On the magnetic properties of cadmium-doped Y-Ba-Cu-O high-temperature superconductors

Abstract

The discovery of the superconducting system Y B a C u O , with a transition temperature above 90 K [1], opened a new field of studies in the high-To superconductors° Substitution of yttrium by different rare-earth elements was found to influence the superconducting properties very weakly. Partial substitution of copper by different elements, especially by 3d transition-metal ions, has a strong effect on the superconducting properties of the material [2, 3]. Material doped with Cd was investigated recently by various researchers, and the results were not similar [4-6]. The main reason was the different method of preparation of the samples and the different dose of doping. In the present case the samples were prepared to have the nominal composition YBa2Cu3CdxOy and the first results were presented in a recent letter [6]. It was found that for x 0.2 CdO in excess was detected and the electrical behaviour above the transition temperature is a semiconductor-like one. The lattice parameters increase with Cd content up to the solubility limit, and decrease for x > 0.2. The best electrical characteristics were found for x -0.05. The resistivity of this material at room temperature decreases by at least two orders of magnitude, compared with the undoped material [7]. Positron annihilation measurements showed a lifetime component of about 320 ps, which has been attributed to some kind of defect complexes. A strong suppression of this component, after Cd insertion, suggests that Cd fills these defects preferentially [8]. In the present letter magnetic measurements, on Cd-doped Y B a C u O superconductors, are presented. The method of preparation of the YBa2Cu3CdxOy compounds is given in detail in a recent letter [6]. It must, however, be mentioned that instead of CuO powder, which was used by most researchers, CuzO powder was used as a starting material. This results in a different temperature of oxygen uptake during the annealing of the samples [7]. The d.c. magnetic moments were measured from 20 to 100 K by a Varian Foner-type vibrational