In chiral magnets, the interplay of symmetric exchange, asymmetric Dzyaloshinskii–Moriya interaction (DMI), magnetic anisotropies, and external magnetic fields not only results in complex magnetic phase diagrams, but also promotes the emergence of topologically nontrivial spin textures such as (anti-) skyrmions and chiral soliton lattices. The talk will review how the combined use of Lorentz transmission electron microscopy (LTEM), resonant elastic X-Ray scattering (REXS), in-situ Hall measurements in the electron microscope, theory and micromagnetic simulations allows to better understand the nature of chiral spin textures, their topological protection, and specifically the magnetic field-induced transitions between these different magnetic states, part of which necessitate the overcoming or bypassing of topological barriers.
Our comprehensive investigations are focused on the half Heusler compound Mn1.4PtSn. It will be shown that the magnetic ground state of the material – a chiral soliton lattice (CSL) with 180° (π) domain walls – undergoes a remarkable transformation into a classical 2π-CSL in increasing magnetic fields. These observations are elegantly captured by a double sine-Gordon model, which not only reveals the relevance of the competition between the magneto-crystalline anisotropy and magnetostatic interactions for tuning this transformation, but also provides the framework to understand soliton lattices in materials with a variety of D 2d , S4, Cnv, and Cn symmetries. The mutual interplay between CSLs and magnetic fan domains emerging in particular field orientations leads to the nucleation of non-topological magnetic bubbles just by providing some right and left-handed chiral "ingredients" to their texture. Understanding the nature of these transformations allows us to unveil the microscopic mechanisms that govern the
formation of anti-skyrmion lattices in the material. Notably, in-situ monitoring the Hall effect during the switching between non-topological bubbles and topological anti-skyrmions does not reveal any signs of a topological contribution to the Hall voltage, i.e., of a topological Hall effect.