Magnetic extraction of superconducting grains from ceramic combinatorial syntheses

Basic experimental steps in the combinatorial synthesis of cuprate superconductors and magnetic separation of ceramic grains obtained within random reaction mixtures were elaborated. By use of two component grains (i/j) in the size range 80–100 μm, reaction conditions were provided which lead to necking in between adjacent grains. The originally introduced single sample concept (SSC) was thus expanded to a random neck synthesis (RNS). In situ demonstration of superconductivity for single grains down to 1 ppm of occurence in random reaction mixtures became possible. Application of AC magnetic fields (at 50 Hz) leads to arbitrary motions of superconducting grains which allowed to distinguish them from normal state matter. Separation was performed by a single Fe-wire magnetized parallel to gravity. Because no magnetic forces are acting in the horizontal direction, in situ inclination of the capturing wire made it possible to collect individual grains in a small container for taking them out of the setup after warming up. Suspensions in liquid oxygen of YBa2Cu3Ox were used to demonstrate the procedure from random neck synthesis to an X-ray and SQUID analyses of magnetically separated grains.

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