Electron diffraction from periodic magnetic fields

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Abstract
Non-uniform magnetic fields act as diffraction apertures on electron beams crossing them, owing to the phase changes introduced. It is shown that periodic fields act as phase gratings, producing a pattern of regularly spaced spots which can be observed in the electron microscope, using low angle diffraction techniques in certain cases of practical interest. In many instances the variation of phase can be adequately described by a series of linear functions. Formulae for the observed intensity are derived for such cases. Three practical applications are discussed: (i) In the case of periodic magnetic domain structures, the calculated results are in good agreement with observations. (ii) In the case of anti-ferromagnetic lattices, the results show that the diffracted intensities are probably too weak to be observed. (iii) In principle it should be possible to observe diffraction effects in a type II superconductor containing a periodic array of flux lines.