Magnetic Circular Dichroism at High Magnetic Field and Low Temperature

The asymmetric wiggler inserted since the end of 1990 on the Super-ACO storage ring in Orsay, has been built to produce high rate and high flux of circularly polarized soft X-rays in the 400-2000 eV range. This insertion device is particularly well suited to measure x-ray absorption spectra corresponding to dipole transitions towards electronic orbitals which are directly responsible for the magnetism (3d states of first row transition metals, 4f states of rare-earths). We report the first magnetic circular x-ray dichroism spectra obtained with this insertion device. They exemplify the wide prospects of this experimental setup.