Magnetic microstructures in nano-granular CoPt-Al-O thin films studied by electron holography and Lorentz microscopy

TEM measurements are carried out on CoPt-Al-O thin films. CoPt-based nanocrystalline phases are found surrounded by Al₂O₃-based amorphous phases, showing nano-granular structures. Domain walls like fishbone are also observed in Lorentz microscope images of the nano-granular films. These domain walls disappear as the applied magnetic field increases. Further in the reconstructed phase images (holograms), it is found that the density of lines of magnetic flux increases with the increase in the magnetic field, indicating a mixed-phase state of the ferromagnetic and superparamagnetic phases.