Quantitative lorentz microscopy of NdFeB magnets
It is now well established that quantitative measurement of domain wall width using Lorentz electron microscopy is nontrivial. The usual technique of extrapolating divergent wall image widths of over-focussed or under-focussed Fresnel images suffers from serious errors since it is based on geometrical considerations and does not take into account the wave optical effects of electron scattering in the microscope. These errors are overcome if one supplements the measurements with image computation for the specific electron optical system and the specimen configuration. Another way of circumventing the errors is by using Differential Phase Contrast Microscopy in a Scanning Transmission Microscope which unfortunately requires instrumentation changes in the electron source and the electron detection system. In this paper we describe a simple method of calculating quantitative values of domain wall energy and domain wall width from Fresnel images obtainable in any standard transmission electron microscope.
