X-ray magnetic scattering

Most x-ray scattering by matter occurrs due to scattering by electronic charge. One can also observe another type of scattering, namely by electron spins, which is very weak and is called x-ray magnetic scattering. One can use this phenomenon in study of the magnetic structure of matter by utilizing the polarized character of SR. The interaction is dependent on the direction and size of the magnetic moments, and their arrangement relative to the polarization of the incident beam. When the incident x-ray energy is close to the absorption edge of the material concerned, this phenomena occurs as resonance magnetic scattering. Further, if rare earth metals are studied at their L2 and L3 edges, the effect is larger by about a factor of 2 than the above mentioned case; this is called "resonance exchange scattering" which is also dependent on the magnetization of the material. These x-ray magnetic resonant scattering techniques give information on the spin state of the magnetic materials. These phenomena are much more informative than magnetic circular dichroism, since the effective use of the polarization of the x-rays can lead to clearer information on the spin states. The figures (b) and (c) show the degree of asymmetry of the Bragg reflection intensity, Ra = (I+ -I-)/ (I+ +I-), which arises when the magnetic field applied to a Gd crystal alternates with the incident x-ray energy tuned to the L3 absorption edge. The figure (a) shows the absorption spectrum, (b) the asymmetry ratio when the incident x-rays are in the horizontal polarization state and (c) the asymmetry ratio in the case of 45 degree linear polarization. The 45 degree polarization state reveals a peak at around -3 eV which is evidence of the contribution of 4f levels by quadrupole scattering. This can not be observed using horizontal polarization.




(a) Absorption spectrum of Gd-L3 edge, (b) and (c) spectra of degree of asymmetry of 004 Bragg reflection. Degree of asymmetry, Ra, is defined as Ra=(I+ -I-)/ (I+ +I-) , where I+@and I-@ are the reflection intensities in the case of the two opposite directions of the magnetic field. Linear polarization is (b) horizontal and (c) 45 degree.

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