Dependence of the critical current density of superconductors on the past history of the magnetic field and the temperature

Abstract

The dependence of the volume pinning force on different paths taken to arrive at a state (B, T) is investigated for a variety of type II superconductors having widely different reversible and irreversible parameters, by measuring the local induction with an a.e. technique. Line pinning and a distorted flux line lattice are properties of those samples which show history dependence. Using a model of Kramer (1973) it is deduced that the history effect is caused by a dependence of the shear modulus on the defect structure of the flux line lattice. The effect occurs at relatively low reduced magnetic fields. It is also observed in materials with high values of the Ginzburg-Landau parameter k and large volume pinning forces.