Critical properties of superconducting Ba1−xKxFe2As2

Magnetisation and magneto-resistance measurements have been carried out on superconducting Ba1−xKxFe2As2 samples with x = 0.40 and 0.50. From high field magnetization hysteresis measurements carried out in fields up to 16 T at 4.2 K and 20 K, the critical current density has been evaluated using the Bean critical state model. The JC determined from the high field data is >104 A/cm2 at 4.2 K and 5 T. The superconducting transitions were also measured resistively in increasing applied magnetic fields up to 12 T. From the variation of the TC onset with applied field, dHC2/dT at TC was obtained to be −7.708 T/K and −5.57 T/K in the samples with x = 0.40 and 0.50.