Nonsaturated Global Pinning Force in Superconducting Nb–Ta with Normal Precipitates

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Nonsaturated pinning characteristic and elastic and plastic properties of a fluxoid lattice are measured by an ac inductive method for superconducting Nb–Ta tapes with normal Nb 2 N precipitates. The interaction distance proportional to a yield strain of the fluxoid lattice is shown to be approximately constant except in the vicinity of the upper critical field, indicating that the fluxoid lattice is stabilized by strong pinning interactions by normal precipitates. The dependence of the pinning force density on the pinning parameters estimated from electron micrographs agrees better with the linear summation theory than the theory of Larkin and Ovchinnikov.