X-RAY REFLECTIVITY AT THE L EDGES OF GD

Preparations are underway for the experimental investigation of the ro ughness of magnetic interfaces in rare-earth multilayers by combining the grazing-angle X-ray scattering technique with the resonant magneti c scattering of hard X-rays. Theoretical considerations show that for small scattering angles, 2 theta, the asymmetry ratio, A = [I(+) - I(- )]/[I(+) + I(-)], depends on 2 theta and varies as 1/cos theta. The fi rst step towards the goal of determining the magnetic roughness has be en taken by measuring the chemical roughness (via specular reflectivit y) of a Gd thin-film sample at five photon energies close to the L-3 a bsorption edge, which yielded the dispersion corrections, f' and f '', to the Gd atomic form factor in good agreement with the calculation o f Cromer & Liberman [J. Chem. Phys. (1970), 53, 1891-1898].