Effect of Fluorine Substitution on Magnetoresistance Pinning Energy and Irreversibility of (Cu, Tl)-1223 Phase.

The magnetoresistance behavior of (CuF₂)_x-substituted (Cu_0.5−x, Tl_0.5)Ba₂Ca₂Cu₃O_y superconducting samples with x = 0.1, 0.2, 0.3, and 0.4 was investigated by varying the flux pinning mechanism. A pronounced broadening of resistive transitions, ΔT, was observed by applying external magnetic fields ranging from 0.29 to 4.40 kOe. The thermally activated flux creep, TAFC, and Ambegaokar–Halperin, AH, models have been studied to explain the broadening of the resistive transition and magnetoresistance. The results revealed that the flux pinning energy, U(H), was reduced as the magnetic field increased while it was raised with increasing (CuF₂)_x substituted up to an optimum concentration of x = 0.2. Moreover, the critical current density, J_c, and the upper irreversibility field, H_irr, were enhanced with (CuF₂)_x—substituted in the (Cu_0.5−x, Tl_0.5)Ba₂Ca₂Cu₃O_y phase, showing a strong flux pinning for x = 0.2 at different magnetic fields. [ABSTRACT FROM AUTHOR]