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 J(C) determined from the high field data is >10(4) A/cm(2) 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 T-C onset with applied field, dH(C2)/dT at T-C was obtained to be -7.708 T/K and -5.57 T/K in the samples with x = 0.40 and 0.50. (C) 2009 Elsevier B.V. All rights reserved.