Model for the reversible magnetization of high- type-II superconductors: Application to high-Tc superconductors

Abstract

A simple theoretical model is proposed for the reversible magnetization of type-II superconductors as a function of the applied field H for the entire field region between Hc1 and Hc2. For HHc1, the theory reduces to a variational model, from which Hc1 can be accurately computed in the Ginzburg-Landau regime. In calculating the free energy, we include, in addition to the supercurrent kinetic energy and the magnetic-field energy, the kinetic-energy and the condensation-energy terms arising from suppression of the order parameter in the vortex core. The model is further extended to include anisotropy by introducing an effective-mass tensor for the case when H is parallel to one of the principal axes. The theory is compared to reversible-magnetization data on a YBa2Cu3O7 single crystal. The method permits an accurate determination of Hc2 versus temperature from measurements of the magnetization versus temperature at fixed magnetic field and explains why the measurements have different slopes in different fields, contrary to what might have been expected from the linear Abrikosov formula near Hc2. The deduced dHc2/dT is (-1.650.23) T/K for H parallel to the c axis near Tc, implying ab(0)=(171). © 1991 The American Physical Society.