Model-Based Iterative Reconstruction of Three-Dimensional Magnetization in a Nanowire Structure Using Electron Holographic Vector Field Tomography

Experimental techniques for the characterization of three-dimensional (3D) magnetic spin structures are required to advance the performance of nanoscale magnetic technologies. However, as component dimensions approach the nanometer range, it becomes ever more challenging to analyze 3D magnetic configurations quantitatively with the required spatial resolution and sensitivity. Here, we use off-axis electron holography and model-based iterative reconstruction to reconstruct the 3D magnetization distribution in an exemplary nanostructure comprising an L-shaped ferromagnetic cobalt nanowire fabricated using focused electron beam induced deposition. Our approach involves using off-axis electron holography to record tomographic tilt series of electron holograms, which are analyzed to reconstruct electron optical magnetic phase shifts about two axes with tilts of up to ±60∘. A 3D magnetization vector field that provides the best fit to the tomographic phase measurements is then reconstructed, revealing multiple magnetic domains in the nanowire. The reconstructed magnetization is shown to be accurate for magnetic domains that are larger than approximately 50 nm. Higher spatial resolution and improved signal-to-noise can be achieved in the future by using more specialized electron microscopes, improved reconstruction algorithms, and automation of data acquisition and analysis.