Flux Pinning Characteristics and Irreversibility Field of Cu_0.5Tl_0.5Ba₂Ca₃Cu₄O_12−δ thin films

Flux pinning characteristics of Cu_0.5Tl_0.5Ba₂Ca₃Cu₄O_12−δ samples synthesized by two-step solid-state reaction method have been studied by physical properties measurement system (PPMS). These thin films are oriented along c-axis and have shown the tetragonal crystal structure. In the resistivity measurements, these samples have shown T_c (R = 0) around 106 K. Asymmetric M vs. H loop of the samples at various temperature shows the interaction bulk and surface pinning. The energy of activation derived from the slope of Log(J_c) vs. reduced temperature enhances with the increase strength of applied field. The irreversibility field suppress with the increase in the measurement temperature. The pinning energy per unit length of flux votex ε and the de-pinning force also suppress with increase of measurement temperature. The H_c1, H_c, and H_c2 (hence the H_irr) are suppress with the increase of measurement temperature, since the H_c determines the free energy difference between the normal and superconducting state. The increase in the H_c at lower temperature shows that the density of superconducting electrons increases with the suppression of temperatures. The enhancement in the density of superconducting carriers at low temperatures would increase the coherence length and suppress the population of flux vortices. It can be seen in the form of decreased values of Ginzburg Landau parameter κ and the penetration depth λ_D.