X-Ray Resonant Scattering from Magnetic Multilayers
Magnetic multilayers are currently the focus of considerable activity because they have potential applications in high-density magnetic data-storage systems. An international team of researchers working at the ALS has used resonant scattering of circularly polarized soft x rays in a model system comprising iron/vanadium magnetic multilayers. This allowed the measurement of the index of refraction of iron near iron absorption edges without the need for Kramers-Kronig analysis, which requires approximations and the introduction of arbitrary parameters.
The dispersive and absorptive components of the index of refraction for iron were derived from the angular position of the Bragg peak for multilayer reflectivity for photon energies near the absorption edges for 2p core electrons (L3 and L2 edges) and from absorption data obtained under the same conditions. Measurements were made for parallel (left) and antiparallel (center) orientations of the sample magnetization and helicity of circularly polarized soft x rays. Also shown (right) is the difference between the two data sets.
From this data, the researchers were able to reconstruct all the components of the dielectric tensor, which quantifies the response of the material to electromagnetic fields. In particular, the diagonal elements give the response of the material to unpolarized radiation, while the off-diagonal elements are directly related to the magnetic properties of the sample. Such information is needed to fully reconcile theoretical models with the results of experiments aimed at understanding and eventually controlling the behavior of magnetic multilayers.
Research conducted by M. Sacchi, C. F. Hague, and A. Mirone (LURE, Orsay), L.
Pasquali (INFM, Modena), J.-M. Mariot (Université Pierre et Marie Curie,
Paris), P. Isberg (Uppsala University), and E. M. Gullikson and J. H.
Underwood (Berkeley Lab), using Beamline 6.3.2.
Funding: Centre National de la Recherche Scientifique (France), Istituto
Nazionale di Fisica della Materia (Italy), and Division of Materials Sciences,
U.S. Department of Energy.
Publication about this experiment: M. Sacchi et al., Phys. Rev. Lett. 81, 1521 (1998).
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