Comparison of irreversibility temperature determined via DC and AC magnetisation techniques in conventional superconductors

Abstract

A comparison has been made of irreversibility temperature determined by four different methods in few specimens of lead (type-I) and niobium (type-II). The merger of M_ZFC(T) and M_FC(T) curves give T_r(H) values lower than those evident from vanishing the hysteresis in isothermal DC magnetization. The identification of peak temperature in χ"_H(T) data with T_r(H) is appropriate only if the contribution from changes in the normal state electrodynamics can be isolated and the peak is narrow. The appearance of differential paramagnetic effect in χ'_H(T) data is adequate to imply reversibility, however, its efficacy to precisely locate irreversibility line remains to be established.