Magnetic x-ray scattering from f-electron systems

Full text: Photons are scattered only very weakly by magnetic moments (some 10-6 less on average than they are scattered by the electron charge) so the observation of magnetism with photon beams always resembles a tour-de-force experiment, and is difficult even with today's new synchrotron sources. On the other hand, what has been discovered is that this small cross section becomes appreciably, and in some cases enormously, enhanced when the photon energy is tuned to a particular absorption edge of the magnetic element in the material. This, and the development of the related theories, has led to a large number of experiments in dichroism and scattering at synchrotrons using resonant photons. Obviously, the information is element specific, but it also gives new information about magnetic materials that was not previously available. For scattering experiments, in particular, the information is complementary to that obtained by neutron scattering. This talk will give the underlying principles of resonant magnetic effects, both dichroism and scattering, and then give a number of examples in scattering investigations of antiferromagnets in 4 f and 5 f systems. In the latter, the enhancements are so great when the energy is tuned to the M-edges (3.73 keV for uranium) that completely new experiments can be performed on thin films, surfaces, and very small samples