Magnetic asymmetry ratio

Fig. 7.10 Magnetic asymmetry ratios measured on a [Fe(2)/V(15)]3o sample in the vicinity of the Fe L-edges in reflection at the second superlattice peak prior (bold line) and after (light line) hydrogen exposure.

While the cross section is the fimdamental measurable quantity in scattering theory, it is frequently more convenient in X-ray scattering from magnetic materials to measure the asymmetry ratio (dichroism). This is defined as the difference divided by the sum of the cross section for the moment in one direction and the moment in the opposite direction. 

As shown by Lovesey and Collins (1996), the asymmetry ratio directly reflects the scattering amplitude rather than the cross section and emphasizes the interference between magnetic scattering and charge scattering. 

Thus different luminescence takes place after activation in air and in vacuum. As it was already mentioned, in the apatite structure Ca5(P04)3F there are two types of Ca site Ca(l) with C3 symmetry and Ca(II) with Cs symmetry. The Dq- Fq transition has been reported to exist in cases where the site symmetry allows an electric dipole process Cs, C , Cnv This is consistent with the conclusion that the centers with the main line at 574 nm belongs to Ca(II) site with Cs symmetry, while the asymmetry of the crystal field is lower for the center with the main line at 618 nm. The ratio between Dq- Fo and Dq- F2 which are forced electric dipoles to Dq- Fi which is magnetic dipole tells us about the synunetry of the site in which Eu + is situated (Blasse and Grabmaier 1994 Reisfeld 1973). In fluor-apatite activated in air the ratio is higher meaning a lower synunetry Ca(II) site, while in namral fluorapatite or synthetic one activated in vacuum the ratio is lower... 

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