Quantitative Lorentz transmission electron microscopy of structured thin permalloy films

The defocusing of images of ferromagnetic particles in the transmission electron microscope gives rise to magnetic contrast (Lorentz microscopy). We have developed a theory which allows from this contrast to determine quantitatively the distribution of the magnetic fields of the specimen. The measurements were performed on permalloy particles of disc (diameter 50 nm), and rectangular (25×50 nm2 and 50×50 nm2) shapes, thickness of 21 nm. These particles had a vortex and Landau–Lifshitz structure, respectively. The determined value of the magnetic induction in the material amounted to 1.1±0.1 T. The stray fields in angular sectors of the rectangular particles reached 0.35±0.05 T. The width of the 90° Neel wall between domains turned out to be equal to 4.5±0.5 nm.