Some theoretical aspects of type‐1 magnetic contrast in the scanning electron microscope

Abstract

KEY WORDS. Difference image, fluxon unit, Fourier methods, Gauss' theorem, Heisenberg uncertainty principle, magnetic induction, magnetic recording head, magnetic tape, Neumann's problem, quantum limit, scanning electron microscope (SEM), secondary electrons (SE), uniaxial magnetic material, uniqueness theorem for magnetic fields. SUMMARY Type-1 magnetic contrast can be obtained in the secondary electron (SE) image in the SEM from a sample having an external magnetic field if the SE detector is directionally sensitive. Gauss' theorem is applied to show that the normal component of induction at the surface of the sample can be calculated from the measured spatial derivative(s) of the SE difference-signal. A method is given in this paper for calculating the three components of the induction in the entire volume above the sample surface. Reasons are given for believing that type-1 magnetic contrast is limited in spatial resolution by the fluxon unit.