Critical current densities and irreversibility fields of a HgBa2Can−1CunO2n+2+δ sample containing n=6–15 phases

A recent report on multilayered superconductors establishes unique constant T-c although the number of inner CuO2 plane (IP) increases. Many hypotheses proposed that the irreversibility field (B-irr) and critical current density (J(c)) are depends on the crystal structures. We have measured the J(c) and B-irr of the HgBa2Can-1CunO2n+2+delta sample containing n = 6-15 phases to investigate the effect of the number of IP's on the B-irr and J(c) and its pinning properties. The rate of fall of J(c) increases and irreversible lines (IL's) shift to lower temperatures with increasing the number of IP's, which suggests that anisotropy increases with n. The IL settled in between those for Bi2Sr2CaCu2Oy with high anisotropy value and YBa2Cu3O7 with less anisotropy value. The double logarithmic plot of irreversibility field versus [1 - (T/T-c)] analysis suggests that the flux line melting model is adopted. The flux pinning force density F-p (approximate to J(c)B) exhibits scaling behavior when the magnetic field B is normalized by the irreversibility field B;- Analysis of the normalized pinning force reveals that a surface pinning mechanism is dominant and reduced magnetic field b(max) = 0.2 agree with surface pinning mechanism with closely spaced pins. (C) 2008 Elsevier B.V. All rights reserved.