Agenda

Magnetic Skyrmions are vortex-like arrangements of spins that constitute a new topo- logical state of matter. They are at the centre of great research efforts because they are con- sidered possible new information carriers in newly developed spintronic devices. Skyrmions were first observed with Small Angle Neutron Scattering (SANS) in MnSi in 2009 [1], since then, they have been observed in other materials with the same space group [2, 3], in non-centrosymmetric compounds [4, 5], in thin films [6, 7], and recently also in frustrated magnets [8].

In bulk materials, skyrmions form only under specific conditions of temperature and applied magnetic field, which correspond to a small region in the magnetic phase diagram, the skyrmion pocket. The small dimensions of this region constitute one of the major drawbacks for possible technological applications. For this reason, in bulk materials, it is crucial to understand how to manipulate the position and the dimensions of the skyrmion pocket, and how these are linked to the microscopic and macroscopic characteristics of the sample.

In this context, SANS is a powerful technique that can directly probe the ordering of the magnetic state, allowing a clear identification of the observed magnetic phase. While this is extremely useful for the comparison with results from other techniques, such as AC susceptibility, SANS provides also unique evidence on the correlation lengths of the system, allowing the extraction of information on the perfection of the skyrmion lattice, thanks to the neutron’ long penetration depth and their high sensitivity to magnetic fields.

In this talk we will present spatially resolved SANS measurements for the characterization of the skyrmion lattice in Ni substituted Cu2OSeO3. We observed an intrinsic non uniformity of the skyrmion lattice structure, which is affected by the macroscopic shape of the sample. Moreover, we also observed significant differences in the stability and metastability of the skyrmion state across. We will also show the possibilities offered by SANS for the study of the three dimensional structure of the skyrmion lattice.