ISSN:
1089-7550
Quelle:
AIP Digital Archive
Thema:
Physik
Notizen:
A new class of Fe-, Co-, Ni-, Cu-, and Ge-based ductile ribbons in which an amorphous matrix containing less than 12 vol. % of a fine dispersion of 0.1–3-μm size particles of immiscible elements M=Pb, Bi, Sn, or In have been produced by a modified melt-quenching technique. The Fe- and Co-based alloys containing Bi and Pb are found to be ferromagnetic above room temperature and also superconducting at temperatures in a range 7–9 K depending on the alloy. The saturation magnetization in these usual alloys range from 92 emu/gm for Co-Si-B-Pb-Bi to 15 emu/g for Fe-P-Pb-Bi at 77 K. At the superconducting transition the resistivity typically is found to drop by 2–3 orders of magnitude with a transition width ∼0.5 K before the "zero'' resistance value is reached. In all the alloys studied the T dependence of the resistivity shows a typical metallic behavior despite its high magnitude (a few thousand μΩ cm in some cases). Extremely high values are found for the upper critical fields (1.6–1.72 T at 4.2 K) with critical current densities typically around 1.3×107 A m−2 at 4.2 K. For Ge-Pb-Bi-Sn Hc2 values of 5 T are obtained at 3 K. Along with detailed studies of magnetic and superconducting properties, extensive TEM, and x-ray characterization data will also be presented. Attempts to explain the above described behavior in terms of proximity, percolation, and surface properties at the dispersed Pb, Bi particles are found to be unsatisfactory. As far as we know there exists no theory that can explain the co-existence of ferromagnetism and superconductivity of the type described above. Time permitting, we will also discuss our recent work on high Tc oxide materials produced by melt-quenching techniques. Thus amorphous composite materials exhibiting unique and useful characteristics which cannot be achieved for homogeneous amorphous alloys can be produced by melt quenching. These materials are of importance both for scientific and engineering points of view.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1063/1.340236
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