Non-linear flux-pinning energies versus current densities in high-T c superconductors: Implications for U o's derived from magnetic relaxation experiments

Abstract

Magnetic relaxation rate measurements of high-T c superconductors in the critical state are often used to determine the characteristic flux-pinning energies of these materials. The relaxation-rate equations used to obtain flux-pinning energies usually assume a linear U vs. J dependence. Recent studies of the flux pinning properties of high-T c materials, however, show that the U vs. J relation is highly non-linear, the relation being more accurately described by a power-law or logarithmic function than a linear one. It is shown here that for a power-law U vs. J dependence, the U o derived from a magnetic relaxation experiment is a closer measure of U( J= J c ) than of U(J≈0). As a result, for a power-law U vs. J dependence U o is not an accurate measure of the absolute depth of the flux-pinning potential, as is commonly assumed.