In contrast to classical ex-situ spectro-microscopic techniques, in-situ characterizations and the combined application of complementary methods on identical samples not only provide for a more comprehensive insight into the structures and phenomena of interest, but also allow to study their kinetic development under the impact of external stimuli [1-3].

The talk will present a short review of our recent endeavors along this line and will specifically report on findings on the helimagnetic Heusler compound Mn_1.4PtSn. Lorentz transmission electron microscopy (LTEM) was used to study the evolution of magnetic phases as a function of (strength and direction of) an external magnetic field. The combination of (i) real space textures as derived from LTEM with (ii) magnetic scattering patterns obtained from complementary small angle resonant X-ray scattering (REXS) and (iii) micromagnetic simulations allowed us to substantially deepen our understanding of the nature and stability of the magnetic phases in Mn_1.4PtSn as a consequence of the competing magnetic interactions at work. We could show that due to the material’s uniaxial magnetic anisotropy, a stripe domain phase derived from a chiral soliton lattice rather than the previously assumed helical phase forms the ground state of the system. The studies also reveal the occurrence a previously overlooked fan state and provide a detailed understanding as to why and how antiskyrmions are formed along a kinetic pathway that is defined through a particular sequence of to be applied external magnetic fields.

Furthermore, by measuring the anomalous Hall effect in-situ in the microscope and simultaneously with the LTEM investigations, we could show that the field-induced formation of antiskyrmions does not cause any additional contribution to the Hall effect thereby indicating the lack of any topological Hall effect in the system.