Off-axis electron holography of epitaxial FePt films

Off-axis electron holography at the nanometer level has been used to investigate the magnetic microstructure of thin epitaxial ${\mathrm{Fe}}_x{\mathrm{Pt}}_{\text{1−x}}$ $\text{(x∼0.5)}$ ordered alloy films. High-resolution electron microscopy in cross section showed high quality epitaxial growth but also revealed some widely spaced regions with structural defects. Lorentz microscopy and off-axis electron holography in field-free conditions established conclusively that similar defective areas were associated with local perturbations of the in-plane magnetic field within the thin films. Further holographic observations with the FePt[001] axis parallel to the film normal revealed variations in phase shifts in the vacuum outside the sample which indicated flux leakage along the film normal. Overall, the results demonstrate that off-axis electron holography is a highly useful technique for mapping local variations of the in-plane magnetic structure associated with defective thin films.