Magneto-optics of Gd and Tb in the soft x-ray resonance regions

We present x-ray absorption spectra around the 3d-4f and 4d-4f excitation thresholds of in-plane magnetized Gd and Tb films measured by total electron yield using circularly polarized synchrotron radiation. By matching the experimental spectra to tabulated absorption data far below and above the thresholds, the imaginary parts of the complex refractive index are determined quantitatively. The associated real parts for circularly polarized light propagating nearly parallel or antiparallel to the magnetization direction are obtained through the Kramers-Kronig relations. The derived magnetooptical parameters are used to calculate soft x-ray reflectivity spectra of a magnetized Gd film at the 3d-4f threshold, which are found to compare well with our experimental spectra.