Frequency and field dependencies of the ac-susceptibility: A probe to the microstructure of high T/sub c/ superconducting materials

The authors report the first measurements of the real and imaginary contributions to the ac-susceptibility and its dependence on frequency and applied fields over a range of a few decades for Y-Ba-Cu-O based high T/sub c/ superconducting materials. The test results indicate that flux pinning at the surface of the grains, flux trapping due to the inhomogenieties in the material, and the porous nature of the sintered oxide superconductors play a significant role in the magnetic properties of the materials