Magnetic Properties of Cu0.5Tl0.5Ba2Ca2Cu3-xKxO10-δ (x=0, 1, 2.5, 3) Superconductors

Abstract

We have synthesized Cu0.5Tl0.5Ba2Ca2Cu3-xKxO10-δ (x=0, 1, 2, 2.5, 3) superconductor samples at 860°C and studied their superconducting features by XRD analysis, SEM and resistivity measurements, the zero field-cooled and field-cooled magnetization as a function of temperature measurements, At constant temperatures, FTIR absorption spectroscopy was used, as well as detailed magnetization as a function of temperature (M-T) and magnetic looping (M-H) of 2, 3.5, 5, 7.5,10, 20, 30, 40, 50 and 60 K. By raising the x concentration of K doping, the tetragonal unit cell's a, b, and c axis lengths vary, although its c axis length decreases. Tc (onset), Tc(R = 0), and the magnitude of diamagnetism are also decreased. The peak location of the apical oxygen modes remains unaltered, whereas increasing x softens the CuO2/KO2 planar oxygen modes. The critical current density Jc and flux pinning force are derived using Bean's critical state model, which suppresses as the field increases. In doped samples, the suppression of Jc is steeper. Doped atoms boost the population of localized defects, which serve as pinning centers. Because the Hc controls the free energy difference between the normal and superconducting states, the Hc1, Hc, and Hc2 (therefore the Hirr) are suppressed as the measurement temperature rises. The high value of Hc at lower temperatures suggests that when temperatures are dropped, the density of superconducting electrons increases. The coherence length in the mixed state of doped CuTl 1223 samples is increasing with the increase in temperature due to enhancement in the density of the vortex line.