Superconducting state parameters, pinning centres and their effectiveness forY1−xPrxBa2Cu3O7−δ single crystals with low Pr contents

Abstract

Magnetic measurements on optimally doped and overdopedY1−xPrxBa2Cu3O7−δ singlecrystals, with x varying from 0 to 0.024, were made over a wide temperature range up to0.99Tc. We concentrate on the effect of inhomogeneity introduced by both the Prsubstitution and the oxygen deficiency on the intrinsic and extrinsic properties ofY1−xPrxBa2Cu3O7−δ. The superconducting state parameters were determined and the vortexpinning behaviour was analysed using a rigorous treatment for themagnetization behaviour, which includes explicit expressions for the equilibriumB(H), based on the Ginzburg–Landau theory, and for the critical current density,Jc(B). The results obtained for Pr-substituted crystals show a highercharacteristic temperature for flux flow activation than for pureYBa2Cu3O7−δ. The extent to which the oxygen content in overdopedYBa2Cu3O7−δ leads to an increase of both the superconducting carrier density,ns, and the thermodynamiccritical field, Hc, and shifts the irreversibility line to higher fields was investigated. Simultaneously, a decreaseof the critical current density was observed at intermediate magnetic field. This effect is foundto be overcompensated by Pr substitution at the Y position in almost fully oxygenatedYBa2Cu3O7−δ, since Pr substitution at the Y site introduces effective pinning centres, leading to anincrease of the critical current density.