AC-susceptibility measurements of Cu1−xTlxBa2Ca3Cu4O12−δ superconductor thin films with different thallium content

We have studied the superconductivity of Cu1−xTlxBa2Ca3Cu4O12−δ (x = 0.8 and 0.5) thin films by AC-susceptibility measurements under various external AC magnetic field strengths. It is observed from these measurements that the χ″ peak of AC-susceptibility measurements which is associated with AC losses in the superconductor samples representing intergranular coupling and pinning strength of the samples is shifted to lower temperature after the application of external magnetic fields. It is observed from these measurements that in the samples with x = 0.5 the χ″ peak is shifted to lower temperature by applying very small AC field (i.e. Hac up to 50 A/m) whereas, the χ″ peak of thallium rich (x = 0.8) samples is only affected by higher magnetic fields up to 800 A/m. These results have shown that Cu1−xTlxBa2Ca3Cu4O12−δ superconductor thin films with higher thallium content have enhanced granular connectivity and stronger flux pinning as compared to the samples with smaller thallium content.