AC magnetic susceptibility of HTSC and its hysteresis in the critical-state model

Abstract

The explanation of hysteresis of real ( chi ') and imaginary ( chi ") parts of the AC magnetic susceptibility of granular YBCO materials with superimposed DC magnetic field (H) has been built upon the hysteresis of critical current density, Jc(H) in a qualitative way. In this communication, theoretical justification of the observed hysteresis in chi '(H) and chi "(H) has been given on the basis of the critical-state model. Recently a numerical solution of a two-component critical state model has been presented by the authors, which is successful in deriving the low field M-H loops for the granular system. In this communication, hysteresis in AC susceptibility has been justified by extending this model further to compute AC magnetic susceptibility. It is seen that, without any modification of this model, at low amplitudes hysteresis is only seen in the imaginary part of AC susceptibility. But if a proper demagnetization contribution is taken into account this model gives hysteresis for both real and imaginary components of the AC susceptibility at all AC field amplitudes. Hysteresis in higher harmonics of AC susceptibility has also been justified. Calculation in this communication includes dependence of hysteresis of chi '(H) and chi "(H) on the amplitude of AC excitation, grain size and maximum DC bias field.