The effect of Gd doping on the critical current of the Chevrel phase superconductor PbMo/sub 6/S/sub 8/

A series of samples of Chevrel phase superconductor with nominal composition Pb/sub 1-x/Gd/sub x/Mo/sub 6/S/sub 8/ (0/spl les//spl times//spl les/0.04) have been made using a hot isostatic pressing (HIP) process. DC magnetic measurements have been carried out on the samples. A small increase followed by a decrease of J/sub c/ is observed by increasing the Gd content. The irreversibility field B/sub irr/ also exhibits a similar change. However, despite the change in J/sub c/ and the irreversibility line it was found that the pinning force curves for all samples follow the Kramer scaling relation F/sub p/=J/sub c/,/spl times/B/spl prop/b/sup 1/2/(1-b)/sup 2/ over a wide temperature range. This striking feature indicates that J/sub c/ is limited by one dominant flux pinning mechanism in these samples. A grain boundary pinning mechanism has been proposed previously to account for the scaling relation. In order to test this suggestion further, measurements have been carried out on powdered samples which consist of few grain boundaries. Magneto-resistivity and ac susceptibility measurements have been performed on the samples to investigate the change of B/sub c2/ and other parameters in the Gd doped samples.