The field dependence (up to 35 T) at 4.2 K of the magnetization of several compounds of the type R1−xYxCo4B (R = rareearth) has been studied. The magnetic isotherms at 4.2 K are analysed with a mean-field model. The magnetic coupling constant JRCo between the moments of the rare earth and cobalt in the Hamiltonian H = ∑RCo2JRCoSR · Sco are shown to be more reliable than the coupling constants derived from a mean field analysis of the Curie temperatures for these compounds.
The influence of additions of chromium, titanium and CuCr on the wettability of vitreous carbon by NiPd azeotropic alloys was studied. The work was carried out at 1523 K under high vacuum by the sessile drop technique. The morphological and chemical features of the metal-carbon interface were determined by profilometry, scanning electron microscopy and microprobe analysis. Chromium and titanium active solutes lead to a decrease of more than 100° in contact angle and an order of magnitude increase in work of adhesion. These effects result from the in situ modification of both the liquid and solid sides of the interface: the formation of an adsorption layer rich in active solute on the liquid side and a metallic-like carbide on the solid side of the interface.
Cold deformation of YBa2Cu3O7 − x (phase 123, Tc = 88.5–92 K) powders and strips causes partial decomposition of the 123 phase, a reduction in the degree of orthorhombicity of the structure up to almost complete degradation, and a decrease in Tc. When they are deformed, yttrium high temperature superconductors acquire basal (001) [110] texture with high pole density (13–15 arbitrary units), low scattering angle (±6°–7° from the normal direction), and a weak preference for a, b or a + b in the rolling direction; traces of (139) orientations may also be found. This texture is known to be favourable for increasing jk. The combined effect of cold deformation and a carbon-containing binder leads, however, to a complete loss of superconductivity at 77 K or above. Depending on the regime of subsequent annealing, the following effects may be observed: degradation of the orthorhombic structure with a decrease in Tc; restoration of the orthorhombic structure and Tc of the 123 phase with complete or substantial loss of basal-type texture; change in texture type or retention of the basal texture (pα = 0(005) = 6–7 arbitrary units) with restoration of the orthorhombic lattice and Tc of the 123 phase. The appearance of a set of orientations from (139) to (001) in the deformation texture is evidence for the process of recrystallization grain growth. This suggests the appearance of plastic deformation of the ceramics (most probably of the shear type). With long annealing and thermocycling, the basal texture changes in accordance with the theory of compromise recrystallization grain growth up to the restoration of basal texture.
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