EFFECTIVE ELECTRIC-FIELD IN DC MAGNETIZATION MEASUREMENTS - COMPARING MAGNETIZATION TO TRANSPORT CRITICAL CURRENTS

We report values of critical current (J(c)) for Tl2Ba2CaCu2Ox(Tl-2212) epitaxial thin films in magnetic fields up to 5 T and at temperatures of 5, 40, and 77 K determined from dc magnetization and using a standard transport technique. Although we verify the applicability of Bean's model [Rev. Mod. Phys. 36, 31 (1964)], these values only agree at small applied magnetic fields and at low temperatures. Our results indicate that the differences observed in J(c)'s determined from the two techniques may be understood by considering only the field-dependent, nonlinear E-J characteristic and the "effective" electric-field criterion used in determining J(c).