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Neutron Scattering from Magnetic Materials part 18

Tham khảo tài liệu 'neutron scattering from magnetic materials part 18', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Small angle neutron scattering investigations of magnetic nanostructures 511 ascribed to random anisotropy effects resulting from a two-phase nanoscaled microstructure 63 . A SANS study with unpolarized neutrons was performed on Fe73.5Si15.5B7Nb3Cu1 alloy which after annealing at 823 K for 1 h contained a volume fraction of about 56 of ultra-fine grained Fe3Si 16 64 65 . 2D scattering patterns were measured in a range of temperatures between 400 K and 750 K and with an applied field between 0 T and 1 T and analyzed according to 13 . For strong external fields the isotropic part A Q is assigned to nuclear contributions resulting from a size distribution of Fe3Si crystallites with a maximum at a radius of 5.5 nm embedded in the amorphous matrix. B Q is of magnetic origin resulting from the difference in the magnetization of the amorphous matrix and the nanocrystals AM Mlr T Msam T . Valuable information on the magnetic couplings between the two phases of the nanocrystalline microstructure were obtained from temperature and field dependent measurements allowing the magnetic contrast to be varied 15 . The integrated anisotropic contribution f B Q dQ measured at high magnetic fields is plotted in Figure 20. With increasing temperature this contribution first increases up to a maximum at Tmax 650 K and decreases above. This behavior was ascribed to a different temperature dependence of the saturation magnetization of the nanocrystals with a Curie temperature TC 900 K and that of the amorphous matrix. The highest magnetic contrast is expected to occur at the Curie temperature of the matrix that is TCam Tmax 650 K. By this method TCam could be precisely determined which surprisingly was found to be by 55 K higher than that of the as-quenched sample. For small external magnetic fields the magnetic moments are no more completely aligned along H. The partial disorder in the orientation of the moments leads to an additional magnetic contribution to the isotropic scattering. A