Flux pinning and superconductivity in in situ prepared Al- and Zn-doped Cu-Nb composite wires

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The effects of Al and Zn on the critical current density, upper critical field and pinning force of in situ prepared Cu-Nb wires have been studied. Doping this system by 1 wt% of these impurities results in a change in critical current density and pinning force. The critical current density increases at lower fields for both additives but decreases at high fields. The upper critical field HC2 shows a decrease for both additives. We have modified the Kramer flux pinning law for these two additives. It is found that the value of n, which is a constant in the scaling law of Fietz and Webb with a value of 2.5, varies in the case of these additives and does not remain constant.