SUPERCONDUCTIVITY OF GALLIUM IN VARIOUS CONFINED GEOMETRIES

The superconductivity of gallium in porous glasses with various pore s izes and in opals is studied using a superconducting quantum interfere nce device magnetometer. The single and double superconducting phase t ransitions are observed for different samples, Magnetization hysteresi s loops are also measured and found to be dependent on pore sizes and geometry. The changes in magnetization below about 6.4 K are treated w ithin the framework of models for granular superconductors, while the alterations in magnetization near 7.1 K are treated as a result of the superconducting phase transition in a coexistent structural modificat ion of confined gallium. X-ray diffraction measurements are performed to confirm the presence of such an additional gallium modification. Th e results obtained allow us to suggest that studies of magnetization a t low temperatures can be used to get information about the geometry o f the pore network and distribution of Josephson links in porous compo site materials. [S0163-1829(98)07425-6].