Magnetization and Critical Supercurrents

The magnetization in high-field superconductors has been investigated using tubular samples. When the sample assumes a critical state, wherein every region of the sample carries critical current density $J(B)$ determined only by the local magnetic field B, the magnetization can be predicted quantitatively from the critical current density $J(B)$. Using observed magnetization data, a critical current density relation αJ=B₀+B is deduced for Nb₃Sn and 3Nb-Zr. α is a direct measure of the current carrying capacity of a sample, and B₀ coincides approximately with the thermodynamic critical field of the material. Since this relation implies JB=α=const for BB₀, the Lorentz force plays an important role in determining the critical current density.