Nanoscale magnetic imaging of chemically modulated FeCo nanowires

Cylindrical magnetic nanowires are promising candidates for future domain wall (DW)-based devices due to their ability to host stable DWs that propagate efficiently without experiencing Walker breakdown. A powerful strategy to tailor the magnetic behavior of these nanowires is through the introduction of a multilayer architecture based on ferromagnetic (FM) and nonmagnetic (NM) layers/segments. In this chapter, we present a detailed study of the magnetic configuration of FeCo/Cu multilayer nanowires synthesized via electrodeposition in anodic aluminum oxide (AAO) templates. Using high-resolution electron holography (EH) in a transmission electron microscope (TEM), we quantitatively map the internal magnetic field distribution of individual nanowires. Complementary magnetic force microscopy measurements reveal a periodic bright/dark contrast consistent with the FeCo/Cu stacking sequence. This contrast is attributed not to conventional DWs but to charge accumulation at FM/NM interfaces. The EH analysis confirms the presence of magnetic frontiers localized in the Cu-rich regions, with magnetic flux extending beyond the nanowire boundaries. Micromagnetic simulations support these findings and reveal the formation of vortex-like structures at the interfaces between magnetic and nonmagnetic segments. These results provide crucial insights into the magnetization reversal processes in multilayer cylindrical nanowires, emphasizing the role of NM spacer layers in stabilizing complex domain configurations. This understanding is instrumental for the development of advanced magnetic nanodevices, particularly for memory and logic technologies based on controlled DW motion.