An H-T diagram characterizing the activation barriers obtained from the magnetic relaxation of HgBa₂Ca₂Cu₃O _8+δ thin film

The magnetic relaxation of an epitaxial HgBa₂Ca ₂Cu₃O_8+δ (Hg-1223) thin film was measured at several fields and temperatures. After the activation energy and the normalized relaxation rate had been analysed, the U-j characteristics were mapped on the H-T diagram. The power-law region with a creep exponent of, which indicates large bundle creep, became a logarithmic region in the small μ limit as j went far below j_c. From this analysis, we found that a large bundle of flux acts like a single vortex, the size of which was temperature independent. This behaviour is quite different from that of other cuprate superconductors. Also, the crossover temperature, T_b, between the power-law and the logarithmic regions was inversely proportional to H^β. The fitting of T_b(β) on the H-T diagram is in good agreement with the field exponent of that was obtained from the scaling of U_eff(H).