Spin densities studied in momentum space Original Research Article

After approximately ten years development, Compton scattering studies of magnetisation density with circularly polarised synchrotron radiation are beginning to provide unique information about the site-dependent distribution of spin density and the limitations of the approximations used in the electronic structure models, as will be illustrated by a selection of recent results which expose the interpretative problems as well as the limitations of the local density approximation to describe exchange and correlation. Technical developments have been restricted to improvements of degree rather than of kind, with limited resolution and the inability to study “hard” ferromagnets, the most damaging.