmions, respectively, we anticipate a deliberate manipulation of the drift velocity and direction of skyrmions via engineering the topography of thin films.