Electron holography and micromagnetic simulations unveil the magnetic domain structure of steel-embedded Fe3C carbides

The rapid development of spintronic devices brings about the need for more efficient experimental methods to explore magnetic domain structures and their response to external fields at the nano- to micrometer scale. Here, transmission electron microscopy (TEM) with inline and off-axis electron holography is used to investigate with nanometer resolution the magnetic domain and domain wall structures in cementite (Fe3C) carbides embedded in thin ferromagnetic steel films. The capabilities of the streamlined inline holography method are compared to those of the more resource-demanding off-axis electron holography. Micromagnetic simulations are employed to interpret the data analysis. The simulations are used specifically to resolve the internal domain wall structure along the film thickness/electron beam direction, which is inaccessible to non-tomographic TEM imaging methods. The cementite carbides reveal a peculiar striped magnetic structure with controllable and reversible properties under an applied external magnetic field.