The force of levitation experienced by a magnet on top of' a superconductor depends on position and how fast the magnet was put into that position. As a result, when the levitation force is measured as a function of the height of the magnet above the superconductor, a plot of the force versus height also depends on the rate at which the magnet position was changed during the experiment. We have measured this dependence of the levitation force (as a function of position) on the average rate of moving the magnet towards the superconductor under zero field cooled conditions. This dependence is appreciable only when the magnet is close to the superconductor. After the magnet is brought to a stop a t the nearest position, we continued to observe the relaxation of the magnetic stress between the magnet and the superconductor. The gross characteristics of the relaxation process after the magnet stops are similar for different speeds of approach before the magnet stops. This study aims a t determining how the long term reliability of a superconductor magnet bearing depend on the process of setting it up.

Experimental and calculated dependences of granular superconductor magnetic susceptibility on the superconducting volume fraction in regimes of shielding (ZFC), Meissner effect (FC) and remanence (REM) were determined. Fractional dependences were calculated with Braggeman's asymmetric theory and allowing for the shape of superconducting grains and the sample and the influence of grain sizes upon their polarizability under different magnetization conditions. A granular superconductor with intergranular links is calculated as a three-component system, where closed clusters are regarded as superconducting particles and the function of distribution of these particles, depending on the superconducting volume fraction, is introduced. The results of calculation agree well with the experimental data in t h e ZFC regime for all fractions f = &I, but in t h e a and REM regimes for f < 0.6. The calculation for the links region gives a qualitative description of singuiarities in the experimental dependences at f > 0.6.Nomograms for determining the superconducting volume fraction in high-T, superconductors were constructed.

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