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- Magnetic domains (2)
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Organisationseinheit der BAM
We present a combined experimental and theoretical study to solve the unit-cell and molecular arrangement of the tetracene thin film (TF) phase. TF phases, also known as substrate induced phases (SIP), are polymorphs that exist at interfaces and decisively impact the functionality of organic thin films, e.g., in a transistor channel, but also change the optical spectra due to the different molecular packing. As SIPs only exist in textured ultrathin films, their structure determination remains challenging compared to bulk materials. Here, we use grazing incidence Xray diffraction and atomistic simulations to extract the TF unit-cell parameters of tetracene together with the atomic positions within the unit-cell.
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 three-dimensional (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.
This paper gives a brief overview on3D imaging of magnetic domains with shearing grating neutron tomography. We investigated the three-dimensional distribution of magnetic domain walls in the bulk of a wedge-shaped FeSi single crystal. The width of the magnetic domains wasanalyzed at different locations within the crystal. Magnetic domains close to the tip of the wedge are much smaller than in the bulk. Furthermore, the three-dimensional shape of individual domains wasinvestigated. We discuss prospects and limitations of the applied measurement technique.
A thorough characterization of base materials is the prereq- uisite for further research. In this paper, the characterization data of the reference materials (CEM I 42.5 R, limestone pow- der, calcined clay and a mixture of these three components) used in the second funding phase of the priority program 2005 of the German Research Foundation (DFG SPP 2005) are presented under the aspects of chemical and min- eralogical composition as well as physical and chemical properties. The data were collected based on tests performed by up to eleven research groups involved in this cooperative program.
During the second European-American Workshop on NDE Reliability, September 99 in Boulder, the term NDE reliability was defined as the degree that an NDT system is capable of achieving its purpose regarding detection, characterization and false calls. The most common but also most expensive - way to determine this degree of capability in e.g. defect detection is to make just a performance demonstration using realistic test samples and to count the correct detections and false calls. For a more efficient way of reliability evaluation we propose to decompose the system into main modules e.g. according to the reliability formula set up on the first workshop: into f(IC) a function of IC the intrinsic capability, determined by the physics and the technique of the NDE method representing an ideal upper bound of the reliability and g(AP) a function of AP the industrial application factor like surface state or limited access to a component in general diminishing the ideal capability and finally h(HF) the function of the human factor which is in general also diminishing the ideal capability. The workshop proposed a rather plain mathematical shape for the formula R = f(IC) g(AP) h(HF) which should be considered merely as a philosophical expression but not as exact mathematical formula to be applied for evaluation of e.g. POD data. We propose to decompose the NDE system into modules in terms of functions of IC, AP and HF if appropriate or additional ones if necessary and then to analyze the mutual relationships of the terms via fault tree analysis. Finally the total reliability of the system is composed of the reliability of the subsystems via the rules of statistical systems theory.
First trials for this approach of data analysis will be presented via examples from NDE systems in the aerospace industry.