Normal state conduction and TAFC in Gd(BaLn)123 (Ln=La,Nd)

We have studied the electrical and magnetic properties of single phase polycrystalline Gd(Ba2-xLax)Cu3O7+δ and Gd(Ba2-xNdx)Cu3O7+δ (0≤x≤0.5) samples. The samples were prepared by the standard solid-state reaction technique. The electrical measurements show the decrease of Tc and increase of ΔTc with the increase of Nd and La-doping. The magnetoresistance of samples has been studied within the thermally activated flux creep (TAFC) model. The pinning energy decreases with the increase of magnetic field and doping for both systems in a similar way. The decrease of pinning energy with applied magnetic field can be scaled with two power law relations for the magnetic field: smaller and larger than 1 kOe. In the H≤1 kOe region, the power coefficient increases with the increase of doping. The normal state resistivity of samples, investigated by the variable range hopping and Columb gap models, indicates that for the superconductor samples the CG model and for the insolator samples 2D-VRH are the dominant mechanisms for both compounds. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)