  The development and characterization of three-dimensional (3D) topological
magnetic textures has become an important topic in modern magnetism both for
fundamental and technological perspectives. Among the novel 3D spin textures,
skyrmionic cocoons have been successfully stabilized in magnetic multilayers
having a variable thickness of the ferromagnet in the vertical direction of the
stack. These ellipsoidal 3D magnetic textures remain vertically confined in a
fraction of the total thickness while coexisting with fully columnar skyrmions.
Here, we use X-ray holography with about 15 nm lateral resolution to
investigate how their properties depend on the field and temperature. We
observe circular objects with different amplitude of contrast which evidences
the presence of different 3D objects located in various vertical parts of the
multilayer. Moreover, we witness during out-of-plane cycling an attractive
interaction between cocoons located at various heights, mainly due to the stray
field, which impacts their horizontal positioning. The X-ray holography
measurements also allow to determine the size of the cocoons at remanence
which, at room temperature, possess diameter close to 100 nm in average.
Combining this transmission technique with magnetic force microscopy and
micromagnetic simulations gives a precise insight into the 3D distribution of
the magnetization which demonstrate the 3D nature of skyrmionic cocoons.

Mesoscale and Nanoscale Physics