Scanning Electron Microscopy


Examination of magnetic domain structure in the transmission electron microscope is generally confined to very thin foils, where the specimen approximates to a pure phase object, and is achieved by the long established methods of Fresnel or Foucault contrast Lorentz microscopy, or by differential phase contrast (DPC) imaging in a scanning transmission electron microscope (STEM).

If no quantitative interpretation of the image is required then magnetic contrast can be observed from thicker foils, and in this paper we describe an attempt to determine experimentally the range of foil thickness over which this is possible. To this end we have examined electropolished foils of single crystal Incalloy using an extended VG HB501 STEM to produce both DPC and Fresnel contrast images of the same area. The foil thickness at points along the domain walls was measured from the change in the Lorentz deflection angle as the STEM probe was moved across the domain wall, and this led to an estimate of ~ 700nm for the limiting thickness at which domain contrast was still visible in the DPC images.

This value is obviously influenced by a number of factors, including the degree of inelastic scattering and the saturation magnetisation of the material, but it is sufficiently high that there might exist a range of thickness over which both transmission and scanning electron microscopes could be used to study the domain structure in the same areas of specimen.

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