Magnetization of K0.8Fe2Se2 superconductor

The magnetization curves of K0.8Fe2Se2 were studied by the extended critical state model. The K0.8Fe2Se2 sample was prepared by solid-state reaction. In the magnetization measurements by SQUID magnetometer, the external magnetic fields were applied perpendicular to c-axis of the sample at 5 ∼ 50 K. The FC and ZFC M-T curves showed the discrepancy below 50 K. The critical current density Jc rapidly decreased at 20 K, but kept small finite values up to 45 K.