Magnetic field dependence of the reversible mixed-state properties of superconducting MgB 2 single crystals and the influence of artificial defects

TLDR: In this paper, the reversible mixed-state properties of superconducting materials are summarized and discussed in terms of new results and evaluations, which take the two band character of the material explicitly into account.

Abstract: The reversible mixed-state properties of superconducting ${\mathrm{MgB}}_{2}$ are summarized and discussed in terms of new results and evaluations, which take the two band character of the material explicitly into account. The magnetic field dependence of the reversible magnetization is analyzed within Ginzburg Landau theory which, however, fits only either at high or at low fields. The resulting parameters (e.g., characteristic fields, lengths, and anisotropy) are quite different in these two regimes. We find large anisotropies of about 4.6 at high fields and low temperatures, but values close to 1 at low fields. Finally, we present neutron irradiation experiments, where new defects, leading to strong irreversibility but also to a modification of the reversible properties, are induced.