Alternating-Field Susceptometry and Magnetic Susceptibility of Supercondoctors.Presented at Office of Naval Research Workshop on Magnetic Susceptibility of Supercondoctors and Other Spin Systems. Held in Berkeley Spring, West Virginia on 20 May 1991

摘要

The review critically analyzes current practice in the design, calibration,sensitivity determination, and operation of alternating-field susceptometers, and examines applications in magnetic susceptibility measurements of superconductors. Critical parameters of the intrinsic and coupling components of granular superconductors may be deduced from magnetic susceptibility measurements. The onset of intrinsic diamagnestism corresponds to the initial decrease in electrical resistivity upon cooling, but the onset of intergranular coupling coincides with the temperature for zero resistivity. The lower critical field may be determined by the field at which the imaginary part of susceptibility increases from zero. Unusual features in the susceptibility of superconductors films, such as a magnetic moment that is independent of film thickness and the variation of susceptibility with angle, are related to demagnetization. Common misunderstandings of the Meissner effect, magnetic units, and formula conversions are discussed. There is a comprehensive summary of critical-state formulas for slabs and cylinders, including new equations for complex susceptibility in large alternating fields. Limitations on the use of the critical-state model for deducing critical current density are listed and the meaning of the imaginary part of susceptibility is considered.