Three-dimensional tomographic imaging of the magnetization vector field using Fourier transform holography

In recent years, interest in expanding from 2D to 3D systems has grown in the magnetism community, from exploring new geometries to broadening the knowledge on the magnetic textures present in thick samples, and with this arise the need for new characterization techniques, in particular tomographic imaging. Here, we present a new tomographic technique based on Fourier transform holography, a lensless imaging technique that uses a known reference in the sample to retrieve the object of interest from its diffraction pattern in one single step of calculation, overcoming the phase problem inherent to reciprocal-space-based techniques. Moreover, by exploiting the phase contrast instead of the absorption contrast, thicker samples can be investigated. We obtain a 3D full-vectorial image of a 800 nm-thick extended Fe/Gd multilayer in a 5$\mu$m-diameter circular field of view with a resolution of approximately 80 nm. The 3D image reveals worm-like domains with magnetization pointing mostly out of plane near the surface of the sample but that falls in-plane near the substrate. Since the FTH setup is fairly simple, it allows modifying the sample environment. Therefore, this technique could enable in particular a 3D view of the magnetic configuration's response to an external magnetic field.