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.