Electron densities in relation to magnetism: γ-ray diffraction from transition-metal monoxides and difluorides

In this article, results are described from an area of solid-state physics that heretofore has remained unexplored by Bragg charge-scattering experiments. It is shown that γ-ray electron densities can provide detailed information on magnetic ground-state properties at a subatomic resolution. The use of 316 keV γ radiation has allowed low-order structure factors at better than 0.1% accuracy to be determined and, at the same time, extended data sets to be collected up to high momentum transfer. Prototypic antiferromagnets such as the late 3d transition-metal monoxides and difluorides have been systematically investigated, in most cases both in the paramagnetic and in the fully ordered phase. At transitions with a lowering of symmetry, multidomain formation was suppressed by application of external mechanical stress or magnetic fields. The results are considered in the context of information provided by recent magnetic neutron and X-ray studies.