Soft x-ray 3D imaging of dipole-stabilized magnetic skyrmions in FeGd thin films*

Topologically stabilized spin structures such as magnetic skyrmions are promising platforms for efficient next-generation technologies including spintronics and low-energy data transport and storage. However, their small size, low-contrast, required fields, and complex textures make them difficult to image directly in three dimensions (3D). In this work we use specially designed FeGd multilayer thin films in which skyrmions are dipole stabilized and exist within the material for extended periods of time (weeks or even months) at room temperature and with no applied field. This creates an additional imaging challenge, however, as the thin-film nature of the sample means that there is only a low-contrast magnetic scatter signal. We therefore extended a soft x-ray vector ptychotomography technique we developed to a system with only magnetic contrast. By combining resonant x-ray magnetic circular dichroism (XMCD) to provide magnetic sensitivity, ptychography for diffraction-limited imaging with phase contrast which is ideal for low-contrast materials, and tomography, we generate full 3D images of dipole stabilized skyrmions at room temperature and with zero applied magnetic field.