METHOD TO EXTRACT THE CRITICAL-CURRENT DENSITY AND THE FLUX-CREEP EXPONENT IN HIGH-T-C THIN-FILMS USING AC SUSCEPTIBILITY MEASUREMENTS

High-precision ac susceptibility measurements have been made on high-q uality Hg-1212 thin films. A method to analyze chi(1)'(T,H-0,f) and ch i(1)'' (T,H-0,f) and extract the temperature dependence of the critica l current density J(c)(T), as well as the temperature and field-depend ent flux-creep exponent n(T,H-0), is presented. With specific measurem ents at external ac fields Ho in the range 7-100 Oe(rms) we determine the temperature dependence of the critical current density from a sing le temperature scan. The obtained temperature dependence, J(c)(T), is found to be in good agreement with data obtained from measurements usi ng the traditional ''loss-maximum'' approach. In addition we present a method to extract the temperature and ac field-dependent flux-creep e xponent n(T,H-0) from a set of temperature scans taken at different cc fields and driving frequencies. The observed power law describing the frequency dependence of chi' is consistent with a current-dependent e ffective activation energy of the form U(J)= U(0)ln(J(c)/J). Furthermo re, the flux creep is found to increase with ac field and with tempera ture except at about 20-30 K below T-c, where our data suggest a slowi ng down of the flux creep.