X-ray Reflectivity at the L Edges of Gd

Preparations are underway for the experimental investigation of the roughness of magnetic interfaces in rare-earth multilayers by combining the grazing-angle X-ray scattering technique with the resonant magnetic scattering of hard X-rays. Theoretical considerations show that for small scattering angles, 2θ, the asymmetry ratio, A = [I(+) − I(−)]/[I(+) + I(−)], depends on 2θ and varies as 1/cos θ. The first step towards the goal of determining the magnetic roughness has been taken by measuring the chemical roughness (via specular reflectivity) of a Gd thin-film sample at five photon energies close to the L₃ absorption edge, which yielded the dispersion corrections, f′ and f′′, to the Gd atomic form factor in good agreement with the calculation of Cromer & Liberman [J. Chem. Phys. (1970), 53, 1891–1898].