Magnetic Scattering in High-Energy Electron Diffraction

Over the past 25 years or so, neutron diffraction has become the standard method of probing the internal magnetic structure of crystals. More recently, however, it has been found that x-ray magnetic scattering, although weak, can be observed using bright x-ray sources. The success of x-ray techniques leads one to wonder whether magnetic scattering might also be observed using electrons, and it is this question that is addressed here. Clearly, electrons are influenced by the internal magnetic fields of specimens_this is the basis of Lorentz microscopy of ferromagnetic domains. Here we examine scattering from more exotic forms of magnetic order, such as anti-ferromagnetism. The interesting point is that antiferromagnets have magnetic Bragg spots which appear between the basic lattice spots as the magnetic order sets in. Analysis of these spots forms the basis of neutron, and now x-ray, studies of magnetic structures. The extra ingredient that electrons might offer is that imaging in such spots could reveal the local magnetic structure including domains, dynamic effects etc., in just the same way that satellite dark-field imaging has contributed to studies of structural phase transitions.