MR-elastography is a new technique

The relation of self-and interdiffusion in a liquid metal, particularly the influence of cross correlations at low concentrations, is studied experimentally. Accurate interdiffusion data are obtained by a combination of x-ray radiography with the shear-cell method on the ground and on the sounding rocket MAPHEUS under microgravity conditions. Self-diffusion coefficients, measured by quasielastic neutron scattering, increase with decreasing Ni concentration, whereas interdiffusion coefficients are about constant. We show that cross correlations influence interdiffusion even at concentrations as low as 2 at. % Ni. Consequently, Darken's equation is not valid in this case.

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The investigation of Li(Ni 1−x Fe x )PO 4 by optical second harmonic generation yields the competition of the antiferromagnetic (AFM) structures and 180 • domain patterns found in the end compounds LiNiPO 4 (point group mm ′ m, spins along z) and LiFePO 4 (point group mmm ′ , spins along y). While AFM order and the distribution of the AFM domains of LiNiPO 4 are unaffected by the ion substitution at x = 0.06, striking changes are observed at x = 0.20. We find that Fe 2+ is dominant in establishing the magnetic order. For x = 0.20 we find that the magnetic order of the solid solution interpolates the magnetic order of its end compounds by exhibiting an orientation of the spins in the (100) plane which include an angle of 40 • ± 3 • with respect to the y axis toward 0 K (point group m). In contrast to the two end members, the associated AFM domains form rods of a few mm length and ∼ 10 µm width occurring in neither of the end compounds. Mechanisms responsible for the magnetic order and domain pattern (180 • domains still being one of the least explored aspects of AFM materials in spite of their omnipresence) are discussed.

A compact-sized shear cell for in-situ interdiffusion measurements in liquid alloys at high-temperature is presented. It is designed for being used with X-ray radiography in microgravity environment and also in ground-based experiments. Within outer dimensions of 40x40x20 mm, the shear cell contains six samples in long capillaries which remain spatially separated during melting, homogenisation and optional µg-injection. The diffusion is then initiated by shearing both material samples together. Operating temperature is as high as 1500 • C. Stable temperature distribution is found and no sample leakage occurs. The thin layout of the shear cell results in a good X-ray contrast supported by making use of graphite heating foils. First results of ground experiments are presented.