Eur. Phys. J. B 43, 305-318 (2005)
https://doi.org/10.1140/epjb/e2005-00058-x

Electrical and magnetic properties of Gd(Ba_2-xLa_x)Cu₃O_7+δ

Magnet Research Laboratory (MRL), Department of Physics, Sharif University of Technology, P.O. Box 11365-9161, Tehran, Iran

Corresponding author: ^a akhavan@sharif.edu

Received: 14 August 2004
Revised: 1 December 2004
Published online: 15 March 2005

Abstract

We have studied the structural, electrical, and magnetic properties of the normal and superconducting states Gd(Ba_2-xLa_x)Cu₃O_7+δ [Gd(BaLa)123] samples with prepared by the standard solid-state reaction. XRD characterization shows an orthorhombic-tetragonal structural transition at x=0.2. Iodometric titration analysis shows the oxygen content of the samples increase with the increase of La doping. The resistivity curves show that for , there is metallic behavior, and for , there is a gradual insulating transition behavior in the normal state. The metal-insulator and superconductor-insulator transitions occur between x=0.35 and x=0.4. The superconducting transition temperature decreases with the increase of La content as two-step curve. The normal-state resistivity is fitted for two and three dimensional variable range hopping (2D&3D-VRH) and Coulomb gap (CG) regimes, separately. The results show that the dominant mechanism is CG for , and VRH for . The pinning energy U, derived from the thermally activated flux creep (TAFC) model and Ambegaokar-Halperin (AH) theory, shows a power-law relation as . The critical current density decreases with the increase of La doping and magnetic field. The E-J curves show that the induced electric field increases with the increase of magnetic field and La concentration. The magnetization measurements indicate that the critical penetration fields and magnetic current density decrease with La doping.