Calculations on the reversible and irreversible magnetic behavior of low-kappa type-II superconductors

Abstract

A simple algebraic expression for the reversible magnetization curve in low-κ type-II superconductors is proposed. This model has been checked on the experimental results of very pure Nb and V, as measured by several authors. A quite good agreement is found forT/T _c >0.4; for lower temperatures the agreement becomes worse, but this model still seems better than any other model known thus far from the literature. Using this relation together with a critical-state model it is possible to calculate the irreversible magnetization curves in increasing and decreasing fields betweenH _{c 1} andH _{Hc H2} . The results are compared with the experimental data we obtained on a rectangular Nb sample. It turns out that Goedemoed's pinning model gives a good description. Also, a method is described to obtain the flux density gradient as a function ofB directly from magnetization measurements. This provides a more sensitive method to compare the experiments with critical-state models.