Pinning potential, its relativity and dependence on temperature and magnetic field studied on the basis of the I-V characteristics of multifilamentary Nb3Sn superconductors

A series of I-V characteristics of multifilamentary Nb3Sn superconductors measured at various temperatures (2.4-4.2 K) and magnetic fields (6-12 T) was analysed with the help of creep process theory. It was shown that the current-dependent effective pinning potential U-ef(I) as well as the temperature- and magnetic field-dependent pinning potential U-0(T, B) depend on the choice of the reference current-voltage point in some of the currently used models. Due to this fact, the values of U-0(T, B) as well as U-ef(I) derived from I-V data have a meaning related to a reference current-voltage point chosen usually in the practically accessible measurement range. In this paper, we used 1 mu V cm(-1) as the reference voltage. Generalizing some features of creep models we found the way to derive U-0(T, B) from experimental data without knowing the precise form of the U-ef(I) dependence. The influence of technological parameters (filament composition and heat treatment conditions) on this relative pinning potential U-0r(T, B) are discussed. A simple scaling of U-0r(T, B) was found for all the conductors under study. Its form is U-0r(T, B) = U*(B)f(T/T*), where the values of scaling temperatures T* are very close to the critical temperatures and U*(B) seems to be a maximum value of the relative pinning potential at a given magnetic field in the whole temperature range.