Three-dimensional imaging of ferromagnetic vortex cores and singularities

Magnetic vortices appear even in ferromagnetic films thin enough to behave as 2D samples. In such cases, a winding pattern of in-plane magnetization surrounds a perpendicular core, whose extent is typically a few nanometers. If the film thickness increases, transmission measurements seem to indicate that the core diameter always remain below ca. 100 nm; on the other hand, simulations hint at a more complex, 3D structure reminiscent of a barrel. We propose to image vortex cores (VCs) using magnetic coherent diffraction imaging (CDI) on micron-sized CoGd beads. In these systems, we have confirmed the presence of vortices with Magnetic Force Microscopy as well as XMCD-PEEM, with VCs over 200 nm in diameter from MFM. Thus, for the first time in 3D magnetic imaging, the resolution would be sufficient to reveal the full structure of such a 3D vortex configuration. Moreover, prior sample demagnetization should promote the presence of micromagnetic singularities (Bloch points) in the cores.