Berlin 2005 – wissenschaftliches Programm

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MA: Magnetismus

MA 32: Mikro- und nanostrukturierte magn. Materialien II

MA 32.9: Vortrag

Mittwoch, 9. März 2005, 13:00–13:15, TU H1028

Theory of polarized neutron diffraction from nano-patterned magnetic films — •Boris P. Toperverg, Katharina Theis-Bröhl, and Hartmut Zabel — Department of Experimental and Solid State Physics, Ruhr-University Bochum, 44780 Bochum

At grazing incidence the projection of the neutron coherence length onto the surface plane is greatly extended. Therefore the Bragg diffraction from lateral patterns with nano- and submicron periods is readily observable experimentally. However, due to strong optical effects, e.g. specular reflection and refraction, the Born approximation fails to correctly describe diffracted signal. The Distorted Wave Born Approximation (DWBA) is shown to be well suitable to the problem over a very broad, but still limited range of lateral scales. One of the limitations is related to the crossover between the period and the lateral projection of the coherence length (LPCL). If they are comparable than the Bragg diffraction cannot be resolved from specular reflection. If the period is greater than LPCL than each of structural elements reflects independently and no Bragg diffraction occurs. DWBA may also fail even if the period is relatively small, but the lateral modulation of the optical potential due to individual elements is so strong that it cannot be treated as a perturbation. A set of alternative methods to treat this situation are suggested. Specific aspects of DWBA application to the case of polarized neutrons is discussed in view of resolving magnetic arrangement within and between the structural elements. We acknowledge funding by DFG, Mercator Visiting Professorship and SFB 491, and BMBF 032AE8BO.