MEASUREMENT OF SUPERCONDUCTING CHARACTERISTICS OF HIGH-TC MATERIALS BY THE MAGNETIC FORCE SENSING SYSTEM

A magnetic force sensing system using a highly sensitive force sensor was developed to measure the two-dimensional distribution of superconducting properties of high T(c) materials. A probing tip made of a small piece of magnetized material was mounted on a cantilever scanned over superconducting surfaces. Magnetic properties of the superconductor generated force on the tip and the force was measured by an optical displacement sensor. Two kinds of YBCO superconductor were examined by the measuring system in order to compare their repulsive force and shielding characteristics. Two-dimensional distribution of repulsive force due to the Meissner effect of YBCO, which was fabricated by the melt powder melt growth (MPMG) process, showed evident nonuniformity which is attributed to the nonuniformity of chemical composition of the material. Although the MPMG materials are capable to be used as a magnetic shield, they have much larger residual flux than the materials fabricated by the solid phase reaction process.