Grazing-incidence small-angle X-ray scattering study of correlated lateral density fluctuations in W/Si multilayers.

A structural characterization of W/Si multilayers using X-ray reflectivity (XRR), scanning transmission electron microscopy (STEM) and grazing-incidence small-angle X-ray scattering (GISAXS) is presented. STEM images revealed lateral, periodic density fluctuations in the Si layers, which were further analysed using GISAXS. Characteristic parameters of the fluctuations such as average distance between neighbouring fluctuations, average size and lateral distribution of their position were obtained by fitting numerical simulations to the measured scattering images, and these parameters are in good agreement with the STEM observations. For the numerical simulations the density fluctuations were approximated as a set of spheroids distributed inside the Si layers as a 3D paracrystal (a lattice of spheroids with short-range ordering but lacking any long-range order). From GISAXS, the density of the material inside the density fluctuations is calculated to be 2.07 g cm-3 which is 89% of the bulk value of the deposited layer (2.33 g cm-3).

Mode-crystallography analysis and magnetic structures of SrLnFeRuO6 (Ln = La, Pr, Nd) disordered perovskites.

The crystal and magnetic structures of SrLnFeRuO(6) (Ln = La, Pr, Nd) double perovskites have been investigated. All compounds crystallize with an orthorhombic Pbnm structure at room temperature. These materials show complete chemical disorder of Fe and Ru cations for all compounds. The distortion of the structure, relative to the ideal cubic perovskite, has been decomposed into distortion modes. It has been found that the primary modes of the distortion are octahedral tilting modes: R(4)(+) and M(3)(+). The crystal structure of SrPrFeRuO(6) has been studied from room temperature up to 1200 K by neutron powder diffraction. There is a structural phase transition from orthorhombic (space group Pbnm) to trigonal (space group R3c) at T = 1075 K. According to group theory no second-order transition is possible between these symmetries. Magnetic ordering for all the compounds is described by the magnetic propagation vector (0,0,0). SrPrFeRuO(6) shows ferrimagnetic order below ca 475 K, while SrLaFeRuO(6) (below ca 450 K) and SrNdFeRuO(6) (below ca 430 K) exhibit canted-antiferromagnetic order. The magnetic moments at low temperatures are m(Fe/Ru) = 1.88 (3)µ(B) for SrLaFeRuO(6) (2 K), m(Pr) = 0.46 (4)µ(B) and m(Fe/Ru) = 2.24µ(B) for SrPrFeRuO(6) (2 K), and m(Fe/Ru) = 1.92µ(B) for SrNdFeRuO(6) (10 K).