Temperature and field dependence of the effective matrix resistivity of Bi:2223/Ag composites

The effective matrix resistivities of several Bi:2223/Ag superconducting composites were calculated from measurements made with a vibrating sample magnetometer at temperatures ranging from 4.2 K to 70 K with a ramping magnetic field amplitude up to 1.7 T applied perpendicular to the wide side of the sample. The samples were untwisted 19- and 7-filament tapes with width to thickness ratios of about 6 and lengths of 1.3 - 1.5 cm. The measured resistivity values were compared to those derived using Block-Gruneisen theory. As the temperature and/or the magnetic field increased, the effective resistivity increased more rapidly than predicted by the Block-Gruneisen function. This is attributed to an increase in the effective resistivity of the Bi:2223 superconducting filaments due to flux creep.