Magnetization measurements on single crystals of superconducting Ba0.6K0.4BiO3

摘要

Extensive measurements of the magnetization of superconducting single-crystal samples of Ba0.6K0.4BiO3 have been made using superconducting quantum interference device and cantilever force magnetometry at temperatures ranging between 1.3 and 350 K and in magnetic fields from near zero to 27 T. Hysteresis curves of magnetization versus field allow a determination of the thermodynamic critical field, the reversibility field and the upper critical field as functions of temperature. The lower critical field is measured separately and the Ginzburg-Landau parameter is found to be temperature dependent. All critical fields have higher T = 0 limits than have been previously noted and none of the temperature dependences of the critical fields follows the expected power laws leading to a possible alternative interpretation of the thermodynamic nature of the superconducting transition. [References: 36]