  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.
