magnetic domains have been the subject of much scientific investigation since their theoretical existence was first postulated by P.-E. Weiss over a century ago. up to now, the threedimensional (3D) domain structure of bulk magnets has never been observed owing to the lack of appropriate experimental methods. Domain analysis in bulk matter thus remains one of the most challenging tasks in research on magnetic materials. All current domain observation methods are limited to studying surface domains or thin magnetic films. As the properties of magnetic materials are strongly affected by their domain structure, the development of a technique capable of investigating the shape, size and distribution of individual domains in three dimensions is of great importance. Here, we show that the novel technique of Talbot-Lau neutron tomography with inverted geometry enables direct imaging of the 3D network of magnetic domains within the bulk of Fesi crystals.

No abstract

Very thin equatorial small-angle scattering of Cu Ka radiation is observed from metallic wires, glass fibres and hard elastic polypropylene which can be explained quantitatively as a refraction phenomenon if the excess refractive indices n = 1 -e of the samples are smaller than unity. For Cu Ka radiation and SiO2 glass e has a value of 7.2x 10 -6. The intensity Is of reflection within a total reflection angle 8 = 3.8 × 10 -3 = 13' is negligibly small compared with the intensity of refraction lB. In addition to refraction, diffraction by gaps and holes in strained polypropylene was observed. The scattering of 60 lxm particles 0108-7673/87/040506-08501.50 of Li-Ba silicate glass powders [Nau & Briickner (1971). Kolloid Z. Z. Polym. 244,[223][224][225][226][227][228][229][230][231][232][233] can be explained by transforming the observed scattering of spheres to cylinders yielding the refraction IB as calculated.

We present transmission electron microscope (TEM) tomography investigations of ruthenium-based fuel cell catalyst materials as employed in direct methanol fuel cells (DMFC). The digital three-dimensional representation of the samples not only enables detailed studies on number, size, and shape but also on the local orientation of the ruthenium particles to their support and their freely accessible surface area. The shape analysis shows the ruthenium particles deviate significantly from spherical symmetry which increases their surface to volume ratio. The morphological studies help to understand the structure formation mechanisms during the fabrication as well as the high effectiveness of these catalysts in the oxygen reduction reaction at the cathode side of fuel cells.

No abstract