Based on the Bean's critical state model and Meissner effect, we can explain the magnetic levitation forces acting on a YBCO superconducting single crystal quite well. However, this calculation can only be applied to the case of small superconductor placing in an uniform magnetic field. By measuring the magnetic levitation forces acting on two types of YBCO superconducting samples: one ceramic-YBCO, and the other one epoxy-YBCO with different weighting ratio of YBCO, we found that the intergranular supercurrent flowing inside the ceramic sample make negligible contribution to the levitation forces. Considering the ceramic-YBCO sample as an ensemble of many isolated small superconducting grains, we obtained good theoretical results for the magnetic leviation force acting on a permanent magnet in comparision with experimental measurements.
Chinese Journal of Physics=中國物理學刊 34(2-II)，頁489-492