Resonance effect in white X-ray magnetic diffraction of GdAl2

Using elliptically polarized white synchrotron radiation and an energy-sensitive detector, the 444 reflection from a single-crystal sample of the ferromagnetic compound GdAl2magnetized along the scattering vector has been measured, and the asymmetry of the diffraction intensity upon the magnetization reversal has been studied in the X-ray energy range across the GdLIIedge. The dependence of the magnetic asymmetry on the scattering angle or on the X-ray energy is understood as the superposition of the sharp near-edge structure and the much broader component arising from the interference between the electric scattering and the resonant and nonresonant magnetic scattering, respectively. To interpret the experimental results, an analytical treatment of the magnetic asymmetry is developed, and in the course of the analysis it is pointed out that in general the pseudo-extinction of the Bragg reflection due to the dispersion effects can be utilized as a technique to raise the magnetic sensitivity in the X-ray scattering from ferromagnetic materials. The potential of an unconventional approach to the resonant X-ray scattering using a white beam, as is clearly demonstrated by the present experiment, is also discussed.