Measurements of three-dimensional fields of bulk superconductors in varying external fields

We measured the magnetic field distribution and the levitation force of a bulk Sm-Ba-Cu-O superconductor as it was moved vertically in magnetic fields generated from a Bi-Sr-Ca-Cu-O superconducting magnet. The levitation forces strongly depended on a radial component of the external magnetic field. We measured magnetic fields on the surface and the interior of the bulk superconductor using a three-dimensional Hall sensor device. The field distribution could be understood by assuming that the shielding currents are flowing concentrically at the periphery as predicted by the critical state model. We also found that the flux lines were not straight but slightly curved due to a cylindrical geometry of the samples.