Magnetization of Superconducting Nb-25%Zr Wire

The magnetization and critical transport-current densities of samples of superconducting niobium-25% zirconium cold-worked wire have been measured quantitatively up to 40 kOe applied field. All of the magnetization characteristics, as measured by several techniques, and the critical transport currents conform to critical-state concepts provided that the equilibrium magnetization is included in the analysis. The equilibrium magnetization curves could be deduced from the hysteretic measured magnetization data, and the results agree with the theory of Abrikosov for type-II superconductors. The irreversible magnetization-current densities $J_c\mathrm{}\left(B\right)\mathrm{}$, where B is the local magnetic induction, just equal the critical transport-current densities $J_t\mathrm{}\left(H\right)\mathrm{}$ in the range 4 to 40 kOe applied field. They are accurately fitted by an empirical critical-state expression of the form $J_c\mathrm{}\left(B\right)=a_0\exp (-\frac{B}{b_o})+c_o$ where $a_o$, $b_o$, and $c_o$ are measured constants of the material. The methods used appear to be generally applicable to the study of hysteretic superconducting wire.