Irreversibility line and flux pinning properties in a multilayered cuprate superconductor of Ba2Ca3Cu4O8(O,F)2 (Tc = 105 K)

Irreversibility line (IL) and flux pinning properties were investigated for a Ba2Ca3Cu4O8(O,F)2 (F-0234) multilayered cuprate superconductor with a Tc of 105 K. The intragrain critical current density (Jc) and irreversibility field (Birr) were determined by using Bean's critical state model for the grain-aligned sample (nominal composition Ba2Ca3Cu4O8.7F1.3). The irreversibility line (IL) of F-0234 is much lower than that of (Cu,C)Ba2Ca3Cu4Oy ((Cu, C)-1234) and HgBa2Ca3Cu4Oy (Hg-1234) in spite of the spacing between the superconducting blocks of F-0234 (7.3 A) being much thinner. The double logarithmic plot of Birr field versus [1-(T/Tc) ] analysis hints that the flux line melting model has been adopted. An anisotropy factor of 65 was calculated from a 3D to 2D crossover field of about 0.95 T. Due to the high anisotropy of this system, a low IL has resulted. The flux pinning force density Fp ( ∼JcB) exhibits scaling behaviour when the magnetic field B is normalized by the Birr field. Analysis of the normalized pinning force reveals that a surface pinning mechanism is dominant and the reduced magnetic field bmax = 0.2 agrees with surface pinning mechanism with closely spaced pins